Presentation on theme: "? 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."— Presentation transcript:
? 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 they stand 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 the bottom 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 faulted intermediate 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, please spend some extra time on the next two slides. Use the arrow keys. A
Please toggle w arrows – (use the “right” one here.) Straight stack (the input)
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 from the 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 believable transition. 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 perspective mentioned.
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.
? ? ? Series start – I suggest you tab through quickly to see how the fault pattern holds for the eight in-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!
#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 (caused by deep plate movement) is very common.
#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.
#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.
#6 A Fault A is probably major here. 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.
#8 Click to repeat. Or click elsewhere to see a few hot spot examples outside the developed area. End of interpreted series.
A Concentrate on geologic believability within 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).
A 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 done here 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.)