ABSTRACT

Existing state-of-the-art diagnostic models neglect fluid inertia. Sometimes fluid inertia distorts the shape of the pump card. This is important because the shape of the pump card is used to diagnose the operating condition of the sucker rod pump, and to effectively monitor and maintain rod pumped wells. This paper presents guidelines for predicting when fluid inertia is likely to cause pump card distortion. This paper then discusses the equations, boundary conditions, and solution method for calculating fluid inertia forces and removing them from a calculated pump card.

BACKGROUND

Gibbs and Neely developed the first commonly used diagnostic model to generate pump cards from surface cards1,2. (For subsequent information see: Eickmeier3, Price4, Nolan and Gibbs5, Kramer, Martin, and Neely6, Chacin7, Everitt8, Bastian9, and Bastian, Keating and Jennings10.) Doty and Schmidt used fluid inertia for sucker-rod design, but not for diagnosis11, Svinos12 measured significant fluid inertia at the pump, and Laine, Keating, and Jennings13 showed that maximum dynamic forces on the pump due to fluid acceleration can be as much as twice the hydrostatic fluid load.

PROBLEM STATEMENT

To predict when fluid inertia distorts pump cards enough to interfere with sucker rod diagnosis.

To explain how to calculate and compensate for fluid inertia forces at the pump.

METHODOLOGY
Table Development

We use diagnostic and predictive models (developed at A & M Univ.) to run a substantial range of cases. Analysis of these results provides information in the form of tables that can be used to predict when fluid inertia is likely to distort the shape of a pump card.

The case parameters and their ranges are: depth 2,000 to 4,000 feet, pump size 1.0625 to 2.73 inches, stroke per minute (SPM) 5 to 30, and barrels fluid per day (bfpd) 100 to 300.

Table Development

We use diagnostic and predictive models (developed at A & M Univ.) to run a substantial range of cases. Analysis of these results provides information in the form of tables that can be used to predict when fluid inertia is likely to distort the shape of a pump card.

The case parameters and their ranges are: depth 2,000 to 4,000 feet, pump size 1.0625 to 2.73 inches, stroke per minute (SPM) 5 to 30, and barrels fluid per day (bfpd) 100 to 300.

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