A Study On Changes Of Reservoir Construction And Rules Of Scaling After Strong Base ASP Flooding

Most oil fields in our country have been in the late stage of development, with the production rate for water flooding declined, remaining oil scatter distribution, there are many difficulties in potential tapping. Alkali-surfactant- polymer ASP flooding is an effective way to improve oil recovery, inhibit production decline and maintain stable production. However, as the ASP flooding testing in fields, many new problems exposed gradually. That alkali react with reservoir water and mineral can lead to scale and hurt the reservoir and as scaling problems become increasingly serious, the work strength increase and production wells work on longer cycle, so that the cost of production increases, which have the serious influence on the normal production in oilfield; moreover, understandings on oil layer using condition and remaining oil distribution are not enough in-depth, which requires to study reservoir physical properties change and the distribution of remaining oil systematically after the Strong Base ASP flooding.In this paper, the type of the micro remaining oil, the rule of its distribution and the content of light and weight components were studied by the confocal laser technology after ASP flooding; microscopic displacement features of compound flooding system was studied through microscopic visual physical simulation experiment; microscopic pore structure, wettability change and scaling status in reservoir were studied by scanning electron microscopy; core scaling mechanization, processing and influential factors were studied through laboratory experiments; finally, chemical scale prevention technology in the ASP flooding was studied through laboratory experiments combined with the actual sceneThe results showed the microscopic remaining oil after the ASP flooding can be divided into three categories which can be divided into seven types further, the first category is the remaining oil at bound state, including pore scale film remaining oil, particle adsorption remaining oil and slit remaining oil; The second category is the remaining oil at half bound state, including corner remaining oil and throat remaining oil; The third category is the remaining oil at free state, including clusters remaining oil and inter particle adsorption remaining oil. Among these, the percentage content of natural core bound state remaining oil relative less 13% than that after water flooding, which convinces that the ASP flooding has a better displacement effect on the residual oil at bound state which left after the simple mechanical flushing during water flooding; The pore scale film remaining oil is the main type among the seven types of the remaining oil and proportion of heavy oil in formation became greater after the ASP flooding; The alkali can dissolute formation rock minerals forming a large number of mud and tiny particles, which results to produce inter particle adsorption remaining oil which does exist after water flooding. The corrosion damage is more noticeable that the displacement agent of the ASP flooding have to the formation, the substance made by alkali soluble reaction have both effect on the injection pressure and produced liquid; the core wettability changed from oil wet to water wet after the ASP flooding, which is advantageous to the oil flowing and displacement; Dissolution of feldspar, quartz and clay mineral is more serious, and pore filling with granular material, and mineral surface has a small piece of secondary quartz, which prevent the process of oil displacement; the Al and Si scale which feldspar and other minerals reacting in formation with alkali could hinder the flow of the fluid; A large number of silicate ions in formation was the root cause of the silicon scale and there were many influence factors of the scale and near wellbore zone meeting the scaling condition lead to serious sand production; the new type of anti scaling agent, SY-401,also had good effect on controlling calcium and magnesium scale and silicon scale, feeding with no power is more suitable for general application. On the contrary, these conclusions will deepen and develop the ASP flooding to improve oil recovery theory and help to drive ASP flooding method to improve recovery efficiency in large-scale application processing.