基于DTS的页岩气水平井人工裂缝识别与产出剖面解释方法

DTS based hydraulic fracture identification and production profile interpretation method of horizontal well

为了准确评价页岩气藏水平井的压裂改造效果,建立了水平井筒温度分布预测模型,基于MCMC算法建立了DTS数据反演模型,并且对产出剖面解释流程进行了优化;在此基础上,对页岩气藏压裂水平井温度剖面特征进行了分析,确定了影响温度剖面的主控因素;进而将所建立的反演模型应用于某页岩气藏实例井产出剖面解释。研究结果表明:①压裂水平井温度剖面呈不规则的“锯齿状”,任意一个“锯齿”都对应着一条有流体流入的有效人工裂缝;②裂缝越长,所对应裂缝位置处的井筒温度降低值越大,并且裂缝中气体流量与该温度降呈正相关关系;③影响页岩气藏压裂水平井温度剖面的因素,按影响程度由强到弱排列依次为裂缝半长、气体流动速度、改造区渗透率、井筒直径、裂缝导流能力、水平倾角、地层综合导热系数,其中前3个是主要的影响因素;④采用MCMC反演模型对实例水平井DTS温度数据进行了反演,模拟预测的温度剖面与实测DTS剖面拟合度较高,各级有效人工裂缝处的温度预测值绝对误差小于0.02℃,解释出的各压裂段气体流量与现场实测值比较接近,单段最大气体流量偏差仅180.35 m^(3)/d,单井气产量与井口实测气产量的绝对误差小于3 m^(3)/d,从而证实了该反演模型的可靠性。

In order to accurately evaluate the fracturing stimulation effect of horizontal wells in shale gas reservoirs,it is suggested to establish a model to predict the temperature distribution in the wellbore of horizontal well and an inversion model of DTS data by using MCMC algorithm,and optimize the production profile interpretation process.In this paper,the characteristics of temperature profile of fractured horizontal wells in shale gas reservoirs were analyzed and the main factors affecting the temperature profile were figured out.Finally,the newly established inversion model was applied to the production profile interpretation of one case well in a certain shale gas reservoir.And the following research results were obtained.First,the temperature profile of fractured horizontal wells is in the shape of irregular"saw tooth",and each"saw tooth"corresponds to an effective hydraulic fracture with inflow fluid.Second,the longer the fracture is,the greater the wellbore temperature drop at the corresponding fracture location is,and the gas flow rate in the fracture is positively correlated with the temperature drop.Third,from the perspective of influence degree,the factors influencing the temperature profile of fractured horizontal wells in shale gas reservoirs are ranked from the strong to the weak as follows:half fracture length,gas flow velocity,permeability of stimulated area,wellbore diameter,fracture conductivity,horizontal dip angle and comprehensive thermal conductivity,among which,the first three are main influential factors.Fourth,the MCMC inversion method is applied to invert the DST temperature data of the case well.The temperature profile predicted in the model is better accordant with the measured DTS profile,and the absolute error of the predicted temperature at different levels of effective hydraulic fractures is less than 0.02℃.The interpreted gas flow rate of each fracturing stage is closer to the field measurement,and the deviation of the maximum gas flow rate of single fracturing stage is only 180.35 m^(3)/d.The absolute error between single-well gas production rate and gas production rate measured at the wellhead is less than 3 m^(3)/d,which proves the reliability of this newly developed inversion model.