Low-damage Water-based Drilling Fluid Technology for Fractured Tight Sandstone Reservoirs
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摘要: 胜利油田某区块致密砂岩储层致密,裂缝发育,钻井过程中易受到钻井液损害。通过储层矿物组成、孔渗特征及敏感性评价,分析了储层伤害主要原因,针对性研发了可在储层温度下自降解的暂堵剂,构建了低伤害水基钻井液体系。研究结果表明,该储层面临钻井液固相堵塞裂缝、水锁损害、水敏以及酸敏损害。研发的环氧树脂类自降解暂堵剂可在高温下通过酯键水解及酯交换反应导致网络解聚,生成可溶性低聚物。在120 ℃储层温度下,其48 h降解率为21.8%,96 h降解率达96.4%,且抗压强度远超常用的暂堵剂碳酸钙。低伤害钻井液性能评价实验表明,其具有良好的流变性、滤失性、润滑性及黏土水化抑制性能。模拟裂缝封堵实验以及岩心渗透率恢复实验表明,钻井过程中暂堵剂等固相快速在裂缝中形成封堵层;120 ℃静置48 h封堵层仍可维持良好的承压能力;静置48~72 h后,封堵层结构发生破坏,返排24 h岩心渗透率恢复值超90%,避免了储层伤害。3口井的现场试验表明,该钻井液防漏堵漏效果良好,且可通过暂堵剂的自降解有效保护储层,较邻井原油增产91.83%。Abstract: The tight sandstone reservoirs in a certain block of the Shengli Oilfield are characterized by high density and well-developed fractures, which make them highly susceptible to drilling fluid damage during drilling. Through evaluations of reservoir mineral composition, porosity and permeability characteristics, and sensitivities, the primary causes of reservoir damage were analyzed. Accordingly, this study developed a new temporary plugging agent capable of self-degradation at reservoir temperatures and constructed a low-damage water-based drilling fluid system. The results indicated that the reservoir faced damage from solid phase plugging of fractures, water blocking, water sensitivity, and acid sensitivity. The developed epoxy resin-based self-degradable temporary plugging agent underwent network depolymerization via ester bond hydrolysis and transesterification reactions at high temperatures, generating soluble oligomers. At a reservoir temperature of 120 ℃, its degradation rate reached 21.8% after 48 h and 96.4% after 96 h. In addition, its compressive strength significantly exceeded that of calcium carbonate, a commonly used temporary plugging agent. Performance evaluation experiments on the low-damage drilling fluid demonstrated that it possessed excellent properties in rheology, filtration control, lubricity, and clay hydration inhibition. Simulated fracture plugging and core permeability recovery experiments showed that solid phases, including the temporary plugging agent, rapidly formed a sealing layer within the fractures during drilling. This sealing layer maintained good pressure-bearing capacity even after standing for 48 h at 120 ℃. After standing for 48–72 h, the structure of the sealing layer broke down, and following a 24 h flowback period, the core permeability recovery exceeded 90%, namely that formation damage was avoided effectively. Field tests in three wells demonstrated that this drilling fluid exhibited excellent lost circulation prevention and control effects. Furthermore, it effectively protected the reservoir through the self-degradation of the temporary plugging agent, resulting in a 91.83% increase in crude oil production in comparison with offset wells. can undergo network depolymerization through ester bond hydrolysis at high temperatures, generating soluble oligomers. At the reservoir temperature of 120 ℃, its degradation rate reaches 21.8% after 48 hours and 96.4% after 96 hours, with compressive strength far exceeding that of calcium carbonate, which is the typical temporary plugging agent. Performance evaluation experiments of the low-damage drilling fluid show that it exhibits excellent rheological properties, filtration control, lubrication, and clay hydration inhibition. Simulated fracture plugging experiments and core permeability restoration tests demonstrate that solid-phase materials such as the temporary plugging agent rapidly form a plugging layer in fractures during drilling. After static placement at 120 ℃ for 48 hours, the plugging layer still maintains good pressure-bearing capacity. After 48 to 72 hours of static placement, the structure of the plugging layer breaks down, and the core permeability recovery value exceeds 90% after 24 hours of flowback, effectively avoiding reservoir damage. Field tests conducted on three wells indicate that the drilling fluid demonstrates excellent performance in leak prevention and plugging. Additionally, the self-degradation of the temporary plugging agent effectively protects the reservoir, resulting in a 91.83% increase in crude oil production compared to offset wells.
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表 1 低伤害水基钻井液基本性能评价实验结果
条件 AV/
mPa·sPV/
mPa·sYP/
PaGel/
Pa/PaFLAPI/
mL极压润滑
系数岩样8 h线性
膨胀率/%岩样滚动
回收率/%热滚前 53.0 38 15.0 5/11 5.0 0.115 7 / / 120 ℃、16 h 47.5 34 13.5 4.5/9 4.8 0.108 2 1.7 90.7 表 2 低伤害水基钻井液的裂缝封堵承压能力及自解堵时间
类型 裂缝
开度/mm最大承压
压力/MPa漏失量/
mL封堵层
垮塌时间/hSTPA 1×0.5 8.9 12 61.5 2×1 8.6 25 59.1 碳酸钙 1×0.5 3.7 49 / 2×1 3.6 75 / -
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