Comparison of Source/Reservoir Rock Petroleum to Produced Petroleum Composition

Abstract

Geochemical assessment of the composition of oil extracted from rocks is substantially different from that of produced oils. There is an obvious fractionation of petroleum during production in gas and oil composition and distribution. Understanding the petroleum in the unconventional source/reservoir rock is fundamental to understanding production results from volumes to phase and oil quality. There are a variety of processes alter petroleum compositions. These include primary migration, expulsion, and secondary migration to conventional reservoirs. In addition there are potential in situ alteration effects such as evaporative fractionation, gas washing, and biodegradation often identified in light hydrocarbon distributions. Thermal processes leads to an exponential series of alkanes that can be utilized to characterize oil type (black or volatile oil, condensate, wet or dry gas) from slope factors to oil quality such as API gravity. The formation of non-linear hydrocarbons including branched and cycloalkanes as well as aromatics is a function of petroleum structures in organic matter that includes both kerogen and secondarily formed products and lithofacies or inorganic chemical composition of source rocks. This interaction results in isomerization reactions that redistribute the hydrocarbons found in oil. As a result of these processes, intrinsic gas-to-oil ratio (GOR) can be predicted for petroleum stored in organoporosity. This technique is now extended source and reservoir rock extracts for pre-drill or organofacies variations in oil quality and GOR. The result of these processes, interpretation, and intrinsic calculations is a better understanding of in situ reservoir hydrocarbon fluids enabling enhanced production engineering decisions.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015