缝洞型碳酸盐岩油藏注氮气致稠机理研究

Research on Crude Oil Thickening Mechanisms during Nitrogen Injection in Fracture-Cavity Carbonate Reservoirs

为了明确缝洞型碳酸盐岩油藏注氮气原油变稠的机理并制定相应的开发对策,提高注氮气的采收率,开展了缝洞型油藏注氮气致稠机理研究。该研究通过注氮气模拟试验,分析了氮气抽提作用、氮气含氧量和伴注水对原油黏度的影响。结果表明,氮气含氧是引起原油黏度增大的主导因素,含氧量为1%时,仅需2 d多即可将氧气耗尽,黏度达到18000 mPa·s,为初始黏度的6倍;含氧量为5%时,在7 d多时间内黏度持续升高达到1122000 mPa·s,为初始黏度的366倍。乳化含水和抽提对原油黏度的影响相当,黏度升高1~3倍。研究表明,提高注入氮气的纯度是防止塔河油田缝洞型油藏注氮气致稠的最有效方法,研究结果为解决缝洞型碳酸盐岩油藏注氮气原油致稠问题提供了理论依据。

Research was conducted on the thickening mechanism of crude oil during nitrogen injection in fracturecavity reservoirs to clarify the thickening mechanism and take corresponding countermeasures,thereby enhancing the oil recovery of nitrogen injection.In this study,simulation experiments of nitrogen injection were performed to analyze the influence on crude oil brought by nitrogen extraction,oxygen content in nitrogen,and mixed water.The experiments showed that the oxygen content in nitrogen was the major influential factor.When the oxygen content was 1%,it took only more than 2 days to exhaust the oxygen,and the viscosity reached 18000 mPa·s,which was 6 times the initial viscosity.When the oxygen content increased to 5%,the viscosity continued to grow to 1122000 mPa·s within more than 7 days,which was 366 times the initial viscosity.Emulsification with water and nitrogen extraction resulted in the same effect on viscosity:the viscosity increased 1–3 times.The results demonstrate improving the purity of injected nitrogen is the most effective way to prevent crude oil thickening of fracture-cavity reservoirs during nitrogen injection in Tahe Oilfield.It has provided a theoretical basis for solving the problem of crude oil thickening brought by nitrogen injection in fracture-cavity carbonate reservoirs.