Stewart, Simon¹, Peter Bentham² 
(1) BP Azerbaijan, Sunbury on Thames, United Kingdom 
(2) BP, Houston, TX

ABSTRACT: Shale and Salt Hold Key to Improved Seismic Interpretation

Seismic interpretation is a principal tool for reducing uncertainty in Exploration and Production projects. Accuracy of seismic interpretation is dependent on several unrelated sources of uncertainty including geological complexity and geophysical signal to noise. Steps that increase the accuracy of seismic interpretation, such as reprocessing projects, are the focus of significant dollar investment. These projects aim to improve geophysical signal to noise. Here we focus on a complementary approach by addressing intrinsic geological complexity. Structural style is a component of geological complexity. Constraints on structural style in a given setting, based on knowledge of the mechanostratigraphy, lead to improved seismic interpretation quality, especially in low signal to noise datasets. The mechanics of fault propagation across multilayers are complex and some scenarios are still the subjects of academic research. But simple rules of thumb based on empirical observations of large datasets plus rudimentary geomechanics lead to a number of endmember building blocks that can be used to construct structural style matrices. Sequences of carbonates and siliciclastics lithify during burial and are prone to brittle deformation. With the exception of freshly deposited siliciclastic megasequences, salt and shale are the weakest layers in most mechanostratigraphies. It is well known that these weak layers, or detachments, form a fundamental control on the style of thrust systems, and extensional systems. They also form the key elements in linked fault systems that are unrelated to, or significantly offset from, structures in the “mechanical basement”. In addition to a primary influence on structural style, salt and shale (if overpressured and mobile) can intrude and evolve the geometry of structures that begin as relatively simple expressions of a tectonic style. With these relationships in mind, knowledge of syntectonic mechanostratigraphy (e.g. well control) should form part of the seismic interpretation process, constraining the viability of a given interpretation.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.