1. Research Institute of Petroleum Exploration & Development-Langfang,Langfang　 065007,China; 2. Daqing Oilfield Engineering Co Ltd. of Daqing Oil- field Co. , Ltd. ,Daqing　 163712,China; 3. No． 5 Oil Production Plant of PetroChina Changqing Oilfield Company,Xi’an　 710200,China

针对准噶尔盆地南缘煤层倾角大、地应力复杂的煤层气井钻探难题,基于弱面理论研究了煤层倾角、地应力、造(降)斜对井壁安全的影响,建立起多目标约束的沿煤层钻井轨迹优化模型。研究表明:(1)昌吉地区煤层倾角为10°~25°,局部达到25°~40°,属于高陡倾斜煤层,具有渗透率各向异性强、地应力各向异性强、岩体力学性质各向异性强的特点。(2)钻水平井时,根据倾角对井壁稳定影响分为作用区、过渡区和反转区,倾角在5°~25°时为作用区,沿倾向钻井最安全,沿走向钻井最危险;倾角大于65°后进入反转区,沿倾向、走向都成为安全钻井方位。地应力各向异性越大,坍塌压力越高、安全钻井方位的范围越小。(3)沿煤层倾向钻井时,倾角小于35°时建议沿煤层上倾方向钻井;倾角大于65°时建议沿煤层下倾方向钻井;倾角在35°~65°范围内井壁安全性最低,建议沿煤层走向钻井;井斜角在45°~65°时是最危险造(降)斜段,应尽量避免在此井斜范围对煤层造(降)斜。(4)为降低煤层着陆点到首靶点的坍塌压力,提出S型、J型两种沿煤层钻井轨迹类型,从对比结果看出本文方法比常规方法设计的井眼进尺更短、摩阻扭矩更小。

Aiming at coalbed methane(CBM) well drilling problems of high dip angle and complex stress in the south- ern margin of the Junggar Basin,the influence of the coal seam dip angle,in-situ stress and building-up (dropping) on wellbore stability were studied based on weak plane theory,and a multi-objective constraint drilling trajectory optimiza- tion model was established. The results show that ① the dip angle of coal seam in Changji area is 10°-25°,and partly reaches 25°-40°,which belongs to high steep coal seam. It has the characteristics of strong permeability anisotropy, strong stress anisotropy and strong rock mechanics anisotropy. ② When drilling horizontal well,according to the influ- ence of coal seam dip angle on wellbore stability,it can be divided into working zone,transition zone and inversion zone. It is working zone when dip angle is between 5°and 25°. Drilling along dip direction and strike direction are the safest and most dangerous orientation,respectively. When dip angle reaches 65°,it enters inversion zone,drilling along the dip direction and strike direction both become the safest orientation. The greater stress anisotropy,the greater col- lapse pressure and the smaller orientation range of safety drilling. ③ When drilling along coal seam,drilling along up- dip direction is proposed if the dip angle is less than 35°;drilling along down-dip direction is proposed if the dip angle is more than 65°;the wellbore safety is the lowest in the range of 35°-65°,then drilling along trend direction is pro- posed. It is the most dangerous building up (drop) section when the inclination angle is between 45° and 65°,build- ing-up (dropping) in coal seam should be avoided. ④ In order to reduce the collapse pressure from the landing point to the first target,S-type and J-type drilling trajectory types are proposed,the comparison results show that the trajectory de- signed in new method is shorter,less friction and torque than the trajectory designed in conventional method.

DONG Zhen,BAO Qingying,ZHANG Jidong,et al. Research on drilling along steep coal seam:A case study of Changji area in southern margin of the Junggar Basin[J]. Journal of China Coal Society,2018,43(4):1041-1051.