Development of saturation functions for thick transition zones in carbonate reservoir

  • Oriyomi Nurudeen Raheem

    Student thesis: Master's Thesis

    Abstract

    Tight carbonate reservoirs exhibit thick transition zones which usually contain large quantities of oil and therefore significant amount of reserves might be left after secondary recovery. Proper characterization and development of saturation functions of transition zones in carbonate reservoirs are utmost important for better understanding the two-phase flow behavior of both water and oil through the zone. In the present study, 3D NMR and conventional core analysis (CCA) data are employed for the petro-physical characterization of the transition zone carbonate samples as a model for similar carbonate reservoirs. Results reveal three distinct rock types with an average NMR-T2 cutoff of 292 ms, 164 ms and 63 ms for the topmost, middle and lowermost samples of the reservoir. Capillary pressure curves were predicted from NMR T2 pore size distribution. Electrical resistivity, formation factor and cementation exponent were also measured at ambient and reservoir conditions. It was found that the cementation exponent increases from 1.9 to 2.3 under overburden conditions and decreases in a stepwise manner respectively during unloading confining pressure, but not to the initial value due to hysteresis. The mean values of cementation and formation factors at reservoir conditions are 30% and 50% higher than those obtained from laboratory conditions. This implies that the electrical parameters in laboratory condition would lead to underestimation in water saturation which is more significant in oil zones as it decreases. Resistivity index and capillary pressure measurements were conducted at reservoir conditions (2300 psi and 80 °C) using a DCI PCRI systems mimicking drainage and imbibition to investigate the hysteresis and saturation exponent changes. The average Swi values determined at reservoir conditions from the capillary pressure measurement has been found to be 15% lower than those obtained from laboratory conditions. Also, the saturation exponent estimated during drainage and imbibition at reservoir conditions range from 1.5 – 4.0 for different rock types. Novel saturation functions were developed for each rock type from measured electrical parameters at reservoir conditions by using the modified Archie's equation for the transition zone of the carbonate reservoir. The outcomes of the present study were able to successfully correct the field resistivity log readings which overestimate the water saturation and predict fluid saturation distribution and mobility for better original oil in place (OOIP). Additionally, this supports the design of successful EOR programs in transition zone of carbonate reservoir. Keywords: Saturation function, cementation exponent, transition zone, carbonate reservoir, electrical properties of rock
    Date of Award2016
    Original languageAmerican English
    SupervisorHadi Belhaj (Supervisor)

    Keywords

    • Applied sciences
    • Carbonate reservoir
    • Cementation exponent
    • Electrical properties of rock
    • Saturation function
    • Transition zone
    • Petroleum engineering
    • 0765:Petroleum engineering

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