Microscale Occurence And Recovery Mechanism Of Remaining Oil In Sazhong Area At Extra-high Water Cut Stage Of Daqing Field

As China is a big crude oil consumption country, improving the proven geological reserves recovery is the eternal theme to achieve efficient development in the oil industry field. However, with the rapid development of national economy, domestic oil and gas resources are in short supply obviously. It has been already entered the extra-high water cut development stage after decades of exploration in Sazhong development zone of DaQing oil field. Although the remaining oil is highly scattered and the comprehensive water cut is as high as 95%, more than half of the remaining reserves in the ground has not been used effectively. Remaining oil is divided into macroscopic remaining oil and microscopic remaining oil. When the well network is under certain conditions, the formation of remaining oil have relationship with reservoir properties, structure characteristics, well-net control degree and displacement mode. Therefore through researches for determining remaining oil distribution and its formation mechanism, a clear understanding of the remaining oil distribution rule and starting condition in the extra-high water cut stage, scatter the distribution of microscopic remaining oil into the movable oil to be produced, constantly improve the oil recovery and achieve an effective development in the extra-high water cut stage, which has a very important practical significance and research value. By a lot of researches working home and abroad in microscope remaining oil's causes and effective producing mechanisms, based on the previous research results, this paper carries on a research and discussion mainly in fluid flow characteristics in micro-channel, fluid motion in water flooding process and microscope remaining oil's causes and effective producing mechanisms under the influence of micro forces.Based on results from fine geological research in SaZhong development area, this paper systematically carries out researches on the micro fluid dynamics mechanism in micro channels, and gets a clear understanding on the influence of Vander Waals and the interfacial tension and confirms that in the micro channel flow in small pores. From the micro interface mechanics, based on the fluid flow characteristics in porous media on the pore scale, focusing on the impact of micro forces on seepage in porous media, the micro tube flow mathematical model of the Newton fluid is established, and the fluid velocity distribution in micro tubes and the average flow model is derived, Oil capillary network mathematical model of water flooding is established. The influence that micro stress in porous wall on the role to the seepage is clear through the simulation analysis; combining with the characteristics of reservoir microscopic pore structure in Sazhong development area, reservoir water flooding three dimensional network dynamic model is established which can also consider the differences when the solid-liquid interface reaction of different types of water with the numerical simulation of variation regularity of micro remaining oil, in order to study the effect of pore structure of reservoir on the formation of microscopic remaining oil; through water flooding three-dimensional network simulation results, it reveals the influence laws on microscopic remaining oil distribution of pore throat radius, pore throat ratio, coordination number and wet ratio in different types of reservoirs. Research on micro remaining oil forming and producing mechanism of porous media, quantitative description on different types of micro residual oil in different reservoirs, understanding different types of remaining oil's causes, revealing the producing mechanism of remaining oil, improving and enriching the theory of microscopic remaining oil:all of above studies can provide theoretical guidance for the effective potential of remaining oil.Studies show that in the micro scale conditions, the effect of the Vander Waals between the molecules on fluid flow patterns in micro-channel can not be ignored. Considering the effect of liquid-solid interface, micro water phase flow rate was significantly lower than the Poiseuille flow; the microscopic distribution of remaining oil affected by the reservoir wettability, capillary pressure and reservoir physical characteristics enrich on the position where the pore throat ratio is bigger, the coordination is smaller, and the constant of the harmmock on the wall of the capillary is bigger; the main manifestations of microscopic remaining oil is in three forms:scattered, sheet and film, the scattered remaining oil mainly distributes in the formation where pore radius and pore throat radius are both relatively larger; the sheet remaining oil mainly exists in the smaller pore throat; the film remaining oil has a close relationship with rock pore throat wettability, the adhesion force of the oil wet rock to the oil getting increased so that it is easily to form oil film. Analysis from studies show that, by improving reservoir pore throat structure and adjusting the displacement direction and displacement system can different types of microscopic remaining oil start, and then enhance the oil recovery.