Innovative Formation Tester Sampling Procedures for Carbon Dioxide and Other Reactive Components

Abstract

Three questions must be answered to optimize any openhole sampling program. These questions are where to sample, when to sample, and how to sample. Samples must be acquired from the right locations in order to answer the critical questions posed by the asset evaluation and production teams. Samples must be obtained at the right time to minimize contamination while using valuable rig time efficiently. Samples must be taken in a manner that provides the laboratory with the most representative analysis of the subsurface reservoir fluid. Carbon dioxide is a corrosive acidic gas component often found in petroleum reservoirs. Special and relatively costly completion and production equipment is required to produce reservoir fluids containing carbon dioxide. Carbon dioxide must be scrubbed from petroleum before that petroleum is shipped. Carbon dioxide may cause flow assurance issues with regards to scale of inorganic and organic components, thereby requiring costly mitigation. An accurate estimate of carbon dioxide concentration in the reservoir fluid is required to make an accurate determination of the cost of CO2 remediation. New formation tester carbon dioxide analysis technology has allowed detailed examination of these questions due to a previously unobserved phenomenon with respect to formation tester sampling and carbon dioxide. Specifically, carbon dioxide may bind with caustic components of drilling-fluid filtrate in either a reversible manner or be consumed by caustic components in an irreversible manner. Observation of a reversible reaction has been used to validate the phenomena but also provides a cautionary warning that for different chemical reactions in which carbon dioxide may be consumed, openhole samples may significantly underestimate the amount of carbon dioxide in the reservoir fluid. New sampling procedures applicable to existing formation testing infrastructure mitigate this sampling issue by determining the correct carbon dioxide content in the reservoir fluid. The new sampling procedures are validated with the carbon dioxide monitoring technology but are not strictly dependent on it. In addition, the proposed sampling procedures are applicable to the measurement of all reactive petroleum components, such as hydrogen sulfide.