Research And Application On Non-darcy Flow Theorical Model Of Co₂ Flooding

There are rich resources of low permeability oilfields in China, whose recovery can only reach 20% commonly limited by the current technical conditions. In order to improve oil recovery and production of the low permeability oilfield, new displacement agents and methods should be urgently investigated. Domestic and foreign research results indicate that CO2 flooding can greatly improve oil recovery, and has no pollution favorable to environment protection, so using CO2 flooding to develop the low permeability oilfield has wide prospect.In order to accurately predict the variations in dynamic indexes of different CO2 injection schemes and determine the optimal scheme, numerical simulation research should be conducted. But the existing commercial CO2 flooding numerical simulation software was developed based on the Darcy flow without considering the influence of actuating pressure gradient, which could not fully reflect the whole CO2 displacement process of low permeability reservoirs, and therefore it is necessary to establish a CO2 flooding numerical simulation model considering non-Darcy flow pattern.This paper firstly conducted CO2 flooding lab experiments to measure minimal miscibility pressure and actuating pressure gradient, and then on the basis of the studies on CO2 flooding mechanisms, the non-Darcy flow pattern of low permeability reservoirs and the existing component model, a three-dimensional three-phase multi-composition percolation mathematical model suitable for CO2 flooding of the low permeability reservoirs has been established, which considered the actuating pressure gradient of oil, gas and water. After that, numerical solution was brought out by finite-difference method and IMPES method, and a set of CO2 flooding numerical simulation software suitable for low permeability reservoirs was then developed. Finally correctness and applicability of the model and developed software both were verified by core experiment.According to geological features and present development situation of Shu101 block and Shu16 blcok, facies-controlled geological models of the two blcoks were established by Petrel geological modeling software. And then using the self-developed numarical simulation software, this paper conducted numerical simulation research on CO2 flooding of Shu101 block and CO2 huff and puff of Shu 16 block.The results of numerical simulation research on CO2 flooding of Shu101 block showed that linear gas injection mode between the two designed well pattern adjustment schemes. Combained with the economic benefit evaluation results, water alternating gas injection mode among the three CO2 injection modes of continuous gas injection, single slug injection and water alternating gas injection has been confirmed to be the best, whose optimum parameters were that 0.3PV of CO2 injection quantity,0.03PV of slug size,1-1 of gas-water ratio,200m3 of liquid CO2 injection rate (i.e.0.050PV of liquid CO2 annual injection rate), and 0.12PV of subsequent water annual injection rate. The recovery degree of this scheme could reach 25.15 percent in 20 years, which could increase 6.15 percent than the foundation scheme.The results of numerical simulation research on CO2 huff and puff of Shu 16 block showed that taking oil-draining rate and oil increment as evaluation indexes, the optimum huff and puff parameters of well 11Y67-611 were that80 m3/d of injection rate,100 m3 of cycle injection volume,30 days of soak time and two cycle of puff and huff, while the oil increment and the oil-draining rate were separately 101.31 m3 and 1.01 m3-m-3. The optimum huff and puff parameters of well 11Y69-56 were that 60 m3/d of injection rate,135 m3 of cycle injection volume,30 days of soak time and three cycle of puff and huff, while the oil increment and the oil-draining rate were separately 154.38 m3 and 1.14 m3·m-3.The above reaserch results showed that the numerical simulaton technique based on the non-Darcy flow theorical model of CO2 flooding could simulate CO2 displacement process in Yushulin oilfield accurately and was suitable for designing the development scheme of Yushulin oilfield, which has important guiding significance for other same type oilfields to improve oil recovery by CO2 flooding.