缝洞型油藏出水规律“类活塞”理论试验研究及现场应用

Experimental study and field application of“piston-like”theory of water outflow law in fractured-vuggy reservoir

针对缝洞型碳酸盐岩油藏储层出水规律极为复杂、难以用常规方法研究探索的难题,提出了“类活塞”概念,引入“类活塞系数”分析推导了油井见水前后的采收率计算公式,阐述了油井见水前的整体预测法和分布预测法以及油井见水后的单、双孔隙渗流特点,研究了注入速度、裂缝储层非均质性极差、原油黏度、原始含油饱和度和溶洞倾角对裂缝型、缝洞型、溶洞型3种储集体出水规律的影响。研究结果表明,在裂缝储集体中,类活塞系数主要随注入速度增大而减小,极差越大类活塞系数越大;在多向连通缝洞储集体中,相同注入速度下,水驱低黏油时的类活塞系数较水驱高黏油时的高,原始含油饱和度为30%时类活塞系数最高;在致密填充溶洞储集体中,当倾角为0、45、90°时,类活塞系数平均值分别为0.98、0.92、0.97,当注水速度为0.1mL/min时所对应的类活塞系数最大,注水速度为1mL/min时对应的类活塞系数最低。现场应用结果表明,“类活塞”理论可一定程度上用以定性、定量地判断注入水流向问题,整体预测法所得的预测数据与实际数据更相符具有整体性和稳定性,分步预测法的误差和波动较大但具有较好的局部准确性,故在实际中结合应用。该研究对研究缝洞型油藏不同的储集体出水规律、采收率预测、储集体类型判断具有重要的理论和实践指导意义。

Aiming at the problem that the water outflow law of fractured-vuggy carbonate reservoirs is extremely complex and difficult to be studied and explored by conventional methods,the concept of“piston-like”was proposed,and the analysis of“piston-like coefficient”was introduced to derive the calculation formula of recovery of oil wells before and after water breakthrough.The overall prediction method and distribution prediction method before the water breakthrough of oil wells,as well as the seepage characteristics of single and double pores after the water breakthrough of oil wells were expounded.The influences of injection velocity,heterogeneity difference of fractured reservoir,crude oil viscosity,original oil saturation and karst cave dip angle on water outflow law of fractured reservoir,fractured-vuggy reservoir and karst cave reservoir were studied.The research results show that in fractured reservoirs,the piston-like coefficient mainly decreases with the increase of injection speed,and the greater the grade difference is,the greater the piston-like coefficient is;in the multi-direction connected fractured-cavity reservoir,under the same injection speed,thepiston-like coefficient of water-driven low-viscosity oil is higher than that of water-driven high-viscosity oil.When the original oil saturation is 30%,the piston-like coefficient is the highest;In the densely packed cavern reservoir,when the dip angles are 0,45 and 90°,the average piston-like coefficients are 0.98,0.92 and 0.97,respectively.When the water injection speed is 0.1mL/min,the corresponding piston-like coefficient is the largest,and when the water injection speed is 1mL/min,the corresponding piston-like coefficient is the lowest.Field application results show that the“piston-like”theory can be used to qualitatively and quantitatively determine the flow of injected water to a certainextent.The prediction data obtained by the overall prediction method is more consistent with the actual data and has integrity and stability.Errors and fluctuations of the step-by-step prediction method are large,but it has good local accuracy,so it is applied in practice.This study has important theoretical and practical guiding significance for the study of water outflow law,oil recovery prediction and reservoir type judgment of different reservoirs in fractured-vuggy reservoirs.