Determination of skin and aquifer parameters for a slug test with wellbore-skin effect

SummarySlug test is considered to reflect the hydraulic parameters in the vicinity of the test well. The aquifer parameters are usually identified by fitting an appropriate mathematical solution or graphical type curves with slug test data. In this paper, we developed an approach by combining [Moench, A.F., Hsieh, P.A., 1985. Analysis of slug test data in a well with finite-thickness skin. In: Memoirs of the 17th International Congress on the Hydrogeology of Rocks of Low Permeability, U.S.A. Members of the International Association of Hydrologists, Tucson, AZ, vol. 17, pp. 17–29] and simulated annealing (SA) approach to estimate five parameters, i.e., three skin parameters and two aquifer parameters. The three skin parameters are hydraulic conductivity, specific storage, and thickness of the wellbore-skin zone, while the two aquifer parameters are hydraulic conductivity and specific storage of the formation zone. It is worthy to note although the thickness of the wellbore-skin zone is usually taken as an input data for the data-analyzed software, it is actually an unknown parameter that cannot be measured directly. This paper proposes a methodology for estimating the thickness of the wellbore-skin zone with other hydraulic parameters at the same time.Eight sets of well water-level (WWL) data of aquifers with both positive and negative skins are generated by Moench and Hsieh [Moench and Hsieh, 1985] and four sets of standard normally distributed noise are then added to each set of WWL data. The results indicate that the negative-skin cases generally give a better estimated result than that of the positive-skin cases. Sensitivity analysis is also employed to demonstrate the physical behavior when slug test was performed under positive-skin effect. For the case of an aquifer with a positive-skin, the use of a longer series of WWL data for analysis is strongly recommended for better estimation of aquifer hydraulic conductivity. Analyzing the WWL data of the test and observation wells simultaneously could significantly improve the estimations on specific storages. Impetuously presuming an arbitrary value for the thickness of the wellbore-skin zone may lead to poor estimation for the other four parameters.