| The oil and gas reserves in carbonate condensate gas reservoir with fracture and cave, which has high condensate content, play an important role in present oil&gas reserves. The charicteristics in development process of this kind of condensate reservoirs is one of the most concerned problems for every worldwide oil company. However, the study about carbonate condensate reservoir with fracture and caveis is little since for the phase transition’s complexity of condensate gas during development process in the formation. In this paper, it will study how to improve the condensatre recovery and develop a proper material balance equation for carbonate condensate reservoir with fracture and cave, based on the Tarim project —study on EOR methods for Tazong I gas reservoirs with high condensate content. The study is important to develop the condensate reservoirs with fracture and cave.In this paper, the physical simulation is combined with the theory study to determine the proper exploitation mode for carbonate condensate reservoirs with fracture and cave. Based on the previous work of others, the full-diameter rock was selected from outcrop carbonate rocks and the fracture and cave in the full-diamter rock was developed by particular artificial technique of creating fracture and cave. After the rock was prepared to test,21 tests were designed according to the direction of cores placement (horizontal and vertical), scale of aquifer, time of injecting water or gas and whether the cave filled with sand. The 21 tests include 9 tests for depletion,3 tests for gas injection,2 tests for gas injection swallowing spitting plug removal and 7tests for water injection. Then, the material balance equation was established for the carbonate condensate reservoirs with fracture and cave; and the recovery of oil and gas was calculated by the derivated material balance equation. Besides, the physical tests results were also simulated by numerical simulation, which had simplified the actual core and established the proper geologic model for the full-diameter core. According to the study, the innovative conclusions are as follows:(1) while the fracture and cave are connected in vertical direction, the recovery of condensate oil is high due to the gravity effect, the bigger the aquifer is, the higher the condenate oil recovery is, the velocity of depletion has little influence on condensate oil recovery. While the fracture and cave is connected in horizontal direction, the recovery of condensate oil is high through water injection and gas injection over dew-point pressure. The high condensate oil recovery could also be obtained by water injection swallowing spitting plug removal while the fracture and cave are connected in vertical direction. The cave is filled could effect the development efficiencyto a certain degree.(2) the material balance equation is established based on material balance principle, which has taken the water invasion, gas injection, phase transition of condensate gas in formation. According the material balance equation, the recovery of oil and gas can be calculated. The calculation results are fit with the results of physical test results, which preserves the material balance equation is correct. The new equation could also distinguish the reserve in matrix with it in fracture and cave.(3)the physical results are well fitted by numerical simulation, which has simplified the full-diameter core with frature and cave used the physical tests and established a proper geologic model, meanwhile, according to comparing the oil and gas recovery obtained by physical tests and numetical simulation, the proper development mode for carbonate condensate reservoirs with fracture and cave are found and the development mode for high condensate content reservoir with fracture and cave has some difference according to the direction of fracture and cave connection. When the fracture and cave is connected in horizontal dirction, the water injection to keep pressure should be chosen preferentially; while it is conneted in vertical direction, the water injection swallowing spitting plug removal should be chosen preferentially.The conclusion has been applied in Tazong I gas reservoirs with high condensate content successfully and the actural development is well. |
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