HYDRODYNAMICS OF GAS-LIQUID FLOW IN THE TUBING OF ROD PUMP INSTALLATIONS

Abstract

During the operation of rod installations, pressure oscillations occur in the pump and compressor pipes due to the influence of hydrodynamic friction and inertia forces under conditions of uneven supply of the plunger pump during the pumping cycle. Pressure oscillations have a negative impact on the operation of pumping units: they lead to an increase in loads on pumping equipment components, the rate of fatigue wear of pumping rods, etc. Promising direction for improving the efficiency of rod installations is the development of methods and technologies for reducing pressure oscillations in pumping pipes. To smooth out pressure oscillations, pneumatic compensators are used. Pneumatic compensators are designed to equalize the speed of the liquid in the pipes. A mathematical model of the unsteady flow of gas-liquid flow in the pumping pipes of rod installations has been developed. By modeling the pumping of products with different rheological properties (differing in water content, viscosity, and compressibility), the features of pressure dynamics in the lower end of the tubing and in the flushing line at the wellhead are analyzed to assess the potential efficiency of placing wellhead (located in the flushing line at the mouth) and deep (located in the lower part of the tubing) pneumatic compensators. By modeling the pumping of high-viscosity oil it is shown that the maximum pressure at the wellhead and the lower end of the tubing is achieved in different half-cycles of the plunger (at the mouth of the upstroke, at the lower end of the tubing - at moving down) that is associated with the influence of relative movement of the rods and fluid on the formation pressure in the tubing. As a result, when pumping out high viscosity products, the wellhead pneumatic compensator reduces the component of the maximum load on the balancer head due to the hydrodynamic friction of the liquid when it moves in the collector, while the deep one reduces the load of hydrodynamic friction acting on the rod column and ensures free movement of the rods downwards. It is shown that when pumping low-viscosity oil with a high gas content, the amplitude of pressure oscillations is small and in the considered examples does not exceed 0.02 MPa. The influence of inertia forces that are crucial for pumping high-water oil is analyzed. Calculations show that the amplitude of pressure oscillations at the mouth is about 70 % of the amplitude of oscillations at the lower end of the tubing, which allows using wellhead pneumatic compensators to reduce the component of pressure pulsations in the tubing caused by the forces of inertia when the fluid moves in the reservoir.