Revival of Openhole DST: Compromising Between Wireline-Formation Testing and Cased-Hole DST

Abstract Exploration well testing has gone through several changes over the past twenty years. While open hole Drill Stem Testing (DST) based on conventional technology with mechanically set packer was gradually replaced by inflatable packer based DST tools, cased hole DST became a standard for many exploration companies, particularly offshore. Today, some companies still avoid open hole testing based result of poor success ratios of outdated conventional tools. Also, wireline formation testing has become more frequent due to advances made in wireline test tools. However, because of greater ability to obtain reservoir productivity and skin measurements, DST continues to be widely used, though cost and environmental issues limit its application in certain areas. Land rigs are natural candidates for open hole DST due to the content and quality of information obtained, as well as well as lower cost of the open hole DST service compared to wireline formation testing. Open hole DSTs are quick and simple to run. Hydrocarbons do not need to be produced to the surface, but a significant volume of reservoir fluid can be produced. Due to these advantages we see an increasing trend to deploy inflatable open hole DST tools on on-shore exploration rigs. The benefits are so convincing that operators using small jack-up rigs consider performing this type of tests as well. This paper summarizes all aspects of open hole DST with respect to information gained, time needed and related cost. The differences between old type of conventional DST and inflatable DST are highlighted and success ratios provided. Safety aspects are discussed by comparing with wireline formation tester and cased hole DST operations as well as the basic economics.