Practical Hydraulics of Positive Displacement Pumps for High-Pressure Waterflood Installations

Abstract

Pressure surges, cavitation, and mechanical vibration prevent water Pressure surges, cavitation, and mechanical vibration prevent water injection systems from operating at maximum efficiency. They cause premature failure of the equipment and excessive operating cost. By using premature failure of the equipment and excessive operating cost. By using the engineering principles outlined here, detrimental effects due to inadequate net positive suction head and poor pipe streamlining can be minimized. Introduction As the demand for oil continues its dynamic climb upward, waterflooding will be an increasingly important factor in this country's energy picture. In 1970, waterflooding accounted for 1 of every 4 bbl of oil produced in the U. S. This number will increase to 1 of every 3 bbl by 1980. To meet this demand, many waterfloods are being installed in fields that were considered nonfloodable just a few years ago because of high fluid injection pressures required. Good engineering is imperative in pressures required. Good engineering is imperative in the design of high-pressure installations and will pay for itself many times over in reduced maintenance costs. The purpose of this paper is to present a summary of the technology used in the hydraulic design of positive displacement pump systems for high-pressure waterflood service. Of the three flow regions in a positive displacement high-pressure waterflood systemthe suction, the pump, and the dischargethe pump is the consistent pump, and the dischargethe pump is the consistent element. The manufacturers spend a great deal of time and money on the hydraulics and mechanics and their pumps. To increase volumetric efficiency, the effects of path tortuosity, entrance and exit losses, and fluid compressibility in the design of pump fluid ends are minimized. The elementary principles of fluid mechanics used for the design and analysis of fluid ends can also be used for the inlet and outlet systems. Poor design of suction and discharge piping results in increased pump repair and decreased life of equipment due to overstressing of components by cavitation, excessive pulsation and mechanical vibration. In the design of new systems good sense must be used to avoid these pitfalls and insure the best possible hydraulic and mechanical operating conditions. Positive Displacement Pumps Positive Displacement Pumps The positive displacement pump is the most widely used pump for high-pressure water injection. (In this paper, 2,500 psi and above is considered high pressure.) paper, 2,500 psi and above is considered high pressure.) It is better adapted to high-pressure service than the centrifugal pump because of its high uniform efficiency. (For typical plunger pumps used in oilfield service, the volumetric efficiency is 95 percent and the mechanical efficiency is 90 percent.)A plunger pump, which is the positive displacement pump used in waterflooding, is relatively simple. Fig. pump used in waterflooding, is relatively simple. Fig. 1 shows a cross-section of a typical plunger pump. The fluid is pumped by use of a plunger and a series of valves. The plunger delivers a specific amount of fluid into the discharge line during the discharge stroke. In this part of the operation, the discharge valve is open and the suction valve is closed. During the charge stroke, the specific amount of fluid is taken from the suction line and the valve action is reversed. It is this action of the pump that causes pressure surges. These pressure surges are natural for all positive displacement pumps and if the system is properly positive displacement pumps and if the system is properly designed, should not be troublesome. JPT P. 173