延川南深部煤层气高产主控地质因素研究

Study on the main controlling geological factors of high yield deep CBM in Southern Yanchuan Block

延川南区块属于深部高阶煤煤层气藏,受地质条件影响,区块单井产能差异大。结合煤层气开发动态资料,分析区块煤层气井富集高产主控地质因素。研究表明,气井产能受“构造、水动力、煤体结构”三因素控制,构造控制煤层气富集成藏,矿化度表征水动力强弱并影响煤层气保存,煤体结构制约储层改造。高产井主要位于埋深800~1200 m的局部微幅隆起带翼部以及构造平缓区,地层水矿化度(3~10)×10^(4)mg/L,原生–碎裂煤厚度大于2.5 m,日产气量大于1000 m^(3);中产井位于埋深大于1200 m的万宝山西部构造平缓区,矿化度大于10×10^(4)mg/L,日产气量500~1000 m^(3);而低产井主要靠近中部Ⅲ级断层以及局部Ⅳ级断层发育的断裂–凹陷带,矿化度低于0.3×10^(4)mg/L,原生–碎裂煤厚度小于2.5 m,日产气量低于500 m^(3)。区块产能的平面变化证实,构造是深部煤层气高产的主要控制因素。深部煤层气藏构造活动不发育的条件下储层渗透率极低,可改造性差,难以获得高产,构造活动的增强达到了改善储层目的,背斜轴部附近产生裂隙增加储层渗透性,易于煤层气富集和储层改造,局部小断层形成微裂缝,有利于煤层气解吸渗流,但是,构造活动较剧烈的断层以及凹陷带附近形成煤层气逸散通道,不利于煤层气的富集高产。

The Southern Yanchuan Block belongs to a deep,high-rank coalbed methane(CBM)reservoir.Due to the influence of geological conditions,the single well productivity varies greatly.Researching on the main controlling geological factors and their changing mechanism of CBM accumulation,combined with the dynamic data of CBM development,the main controlling geological factors of the CBM well enrichment and high production are analyzed.The research results show that the productivity of the gas field is controlled by the geological factors of“tectonic,hydrology,coal structure”.Tectonic restricts the accumulation of CBM;the degree of salinity characterizes affects the preservation of CBM;and the coal structure restricts the reformation of the reservoir.The high-yield wells are mainly located in the wing parts of the local micro-uplift belt with a buried depth of 800 to 1200 meters where the formation water salinity is 30000 to 100000 mg/L,with thickness of primary-fractured coal greater than 2.5 m,and the daily gas production is greater than 1000 m^(3).The middle-production wells are located in the gentle tectonic in the western part of Wanbaoshan with a buried depth of more than 1200 m,where the water salinity is greater than 100000 mg/L,with a daily gas production volume of 500-1000 m^(3);The low-yield wells are mainly distributed in the fault-sag zone near the middle levelⅢfaults and local levelⅣfaults where the salinity is less than 3000 mg/L,with thickness of primary-fractured coal less than 2.5 m,and the daily gas production is less than 500 m^(3).The plane change of the block productivity confirms that the tectonic is the main controlling factor for the high production of deep CBM.Under the condition of underdeveloped tectonic activity in deep CBM reservoirs,the permeability of the reservoir is extremely low with the poor rebuildability,so it is difficult to obtain high production.The enhancement of tectonic activity achieves the goals of improving the reservoir,and the formation of fissures near the axis of the local anticline increases the permeability of the reservoir.Therefor,it is beneficial to CBM enrichment and reservoir reformation,and local small faults form micro-fractures,which are conducive to the desorption and seepage of CBM.However,the faults with violent tectonic activity and the vicinity of the depression zone form CBM escape channels,which has a negative effect on the enrichment and high yield of CBM.