Wireline formation testing (WLFT) is a downhole testing technique used to determine the formation pressure, the formation pressure gradient, and the formation permeability and to collect formation fluids. Current WLFT tools are designed for high to medium permeability reservoirs. In this study, the results from WLFT runs in eight wells drilled in cooperation with the Gas Research Institute are presented. The tests were conducted by three major service companies. The merits of the WLFT tools, the information provided, and the possible misinterpretations of the data are reported.

A brief description of each formation tested is made in each well: rock type, shaliness, porosity, permeability, saturation, and formation pressure. The test results are characterized by the flowrate, the chamber size, the duration of drawdown, and the duration of the pressure buildup. Typical curves are presented. A statistical study of the successful tests is attempted.

The results obtained with a slow flow wireline tester (SFWT) are also presented. Based on the analysis of the SFWT runs and using a new modeling technique, a new interpretation method is proposed. The results indicate that the current WLFT tools will have to be modified to allow a better analysis of the drawdown period.

This study shows that meaningful data can be obtained with the WLFT tool in many instances, especially when a slow flow rate is used. The drawdown portion as well as the build-up portion of the pretest can be interpreted, and the drawdown data can confirm or, to some extent, replace the build-up data. The evaluation of low permeability gas formations will be greatly enhanced by using the new slow flow testers and the new interpretation technique.

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