A Study on Borehole Wall Strengthening Technique and Its Application in Block Ledong
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摘要: 乐东区块构造位于莺歌海盆地的凹陷斜坡带,属于典型的海上超高温高压区块,地层安全密度窗口窄,深层井漏问题突出,严重制约了乐东气田的勘探与开发。针对该区块的井漏技术难题,通过井史资料统计,分析了该区块的漏失特征及漏失机理。基于黏滞单元法,模拟了井壁强化作用前后的井周应力变化,并预测了预充填裂缝开度。基于新型可变裂缝封堵模拟实验装置,开展了井壁强化材料粒径及浓度优化实验研究。实验结果表明,较优粒度匹配准则为D50准则,合理浓度为5%。基于乐东区块抗高温油基钻井液,优化构建了井壁强化钻井液体系配方。综合评价表明,该井壁强化配方对钻井液的流变性影响较小,砂床滤失侵入深度仅为1.5 cm,1 mm动态裂缝封堵承压能力达12 MPa以上。Abstract: The Ledong block, a typical high temperature high pressure offshore block, is located in the depression slope zone of the Yinggehai Basin. Some formations drilled in this block have narrow safe drilling windows and mud losses in deep hole occurred frequently during drilling. To deal with the mud losses, the drilling data was studied and the mechanisms and nature of the mud losses were analyzed. Using the viscous element method, the change of the stresses around the borehole before and after borehole wall strengthening was simulated, and the opening of the prefilled fractures predicted. Using a new experiment apparatus which can simulate the plugging of variable fractures, a study was conducted on the particle size distribution and concentration optimization for borehole wall strengthening. The experimental results show that the D50 criterion is a better particle size matching criterion, and a reasonable concentration of the particles is 5%. A drilling fluid that is suitable for use in the Ledong block and has the ability of borehole wall strengthening is developed through optimization experiment. In a comprehensive evaluation experiment, the additives for borehole wall strengthening showed little effects on the rheology of the drilling fluid. Sand bed test showed that the depth of the filtrate invasion was only 1.5 cm. Dynamic pressure bearing capacity of 1mm fractures tested with the drilling fluid can be as high as 12 MPa.
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表 1 乐东区块黄流组漏失复杂情况统计结果
井号 漏失深度/m ρ钻井液/(g·m−3) 漏失量/m3 漏失速率/(m3·h−1) 漏失原因 处理结果 X-1-1井 4085、4098、4050 2.21 7.25 23、10、35 高密度钻井液压漏地层 堵漏成功 X-1-2井 4103 2.15 55.6 15 压力窗口窄,地层承压能力低 堵漏6次,未成功 X-1-4井 4052 2.23 90.0 压井期间高密度钻井液压漏地层 井底未压稳下发生井漏,无有效处理方案 X-1-6井 4105、4329 2.33、2.31 黄流组二段II、IV、V气组地层存在大段诱导缝 堵漏成功 X-1-10井 3936、3972 2.30、2.28 3936 m压井期间高密度钻井液压漏地层,3972.5 m钻井期间漏失 堵漏成功 表 2 不同封堵配方砂床滤失封堵实验结果
粒径匹配准则 16~18目/% 18~24目/% 24~30目/% 30~45目/% 45~80目/% 侵入深度/cm 承压强度/MPa D90 10.0 22.5 22.5 22.5 22.5 2.43 6.42 D50 50.0 12.5 12.5 12.5 12.5 1.81 8.71 1/3 12.5 12.5 12.5 12.5 50.0 1.97 7.53 2/3 25.0 25.0 16.0 17.0 17.0 2.21 7.87 表 3 不同加量井壁强化材料的砂床滤失封堵实验
井壁强化材料/% 侵入深度/cm 承压强度/MPa 井壁强化材料/% 侵入深度/cm 承压强度/MPa 3 1.83 8.62 6 1.31 12.86 4 1.68 10.28 7 0.84 13.11 5 1.52 12.19 注:测试条件为30 min、0.7 MPa 表 4 井壁强化工作液热滚前后的流变性能
工作液
类型老化
条件AV/
mPa·sPV/
mPa·sYP/
PaGel/
Pa/Pa油基钻井液 热滚前 66 58 8 3/4 200 ℃、16 h 82 71 11 5/11 油基钻井液+
碳酸钙热滚前 70 60 10 3/5 200 ℃、16 h 85 70 15 6/13 -
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