The Impact of Reservoir Heterogeneity in the Modelling of Scale Inhibitor Squeeze Treatments

Abstract

The oil and gas industry require technologies to prevent mineral scale formation and deposition in reservoirs and production systems. One commonly used method to achieve this is the scale inhibitor squeeze treatment. The challenge addressed here using modelling is to prolong the squeeze treatment lifetime in heterogeneous reservoirs, thus, reduce the cost per barrel of oil produced, especially in deep offshore and remote locations. Key to squeeze life extension is ensuring optimum scale inhibitor retention on rock matrix. Therefore, the inhibitor must contact the reservoir rocks and be distributed amongst the layers in proportion to the expected water production rates per layer, which will be determined by reservoir heterogeneity, system geometry and gravitational effects. These effects are studied for an offshore water flooded reservoir by means of a reservoir simulation model. The study reveals that reservoir heterogeneity generally improves inhibitor squeeze treatment performance as measured at surface for the entire well, with more inhibitor being placed in the zones with high permeability-thickness product (kh). However, downhole pressure differentials can result in higher pressure layers being unprotected for longer periods before the inhibitor concentrations for the entire well goes below the Minimum Inhibitor Concentration (MIC). The use of diversion techniques is shown by simulation work to improve placement and thus help achieve a successful inhibitor squeeze treatment in all the reservoir layers. However, inhibitor concentrations may remain relatively high in layers that do not produce much water, resulting in some wastage of inhibitor as a penalty for delaying the time before re-squeezing is required. The modelling helps understand where scale could occur and the best management strategy for scale prevention or control; identifying the impact of scale; giving insight into the best inhibitor squeeze treatment options and expected performance; and providing input needed for the economic model required for good reservoir scale management.