海石湾矿区煤层气富集高产主控地质因素

Main Geological Controlling Factors for Coalbed Methane Accumulation and High Production in the Haishiwan Coal Ming Area

甘肃省煤层气产业起步相对较晚,开展重点矿区煤层气富集和高产等主控基础地质理论研究对于推动甘肃煤层气产业发展意义重大。为此,以民和盆地海石湾矿区为研究对象,基于矿井地质、煤层气参数井资料,采用数理统计、地质类比、测试化验等方法,分析了海石湾矿区的煤层气地质赋存特征、资源条件及富集高产主控地质因素。研究表明:该区主要发育五层煤层(煤三、煤二、煤B3、煤B2、煤B1)和一层油页岩(油A层),其中煤二层全区发育,分布稳定且厚度大,为0~59.28m,平均19.61m;埋藏深度适中,为506.72~1013.14m,平均685m;含气性条件好,含气量较高,平均7.89m^(3)/t,甲烷平均占比达到37.29%;资源量大,资源丰度高,达到2.24×108m^(3)/km^(2);顶底板均为低透气性泥岩或细粒砂岩,封闭性好,且区内断层不发育(7.59条/km^(2)),规模较小(落差一般小于5m,不切穿煤层和顶底板),而由于井田东部边界靠近F19断裂,促进了CO_(2)向煤层中运移扩散,使得断裂作用形成的厚煤区CO_(2)含量更高;为煤层气的赋存和富集创造条件。通过对典型的高、中、低产井生产数据分析,富集高产区域煤二层处于高储层压力和高温环境,储层压力梯度达到0.01MPa/m以上,地温最高可达48.9℃,同时具有较高的孔裂隙系统(孔隙度达到9.63%)、渗透性(渗透率0.692×10^(-3)~3.248×10^(-3)mD),含气饱和度在70%以上,为煤层气高产提供有利的地质和物性条件。

The coalbed methane industry in Gansu Province started relatively late.It is very important to research the main controlling factors of coalbed methane enrichment and productivity in key mining areas to promote the development of the coalbed methane indus-try.Taking the Haishiwan mine field in Minhe Basin as the research object,based on mine geology and coalbed methane parameter well data,this paper analyzes the occurrence characteristics and resource conditions of coalbed methane in the Haishiwan minefield by using the methods of mathematical statistics,geological analogy and testing,and discusses the main geological factors affecting the en-richment and high yield of coalbed methane.Research shows:five sets of coal seams(coal III,coal II,coal B3,coal B2 and coal B1)and one layer of oil shale(oil A)are mainly developed in the minefield.Among them,coal II is developed in the whole area,with stable distribution and large thickness.The coal thickness is 0~59.28 m,with an average of 19.61 m.The buried depth of the coal seam is moderate,ranging from 506.72 to 1013.14 m,with an average of 685 m.The gas content is high,with an average of 7.89 m^(3)/t,of which CH_(4) accounts for 37.29%on average.The amount of resources is large and the abundance of resources is high,reaching 2.24×108 m^(3)/km^(2),The roof and floor have low permeability and good sealing,and the faults in the area are undeveloped(7.59 strip/km^(2))and small in scale(the drop is generally less than 5m,and does not cut through the coal seam and roof and floor),the eastern boundary of the minefield is close to the F19 fault,which promotes the migration and diffusion of CO_(2) into the coal seam,resulting in a higher CO_(2) content in the thick coal area formed by the fault;Create conditions for the occurrence and enrichment of coalbed methane.By analyzing the production data of typical high,medium,and low production wells,the second coal layer in the enrichment and high production area is in a high reservoir pressure and high-temperature environment,and the reservoir pressure gradient is above 0.01MPa/m,the maximum ground temperature can reach 48.9℃.At the same time,it has high porosity and fracture system(porosity reaches 9.63%)and permeability(0.692×10^(-3)~3.248×10^(-3)mD),with gas saturation above 70%,it provides favorable geological and physical conditions for high production of coalbed methane.