A novel framework for acoustic diagnostic of artificial lift system for oil-production

Abstract

Oil extraction on many reservoirs requires the use of rod pump systems to pump the fluid to the surface. A longstanding challenging issue in the operation of rod-pump system is the ability to determine the downhole pump conditions based on the knowledge of a finite set of measurables at the top. A novel acoustic-based diagnostic method is put forward as an enabler for determining the downhole conditions. It consists of reconstructing the pressure signal generated by the pump from an acoustic measurement made at the top. Knowing that the operating pump radiates pressure waves in the fluid, the pump operation can thus be monitored. The physical basis of this acoustic method is demonstrated using results from a model of the rod-pump system complemented by field data measured from representative operating oil wells. The rod pump model has shown to be in good accord with available data. The unique feature differentiating the model formulation from the state of art is that each of the model attributes is linked to the physical process that set the pump operation. The wave equations in the rod string and in the tubing are solved using a custom numerical scheme, and the coupling between the rod and the fluid surrounding it is taken into account. The field measurements and the model results are in accord as they prove the hypothesis that a surface measured pressure can be used to determine the downhole condition of the well. Likewise both the field measurements and the model results provide the physical basis for formulating the scaling rule for generic rod pump system which is used in turn to design a scaled down experimental setup. Specifically, the effect of gas on the pump acoustic signature has been characterized and this general scaling allow one to compare different wells to one another and to obtain a universal scaling parameter to measure the amount of gas in wells pumps. The anticipated technological impact on oil production infrastructure is an acoustic diagnostic framework for assessing a broad class of wells operation, from vertical to horizontal oil wells.