Improved Recovery of Carbonate Reservoir by Optimizing Acidizing Strategy; Coupled Wellbore, Reservoir, and Geomechanical Analysis

Abstract

One of the sources of damage in stimulated carbonate rock is the loss of near wellbore formation compressive strength which may results in casing collapse under extreme conditions. Field studies have shown that the failure of acidized rock may cause damage and thereby negatively impact production. In this work, an integrated analysis workflow is presented to simulate acid placement in carbonate reservoirs and model stimulated rock behavior during the productive lifetime of the well. The workflow is utilized to design a unique approach to horizontal wellbore acidizing and optimize the strategy to maximize hydrocarbon recovery.

The presented workflow is based on the interaction between the distributions of reactive fluid along a wellbore, a two scale continuum model to simulate porosity evolution during stimulation, and stimulated rock performance during production time. The model first simulates stimulation fluid movement in the wellbore and couples it with transient reservoir flow. The primary analysis provides the distribution of reactive fluid along the well. The rock dissolution at each section of reservoir is then analyzed by continuum two-scale model (pore-scale and Darcy scale). This analysis presents porosity evolution at different locations along the well and at different radial distance from the wellbore center. Then, the developed geomechanical engine simulates the weakened rock under the in-situ stresses and bottom-hole pressure and predicts any possible compressional or shear failure. The effect of rock failure is then considered on the production prediction.

The workflow is best used to analyze and optimize acid stimulation for a horizontal well. The analysis results show that the induced wormholes are stable and open since reservoir depletion increases the effective mean stress. At the elevated mean effective stress, wormholes or pores start to collapse and the failure extended away from near wellbore region and neutralized the stimulation effects. Since in the acid treated zone the rock is softened, the stress concentration around the wellbore might extended more into the reservoir. Analyzing this phenomenon showed that at a certain level of lowered stress concentration extension, in other words at certain strength and volume of acid, the wormhole can be stable and open during expected production time. Furthermore, the coupled analysis also demonstrates that at specific environment, the wormholes penetrated further into the rock, longer than possible

induced failure. The workflow can be used to determine how weak or strong the acid should be at specific environmental condition to have longer life for the induced wormholes and hence extra hydrocarbon recovery.