An innovative technique to evaluate shale sweetspots

Date

2016-05

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Abstract

Shale plays that have unfavorable characteristics, such as formation depths of more than 10,000 ft. (TVD) or a scarcity of fresh water needed for hydraulic fracturing, present a special challenge for determining the feasibility of economic development. A new technique (introduced by Algarhy, Bateman and Soliman at SPE NATC 2015) to evaluate shale sweetspots takes into consideration their characteristic properties and represents them using only a single index, the “Sweetspot Quality Index” (SSQI). This index reflects the grade and scale of the sweetspot. The SSQI enables the comparison of sweetspots and it is calculated from four indices: the Reservoir Quality Index (RQI), the Completion Quality Index (CQI), the Conventional Behavior Index (CBI) and the Operation Index (OI). The RQI is calculated from sweetspot area, average thickness, TOC, effective porosity, saturations, free gas, adsorbed gas and residual hydrocarbon. The CQI is calculated from Young’s modulus, Poisson's ratio, overburden stress, closure stress, mineralogy, and the existence of micro fractures and lamination. The CBI is calculated from measurements of trapped sand or carbonate layers that are charged with hydrocarbon and have a conventional production behavior. The OI takes into account field operations cost, hydrocarbon prices, technical challenges and HSE issues. For validation purposes, the proposed technique has been applied to different data sets from North American shale plays, and the final results are very consistent with best practices. A detailed case study is presented that applies the SSQI to an economically borderline shale play in North Africa. The results are compared to similar cases in North America. Both were challenging cases mainly because of deep reservoirs (economic challenge). The work shows that a shale play under some challenging conditions can has an acceptable quality index and be developed economically. Calculating the SSQI gives an improved approach to evaluation, comparisons and recommendations for new sweetspots discovered. It lends itself to become a standard evaluation technique for both E&P and service companies.

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Keywords

Shale, Sweetspot, Evaluation, Quality, Index, Reservoir, Completion, Conventional, Behavior, Operation

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