Integrated Shale Gas Reservoir Modeling
C. Mike Du, Brad Melton, Sherif Gowelly, Xu Zhang, Y. Zee Ma, Peter Kaufman, 2011. "Integrated Shale Gas Reservoir Modeling", Uncertainty Analysis and Reservoir Modeling: Developing and Managing Assets in an Uncertain World, Y. Zee Ma, Paul R. La Pointe
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Gas production from shale reservoirs has led to an era with a new source for energy. Like many other exploration and production activities, uncertainty and risk in developing shale gas reservoirs are quite significant. Although many reservoir characterization efforts have been made to help understand shale gas reservoirs, a systematic reservoir modeling–based approach appears lacking in the literature. This chapter presents a methodology to integrate various sources of data for characterization and modeling of shale gas reservoirs, including seismic, geologic, borehole image, conventional well-log, hydraulic fracturing treatment, and microseismic data. An integrated reservoir characterization workflow enables uncertainty analysis and quantification, including multidisciplinary integration for better characterization of reservoir properties, experimental design to rank most critical parameters and dynamic reservoir simulation for probabilistic production forecasting. Such an integrated workflow is efficient in capturing main characteristics of shale gas reservoirs and offers a quantitative means for optimizing developments of these fields.
Driven by the gas demand in the last several years, shale gas production has continued to increase. Some of the characteristics of shale gas reservoirs include extremely low permeability, relatively low porosity, and moderate gas adsorption. For example, the Barnett Shale typically has permeability in the range of 100 to 600 nanodarcys, porosity in the range of 2 to 8%, and gas content in the range of 50 to 150 SCF/ton (Frantz et al., 2005; Gale et al., 2007; Loucks and Ruppel, 2007). To date, a large number of horizontal wells have been drilled, and massive multi-stages of hydraulic fracturing treatments (HFTs) have been commonly applied to achieve economic production and enhance productivity. The complex nature of the shale gas reservoirs is multifaceted, including total organic carbon (TOC), mineralogy and lithology, pore and throat geometry, texture, anisotropy and heterogeneity, natural fracture network, rock mechanical property heterogeneities and in-situ stress distributions, faults/karsts and structure impact, and production operation interaction with the reservoir. The latter itself included horizontal well pattern, well completion, hydraulic fracturing process (such as different fracturing operation schemes), the number of stages, perforation clusters, pumping rate, total volumes, and so on. Therefore, the development of shale gas reservoirs is quite different from that of conventional or other types of unconventional reservoirs. It is commonly difficult to obtain a clear understanding and an accurate description of the post-HFT reservoirs. To quickly acquire knowledge and guide well placements, various well-spacing pilots are commonly used, and various hydraulic fracturing operation schemes, such as “zipper-frac” and “simul-frac,” have been tested (Waters et al., 2009).