Improved Design of Rod Pump Valves For Thermal And Horizontal Wells-Laboratory And Field Results

Abstract

Abstract This paper presents results from a multi-participant project conducted by AOSTRA, ARC and industry to improve rod pumping efficiency for thermal and non-thermal oil fields in Alberta. It describes experimental and theoretical investigations on the hydrodynamics of rod pump valves that resulted in improved valve design and increased field production rates; and shows that, two of the most frequent problems encountered in the field are associated with sand and gas/steam inflow and may be alleviated through a better design of pump valves. These problems were examined in the laboratory (ARC) by testing ball-valve hydrodynamics at different GOR and inclination angles. Nineteen different valve designs were investigated using two laboratory facilities. Visual observations regarding critical GOR and inclination angles and quantitative measurements of pressure drop at different pump rates and fluid viscosity were obtained. A diagram, in which measured drag coefficient was plotted versus Reynolds number, was used to capture the steady and unsteady behaviours of the cage-ball systems. This diagram provided a basis for improving valve design. Following discussions of the laboratory findings with the project participants (field operators and manufacturers), and at the instigation of one particular manufacturer, a new valve design (HIVAC) was completed, manufactured and field tested at numerous sites. The field test results showed a significant increase in flow compared to conventional API valves previously used at the same sites. Introduction The design and operation of sucker rod operated bottom hole oil pumps, used in 80 – 90% of artificial lift wells, reached a mature stage during the period 1970 – 1980(1).Improved diagnostic tools for evaluating their performance appeared during the 1980s. These tools included automated dynamometer cards that aided rapid and relatively inexpensive de-convolution and interpretation of load-stroke diagrams(2,3). During the last decade, the development of heavy oil reservoirs in Alberta, Saskatchewan, and Venezuela and the widespread use of horizontal and deviated wells for both conventional and heavy oil reservoirs has imposed additional constraints on sucker rod pump applications. In Alberta, thermal projects have always experienced difficulties with pumping operations. In 1988, a survey conducted by the Alberta Department of Energy-Oil Sands and Research Division (formerly AOSTRA) found that the most common problems encountered were pump seizure (customarily related to sand-laden fluids), and pump inefficiencies due to steam and non-condensible gases(4). A multi-disciplinary team consisting of ADOE-OSRD, ARC, eight major field operators and four rod pump manufacturers in Alberta was formed to address those problems. Although the major objective was to improve existing thermal pumping technology, more general applications to horizontal well and high gas/oil ratio situations were put at a high priority. An overview of the program and its major laboratory achievements during 1988 – 1991 has been discussed elsewhere(4). This paper describes further laboratory observations on valve hydrodynamics with conventional and slanted wells obtained during 1991 – 1992, as well as significant field results achieved using a novel valve design. Equation 1 (available in full paper)