The popularity of matrix stimulation as production enhancement operation is evidenced by the abundance oftechnical resources on the subject matter. Developments in technology have continued to address the challenges of the operation. This paper identified three critical success for well stimulation as good candidate selection, well-engineered treatment design and improved field operations. The approach was simple and involved a review of existing case histories with a view to identifying issues that need closer attention for the optimization of matrix treatments. The use of the R-Factor for candidate selection was revisited and an expression that excluded BHP data and rock and fluid properties was derived to ease the calculation of this factor. An attempt was also made towards the design of the treatment volume of the acid based on the completion details of the well. Charts were presented for this. Field cases that illustrate the importance of this new approach were also presented. Introduction Well Stimulation has continued to gain increased importance as a productivity improvement method especially as conventional oil reserves continue to deplete and new frontiers demand advances in technology for commercial viability. Several parameters affect the productivity of a well. Whereas models exist for the evaluation of well performance, the uncertainty arises from the complexities involved in accurately predicting downhole conditions at any given time in the life of the well. Stimulation methods are used in improving the performance of wells either by removing formation damage or bypassing the formation damage through induced fractures in the reservoir. Most producing formations are impaired whether from drilling, completion or production activities. This impairment is the reason for productivity loss and associated production gap from these wells. While formation damage mainly arises from the drilling mud used in the conventional overbalanced drilling of wells, other forms of damage develop over time as the well produces. It is imperative to characterize the source of productivity impairment so that the right solution can be proffered to avert loss of revenue due to wrong treatment. Different forms of damage with the corresponding "general" treatment have been identified. For tight formations, the formation damage may not be critical but fracturing may be required to provide alternative flow path to wellbore because of the low natural formation permeability.

Matrix stimulation improves well productivity through the removal of formation damage in the near-wellbore region of the reservoir. Success and failure of stimulation treatments are often attributable to candidate selection. Lack of a structured approach to candidate selection has had an adverse effect on the outcome of stimulation treatments industry-wide. Where good candidates have been identified, the absence of robust techniques for the determination of damage radius introduces uncertainty on the accurate volume of treatment fluid to deploy. This paper presents a robust approach to candidate selection based on analysis of the relative impact of various skin effects in the well. Simple mathematical expressions that describe the relative impact of formation damage and partial penetration were also derived. A novel approach for the determination of damage radius is also introduced. The damage radius so determined is considered useful for accurate calculation of matrix treatments volumes.