巨厚砾岩层气体钻井井眼特征

由于具有常规钻井所不具备的多方面优势,气体钻井技术在中国正受到越来越多的关注。作为一项打开油气层新技术和提速技术,气体钻井技术在矿场应用中存在一些特殊问题,包括巨厚砾岩层提速钻井中井斜控制难和套管下入遇阻现象。现有的空气锤和钟摆钻具组合控制井斜方法在塔里木油田山前巨厚砾岩层中都很难起到很好的井斜控制效果,而且套管遇阻情况严重。基于实测井径数据,利用3次样条曲线重构井眼截面形状特征,并探讨巨厚砾岩层空气锤钻井椭圆井眼形成机理。结果表明,空气锤以高频冲击破坏岩石,受地层的非均质性和各向异性的影响,所形成的井眼体现为高度椭圆性。431.8 mm井眼的平均井径达495.3 mm,长轴达551.2 mm,而短轴仅为427.7 mm。正是这种井径短轴偏小和井壁不规则造成了套管下入遇阻问题。为了在塔里木盆地山前巨厚砾岩层推广气体钻井技术,不但要有效控制井斜,而且要尽可能增大井眼短轴长度。博孜101井的钻井实践表明,采用预弯钟摆BHA(底部钻具组合)不但可以较好地控制井斜,而且可以有效地改善井径截面形状,提高井壁的光滑度。

Wellbore characteristic of gas drilling in thicker conglomerate

As compared with conventional drilling techniques, gas drilling presents many advantages and has been attracting more and more attention in China. It is an emerging and drilling acceleration technology, for which there still exist some special problems when applied in the mining industry, i.e., difficulties in well deviation control and resistance in running casing during the drilling of thick conglomerate layers. When the air hammer and pendulum drill-string technique are applied to develop thick conglomerate layers in the piedmont belt of Tarim Oilfield, well deviation can be hardly controlled, and a large resistance is also encountered in running casing. Based on the measured borehole diameter data, the shape feature of borehole cross section was reconstructed using the cubic spline curve. Meanwhile, this study explored the formation mechanism of the elliptic borehole drilled by air hammer. The results show that air hammer can destroy rocks through high-frequency drilling, and highly elliptical boreholes are formed under the effect of reservoir heterogeneity and anisotropy. The average diameter of 431.8 mm borehole is 495.3 mm, and the long and minor axis is 551.2 mm and 427.7 mm respectively. The short minor axis and irregular shape of boreholes lead to the resistance in running casing. Aiming to promote the application of gas drilling technology in developing the thick conglomerate layers of Tarim Oilfield, it is required to not only effectively control the well deviation, but also increase the length of minor axis. The drilling practice of Bozi A well indicates that pre-bending pendulum assembly can be used to better control the well deviation, adjust the cross-sectional shape of borehole, and smooth the borehole wall.