Martin Schoell¹, Leroy Ellis², Karlis Muehlenbachs³, Dennis D. Coleman⁴, Ian Underdown⁵

(1) Chevron Research and Technology Company, San Ramon, CA
(2) Terra Nova Technologies, Dallas, TX
(3) University of Alberta, Edmonton
(4) Isotech Laboratories, Inc, Champaign, IL
(5) Datalog, Calgary, Alta

ABSTRACT: Gas Isotope Analyses While Drilling (GIAWD): An Emerging Technology for Exploration and Production

Mudgas logging, i.e. the compositional analysis of gases returned with the drilling mud, is a standard monitoring and safety tool in the oil and gas industry . However, with the advent of modern formation evaluation technology, information from mudgas analyses is less and less used for reservoir appraisal. Although it is long known that isotope analyses on natural gases provide detailed information on the origin of gases, isotope analyses have so far not been routinely applied to mudgases while drilling. However, modern analytical techniques are now available for the precise and rapid analysis of carbon isotope signatures of variable concentrations of hydrocarbons in mudgases. When applied in a profiling mode, i.e. narrowly spaced sample sets across reservoir zones, GIAWD can provide valuable information related to exploration and reservoir appraisal. We will demonstrate case histories for the following applications:

1. Exploration a) Maturity of petroleum system b) Gas risk assessment c) CO2 risk assessment d) Type of gas/oil in an area e) Prediction of co-produced liquids in gas fields

2. Production a) Prediction of Compartments in horizontal and vertical wells b) Definition of gas hydrate horizons c) Definition of reservoir seals d) Reservoir communication e) Recognition of pay zones f) Production allocation

Future developments of this technology in a proposed Joint Industrial Project will include the development of 1) software for data interpretation in conjunction with FE software 2) a well-site-deployed isotope analyzer Internet-based data reporting and interpretation

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado