Wireline Fluid Sampling

Abstract

Abstract Accurate PVT data are crucial to well completion and production, formation evaluation and reservoir characterization. This is especially true for initial reservoir characterization where the PVT sample needs to be obtained prior to production. It is essential that the fluid sample be recovered as closely as possible to in-situ conditions whether by drill stem or wireline formation tester. The need to remove drilling mud filtrate prior to collecting a sample has been widely recognized. Wireline testers which can pump fluid from a formation until filtrate is reduced to a minimum overcome this problem. While reducing sample contamination has been addressed, little emphasis has been placed on the need to control inlet pressure during filtrate removal or during sampling. Reducing contamination is important; however, there is equal need to determine the critical sampling pressure. The purpose is to prevent phase separation in the formation by regulating the sampling process based on this information and thereby obtain a more representative reservoir fluid sample. A recently introduced wireline instrument provides the capability of measuring the critical pressure prior to sampling, of controlling the sample pressure and of increasing the pressure in the sample container to compensate for temperature decline during delivery of that sample to a testing laboratory. Example of pressure tests while pumping and during pressure buildup are presented along with indicated sample properties.