--> Sweet-Spotting Unconventional Plays Using Geo-Microbial Hydrocarbon Detection and 4G Exploration Model

AAPG Annual Convention and Exhibition

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Sweet-Spotting Unconventional Plays Using Geo-Microbial Hydrocarbon Detection and 4G Exploration Model

Abstract

It is well documented that mature source rocks and most oil and gas accumulations have hydrocarbon microseepage, a process in which small, light hydrocarbon molecules (mainly C1-C5) driven by reservoir pressure and buoyancy penetrate overlying rocks through natural microfractures and migrate to the surface. Hydrocarbon microseepage is widespread, predominantly vertical, and is dynamic. The flux of hydrocarbon microseepage is found strongest over hydrocarbon accumulations, faults and fractures. In order to make reliable detection and interpretation of hydrocarbon microseepage, Geo-Microbial Hydrocarbon Detection (GMHD) technique and the concept of “4G” exploration model were developed. GMHD method measures the population of specific hydrocarbon oxidizing bacteria (HOB) in surface soil or sediment which use the continuing supply of trace concentrations of hydrocarbons from microseepage as their only carbon and energy source (or food). There is a dynamic equilibrium and direct relationship between the population of HOB and the flux of hydrocarbon microseepage. Proper integration of geology, geophysics, geochemistry and geo-microbiology information, so-called “4G” interpretation, can greatly improve the sensitivity, accuracy and reliability of hydrocarbon detection of potential traps as well as identifying sweet-spots in unconventional plays. For conventional oil and gas exploration, GMHD technology and 4G model have been applied in over 70 surveys in China with varying terrains (deserts, mountains, permafrost, loess plateau, shallow seas and deep water) and different exploration targets (structural, stratigraphic). The effectiveness of the GMHD technology and 4G model has been validated by the drilling results of over hundreds wells and numerous major oil and gas discoveries, in both onshore and offshore China. For unconventional oil and gas exploration, the current challenge is to predict the sweet spot or area of most economical productivity prior to drilling and fracturing. GMHD application on tight gas survey in Ordos basin and shale gas survey in Sichuan basin have successfully demonstrated its ability of identifying sweet spots in unconventional plays. It could be used as a predictive tool to delineate the unconventional gas field, core area, and probably high production zone. The basic principles, methodology, case studies with drilling results of GMHD and 4G exploration model will be illustrated in the presentation.