注水井裸眼坍塌临界压差预测方法比较分析

Comparative Analysis on Prediction Methods of Critical Pressure Difference of Wellbore Collapse for Injection Wells

塔河油田奥陶系碳酸盐岩储层主要采用裸眼酸压完井,注水井井眼坍塌频发,严重影响注水开发效果和井筒注采安全。针对塔河油田注水井裸眼坍塌状况,比较了3种井壁稳定临界压差预测模型,并结合预测实例分析了井眼坍塌的原因。地层稳定指数法预测的临界压差值相对最大,含弱面预测模型预测的临界压差值相对最小;临界压差随岩石抗压强度的降低而逐渐降低。注氮气诱喷时连续油管下深过大和周期注水替油阶段井筒液面下降过大是导致注水井裸眼坍塌的主要原因。推荐采用含弱面预测模型,建议将试油阶段连续油管下深和替油阶段井筒液面均控制在500 m以内,防止井底压差过大。

Open-hole acid fracturing is mainly used for well completion system for Ordovician carbonate reservoirs in Tahe Oilfield.And wellbores collapse frequently,which seriously affects the exploitation effects of water injection and the safety of wellbore injection and production.Aiming at the present collapse situation,three kinds of wellbore stability critical pressure difference prediction models are compared,and the wellbore collapse causes are also analyzed with a sample well.The formation stability index method predicts the maximum value of critical pressure difference;the weak surface model has the smallest prediction value,and the critical pressure difference decreases gradually with the decrease of rock compressive strength.The main causes of wellbore collapse for water injection wells are the excessive depth of coiled tubing when inducing flow with nitrogen injection and the excessive drop of liquid level during cycle water injection.The weak surface model is recommended.Meanwhile,the depth of the coiled tubing during inducing flow and that of the liquid level should both be controlled in 500 m for preventing excessive pressure difference at the bottom of the well.