煤层气井压裂裂缝扩展规律分析

ANALYZING THE FRACTURE EXTENDED LAW OF HYDRAULIC FRACTURING IN COALBED GAS WELLS

煤层中含有大量优质清洁的煤层气,通常使用水力压裂技术才能正常生产。由于煤层中含有大量天 然裂缝,所以压裂时压裂液滤失严重、裂缝扩展极其复杂。因此,了解煤层气井压裂的裂缝扩展对于指导高效开采 煤层气具有重要作用。通过统计分析中国石油在华北地区的5个试验区块的压裂施工资料,发现煤层压裂中地层 破裂压力梯度集中在0.0144～0.053MPa/m之间,施工压力普遍较高。使用井温测试法和大地电位测试法测量了 煤层裂缝的方位和高度,分析发现:压裂后的煤层裂缝一般都穿越其上下隔层,最大时裂缝的高度超过压裂层厚度 的4倍;裂缝的长度大部分为50～70m,形状基本以垂直裂缝为主,也有垂直裂缝和水平裂缝共生的情况,少数压 裂井出现单翼垂直裂缝。裂缝方向存在着随机性,但在某方向上出现的概率较大,说明裂缝扩展是地应力、局部地 层构造和煤层割理共同作用的结果。

There is a lot of valuable and clean gas in a coal bed. In general, the coalbed gas can be produced by hydraulic fracturing. During the operation, because the coalbed is the formation with many natural fractures, large number of fracturing fluid leaks into the formation and the propped fracture geometry is very complicated. So, it is very important to understand the fracture extended law while hydraulic fracturing for producing coalbed gas effectively. According to the statistical data of five test tracts of PetroChina in north China, it is concluded that the value of fracturing pressure gradient is mostly 0. 0144 - 0. 053 Mpa/m and the operating pressure is generally high. The fracture orientation and height are monitored by the methods of temperature logging and geodetic potential survey. The results of analyzing the data show that the hydraulic fractures grow into the over and under lying coal seams. The maximal fracture height is more 4 times longer than the perforated interval thickness and most of the fracture length is 50-70 meters. The fractures are mainly vertical, but sometimes both horizontal and vertical fractures are also created in the same well. Single wing vertical fracture can be found in a few of fractured wells. The fracture directions are extended randomly and a predominant orientation appears in the coal formation. All of the treatment data show that the fracture orientation is the comprehensive result of ground stress, local structure and cleat.