Research On Optimization Technology Of Downhole Oil-Water Separation Production System With Screw Pump

The downhole oil-water separation is an efficient,environmental-friendly and energy-saving new technology.It can accomplish oil-water recovery,separation,oil lift and injection of the produced water in the same wellbore.At present,the technology is still in the period of devices research & development and trial extension in domestic.Early field trials and demonstration applications show that working parameters of production layer and injection layer,booster pump and downhole oil-water separator have important effects on system design.It causes system matching design more difficult.And it is difficult to effectively diagnose opertating conditions of downhole oil-water separator,booster pump,production layer and injection layer without increasing the system complexity.Aiming at these problems,for a new surface driving screw downhole oil-water separation system,the optimization design model of this system was built with the combination of the theoretical analysis,numerical simulation and laboratory simulation experiment and an approach of optimization design of this system was proposed.Meanwhile,an approach of operating condition diagnosis of this system was proposed.Firsly,the structure and working principle of a new surface driving screw pump downhole oil-water separation production system was introduced,and the module division and coordination relations of this system were analyzed.An approach of using large eddy simulation(LES)model and algebraic slip mixture(ASM)model for numerical calculation of downhole hydrocyclone was researched.Based on structural parameters of the downhole oil-water separator indentified in early research,the shape and structural parameters of the inlet flow channel were optimized by the numerical calculation approach.Plackett-Burman experimental design was used to select significant factors,and the steepst ascent method was used to design test and determined the center point of response experimental design,then the two order response model between significant factors and underflow oil concentration was built based on the respone surface approach.Finally,the optimal structural parameters were determined using particle swarm global algorithm.The reliability of this optimization method was verified by laboratory experiment.Secondly,the split characteristic and separation characteristic of the two-stage tandem downhole oil-water separator were researched by numerical simulation and laboratory simulation experiment.For the split characteristic,the results show that the overflow ratio decreases rapidly and then gently with the increase of the total split ratio.The relational expression of the first and second split ratios with total split ratio was derived.Based on a large number of experimental data,the relationship between the inlet flow rate,total split ratio and underflow oil concentration were analyzed respectively.And the mathematical model of the three was established to lay a necessary foundation for the establishments of optimization design model and operating condition diagnosis model of this system.For the separation characteristic,the numerical simulation results indicate that the underflow oil concentration becomes smaller gradually with the increase of the total split ratio and inlet flow rate respectively.While the experimental results show that the underflow oil concentration becomes smaller gradually with the increase of the inlet flow rate,then increasing rapidly when the inlet flow rate is greater than 40m3/d.And the underflow oil concentration decreases with the increase of the total split ratio,then begining to increase when the total split ratio is greater than 0.55.In addition,the effect on separation performance of the downhole oil-water separator of the two downhole hydrocyclone at the design conditions was analyzed through laboratory simulation experiment and numerical simulation.The results show that the first downhole hydrocyclone plays a major role in the separation performance and separates most of the oil,and the second plays a key role for further reducing the underflow oil concentration.Finally,the mathematical models were built through analyzing the working characteristic,hydraulics characteristic or stress of production layer module,single screw pump module,downhole oil-water separator module,wellbore pipe flow module,injection layer module and sucker rod module.Based on pressure,flow rate and water content coordination relationships of the overall system,an optimization design approach was proposed with the optimization objective of the oil concentration of injected liquid and downhole efficiency.Its reliability was verified by an example design.At the same time,the operating condition diagnosis method of the system was developed,and its validity was verified elementary by an example application.The influence of injection pressure,wellhead casing pressure and screw speed on operating condition were analyzed by this model.