Petroleum Exploration

Upstream | Petroleum Exploration

The role of exploration is to provide the information requiredto exploit the best opportunities presented in the choice ofareas, and to manage research operations on the acquiredblocks.

An oil company may work for several years on a prospectivearea before an exploration well is spudded and during thisperiod the geological history of the area is studied and thelikelihood of hydrocarbons being present quantified.

Stages of a typical exploration program

Exploration is responsible for handling the risk intrinsic inthis activity, and this is generally achieved by selection ofa range of options in probabilistic and economic terms.

Indeed, exploration is a risk activity and the management ofexploration assets and associated operations is a major task

for oil companies.

The risk cannot be eliminated entirely but can be controlledand reduced adopting appropriate workflow, conceptual andtechnological innovations.

When it’s been decided to start up with an exploration projectin a basin or in a larger area containing several basins, thequantity and quality of available data must be acquired andevaluated – geological data, type of reserves, production ofexisting fields (if any), etc.

Basin assessment/evaluation is the first step to undertake thestudy of the area under interest.

Technological development has provided oil companies withBasin Modeling – which is a numerical simulations that allowsthe temporal reconstruction of the history of a sedimentarybasin and the associated evolution of the processes related tothe formation of petroleum accumulations.

Basin modeling – Petroleum system

On the basis of data and evidences collected from thepreliminary studies, the company management, in the light ofthe possibilities and the probabilities of a discovery basedon G&G data, aside from considerations of an economic nature,may decide to move to the following stage, which is theacquisition (through direct negotiations or by taking part inbids, etc.) of the legal right to perform prospecting in theselected area/block.

The owner of the mining right is normally the State, withwhich the oil company stipulates a contract establishing thecontracting parties’ rights.

Production Sharing Contracts and service contracts arefrequently adopted nowadays.

The sequence of activities covered by an exploration permit is

fairly uniform, and include

the creation of a databasethe analysis of available datathe programming of mapping and geological and photo-geological surveysseismic surveys and interpretation of seismic datathe choice of well locations, drillingthe analysis of results and the decision as to whetheror not to proceed with the application for a lease or torelease the area after fulfilling obligations

Goal of exploration is to identify and locate a prospect, toquantify the volume of hydrocarbon which might be contained inthe potential reservoirs and to evaluate the risk inherent theproject itself.

A prospect is a viable target evidenced by geological andgeophysical indications that is recommended for drilling anexploration well.

A detail of seismic section (time) and A horizon depth map(meters) referred to prospect X – (Treccani Petroleum

Encyclopedia)

The prospects identified must be technically practicable andmeet the market conditions to guarantee a financial return oninvestments.

The results obtained by drilling the exploratory wellsindicate whether the initial geological hypotheses are corrector whether variations are found.

All this will allow the fine-tuning of the economic analysisof the project possibly turning hypothetical reserves intoproved ones.

Where profitability does not meet the standards of thecompany, it leads to the termination of further investments.

The main petroleum exploration techniques

Geological mapping and prospecting

Geological mapping and prospecting are valuable techniques in

an petroleum exploration.

Geological mapping It is basically a technique which allows agraphical presentation of geological observations andinterpretations.

Geological prospecting make use of geological disciplines suchas petrography, stratigraphy, sedimentology, structuralgeology, geochemistry.

Such disciplines are used to achieve different targets but itmust be stressed that their integration is fundamental todepict a picture of reality.

Geophysical methods

Geophysical methods allow to study the physical properties ofthe subsurface rocks and they can be used in different phasesof the exploration in order to collect different types ofinformation.

Geophysical methods such as gravimetric, magnetometric,magnetotelluric, seismic are often combined to obtain moreaccurate and reliable results.

Gravimetric prospectingGravimetric prospecting is a geophysical techniquewhich is able to identify anomalies in the gravityacceleration generated by contrasts in densityamong bodies in the subsurface.Gravimetric prospecting is used to reconstruct ofthe main structural elements of sedimentary basinssuch as:

extension, thickness, salt domes, intrusiveplutons and dislocations or fault lines.

Magnetometric prospectingThis method involves measuring local anomalies inthe Earth’s magnetic fields.The method enable acquisition of data onstructural characteristics and depth of thesusceptive basement and therefore, indirectly, onthe thickness of sedimentary overburden andidentifies the presence, depth and extension ofvolcanic or plutonic masses within the sedimentarysequences.

Seismic prospectingSeismic prospecting has become the most valuabletechnique to reduce exploration risk of beingunsuccessful in locating a prospect.The technique is based on determinations of thetime interval that elapses between the initiationof a seismic wave at a selected shop point and thearrival of reflected or refracted impulses at oneor more seismic detectors.The phase of seismic data acquisition is followedby the seismic data processing phase (aimed to thealteration of seismic data to suppress noise,enhance signal and migrate seismic events to theappropriate location in space) than by theinterpretation of the generated subsurface image.

Left: Onshore seismic survey

Right: Marine seismic survey

Geophysicists interpret the processed seismic data andintegrate other geoscientific information to make assessmentsof where oil and gas reservoirs may be accumulated.

A 2D interpreted seismic section

Powered by advanced supercomputer power, rapid data loading,high-speed networking and high-resolution graphics,visualization centers provide the ability to display andmanipulate complex volumes of 3D data resulting in betterinterpretation of more data in less time.

Drilling the exploration wellOnce geological and geophysical information havedefined and evaluated (technically andeconomically) the drillable prospect, it ispossible to move to a fundamental phase of theexploration project – the drilling of the firstexploratory well.The drilling of the exploration well is aimed toconfirm the presence of the petroleumaccumulation.

Well loggingThe well logging technique consists of lowering a‘logging tool’ into the well to acquire geologicaldata and to reveal reservoir fluidscharacteristics.Well logging help geoscientists and engineers tounderstand:

Presence of reservoirPresence of hydrocarbons and characteristics

Reservoir properties, etc.. Coring

Coring provides the only means of obtaininghighquality samples for the direct measurement ofrock and reservoir properties.Core samples are then used to perform Routine CoreAnalysis and/or Special Core Analysis to obtaindetailed petrophysical data.

Coring and coring equipment at surface

Well testingA well test is the measurement under controlledconditions of all factors relating to theproduction of oil, gas, and water from a well.Well tests are conducted to acquire dynamic rate,pressure, temperature, and fluid property data.The acquired information is used to determinereservoir capabilities and important decisionssuch as production methods, well productionequipment, and field development drilling are madefrom the interpretation of well test results.

Well testing on board of semisub rig

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Treccani – Encyclopaedia of HydrocarbonsGeomore