BEFORE WE CAN INTERPRET ONSHORE PRESTACK DATA: This is a typical example of what onshore prestack seismic data looks like, and the steps it must go through before it can be used for AVO analysis. It is very important for the interpreter to work closely with the processor to get the desired result, and for the interpreter to understand what is being done with the data to make sure the conditionin
TRENTON LIMESTONE, East Central Indiana: These gathers are from three productive wells in the Trenton carbonate and are a combination of porous hydrothermal dolomite and porous limestone.
Conventional wisdom in seismic exploration is that the frame modulus of carbonate reservoirs is too ridged to produce an AVO response. In my 20+ years of experience, productive carbonates are just as prone to pro
KNOX FORMATION, East Central Indiana: These gathers are from three productive wells in a Knox sand at the top of a Knox remnant. This is a very challenging play as the crest of the Knox remnant is not always very evident.
These gathers also demonstrate how challenging pre-stack data can be to interpret. The processing of the pre-stack seismic data is the key to the successful use of the AVO interp
RED FORK SAND, Oklahoma: Channel sand and non channel sand examples. Both produce a Class II AVO response but with differing intercept responses.
UPPER MORROW SAND, Oklahoma: These gathers along with the seismic section and map view below demonstrate how three different geologic combinations result in the same amplitude on the stack, but have completely different responses in the prestack domain. All three stack as a positive amplitude, but only one is productive.
PSTM wiggle traces over AVO gradient. In this example, both the ten foot productive sand and non sand interval of the dry hole produce a peak on the stack. However, the producer has a strong negative AVO gradient and the dry hole does not. Inferring a stacked amplitude by itself to be analogous to pay can easily lead to a dry hole.
Standard pre-stack time migration offers superior imaging over post-stack time migration. PSTM does a better job of tightening up structural features and improves fault resolution. Prestack-depth migration provides even further improvement to the image, and should always be an added consideration.
Pre-stack time wiggle traces over the AVO attribute. When combined with structure, the AVO attribute makes finding a productive well location all the more easier.
Acoustic impedance inversion (AI) provides additional information about the rock properties in a given location. High impedance (red) is indicative of rocks having high density values and therefore low porosity, whereas low impedance values (blue) are indicative rocks with lower density values which may correspond with higher porosity than adjacent areas.