Time-lapse Porosity and Velocity Analysis Using Rock Physics Models in Niger Delta, Nigeria
Publication Date : 18/05/2022
In reservoir characterization, modeling the effects of production-related changes on elastic properties of the reservoir is a very challenging task because of the non-uniqueness and uncertainty of reservoir system. However, the analysis of 3-D and time-lapse seismic data has offered the possibility of dynamic characterization of the porosity and velocity changes in the reservoir during hydrocarbon production using rock physics models and vertical information available from the well logs. The changes in the fluid properties as production progresses was analysed using fluid substitution and depth domain seismic velocity models. The result of the initial average porosity of the reservoirs was 29.50% with a very low water saturation of 12%. The oil and gas drive maintained average saturation of 40% and 48% respectively. The average compressional and shear wave velocities is 2905m/s and 1634m/s respectfully with velocity increasing with decrease in porosity. However, in fluid substitution modeling, the results reflect a change in fluid properties where average gas and oil saturation assume new status of 34% and 24% which indicates a decrease by 14% and 16% respectively.The average water saturation increases by 30% with an average value of 42%. The decrease in hydrocarbon saturation and increase in the water saturation influence the elastic moduli of the reservoir rocks, pressure, temperature and porosity. Thus, porosity decreased by 4.16% which probably arose from the closure of the aspect ratio crack due to pressure increase. The velocity depth model of the monitor shows significant increase in velocity and water saturation that are gradually replacing hydrocarbon in the reservoir which is an indication of reservoir depletion.
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