Fundamentals of Oilwell Jet Pumping (includes associated papers 17106 and 17113 )

Abstract

Summary This paper explains the theory behind the operation of jet pumps, includingthe effect of density differences between power fluid and produced fluids. Bydifferentiating between the pump intake pressure and the throat-entrancepressure, we provide insight into the factors that affect jet pump performance.A stepwise procedure is given for sizing and selecting a jet pump. Introduction Jet pumping can be an attractive method of artificial lift in oil wells. Thepump is simple because it has no moving parts. In addition, during installationof a free pump, it can be pumped into and out of the well with the hydraulicpower-fluid system. Jet pumping was first described by Gosline and O'Brien, 1 wasintroduced in the oil industry in 1970, 2,3 and has gradually gainedacceptance. Several publications have appeared recently that describe theperformance of jet pumps and present equations for selecting a pump andauxiliary equipment.4–6 This paper reviews the fundamentals of jet pumping and presents equationsfor an optimum selection of pump and equipment. Jet pump Fig. 1 shows a simplified drawing of the component parts of a jet pump. Power fluid with pressure pn and at rate qnis pumped through a nozzle with flow area An. This produces ahigh-velocity jet with pressure pe and flow areaAn at the throat entrance. Well fluids with pressurepp and at rate qf are accelerated into thethroat suction area, Ae, and mix in the throat with the powerfluid to form a homogeneous mixture that leaves the throat with pressurept. In the diffuser, the mixture is slowed and the pressurebuilds up to the pump discharge pressure, pd, which issufficiently high to move the mixture to the surface. The dimensionless nozzle-to-throat-area ratio of a jet pump is defined asAn/A t=FAD consequentlyAe/At= 1-FAD andAe/A n=(1-FAD)/FAD. The principle of jet pumping is simple and depends on Bernoulli's law, whichmay be written asEquation The term ?g(h2- h1) and the velocity term associated with the high pressure may be neglected, whichresults inEquation (1) In the analysis of jet pumping, two dimensionless parameters are defined: the dimensionless mass flow ratio,Equation (2) and the dimensionless pressure recovery ratio,Equation (3) Expression for Pressure Losses As Fig. 2 shows, the dimensionless pressure recovery ratioFpD, can be divided into the following components:Equation (4) When Eq. 1 is applied to, the diffuser,Equation The losses result mainly from friction and can be written as soEquation (5) Applying Eq. 1 to the thoat suction area yieldsEquation (6) With a property rounded throat entrance, the suction-loss coefficient,Ksl, is zero. Applying Eq. 1 to the nozzle, we obtainEquation There are two types of pressure loss associated with the jet stream.Friction losses in the nozzle. These may be written, in the form Kn[].Pressure losses of the jet after the jet steam leaves the nozzle. Cunningham7has shown that the pressure drop (pp-pc) of the jet, whentraveling the distance from the nozzle tip to the throat entrance, L, must be regarded as a fluid frictional energyloss.