Pressure Prediction Of Nitrogen - Water System In Tahe Oilfield

After water flood development of Tahe Oilfield, in the specific fracture-cavity units gathered huge amount of attic oil, which is difficult to be swept by water. In reaction to the phenomenon, nitrogen injection technology is used to improve oil recovery in this oilfield. But, it found that, because of the different reservoir space, fractured-vuggy development and connectivity, the difference of bottom pressure curves and injection volume between each well is obvious. There is no theoretical reference for the designing of injection volume, pressure, and closed time. Therefore, it is imperative to establish a series of pressure prediction model for nitrogen-water injection well of fractured-vuggy reservoir. The flow behavior of fluid in well and reservoir is different. So this paper divides single well injection system into two parts:they are wellbore system and reservoir system, and establishes the pressure prediction models of each system for nitrogen-water injection. For the wellbore system, the drift flux model is been improved for vertical well of injection. The interface effect of two phase fluid is taken into full consideration, thus the drift flux model is applicable to situations with various injection gas-water ratio. For the reservoir system, the physical model of injection well is been developed based on the reservoir characteristics and the performance of Tahe Oilfield. Then on the basis of material balance theory, the relation expression of the pressure in cave and the injection volume is been proposed. By the law of conservation of mass and deliverability equation, the bottom-cave pressure models for periods of injection and closed are been established for nitrogen injection and nitrogen-water injection respectively. The models are simplified by dimensionless treatment. Then it analyses the reservoir structure and the flow conductivity of the reservoir, which are influencing the bottom pressure. In order to verify the validity and practicability, several application cases for wellbore pressure mathematical model and bottom-cave pressure prediction model are presented in the end of this paper. The establishment of pressure model for Tahe Oilfield of nitrogen and water injection provide the theoretical basis of parameter optimization.