Integrated Static and Dynamic Uncertainty Workflows for Field Development Planning: An Example From the Jackdaw Discovery, Central North Sea

Abstract

Integrated static and dynamic uncertainty workflows are a powerful tool for quantifying subsurface risks and guiding decisions during field development planning. A multi-disciplinary workflow that incorporates geophysical, geological and production uncertainties has been developed for the Jackdaw discovery, a High Pressure, High Temperature, gas-condensate field in the central North Sea. As a result of high well costs and the challenges of operating in extreme sub-surface conditions at depths approaching 19000 ft (5800 m), the exploration and appraisal programme, conducted between 2005 and 2012, was recognised as being unable to resolve various key uncertainties. In order to progress the development through the decision chain and provide key stakeholders with a robust, reasoned and accurate resource range, a key element in evaluating overall value, the sub-surface team developed innovative approaches to dealing with and quantifying the key uncertainties. This workflow draws on a geological model built with PETREL with uncertainty parameters defined within MEPO. In addition to modification of geological and petrophysical parameters, each realisation runs additional nested workflows. The first of these nested workflows modify the structure of the grid to account for gross rock volume and seismic interpretation uncertainty. The second workflow automatically calibrates the generated static model to the available drill stem test data. Each model realisation is simulated with ECLIPSE, with results sent back to MEPO for statistical analysis and the generation of probability distribution curves for both GIIP and reserves. Sensitivity analysis reveals the key uncertainty on in place volumes in both the appraised and un-appraised fault blocks are the gas-water contacts. However recovery from the reservoir is largely controlled by abandonment pressure and permeability. The reservoir comprises a bimodal permeability system that is primarily controlled by depositional facies. High permeability turbidite or gravity flow deposits are found within a background of low permeability, bioturbated shelfal sand. The shelf sand facies has core measured permeabilities of 0.005–1 mD (air permeability). As a result of this low permeability, uncertainty around the Klinkenberg correction factor and vertical permeability can significantly impact recovery.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015