二连盆地吉尔嘎朗图凹陷低煤阶煤层气勘探

二连盆地群低煤阶煤层气资源丰富但勘探程度相对较低,煤层气富集和主控因素认识不足,制约了开发实践。以吉尔嘎朗图凹陷为重点,对二连盆地群的构造、沉积、水文、物性和含气量分布进行精细解剖,总结了煤层气富集成藏规律。二连盆地群具有断陷小湖盆和残留盆地的特点,分割性强。煤系主要发育中、下侏罗统阿拉坦合力群及下白垩统巴彦花群赛汉塔拉组两套含煤建造,以辫状河三角洲相为主,煤层层数多且与砂泥岩叠置发育,煤层倾角平缓。针对研究区"浅部低煤阶、平缓厚煤层、多层砂煤组"的特点,建立了符合吉尔嘎朗图"斜坡区正向构造带富集模式",提出在煤层气勘探中应注意优选埋深适中、相对高渗、高含气量的"甜点区",并需要规避断层,在向斜两翼、背斜和单斜地层中寻找高产区。优选部署的吉煤4井在埋深430~470 m煤层段获得大于2 000 m~3/d的产气量,证实中国低含气量、厚煤层的褐煤区煤层气可以获得高产工业气流,有助于推进低煤阶煤层气资源的勘探进程。

Low-rank coalbed methane exploration in Jiergalangtu sag,Erlian Basin

In Erlian Basin Group, abundant low-rank coalbed methane (CBM) resources exist but with lower exploration degree, where the development practice is restricted by insufficient understandings of CBM enrichment and main control factor. With a focus on Jiergalangtu Depression, based on a fine dissection of the structure, sedimentation, hydrology, physical properties and gas content distribution in Erlian Basin Group, the CBM enrichment and accumulation laws are summarized. Erlian Basin Group is characterized by small faulted lake basins and residual basins with high divisibility. In the coal seam, two sets of coal-bearing formation are developed, i.e., the Mid-Lower Jurassic Alatanheli Group and the Lower Cretaceous Saihantala Formation of Bayanhua Group, dominated by braided river delta facies, where several coal seam layers are developed together with superimposed shale, showing a gentle dip angle. Aiming at the characteristics of "shallow low-rank CBM, thick coal seams with gentle slope and multi-layer sand coal" in the study area, the enrichment model consistent with "the positive structure zone in the slope area" of Jiergalangtu is established, suggesting that the CBM exploration should focus on the "sweet spot area" with moderate buried depth, relatively high permeability and high gas content, avoid the faults and find high-yield zones on the both wings of syncline, anticline and monoclinal strata. In the optimized Well Jimei 4, the gas production greater than 2 000 m³/d is obtained at the buried depth of 430-470 m in the coal seam, proving that high-yield industrial gas flow can be achieved in China's lignite area with low gas content and thick coal seam, conductive to push forward the exploration process of low-rank coal.