probGRV: a workflow for geostatistical depth conversion and probabilistic assessment of gross rock volume
Shane Squire A , Sharon Langston A and James Donley ASantos Ltd
The APPEA Journal 54(1) 91-106 https://doi.org/10.1071/AJ13012
Published: 2014
Abstract
Understanding and estimating the probability of geological success (Pg) and original hydrocarbon-in-place (OHIP) are an integral part of the geoscientist’s role from exploration though to development. This paper presents a workflow developed at Santos for the systematic assessment of two key elements in this process: the probability of structural closure (Pcl); and, the estimation of the uncertainty of gross rock volume (GRV). There are two distinct parts to the workflow. Firstly, Kriging and sequential Gaussian simulation (SGS) are used in map-based, seismic time-to-depth conversion to generate multiple equi-probable depth maps (in the order of 1,000+ realisations). Numerous depth conversion methods are considered where appropriate. Secondly, every depth map realisation is validated for structural closure around a target location (e.g. a proposed or existing well). Primary outputs from the workflow include estimates of Pcl, and probability distributions of GRV and pool area for valid maps, which may then be used directly in estimating geological risk and OHIP. Secondary outputs from the workflow include basic statistics associated with depth conversion uncertainty, such as target depth prognosis and the distribution of the depth to lowest closing contour. The ultimate objective is to provide the interpreter with a greater appreciation of the range of possible outcomes given the uncertainty in structural geometry.
This workflow, named probGRV, has been designed and developed within Santos using commercially available geophysical software and in-house proprietary software. During the past few years, the workflow has been implemented on key assets at various stages of the prospect/field life cycle and in both pre- and post-drilling campaigns for audit purposes. Case studies from the Cook Field in the onshore Eromanga Basin and the Finucane South Field in the offshore Carnarvon Basin are shown to illustrate the methods and results.
Shane Squire graduated from the University of Adelaide in 1994 with a Bachelor of Mathematical Sciences degree majoring in geophysics, geology, applied mathematics and statistics, and in 1995 with an Honours Degree in geophysics. He immediately joined Santos in 1995 and has built an extensive 19-year career involving portfolio risk analysis, seismic interpretation in exploration and appraisal—both onshore and offshore—and, most recently, rock physics, seismic inversion, AVO modelling, and analysis and geostatistics. Shane’s present role as a staff geophysicist with the Quantitative Interpretation Group is focused on providing high-end geophysical support to Santos. Member: SEG, ASEG and PESA. shane.squire@santos.com |
Sharon Langston completed a Bachelor of Applied Science (Honours) in geology in 2001 at the Queensland University of Technology. She commenced working with Santos in 2003 and since then has worked in a number of challenging development geology roles in the Bowen/Surat, Cooper/Eromanga, Amadeus and Carnarvon basins, and is presently working on PNG LNG assets. Sharon’s main area of interest is in the topic of reservoir characterisation and modelling. sharon.langston@santos.com |
James Donley graduated from the University of South Australia in 1993 with a BSc (Hons) in petroleum geology. Upon graduation James joined Origin Energy, and has subsequently built a 20-year career as a development geologist with Shell-Todd Oil Services, Shell UK and Santos. With Shell came the opportunity to work at a number of world-class oil and gas fields, including the Maui Field in New Zealand and the Nelson Oil Field in the Central North Sea. More recently, James held the role of geoscience team leader during the development phase of the Santos Fletcher/Finucane oil fields in WA. James’s areas of special interest and expertise include reservoir characterisation, sequence stratigraphy, geo-cellular modelling, and reservoir appraisal and development. Member: AAPG and PESA. james.donley@santos.com |
