Low Damage Highly Inhibitive Water Based Drilling Fluid for Drilling Shale Oil Reservoir
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摘要: 长73页岩储层发育微纳米级孔缝,地层岩石强度低,钻井液滤液易侵入储层造成井壁失稳和储层伤害。厘清了长73页岩井壁失稳机理及钻井液技术难点,借鉴“1/3和2/3架桥封堵规则”,引入刚性和可变形封堵材料,构建了广谱型多级粒径分布区间。以瞬时滤失量为评价指标,通过曲面响应建模优化出最佳配比,室内优选了防塌抑制剂组合,在此基础上研发出一套低伤害强防塌水基钻井液体系,评价实验结果表明,所构建的钻井液能够有效平衡地层坍塌应力,老化后静置72 h流变性依旧良好,抑制性强,页岩线性膨胀率较清水环境和现场钻井液分别降低了16.74%和13.61%;封堵性显著,瞬时滤失量仅为1 mL,对岩心的封堵率高达93.5%,储层保护性好,泥饼清除后岩心板中无孔喉堵塞现象,渗透率恢复值高达95.2%;润滑性能适中,钻井液老化前后摩阻系数均保持在0.08左右,现场试验水平段平均井径扩大率仅为4.27%,平均机械钻速可达18.4 m/h,钻进期间水平段无井下复杂事故,各项性能能够满足长73页岩油水平井钻井的需要。Abstract: Chang 73 reservoirs have the characteristics of micron-nano crack development and low strength of formation rocks. It can lead to the intrusion of drilling fluid filtrate into the reservoir causing borehole collapse and reservoir damage. We clarified the destabilization mechanism of Chang 73 shale and the technical difficulties of drilling fluids. Then the multi-stage particle size distribution intervals with broad spectrum was constructed by introducing rigid and deformable plugging materials, which was based on the "1/3 and 2/3 bridging rule". Next, using the instantaneous water loss as the evaluation index, the optimal ratio was optimized by surface response modeling, and the combination of anti-collapse inhibitor was preferred in the room. Based on which a low damage and anti-collapse water-based drilling fluid was developed. The results of the evaluation indicated that the drilling fluid can effectively balance the formation collapse stress, and the rheological properties remain satisfactory after aging for 72 h. It also reduced shale linear swell by 16.74% and 13.61% compared to clear water environments and in the field drilling fluids respectively. Due to its remarkable plugging properties, the instantaneous filtration loss of the drilling fluid was only 1mL and the plugging rate of the core was as high as 93.5%. Based on the reservoir protection capability of the drilling fluid, there was no pore throat plugging in the core slab after mud cake removal and the permeability recovery value of the core was as high as 95.2%. It was important that the lubricity of the drilling fluid was moderate and the friction coefficient remain around 0.08 before and after the drilling fluid ages. The average diameter expansion rate of the horizontal section in the field test was only 4.27%, and the average mechanical drilling speed could reach 18.4m/h. There were no complicated downhole accidents in the horizontal section during the drilling period, and all the performances could meet the needs of horizontal wells in the Chang 73 reservoirs.
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表 1 长73页岩全岩矿物衍射分析
% 石英 斜长石 钾长石 正长石 黄铁矿 碳酸盐 TCCM 46.42 8.28 13.56 2.95 5.35 0.68 22.76 表 2 长73地层岩石力学参数分析
地层
岩性取心深度/
m泊松比 弹性模量/
MPa内摩擦角/
(°)地层坍塌压力
当量密度/(g·cm−3)地层破裂压力
当量密度/(g·cm−3)最大剪应力/
MPa抗剪强度/
MPa页岩 2420.00 0.26 20.30 27.53 1.22 2.18 20.30 18.30 表 3 多级封堵材料粒径分布区间
代号 级别 封堵材料种类 D50/
μm备注 X1 一级(刚性) 8000目碳酸钙
(现场)1.6 2 μm的2/3~1/1 X2 二级(刚性) 10 000目碳酸钙 1.3 2 μm的1/3~2/3 X3 三级(可变形) G325(现场) 0.76 <2 μm的1/3 表 4 模型方程各参数及误差分析
方程
系数数值 标准
误差Reduced
Chi-Sqr残差平
方和R2 调整R2 a 32.186 28 0.959 06 0.327 77 3.605 47 0.968 57 0.952 14 b −0.746 32 0.065 61 c −0.719 44 0.040 18 d 0.007 34 8.054 76×
10−4e 0.004 61 3.723 16×
10−4f 0.007 29 7.915 67×
10−4表 5 不同密度下钻井液流变性能评价
ρ/(g·cm−3) 测试条件 AV/mPa·s PV/mPa·s YP/Pa Gel/(Pa/Pa) YP/PV/(Pa/mPa ·s) FLAPI/mL pH 1.20 老化前 24.5 15.0 9.5 4.5/8.0 0.63 2.2 8.0 老化后 25.5 17.0 8.5 3.0/6.0 0.50 2.6 8.0 1.30 老化前 29.5 16.0 13.5 5.0/9.0 0.84 3.6 8.0 老化后 31.5 19.0 12.5 4.0/8.0 0.66 3.6 8.0 1.40 老化前 32.0 19.0 13.0 5.0/9.0 0.68 4.5 8.0 老化后 31.5 19.0 12.5 4.0/8.0 0.66 4.5 8.0 注:钻井液体系加重材料选用重晶石,老化条件:120 ℃×16 h,静置72 h。 表 6 岩样滚动回收率评价
层位 实验方案 初始质量/
g回收质量/
g岩样回收率/
%长73 清水 50.0 43.6 87.2 现场钻井液 50.0 46.2 92.4 强封堵防塌钻井液 50.0 48.8 97.6 注:老化条件:120 ℃×16 h。 表 7 储层保护性能评价
岩心
编号驱替
介质T/
℃t/
hK/mD 封堵率/
%渗透率恢复/
%伤害前正向 伤害后正向 伤害后反向 1# 煤油 65.0 2.0 14.98 4.56 10.88 69.6 72.6 2# 2.0 15.60 1.01 14.85 93.5 95.2 注:1#为现场钻井液;2#为低伤害强防塌水基钻井液。 -
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