Gas Tracer Interpretation Theory And Application Technology In Miscible Hydrocarbon-Gas Flooding

Gas tracers began to be used in oil fields in 1960s. They were mostly radioactivematerials in early years. Various Freons were often been applied in 1980s. Due to theirharmfulness to human body and environment, Perfluorocarbons were introduced in mid1990s. With high chemical and thermal stability, these substances can also be detectedat a very low concentration of 1/1015. According to literatures, although applicationtechnology of gas tracers has got in shape, interpretation method related has not by farbeen investigated. Therefore, associated with miscible hydrocarbon-gas flooding pilottest in Wen88 Block in Zhongyuan Oil Field, this dissertation is dedicated to doingsome research in this scientific field. The diffusion equation, which characterizes displacement in porous media, is thebasic theory for tracer interpretation. Through studying the equation about its'derivation, presumptions, influence factors and solving method, we can know theessence, application conditions and physical meaning behind it. Based on all thisknowledge and investigation about gas tracer flow features, a gas tracer flow model isset up. Associating this flow model with the regular diffusion equation concludes thediffusion equation for gas tracer flow modeling which features "flow lagging". Tracer production concentration is not only affected by diffusion, but also by wellpattern. Former tracer theory reflects the well-pattern effect by its control on fieldstreamlines because tracer production profile changes when streamline pattern alters.But it is not suitable to apply directly the method to miscible gas flooding because ofthe old assumption of only-one–phase presentation in well pattern and its significantgas-oil mobility ratio that can leads to gas fingering. So a feasibility study of atwo-phase mathematic model is carried out for miscible gas displacement modeling.By introducing a method of modifying model parameters, a two-phase miscible gasdisplacement model is founded in a stream-tube coordinate. Because different fluidsaturation at different gas injection stage can leads to different streamline distribution,the two-phase model describes an ever-changing stream tubes. When used to describegas tracer production process, the ever-changing-stream-tube method comes withdifficulty, because we can not determine where the gas frotier is in the ever-changingstream tubes. For this reason, and based on reliable proofs, a semi-changing streamtube method is proposed, which can solve the problem properly. In applicationtechnology, not only characteristics of typical gas tracers briefly presented, includingtheir categories, physical properties, injection and detection methods, but also amethod of volume calculation is worked out in detail for gas tracer field design whereonly a much lower areal sweep is reached in miscible gas displacement.