Combining Selective Stimulation With Tailored Perforating Improves Injection Profile in a Carbonate Reservoir: A Case Study

Abstract

In a multi-layer heterogeneous carbonate reservoir in which production and injection is being carried out, one of the biggest challenges faced is to produce/inject evenly from/to the different layers. At elevated temperatures this heterogeneity limits the success of conventional stimulation techniques. A novel acid diversion technique involving selective stimulation and tailored perforation design techniques was applied in an offshore UAE well to improve injectivity in a multi-layered heterogeneous carbonate reservoir.The well in question was re-completed from a dual string water injector well to a single string gas injector re-perforated in four different sub-zones. Well test and production logging data were used to estimate permeability and flow profile before the workover. These data were then used to run NODAL analysis, stimulation simulation, and perforation simulation models. The final workover proposal called for:• Perforation over the same interval as was previously perforated using different gun and charge sizes to establish controlled injection based on the different zones permeability. • Optimized coiled tubing (CT) selective stimulation using high strength retarded acid pumped in stages with a self diverting acid.The well injection performance was dramatically improved as evidenced by the gross injection value and the injection profile obtained in a post treatment production logging run.This paper details the planning, execution and final evaluation of this job which is unique in that the same interval was tested twice, before and after workover, after being completed using different perforating and stimulation techniques. BackgroundCarbonate reservoirs tend to be complex and often exhibit large variations in permeability over different sections of the same producing zone 1 . These variations in the permeability profile create challenges when planning to inject acid (commonly done in carbonates), produce hydrocarbons, or inject water or gas. It is often the high permeability zones that will dominate while the lower permeability zones will miss the treatment or not be produced.