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Interactive interpretation of a tight gas sand using an intergrated workstation

James Culbertson, Andre Erlich, and Ken Landgren

Schlumberger

ABSTRACT

This paper describes a case history of log analysis and interpretation using new interactive processing and interpretation software. The sub­ject is a tight gas sand located in Southern Wyoming. Data include a full suite of openhole logs, including geochemical and borehole imaging data.

Lower resistivity anomalies in the main pay sand showed an increase of water at the top of the sand. This increase was difficult to explain from standard logs alone. The combination of borehole image information dis­played with the geochemical. log interpretation indicated that the zone was probably bioturbated, with illite filling the reworked sediment. The higher irreducible water saturation, which is often exhibited by this dep­ositional environment, was interpreted as the explanation for the increase of water at the top of the sand. The interpretation was later con­firmed by core analysis.

Bedding and texture characteristics of the rock greatly affect log mea­surements but are often ignored. The ability to combine the micro-geological features of the Formation MicroScanner measurement with the larger scale of the petrophysical interpretation brings added insight to the interpretation of the reservoir. These abilities are especially enhanced with an integrated, interactive workstation.

Interactive processing and interpretation also speed conventional data preparation activities such as edit, depth match and splice, and permits fast iterative parameter selection for accurate petrophysical analysis.

The study was performed using recently developed workstation software that was designed to satisfy the diverse requirements of varied applica­tions from different domains. The software architecture and its implementation provide data loading, data management, uniform sup­port for batch and interactivity, and powerful and flexible graphics functions.

The processing and interpretation of the subject data show the utility of an interactive analysis system for solving complex petrophysical prob­lems.