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Mapping of gulf coast strike slip faults To the left is a set of associated strike slip and adjustment faults on

the Lousiana coast. The section itself may be thought of as a series

of simulated sonic logs. It is land data, of medium quality. The work

is an extension of my strike-slip North Sea work.

Important preliminaries – 

Before starting on supporting details consider this slide.

I jumped to a spot in the project where faults were so clear theystand by themselves. Within any one fault block there is almost no

stratigraphic thinning or thickening, while between blocks substantial

changes occur. On fault A you will see this overall difference result in an

apparent normal attitude at the top and a reverse fault attitude at thebottom Also note that the “drag  effects”  often disagree with the fault

slope. These factors, plus the curved nature of the faults themselves tell

us we are looking at strong parallel movement. Some adjustments are

inevitable but strike slip is the nature of the main structure.

Within the main series we see probable salt intrusions affecting the

structure. This phenomenon makes it tough to track the faults at depth.

The first structural priority of this study is to understand the highly faultedintermediate section.

The motivations for this show are several.  As an unreconstructed

structural geologist, the ability to see this complex geology is exciting,

even if no others pay attention. The probability that missed reservoirs

can be found within the bounds of this shooting raises my personal

economic frustration level. Finally, the fact that the ADAPS resolution

system is not yet accepted keeps me awake at night.

On the slide pair that follows I ask you to spend time toggling back

and forth between the stacked input and my detuned output. I hope you

pay close attention to the lithologic character being brought out. Nowhere

is correlation quality more important than in complexly faulted zones. To

understand the importance of horizontal movement is basic to structural

geology. In short there are many facets to study.

On the next slide I show that mapping these faults has an economic

 justification by pointing to previous drilling activity..

To prepare this short show I ran 74 in-lines, then repeated with

no detuning. My first concern was whether I could satisfactorily track the

faults from one end of the prospect to the other. Satisfied that I could, I

then just interpreted a short series to prove my point. This set follows.

Toggling –  If you have never used this method of comparing, pleasespend some extra time on the next two slides. Use the arrow keys.

A

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Please toggle w arrows – 

(use the “right” one here.) 

Straight stack (the input)

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Please toggle w arrows

ADAPS high resolution output.

Please notice the greatly improved clarity

of the fault breaks. While they are visible on the

input (toggle with left arrow to see), it would

have been hard to establish the pattern without

this improvement.

As important (but more subtle) is

the increased geologic believability supplied by

the sonic log nature of the final product. While

toggling you will hopefully notice that a number

of superfluous lobes have been eliminated fromthe input (left slide) by the advanced detuning.

Later you’ll  see a set of in-lines 

with the faults defined. It is important that you

notice how consistent the patterns are, even

though every fifth one was chosen. There are

Detailed changes, but they follow a believabletransition. This consistency is a logical proof of

the system itself.

Before going to that series,  I will

show you that a bunch of wells were drilled in

this faulted zone. I have no knowledge of their

targets, but since they are older, one would

assume they found oil in the zone we are

looking at.

So, if you are through toggling,  

click anywhere to see the drilling perspectivementioned.

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Comments blanked

for security.

Before intelligent detuning, section amplitudes derive from

individual primary reflections. These, in turn, come from both the tops

and the bottoms of lithologic beds. Depending on detailed interface

amplitudes for hydrocarbon indicators is fairly dangerous. Sonic log

simulation attempts to measure the energy coming from the integrated

beds. While not always perfect, this transition seems to check out nicely

Many ADAPS great well matches verify this observation.A collection of examples can be accessed via the ADAPS router.. 

Most oil & gas will be long gone from this old field,  but we should be able to spot obvious trapping situations, and we may

find missed reservoirs. Early in the ADAPS development game I was

encouraged to see abrupt positive amplitude changes connected with

obvious trapping situations. Hopefully you will find some of these in the

next series.

After the fault displays  I go through the entire prospect,

displaying a few promising in-lines.

My statements on previous drilling come from the partial

map shown below. The section at the left traverses along the red line on

this excerpt. These early wells predate the seismic shooting.

While I have not extended my fault series this far, let me say the pattern we see here is very similar to what you have seen

on the first slide, and will see on the following group . Orienting yourself

between the mapped line and the section, you should agree that most of

the wells fall within the obviously faulted zone.

The challenge for ADAPS is to show where they found the

oil.Unfortunately, the owner of this data objected to my showing a portion

of the project map that showed many old wells drilled in the faulted area.

They appeared to have no interest in that zone, being mainly concerned

with deep events that are not clearly defined even in this advanced work.

In any case you will just have to take my word that those wells

exist.

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Series start – 

I suggest you tab through

quickly to see how the fault

pattern holds for the eightin-lines. At the end you will

be given a repeat option.

Next time through  take

the time to see the geologic

reasonableness I spoke of,.

Sine this is a form of logical

proof.

Notice the cases where

the event correlation is

good across a fault, yet

there is a big change in

amplitude. Could it be the

bright spots were missed?

Keep running through 

the series, noticing how the

bright spots carry from one

in-line to the next. This is

direct reservoir detection!

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#2

Note the remaining

bright spots holding

steady.

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#3

Deep plate movement – 

While we are here, some talk on

the difficulty presented by lateral

faults is in order. Old habits die

hard, and we’re used to searching

for nicely lined up vertical throws.

In cases where the stratigraphy is

constant, we might see no offsets

across major strike slip faults! It

could well be that once we start

looking intelligently we will find

that this type of structure (causedby deep plate movement) is very

common. 

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#4

The more you work with

parallel faults the more

you’re  willing to believe

the quirky twists. Shear

is the determining thing.

Here it is horizontal. If

these faults were normal

the twists would have

been sheared off.

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#5

Too much salt is bad, and it

certainly has given us problems in

seismic interpretation. While this is

pure conjecture, what might have

started as a major (but simple) set of

lateral faults turned into a complex

structure when weaknesses along

the faults allowed salt to be injected.Since much current emphasis is on

deeper events, our challenge is to

extend our resolution downward. 

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#6A

Fault A is probably majorhere. Stratigraphic correlations across

the others are fairly good, with minor

layering changes, while there’s almost

no matching in the upper zone on this

one. Deeper events do better, but this

is probably because the stratigraphy is

more constant down there. 

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#7

See comments on #5.

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#8

Click to repeat.

Or click elsewhere to see a few

hot spot examples outside the

developed area.

End of interpreted series.

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A

Concentrate on geologic believabilitywithin the individual fault blocks. You might note I might

have added a couple more detail faults at the very center,I wager they’ll show up on adjacent in -lines if I run them.

Once you believe (as I do) in what you are seeing, picking

faults gets easier.

Probable reservoir A is another example where the

amplitude increases across a fault (in an obvious trapping

situation). 

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To end the show – Possible reservoir A is

a good example of what I look for, both in

structure and amplitude.

And note the big stratigraphic differences 

across the arrowed fault. Obviously there a large

horizontal movement is involved. This one reality,

coupled with the splintered nature of the reservoirs

obviates the use of most current automatic picking

and mapping routines. The kind of analysis donehere seems an obvious precursor to any drilling.

Click here to start over.

Or here to repeat faults.

Or here for ADAPS router.

Or here for well matches.(Give it time to load.)