沁水盆地南部煤层气井产出水源解析及合层排采可行性判识

Source apportionment of produced-water and feasibility discrimination of commingling CBM production from wells in Southern Qinshui Basin

长期以来,沁水盆地南部丰富的太原组煤层气资源无法规模性动用,煤层气单井产量难以进一步提高,合层排采产出水来源得不到有效判识,合排难易程度无法客观评价。面对这些生产技术难题,基于28口单层及合层排采井产出水样品的微量元素测试分析,建立了产出水来源判识及合层排采可行性评价方法,进而以7口合层排采井为例进行了初步判识。分析表明,煤层气井产出水微量元素中蕴含着丰富的产出水来源信息,基于水岩作用原理可合理提取产出水源解析的特征微量元素。在甄别煤储层返排清污程度基础上,初步建立了由提取产出水特征微量元素、建立单煤层产出水特征微量元素标准模板、产出水来源与合排可行性判识3个步骤构成的评价流程。应用这一方法,在7口合层排采井中识别出产出水来源和层间干扰程度的3种情况。

During the past years,the rich coal-bed methane(CBM) resources in the Taiyuan Formation of the southern Qinshui Basin is unable to be extracted in a large scale,it is difficult to further improve the single CBM well production,the source of the water produced from the commingling wells is unable to be effectively discriminated,and the feasibility of the commingling CBM production is unable to be objectively evaluated. To overcome these technical problems from production,an evaluation method of the produced water source and commingling CBM production feasibility had been developed based on the trace element data of the produced water samples collected from 28 CBM wells,and then the preliminary apportionment has been implemented in 7 commingling-production wells. It is shown that the rich information of the produced water source can be obtained from the trace element in the water,and the characteristic trace elements can be reasonably extracted based on the principle of water-rock interaction. With the identification of the flow-back and pollution clean-up status from coal reservoirs,a preliminary evaluation process was established. The process consists of three steps:1 extracting the characteristic trace elements of the produced water;2 establishing the standard templates of the characteristic trace elements in the water from a single coal reservoir;and 3 discriminatingthe produced water source and commingling CBM production feasibility. According to this method,three kinds of the circumstances on the produced water sources and inter-reservoir interference were discerned in 7 commingling wells,which provides a valuable practical basis for the optimized CBM-extraction design and management.