SERRA, OBERTO, DANIEL MOTET, and JORGE VASQUEZ, Schlumberger, Montrouge, France

ABSTRACT: Detailed Facies, Genetic Sequences and Depositional Environment Analysis from Well Logs and Electrical Images

Any sequence stratigraphy analysis must integrate both volumes and surfaces. In the subsurface the full integration of well log and borehole image data allows determination of facies (mainly volume related) and genetic sequences (limited by surfaces).

As a first step, a precise lithology is derived from well logs using a complete set of measurements. When attempted with a reduced set of logs without calibration on core data a simplistic use of log patterns can lead to misinterpretation. The integration of geochemical well logs produces an even more reliable lithology determination. Examples of lithology analysis from standard well logs and geochemical logs illustrate this first step of the method.

As a second step, borehole images provide an identification of the rock texture and internal structure. They also permit the classification of surfaces and definition of the nature and origin of sedimentary breaks. This allows the user to assign a hierarchical relationship between surfaces. The information provided by logs and images, integrating thickness and bed boundary nature, leads to an accurate definition of facies.

Analyzing the facies organization permits the definition of genetic sequences and the recognition of the major breaks. The genetic sequence organization at a larger scale allows determination of the depositional environment. The major breaks will be used as time markers at the reservoir scale as well as at the basin scale. Images are also fundamental in not confusing breaks linked to faults with sedimentary breaks.

This approach is illustrated by examples from various sedimentary environments.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.