advances in unconventional shale gas resources_lecture1920_gas flow and permeability in shale gas systems

1、Instructor: Dr. Farzam JavadpourTel. (512) 232-8068Fall 2010GEO391Advances in Unconventional Shale Gas Resources Lecture 19 & 2011/08/2010Gas flow and permeability in shale gas systemsMacro-scale(Reservoir)Meso-scale(micro-fractures network)Micro-scale(Nano-pores network)Nano-scale(gas desorptio

2、n from nano-pore walls)wellboreMolecular scale (mass transfer from kerogen/clay bulk to pore surface(a)(b)(c)(d)(e)Gas is stored in kerogen and claysas dissolved gas and in pores as compressed gasCompressed gas in pores flowsthrough the pores first Then gas desorbs from the pore wallsThen gas diffus

3、es from the kerogen/claysto the pore walls and from there to the pore networkShale gas reserves and deliverability at different ScalesTriple porosityGanister GasJavadpour et al., JCPT, 2007Gas Evolution Lost Gas Estimation Average canister gas compositionImportant parameters to measurePorosity Measu

4、rements (boyles law)Boyles law: Grain volume or grain densityor sample skeleton densityArchimedes Law: Bulk volume or bulk densityHg injection: Bulk volume or bulk densityPycnometer apparatusMatrix permeability and productionGas flow in nanoporesnmU=0U=0U=UmaxmLprq84Poiseuille flowrGas flow in nanop

5、oresdKnPTkB22Knudsen numberMean free pathCriteria for validity of Poiseuille flowNavier-Stokes EquationNo-slip (Kn0.001)Slip (0.001Kn0.1)Continuum flowSlip flowDarcy flowKnudsen DiffusionJavadpour et al., JCPT, V. 46, No. 10, 55-61, 2007Kinetic theoryMaxwell-Boltzmann law of distribution of molecula

6、r velocitiesDistribution of molecular velocitiesVelocity formulationsMolecules collisions and mean free pathMean free pathMean free pathGas componentsMole(%)Collision diameter (, nm)Molar mass (kg/kmol)CH487.40.416.0C2H60.120.5230.0CO212.480.4544.0average0.4119.5Shale gas sample400 K350 K300 KMean f

7、ree path for the shale samplePTkB22Javadpour et al., JCPT, V. 46, No. 10, 55-61, 200710 nm50 nm300 nm10 m1 m50 mNo-slip flowSlip flowTransition flow Knudsen number for the shale sampledKnJavadpour et al., JCPT, V. 46, No. 10, 55-61, 2007LpprFMRTRTrJavg)(88321225 . 012815 . 0rpMRTFavgKnudsen diffusio

8、n and pressure flowDiffusionPressure flowF. Javadpour, JCPT, V. 49, No. 8, 55-61, 2009, Distinguished Author SeriesArtificial nanoporesNASA Ames Research CenterDiffusion contribution in total fluxP=5 MPaT=300 KDiffusion contribution in total flux10 nm Diffusion contribution in total flux10 nm 128188

9、10325 . 05 . 03rpMRTrMRTRTMkkavgavgDappApparent permeability88103225 . 03rFMRTRTMrkavgappF. Javadpour, JCPT, V. 49, No. 8, 55-61, 2009, Distinguished Author SeriesApparent permeabilityP=5 MPaT=300 KApparent permeability10 nm Apparent permeability10 nm A new formulation for gas permeability in fine-g

10、rained systems is proposed that was derived from theoretical aspects of gas-molecule interactions and pore walls but is written in a form that can be used easily in simulators developed on the basis of the Darcy equation. This new permeability formulation is termed apparent permeability. It is shown

11、 that at the nanoscale, fluid flow is not only a characteristic of the solid matrix, but gas type and operating conditions affect gas permeation through the media. Some concluding results are Conclusions 1Conclusions 2 The proposed “apparent permeability” for mudrock systems suggests that permeabili

12、ty is much higher than Darcy permeability, which may explain the unusually high gas production from such strata. The apparent permeability:Darcy permeability ratio is higher at smaller pores and lower pressures. Temperature and gas molar mass have minimal effects. Knudsen diffusion is an important gas transport process in mudrock systems. Diffusion contribution is higher in smaller pores and at lower pressure and temperatures