井眼尺寸对井壁稳定性影响研究

Study on the Effect of the Hole Size on Wellbore Stability

根据岩石强度的尺寸效应理论,讨论了岩石的尺寸效应对强度的影响;并以此建立了井眼尺寸对井壁坍塌压力、破裂压力的影响规律的预测模型。将该模型应用于克拉玛依油田呼2井的井壁稳定性预测,发现:5 in、6 in小井眼的坍塌压力分别比常规井眼8(1/2)in坍塌压力降低了3.2%和1.1%;而破裂压力分别增加了0.22%和0.14%。井眼尺寸越小,其对应的坍塌压力值越小而破裂压力值越大;小井眼钻遇地层的安全泥浆密度窗口比常规井眼安全泥浆密度窗口宽,井眼尺寸越小,对维持井壁稳定的泥浆密度要求降低。

According to the theory of size effect about rock strength,discussing the effect of size effect on rock strength,and thus established prediction model of influence law of the hole size on hole collapse pressure and fracture pressure.The model is applied to predict wellbore stability in karamay oilfield,found that： the collapse pressure of the slim-holes 5 in、6 in respectively,compared with conventional borehole 8 12 in,collapse pressure was reduced by 3.2% and 1.1%,and the fracture pressure increased by 0.22% and 0.14% respectively.Hole size is smaller,its value of collapse pressure is smaller,and the value of fracture pressure is greater.The width of safe mud density window of slimhole is wider than that of safe mud density window of the conventional borehole,and hole size is smaller,the requirement of mud density to maintain wellbore stability is lower.