煤层气高产水井原因分析及水源识别——以沁水盆地柿庄南区块3号煤井为例

Reasons on high water production and identifying water source in CBM wells:An example from No.3 coal seam,southern Shizhuang block,Qinshui Basin

高产水、低产气是煤层气生产过程中常见的一种现象,查明煤层气井高产水原因、确定产水来源一直是行业性难题。为此,以柿庄南区块3号煤层高产水井为例,根据测井、录井、微地震监测及生产数据,运用排除法找到了该区高产水井产水高的原因,通过同位素示踪、产水量和含水层发育特征相关性分析等技术手段,弄清了高产水井的产水来源。分析结果表明:①断层和压裂缝沟通含水层是该区煤层气井高产水的主要原因;②断层沟通含水层型高产水井产出水主要为来自于上石炭统太原组及奥陶系的石灰岩岩溶水;③压裂缝沟通含水层型高产水井产出水主要来源于下二叠统山西组底部的K_(7)砂岩。

Both high water yield and low gas yield are common in the same coalbed methane(CBM)well during the production.To find out reasons on the high water production and to identify water source have always been challenges.Thus,taking a well with high water production in No.3 coal seam of southern Shizhuang block as an example,we found the reasons by the process of elimination based on well logging,mud logging,microseismic monitoring and production data.In addition,the source was identified through isotopic tracing as well as correlation analysis on water production and aquifer development.Results indicate that(i)both faults and induced fractures connecting with aquifers should be the main reasons why there exists high water yield in CBM wells of this area;(ii)deriving from the connection of faults with aquifers,rich water mostly comes from limestone karst water in Taiyuan Formation and the Ordovician;and(iii)resulting from the other connection of induced fractures with aquifers,abundant water production has mainly root in K_(7) sandstone at the bottom of Shanxi Formation.