3D Facies Modeling of Mangahewa C Sand in Maui B Gas Field, Taranaki Basin, Offshore New Zealand

Abstract

Building a reservoir model for volumetric calculation is often done based on a single geological concept which is expected to represent the true geological picture. This approach might not capture the full range of uncertainties related to the complexities of geology. The objective of this study is to build an alternative model based on a separate geological concept from the one that is the most likely case and then to compare the net rock volume calculation of these models to see the impact on the final results. The depositional environment was interpreted based on a combination of paleogeography maps, well logs, seismic attributes and core description in Maui B field, Taranaki Basin, offshore New Zealand. The facies models contain eight depositional facies broken down into three groups, namely marginal marine, shallow marine and shelf. The first model has the main reservoir interpreted as upper shoreface sand while the second model assumes that the sand has been deposited in tidal channel systems. The modeling uses Petrel software package which combines object-based and pixel-based modeling termed Sequential Indicator Simulation (SIS) to generate an output. The SIS algorithm was applied to define the background and then objects such as channels and tidal mouth bars were introduced to the previously defined background. The results indicated there is a 42.8% difference in net rock volume between the two models corresponding to 33.2 Bcf of net rock volume or 340 Bcf of gas recoverable reserves. This suggests the geological concept has a great effect on the final volumetric estimation and an alternative model should be constructed in order to capture the range of uncertainties related to net rock volume calculation.