一种地震裂缝预测与岩石力学相结合评估井漏风险的新方法——以准噶尔盆地玛湖油田A井区为例

A new method of leakage risk evaluation based on seismic fracture prediction and rock mechanics:Case study in A wellblock of Mahu Oilfield in Junggar Basin

钻井过程中发生井漏的情况较为复杂,引起井漏的因素有多种。准噶尔盆地玛湖油田A井区二叠系上乌尔禾组储层低孔、低渗、横向非均质性强,井漏主要是由裂缝和地层破裂引起,常规利用地震裂缝预测评估井漏风险的方法效果不佳,需要探索更有效的井漏风险评估方法。通过对玛湖油田A井区已有钻井井漏、裂缝、岩石物理和地震的综合分析,形成了利用地震预测裂缝相对强度和裂缝视长度与利用叠前地质统计学反演预测岩石力学参数杨氏模量相结合的一种评估井漏风险的新方法——井漏综合指数法。该方法同时反映了裂缝和地层破裂对井漏的影响,并建立了井漏综合指数风险评估模型及分级评价标准。应用该方法对玛湖油田A井区2口最新完钻井进行井漏风险评估,评估结果与实钻情况吻合。基于井漏综合指数的井漏风险评估方法能有效评估储层低孔、低渗、横向非均质性强及水平井钻井地区的井漏风险,为油田现场钻井井漏评估,特别是水平井钻井轨迹优化提供了新的手段。

Leakage of drilling wells is complex because there are several factors.In A wellblock of Mahu Oilfield in Junggar Basin,reservoir is low porosity,low permeability and heterogeneous in upper Wuerhe Formation of Permian.Fracture and formation rupture are the main factors causing leakage.The common leakage risk evalua⁃tion methods by seismic fracture prediction are not satisfactory.A more effective leakage risk evaluation method is in demand.Leakage,fracture,rock physics and seismic data of the existing wells are analyzed in A wellblock of Mahu Oilfield.Comprehensive index of leakage,a new method for evaluating leakage risk,is proposed.It is based on seismic fracture prediction and rock mechanics parameters analysis,and represents the influence of fracture and formation rupture.Prestack geostatistical inversion is used to predict Young modulus.Ant tracking is used to predict fracture.The evaluation model of leakage risk and classification standard are built by combin⁃ing Young modulus with relative intensity of fracture development and fracture length.This method is used for leakage risk evaluation of the recent drilled wells in A wellblock of Mahu Oilfield.The result is consistent with the real data.The new leakage risk evaluation method is effective on the low porosity,low permeability and het⁃erogeneous reservoir in horizontal well drilling area.It can warn early about the possible leakage of drilling wells and optimize horizontal well trajectory.