Reconciling Log-Derived Water Saturation and Saturation-Height Function Results through Resistivity Modeling, Core-Log Integration and Image Log Data: A Case Study from Deepwater Gulf of Mexico

Abstract

Abstract Saturation Height Functions (SHF) have a key role in reservoir description and in quantifying oil in place. The function(s) must compare well with other sources of water saturation (Sw) when available, such as core measurements and well-log interpretations. We have reconciled the different Sw sources through a reliable SHF function based on the Brooks-Corey model with parameters optimised for Thunder Horse (TH) Field. The function is used to populate oil volumes in the 3-D static and dynamic models. Thunder Horse is one of the largest deep-water fields in Gulf of Mexico and is operated by BP, with ExxonMobil as a co-owner. TH is divided in two trapping structures: TH North (THN) and TH South (THS). The field has multiple Miocene turbidite reservoirs commonly grouped in units known as the Pink, Brown, and Peach. Thunder Horse is fortunate to have Dean-Stark (D-S) and well-log data sets that detail the Sw changes at and above the oil-water contact (OWC). We developed a continuous log-derived Sw after appropriate model calibration with D-S measurements. Subsequently, we applied the Brooks-Corey SHF model with parameters defined for each rock type in TH area based on an iterative regression to the log-interpreted Sw following a workflow we developed. This case study illustrates methods and results of reconciling saturations determined from a number of techniques and validation of the outcomes with independent borehole and direct measurements from core. Two cases where differences were observed are addressed by combining resistivity modeling and borehole images with core-log integration. A comparison of binary vs. continuous net-to-gross (NTG) on Hydrocarbon Pore Volume, based on SHF and log-derived Sw, proved the volume impact is not significant for the highest NTG TH Pink reservoirs. However, the deliverable provides significant value through a consistent and defendable linked saturation and net-to-gross suitable for use in reservoir modelling.