中国煤层气富集高产规律、开采特点及勘探开发适用技术

The regular patterns of highly-produced CBM,its production performance and the progress of prospecting technologies in China

与国外相比,中国煤层气构造条件复杂,成藏类型复杂,层内非均质性强。根据煤层气勘探开发现状总结了我国煤层气富集高产规律:①区域含煤区构造高点是高产富集有利部位;②上斜坡区域煤层后期受构造运动抬升幅度大,次生割理发育,煤层变浅压实作用弱,渗透性好,在稳定的盖层条件下,处于承压水滞流封闭环境,下倾部位有充足的烃类补给,高产条件优越;③构造抬升盆地凹中隆火山岩活动区有利于高产;④封闭好的浅层,低煤阶厚煤层有利于煤层气富集;⑤断裂活动次生割理发育区是煤层气聚集的有利场所。同时系统分析、总结了中国煤层气开采特征和不同措施影响煤层气井产气特征,以及受构造部位和层内非均质性影响的单井产气特征,列举了中国煤层气勘探开发的适用技术,包括二维地震AVO高产富集区预测技术、羽状水平井钻井技术、超短半径水力喷射钻井技术、煤层气井重复压裂技术等。

Compared with those in other countries,the coalbed methane gas reservoirs in China are featured by complicated structural environment,complex pooling types,and strong anisotropy.According to the present status of the CBM exploration and development in China,we summarized the regular patterns of highly-accumulated CBM as follows:①Structural high:Deep buried depth of coal bed is beneficial in early stage,and shallow buried depth of coal bed is easy for tectonic uplift with the characteristics of developed secondary cleats,good permeability and weak compaction.The creak of cleat is not mineralized in the dead water environment,and CBM reservoir has not been damaged by the water.It has formed the productive and enriched zones in both flanks with high permeability,high gas content and high saturation.②Acclivity:Shallow buried depth,developed secondary cleats,weak compaction,good permeability and intense uplift are the features of the coal bed.CBM reservoirs have not been damaged by the water for stable regional direct cap rock,dead water environment and non-mineralized cleats.There is abundant hydrocarbon in the down-dip trap,which can form CBM reservoirs with high permeability,high gas content and high saturation.③High palaeogeothermal:Regional volcanic rock invaded coal bed strongly causes gas generation.Volcanic dike is the barrier bed.The secondary cleat is developed in the coal bed for the coal to rapidly chill and shrink and then the high production and enrichment block is formed in the later stage.④Thick coal with low coal rank,low gas generation and high saturation:The coal rank,gas generation and gas content are lower,however,heavy coal layer makes up lower gas content.Effective cap rock stops top water forming dynamic flow along coal cleat.The high permeability and saturated gas reservoir formed in up-dip places.⑤Deep fractured zone:The buried depth of coal is deep,however,the secondary cleats developed in the local structural high for the fault action.The existence of high permeability zones resulted in the formation of reservoirs.Free gas and adsorbed gas are paragenetic.Meanwhile,through systematic analysis,this paper also outlined(1)the characteristics of CBM gas recovery and how the well production performance was influenced by different recovery methods,and(2)how a single well production performance was affected by structural levels and layer anisotropy.In the end,this paper summarized the progress of prospecting technology,which includes two-dimensional seismic AVO forecasting techniques,multi-branched horizontal well drilling,short-radius hydraulic jet drilling,open hole cave completion and adaptive control techniques of producing fluid level.