Permeability is one of the most fundamental reservoir-rock properties required for modeling hydrocarbon production. However, the ultrafine pore structure of shale-gas reservoirs (pore-throat radii in the range of 1 -200 nm) cause the violation of the basic assumptions behind Darcy’s law. Depending on a combination of pressure-temperature conditions, pore structure and gas properties, non-Darcy flow mechanisms such as Knudsen diffusion, and/or gas-slippage effects will affect the matrix apparent permeability. Additionally, formation compaction and the release of the adsorption gas layer will affect the matrix apparent permeability during reservoir depletion.
The authors of this paper propose a unified matrix apparent-permeability model for shale-gas formations, which unifies non-Darcy flow / gas-slippage mechanisms, adsorption gas layer release, and geomechanical effects into a coherent global model, as shown below.
Mechanisms that alter shale-matrix apparent permeability during production
The fully coupled unconventional reservoir simulator developed in this study provides a comprehensive tool to investigate the combined real-gas nanoflow mechanisms and rock deformation effects on the matrix apparent-permeability, as well as the long-term productivity of hydraulically fractured shale-gas formations.
Conclusions from this research work are:
- Matrix apparent permeability in a shale formation is not only determined by the non-Darcy flow / gas-slippage behavior but also by the intrinsic permeability within the nanopore structure.
- Shale-matrix permeability derived from core samples at laboratory conditions needs to be correlated to reservoir conditions cautiously due to the extreme sensitivity of factors to the pore radius.
- While geomechanical effects (formation compaction) can temporarily dominate the matrix apparent-permeability evolution during the early-production stages, these will be offset by non-Darcy flow / gas-slippage behavior and gas-desorption effects and matrix apparent-permeability will start to increase due to pressure depletion.
- Impaired productivity in fractured shale formations during depletion is most-likely caused by reduction in fracture conductivity, rather than reduction in matrix permeability.
- The gradual release of the molecular adsorption layer has a significant impact on the matrix apparent-permeability evolution for small pore radii.
- Matrix apparent-permeability evolution during production can make a difference in well performance and long-term shale-gas production – even with the presence of a conductive natural-fracture network.
This summary, written by Special Projects Manager Nancy Musick, contains highlights of the following paper: Wang, H. Y. and Marongiu-Porocu, M. 2015. Impact of Shale-Gas Apparent Permeability on Production: Combined Effects of Non-Darcy Flow / Gas Slippage, Desorption, and Geomechanics. SPE Res Eval & Eng. SPE-173196-PA (in press; posted 7 October 2015).
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The SPE Research and Development Technical Section will host a special topical luncheon at ATCE 2015 on Tuesday, 29 September, to facilitate focused dialogue on new materials, techniques, and their applications to oil and gas. In a series of informative and thought-provoking presentations, a panel of industry experts will discuss current uses and future opportunities for these technologies as well as outline the various R&D challenges and needs that must be addressed to overcome their present limitations. A panel question-and-answer session will follow the presentations. Learn more about ATCE and register here.
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The start of this year saw most oilfield companies cut back significantly their spending plans in response to the dramatic drop in the oil price. The SPE Technical Directors have arranged a special session titled “Managing the Future Impact of Current Cost Cutting” to explore what the industry could and should be doing to minimize the impact this cost cutting will have both now and in the future. Plan to attend this special session at ATCE on Tuesday, 29 September. Register today!
Hear a web event on “Proposed Technologies to Address E&P’s Growing Energy Challenges” on 8 September. The oil and gas E&P industry faces big challenges to meet the world’s fast-growing energy needs and we don’t have all the answers. To address these situations, SPE held a Research & Development Competition specifically to encourage researchers from the basic sciences and other engineering disciplines to engage in our challenges. This webinar will feature the three winning projects that address these challenges. The featured speakers will be Vaihab Bahadur (first place) and Omar Laghrouche (third place).
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“Easy oil” is gone! The recovery challenge grows as the industry moves towards producing from increasingly more difficult reservoirs. Enhanced oil recovery (EOR) has reached new levels of technology. And improved oil recovery (IOR) has made significant advances. Yet, current recovery processes and their applications still have serious technical, resource, and commercial hurdles. Surmounting these hurdles and pushing recovery to higher levels requires a new mindset – innovative solutions now and into the future.
SPE will conduct a forum 18-23 October 2015 in Cancun, Mexico to discuss methods to accelerate new technologies deployment, explore smart integration of disciplines and professions, and examine ways to make EOR standard in the field development cycle. All with a view to developing a new culture focusing on recovery from the beginning.
Forum participants from all corners of the oil industry, government, and academia will address such challenges as:
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