An Integrated Transport Model for Ball-Sealer Diversion in Vertical and Horizontal Wells

Abstract

Abstract Ball sealer diversion has been proven to be both an effective and economic way to selectively stimulate low permeability oil and gas reservoirs in hydraulic fracturing and matrix acidizing treatments. However, the design and implementation of a successful ball sealer diversion treatment is still a challenge. Often the designer depends on experience, and lacks the knowledge of accurate ball transport and sealing behaviors. An integrated model for selecting operating factors such as fluid and ball properties, as well as predicting the ball sealers transport and hydraulic behavior prior to pumping is needed for optimizing the stimulation process. In this paper, an integrated transport model is presented to describe the relationships among the ball sealer transportsealing behavior, wellbore deviation, wall effect, perforation density and size, fluid properties, pumping rate and ball properties. In addition, the smoothness of ball, perforation phasing, and velocity profile inside the wellbore during ball seating are also taken into consideration. Recommendations are provided for determining the number of ball sealers per job for either single or multiple stage treatment, the designed pumping rate, and the physical properties of the fluid and ball sealer. A hydraulic analysis model is presented for the overall fluid dynamics starting from surface, through wellbore, to reservoir. This analysis describes the effects of reservoir condition, pressure drop on perforations, and actual sealing efficiency on the surface treatment pressure profile. This paper will investigate the effects of the diversion factors on the ball transport behaviors such as transport time, ball sealer efficiency and surface pressure. Introduction One of the first ball sealer process was performed by the Western Company in 1956[1]. Since then, it has been widely applied in the selective well treatment and stimulation[2]. During this ball sealer process development, a significant improvement was reported by using near-neutral buoyancy balls instead of conventional ball sealers. It was reported that the buoyant ball sealer seating efficiency was increased to 100%[3,4]. Although there are several references that have studied the properties of this diversion process, the implementation of this technique in the industry is still relies on the field experience and rules of thumb. Modern techniques such as Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV) provide useful measurement tools to observe transport behaviors in the solid particle-fluid system. And advanced CFD simulators offer numerical analysis in the fluid dynamics. However, the mechanism of transport phenomena in the particle-fluid system is still not fully understood. Hydrodynamic forces and moments acting on particles enclosed by fluids depends on many factors, such as the local (undisturbed) flow field, fluid and particle inertia, external forces and particle shape. Non-Newtonian fluids and turbulent flow increase the degree of the problem's complexity. For thisdiverting process, these factors are fluid and ball properties, pumping rate, well geometry and perforation data. In order to understand this transport process, an integrated transport model was developed to describe the relationships among these factors and to develop a software product as a design and simulation toolfor guiding the implementation of the process.