【作者】 吴家文；

【导师】 宋考平； 程杰成；

【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,本文以润湿性实验、驱油实验和岩心微观解剖实验为基础,结合理论分析和软件计算,研究了不同渗透率、不同润湿性岩心的孔隙结构特征、微观剩余油分布规律及其与孔隙结构的关系,取得的成果如下:研制了岩心微观解剖实验方法并完成了设备组装。该方法综合荧光显微镜与金相显微镜的观测结果,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、平面配位数、平面迂曲度、形状因子等微观参数和剩余油饱和度的测量。选取5块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。为了研究低渗透岩心与高渗透岩心孔隙结构上的差异,另外选取5块中高渗透岩心同时进行实验,以便于对比分析。对拟进行驱油实验和岩心微观解剖实验的10块天然岩心分别测量了洗油前、洗油后和水洗后的润湿性。结果表明,低渗透岩心以亲水为主;驱油实验时常用的洗油方法严重地改变岩心的润湿性,使其更加偏于亲油。通过一定时间的水洗,可基本消除这种影响,使岩心的润湿性基本恢复到初始状态。因此,研究岩心的润湿性时应在洗油前或水洗后进行。测量完天然岩心水洗后的润湿性后,开展了驱油实验,并立刻进行了岩心微观解剖实验,拍摄了岩心自然断面上的金相和荧光两种模式的照片,测量了各岩心的孔隙半径、喉道半径、孔喉比、平面配位数、平面迂曲度、形状因子等参数。实验结果表明:(1)随着渗透率的减小,岩心平均孔隙半径减小,但这一趋势并不明显,说明孔隙半径对渗透率的影响不显著;(2)孔喉比随渗透率的减小而增大。分类特征明显,低渗透岩心与高渗透岩心的孔喉比存在明显的差异;(3)渗透率越小,平面配位数越小,这说明低渗透岩心孔隙连通差;(4)随着渗透率的减小,平面迂曲度变大,这说明低渗透率岩心中孔隙的空间展布情况较高渗透岩心复杂;(5)低渗透岩心的形状因子较高渗透岩心小很多,说明低渗透岩心孔喉截面形状更加复杂,不利于油水在其中的流动。(6)孔喉比大、形状因子小是低渗透岩心与高渗透岩心最显著的差异。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:(1)在油湿和中性润湿岩心中,孔隙半径越小,存在剩余油的概率越大。而水湿岩心中的剩余油主要存在于大孔隙中;(2)无论水湿还是油湿岩心,随着孔喉比的增加,孔隙中存在剩余油的概率均增大;(3)无论水湿还是油湿岩心,随着平面配位数的增加,存在剩余油的概率均减小,说明改变孔隙微观上的连通情况有助于提高采收率;(4)无论水湿还是油湿岩心,随着迂曲度的增加,存在剩余油的概率均增大,说明孔隙形状越复杂,越不利于驱出剩余油;(5)水湿和中性润湿岩心中形状因子越小,存在剩余油的概率越大。而在油湿岩心中,随着形状因子的减小,存在剩余油的概率变小;(6)低渗透油层孔喉狭小、形状复杂,油滴在孔道中的卡断是形成剩余油的主要形式;(7)孔喉比大、形状因子小是低渗透油层驱油效率低的主要原因。油滴从喉道进入孔隙的过程中,毛管压力由大变小,毛管力始终是水驱油的动力。间断的油滴在从喉道进入孔隙时更加容易被捕获形成剩余油。一旦剩余油在孔隙中形成,就无法建立有效的压力梯度将其驱出。低渗透油层由于喉道细小,以油滴形式捕集下来的剩余油占有更大比重。孔喉比大所造成的卡断是低渗透油层驱油效率低的主要原因。更多还原

【Abstract】 In order to learn the difference of pore structure between low permeability layer and high permeability layer, find out the reason why the displacement efficiency in low permeability layer is lower than that in high permeability layer, the character of pore structure, distribution law of microscopic remaining oil along with its relation with pore structure in cores with different permeability and different wettability was researched based on the wettability experiment, oil displacement experiment and the core dissecting experiment,. The outcome of this study is as bellowed.The technique of core micro-anatomy experiment was developed and the equipment assembly was completed. By the combination of fluorescence microscope and the metallography microscope, by the union of depth of field expansion software and measurement software and the fluorometric analysis technique, this method can realize the measurement on microscopic parameter such as pore radius, the pore-throat ratio, the plane coordinate number, the plane circuitous degree, the shape factor and the measurement on remaining oil satruation of natural cross section in low permeability cores.The wettability experiment was carried on 5 piece of low permeability cores, and the flooding experiment, the core micro-anatomy experiment was carried in turn. The same experiment was carried on 5 piece of high permeability cores in order to contrast the pore structure between low permeability cores and high permeability cores.Wettability of 10 piece of natural cores that after and before washing oil was measured.The result indicated that the often used oil washing method may change the wettability of cores seriously, which causes it more pro-oil bias. Through flooding of a certain time, this impaction can be basically eliminated, and the wettability of the cores return to the initial state. Then the experiment should be carried on before the procedure of washing oil or after water flooding when the wettability of cores are studied.After the measurement on wettability, the oil displacement experiment was launched before the core dissecting experiment. Both metallographic picture and fluorescent picture of nature fractured surface in cores were shoot, the parameters of cores including pore radius, throat radius, ratio between pore and throat, plane coordinate number, plane tortuous degree and form factor were measured. The result of experiment shows that: (1) With the increase of permeability, the average pore radius of cores increase, but this trend was not apparent which indicates the impact of the pore radius on permeability was not significant; (2) with the increase of permeability, the ratio between pore and throat decrease. The classification feature is obvious, there is a significant differences in ratio between pore and throat between low permeability cores and high permeability cores; (3) the greater the permeability is, the greater the plane coordinate number is, which indicates that low permeability cores have poor pore connectivity; (4) With the increase of permeability, plane tortuous degree become smaller, which indicates that the distribution of pore is more complex in low permeability cores than that in high permeability cores; (5) the form factor in low permeability cores is much smaller than that in high permeability cores, which shows that the pore-throat section shape in low permeability cores is too complex to allow the flowing of water and oil in it; (6) the most significant difference between the low permeability and high permeability cores is that the ratio between pore and throat is greater and form factor is smaller in low permeability cores.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 indicates that: (1) In the oil-wet and intermediately wet cores, the smaller the pore radius is, the larger the probability of the existence of remaining oil is. However, the remaining oil in the water-wet cores is mainly contained in large pores. (2) Whether the cores are water-wet or oil-wet, with the increase of the pore-throat ratio, the probability of the existence of remaining oil in the pore would both increase. (3) Whether the cores are water-wet or oil-wet, with the increase of the coordinate number, the probability of the existence of remaining oil would both decrease. It indicates that improving the microcosmic connected conditions of pores is conducible to enhance oil recovery. (4) Whether the cores are water-wet or oil-wet, with the increase of tortuous degree, the probability of the existence of remaining oil would both increase. It shows that it is much harder to displace the remaining oil when the pore shape is more complex. (5) The smaller the shape factor in the water-wet cores and intermediately wet cores is, the larger the probability of the existence of remaining oil. While in the oil-wet cores, as the shape factor decreases, the probability of the existence of remaining oil would also decrease. (6) As the pore throat in the low permeability layer is narrow and the shape is complex, the resection of oil globule in the channel is the primary form to generate remaining oil. (7) Large pore-throat ratio and small shape factor is the main reason for the low displacement efficiency in the low permeability oil layer.When the oil droplet moves from the pore throat to the pore, capillary pressure gets bigger and is the driving force all through the displacement. Discontinuous oil droplets tend to be easily captured and become remaining oil when moving from the pore throat into the pore. Once remaining oil is formed, it is impossible to establish effective pressure gradient to drive it out. The size of the pore is very small in the low permeability layer and the remaining oil in the form of the oil droplets due to capture accounts for a big percentage. Disconnection due to the big ratio in size of the pore to the throat is the main reason for the low displacement efficiency in the low permeability layer.更多还原