A New Approach for Modeling Scale Formation during Water Injection into Carbonate Reservoirs

Abstract

Abstract Water injection is commonly used in oil fields for pressure support and productivity enhancement. Injection water, if incompatible with formation water, can induce scale precipitation and impose a significant threat to economic and efficient field operation. Reliable scale prediction is of critical importance for the selection of suitable injection water and development of an effective scale management strategy. The traditional (thermodynamic) approach for scale prediction only provides precipitation potential at different mixing ratios. It describes the initial and final states of the system and omits some intermediate processes and products that may be important for operations. In addition, it may overestimate the total amount of the scale forms. In this paper, we describe a new approach, the kinetic approach, to facilitate more accurate prediction of scale formation. We demonstrate the kinetic approach in a parametric study of seawater injection into a carbonate reservoir in Saudi Arabia using Reactive Transport Modeling (RTM). RTM simulates coupled multiphase fluid flow and chemical reactions, and has the capability of predicting time-dependent mineral scales formation and associated reservoir quality deterioration. Formation of calcium sulfate scale in the reservoir and near wellbore is a major concern due to high calcium concentration in formation water and high sulfate concentration in the seawater. We built a two-dimensional RTM using TOUGHREACT v1.2 with GUI pre- and post-processor PetraSim v2015, and simulated scale formation over a 20-year time span. Reservoir heterogeneities was considered in our model. The impact of scale formation on the reservoir and well properties during waterflooding operations was evaluated. The results indicate that the migration path of the solutes depends highly on the reservoir permeability distribution; preferential flow paths form in the high permeability layers. At 20 years, up to 11.6% anhydrite scale forms in the mixing zones of injection and formation waters and up to 18% calcite scale forms near injection wellbore (~ 10 m radial distance to the wellbore). Severe porosity reduction is predicted near the injection wellbore and in the mixing zones at 20 year due to the formation of calcite and anhydrite scales, respectively. A negative feedback forms between the initial exploitation of preferential flow paths and subsequent reservoir quality deterioration in these paths. The kinetic approach described in this paper will offers a significant improvement on scale prediction results over the traditional approach for field development and cost-effective scale management strategy.