Abstract

Since matrix acidizing is a low-budget stimulation operation, there has been little incentive to improve acidizing treatments including real-time technology, despite the wide usage of matrix stimulation. Hence, for matrix acidizing real-time quality control, job monitoring and job optimization is seldom practiced and nosophisticated tools were available. However, the ever increasing length of stimulated segments and the associated technical and economical problems in combination with reports on high stimulation failure rates have created an emphasis on the development of real-time tools, not only for monitoring and analyzing acidizing treatment efficiency but also for evaluating pre- and post-treatment job performance. All the tools available today use the evolution in skin factor as a quantitative measure of the overall treatment. For the calculation of the skin factor three methods, based on measuring the injection rate and pressure, are presented. The methods differ widely, from applying a steady-state approach to the fully transient flow regime accounting for various effects influencing the pressure response. Comparisons are presented, based on detailed analysis of the models' features and matching of field data.

An obvious conclusion is that the fully transient method is the most promising means of real-time monitoring and analysis of matrix treatments for the future.

Introduction

Matrix acidizing is a stimulation technique involving the injection of an acid solution at pressures below the parting pressure of the formation. The acid dissolves some of the minerals present in the near-wellbore vicinity and hence original permeability is recovered (in sandstones) or enhanced (in carbonate formations). When compared to other oilfield operations such as hydraulic fracturing, significant failure rates were reported for matrix stimulation applications, i.e. the technical and economical objectives are not reached. Since in previous times acid treatments were regarded as relatively cheap operations, few efforts to improve acidizing technology were undertaken. However, the industry's attitude towards matrix acidizing has recently changed due to the ever increasing length of wells to be stimulated, as a result of evolving horizontal well technology, and the associated logistic, operational and economic problems involved. This situation promotes focused efforts for the development of new acidizing tools and technology such as the red-time techniques discussed in this paper.

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