Effect of Retained Fracturing Fluid on the Imbibition Oil Displacement Effciency of Tight Oil Reservoir
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摘要: 统计长庆油田罗*区块2015年存地液量与油井一年累积产量的关系发现，存地液量越大，一年累积产量越高，与常规的返排率越高产量越高概念恰恰相反，可能与存地液的自发渗吸替油有关。核磁实验结果表明，渗吸替油不同于驱替作用，渗吸过程中小孔隙对采出程度贡献大，而驱替过程中大孔隙对采出程度贡献大，但从现场致密储层岩心孔隙度来看，储层驱替效果明显弱于渗吸效果。通过实验研究了影响自发渗吸效率因素，探索影响压裂液油水置换的关键影响因素，得出了最佳渗吸采出率及最大渗吸速度现场参数。结果表明，各参数对渗吸速度的影响顺序为：界面张力 > 渗透率 > 原油黏度 > 矿化度,岩心渗透率越大，渗吸采收率越大，但是增幅逐渐减小；原油黏度越小，渗吸采收率越大；渗吸液矿化度越大，渗吸采收率越大；当渗吸液中助排剂浓度在0.005%~5%，即界面张力在0.316~10.815 mN/m范围内时，浓度为0.5%（界面张力为0.869 mN/m）的渗吸液可以使渗吸采收率达到最大。静态渗吸结果表明：并不是界面张力越低，采收率越高，而是存在某一最佳界面张力，使地层中被绕流油的数量减少，渗吸采收率达到最高，为油田提高致密储层采收率提供实验指导。Abstract: The flowback of fracturing fluid directly affects the production rate of a reservoir in the later stage of production. In laboratory studies, the basic physical properties of reservoir core and fracturing fluid were measured. Based on the measurement, factors affecting automatic imbibition and key factors affecting oil/water replacement by fracturing fluid were studied through experiment. The optimum imbibition recovery rate and the maximum imbibition rate for feld use were determined in laboratory studies. Differences between imbibition and displacement are explained by nuclear magnetic experiment. The experimental results have shown that influencing factors affected imbibition rate in an order of:interfacial tension > permeability > viscosity of crude oil > salinity. The imbibition recovery rate increased with increase in permeability, while the amplitude of increase was gradually reducing.When the viscosity of the simulated oil was in a range of 1.204-4.864 mPa·s, the imbibition recovery rate increased with decrease in the viscosity of the simulated oil. When the salinity of the imbibition fluid was in a range of 1 000-80 000 mg/L, the imbibition recovery rate increased with increase in salinity, When the concentration of cleanup additive in imbibition fluid was in a range of 0.005%-5%, i.e., the interfacial tension was in a range of 0.316-10.815 mN/m, the use of the imbibition fluid containing 0.5% cleanup additive (interfacial tension 0.869 mN/m) got the maximum imbibition recovery rate. Static imbibition experimental resultshave shown that higher interfacial tension did not necessarily result in higher recovery rate; instead, there was an optimum interfacial tension at which the amount of bypassed oil was minimized, and the imbibition recovery rate was maximized. This fnding provides a guide to enhance recovery rate from tight reservoirs.
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Key words:
- Tight oil /
- Automatic imbibition /
- Nuclear magnetic /
- Orthogonal analysis /
- Oil driving fracturing fluid
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