Abstract: Liberated, Produced, Recycled, or Contamination?

R. F. Mercer

Sufficient evidence exists to suggest that misinterpretation of well-site gas-detection data is quite common. The question often is asked, "How big a gas kick should I expect to get from a zone that will make a well?" Such misunderstanding often may be traced to a lack of familiarity with the fundamental principles of gas detection and interpretation.

To illustrate these fundamental principles, a drilling model demonstrates the effects of bit penetration. Analysis of the model explains theoretical gas-detection response to penetration of a hydrocarbon-bearing zone. Gas-kick characteristics, as transmitted to the surface by the drilling fluid, are related specifically to bit penetration. Careful analysis of the drilling model derived four classifications of gas present in the drilling fluid. These are (1) liberated gas, (2) produced gas, (3) recycled gas, and (4) contamination gas. Strong evidence indicates that all drilling-fluid hydrocarbons may be classified into one of the four categories. Each category has special geologic and drilling-engineering implications. Abnormal pressure detection and surveillance are especially importa t.

AAPG Search and Discovery Article #90971©1976 AAPG-SEPM Rocky Mountain Sections 25th Annual Meeting, Billings, Montana