The last several years have seen an increase in the popularity of horizontal wells. There are a number of applications for horizontal wells that are an enhancement to the traditional vertical well. By increasing the wellbore's contact area with the reservoir, a horizontal well increases the drainage efficiency of a marginal reservoir by: * more efficiently exploiting naturally fractured formations* reducing the likelihood of water coning and/or fingering* improving EOR via horizontal injection wells* intersecting vertical or near vertical formations To determine if a horizontal well will indeed provide the intended enhancement to productivity (or injectivity), an evaluation of the formation parameters and characteristics is recommended. Drill stem testing of vertical wells has long been a popular means of formation evaluation. However, the testing and subsequent formation evaluation of a horizontal well presents additional challenges. The successful operation of the downhole tools as well as the analysis of the collected data are not as straightforward as for a vertical well. This paper presents a case study of the successful testing and subsequent analyses of four open hole DSTs of a horizontal well. These DSTs were conducted during the well's drilling phase at ever increasing degrees of deviation; from 45 degrees for the first test to 90 degrees for the fourth test. This paper presents and discusses the: * downhole tools used and their relative positions in the hole* planning and preparation for the tests* analysis of the collected data for formation parameters and characteristics* aspects of the horizontal hole that affected the analysis. P. 371^

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