Challenges during shallow and deep carbonate reservoirs stimulation

Carbonate reservoir stimulation has been carried out for years using HCl or HCl-based fluids. High HCl concentration should not be used when the well completion has Cr-based alloy in which the protective layer is chrome oxide which is very soluble in HCl. HCl or its based fluids are not recommended either in shallow reservoirs where the fracture pressure is low (face dissolution) or in deep reservoirs where it will cause severe corrosion problems. Different chelating agents have been proposed to be used as alternatives to HCl in the cases that HCl cannot be used. Chelating agents such as HEDTA (hydroxyethylenediaminetriaceticacid), and GLDA (glutamic -N,N-diacetic acid) have been used to stimulate carbonate cores. The benefits of chelating agents over HCl are the low reaction, low leak off rate, and corrosion rates. In this study, the different equations and parameters that can be used in matrix acid treatment were summarized to scale up the laboratory conditions. The conditions where HCl or chelating agents can be used were determined. The leak off rate was determined using the data from coreflood experiments and CT scans. Indiana limestone cores of average permeability of 1 md and core lengths of 6 and 20 in. were used. Chelating agents will be used at pH value of 4 and 0.6M concentration and compare that with the 15 wt% HCl. The experimental results showed that HCl has high leak off rate and caused face dissolution at low injection rate. The model to scale up the linear coreflood results to radial field conditions was developed and can be used to design for the optimum conditions for matrix acid treatments. Chelating agents can be used to stimulate shallow reservoirs in which HCl may cause face dissolution because it can penetrate deep with less volume or can be used in deep reservoirs where HCl may cause severe corrosion to the well tubular.