Abstract

Over the past 5 years there has been a huge increase in the production of crude oil from unconventional shale plays. During this time the major unconventional plays in the USA (e.g. Permian Basin, Anadarko Basin, Eagle Ford) have become some of the world's largest oil producers. However, unlike in ‘conventional’ exploitation, the target zones in Unconventional systems are generally the source rocks themselves and the wells are horizontal laterals requiring stimulation via hydraulic fracturing. In order to maximize hydrocarbon production operators have developed various well stacking methods, all of which require some form of monitoring to ensure spacing is optimized and fluid production is not being ‘stolen’ from adjacent formations, thereby reducing production potential in associated wells. This necessity – amongst other geochemical considerations – has resulted in the expansion of ‘production allocation’ and ‘time lapse geochemistry’ methods, initially developed for conventional systems, to be applied to these unconventional plays. However, direct applicability of this method to unconventional systems is not straightforward and numerous considerations and limitations need to be taken into account, foremost of which would be ‘what defines your end-members?’ In this paper we will outline the results of a case study from the Delaware Basin, for which we have both core material and produced fluids. The produced fluids cover 4 rounds of sampling spread across a 12 month time period and include target zones from the Bone Spring Shale (2) down to the Wolfcamp C Formation with equivalent core to compare against the target zones. The analytical program was consistent across all rounds and includes bulk, gas chromatography and biomarker methods (both traditional and non-traditional). The objective of the paper is to highlight the power and flexibility of both maximizing data collection methods and approaching the questions from a big data, statistical standpoint. Emphasis will be placed upon the considerations which must be made when designing and implementing a ‘reservoir geochemistry’ program in an unconventional play and how the approach outlined provides robust and applicable data on fluid relationships and statistically 'significant' changes through time.

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