水力压裂微地震井地联合监测系统及仪器

水力压裂技术是油气田增产和低渗透油田开发的有效技术手段,通过监测油层裂缝延展过程中产生的微地震事件,能够有效地判断裂缝走向.现有的井中监测方法存在成本较高、施工难度大的问题;地面监测存在信号信噪比低、垂向分辨能力差等问题.本文采用井地联合微地震监测的方法,在地面布置采集仪器的同时,选择邻近的单口监测井放置井中仪器,对微地震事件进行联合监测定位.采用联合监测的方法,在水平方向和垂直方向上都能够获得较好的监测视角,对比单一监测方法提高了微地震事件的定位精度.在此方法的基础上研制的井地联合微地震监测仪器系统,解决了现有仪器系统在进行联合监测时通讯链路不通的问题,实现了在压裂施工现场对微地震联合监测数据的实时回收、处理及结果呈现.应用本系统在大庆油田进行现场监测,获取的微地震事件对压裂裂缝进行了有效评价;通过对已知射孔点进行反演定位,采用井地联合监测将定位误差由地面监测的32 m降低至14 m,验证了本文技术的有效性.

Micro-seismic monitoring and instrument for hydraulic fracturing in the low-permeability oilfield

Hydraulic fracturing is an effective approach in Enhanced Oil Recovery for old oilfields and in low-permeability oilfield exploitation. It can accurately determine the direction of fracture by monitoring micro-seismic events in the process of the formation of cracks reservoirs. This paper introduces an approach for monitoring borehole-surface micro-seismic events. The optimal layout of a borehole-surface monitoring system is that the borehole instruments are sited at a suitable location close to the monitoring well where fracturing is to occur and a number of surface geophones positioned in an array over this site. The borehole-surface method can improve the location accuracy, and only one monitoring well is needed. Based on this method, we design a new monitoring instrument system that can implement weak signal acquisition, wireless communication and database management. The oilfield test in Daqing proves that the borehole-surface micro-seismic instrument has better performance and higher accuracy for hydraulic fracture monitoring. Through the inversion positioning of the known perforation points, and comparison with the ground monitoring method, the location error is reduced from 32 m to 14 m by the borehole-surface monitoring method, which verifies the effectiveness of the proposed technique in this paper.