Applications of natural gas tracers in the detection of reservoir compartmentalisation and production monitoring

Abstract: This paper describes the application of stable carbon isotope ratios as natural tracers in hydrocarbon reservoirs. Detailed mapping of hydrocarbon composition from closely spaced mud gas samples taken during drilling of horizontal production wells allows for the identification of reservoir compartmentalisation. This applies to reservoirs where fluid heterogeneities exist as a result of filling history or post accumulation hydrocarbon alteration. Case examples assessing fault seal properties are provided. An additional application of the methodology presented is in the detection of subtle spatial variations in reservoir rock quality that may have an influence on fluid flow within the reservoir. In several cases where fluid heterogeneities were detected in horizontal wells, subsequent time-lapse sampling of produced gas and stable carbon isotope measurements of these samples gave means for production allocation. The identification of lost production permitted the identification of an infill well target, and resulted in increased oil recovery by the drilling of a new production well. The use of gas isotopes in the evaluation of reservoir fluid heterogeneities and as natural tracers in the monitoring of reservoir fluids has proved useful in the understanding of reservoir connectivity and fluid flow. The work processes described give valuable insights and help improve reservoir management. [Copyright &y& Elsevier]