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Play-level Identification of Sweet Spots: Integrated Shale Play Resource Assessment Methods

Abstract

An approach that is integrated from the initial interpretation of the available data, through the petroleum system modeling, to the delineation of the sweet spot area, and finally, the calculation of the resources has the best chance for yielding a resource assessment that will be the foundation for accurate economic evaluation and profitable development. Assessment of the resource potential of a shale play relies on the identification of the sweet spot and non-sweet spot areas. Often the major differentiating factor between the potential resources in one play or another is the areal extent of the sweet spot. Having a geologically-based, objective method for identifying these areas is the foundation for making reliable and consistent assessments of the shale play resources. This paper will define the key steps for shale reservoir analysis through several phases: regional reconnaissance, prospect delineation, and resource development as a continuum process. This reconnaissance phase of the study includes regional mapping of well calibrated shale zone potential that delineates shale thickness, source maturity, and porosity and permeability measures. Key to analysis of these geologic parameters is developing an understanding of the entire geologic section's depositional and structural history to better assess the development and orientation of natural fracture systems. Additionally, 2D seismic inversion analysis of the well calibrated seismic data will aid in defining the rock quality fairways. These fairways are analyzed within the context of a complete 3D petroleum system model which produces an integrated evaluation of hydrocarbon generation and remaining potential of hydrocarbon in place. Output from this model along with all of the analysis from the reconnaissance phase are used as proxies for the key elements of shale play adequacy when creating play-level continuous adequacy maps. Continuous chance of adequacy maps are created for Reservoir, Charge, and Mechanical success. These maps were combined into a Total Shale Play Adequacy map. This chance of adequacy map is used to define the minimum, most-likely and maximum sweet spot areas. This range of areas is used in the probabilistic resource assessment. It is combined with ranges for well density, EUR per well, and well success rate to give probabilistic estimates of the hydrocarbon resource volumes. These maps are kept current and used through the subsequent decision processes.