K.B. Nolen & S.G. Gibbs, Nabla Corporation
As often discovered, determining downhole pump conditions by visual interpretation of a surface dynagraph card can be very difficult even for highly trained personnel. In addition, visual surface interpretations are more qualitative than quantitative. With the computerized method, surface measurements (load and displacement versus time) are used to calculate a downhole dynagraph card that is quantitative and much more easily interpreted. Basically, the computer program takes surface rod loads and displacements and removes rod weight, dynamic effects (harmonics) and rod stretch. The result is a pump card. Intermediate downhole cards are also calculated at critical stress points in the rod string such as at the junction points in a tapered rod design. Thus, rod taper designs can be easily evaluated. Besides calculating downhole conditions, measured data are also used to analyze surface equipment loading such as gearbox torque, prime mover loading and structural loading. All calculations can be made in a matter of minutes on the well site. Thus, conclusions can be drawn and changes can be initiated immediately for increasing production and/or reducing operating costs.