TECHNICAL-ECONOMIC EVALUATION OF CONTINUOUS CO2 REINJECTION, CONTINUOUS WATER INJECTION AND WATER ALTERNATING GAS (WAG) INJECTION IN RESERVOIRS CONTAINING CO2
Bruno C. Schaefer1; Marcella H. Reis2; Michele F. Lazzari Schaefer3; Paulo Celso Muratore Zuliani4; Marcio Augusto Sampaio Pinto5
1 PETROBRAS - Petróleo Brasileiro S.A.; 2 Universidade Católica de Santos (UNISANTOS); 3 Universidade Católica de Santos (UNISANTOS) e Universidade Federal de São Paulo (UNIFESP); 4 Schlumberger Serviços de Petróleo S.A.; 5 Universidade de São Paulo (USP)
doi:10.20906/CPS/CILAMCE2017-1086
Resumo
Oil reservoirs that contain high carbon dioxide (CO2) concentrations associated with produced gas, along with an elevated GOR (gas-oil ratio) in the reservoir fluid, are excellent candidates for implementing CO2 injection techniques as secondary recovery method. It allows the recovery of residual oil combined with environmental benefits by reinjecting in its own reservoir a fluid that could be a contaminant if discarded. The approach of water alternating gas (WAG) injection appears as an interesting solution to keep the well productivity, while bypassing the usual problems of single fluid injection. This study evaluates the efficiency of the WAG technique compared with continuous fluid injection of water or gas. The proposed reservoir model consists of a rectangular box geometry with a quarter of a five-spot configuration with two wells - one injector and one producer, diagonally opposite from each other. Simulations were made to compare the total volume of oil recovered in four different secondary recovery injection scenarios: 1) continuous water injection, 2) continuous gas injection, 3) WAG injection with cycles of 2 years and 4) WAG injection with cycles of 4 years. For each scenario, the reservoir would produce for two years, and then would start its secondary recovery stage. The parameters analyzed were the gas injection rate and the water injection rate, in order to evaluate how they would affect the production rate. Both parameters were optimized using DECE method, available in the CMG suite, to reach the maximum net present value (NPV) in each case. The reservoir model was built with similar fluid characteristics of the pre-salt in the Santos basin - a light oil with CO2 concentrations of up to 30%. The results show that the use of WAG injection as an EOR method improved the total volume of oil recovered significantly, improving its respective NPV in approximately 30%, when compared to the scenario of continuous water injection. One can also observe that the EOR techniques helped prevent the increase
Palavras-chave: Enhanced oil recovery; WAG; NPV; CO2; EOR