An Integrated Approach For Evaluating Matrix Stimulation Effectiveness And Improving Future Design In The Gullfaks Field

Abstract

Abstract Production decline in several wells in the Gullfaks field in the Norwegian sector of the North Sea has been attributed to various formation damage mechanisms. These include fines migration, scale formation, relative permeability changes after floodwater breakthrough, possible emulsion formation and byproducts of bacteria. To address this decline, many types of treatment operations are employed. This paper describes how a software program for design of matrix acidizing treatments has been validated for the Gullfaks field. Emphasis has been given to sensitivity analysis of this particular software as a function of variations in critical design parameters. The paper also describes how this program, StimCADE, has been used as an integrated part of a chain of analytical engineering applications, introduces a complete design methodology for possible identification of the damage mechanisms. The method revolves around analyzing each well's historical production data, immediately before and after a given treatment operation, for changes in reservoir skin using nodal analysis. The actual treatment parameters of the chosen job are input to the StimCADE simulator. The pre-treatment actual and predicted skin values are calibrated to one another by adjusting various input reservoir parameters in either one or both of the nodal analysis and StimCADE programs. Differences between the post-treatment actual and predicted skin values are interpreted to determine the formation damage mechanism. This improved damage determination is used to design more effective future treatments. The subsequent skin reduction prediction from the StimCADE program is input into nodal analysis to assess the production and thus economic impact of the new design. Four wells in the Gullfaks field in the Norwegian Sea, operated by Statoil, serve as the basis for a case study. Recommendations are made on how to extend the technique to other similar fields. P. 413