Determination method of CO2 displacement minimum miscible pressure of low and ultra-low permeability reservoir

Abstract

The invention relates to a determination method of the CO2 displacement minimum miscible pressure of a low and ultra-low permeability reservoir. The method includes the steps of 1, selecting a physical model core; 2, conducting anti-corrosion treatment on the physical model core; 3, applying confining pressure to the physical model core and conducting vacuumizing; 4, measuring the pore volume of the physical model core and calculating the porosity of the physical model core; 5, heating the physical model core to a target formation temperature and measuring the permeability to water; 6, simulating the oil saturation process, recording the volume of saturated simulated oil and calculating the initial oil saturation; 7, simulating CO2 displacement, recording the displacement pressure and the outlet end liquid and gas volumes and calculating the CO2 displacement recovery rate; 8, replacing the physical model core with another physical model core with the same permeability and repeating the steps 1-7 to obtain CO2 displacement recovery rates under different displacement pressures and return pressures; 9, drawing a relation curve of the CO2 displacement recovery rates and the return pressures, wherein the return pressure corresponding to the recovery rate inflection point on the relation curve is the CO2 displacement minimum miscible pressure of the low and ultra-low permeability reservoir.

Description

technical field [0001] The invention belongs to low permeability reservoir CO 2 In the field of flooding development technology, especially a kind of low and ultra-low permeability reservoir CO 2 The determination method of minimum miscibility pressure. Background technique [0002] Many scholars at home and abroad have shown that among many methods of enhancing oil recovery, CO 2 Miscible flooding plays an important role. In the United States, Canada and other regions, CO 2 Miscible flooding has achieved great success in enhancing oil recovery. And with my country's CO 2 The continuous discovery of gas sources and the CO 2 The maturity of the capture technology, in my country's CO 2 Miscible flooding technology will also become a cost-effective enhanced oil recovery technology. CO 2 The miscibility of is a dynamic multi-stage contact miscible process, that is, relying on the injected CO in the flow process 2 Mass transfer of the components caused by repeated contac...

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Problems solved by technology

[0004] 1. There are different degrees of cementation in actual reservoirs, and the particle size is not evenly distributed, so the narrow tube model cannot simulate the real oil layer conditions. In fact, the pore throat size of the thin tube model is usually the same as that of the real reservoir. There is an order of magnitude gap, which leads to the fact that the minimum miscible pressure determined by the thin tube model cannot truly reflect the CO2 under reservoir conditions. 2 Miscibility with crude oil;

[0005] 2. (Extra) low permeability reservoirs have poor permeability, and the reservoir permeability is usually less than 100×10 -3 μm 2 , and the quartz sand or glass beads required to fill the thin tube model are usually large in particle size, and the permeability of the filled thin tube model is usually above thousands of millidarcy, which cannot simulate low-permeability reservoirs at all;

[0006] 3. Serious viscous fingering and reservoir heterogeneity often exist in actual reservoirs, especially (extra) low-permeability reservoirs. However, in the thin tube model, uniform quartz sand or glass beads are filled, which excludes Due to the influence of factors such as mobility ratio, viscous fingering, gravity separation, and reservoir heterogeneity, the minimum miscible pressure determined by the thin tube model cannot truly reflect the miscible pressure under reservoir conditions;

[0007] 4. From the perspective of experimental operation, multiple sets of repeated displacement experiments are required to determine the minimum miscible pressure. In the process of narrow tube experiment operation, the thin tube model is often reused, so at the beginning of each displacement experiment Sometimes it needs to be cleaned with reagents such as toluene and petroleum ether. Not only is the operation cumbersome, but if the above reagents are not completely removed, their residues will affect subsequent experiments, resulting in the inability to accurately measure the minimum miscible pressure.

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