Wellsite Detection Of Gas Reservoirs With Advanced Wireline Logging Technology

A new integrated openhole logging system has been introduced to replace conventional logging technology for density, neutron porosity and natural gamma ray spectrometry evaluations. Combined with another recently introduced induction device measuring an array of formation resistivities at different radii of investigation, this system provides new measurements and improved replacement measurements that are particularly suited for the detection and evaluation of thin, shaly gas reservoirs. This paper presents a simple wellsite technique that takes advantage of the high-quality measurements provided by this logging system to evaluate gas-bearing intervals in shaly sands. Emphasis is on taking advantage of sophisticated logging systems to assess hard-to-evaluate formations while keeping the evaluation process extremely simple and robust, and thus, objective and suitable for wellsite evaluation. Examples comparing conventional logging data to the information provided by this new technology are discussed. Log evaluations are confirmed with core analysis or production data. Examples of gas detection in clean and shaly sands involving a tool sting free of chemical nuclear sources are also discussed. In several cases the new information has turned plug-and-abandon candidates into commercially successful wells. Adoption of this logging and evaluation technique by a major South Texas gas operator has allowed the operator to greatly increase proven reserves.