Near-Wellbore Model To Analyze Particulate Diversion in Carbonate Acidizing

Abstract

In this paper we present an integrated analysis method for understanding and quantifying the effect of particle-jamming near the entrance of a perforation/wormhole tunnel. Advanced wellbore-scale, 3D numerical studies with coupled computational fluid dynamics (CFD), and a discrete-element model (DEM) were performed to study the different mechanisms involved in particulate diversion. The results of the wellbore-scale simulation were translated into an engineering-particulate-diversion model on the basis of the diversion mechanisms from the simulation. The model was then incorporated into an integrated carbonate-acidizing simulator.

Particulate diversion is not generally used in carbonate acidizing because of the formation of wormholes and the potential difficulty in removing particles from the induced perforation/wormhole tunnels. This new degradable particulate system addresses the issue and presents an efficient approach for diverting acid in carbonate stimulation. Detailed physics-based simulations demonstrated that the induced perforations/wormholes would plug through two distinct mechanisms and either temporarily seal the entrance of small-scale perforations/wormholes with a combination of small and large particles, or bridge large particles along tapered paths of perforations/ wormholes and form a temporary filter cake deeper within the opening. Either of these diversion mechanisms would decrease the injectivity locally and promote fluid diversion from inside the well into other normally understimulated locations. These procedures were translated into engineering equations, thus providing the modeling capabilities.

An integrated simulator was used to optimize the acid stimulation of a vertical wellbore and explain the impact of operational parameters and subsurface conditions on the stimulation efficiency. The model results showed that most bullheaded treatments were significantly improved by using the particulate diversion system. It was shown that the developed skin from jammed particulates provided a considerable diversion. The results also demonstrated the relationship between the treatment pressure, the quality of diversion, and the subsurface conditions (e.g., permeability, porosity, reservoir pressure, and temperature).