How Did It All Begin? In the 1850's, unlike today, drillers took Sundays off, but one Sunday afternoon in August 1859, William Smith decided to inspect a well he was drilling. Perhaps Smith, known as Uncle Billy to his friends, was curious to see if anything had happened while he was in church. The well, nearOil Creek just outside Titusville, Pennsylvania, sat next to an oil seep, a place where oil from subterranean rocks oozed to the surface. Uncle Billy had begun drilling the well in April for a former railroad conductor named Edwin Drake. Drake, whom everyone called"Colonel," was overseeing a remarkable project. He was supervising the drilling of a well whose sole purpose was to produce oil. Asians and Europeans had drilled oilwells, but no one in the United States had. Some of the local residents had also drilled wells near Titusville before 1859. These wells, however, were saltwater wells. Uncle Billy's visit to the well that particular Sunday turned out to be fruitful. He peered into the pipe that encased the top of the hole and saw that it was full of crude oil. When word spread, dozens of new rigs appeard in the area and the boom was on. This small project in Titusville marked the beginning of the petroleum era in the United States. Why Was It Important To Find Oil? There were two reasons Colonel Drake and his backers from New haven, Connecticut, decided to drill for oil. A shortage of whale oil. Oil that seeped naturally from the earth could not be held in a dam. By the 1850's, New England seafarers had hunted whales nearly to extinction. Because people used whale oil as a high quality lubricant and as an illuminating oil, it was scarce and expensive. Reports of an oil spring near a Pennsylvania creek, where the oil literally leaked out of the rocks, therefore sparked the interest of the New Haven entrepreneurs. They reasoned that if they could
Transcript
How Did It All Begin?
In the 1850's, unlike today, drillers took Sundays off, but one Sunday afternoon in August 1859, William Smith decided to inspect a well he was drilling. Perhaps Smith, known as Uncle Billy to his friends, was curious to see if anything had happened while he was in church. The well, nearOil Creek just outside Titusville, Pennsylvania, sat next to an oil seep, a place where oil from subterranean rocks oozed to the surface.
Uncle Billy had begun drilling the well in April for a former railroad conductor named Edwin Drake. Drake, whom everyone called"Colonel," was overseeing a remarkable project. He was supervising the drilling of a well whose sole purpose was to produce oil. Asians and Europeans had drilled oilwells, but no one in the United States had. Some of the local residents had also drilled wells near Titusville before 1859. These wells, however, were saltwater wells.
Uncle Billy's visit to the well that particular Sunday turned out to be fruitful. He peered into the pipe that encased the top of the hole and saw that it was full of crude oil. When word spread, dozens of new rigs appeard in the area and the boom was on. This small project in Titusville marked the beginning of the petroleum era in the United States.
Why Was It Important To Find Oil?
There were two reasons Colonel Drake and his backers from New haven, Connecticut, decided to drill for oil.
A shortage of whale oil.
Oil that seeped naturally from the earth could not be held in a dam.
By the 1850's, New England seafarers had hunted whales nearly to extinction. Because people used whale oil as a high quality lubricant and as an illuminating oil, it was scarce and expensive. Reports of an oil spring near a Pennsylvania creek, where the oil literally leaked out of the rocks, therefore sparked the interest of the New Haven entrepreneurs. They reasoned that if they could
recover enough rock oil from the Oil Creek site, they could sell it as an inexpensive substitute for the shale oil. They formed the Pennsylvania Rock Oil company of Connecticut in 1855 and began thinking of ways to extract the oil.
Since the oil seeped onto the ground near the creek, it had to be contained, First, the bankers hired workers to dig trenches and direct the oil into holding ponds. To make the ponds, the laborers simply dug out the soil and piled it around the edges of the
pond. Unfortunately, everytime they built such a wall, rainwater and groundwater washed it out and the oil ran off into the creek.
To solve the problem, James Townsend, president of the newly formed oil company, proposed drilling for the oil, rather than merely trying to contain what seeped to the surface. Others in the area had been drilling for salt water, or brine, for many years. Townsend hired Drake, declared him an honorary colonel, sent him to Oil Creek to supervise the drilling for oil. Drake, in turn, hired Uncle Billy Smith, and experienced saltwater driller.
Spindletop
Spindletop is the name of a small knoll just south of Beaumont Texas.
Anthony Lucas, an Austrian-born mining engineer, has been supervising the drilling of an oilwell since October 27, 1900.
His crew must install a new drilling bit on the string of a drill pipe. The date is January 10, 1901. The drilling crew begins lowering the new bit to the bottom of the hole. They run about 700 feet (200 meters) of drill pipe into the 1,000-foot (300-meter) hole. Suddenly, the well starts spewing drilling mud. The mud, a liquid concoction that carries rock cuttings out of the hole, drenches the rig floor and shoots up into the derrick.
The crew evacuates the rig and waits to see what will happen. The flow stops. The workers return to the rig and start cleaning up. Without warning, mud erupts again. Then a geyser of oil gushes 200 feet (60 meter) above the 60-foot-high (18 meter high) derrick.
The spouting oil blows all the drill pipe out of the hole. The blowing well elates Lucas and his crew as they watch the display from a safe distance. They estimate that it is flowing over 3 million gallons (over 12,000 cubic meters) of oil per day. In oilfield terms, that's over 80,000 barrels of oil per day.
Before Spindletop, a big producer flowed 50 barrels (8 cubic meters )per day. The Lucas well produced 1,600 times that amount. It showed that buried layers of rock could contain tremendous amounts of oil. What is more, it proved that rotary drilling was an effective way to obtain it. Spindletop marked the beginning of the modern petroleum industry.
Oil Definition
Let’s see: snake oil, rock oil, black gold, and - Texas tea? Over the years, oil has gone by a number of colorful and descriptive names by both technical and non-technical people.
Technically speaking, oil can be both refined and unrefined. Refined oil is transformed into familiar products such as gasoline, kerosene, diesel fuel, motor oil, etc. Unrefined oil is known simply as crude oil due to the presence of various amounts of impurities that have mixed with the oil deep down in the earth.
Crude oil typically ranges from black to brown to green in color and can have a waxy feel to it. It also has a strong scent. When oil is produced from wells it is known as crude oil until that time when it is delivered to a refinery and is processed into some of the refined products mentioned above.
But, there are other terms for oil. The most common term not mentioned already is petroleum (the literal oil definition: “petra” = rock, “oleum” = oil).
Petroleum is a name pretty much synonymous with oil but differs primarily in that petroleum can be a gas (i.e., vapor), a liquid, a solid, and a semi-solid. These different forms are known as phases.
Therefore, crude oil is a liquid phase of petroleum.
Some of the other terms for petroleum are called natural gas, and bitumen (i.e., asphalt, and tar).
So, what makes the various forms or phases of petroleum related? What do they have in common?
The answer is their chemistry. They are all forms of simple and complex hydrogen and carbon compounds known as hydrocarbons.
Simple hydrocarbon compounds like methane have one carbon atom and four hydrogen atoms (CH4) and are so light that they are a gas in normal atmospheric conditions.
Other hydrocarbon compounds are liquid under normal atmospheric conditions, meaning they are heavier than natural gas but are often lighter than water. This remarkable fact means that oil will float on water, and it is one of the main principles utilized by oil companies to locate and extract crude oil from the earth.
Heavier hydrocarbon compounds still, are solid or almost solid to the point that they will not flow under normal atmospheric conditions thus requiring special techniques to recover them (i.e., bitumen, asphalt, and tar). These types of hydrocarbon can have in excess of 25 carbon atoms.
Hydrocarbon Series
Hydrocarbons have generally been divided into four main series based on differing chemical properties. They are paraffins, isoparaffins, naphthenes, and aromatics.
Paraffins (or alkanes) are straight-chained hydrocarbons, and are typically the predominant hydrocarbon present in gas and liquid petroleum. They represent some of the most common and familiar hydrocarbon compounds beginning from light to
heavy: methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), pentane (C5H12), hexane (C6H14), heptane (C7H16), and octane (C8H18). Methane (the most common constituent of natural gas) through butane are gases under normal atmospheric conditions, while pentanes through octane are liquids.
Isoparaffins are molecules that have the same molecular formula composition as their paraffin counterparts, but differ with their branched-chain structures. For
example, isobutane (C4H10) has the same number of molecules as butane (C4H10), but because of its different structure, has different physical characteristics.
Naphthenes (cycloparaffins) are closed-ring hydrocarbons that constitute up to 30 percent of straight run (uncracked) gasoline. Cyclopentane (C5H10) and cyclohexane (C6H12) are the most common naphthenes found in petroleum.
Aromatics (benzene) are also closed-ring, but strongly scented hydrocarbons that generally comprise up to approximately 10 percent of crude oils. Benzene (C6H6) is its most common member.
OIL’S ORIGIN
The truth is, no one is completely certain how oil originated, migrated and accumulated.
Prevailing wisdom, based on over a hundred years of production history, has it that crude oil was formed from layers of dead organisms lying on the sea floor for millions of years. Over time, sand, clay, and limestone layers covered the rich organic sediments, which are typically fine-grained shales, choking out oxygen and allowing
bacteria to break down the organisms.
As the organic-rich sediment was covered with more and more layers of earth, the weight of the overburden caused pressure and heat to transform
the organic material into one of the various phases of hydrocarbon (natural gas, crude oil, or bitumen. Scientists call this organic-rich sediment layer the source rock, as it is where oil is created.
It is estimated that it took millions of years to convert the organic matter into the quantities of
hydrocarbon produced in the oil fields of today. As a result, oil is considered a finite resource. As the oil fields around the world are identified, and oil increasingly produced, the earth’s oil generating machine cannot keep pace, and the world’s overall oil balance declines.
Another novel theory for oil’s origin suggests that it is an inorganic product originating deep in the earth, between the mantle and the crust. Miles below the earth’s surface, it is theorized, the interaction of a now mobile, inorganic methane and high temperature pockets takes place and results in the condensing of crude oil.
An intriguing aspect of this theory is that oil is constantly being generated in numerous places around the world, and at rates that can continue to sustain our current way of life. So now, according to some, oil is not a limited resource after all.
It should be noted that this inorganic theory is held by a minority of industry professionals. The oil discoveries and development plans throughout the world have been based on the organic theory of hydrocarbon origination and a declining inventory. Seems to me like conventional wisdom wins the day.
PETROLEUM PRODUCTION CHART
Oil Location
So, Where Is Oil Found?
Oil is found in underground pools of oil called reservoirs. This oil location is not what one might typically expect when considering the term "pool". It is impossible to go swimming in these pools! Industry experts use the term "pool" to define accumulations of hydrocarbon in zones of subsurface rock. What? How can oil reside in rock?
Well, if you were to zoom in on a chunk of rock, let's say a sandstone (down to about 0.000001 meters!), you would see thousands of little flecks of stone stuck together with spaces in between them. These spaces are called pores and the term porosity refers to the percentage of pore space to little stones over a given area.
It is within these pore spaces that oil, gas and water reside.
The rock containing the hydrocarbon is called the reservoir rock, and can be a variety of rock types, but is typically a sandstone or limestone. This is due to the relatively high porosities these rock types possess. High quality sandstone reservoirs can have porosities in excess of 25%.
High porosities usually mean higher reserves potential.
Another term used to describe the quality of a reservoir is permeability. Permeability is the measure of the connectivity of the pore spaces to each other. If the pore spaces were not connected to each other, oil would not be able to flow, regardless of
whether or not there was good porosity.
Industry experts experience great difficulty (i.e., expense) producing poor permeability reservoirs.
A noteworthy aspect of reservoirs is that you can (and do!) have several reservoirs atop each other, all of which are capable of oil production. Oil and gas, migrating from one or more source rocks can be trapped in alternating sandstone/limestone zones by clay/shale barriers.
Based on the characteristics of each zone, industry experts can produce oil, with one well or several wells, or decide only to produce from one zone alone
A sole reservoir with a shale barrier, and multiple alternating reservoirs of petroleum reserves, with sealing barriers are known, singularly, as an oilfield.
Oilfields can exist in the ocean, on land, at depths of several miles, or near the surface. They are found in barren locales or in urban areas. Industry travels the world, enduring harsh extremes to find and produce the coveted treasure.
So, How Does Oil Accumulation In Reservoirs Happen?
For a commercial sized oil accumulation to exist, an ample volume of oil has to be generated from a source rock; it has to migrate into a porous rock formation with fair permeability; and, it has to be trapped in that formation by some relatively impervious layer, or cap rock, above it.
Hydrocarbons are thought to be generated from organic-rich rocks known as shales. Shales typically have poor porosity and permeability, and are consequently considered poor reservoir rocks. Shales do, however, contain high organic content necessary for oil generation, and are considered prime source rocks.
As pressure and temperature work on the organic-rich source rock, oil is created and
squeezed out of the formation and into an oil sand or limestone reservoir. Due to the
relative densities of oil, water and gas, gas and oil tend to rise in relation to water present
in the pores of the reservoir rock. The hydrocarbon continues to rise until it either reaches
the surface, the top of the water column or the top of a trap. Hydrocarbon that is trapped
forms today’s producing reservoirs.
Petroleum Traps
Traps are physical features, concave impediments to the upward migration of reservoir fluids.
A hydrocarbon reservoir has a distinctive shape, or configuration, that prevents the escape of hydrocarbons that migrate into it. Geologists classify reservoir shapes, or traps, into two types;
Structural (anticlines) traps: a deformation in the rock layer that contains the
hydrocarbons. Examples; fault traps and anticlinal traps.
stratigraphic (unconformities) traps: form when other beds seal a reservoir
bed or when the permeability changes within the reservoir bed itself.
combination trap: this happens when more than one kind of trap forms.
The result of these independent occurrences is the main objective of all oil exploration, the location of a column of reservoir fluids, usually the lightest on top
(gas, oil, then water) with no place for the hydrocarbon to escape - a prime situation for
exploitation.
Chacteristics of Reservoir Rocks
Nothing looks more solid than a rock. Yet, choose the right rock, (a piece of sandstone or limestone) and look at it under a microscope. You will see many tiny openings. Geologists call these tiny rock openings pores.
A rock with pores is referred to as porous. This means it has tiny holes through which oil may flow.
Reservoir rocks must be porous, because hydrocarbonscan occur only in pores.
A reservoir rock is also permeable. That means its pores are connected. If hydrocarbons are in the pores of a rock, they must be able to move out of them. Unless hydrocarbons can move from pore to pore, they remain locked in place, unable to flow into a well. A suitable reservoir rock must therefore be porous, permeable, and contain enough hydrocarbons to make it economically feasible for the operating company to drill for and produce them.
Oil Exploration
Finding Oil The task of finding oil is assigned to geologists, whether employed directly by an oil
company or under contract from a private firm. Their task is to find the right conditions
for an oil trap -- the right source rock, reservoir rock and entrapment. Many years ago,
geologists interpreted surface features, surface rock and soil types, and perhaps some
small core samples obtained by shallow drilling. Modern oil geologists also examine
surface rocks and terrain, with the additional help of satellite images. However, they also
use a variety of other methods to find oil. They can use sensitive gravity meters to
measure tiny changes in the Earth's gravitational field that could indicate flowing oil, as
well as sensitive magnetometers to measure tiny changes in the Earth's magnetic field
caused by flowing oil. They can detect the smell of hydrocarbons using sensitive
electronic noses called sniffers. Finally, and most commonly, they use seismology,
creating shock waves that pass through hidden rock layers and interpreting the waves that
In seismic surveys, a shock wave is created by the following:
Compressed-air gun - shoots pulses of air into the water (for exploration over
water)
Thumper truck - slams heavy plates into the ground (for exploration over land)
Explosives - drilled into the ground (for exploration over land) or thrown
overboard (for exploration over water), and detonated
The shock waves travel beneath the surface of the Earth and are reflected back by the
various rock layers. The reflections travel at different speeds depending upon the type or
density of rock layers through which they must pass. The reflections of the shock waves
are detected by sensitive microphones or vibration detectors -- hydrophones over water,
seismometers over land. The readings are interpreted by seismologists for signs of oil
and gas traps.
Although modern oil-exploration methods are better than previous ones, they still may
have only a 10-percent success rate for finding new oil fields. Once a prospective oil
strike is found, the location is marked by GPS coordinates on land or by marker buoys on
water.
So, How Is Oil Found?
It all begins with oil exploration...
Petroleum geologists and engineers have established that oil, when trapped, collects into underground pools called reservoirs. It is from these reservoirs that oil is produced. So, all these geologists have to do is find the oil reservoirs and sit back and watch the oil production flow! Couldn’t be easier right? Well, not exactly.
It is said that the best place to find oil is in an oilfield. This is true, without question. But, what do you do when there is no defined oilfield, and there are no nearby wells? It sounds quite simplistic but, think about it, every major oilfield must have begun with the drilling of the field’s first well.
How did they know where to drill the well, and how did they convince their bosses that drilling that well was worth the expensive research and drilling costs? Doesn't sound so easy now, eh?
If you're thinking there's some risk to all of this, well there definitely is tremendous risk!
The industry calls these wells miles away from known production, wildcats. Depending on the results of their attempts at finding hydrocarbon, the wells are known as discovery wells or dry holes.
If the discovery well shows hydrocarbon, other development wells are drilled to confirm the find. If nothing is found, well, the operator will simply abandon the well and move on to other prospects and plays.
Through the utilization of a variety of high and low-tech tools and methodologies, today’s producing reservoirs were discovered.
The presence of oil seeps and pits at surface is a strong indication that oil may be present underground. If a trapping mechanism exists below, one may have found a reservoir.
The surface exposure (outcropping) of known source and reservoir rock suggests the right conditions for oil generation and storage may be present. If a trap of some kind were detected, it is possible that a reservoir could be discovered.
So, how do geologists detect reservoirs miles below the surface of the earth?
The only direct way of confirming oil’s presence is to drill a well.
But, drilling a well is an expensive proposition. Most wells cost in excess of $100,000 to drill, and many cost over $1,000,000. Given that the success of finding commercially producible-sized hydrocarbon reservoirs is approximately 1 in 10 chances, oil companies - out of sheer necessity - seek to minimize the cost of failed wildcats by exhausting all reasonable indirect methods of locating hydrocarbons first.
Seismic surveys, using a variety of sonic wave producing guns and extra-sensitive listening devices, allow geophysicists to obtain profiles (cross-sections) of subsurface rock at great depths. If a trap of some sort can be deduced from the sub-surface reflections, there is a chance that oil or gas can be found.
Gravitational and magnetic surveys are flown by aircraft over areas on land and sea to identify the geophysical properties which might suggest the presence of hydrocarbon bearing traps.
Ultimately, though, it is only by drilling the well that the indirect observations will be confirmed.
Oil Well Drilling
Preparing to Drill Once the site has been selected, it must be surveyed to determine its boundaries, and
environmental impact studies may be done. Lease agreements, titles and right-of way
accesses for the land must be obtained and evaluated legally. For off-shore sites, legal
jurisdiction must be determined.
Once the legal issues have been settled, the crew goes about preparing the land:
1. The land is cleared and leveled, and access roads may be built.
2. Because water is used in drilling, there must be a source of water nearby. If there
is no natural source, they drill a water well.
3. They dig a reserve pit, which is used to dispose of rock cuttings and drilling mud
during the drilling process, and line it with plastic to protect the environment. If
the site is an ecologically sensitive area, such as a marsh or wilderness, then the
cuttings and mud must be disposed offsite -- trucked away instead of placed in a
pit.
Once the land has been prepared, several holes must be dug to make way for the rig and
the main hole. A rectangular pit, called a cellar, is dug around the location of the actual
drilling hole. The cellar provides a work space around the hole, for the workers and
drilling accessories. The crew then begins drilling the main hole, often with a small drill
truck rather than the main rig. The first part of the hole is larger and shallower than the
main portion, and is lined with a large-diameter conductor pipe. Additional holes are
dug off to the side to temporarily store equipment -- when these holes are finished, the rig
equipment can be brought in and set up.
Depending upon the remoteness of the drill site and its access, equipment may be
transported to the site by truck, helicopter or barge. Some rigs are built on ships or barges
for work on inland water where there is no foundation to support a rig (as in marshes or
lakes).
Drilling The crew sets up the rig and starts the drilling operations.
First, from the starter hole, they drill a surface hole down
to a pre-set depth, which is somewhere above where they
think the oil trap is located. There are five basic steps to
drilling the surface hole:
1. Place the drill bit, collar and drill pipe in the hole.
2. Attach the kelly and turntable and begin drilling.
3. As drilling progresses, circulate mud through the
pipe and out of the bit to float the rock cuttings
out of the hole.
4. Add new sections (joints) of drill pipes as the
hole gets deeper.
5. Remove (trip out) the drill pipe, collar and bit
when the pre-set depth (anywhere from a few
hundred to a couple-thousand feet) is reached.
Once they reach the pre-set depth, they must run and
cement the casing -- place casing-pipe sections into the hole to prevent it from
collapsing in on itself. The casing pipe has spacers around the outside to keep it centered
in the hole.
The casing crew puts the casing pipe in the hole. The cement crew pumps cement down
the casing pipe using a bottom plug, a cement slurry, a top plug and drill mud. The
pressure from the drill mud causes the cement slurry to move through the casing and fill
the space between the outside of the casing and the hole. Finally, the cement is allowed to
harden and then tested for such properties as hardness, alignment and a proper seal.
So, How Are Oil Wells Drilled?
Oil well drilling has been the main means of producing oil ever since Colonel Drake drilled that first well in 1859, which signaled the start of the American petroleum industry.
Drilling techniques and equipment have changed throughout the decades from cable tools to rotary-based ones, from straight holes to sidetrack and GPS-based directional drilling, and from “guess-timates” and “feel” to computer-based accuracy.
The biggest improvement in oil well drilling, however, has been in the preparations prior to ever breaking ground.
Photo courtesy Phillips Petroleum Co.
Rotary workers trip drill pipe
The drilling of a well, especially a “wildcat” is a milestone event, involving practically every sub-discipline of the oil business, and signifies the start of direct field investigation.
For the oil exploration and production company, the drilling of the well represents final exploration sunk costs prior to the possibility of recovering those costs through well production revenues. For the petroleum geologist and the reservoir engineer, the drilling of the well represents the final confirmation of the interpretation of numerous strands of indirect evidence of oil’s presence. For the production and facilities engineers, it represents the soon to be realized asset requiring sub-surface and surface management and equipment to maximize production. And, for the
drilling engineer, well, it is time to earn their pay!
Through experience and communications with geologists, reservoir engineers, production engineers, and facilities engineers - the technical team - the drilling engineer develops a plan for reaching the targeted formation at the bottomhole location identified, from the surface location specified – at the cost authorized.
Before ever setting up on the drilling location, the drilling engineer has gained all of the necessary approvals to drill from company and regulatory authorities . The appropriate hole dimensions, the wireline testing procedures, the well casing program, and the cement volumes are all known upfront.
The drilling engineer has already scheduled an oil well drilling rig, alerted a wireline and cementing service company, and ordered necessary drilling fluids, tanks, pipe and safety equipment (including blowout prevention equipment; Operations normally proceed on a 24 hours per day basis and depending on methods, depths, and rock types encountered, can last anywhere from a few days to several months.
History has shown that rarely do operations proceed in a “normal” fashion. Each well is its own story. It is quite normal to encounter hard rock zones, and experience sand control problems, as well as for minor equipment breakdowns to occur - right next to a well which didn't experience half of the problems! Drill bits wear out, wrong auxiliary equipment is delivered, and various other events happen that slow progress, raise corporate anxieties, and compromise schedules.
Due to all of the problems, which can and do happen on site, oil companies have increasingly focused on safe operations. This is something everyone can control.
Most oil well drilling operations are actually completed by drilling service companies, with oil company drilling engineers supervising. Oil companies are using their natural leverage by insisting on safe operations by contractors, which minimize employee “accidents” and environmental impacts, and maximize accountability. Drilling service
companies with poor safety records are not kept for long.
Drilling Operations
Operations proceed in accordance with terms of a permit issued by the regulatory agency with jurisdiction. Normally, a drilling location is graded, a conductor pipe is set to support subsequent casing strings, blowout control equipment is installed and
tested for well safety, the drilling rig and auxiliary equipment is moved in and set up, and drilling operations are underway.
Contemporary drilling operations consist of downhole tools (drill bits, reamers, shock absorbers, etc.), drill string components (drill collars, drillpipe, kelly, etc.), suspension equipment (rotary swivel, hook, blocks, and wire rope), supporting structures (derrick), rotary drive mechanism (rotary table, turbodrill, dynadrill), hoisting equipment (drawworks, auxiliary brakes, cathead, etc.), transmission systems (mechanical transmission, clutch, belts, and chains), prime movers (diesel, turbo-electric), hydraulic circulating system (slush pump, high pressure surface equipment, drill string, shale shaker, desander, degasser, mud tanks/mixers), and
rig floor and wellhead accessories/tools (cat lines, elevators, rotary slips, power slip, safety clamps, power tongs, rig instrumentation, blowout prevention equipment, etc.)
Although each area is vitally important to safe and efficient drilling operations, the drill string including the downhole tools is the most important area; being at the point of impact, transmitting surface derived energy into bottom-hole torque and
hole digging.
The drill string/subsurface assembly is composed primarily of a swivel, a kelly, drillpipe, a drill collar, and a bit. The swivel connects the rotating drill string to the drilling rig support system. It suspends the drill string, permits free rotation and serves as the means for drilling fluid circulation. Drilling fluid is circulated through the drill pipe and bit to cool the bit and assist in cuttings removal. The drilling fluid also serves to coat the open-hole to prevent cave-ins and prevent any reservoir fluids (oil, gas and water) encountered from rushing in.
The swivel connects to the kelly, which is usually either a square or hexagonal-sided pipe of about 43 feet long, that transmits the torque from the rotary table on the rig floor to the drill string causing the bit to turn and make hole. Drill pipe sections are
connected to the kelly one at a time allowing the bit to work deeper and deeper in the hole.
The drill collar is a heavy-walled pipe which connects the drill bit to the drillpipe. Its weight puts pressure on the bit to keep it working at the bottom of the hole.
The drill bit is the primary downhole tool, cutting up formation as it rotates. Diamond bits are used for hard formations. However, tri-coned steel-teethed bits are most commonly used today. Sometimes, geologists inspect the cuttings that are circulated to surface to identify and confirm the formation that is currently being drilled.
At various and defined intervals, the well may be logged by wireline service companies. Why is this done? Well logging tells the industry experts the formations they are in, the fluids present within the formation (including oil!) and the quality of the cement job.
Metal pipe called surface casing is inserted into the well once the drillpipe is removed, and is cemented to the earth by cementing service companies. Cement is
pumped and circulated within the well to permanently affix the pipe to the earth.
This provides support, and limits communication between the surface and the subsurface to just that space inside of the pipe.
Subsequent drilling punctures the bottom of the recently placed cement sheath and continues down to the objective depth. To drill deeper, the rig crew performs the seemingly routine act of ceasing rotary table rotation and mud circulation, lifting the drill string, setting it on slips at the rig floor, breaking the joint between the kelly and the topmost drillpipe with tongs, screwing on an additional length of drillpipe at the kelly, lifting the string again, removing the slips, lowering the string downhole, and reestablishing mud circulation and rotary table rotation.
Intermediate casing might be run in hole and cemented, too, depending on well design criteria and formation characteristics. When the total depth is reached a final cement job is conducted to either plug the well back up because no significant hydrocarbon was found, or to secure the production casing string in place for future completion and production.
The drilling contractor rigs down and moves off of the drilling location and heads on to the next assignment.
e.g
The drill rig being used for the larger 8 5/8 inch diameter borehole appears to be a
standard rotary rig. This particular rig is mounted on a large truck chassis and the truck
frame is then anchored and raised onto supports once it has driven to the well site. There
is a tall mast (sometimes mistakenly called a derrick) that is raised into a vertical position
above the borehole. At the top of this mast is a device known as a crown block (a pulley)
that along with several cables is used to lift and lower another block (another pulley)
called the traveling block. The traveling block is attached to what is called the "drill
string" which is a long set of pipes with a drill bit on the bottom end. This pair of blocks
allows the drillers to add sections of drill pipe (typically about 30 ft long) to the drill
string as the drill penetrates the earth.
The drill string is rotated in the hole as it is being drilled, using power from an electric
motor, which in turn is usually powered by a large diesel engine. The drill string has a
mixture of water and mud pumped through it from the top of the pipe. This mud is
pumped down the drill string, through the drill bit, and returns up the sides of the hole
around the drill string. This helps lubricate the drill string allowing it to turn in the hole,
and pushes the crushed rock from the drill bit out of the hole and back up to the surface.
The mud is filtered and recirculated through the system at the surface. This mud also
serves to stabilize the borehole and prevent it from collapsing inward around the drill
string.
The drill bit itself is about 8 inches in diameter and has several moving parts. A typical
drill bit has tungsten-carbide, or diamond tipped teeth that cut the rock as the drill string
turns. The weight of the drill string and the drill rig help to push the drill bit downward to
cut the rock.
I have not seen any pictures of the drill rig that cut the small diameter borehole, but it is
possible, and even likely that it is a different type of drill rig that was chosen because
even though it cannot drill as large a hole, it is faster. It may be an air drill rig, or a coiled
tubing rig. These types of drill rigs use air as the circulation medium and for small holes
in the right type of well-consolidated rock can drill much faster. Coiled tubing is simply a
method of using a long length of continuous flexible drill pipe that is fed off of a reel as
the well drilling progresses. This method can also accelerate drilling, since it is not
necessary to stop drilling to add a new length of pipe as the borehole gets deeper and
deeper.
Oil Rig Systems Once the equipment is at the site, the rig is set up. Here are the major systems of a land
oil rig:
Anatomy of an oil rig
Power system
large diesel engines - burn diesel-fuel oil to provide the main source of
pumped down the well and out the perforations. The pressure from this fluid makes small
fractures in the sandstone that allow oil to flow into the well, while the proppants hold
these fractures open. Once the oil is flowing, the oil rig is removed from the site and
production equipment is set up to extract the oil from the well.
Oil Industry Production
So, How Is Oil Produced?
When discussing oil industry production, consider this: geologists have estimated
that the migration of petroleum from their place of origin deep inside the earth into surrounding reservoir rocks takes a long time. Time is measured in millions of years, not centuries!
They argue that this fact is based on the physics of fluid flow through semi-permeable material (rock) under a pressure gradient. The fluid must travel from pore to pore, micrometer by micrometer until settling in its host reservoir – and that
simply takes time.
If no trapping mechanism exists, then the hydrocarbon rises to the top of the fluid column and/or surface where it seeps out. Although seeps are plentiful, their natural flowrates are not enough to meet demand.
Blowouts and Fires In the movies, you see oil gushing (a blowout), and perhaps even a fire, when drillers reach the final depth. These are actually dangerous conditions, and are (hopefully) prevented by the blowout preventer and the pressure of the drilling mud. In most wells, the oil flow must be started by acidizing or fracturing the well.
Society, today, needs lots of oil – and, right now! Oil industry production must continually be produced in the millions of barrels per day to quench our thirst. So, how do oil companies produce oil to satisfy this need?
They explore, drill wells, and produce oil at the field’s maximum efficient rate.
In places where a oil trap exists, prior to well penetration, little if any fluid movement occurs, as the trapping mechanism prevents any escape of hydrocarbon within the structure. An equilibrium condition is established, balancing fluid phases and reservoir pressures - that is, until a well is drilled.
Imagine for a moment that the oil reservoir, located a mile or so beneath the earth’s surface, is like a giant sponge sitting on a kitchen counter. Oil saturates the reservoir like water saturates the sponge, filling most of the available pore spaces.
Just like a sponge sitting on a counter, the oil sits in suspension within the reservoir
with no droplets escaping. Only when pressure is applied to the sponge by squeezing it or placing something on it, will the sponge give up some of its water.
Similarly, oil will not move until its equilibrium condition is upset. Once a well penetrates this isolated environment, releasing stored pressure, the well balance suddenly shifts and its characteristics will never again be the same.
So, how is oil produced?
Oil is produced through the creation of a significant pressure drop between the outer reaches of the reservoir and the wellbore at depth.
With pressure drops sufficient to overcome pore pressures, oil stored deep in reservoirs will flow to the low-pressure sink.
Getting oil to move out of the ground and to the market is what oil industry production and the petroleum business is all about. The challenge for the production engineer then is to first get the oil to the wellbore. The next challenge is to get it to
the surface.
With the drilling of a well, subsurface pressures can be released. These pressures can and do exceed thousands of pounds per square inch (psi). When producing without artificial support, the reservoir pressure automatically begins to decline.
It is estimated in most producing wells, half of the total reservoir pressure drop occurs within the first 10-20 feet from the wellbore.
Now, having a means of escape, the enormous weight of the rock sitting atop of the reservoir squeezing the once resistant pores, now forces the pores to compress, expelling oil, gas and water through the well. The characteristics of the oil itself contain entrained lighter hydrocarbons (gases), which in the presence of a drop in
pressure, begin to separate from heavier liquids and cause hydrocarbon to exit the reservoir. Water inflow, fed from external sources, constantly pushes against the hydrocarbons, which now can escape through the well.
These characteristics of a reservoir are known as natural drive mechanisms and are individually called compaction drive, solution gas/gas cap drive, and water drive. Reservoirs typically have components of several, if not all of the drive mechanisms at work, but usually have one of them behaving in a more dominant fashion than the others.
Understanding the particular drive mechanisms at work within a specific reservoir is essential to efficient and effective petroleum extraction. A company can easily drill and produce wells in locations that hamper natural drive mechanisms, leaving oil behind that will never be recovered.
The rate of flow of the fluids in the reservoir is governed by the fluid densities and the drop in pressure from the reservoir to the wellbore. Henry Darci, a nineteenth
century engineer, was first to document the proportional relationship of flow rate and pressure drop in porous media.
As fluid is produced from a well under natural drive mechanisms, the pressure drop from the well, which was highest when the well was first produced, begins to diminish.
As a consequence, the flow rate of the well, normally measured in terms of barrels per day, also diminishes. Without any assistance from the engineer, the
well’s production will eventually slow to a trickle, and finally cease. This could take days, years, or decades to occur.
In some cases, the natural drive mechanisms currently aren’t or never were sufficient to produce oil at the surface. But, just because the oil can’t flow to the surface doesn’t mean it is not sufficient in size or quality for commercial production.
It is estimated that primary drive mechanisms can typically produce about
30% of the oil in place within a reservoir. That means seventy percent of the original oil remains in place!
Once the oil is in the wellbore, pumps are used as necessary to lift oil to the surface. Oil, gas and water enter the well through perforations placed in the cemented pipe at the reservoir depth.
Typically, a ball and seat pump is attached to a series of slender metal rods called “sucker rod” that is ultimately connected to a pumping unit sitting on the surface, adjacent to the wellhead. As the pumping unit head bobs up and down each time, the pump completes a stroke, lifting a column of fluid closer to the surface. Once at the surface, the reservoir fluids are piped to production facilities.
Supplementary production techniques (also called secondary and tertiary recovery) like waterflooding and gas injection serve to replenish reservoir pressures, driving oil towards the wellbore. Steam injection and in situ combustion techniques are generally designed to improve the viscosity of the oil (enhance its ability to flow).
Miscible flooding, carbon dioxide flooding, and surfactant flooding focus on improving oil’s relative permeability to water and increase recovery.
Supplementary production techniques can add approximately 30% recovery of the original oil in place.
Production Monitoring/Forecasting
Current production rates are often compared with historical records and reservoir data to project future production trends and to assist in characterizing well performance. Production forecasts are vital to estimating the producible life of a well and its potential economic profitability.
How's it done, you might ask?
Well, engineers have derived functions that describe and match a given well's declining production history.
This function can be extended to predict future well performance.
If a well deviates considerably from the history matched projection, it could suggest a change in the condition of the reservoir, well, well equipment, or operations and measurement devices (i.e. surface or subsurface deviations).
Various staff and/or resources can then be employed to investigate the situation. Remedial work can be scheduled to fix the identified problem (such as tubing leaks, water breakthrough, rod spacing, pumping unit imbalance, pump malfunctions, scale development, broken flowmeter impeler, test station malfunction, etc.). Service companies are hired to conduct a variety of tasks like oil well stimulation by injecting acid into wells to dissolve downhole obstructions, and rod, pumps and tubing retrievals.
The regular and disciplined surveillance of production operations and subsequent repair and maintenance cannot be stressed enough to ensure optimal well performance and maximize efficient oil production.
Oil well stimulation plays a vital role in production operations. With oil prices at all-time highs, it is imperative from an oil company's perspective and the consumer's perspective that as much production as possible be safely extracted from the reservior.
Why? So, the oil company can realize the highest price per barrel, and the consumer can get more oil circulating in supply to balance demand. But then, we digress...
It has been said by many wise petroleum investors (oxymoron?) that the industry's saving grace is that their assets are in the ground! Once found, they argue, it is difficult to lose. Clearly, these investors weren't reservoir engineers as will be explained below.
Producing that oil isn't as simple as running the kitchen faucet and watching the basin fill-up. Natural production tendencies for wells are for the oil production rates (and reservoir pressure) to be at its highest at initial production, and fall-off considerably as the well is produced. Typically, one finds oil rates declining as water
production increases, driving up operations costs while revenue shrinks. This scenario continues until the well fails and/or becomes uneconomic to operate or repair.
The purpose of oil well stimulation, then, is to increase a well's productivity by restoring oil production to original rates less normal decline, or to boost production above normal predictions.
So, what is oil well stimulation?
Oil well stimulation is the general term describing a variety of operations performed on a well to improve its productivity.
Stimulation operations can be focused solely on the wellbore or on the reservoir; it can be conducted on old wells and new wells alike; and it can be designed for remedial purposes or for enhanced production. Its main two types of operations are
matrix acidization and hydraulic fracturing.
Matrix acidization involves the placement of acid within the wellbore at rates and pressures designed to attack an impediment to production without fracturing or damaging the reservoir (typically, hydrofluoric acid is used for sandstone/silica-based problems, and hydrochloric acid or acetic acid is used for limestone/carbonate-based problems). Most matrix stimulation operations target up to a ten foot radius in the
reservoir surrounding the wellbore.
Hydraulic fracturing, which includes acid fracturing, involves the injection of a variety of fluids and other materials into the well at rates that actually cause the cracking or fracturing of the reservoir formation.
The variety of materials includes, amongst others: water, acid, special polymer gels, and sand. The fracturing of the reservoir rock and the subsequent filling of the fractured voids with sand ("proppant") or the creation of acid channels allows for an enhanced conduit to the wellbore from distances in excess of a hundred feet.
So, why do wells need oil well stimulation?
Hydraulic fracturing and acid fracturing in practically all types of formations and oil gravities, when done correctly, have been shown to increase well productivity above that projected in both new and old wells. From an economic standpoint, oil produced today is more valuable than oil produced in the future. Fracturing candidates may not necessarily "need" oil well stimulation, but the economics may show that such a treatment would pay=off.
To understand why remedial stimulation (matrix acidization) is necessary, you have to consider the conditions at work, deep down inside the reservoir...
Before the well is ever drilled, the untapped hydrocarbons sit in the uppermost portions of the reservoir (atop any present water) inside the tiny pore spaces, and in equilibrium at pressures and temperatures considerably different from surface conditions.
Once penetrated by a well, the original equilibrium condition (pressure, temperature, and chemistry) is permanently changed with the introduction of water or oil-based
drilling fluids loaded with suspended clays, and the circulation of cement slurries. The interaction of the introduced fluids with those originally present within the reservoir, coupled with pressure and temperature changes can cause a variety of effects which, in turn, can plug the numerous odd-shaped pores causing formation damage. Some of the types of damage include: scale formation, clay swelling, fines migration, and organic deposition.
Petroleum engineers refer to the level of formation damage around the wellbore as skin effect. A numerical value is used to relate the level of formation damage. A positive skin factor reflects damage/impedance to normal well productivity, while a negative value reflects productivity enhancement.
Formation damage, however, is not limited to initial production operations. Remedial operations of all kinds from well killing to well stimulation itself, can cause formation damage. Nor is fines and scale generation limited to the reservoir. They can also develop in the wellbore in casing and tubulars, and be introduced from surface flowlines and incompatible injection fluids. These fines and precipitates can plug pores and pipe throughout an entire oil field.
In short, any operation throughout a well's life can cause formation damage and impede productivity.
So, how do you keep from damaging the formation while stimulating a well?
Oil field service companies offer chemical inhibitors useful for the full spectrum of well operations that can be injected into the well ahead of acidization or other such stimulation activities to reduce fines generation and organic deposition, or introduced in surface flowlines on a regular basis to prevent scale precipitation and build-up.
Operational techniques such as bringing on production or injection slowly after stimulation activities (to prevent damaging flow surges which could mobilize once immobile fines within the pores, plug perforations, or cause sand control problems downhole or at the surface), and routine maintenance and surveillance (like cleaning out process filter traps which can easily clog lines and cause the transfer of damaging suspended particles, or monitoring production decline to identify potential
deviances before the problem is exacerbated).
Importantly though, a sound understanding of formation damage causes, and the
inclusion of chemists/chemical engineers on the production team will lead to increased
well productivity and life.
So, What About Oil Refining?
You may have seen an oil refining facility while driving along the highway. Was it dark even during the day, with lights and strange noises? Were there enumerable pipes of all sizes running here and there? Did you see plumes of white and gray smoke billowing from numerous short and tall stacks, and eternal flames lighting up the evening sky?
By day it is a mysterious collection of odd-shaped pressure vessels and storage tanks – some large, some short; some narrow, others wide. At night, with the vessel shapes somewhat obscured by the escaping steam and the amber safety lights, the refinery at a distance can be easily confused for a small city more than the industrial facility it is.
It is a vital element of the oil industry, creating the refined products that are the foundation of state economies. But how does it work, and what is the controversy all about?
Well, let’s deal with the controversy first...
The process of refining oil is complex. High temperatures and various techniques and chemicals are required to safely refine oil into the products that society requires.
As a consequence of refining the oil, numerous chemicals can be released into the
atmosphere in a gaseous state, creating potential air pollution impacts.
Who wants to live next door to a refinery? Who wants their kids going to school downwind of the constantly emitting smoke stacks? Who would rather see the amber glow from the neighboring refinery than the evening stars? Clearly, the answer in each case is few. But, it is this negative perception of the refining industry that is its
own impediment.
The truth is, technologies have improved, but no new refineries have been built in the U.S. for thirty years!
Why? Because it is nearly impossible for businesses to navigate the political/social/regulatory gauntlet to finally gain permission to build a new refinery and economically refine oil.
Renovations and retrofits also present problems to industry as the act of retiring antiquated equipment and processes trigger requirements to adhere to current permitting rules and standards that are in some cases, impossible for the pre-1970 technology refineries to meet.
So, the aged refineries remain in place, continuing to serve their intended functions, but unable to change their dirty images.
The other area of controversy stems from the scheduled shutdowns and its impact
on supply and fuel costs. It is much easier to believe that industry executives with sinister motives are negatively impacting supply and driving up costs than to accept the fact that old-fashioned refineries require constant attention and maintenance to operate effectively.
Due to the fact that there are so few of them, every shutdown of an oil refinery - scheduled or not - has a ripple effect on supply.
So, how do refineries work anyway?
Refineries exist to process hydrocarbon delivered from oil fields into various blends and products to meet market demand. The odd-shaped vessels and auxiliary equipment are vital for refining oil – separating elements of crude oil into purer
components for consumer use.
The process of separation actually begins miles if not continents away from the refineries. As oil, gas and water are produced from a well; the well fluids are routed through metal pipelines from the well to production gathering facilities located within the oil field leases.
The primary functions of production facilities are to separate the water from the hydrocarbon, and to separate the hydrocarbon into products that meet required specifications for transfer and sale.
For efficiency reasons, the production facilities are sized to accommodate concurrent production from several wells and contain several tanks designed to assist in separation and storage of the various fluids (gas, oil and water).
Fluid volumes, temperatures and pressures are measured by flow meters and gauges placed throughout the process. The operator and engineers can determine individual well performance by operating wells in production test mode. This is vital for confirming reservoir conditions and forecasting future production. If a well’s
production performance deviates from expected volumes, some malfunction may have occurred, requiring immediate attention by company and oil field services specialists.
Most facilities utilize inherent fluid properties to separate them from each other. Gas will rise above liquids; most oils will float on water. The production facility, then, captures the fluids through gravity separation.
Produced water, unfit for human consumption, is processed to strip residual hydrocarbon and is typically re-injected into the producing formation for reservoir pressure support, or injected into some barren formation for disposal.
Associated gas, uneconomic for sale, is usually routed to a flare and consumed.
Gas that is marketable is compressed and stored in pressure vessels until transferred most likely in pipelines to market. Oil is trucked or piped in the most economical
means to refineries for further processing. Tanker ships also play a vital role in meeting global gas and oil demands.
Once delivered to the refinery, crude oil is heated in pressure vessels to temperatures in excess of 1000 degrees Fahrenheit. As the temperature rises, different components of the oil begin to separate from the remaining crude – first the light hydrocarbons precipitate out, then the heavier ones.
This process of refining hydrocarbon is called distillation, and it is the primary method for obtaining refined liquid petroleum gases (LPGs, butane and lighter), light straight naphtha (gasoline), kerosene (jet fuel), distillates (diesel fuel and home heating oil), and heavy gas oil and residuum (used in catalytic cracking and coking).
As the lighter distilled products are consumed most in the U.S., heavy gas oil and residuum are commonly further refined in a process called catalytic cracking to produce lighter, high-valued product. Based upon the sophistication of the individual refinery, a barrel of crude oil can provide 20-60% gasoline product.
For environmental reasons, the federal government, various states and regions within the states have established different requirements on the quality/characteristics/contents of gasoline sold in their areas of jurisdiction. The requirements help the regulatory agencies meet mandated air quality goals. However, the consequence of these requirements is the limited use of various and available blends of gasoline in times of short supply.
