Characteristics of shallow coal measure gas reservoir and key technologies of exploration and development in Yaojie mining area
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摘要: 煤系气勘探开发不仅可以减少资源浪费,而且可以缓解我国能源危机,降低煤矿瓦斯事故,保护大气环境,为实现碳达峰、碳中和目标做出贡献。依托窑街矿区海石湾井田三采区浅层煤系气开发示范工程,分析窑街矿区煤系气储层特征,探讨煤系气勘探开发关键技术。研究表明:井田煤系气主要赋存于侏罗系中统窑街群煤系第四岩组(J2yj4)的油页岩、油砂岩和第二岩组(J2yj2)的油A层、煤二层等特厚产层中;油A层、煤二层气含量随着埋深的增加而增大;CO2浓度较高,且随着埋深增加而减小;煤二层吸附能力较强,油A层更容易解吸;各层渗透率为油砂岩 > 油A层 > 煤二层 > 油页岩;抗压强度、抗拉强度、弹性模量、泊松比和脆性指数显示各产层改造难易程度由小到大依次为油砂岩、油A层、油页岩、煤二层。油页岩有机质丰度4.06%,干酪根类型Ⅱ2–Ⅲ型;油A层有机质丰度43.27%,变质程度呈两极分化,腐泥煤镜质体反射率0.48%~0.53%,腐植煤镜质体反射率0.89%~0.97%;煤二层有机质丰度92.87%,其中镜质组体积分数67.90%,惰质组29.10%,壳质组3.50%,变质程度以肥煤为主,含少量气肥煤。与我国大部分欠压地层相比,各产层储层压力正常,产气潜力大;煤系气开发应优选煤二层、油A层和油页岩;多段分簇、限流法射孔工艺和细砂防滤失、投球暂堵、两高一低(高排量、高砂量、低砂比)的压裂工艺适合于该区致密特厚储层改造,挂泵位置低于煤二层射孔段和重力式螺旋气锚排采工艺可减少CO2的影响,提高排采效率。这些关键技术的应用显著提高了井田示范工程产气效果,单井日产气量超过2 000 m3。Abstract: The exploration and development of coal measures gas can not only effectively improve the single well production of coalbed methane in coal mining areas, reduce the waste of resources, but also alleviate the energy crisis in China, reduce coal mine gas accidents, protect the atmospheric environment, and contribute to the realization of carbon peak and carbon neutralization. Based on the shallow coal measure gas development demonstration project in the third mining area of Haishiwan mine field, the characteristics of coal measure gas reservoirs in Yaojie mining area are analyzed, and the key technologies for coal-measure gas exploration and development are discussed. The research showed that coal measure gas in the mine field is mainly present in the oil shale and oil sandstone of the fourth rock group(J2yj4) of the Jurassic Yaojie Formation coal system, and the oil A layer and the second coal layer of the second group(J2yj2). The gas content of oil layer A and second coal layer increases with the increase of burial depth; The CO2 concentration in oil layer A and second coal layer is higher, and decreases with the increase of burial depth; The second coal layer has a strong adsorption capacity, and the oil layer A is easier to desorb; Oil sandstone permeability > oil layer A permeability > second coal layer permeability > oil shale permeability; Compressive strength, tensile strength, elastic modulus, Poisson's ratio and brittleness index show that the difficulty of reformation of them in descending order is oil sandstone, oil layer A, oil shale, and coal second layer; The organic matter abundance of oil shale is 4.06%, and kerogen type is Ⅱ2-Ⅲ. The abundance of organic matter in the oil layer A is 43.27%, and the degree of metamorphism is polarized. The saprolite vitrinite reflectance is 0.48%-0.53%, and the humic coal vitrinite reflectance is 0.89%-0.97%. The abundance of organic matter in the second layer of coal is 92.87%, including vitrinite 67.90%, inertinite 29.10%, exinite 3.5%, the degree of metamorphism is mainly fat coal with a small amount of gas fat coal; Compared with most low pressured formations in China, the reservoir pressure of each producing layer is normal and the gas production potential is great; The second coal layer o, the oil layer A and the oil shale should be optimized in the development of coal measure gas. The fracturing technology of multiple clusters, flow-limiting perforating technology and fine sand filtration loss, ball drop temporary plugging, two large and one low(large displacement, large sand volume, low sand ratio) fracturing technology are suitable for the reservoir transformation of the ultra-thick and tight formation in this area, and the pump hanging position is lower than the two-layer perforating section of coal and the gravity spiral gas anchor drainage process can reduce the effect of CO2 and improve the drainage efficiency. The application of these key technologies has significantly improved the gas production effect of the mine field demonstration project. The daily gas production of a single well exceeds 2 000 m3
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表 1 海石湾井田产层气含量和气成分测试结果
Table 1 Test results of gas content and gas composition of the gas-producing layers in Haishiwan mine field
井号 产层 总气含量/(cm3·g–1) 甲烷含量/(cm3·g–1) 气成分/% 空气干燥基 干燥无灰基 空气干燥基 干燥无灰基 CH4 CO2 N2 C2+ HSW01-2V 油A层 2.95 6.13 1.53 3.17 51.52 18.69 22.44 7.35 煤二层 7.24 8.33 2.69 3.1 38.20 42.03 17.73 2.04 HSW06-3V 油A层 2.59 7.79 1.53 4.57 59.71 16.62 13.42 10.26 煤二层 7.93 8.79 4.33 4.78 54.68 30.02 12.78 2.52 表 2 各产层压汞实验测试结果
Table 2 Test results of laminated mercury injection experiments of different gas-producing layers
产层 比表面积/(m2·g–1) 总孔容/(cm3·g–1) 中位孔径/nm 平均孔径/nm 孔隙率/% 渗透率/10–3 μm2 油砂岩 0.288 0.036 1 005.600 675.515 8.557 0.203 油页岩 3.486 0.011 24.310 12.440 2.811 0.026 油A层 9.185 0.028 24.610 12.160 4.685 0.049 煤二层 18.973 0.049 16.120 10.130 5.967 0.033 表 3 各产层力学参数
Table 3 Mechanical parameters of different gas-producing layers
产层 抗压强度/MPa 抗拉强度/MPa 弹性模量/104 MPa 泊松比 脆性指数/% 油页岩 15.01 1.46 0.88 0.25 27.19 油砂岩 34.47 2.56 2.05 0.21 40.95 油A层 29.44 2.25 1.69 0.22 36.51 煤二层 7.97 0.70 0.44 0.26 23.54 表 4 油A层镜质体反射率测试结果
Table 4 Test results of vitrinite reflectance of oil layer A
样品编号 测定对象 反射率Rmax/% 标准差 油A层-1 腐泥质 0.39~0.65/0.50(18) 0.051 腐植质 0.78~1.11/0.97(6) 0.092 油A层-2 腐泥质 0.48~0.65/0.53(9) 0.037 腐植质 0.89~1.00/0.94(3) 0.038 油A层-3 腐泥质 0.40~0.63/0.48(13) 0.054 腐植质 0.75~1.10/0.89(7) 0.108 注:表中0.39~0.65/0.50(18)表示最小~最大值/平均值(测点数)。 表 5 各产层储层压力与地应力参数
Table 5 Reservoir pressure and in-situ stress parameters of different gas-producing layers
产层 储层压力/ MPa 压力梯度/(MPa·hm–1) 闭合压力/ MPa 闭合压力梯度/(MPa·hm–1) 破裂压力/ MPa 破裂压力梯度/(MPa·hm–1) 油页岩 8.88 1.10 8.97 1.09 15.00 1.84 油A层 10.52 1.01 10.79 1.03 15.36 1.47 煤二层 9.31 0.93 16.10 1.61 17.64 1.77 表 6 海石湾一期工程4口井射孔数据
Table 6 Perforation data of 4 wells in Haishiwan project of phaseⅠ
井名 目标产层 产层深度/m 产层厚度/m 射孔深度/m 射孔厚度/m HSW01-2V 油页岩 803.80~827.95 24.15 805.5~808.5
821~8243 油A层 890.60~899.80 9.20 893~896 3 煤二层 907.90~923.30 15.40 913.5~916.5 3 HSW02-2V 油A层 903.40~912.70 9.30 906~909 3 煤二层 925.92~941.57 15.65 928~931
936~9393
3HSW04-1V 油页岩 710.35~746.30 35.95 718~721
732~7353
3煤二层 823.92~877.06 53.14 831~834
850~854
867~8703
4
3HSW06-3V 油A层 1 033.70~1 050.40 16.70 1 036~1 039
1 044~1 0473
3煤二层 1 062.70~1 102.15 39.45 1 071~1 074
1 091~1 0943
3表 7 海石湾一期4口井压裂参数
Table 7 Fracturing parameters of 4 wells in Haishiwan project of phaseⅠ
井号 目标产层 施工压力/MPa 施工排量/(m3·min–1) 平均砂比/% 加砂量/m3 压裂液量/m3 HSW01-2V 油页岩 20.4~27.1 8~11 9.27 79.06 1 346.74 油A层
煤二层19.5~27.6 8~11 9.27 87.33 1 745.59 HSW02-2V 油A层 22.1~25.9 8~9 9.00 56.80 956.61 煤二层 20.3~28.2 8~9 9.08 70.96 1 294.26 HSW04-1V 油页岩 22.5~26.3 9 6.86 52.49 1 230.91 煤二层 24.7~42.0 8~10 6.84 112.40 2 419.00 HSW06-3V 油A层 16.6~21.2 9 9.14 57.97 957.86 煤二层 20.9~25.5 8 7.20 83.05 1 635.80 -
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