On the evaluation of Fast-SAGD process in naturally fractured heavy oil reservoir

摘要

Very recently, Fast-SAGD as a modification of steam assisted gravity drainage (SAGD) has been much attended due to lower cumulative steam oil ratio as well as higher cumulative oil production. However, there are still many suspicions about the successful application of this method in naturally fractured reservoirs (NFR) in which faults, fissures, vugs, micro-fractures, poorly interconnected matrix pore structure as well as undesirable wettability are combined with high-viscosity oil. In this communication, initially, Fast-SAGD has been compared with traditional SAGD in an Iranian naturally fractured heavy oil reservoir with oil wet rock using CMG-STARS thermal simulator. Moreover, the effects of operational parameters on Fast-SAGD method have been investigated. In addition, a novel economical model has been established in which all economical parameters including input cash flow costs such as the rate of oil production and oil price, and the output cash flow costs such as capital expenditures (CAPEX), operating expenditures (OPEX), injection material and pipe line tariffs, have been considered. During the optimization of the operational parameters, it was observed that by increasing steam injection rate into both offset and SAGD wells in Fast-SAGD system, ultimate recovery factor (RF) increased, but ultimate net present value (NPV) increased up to an optimal point which could be due to the increased SOR value. By increasing steam injection pressure into offset well, both the ultimate RF and NPV increased up to an optimal point. To optimally select parameters such as the number of cyclic steam stimulation (CSS) cycles, elevation of CSS well and well spacing of SAGD well pair, sensitivity analysis should be performed to achieve the best case economically and technically due to the lack of a decrease or increase trend. In contrast to conventional reservoirs, the performance affected by start-up time at the offset well during Fast-SAGD process in fractured reservoirs indicates that earlier start-up time of steam injection leads to high RF and NPV.