Shale Gas and Shale Oil Identification Through Geophysical Inversion of Well Logs

Abstract

Abstract

The Ocean* development framework allowed the creation of a Petrel* plug-in that helps to accurately identify shale gas and shale oil formations. The three different modules allow, by using conventional well logs and in a matter of seconds, the delimitation of lithological layers and the determination of key reservoir parameters for shale deposits. These parameters are: Total Organic Carbon (TOC), kerogen volume and its level of maturity (LOM), vitrinite reflectance (Ro%) and mineral volumes.

First, a filter is applied to the Gamma Ray well log to eliminate statistical variations and then the second derivate is used to determine the boundary of the different lithological layers. Once the limits are determined, all well logs are corrected, eliminating the influence of underlying and overlying layers. As a result, the reservoir parameters can be determined more accurately. Second, the LOM is determined by applying the Passey equation once the TOC has been calculated. This is done by either the Schmoker equation or the modified Schmoker equation. Both equations relate the density log with the amount of organic matter present in the formation. After the LOM is determined, the value of the vitrinite reflectance is calculated by using an equation developed through laboratory core analysis. Finally, the volume of minerals in the well is calculated. This is done through the Minimum-Length Least-Squares inversion method.

The different reservoir parameters provide useful information about shale plays. The TOC offers information about the amount of organic matter present in the rock. Both the LOM and vitrinite reflectance allow the identification of the oil and gas generation window. They indicate whether the reservoir contains oil, wet gas, dry gas or no hydrocarbons. Furthermore, the efficacy of the hydraulic fracturing can be determined, based on the brittle minerals in the reservoir.

By using the Petrel* Plug-in, a shale gas horizon was successfully identified in a Mexican well and, based on the reservoir parameters, the well was predicted to be an effective dry gas producer, which matches with the information provided by PEMEX, Mexico's national oil company. For this reason, it is certain that the new Petrel* plug-in is functional to effectively identify shale gas and shale oil reservoirs, determine the type of hydrocarbon existent, and the efficacy of the hydraulic fracking.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016