| CPC G01N 15/0826 (2013.01) [E21B 49/087 (2013.01); G01N 2203/0044 (2013.01)] | 9 Claims |
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1. A gas based testing method for a pore volume compressibility of a low-permeability rock, comprising the following steps:
obtaining an original pore pressure of a reservoir, dropping the original pore pressure level by level, obtaining a P-V relationship curve of experimental gas after each level of pressure drop at reservoir temperature, and calculating a compressibility of the experimental gas at all levels of pore pressures according to the P-V relationship curve: wherein the compressibility of the experimental gas is Cgi=1/Pi−∂Zi/(Zi∂Pi), Cgi represents the compressibility of the experimental gas at the ith-level pore pressure: Pi represents the ith-level pore pressure: Zi represents the compressibility factor of the experimental gas at reservoir temperature and the ith-level pore pressure; and ∂ is the differential symbol;
obtaining a reservoir core, measuring parameters of the reservoir core, and measuring isothermal adsorption capacity of the experimental gas in the core and isothermal desorption capacity of the experimental gas in a pressure drop process at all levels of pore pressures;
selecting a steel core with the same size as the reservoir core, drilling a through hole along an axial direction of the steel core, and measuring a through hole volume of the steel core at the reservoir temperature; meanwhile, based on a finite element method, obtaining volume deformation of the steel core at different overburden pressures; finally obtaining the through hole volume of the steel core at reservoir temperature and different overburden pressures;
based on a physical simulation experiment of depletion production, when the core is a steel core, and an overburden pressure is an initial overburden pressure of the reservoir, measuring a gas production volume of the experimental gas in the pressure drop process, and further obtaining system deformation Vsi=Vi−ΔVN2i, ΔVN2i=VG2i·Cgi (Pi−0.101), wherein Vsi represents the system deformation at the ith-level pore pressure, Vi represents the gas production volume of the experimental gas in the steel core in the ith-level pressure drop process, ΔVN2i represents the deformation of the gas in the through hole at the ith-level pore pressure, VG2i represents the through hole volume at the ith-level pore pressure, and Pi represents the ith-level pore pressure;
based on a physical simulation experiment of depletion production, when the core is a reservoir core, and an overburden pressure is an initial overburden pressure of the reservoir, measuring a gas production volume of the experimental gas in the pressure drop process, and further obtaining a pore volume of the reservoir core Vpi=Vpo−Vi′+Vsi+mΔVbi, wherein Vpi represents the pore volume of the reservoir core at the ith-level pore pressure, Vpo represents the pore volume of the reservoir core at room temperature and atmospheric pressure, Vi represents the gas production volume of the experimental gas in the reservoir core in the ith-level pressure drop process, ΔVbi represents a desorption gas volume of the experimental gas per unit mass in the pressure drop process, and m represents a weight of the reservoir core; and
obtaining the pore compressibility of the reservoir rock based on the overburden pressure and the pore volumes of the reservoir core at different pore pressures: Cp=−γ∂Vp/Vp∂Peob, wherein Cp′ refers to rock pore compressibility: Vp refers to experimental core pore volume, γ represents volume strain conversion coefficient, and Peob represents effective overburden pressure.
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