An Experimentally Validated Wormhole Model for Self-Diverting and Conventional Acids in Carbonate Rocks under Radial Flow Conditions

Abstract

fax 01-972-952-9435. AbstractSelf-diverting acids are commonly used in matrix acidizing treatments of carbonate formations, not only to increase permeability by generating wormholes, as with conventional acids such as HCl, but also to self-divert into zones of lower injectivity, in the goal of optimizing zonal coverage. In this paper, a new model for wormhole propagation is proposed, which describes both stimulation and diversion processes. A preliminary model is presented, which predicts wormhole propagation under radial-flow conditions for conventional acids. Then, a new set of parameters characterizing the reactive flow of self-diverting acids is developed, and the above model is extended to include self-diverting mechanisms. In particular, it is shown how the new parameters related to wormhole growth and those to diversion can be assessed from linear core-flood experiments and integrated into a new radial-flow model for field-scale prediction. Using this model, a new criterion is developed for diverter efficiency as a function of permeability contrast. Finally, the model is validated against radial flow experiments. It is found that self-diverting acids are characterized by two new parameters which, when combined with the model for wormhole propagation, can be used to predict the performance of self-diverting acids, both in terms of wormhole penetration and in terms of zonal coverage. Some criteria are also developed to assess the diversion ability of acids.

From pore scale to wellbore scale: Impact of geometry on wormhole growth in carbonate acidization

“…Thus their observations on the influence of core length and core diameter on wormholing were probably caused by a rapid interaction of the geometry with the fluid loss of the unique dominant wormhole, and not by a significant change in wormhole competition. Recently, a paper by Tardy et al (2007) compared simulations of core acidizing in both confined and unconfined domain. They measure the pressure drop between the core inlet and a short distance along the core, and observe no significant difference in the pressure drop versus time, between confined and unconfined domain.…”

Understanding Diversion with a Novel Fiber-Laden Acid System for Matrix Acidizing of Carbonate Formations

“…This model was subsequently incorporated into an existing acid placement simulator, which had been developed to model viscoelastic acid fluids (Tardy et al 2007) and used for the fiber-laden acid field case studies (Thabet et al 2009). Experiments were conducted along with the development of the model to…”

“…Many experiments were run with varying various factors (fiber loading, fluid formulation, rate, effects on the ability of fiber-laden acid to bridge and that the fiber-laden acid stimulates and diverts in 1. As the acid penetrates the rock matrix, the wormholes and the self they would without the fibers (Tardy et al 2007) 2. After a certain volume of fibers start accumulating into a fiber cake 3.…”

“…A mass balance equation is used to track the amount of f 2. A wormhole and self-diversion model is used to represent the flow in the matrix Many experiments were run with varying various factors (fiber loading, fluid formulation, rate, to bridge and, hence, its ability to divert, were analyzed den acid stimulates and diverts in three steps: As the acid penetrates the rock matrix, the wormholes and the self-diverting ability of the viscoelastic acid develop, as (Tardy et al 2007). After a certain volume of fibers (the spurt volume) is exceeded, fibers bridge in the wormholes and/or fissures and start accumulating into a fiber cake.…”

“…3: A mass balance equation is used to track the amount of fibers in the wellbore at any time and any depth diversion model is used to represent the flow in the matrix (Tardy et al 2007). Many experiments were run with varying various factors (fiber loading, fluid formulation, rate, and slot geometry).…”