【作者】 高明；

【导师】 宋考平；

【作者基本信息】 大庆石油学院 ， 油气田开发工程， 2009， 博士

【摘要】 为了研究低渗透油层与高渗透油层孔隙结构的差异,从微观上找出低渗透油层驱油效率低的原因,本文以天然岩心压汞实验、扫描电镜实验、润湿性实验、驱油实验和岩心微观解剖实验为基础,结合统计分析和数值计算,研究了不同渗透率和润湿性的天然岩心中孔隙结构的分布规律、微观剩余油分布规律及剩余油饱和度与孔隙结构微观参数之间的关系;建立了适合水湿低渗透岩心的孔隙网络模型,研究了相渗曲线和剩余油饱和度与孔隙结构微观参数之间的关系,取得结果如下:统计分析了大庆油田外围低渗透油层的取芯井压汞资料,得出了渗透率和孔隙度的关系。通过作图可以看出,随着渗透率的增加,储层平均半径、中值半径和半径均值增大,且规律性较强;随着分选系数的增大,最大汞饱和度逐渐增大;随着渗透率的增加,孔隙结构特征参数、储渗参数逐步增加,在低渗透范围内( 0.01×10^-3μm² 50×10^-3μm²),储渗参数增加较快。取大庆油田不同渗透率级别天然岩心,首先进行室内实验,确定岩心的孔隙度、渗透率、原始含油饱和度、水驱采收率等参数,而后对进行了驱油实验的岩心进行处理,进行电镜扫描,得到不同放大倍数下能够清楚观察孔喉特征的图片,通过统计分析颗粒、孔隙、喉道等参数,分析其分布特点。实验结果表明:平均岩石颗粒半径随着渗透率增加较快,平均颗粒面积与周长比随着渗透率的增加而增大;孔隙面积、孔隙周长和两者之间的比值随着渗透率增加呈现不规则变化,但孔隙半径随着渗透率的增加而缓慢增大;喉道面积、喉道周长和二者之间的比值与渗透率无直接关系,喉道半径随着渗透率的增加而增大;低渗透岩心的平均配位数较小,随着渗透率的增加,平均配位数逐渐增大;随着渗透率的降低,平均孔喉比迅速增大,平均形状因子变小;随着孔隙半径、颗粒半径、喉道半径的增大,水驱采收率都有增大的趋势,喉道半径的增加对水驱采收率影响比较明显;水驱采收率随着平均配位数、平均形状因子、平均颗粒和平均孔隙面积周长比的增大而增加,而与平均喉道面积周长比无明显关系。通过回归分析可以看出,孔喉比形状因子对采收率的影响最大,是低渗透油田水驱采收率低的主要原因。利用景深扩展软件、测量软件,结合荧光分析技术,可实现对低渗透天然岩心自然断面上的孔隙半径、孔喉比、配位数、迂曲度、形状因子等微观参数和剩余油饱和度的测量。选取4块大庆外围和两块长庆油田低渗透岩心依次进行了润湿性实验、驱油实验和岩心微观解剖实验。结果表明:低渗透岩心以亲水为主;低渗透岩心的喉道半径分布范围比较集中,峰值高,喉道半径较小,是大庆油田低渗透油层区别于高渗透油层的显著特征,不同渗透率岩心的孔隙半径差别不大,而喉道半径相差较大,因此随着渗透率的降低,孔喉比急剧增加;随着渗透率的降低,各岩心配位数越小的分布频率越大、形状因子越小的分布频率越大、迂曲度越大的分布频率越大;大庆油田的不同渗透率岩心的配位数在2～3之间较集中,且曲线形态比较接近,而长庆油田的两块岩心配位数较大,孔隙连通好;大庆油田与长庆油田的相同渗透率级别岩心比较,迂曲度较大,形状因子较小,孔隙形状复杂。通过金相模式和荧光模式两种照片的对比,研究了岩心中微观剩余油分布规律。结果表明:水湿岩心中含剩余油的孔隙比例随孔隙半径减小而减小,而中性润湿岩心中含剩余油孔隙比例随孔隙半径的增加而减小;随着孔喉比的增大,含剩余油孔隙比例增加;随着配位数的减小,含剩余油孔隙比例增加;随着迂曲度的增大,含剩余油孔隙比例均增大;随着形状因子的减小,含剩余油孔隙比例增加。长庆油田的两块岩心与同等渗透率的大庆油田的岩心相比较,相同孔喉比、迂曲度或形状因子条件下,含剩余油孔隙比例较小,说明驱替效果较好。为了研究相渗曲线和剩余油饱和度与孔隙结构微观参数之间的关系,建立了适合水湿低渗透岩心的孔隙网络模型,并进行了模拟计算,结果表明:在水湿条件下,毛管力作用在驱油过程中是一种水驱油的动力,随着半径的减小,残余油饱和度减小,两相区变大,水驱采收率增加;随着孔喉比增大,残余油饱和度增大,两相共渗区变小,水驱采收率变小;随着配位数的增大,两相共流区变大,残余油饱和度减小,端点处饱和度下的相对渗透率增大,相对来说,对非润湿相油的相对渗透率影响更大,油滴流动通道增加,提高了油相渗透率,流体被捕集的机会减少,使形成剩余油的概率下降,水驱采收率提高;随着形状因子的减小,残余油饱和度增加,两相共流区变小,水驱采收率变小。更多还原

【Abstract】 For researching the differences of pore configuration between low permeability reservoir and high permeability reservoir, we found out the reasons of low permeability reservoir with low flooding efficiency from the microscope, the paper was on the base of five experiments（the pressing mercury experiment of the natural core, the scanning electron microscope experiment, the wetting experiment, the driving oil experiment and the micro-dissection experiments of the core ） and combined with statistical analysis and number value analysis, the distribution law of the pore structure in the natural cores with different permeability and wettability, the law of the micro surplus oil distribution, and the relationship between the saturation of remaining oil and micro parameters of the pore structure was studied; The pore-scale modelling which is suitable of the deluge low permeability cores has been set up and the relationship between the relative permeability curves, the saturation of remaining oil and micro parameter of the pore structure was also studied. The results showed as follow:According to the statistical analysis of the mercury penetration data of coring well from Daqing outside oil fields with low permeability, we obtained the relationship between permeability and porosity. As can be seen through the mapping, the average radius of reservoir, the median radius and the mean radius increased with the permeability increasing, and it presented apparent regularity; The maximum mercury saturation increased gradually with grading factor increasing; At the same time,pore configuration characteristic parameters and reservoir permeable parameters also increased gradually with permeability increasing, within low permeability reservoir( 0.01×10 ^-3μm 2 50×10 ^-3μm²), reservoir permeable parameters had a relatively rapid growth .Taking of natural cores with different permeability levels from Daqing Oilfield, first of all, we carried out indoor experiments to confirm some parameters such as porosity, permeability, initial oil saturation, water flooding recovery and so on, then we coped with the cores using flooding experiments and processed them with scanning electron microscope, at last we obtained the characteristics of pore throat pictures which can be observed clearly under different magnifications. Through statistical analysis of particles, pores, throat and other parameters, we can analyze their distribution.The experiment results showed that the average rock particle radius increased rapidly with permeability increasing, and the ratio between the average particle area and perimeter increases when the permeability increased; The pore area, the pore perimeter and the ratio between them presented irregular changes but the pore radius increased slowly with permeability increasing; The throat area, the throat perimeter and the ratio between them had no direct relationship with permeability, and throat radius increased with permeability increasing; The average coordination number of low permeability core was less, and the average coordination number increased with permeability increasing; The average pore throat ratio increased rapidly and the average shape-dependent constant became small when the permeability reduced; As the pore radius, the particle radius and the throat radius increased, the water flooding recovery has increased trend, then increasing throat radius had an obvious effect on water flooding recovery; The water flooding recovery increased with the average coordination number, the average shape-dependent constant and the ratio between the average pore area and perimeter increasing, but it had no obvious relationship with the ratio between the average throat area and perimeter.By the combination of depth of field expansion software and measurement software with the fluorometric analysis technique, the measurement on microscopic parameter such as pore radius, the pore throat ratio, the coordination number, the tortuosity, the shape-dependent constant and the measurement on remaining oil saturation of natural cross section in low permeability cores can be realized.The wettability experiment was carried on 4 pieces of low permeability cores in Daqing peripheral oilfield and 2 pieces of low permeability cores in Changqing oilfield, and the flooding experiment, the core micro-anatomy experiment was carried in turn. The result indicated that the low permeability cores were more water wetting, and that the throat radius distribution of low permeability cores were relatively concentrated with high peak and smaller throat radius, which were the significant features of the low-permeability reservoirs different from the high-permeability reservoirs in Daqing oilfield. In the cores of different permeability pore radius were not very different, while the throat radius had big differences, so with the decrease of permeability, the pore throat ratio increased sharply; And with the decrease of permeability, the distribution frequency of the cores with smaller coordination number or with smaller shape-dependent constant or with bigger tortuosity were larger. The coordination number of different permeability cores was concentrated between 2³ and whose curve shape was closer in Daqing oilfield, while the coordination number of the two cores in Changqing oilfield was relatively bigger with good pore connectivity. Comparing the cores of the same permeability level in Daqing oilfield with that in Changqing oilfield, the tortuosity was lager and the shape-dependent constant was smaller and the pore shape was more complex.According to the comparison between two kinds of photographs of the metallographic type and the fluorescent type, the distribution law of the microcosmic remaining oil in cores was studied. The result indicated that: In the water wetting cores the pores containing remaining oil proportion decreased with the decrease of the pore radius, while in the intermediate wetting cores the pores containing remaining oil proportion decreased with the increase of the pore radius; With the increase of the pore throat ratio, the pores containing remaining oil proportion increased; With the decrease of the coordination number, the pores containing remaining oil proportion increased; With the increase of the tortuosity, the pores containing remaining oil proportion all increased; With the decrease of the shape-dependent constant, the pores containing remaining oil proportion increased. Comparing the two cores of Changqing oilfield with the same level permeability cores of Daqing oilfield, under the situation of the same pore throat ratio, plane tortuosity or shape-dependent constant, the proportion of the pores containing remaining oil were smaller, which showed the displacement effect was better.In order to study the relationship between permeability ratio curve and remaining oil saturation and pore structure microcosmic parameters, the pore-scale modelling fitting for the water wetting low permeability cores was established , and the simulation calculation was carried out. The results showed that: under the water wetting condition, capillary force was a kind of driving force for water-flooding in oil displacement process; With the decrease of the radius, the residual oil saturation decreased, and the two-phase region become larger, and the water-flooding recovery efficiency increased; With the increase of the pore-throat ratio, the residual oil saturation increased, and the two-phase flow region become smaller, and the water- flooding recovery efficiency decreased; With the increase of the plane coordination number, and the two-phase flow region become larger, and residual oil saturation decreased, and the relative permeability along the saturation of end point increased. Relatively speaking, the influences on the non-wetting oil phase were larger, and oil-dripping flow channel increased, which improved the oil permeability, and the opportunity of fluid being captained decreased, so the forming probability of remaining oil decreased, and water-flooding recovery efficiency increased; With the decrease of the shape factor, the residual oil saturation increased, and the two-phase flow region decreased, and water-flooding recovery efficiency increased.更多还原