滇东地应力场深度分带及其对煤储层渗透率控制

Depth Division Zone of In-Situ Stress Field in Eastern Yunnan and Its Control on Coal Reservoir Permeability

地应力贯穿于煤层气生产整个过程,对煤层气的勘探选区和工程实施具有重要的现实意义。为研究滇东地应力特征,收集了滇东地区15口井(35层煤)注入/压降试井数据。研究发现:滇东煤层埋深介于497.12~1234.31m(平均780.44m),破裂压裂介于10.26~22.31MPa(平均16.55MPa),闭合压力介于9.75~21.44MPa(平均15.52 MPa)。煤层的破裂压力与埋深、闭合压力均表现正相关性。滇东地区垂向地应力场可划分3部分,分别是走滑断层应力场(<700m)、过渡应力场(700~1000m)和正断层应力场(>1000m)。滇东地区煤储层渗透率为0.0045~1.86mD(平均0.1879mD),随着埋深的增加,表现为“先降低后增加”的趋势,与地应力场转化位置基本一致。煤储层天然裂缝的发育规律与现代地应力场垂直分布特征,共同控制滇东地区煤储层的渗透率。

In-situ stress runs through the whole process of coalbed methane(CBM)production,which has important practical significance for the exploration selection and engineering implementation of CBM.To study the in-situ stress characteristics in eastern Yunnan,this paper collected the injection/falloff well test data of 15 wells(35 coal seams)in eastern Yunnan.The study found that the burial depth of the coal seam in eastern Yunnan is between 497.12~1234.31m(avg.780.44m),the fracture fracturing is between 10.26~22.31MPa(avg.16.55 MPa),and the closure pressure is between 9.75~21.44MPa(avg.15.52 MPa).The fracture pressure of coal seams is positively correlated with burial depth and closure pressure.The vertical in-situ stress field in eastern Yunnan can be divided into three parts,which are strike-slip fault stress field(<700m),transition stress field(700~1000m)and normal fault stress field(>1000m).The permeability of coal reservoirs in eastern Yunnan is 0.0045~1.86mD(average 0.1879MD).With the increase of burial depth,it shows a trend of"decreasing first and then increasing",which is basically consistent with the transformation position of the in-situ stress field.The development law of natural fractures in coal reservoirs and the vertical distribution characteristics of modern in-situ stress field jointly control the permeability of coal reservoirs in eastern Yunnan.