煤层气储层毛管压力对煤层气开发效果的影响
Influence of Capillary Pressure on CBM Reservoir Development Effect
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摘要: 为研究煤层气储层毛管压力对煤层气开发的影响,基于润湿性实验和现场生产数据,提出了毛管压力对煤层气封堵的机理及类型,进而提出了3种煤层气储层类型及其生产曲线。结果表明:研究区煤岩为水湿,毛管压力在煤层气产出过程中为阻力;甲烷气体生成后在毛管压力及储层静水压力作用下吸附在煤岩孔隙表面,当孔隙中气体压力小于突破压力时,气体被封闭在孔隙中;根据毛管压力对气体的封堵类型差异,可将煤层气储层划分为毛管力圈闭型、欠饱和型和饱和型3种类型,其中毛管力圈闭型储层的毛管压力大于孔隙中气体压力,持续排水降压不能克服毛管压力,开发效果最差;欠饱和型储层孔隙中气体压力大于毛管压力,可通过持续排水降低静水压力使气体持续产出,开发效果相对较好;饱和型储层孔隙中气体压力大于气体突破压力,不需要排水降压甲烷气体即可产出,能够实现高产稳产。Abstract: To research the effects of capillary pressure of coalbed methane reservoir on the development of coalbed methane, this paper, based on wettability experiments and field production data, proposes the seal mechanism and types by capillary pressure of coalbed methane formation, and then proposes three types of coalbed methane reservoirs and their typical production curves. The results show that the wettability of coal and rock is water wet and capillary pressure is resistance in the process of coalbed methane production. After the methane is generated, it is adsorbed on the pore surface of coal under the influence of capillary pressure and reservoir hydrostatic pressure. When the gas pressure in the pore is less than the breakthrough pressure, the gas is closed in the pore. According to the difference of gas-sealing type of capillary pressure, coalbed methane reservoir can be divided into three types: capillary pressure trapping type, under-saturated type and saturated type. The capillary pressure of capillary trapping type reservoir is greater than the gas pressure in the pores. Continuous drainage cannot overcome the capillary pressure, and the development effect is the worst. The gas pressure in the pores of the unsaturated reservoir is greater than the capillary pressure, and the static water pressure can be reduced by continuous drainage, making the gas continuously produced, and the development performance is relatively good. The gas pressure in the pores of saturated reservoirs is greater than the gas breakthrough pressure, and methane gas can be produced without drainage and depressurization, so high and stable production can be achieved.