Methods and systems for determining core permeability pulse decay experiments

A system for determining core permeability, the system comprising:

• a sample holder holding a core sample of a subsurface formation;
• an upstream reservoir connected to one end of the sample holder;
• a downstream reservoir connected to another end of the sample holder;
• an inlet pump connected to the upstream reservoir;
• an outlet pump connected to the downstream reservoir;
• a plurality of pressure sensors connected to the upstream reservoir, the downstream reservoir, and the sample holder;
• and
• a processor configured to receive signals from the plurality of pressure sensors, and determine the core permeability based on a pressure in the upstream reservoir and a pressure in the downstream reservoir, wherein the system is further configured to:
• provide a constant confining pressure (Pc) within the sample holder;
• saturate the sample holder and the core sample with nitrogen at a saturation pressure, Psaturation;
• and
• apply a pressure pulse, Ppulse, to one end of the sample holder, wherein the core permeability is determined using the formula:
• Pu(t)−Pd(t)=f(ϕf,L,A,Vbulk,c,μ,Vf,Vu,Vd,k,t)
• where ‘Φf’ is the porosity of the sample from the mobile continuum, ‘L’ is the sample length, ‘A’ is the cross-sectional area of the sample, ‘Vbulk’ is the bulk volume of the sample (where Vbulk=L×A;
• and ϕ=Vs/Vbulk), ‘c’ is the gas compressibility, ‘μ’ is the gas viscosity, ‘Vf’ is the pore volume of the mobile continuum, ‘Vu’ is the upstream reservoir volume, ‘Vd’ is the downstream reservoir volume, ‘Pu(t)’ is the pressure of the upstream side, ‘Pd(t)’ is the pressure of the downstream side, ‘k’ is the sample permeability, and ‘t’ is time.

A computer program for use in a method for determining core permeability, the method comprising the steps of:

• connecting an upstream reservoir to one end of a sample holder holding a core sample of a subsurface formation;
• connecting a downstream reservoir to another end of the sample holder;
• providing a constant confining pressure (Pc) within the sample holder;
• saturating the sample holder and the core sample with nitrogen at a saturation pressure, Psaturation;
• applying a pressure pulse, Ppulse, to one end of the sample holder;
• and
• the computer program comprising program instructions that when executed by a processor, cause the processor to determine core permeability of the subsurface formation using the formula:
• Pu(t)−Pd(t)=f(ϕf,L,A,Vbulk,c,μ,Vf,Vu,Vd,k,t)
• where ‘Φf’ is the porosity of the sample from the mobile continuum, ‘L’ is the sample length, ‘A’ is the cross-sectional area of the sample, ‘Vbulk’ is the bulk volume of the sample (where Vbulk=L A;
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• ‘c’ is the gas compressibility, ‘μ’ is the gas viscosity, ‘Vf’ is the pore volume of the mobile continuum, ‘Vu’ is the upstream reservoir volume, ‘Vd’ is the downstream reservoir volume, ‘Pu(t)’ is a pressure of the upstream side, ‘Pd(t)’ is a pressure of the downstream side, ‘k’ is the sample permeability, and ‘t’ is time.