高陡倾斜煤层沿煤层钻井研究——以准南昌吉地区为例.

Aiming at coalbed methane( CBM) well drilling problems of high dip angle and complex stress in the southern 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 optimization model was established. The results show that ① the dip angle of coal seam in Changji area is 10°-25° ,and partly reaches 2 5 ° -4 0 ° , 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 influence 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 6 5 ° ,it enters inversion zone, drilling along the dip direction and strike direction both become the safest orientation. The greater stress anisotropy, the greater collapse pressure and the smaller orientation range of safety drilling. ③ When drilling along coal seam, drilling along updip 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 3 5 ° -6 5 ° , then drilling along trend direction is proposed. It is the most dangerous building up (drop) section when the inclination angle is between 45° and 65°,building- 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 designed in new method is shorter, less friction and torque than the trajectory' designed in conventional method. [ABSTRACT FROM AUTHOR]