基于地面微地震监测定位和成像的煤层气水力压裂效果评价研究

Evaluation of the coalbed methane hydraulic fracturing effect based on microseismic event locations and tomography results for surface microseismic monitoring

1.中国科学技术大学地球和空间科学学院,安徽合肥 230026;
2.华阳新材料科技集团有限公司,山西阳泉 045000;
3.安徽万泰地球物理技术有限公司,安徽合肥 230601;
4.河海大学海洋学院,江苏南京 210024;
5.Institute of Geophysics,Polish Academy of Sciences,Poland

1. School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China;
2. Huayang New Material Technology Group Ltd.,Yangquan 045000,China;
3. Anhui Wantai Geophysical Technology Co.,Ltd.,Hefei 230601,China;
4. College of Oceanography,Hohai University,Nanjing 210024,China;
5. Institute of Geophysics,Polish Academy of Sciences,Poland

水力压裂技术已经广泛应用于煤层气抽采以提高抽采效率。水力压裂产生裂缝的空间分布评价对于提高资源的利用率和降低潜在的瓦斯突出风险至关重要。在水力压裂过程中,裂缝的产生会伴随微地震的产生,因此微地震监测可以用于水力压裂效果的评价。目前煤层气水力压裂微地震监测主要是依赖微地震定位得到的空间分布,不能准确和全面评价储层的改造效果。为此,提出综合利用微地震定位和速度成像综合评价煤层气水力压裂改造效果。针对中国山西的两口煤层气水力压裂井地面微地震监测数据,利用双差地震成像算法确定了更精确的地震定位和目标煤层附近的速度异常分布。定位结果显示微地震主要分布在压裂井附近并且呈簇状分布,和传统定位相比双差成像给出了更精确的微地震空间分布。根据微地震的空间分布,估算了储层的压裂改造区域。双差地震速度成像显示微地震位于相对低的v_P异常、高的v_S异常和低的v_P/v_S异常区域。结合前人岩石物理实验结果,推测在微地震刻画的储层改造区,裂缝中的煤层气处于饱和状态,表明水力压裂有效释放了煤层气。因此综合通过微地震定位和速度成像可以更全面地刻画煤层的改造情况。

Hydraulic fracturing is a technique that is widely employed to increase the efficiency of coalbed methane (CBM) extraction.The evaluation of the spatial distribution of fractures produced by hydraulic fracturing is crucial for improving resource utilization and reducing potential gas outburst risks.In the process of hydraulic fracturing,microseismic events occur in tandem with the formation of cracks;therefore,microseismic monitoring can be used to evaluate the effect of hydraulic fracturing.At present,the microseismic monitoring of CBM hydraulic fracturing relies on the spatial distribution of microseismic events,which cannot accurately and comprehensively evaluate the effect of reservoir stimulation.In this study,the combined use of microseismic locations and velocity tomography was used to comprehensively evaluate the effect of CBM hydraulic fracturing.Based on the surface microseismic monitoring data of two CBM hydraulic fracturing wells in Shanxi,China,we used the double-difference seismic tomography method to determine seismic locations and velocity anomalies near the target coal seam.The location results showed clusters of microseismic occurrences in the vicinity of the fracturing well.Compared with the traditional location method,double-difference seismic tomography can obtain a more accurate spatial distribution of microseismic events,and this was used to estimate the fracturing area of the reservoir.Double-difference seismic tomography results showed that microseismic events were located in regions with relatively low v_P,high v_S,and low v_P/v_s anomalies.Combined with previous petrophysical experiment results,we speculated that methane was in a saturated state in the fractured areas,indicating that the hydraulic fracturing effectively released CBM.Therefore,the stimulation of coal seams can be described more comprehensively through microseismic event locations and tomography results.

国家自然科学基金国际(地区)合作与交流项目(41961134991)和青年项目(42004034)、波兰国家科学中心(UMO-2018/30/Q/ST10/00680)以及华阳新材料科技集团有限公司共同资助。

10.3969/j.issn.1000-1441.2023.01.002