无黏土水基钻井液在长庆油田米 38 区块水平井的应用

陕北神木气田米38区块致密砂岩气藏主要以水平井方式开发,由于储层段含有大段泥页岩,前期使用的钻井液体系固相含量高,在钻进过程中托压严重、摩阻大,常发生井壁失稳、下钻遇阻等情况。针对米38区块储层特征,优选了关键处理剂,形成了无黏土低固相水基钻井液体系。室内实验表明,该钻井液具有良好的封堵性和抑制性,高温高压砂床(150℃、3.5 MPa)侵入深度为7.2 cm,16 h的页岩膨胀高度仅为0.76 mm。现场应用表明,该钻井液体系具有良好的流变性、抑制性和封堵能力,较好地满足长庆油田米38区块水平段易坍塌地层的钻进需要。已施工的3口水平井钻进过程中摩阻小、无明显托压,起下钻顺畅,未出现任何井下复杂情况,钻井周期较设计周期平均缩短10.85 d,下套管一次到位。与邻井相比,单井产气量显著提高,有效提升了神木气田的开发效果。

Application of a Clay-Free Low Solids Water Based Drilling Fluid in Block Mi-38 in Changqing Oilfield

Horizontal drilling has long been used to develop the dense sandstone natural gas reservoirs in the Block 38 in Shenmu gas field (part of Changqing Oilfield) in the north of Shaanxi Province. The drilling fluid used to drill the upper formations had high solids content, which resulted in many problems in drilling the reservoir section, such as difficulties in exert pressure on the drill bit, high friction, borehole wall collapse and resistance to tripping into the hole. Based on the reservoir characteristics of the reservoirs in the Block Mi-38, a clay-free low solids drilling fluid was formulated with carefully selected key additives to address these problems. Laboratory experiment on this drilling fluid showed that this clay-free low solids drilling fluid has good plugging and inhibitive capacity; depth of fluid invasion at HTHP (3.5 MPa, 150℃) into a sand-bed was 7.2 cm, and the length of a shale core had an extension in length of only 0.76 mm after experiment for 16 hours. In field application, this drilling fluid showed good rheology, inhibitive capacity and plugging capacity, satisfying to some extent the needs of drilling the easy-to-collapse horizontal sections of wells drilled in the Block Mi-38 in Changqing Oilfield. Three wells drilled with this clay-free low solids drilling fluid showed low friction and no difficulties in exerting pressure on bit during drilling. Tripping of the drilling pipe into or out of hole was smooth and no downhole troubles have ever been encountered. The drilling time was 10.85 d less than the designed drilling time, casing string was run into the hole with no resistance. Compared with wells drilled nearby, the production rate of gas of a single well drilled with the clay-free low solids drilling fluid was significantly increased.