Text Oilfield Gas Injection For Enhanced Oil Recovery Feasibility Study

Recently the oilfields discovered and not brought into development in our nation are mainly low-permeability oilfields, which account for about 50%-60% of the discovered reserves and of which the extreme low-permeability reservoirs occupy 60%-70%. The low-permeability reservoirs are difficult to be developed by water injection due to the poor physical properties and high injection pressure; therefore, how to develop this kind of reservoirs presents a worldwide problem. This paper, through the feasible research of EOR by gas injection in Wennan low-permeability, high-temperature and high-pressure volatile reservoir, provides a new approach for the development of Wennan oilfield.Both in home and abroad, a series of laboratory studies and spot precursor trials about EOR in low-permeability reservoirs by gas injection have been performed, and achieved some successful experience. But there were no report of laboratory study and spot precursor trial about EOR in low-permeability, high-temperature and high-pressure volatile reservoir found. Based on the detailed dissertation of mechanism of gas injection flooding, we carried out the works of theory study of gas injection miscible flooding and immiscible flooding as well as laboratory experiment evaluation and spot gas injection trial. Consequently formed the research method of EOR by gas injection in low-permeability, high-temperature and high-pressure volatile reservoir and corresponding gas injection process and technics. Thereby provide the technology guarantee for EOR by gas injection in Wennan oilfield. The feasible research works are as follows:1. Roundly analyzed the structure system, applicability and precision of the cubic EOS which is now widely used by petroleum industry, choosed the EOS which is applicable to phase equilibrium calculation of gas-liquid two phase. Established the phase behavior simulation and calculation model for gas injection miscible and immiscible flooding, and embedded analyzed the mechanism of miscible and immiscible flooding;2. Carried out water flooding, immiscible gas flooding and immiscible WAG long core displacement test, evaluated the influence of different injection medium and WAG on EOR. At the time, evaluated the maximum injection pressure differential of water injection, gas injection and WAG, testified that low-permeability reservoirs can not be processed by WAG injection;3. Obtained the minimum miscible pressure according to slim-tube test. Designed the enriched gas drive slim-tube test, fixed the content of intermediate hydrocarbon that could make natural gas and formation crude oil miscible, performed the long core displacement test of miscible flooding, evaluated the crude oil recovery of long core displacement under thecondition of miscible;4. Completed the liquid phase behavior matching and analysis, established the three-dimensional geological model, and also completed the production history matching ofthe choosed precursor trial area. On this basis, simulated and studied the development effect of natural gas injection or different enrichment natural gas drive using three-dimensional and three-phase polycomponent model in Wennan oilfield;5. Analyzed the mechanism of organic solid deposition during gas flooding, and assisting with the results of experiment study, studied and analyzed the solid deposition might exist in the process of gas injection in Wennan oilfield.6. Based on nitrogen injection test and the researching of gas booster equipment home and abroad, analyzed whether the present natural gas compressors > gas injection wellhead > down-hole strings and packers etc, could all satisfy the requirements of gas injection in Wennan oilfield;7. Performed economy evaluation for the precursor trial area using cash flux method.The studies ahead indicated that the oil recovery of Wennan low-permeability ^ high-temperature and high-pressure volatile reservoir can be remarkably improved by natural gas injection. The economy evaluation and the research of gas booster equipment home and abroad also indicated that there will be a good economy benefit on natural gas injection in Wennan oilfield and all the present natural gas compressors > gas injection wellhead > down-hole strings and packers etc, could satisfy the requirements of gas injection in Wennan oilfield. The research in this paper has been established significant item by SinoPec. Especially, the study of enhanced oil recovery by natural gas injection in Wennan oilfield with low-permeability > high-pressure and high- temperature has been published in SPE.(SPE77799)...