Petrophysical Considerations in Evaluating and Producing Shale Gas Resources
- Carl H. Sondergeld (U. of Oklahoma) | Kent Edward Newsham (Apache Corp.) | Joseph Thomas Comisky (Apache Corp.) | Morgan Craig Rice (Apache Canada Ltd.) | Chandra Shekhar Rai (U. of Oklahoma)
- Document ID
- Society of Petroleum Engineers
- SPE Unconventional Gas Conference, 23-25 February, Pittsburgh, Pennsylvania, USA
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 5.1.1 Exploration, Development, Structural Geology, 4.3.4 Scale, 5.8.2 Shale Gas, 5.2 Reservoir Fluid Dynamics, 1.2.2 Geomechanics, 1.6.9 Coring, Fishing, 4.1.5 Processing Equipment, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 4.1.3 Dehydration, 4.6 Natural Gas, 2 Well Completion, 4.3.1 Hydrates, 1.2.3 Rock properties, 1.6 Drilling Operations, 4.1.2 Separation and Treating, 7.4.3 Market analysis /supply and demand forecasting/pricing, 5.1 Reservoir Characterisation, 2.4.3 Sand/Solids Control, 1.6.6 Directional Drilling, 7.4.4 Energy Policy and Regulation, 6.5.4 Naturally Occurring Radioactive Materials, 5.8.1 Tight Gas, 5.5.2 Core Analysis, 1.8 Formation Damage, 5.6.1 Open hole/cased hole log analysis, 1.10 Drilling Equipment, 5.4.2 Gas Injection Methods, 6.6.2 Environmental and Social Impact Assessments, 5.6.2 Core Analysis
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We present a practical assessment of petrophysical properties of shales and their measurement in the lab and via logs. Gas-bearing shale present unique measurement challenges due to their ultra-low permeability and complicated pore volume connectivity. The combination of low intrinsic permeability and gas sorption effects renders these reservoirs "unconventional??. Advances in horizontal drilling and hydraulic stimulation have transformed gas-shale resources into economic reserves. Given their economic significance, there is a strong drive to understand gas shale petrophysical property measurements, both in the laboratory and in the subsurface. We note that various core analysis protocols are used in different laboratories leading to physical property measurements that are inconsistent, even when measured on identical sample sets. In addition, log analysis of kerogen-rich shale is ‘unconventional' compared to classical techniques used in tight gas sands.
As shale gas evaluation is becoming widely practiced among service companies and operators, we will focus on three reservoir assessment categories: storage capacity (gas-in-place), flow capacity (gas deliverability) and mechanical properties impacting hydraulic stimulation. Within each of these categories we have identified influential petrophysical properties such as rock composition, total organic carbon (TOC) content, porosity, saturation, permeability and mechanical properties. Specifically, we demonstrate the importance of estimating accurate mineral and kerogen content as these properties directly impact rock quality, hydraulic fracturing protocols, and gas-in-place estimations. In reviewing these practices, we also will show the need and possible direction of new technologies that will be required for making evaluations more accurate and quantitative in the future.
The U.S. Energy Information Administration (EIA) states that natural gas currently constitutes approximately 25% of total primary energy consumption and 29% of primary energy production in the United States, based on a Btu-equivalent basis (Holtberg 2009). Advances in drilling and completion technologies combined with new gas-shale discoveries have opened abundant new supplies of natural gas in North America. America's Natural Gas Alliance (ANGA) states that due to dramatic increases in shale gas development in recent years, North America today has more than a 100-year supply of natural gas. The EIA states,?? natural gas from tight sand formations is currently the largest source of unconventional production, accounting for 30 percent of total U.S. production in 2030, but production from shale formations is the fastest growing source.?? According to the EIA, production of natural gas from shale formations is expected to triple by 2030 to 4.2 trillion cubic feet (TCF) representing 18 percent of total U.S. production (Thomas 2009). The expected growth in natural gas production from shale formations is far from certain; additionally, uncertainty exists in the accurate assessment of the basic reservoir attributes that describe a commercial gas-shale system.
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