Integrating Basic and Advanced Mud Gas Analysis With Classical Formation Evaluation for Enhanced Compartmental Characterization

Abstract

Mud gas logging is a standard service on almost every drilling job. One of the many advantages of such datasets are its capital efficient data acquisition with a wide range of potential utilizations. Classical wellsite safety measures are just one of the applications, however, the identification of potentially productive zones in the subsurface with geoscience interpretation which lead to better decisions in the completion program are also possible.

This study is the first approach to assess a whole hydrocarbon field based on mud gas analysis data. Historically, these datasets were primarily used to describe and interpret single wells. However, in heavily compartmentalized fields, classical formation evaluation data is often not sufficient to identify fluid boundaries and what degree of communication exists, if any.

The approach presented uses various ratios of the hydrocarbon concentrations of methane (C₁) to pentane (C₅), to eliminate uncertainties related to geochemistry. In addition to the standard mud gas concentrations (C₁ to C₅), advanced gas analysis data including hexane (C₆) and heptane (C₇) were available on two wells, which bring additional answers and value into this field study.

During this field-wide study, the mud gas analysis yields a distinct pattern, separating the field into twelve compartments with major geochemical differences. These zones show variances in biodegradation and maturity and are in good alignment with structural data.

Besides the determination of fluid segments, the gas ratio interpretation indicates gas-oil and oil-water contacts that coincide with both the contacts published in literature and the ones determined by classical formation evaluation.

Geochemical evaluation of mud gas data proves to be a beneficial tool to evaluate and determine compartment boundaries, without requiring time consuming laboratory experiments. Important reservoir and fluid parameters can be highlighted by analyzing the datasets commonly available at a majority of wellsites, in either a gas-while drilling application or for post well analysis tying this value to a field based understanding of the reservoir. The analysis of these accessible datasets can influence drilling and production decisions much faster than conventional laboratory geo-chemistry datasets.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018