SENSITIVITY OF DEPOSITIONAL ENVIRONMENT ON HYDRAULIC UNIT DETERMINATION USING RESERVOIR QUALITY INDEX (RQI) AND FLOW ZONE INDICATORS (FZI)

Abstract

Taranaki basin is situated on the western coast of the Northern Island of New Zealand. It is prospective and currently the only producing basin in New Zealand. It consists of thick siliciclastic sedimentary strata up to 11 km thick of Upper Cretaceous to recent sediments. The sequence overlies basement rocks of Paleozoic and Lower Mesozoic age. An attempt has been made for reservoir characterization of the formations encountered in two of wells of the Taranaki basin- Amokura-1 and Standish-1. For this purpose, the geophysical well log data of the two wells have been used. Lithofacies and depositional environment interpretations were carried out using industry accepted interpretation techniques using the gamma ray, resistivity, neutron and density logs obtained from the Amokura-1 and Standish-1 wells. Reservoir quality determination and interpretations were made using the Hydraulic Flow Unit approach using RQI and FZI. The RQI vs PHIZ and RQI vs FZI plots were used for reservoir quality recognition of the formations. The GR log pattern was used for the facies interpretation which indicated the presence of boxcar/ blocky pattern in Moki-A sandstone in the Amokura-1 well, and irregular or serrated pattern in Manganui formation in the Standish-1 well. The RQI vs PHIZ plot shows that Moki-A has higher RQI values while Manganui formation has lower RQI values. Therefore, Moki-A which is a turbidite fan system has good reservoir quality while Manganui which is basin floor mudstone deposit has inferior reservoir quality.