Study On Optimal Design And Technical Policy For CO₂ Huff & Puff In Tight Oil Reservoir

It is a key problem which is urgent in petroleum industry about developing the tight oil reservoir in our country economically and effectively. The technology of CO₂ huff-n-puff after hydraulic fracturing horizontal wells is one of the best effective methods for developing tight oil reservoir.The geological characteristics and reservoir fluid property in tight oil reservoir of A wellblock in J oilfield was studied. We did the laboratory analysis of the formation fluid, including single degassing test, constant composition expansion experiment, differential liberation experiment, viscosity test, and tubule experiment. According to the data obtained in the study area, a conceptual model was built, and a 3-dimensional 3-phases compositional model was used to simulate the exploitation of a horizontal well using CO₂ huff-n-puff in A wellblock. An optimization design of reservoir engineering parameters and the economic evaluation was made.Detailed flow parameters are got, and the minimum miscible pressure in the reservoir of CO₂ is 19.1 MPa, so it is an immiscible flooding. The optimization design of reservoir engineering parameters（CO₂ injection rate, injection time, soaking time, number of cycle, and the type of bottom hole flowing pressure for constant pressure production） is made: CO₂ injection rates as 20000 m3/d, injection time for 3 months, soaking time for 3 months, the bottom hole flowing pressure for constant pressure production as 5 MPa, for two cycles in the process. Among them, the orthogonal experiment design is used for CO₂ injection rate, injection time, soaking time, etc. The recovery influence of these factors is sorted out. The influence of CO₂ injection rate is bigger than other factors, which implies injection rate is a key factor. Finally, the incremental oil recovery factor at 30 years of production is obtained as 5.5% comparing with depletion production, which proves that CO₂ huff-n-puff stimulation development scheme is feasible.In the end, we study the feasibility of CO₂ huff-n-puff stimulation from the perspective of economic evaluation. Its cumulative net cash flow, internal rate of return, the dynamic payback period in 30 years of production is better than depletion production. And internal rate of return under the oil price of $30/barrel could still reach 9.73%, showing a strong profitability, proving that the horizontal well with CO₂ huff-n-puff stimulation in tight oil reservoir is feasible.