强抑制聚合物体系解决川渝地区大井眼段钻井液回收利用率低的问题

川渝地区大井眼段中途完钻后钻井液密度、黏度和劣质固相含量等均大幅上涨，无法回收利用，需报废处理，增加了处理成本和安全环保风险。分析了该地区大井眼段岩样矿物成分，其中伊利石、伊/蒙混层占岩样中黏土矿物的70%以上，黏土矿物中的交换性阳离子钙、镁离子被吸附在颗粒表面，使黏土颗粒具有较高的物化活性及亲水性，遇水后极易水化膨胀和分散。采用川渝磨溪地区沙二段泥岩进行抑制性评价实验，由于钙离子通过降低水的活度和压缩黏土颗粒的双电层来抑制水化，区别于钾离子的抑制机理，得出钾钙协同抑制效果优于单一离子的抑制效果，优选出钾钙离子的最佳配比。通过继续引入插层、疏水抑制剂，得到钾钙抑制结合插层、疏水抑制的综合抑制性能最强。在抑制剂评价基础上，优选出抗盐聚合物WN2-2，最终优化形成了适用于川渝地区大井眼段的强抑制聚合物钻井液体系。该体系具有极强的抑制性，极大限度地抑制了黏土的水化分散，对比现场3口井磨溪009井、磨溪022井、磨溪019井的应用情况，采用强抑制聚合物钻井液体系的磨溪019井，钻井液回收利用率从0大幅提升至75%，现场应用效果明显。

Highly Inhibitive Polymer Drilling Fluid Help Resolved Problem of Low Recycling Rate of Drilling Fluid Use to Drill Fat Holes in ChuanYu Area

Drilling fluids used to drill fat hole in ChuanYu area always have high density, high viscosity and high content of poor-quality solids, making them difficult to reuse. Disposal of them as waste drilling fluids greatly increases operational cost and environmental risks. Analyses of the mineral components of formation rocks taken from the fat hole sections show that the clay minerals in the rock contain more than 70% illite and illite/smectite mixed layer mineral. Exchangeable cations, such as calcium and magnesium ions, are adsorbed onto the surfaces of clay particles, rendering clay particles high activity and hydrophilicity. These clay particles are thus very easy to hydrate, swell and disperse when in contact with water. Mudstone samples were taken from the Sha2 member in Moxi, ChuanYu area for inhibition test. Since calcium ions inhibit clay hydration by reducing water activity and suppressing electric double layer of clay particles, a mechanism different than that of potassium ions, it was concluded that the synergy of calcium ions and potassium ions is better than using just calcium ions or potassium ions to inhibit clay minerals. An optimum ratio of calcium ions over potassium ions was selected through laboratory experiment. By introducing intercalation and hydrophobic inhibitive agents into the drilling fluid, it was found that a drilling fluid with optimum concentration of calcium/potassium, intercalation and hydrophobic additives has the strongest inhibitive capacity. Based on this idea, a highly inhibitive polymer drilling fluid was formulated with selected inhibitive additives and WN2-2, a salt-resistant polymer. Tis drilling fluid is suitable for use to drill the fat hole sections in ChuanYu area. It has very strong inhibitive capacity, greatly inhibit the clay formation from hydration and dispersion. Comparison of the drilling operation of the well Mox-009, well Moxi-022 and well Moxi-019 shows that the highly inhibitive polymer drilling fluid, which was used to drill the well Moxi-019, was recycled by 75%, while the drilling fluids used to drill the other two wells were not recycled. This highly inhibitive polymer drilling fluid is worth spreading for its high rate of recycling.