System for measuring the pore volume and permeability of very tight core plugs and method therefor

Abstract

A system and method for measuring Klinkenberg permeability and pore volume of a tight core plug sample is provided wherein a pressure transducer is positioned between the sample cell and the manifold of the system.

I claim: 
     
       1. A method for determining the pore volume of .Iadd.a .Iaddend.very tight core .[.samples.]. .Iadd.sample .Iaddend.with an apparatus having a manifold in selective fluid communication with a sample holder holding said core sample, said sample holder having an outlet, said method comprising the steps of: (a) sealing the outlet of the sample holder .Iadd.while maintaining the sample holder in fluid communication with the manifold.Iaddend.,   (b) pressurizing the manifold .[.volume.]. and the sample holder with a gas to a predetermined pressure, P FILL ,   (c) sealing the .[.core.]. .Iadd.sample .Iaddend.holder and .Iadd.a .Iaddend.pressure transducer from the manifold .Iadd.while maintaining the pressure transducer in fluid communication with the sample holder.Iaddend.,   (d) waiting for the gas pressure in the .[.core.]. .Iadd.sample .Iaddend.holder to reach a first equilibrium .[.state.]. .Iadd.pressure.Iaddend., P E1 ,   (e) measuring the value of .Iadd.said .Iaddend.pressure P E1  .Iadd.with the pressure transducer at a location between the manifold and the sample holder.Iaddend.,   (f) venting the manifold to .Iadd.the .Iaddend.atmosphere so that the manifold .[.pressure obtains zero psig.]. .Iadd.is at atmospheric pressure.Iaddend.,   (g) sealing the manifold in response to said venting so that the sealed manifold .[.contains zero psig.]. .Iadd.remains at atmospheric pressure.Iaddend.,   (h) delivering the pressurized gas at said first equilibrium pressure, P E1 , from the sample holder into the manifold .Iadd.such that the sample holder, manifold and pressure transducer are in fluid communication wiht one another.Iaddend.,   (i) waiting for the delivered pressurized gas to reach a second equilibrium .[.state.]. .Iadd.pressure.Iaddend., P E2 ,   (j) measuring the value of said .Iadd.said .Iaddend.pressure .[.PE2.]. .Iadd.PE 2  with the pressure transducer at the aforesaid location.Iaddend., and   (k) determining the pore volume, .[.Vp.]. .Iadd.V p  .Iaddend., of the core .[.plug.]. .Iadd.sample .Iaddend.in the sample holder based upon the measured values of .Iadd.said first and second equilibrium .Iaddend.pressures.Iadd., .Iaddend.P E1  and P E2 .   
     
     
       2. A method for determining the pore volume of .Iadd.a .Iaddend.very tight core .[.samples.]. .Iadd.sample .Iaddend.with an apparatus having a manifold in selective fluid communication with a sample holder holding said core sample, said sample holder having an outlet, said method comprising the steps of: (a) providing a manifold volume, V o , that is substantially equal to the pore volume, V p , plus the dead volume.[., V d ,.]. of .[.the line and.]. the sample holder .Iadd.and a line between the manifold and the sample holder, V d  .Iaddend., (FORMULA 5),   (b) sealing the outlet of the sample holder .Iadd.while maintaining the sample holder in fluid communication with the manifold.Iaddend.,   (c) pressurizing the manifold .[.volume.]. and the sample .[.holders.]..Iadd.holder with a .Iaddend.gas to a predetermined pressure, P FILL ,   (d) sealing the .[.core.]. .Iadd.sample .Iaddend.holder and .Iadd.a .Iaddend.pressure transducer from the manifold .Iadd.while maintaining the pressure transducer in fluid communication with the sample holder.Iaddend.,   (e) waiting for the gas pressure in the .[.core.]. .Iadd.sample .Iaddend.holder to reach a first equilibrium .[.state.]..Iadd.pressure.Iaddend., P E1 ,   (f) measuring the value of .Iadd.said .Iaddend.pressure P E1  with the pressure transducer,   (g) venting the manifold to .Iadd.the .Iaddend.atmosphere so that the manifold .[.pressure obtains zero psig.]. .Iadd.is at atmospheric pressure.Iaddend.,   (h) sealing the manifold in response to said venting so that the sealed manifold .[.contains zero psig.]..Iadd.remains at atmospheric pressure.Iaddend.,   (i) delivering the pressurized gas at pressure, P E1 , from the sample holder into the manifold .Iadd.such that the sample holder, manifold and pressure transducer are in fluid communication with one another.Iaddend.,   (j) waiting for the delivered pressurized gas to reach a second equilibrium .[.state.]. .Iadd.pressure.Iaddend., P E2 ,   (k) measuring the value of .Iadd.said .Iaddend.pressure.Iadd., .Iaddend.P E2 , .Iadd.with the pressure transducer.Iaddend., and   (l) determining the pore volume, .Iadd.V p  .Iaddend., of the core .[.plug.].  .Iadd.sample .Iaddend.in the sample holder based upon the measured values of .Iadd.said first and second equilibrium .Iaddend.pressures.Iadd., .Iaddend.P E1  and P E2 .   
     
     
       3. A method for determining the pore volume of .Iadd.a .Iaddend.very tight core .[.samples.]. .Iadd.sample .Iaddend.with an apparatus having a manifold in selective fluid communication with a sample holder holding said core sample, said sample holder having an outlet, said method comprising the steps of: (a) providing a manifold volume, V o , that is substantially equal to the pore volume, V p , plus the dead volume.[., V d ,.]. of the .[.line and the.]. sample holder .Iadd.and a line between the manifold and the sample holder, V d , .Iaddend.(FORMULA 5),   (b) sealing the outlet of the sample holder .Iadd.while maintaining the sample holder in fluid communication with the manifold.Iaddend.,   (c) pressurizing the manifold .[.volume.]. and the sample .[.holders.]. .Iadd.holder .Iaddend.with a gas to a predetermined pressure, P FILL ,   (d) sealing the .[.core.]..Iadd.sample ep holder and .Iadd.a .Iaddend.pressure transducer from the manifold .Iadd.while maintaining the pressure transducer in fluid communication with the sample holder.Iaddend.,   (e) measuring the value of .[.the.]. .Iadd.a .Iaddend.first equilibrium pressure.Iadd., .Iaddend.P E1 , with the pressure transducer at a location .[.above.]. .Iadd.on said line between .Iaddend.the .[.core.]. sample .Iadd.holder .Iaddend.and .[.below.]. the manifold,   (f) venting the manifold to .Iadd.the .Iaddend.atmosphere so that the manifold .[.pressure obtains zero psig.]..Iadd.is at atmospheric pressure.Iaddend.,   (g) sealing the manifold in response to said venting so that the sealed manifold .[.contains zero psig.]..Iadd.remains at atmospheric pressure.Iaddend.,   (h) delivering the pressurized gas at .Iadd.said first equilibrium .Iaddend.pressure, P E1 , from the sample holder into the manifold .Iadd.such that the sample holder, manifold and pressure transducer are in fluid communication with one another.Iaddend.,   (i) measuring the value of a second equilibrium pressure, P E2 , .Iadd.with the pressure transducer .Iaddend.at the aforesaid location, and   (j) determining the pore volume.Iadd., V p , .Iaddend.of the core .[.plug.]. .Iadd.sample .Iaddend.in the sample holder based upon the measured values of .Iadd.the first and second equilibrium .Iaddend.pressures.Iadd., .Iaddend.P E1  and P E2 .   
     
     
       4. An improved apparatus for determining the pore volume of .Iadd.a .Iaddend.very tight core .[.samples.]. .Iadd.sample.Iaddend., said apparatus having a manifold (40) in selective fluid communication through .[.a line.]. .Iadd.lines .Iaddend.(112, 114) with a sample holder (60) holding said core sample (70), said sample holder (60) further having an outlet valve (.Iadd.120).Iaddend. being capable of being opened to atmospheric pressure, said improved apparatus comprising: a valve (110) connected to said .[.line.]..Iadd.lines .Iaddend.(112, 114) for selectively opening and closing said .[.line.]. .Iadd.lines .Iaddend.(112, 114),   a transducer (50) connected to said line (.[.112,.]. 114) at a location .[.below.]. .Iadd.between .Iaddend.said valve (110) .Iadd.and said sample holder .Iaddend.(60),   said manifold (40) being formed to have a volume.Iadd., V o , .Iaddend.substantially equal to the pore volume, .[.Vp.]. .Iadd.V p  .Iaddend., of said core sample plus .[.the.]. .Iadd.a .Iaddend.dead volume.[., V d ,.]. of said line (114) .[.below said valve (110.]., said sample holder (.Iadd.60).Iaddend., and .Iadd.a .Iaddend.line (52) to said transducer (50).Iadd., V d  .Iaddend.,   means (130, 132, 134) for delivering gas into said manifold (40) and sample holder (.Iadd.60).Iaddend. at a fill pressure, P FILL , when said valve (.Iadd.120).Iaddend. is closed, said transducer (50) being capable of ascertaining a first equilibrium pressure, P E1 , when said valve (.Iadd.110).Iaddend. is closed,   means (100, 102, and 104) for venting gas into the atmosphere from said manifold (40) when said valve (.Iadd.110).Iaddend. is closed in response to said ascertainment of said first equilibrium pressure, said venting means becoming closed when said manifold (40) obtains zero psig,   said transducer (.Iadd.50).Iaddend. being capable of ascertaining a second equilibrium pressure, P E2 , when said valve (110) is opened, and   means (.Iadd.160).Iaddend. connected to said transducer (50) for determining .Iadd.the pore volume of the core sample from .Iaddend.said first and second equilibrium pressures, P E1  and P E2 .   
     
     
       5. A method for determining the permeability of .Iadd.an .Iaddend.extremely tight core .[.samples.]. .Iadd.sample .Iaddend.with an apparatus having a manifold in selective fluid communication with a sample holder holding .[.a.]. said core .[.plug.]. .Iadd.sample.Iaddend., said sample holder having an outlet, said method comprising the steps of: (a) closing the outlet of the sample holder,   (b) pressurizing the manifold .[.volume.]. and .[.core.]. .Iadd.the sample .Iaddend.holder with a gas to a predetermined pressure, P FILL ,   (c) selectively sealing the manifold from the .[.core.]. .Iadd.sample .Iaddend.holder,   (d) opening the outlet of the sample holder .[.in order to obtain atmospheric pressure.]. .Iadd.to the atmosphere.Iaddend.,   (e) allowing the pressure P FILL  in the sample holder to decay .Iadd.to atmospheric pressure .Iaddend.as the gas flows from .[.the.]. .Iadd.a .Iaddend.volume at the seal .[.above.]. .Iadd.between .Iaddend.the .[.core.]. .Iadd.sample .Iaddend.holder .Iadd.and the manifold .Iaddend.through the core .[.plug.]. .Iadd.sample.Iaddend., and through the outlet, .[.thereby venting the gas to atmospheric pressure,.].   (f) measuring a predetermined number of .[.values, in time, of the.]. instantaneous pressure .Iadd.values over time .Iaddend.near said seal during the .[.period of.]. pressure decay, and   (g) determining the permeability of the core .[.plug.]. .Iadd.sample .Iaddend.from said instantaneous .[.time and.]. pressure .[.measurements.]. .Iadd.values over time.Iaddend.. .Iadd.6. The method of claim 2 wherein the sample holder and pressure transducer are sealed from   
     
     
        the manifold by sealing the line therebetween..Iaddend. .Iadd.7.  The method of claim 3 wherein the sample holder and pressure transducer are sealed from the manifold by sealing the line therebetween..Iaddend.