延川南煤层气田深部煤层气藏排采制度的建立与优化

Establishment and optimization of drainage system for deep coalbed methane in South Yanchuan CBM Field

为了建立适合延川南煤层气田深部煤层气藏的排采制度,一方面通过镜质组反射率测试、压汞试验和核磁共振试验等手段,分析了延川南煤层气田煤层孔隙性发育在各煤阶煤层中所处的水平;另一方面主要通过与沁水盆地南部煤层孔隙发育、地应力特征、煤岩力学特征进行对比,分析了延川南与沁南煤层气地质条件差异,并结合延川南煤层气井现场排采参数,建立了相适应的排采制度。结果表明:延川南煤层气田煤层镜质组反射率在2.5%左右,压汞孔隙度和可动流体孔隙度在所有煤阶中处于最低水平,且孔隙系统以微小孔为主,各级别孔隙间连通性差,对煤储层渗透性极为不利;与沁水盆地南部相比,延川南煤层气田煤储层具有孔渗性差、地应力高的特点,加之煤岩本身抗压强度低,所以在排采控制过程中要采取比沁水盆地南部更为缓慢的排采制度;将延川南煤层气田深部煤层气藏排采制度划分为5个排采阶段,分别是:快速降压阶段、稳定降压阶段、上产阶段、产量波动阶段和稳产阶段,其中快速降压阶段日降井底流压控制在0.100 MPa左右,稳定降压阶段、上产阶段和产量波动阶段要采取精细化排采控制,稳定降压阶段日降井底流压在0.003 MPa左右,上产阶段日降井底流压0.005 MPa左右,产量波动阶段日降井底流压要控制在0.003 MPa左右。

In order to establish the drainage system suitable for deep coalbed methane in South Yanchuan CBM Field,on the one hand,the vitrinite reflectance test,mercury intrusion test and nuclear magnetic resonance test were used to analyze the coalbed porosity of the coal⁃bed methane field in South Yanchuan coalbed methane field.On the other hand,the difference in geological conditions between South Yan⁃chuan and Qinnan coalbed methane was analyzed by comparing with the pore development,in-situ stress characteristics and coal rock me⁃chanics characteristics of the coal seams in South Qinshui Basin,and combined with the drainage parameters of coalbed methane in South Yanchuan,a suitable drainage system was established.The result show that the vitrinite reflectance value Ro of coal seam in South Yan⁃chuan CBM field is about 2.5%in South Yanchuan,the mercury porosity and movable fluid porosity are the lowest among all coal grades,and the pore system is dominated by micropores with poor connectivity among all levels of pores,which is extremely unfavorable to the per⁃meability of coal reservoir.Compared with southern Qinshui basin,the coal reservoir of South Yanchuan CBM field has the characteristics of poor porosity and permeability,high in-situ stress,and low compressive strength of coal rock itself.In the process of drainage control,a slower drainage system should be adopted in process of drainage control;the drainage process for deep coalbed methane in South Yan⁃chuan CBM filed can be divided into five stages,namely the rapid depressurization stage,stable depressurization stage,gas yield rising stage,gas yield fluctuation stage,and stable yield stage.In the rapid depressurization stage,the daily downhole flow pressure should be con⁃trolled at about 0.100 MPa.In the stable depressurization stage,the production stage and the production fluctuation stage,refined drainage control should be adopted,and the daily downhole flow pressure in the stable decompression stage should be around 0.003 MPa.The daily downhole flow pressure during the up-production stage should be about 0.005 MPa,and the daily downhole flow pressure during the pro⁃duction fluctuation stage should be controlled at about 0.003 MPa.