Study On The Estimation Method Of Coal Measure Gas Resources Based On Overpressure Environment In The Matrix Pore

As a kind of unconventional energy,coal measure gas has a very promising prospect in the background of serious imbalance between supply and demand of natural gas.However,the pressure environment of coal measure reservoir is complex,the existing method for reservoir pressure is not the same as the gas phase pressure.In order to calculate accurately the resources of coal measure gas,the overpressure environment and gas phase pressure need to be understood sufficiently.Through the experiments such as XRD,FE-SEM,mercury injection,low-pressure N₂ adsorption-desorption and low-pressure CO₂ adsorption-desorption etc.The systematical research was carried out into the pore characteristics of the lower Shihezi coal measures shale.The gas reservoir of coal measure is mainly composed of coalbed methane reservoir and coal measure shale gas reservoir.In the coal measures shale,most of pore are nm^?m scale which organic matter pore,fluid escape pore,interlayer pore,inter-crystalline pore and inter-particle etc.The pore distribution characteristics are complex,Mercury injection testing shows that the pore volume change along with the pore size takes on three types including the single peak,dual peaks and multiple peaks,and the pore with the size larger than 100nm makes the major contribution to the pore volume,and the pore with the size less than 100nm makes the major contribution to the specific surface area.The low-pressure N₂adsorption-desorption results show that the pore volume and specific surface area vary greatly at the pore size 5 nm,below 5 nm the specific surface area plays the dominant status,while above 5nm the pore volume plays the dominant status.The low-pressure CO₂ adsorption-desorption discovers a lot of micro-pores below 2 nm.In this premise,the capillary pressure test and adsorption and desorption test were used to analyse the formation mechanism of the overpressure environment in the reservoir matrix of coal gas reservoir,the calculation method of the coal gas resource was build according to the overpressure of matrix pore,the resources of coal measure gas in the Lower Shihezi Fm.across the Su'nan Syncline were evaluated.The results showed that:?1?Because of the effect of capillary force what due be the objective existence of the liquid in the reservoir of coal measure,special pressure environment formed in matrix pores,matrix pores pressure which constitute by capillary force and reservoir pressure is different from formation pore pressure.When there is liquid slug in the pore which less than the second limit pore diameter,the matrix pore overpressure environment is formed.?2?The resources of SN-01 block in the Lower Shihezi Fm.in the Su'nan Syncline were calculated with the calculation method of the coal measure gas resources based on overpressure environment and the conventional calculation method.The calculation result of consinder overpressure environment is higher than that of conventional calculation method.The calculation result of consinder overpressure environment is that the total resources of coal measure gas are 21.50×10⁸ m³ and have the resources abundance of 5.10×10⁸ m³/km²,the latter result shows that the total resources of coal measure gas 15.46×10⁸ m³ and have the resources abundance of 3.66×10⁸ m³/km².