欠平衡钻井技术在元坝121H井的应用

元坝121H井是一口部署于川东北巴中低缓构造带元坝区块的海相超深水平井,钻遇地层复杂,地层压力和温度高,地层流体含H2S和CO2,钻井施工难度大、周期长.尤其是陆相的千佛崖、自流井和须家河组大尺寸井段,地层岩石硬度高,研磨性强,可钻性差,机械钻速低,严重制约了开发效益和周期.为了提高钻井速度,缩短钻井周期,分别在一开、二开和三开部分井段采用了泡沫、气体和液体欠平衡钻井技术,机械钻速约是常规钻井液钻速的1.2～6.0倍,最高达9.41 m/h,提速效果显著.该井欠平衡钻井效果在提高机械钻速方面与常规钻井方式相比具有明显优势,也为该地区钻井提速和及时发现油气显示提供了宝贵经验.

Application of underbalanced drilling technology in Well Yuanba 121H

Well Yuanba 121H is an ultra-deep horizontal well deployed in low and slow structural belt of Yuanba District in Northeast Sichuan Basin.The drilled formation is complex,pressure and temperature is very high and formation fluid contains etchant gas H2S and CO2.The drilling operation is very difficult and drilling cycle is long,especially for the Qianfoya Formation,Ziliujing Formation and Xujiahe Formation intervals,the rock hardness is high,grinding is strong,drillability is poor and penetration rate is slow,which seriously restrict the benefits and cycle of development.In order to improve drilling speed and shorten drilling cycle,foam drilling is used in the initial flow period,gas drilling in the second flow period and mud underbalanced technology in the third flow period.In such condition,maximum penetration rate reaches 9.41 m/h,which is 1.2-6.0 times more than that of conventional drilling fluid and creats significant effect.In improving the rate of penetration,the effect of underbalanced drilling has a clear advantage comparaed with the conventional drilling,which can provide a valuable experience for increasing the drilling speed and timely finding oil and gas showing in this area.