渤中19-6区块钻具安全下放速度图版建立及应用

Establishment and Application of Safe Lowering Speed Chart of Drilling Tools in Bozhong 19-6 Block

渤中区块薄弱地层承压能力低,钻具下放产生的激动压力易造成薄弱地层发生破裂、循环漏失等井下复杂情况,设计合理的钻具下放速度至关重要。考虑钻井液渗滤效应,得到了激动压力作用下的井周应力及地层压力分布规律,以井壁有效周向应力达到岩石抗拉强度为破裂准则,得到薄弱地层安全评估模型。综合考虑钻具下放速度、下放深度、钻井液密度对井底安全的影响,建立了包含以上3个参数的井底安全评估图版。渤中区块已钻7口井应用该安全评估图版效果,验证了图版的便捷性及准确性。钻井设计过程中,应考虑钻具下放速度、下放深度及钻井液密度3个因素对井底安全的综合作用,防止井底岩石破裂,从而保证下钻时井底安全。

The pressure bearing capacity of weak formation in Bozhong block is low,and the exciting pressure produced by drilling tool lowering is easy to cause complex downhole situations such as weak formation fracture and circulation loss,so reasonable drilling tool lowering speed is very important.Considering the percolation effect of drilling fluid,the distribution laws of the circumferential stress around the well and formation pressure under the action of exciting pressure are obtained.Taking the effective circumferential stress of the well wall reaching the tensile strength of rock as the fracture criterion,the safety assessment model of weak formation is obtained.Considering the influence of drilling tool lowering speed,drilling tool lowering depth and drilling fluid density on bottom hole safety,a bottom hole safety evaluation chart is established.The bottom hole safety assessment chart is applied to 7 wells drilled in Bozhong block,which verifies the convenience and accuracy of the chart.In the process of drilling design,the effects of three factors of drilling tool lowering speed,drilling tool lowering depth and drilling fluid density on the bottom hole safety should be considered comprehen⁃sively,so as to prevent the rock at the bottom of the well from breaking and ensure the safety of trip-in.