Development of a Recommended Practice for Formation Damage Testing

Well productivity can be significantly affected by damage to the near well-bore area caused during drilling in the reservoir section of a well. Historically, the use of perforated completions allowed for penetration of the producing formation beyond the damaged area but the recent trend towards non-perforated completions has resulted in an increased emphasis on damage minimisation. This, in turn, has increased the importance of evaluating drilling fluids and completion techniques used from a reservoir damage perspective. The suitability of a drilling or completion fluid for use in a particular reservoir can, and should, be determined using the measurement of return permeability or some other indication of formation damage. A major factor which limits this practice is that no industry standard equipment or methodology exists for this type of testing and differences in results obtained at different times or in different laboratories cannot be reliably compared. Repeatability and reproducibility of the tests conducted have not been widely established. In order to address these problems, a recommended practice for formation damage testing has been developed which covers all aspects of the test methodology from core selection and preparation to the writing of the final report and interpretation of the results. By standardising on equipment and methodology, it has been possible to establish the degree of variation which can be expected when the same samples are tested in the same way in different laboratories. Further testing in which selected parameters have been varied has also given an indication of the degree to which the setting of these variables affects the final result. It is hoped that this recommended practice will now gain acceptance throughout the industry and that the process of evaluating fluids for formation damage potential will become simpler and more efficient through the greater use and validity of comparisons between data from different sources.