Rock Physics Models for Integration of Petrology, Well, and Seismic Data for Triassic Reservoir De-risking
Authors: Gelinsky Stephan , Glass Frank , Espejo Irene 
Published: May 2016

Over the last decade Shell has developed and globally deployed a Quantitative Interpretation workflow (DRHI) which combines relevant subsurface data from a variety of sources to predict vertically and laterally variable reservoir properties from seismic data. In a study like this, relevant data are integrated over a wide range of scales, from the thin section over the core, well log, seismic, all the way to the basin model scale, with the objective to de-risk exploration and development opportunities.

This paper showcases a successful application of this workflow for the Mungaroo Fm sandstones in the Carnarvon Basin, North West Shelf, Australia. The application of the integrated QI workflow has provided the local Shell operating company with three important tools to optimize its exploration drilling sequence and implement a lean appraisal strategy ahead of joint venture investment decisions. The three key tools derived from the workflow are:Vertical rock property trends of reservoir and non reservoir rocks, based on well log and core data, utilizing rock physics for acoustic properties and combining sediment-petrology analyses in combination with 3D burial history to predict porosities away from well control.Delineation of lateral rock property variability of reservoir and non-reservoir rocks away from well control, based on detailed depositional environment mapping and correlation with well-based petrofacies.Detailed understanding of seismic data integrity and quality with analysis of options to optimize the data's suitablity for QI application.

Several wells have been drilled that allow for an early assessment of study predictions. Differences between pre-drill predicted total porosity and the actual measured and/or log-calculated porosity, and of predicted versus logged acoustic properties were found to be small The DRHI workflow has provided a key pre-drill tool to predict reservoir properties within the Mungaroo formation with a high level of confidence.

Introduction

The Carnarvon basin located on the North West Shelf of Australia, has seen a recent surge of exploration and appraisal activity, following the discovery of several large gas fields and commitment to develop Gorgon and surrounding fields via LNG on Barrow Island. Most of the discovered gas is reservoired in the Triassic Mungaroo Fm, which extends along much of the NW Shelf of Australia. Most of the fields and exploration acreage is covered by quality 2D and 3D seismic data, and the integrated DRHI workflow was applied to understand the Triassic Mungaroo Formations vertical and lateral variability of acoustic rock properties. In combination with the seismic data, the rock properties trends are the input to quantitative seismic data analysis to reduce risk in exploration activities, decrease volumetric uncertainty, and to predict reservoir property sweet spots within already discovered fields.

The prolific Mungaroo Formation extends across much of the NW Shelf of Australia. Figure 1 shows the study focus area and a generalized stratigraphic column of the Northern Carnarvon Basin.