压裂施工曲线应用于深层页岩气水平井裂缝评价

Application of Fracturing Construction Curve in Fracture Evaluation of Deep Shale Gas Horizontal Wells

页岩气水平井通常没有取芯、电成像等资料,增加了裂缝识别难度,而压裂施工曲线能较好地反映出压裂效果和压前天然裂缝的发育情况。以川南泸州Y101区块深层页岩气地层为例,根据携砂液阶段压裂施工曲线类型及特征刻度水平井压前裂缝层段、基质层段的测井响应特征,利用小波变换提取反映裂缝信息的高频微弱信号建立小波变换综合系数(W_(I))、交会图优选6项对裂缝响应敏感的参数指标、层次分析法与模糊数学法构建裂缝评价综合系数(F_(I)),并进一步结合不同压裂施工曲线类型与测井信息的关系,实现了水平井裂缝层段识别及发育级别评价。研究结果表明,携砂液阶段压裂施工曲线形态有下降型(Ⅰ)、下降稳定型(Ⅱ)、稳定型(Ⅲ)及上升型(Ⅳ)4种类型,其中,当自然伽马高值、补偿中子和密度明显增大、声波时差增大伴“锯齿状”周波跳跃、双侧向呈“正差异”且W_(I)>0.18,F_(I)>0.430时,压裂施工曲线为下降型,裂缝发育好(F-A级);0.3906F_(I)<0.430时,既有下降型又有下降稳定型,裂缝较发育(F-B级);0.3506F_(I)<0.390时,为下降稳定型,裂缝一般发育(F-C级)。

Shale gas horizontal wells usually do not have coring and electrical imaging scales,which makes it difficult to identify fractures.The fracturing operation curve can reflect the fracturing effect and the development of natural fractures before fracturing.Taking the deep shale gas formation of Block Y101 in Luzhou,southern Sichuan as an example,according to the type and characteristics of the fracturing operation curve in the sand-carrying fluid stage,the logging response characteristics of the fracture layer and the matrix layer before the fracturing of the horizontal well are calibrated.The wavelet transform is used to extract the high-frequency weak signal reflecting the fracture information to establish the wavelet comprehensive coefficient(W_(I)),the crossplot is used to select six parameter indexes sensitive to the fracture response,the analytic hierarchy process and the fuzzy mathematics method are used to construct the fracture evaluation comprehensive coefficient(F_(I)),and the relationship between different fracturing operation curve types and logging information is further combined to realize the identification and development level evaluation of horizontal well fracture layers.The results show that the fracturing construction curve of the sand-carrying fluid stage has a descending type(Ⅰ),a descending stable type(Ⅱ),a stable type(Ⅲ),and an ascending type(Ⅳ).Among them,when the natural gamma high value,the compensated neutron and the density increase significantly,the acoustic time difference increases with the“jagged”cycle jump,the double lateral shows a“positive difference”and W_(I)>0.18,F_(I)>0.430,the fracturing construction curve is a descending type,and the fracture is well developed(F–A grade);When 0.3906F_(I)<0.430,there are both downward type and downward stable type,and the fractures are more developed(F–B grade);when 0.3506F_(I)<0.390,it is a descending stable type,and the fractures are generally developed(F–C grade).