Abstract
Background:The integrity of the extracted core in loose sandstone gas reservoirs is poor, and because hydration and collapse easily occur, it is difficult to evaluate the sensitivity characteristics accurately by the traditional core flooding experiments.Objectives:We instead investigate the stress sensitivity and water sensitivity of the formation water soaking time using digital core technology.Methods:We take the core of a loose sandstone gas reservoir as a research object and begin by scanning the core samples with a CT scanner. A three-dimensional image of the core can be obtained, the digital information extracted, the pore structure of the porous media mapped directly to the network, and a digital core established using the principles of fractal geometry. The three-dimensional pore network model can also be extracted. Next, we can compare and correct the results calculated by the model based on the real core experimental results, and an objective and effective digital core model can be obtained.Results and Conclusion:Finally, we can calculate the different effective stress, pore throat parameters (pore throat radius, shape factor, coordination number, pore-throat ratio) and relative permeability of different formation water injury times. The research results demonstrate that in sandstone gas reservoir development, as the effective stress continuously increases, the rock pore-throat parameters continue to decrease, and the permeability of the reservoir rock ultimately declines by more than 43.2%. Clay minerals will expand after the edge and bottom water intrude into the reservoir and soak it for a long time: the pore throat is significantly narrowed within 30 days, while after 30 days more, the pore throat undergoes any only slight further changes, and the final permeability decline of the reservoir rock is up to 5.7%. The research results provide important basic petrophysical data for the development of loose sandstone gas reservoirs which, in turn, provide a scientific basis for formulating a reasonable gas production rate in a gas reservoir.
Highlights
The integrity of the extracted core in loose sandstone gas reservoirs is poor, and because hydration and collapse occur, it is difficult to evaluate the sensitivity characteristics accurately by the traditional core flooding experiments
The Open Petroleum Engineering Journal, 2018, Volume 11 85 technology has been gradually introduced into physical reservoir research, resulting in a new research method [4, 5] Using a real rock pore space reaction 3D digital core based on a rock microstructure reconstruction [6 - 8], the research scope involves microscopic percolation mechanisms, core displacement simulation experiments, prediction of core macroscopic conductivity, evaluation of oil displacement effects, production dynamic simulation of reservoirs and determining the boundaries of oil and gas field development technology policies [9]
As the digital core technology has been successfully applied in all types of complex hydrocarbon reservoirs, it will be introduced for loose sandstone gas reservoir physical analysis in this study, to examine the sensitivity of rock through establishing a digital core of loose sandstone
Summary
The integrity of the extracted core in loose sandstone gas reservoirs is poor, and because hydration and collapse occur, it is difficult to evaluate the sensitivity characteristics accurately by the traditional core flooding experiments. The Open Petroleum Engineering Journal, 2018, Volume 11 85 technology has been gradually introduced into physical reservoir research, resulting in a new research method [4, 5] Using a real rock pore space reaction 3D digital core based on a rock microstructure reconstruction [6 - 8], the research scope involves microscopic percolation mechanisms, core displacement simulation experiments, prediction of core macroscopic conductivity, evaluation of oil displacement effects, production dynamic simulation of reservoirs and determining the boundaries of oil and gas field development technology policies [9]. As conventional displacement experiments are difficult to achieve, it is difficult to evaluate the sensitivity of the rock under coring conditions accurately, which increases the difficulty of developing gas reservoir development technology policy [17]. As the digital core technology has been successfully applied in all types of complex hydrocarbon reservoirs, it will be introduced for loose sandstone gas reservoir physical analysis in this study, to examine the sensitivity of rock through establishing a digital core of loose sandstone
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