A Unique Stimulation Approach to Enhance Production Efficiency of Horizontal Wells in Heterogeneous Carbonate Reservoirs

Abstract

Matrix stimulation treatments are applied to improve well productivity and enhance the hydrocarbon recovery from the formation. However, in some wells optimum results cannot be achieved using conventional stimulation techniques since it is difficult to ensure efficient placement of the stimulation fluid across the entire stimulation interval. This is a prerequisite for a successful result. The situation becomes even more challenging in heterogeneous reservoirs with large permeability variations or possible presence of natural fractures in a complex geological environment. Other complications may occur when conventional stimulation treatments keeps creating undesired wormholes throughout the same spot within existing (horizontal) bore hole. These complications may result in making future diversion jobs even more challenging and sometimes enlarges the hole to the limit of affecting accessibility in future interventions. The paper describes a unique approach that has been successfully executed in one of the super giant onshore fields in Abu Dhabi through an extensive study over different types of heterogeneous reservoirs. The objective was to develop an economically justified stimulation strategy utilizing different treatment fluids and a unique placement approach which led to proper reservoir drainage. In this field the production comes from various carbonate reservoirs, where the different layers are subject to different methodologies to support the reservoir pressure. The approach consists of chemical diversion, dual injection for acid placement, and optimized jetting tool. The paper also describes the results of re-stimulation of a group of wells as part of field pilot. Actual data from several treated horizontal wells are presented. The methodology of candidate selection, treatment design and execution is described along with pre and post stimulation production logging. The paper highlights the impact of production improvements of the treated wells. Chemical diversion, as proved in the pilot wells, enhanced the acid stimulation. It was shown that previously untreated subunits, were now contributing to flow. The pilot wells have validated the engineered methodology adopted for the work-scope.

An Innovative Methodology for Real-Time Control and Optimization of Dual Injection Increases Efficiency of Carbonate Stimulation in Horizontal Openhole Water Injectors

“…By doing so, one can maintain a higher pressure further along the horizontal section, so that fluid pumped in deeper, less conductive intervals cannot travel back to the thief zones. This pumping technique had been successfully used in several studies, mostly focusing on water shutoff treatments (Shah and Gao 1996;Plahn et al 1998;Burrafato et al 2005) and matrix acidification (Kalfayan and Martin 2009;Fahim et al 2011). Its implementation particularly suited the water injectors of this study, as the water normally injected in the well could be used as protective fluid, without any risk of generating particular damage to the formation or of being detrimental to the later injectivity of the wells.…”