四川长宁页岩气套管变形井微地震特征分析

Microseismic characteristics of shale gas wells with casing deformation in Changning,Sichuan

针对四川页岩气井套管变形问题,利用通过的小桥塞尺寸和多臂井径测井(MIT)数据计算了H19平台套管变形的变形量,同时分析了套管变形点处微地震事件点的时空分布和矩震级大小特征。然后在识别出的天然裂缝空间分布特征基础上建立了裂缝面模型,并利用该模型分析了套管变形量、天然裂缝尺度和微地震地震矩之间的定量关系。该平台共测得9个套管变形点的变形量,最小变形量为6.10mm,最大为50.43mm,平均为28.03mm,分析后得到天然裂缝的微地震时空特征:①微地震事件关于井筒不对称;②不同压裂段的微地震事件点大部分重叠,呈线性分布;③出现了较多的大矩震级事件;④时间上,大矩震级事件点出现在压裂中后期的频率较高。根据裂缝面模型,计算出引起长宁地区页岩气套管变形的裂缝面积为40000~70000m^(2),地震矩为2.57×10^(9)~7.57×10^(10)N·m,矩震级范围为-1.16~0.79。研究结果对利用微地震实时监测、预警套管变形和判断天然裂缝尺度、预防套管变形具有指导作用。

To address the casing deformation of shale gas wells in Sichuan Basin,this paper calculates the casing deformation of the H19 platform with a small bridge plug size and multi-finger image tool(MIT)data and analyzes the characteristics of the spatial and temporal distribution and moment magnitude of microseismic events at casing deformation points.The fracture surface model is established depending on the spatial distribution characteristics of identified natural fractures.The quantitative relationship among casing deformation,natural fracture scale and microseismic moment is analyzed by the model.There were 9 deformation values,with the minimum of 6.10mm and the maximum of 50.43mm,averaged to be 28.03mm.The spatial and temporal distribution characteristics of microseismic events are as follows:①The microseismic events are not symmetric about the wellbore;②most of the microseismic events in different fracturing stages are overlapped spatially,showing linear distribution;③there are many large-moment-magnitude events;④the frequency of large-moment-magnitude events is relatively high in the middle or late fracturing period.According to the calculation with the fracture surface model,the area of the fractures causing casing deformation in shale gas wells in the Changning area is 40000~70000m^(2),the seismic moment 2.57×10^(9)~7.57×10^(10)N·m,and the moment magnitude range is-1.16~0.79.These results have guiding significance for real-time monitoring and early warning of casing deformation according to microseismic events and prevention of casing deformation via the judgment of natural fracture scale.