Applications of viscous oil in a rod sucker pump system.

摘要

When producing a well for some amount of time, there always comes a moment when there is not enough natural energy in the reservoir for oil to rise to the surface. The pressure decreases significantly over time which will, in turn, decrease production. Artificial lift is a process used in production engineering on oil and gas wells that can solve these problems through a variety of pumps and lifts by reducing the bottomhole pressure and thereby increasing the production rate of the well. This stimulation is necessary for about 95% of all oil and gas wells, of which the majority being sucker-rod pumps; beam pumping is the most common artificial lift method used in the industry. There are many aspects of a sucker rod pump that must be designed very carefully to not only avoid failure, but to also ensure safety of the operators. The API-RP 11L procedure is a trial and error method based on correlations of research test data which, in summary, helps the designer to calculate the important parameters of a pumping unit. These include polished rod loads, torque, horsepower, etc. based on the preliminary selection of components through a series of steps. However, there is a limitation of the API-RP 11L procedure; it does not take into account the viscosity of the oil when predicting pump displacement and associated loads.;In this work, a computer simulator was developed according to the API-RP 11L procedure to predict the important output parameters of a pumping unit. Many of the operating characteristics used to calculate these output parameters are found in tables and figures, but in order to implement them into a program, these plots had to be digitized. The effect of heavy oil also was investigated by introducing an original equation for the frictional pressure losses gradient. This equation was used in order to predict the magnitude of increase of the peak polished rod load (PPRL), minimum polished rod load (MPRL) and peak torque (PT). Studies were also done to see the effect the length of the rod and viscosity has on the rod loads and torque, respectively. Efficiency was also incorporated in this study, as the effect of the inertial forces and dynamic fluid loads were seen when studying the relationship between both polished rod loads and polished rod horsepower and efficiency.;Based on the simulator results and sensitivity analysis, the API-RP 11L procedure is an effective tool to predict pump displacement, polished rod loads, torque requirements, and horsepower within certain bounds of some parameters of inviscid fluids. From the results of the simulator and the equation developed, it has been determined that heavy oil has a major effect on rod loads and torque on a sucker rod pumping unit. For example, oil with a viscosity of 6000 centipoise can add almost 3500 psi onto the polished rod loads that a sucker rod pump can handle and about 130000 in-lbf of torque. Viscosity effect comparisons between three of the most common pumping units: conventional, air balanced, and Mark II are also found in this work. The incorporation of efficiency and its relationship with the polished rod loads and polished rod horsepower (PRHP) is also quite a significant finding: with an increase in the efficiency, a decrease in the PPRL and PRHP are seen, while an increase in the MPRL is observed.