Detecting Production Effects and By-passed Pay from 3D Seismic Data Using a Facies Based Bayesian Seismic Inversion

We apply new facies based Bayesian simultaneous inversion technology to two 3D seismic datasets covering the Forties field in the UKCS. The inversion jointly solves for seismic facies and their corresponding impedances, without the pre-requisite low frequency background model that other inversion schemes require. The 3D simultaneous AVA inversion was applied separately to two vintages of 3D seismic, acquired in 1988 and 2013. The objective of the inversions was to characterise the seismic response into facies (overburden shale, Forties shale, Forties brine and Forties oil reservoir) and impedances and subsequently use these volumes to identify areas of ‘high risk of pre-1988 sweep’ and ‘remaining attic oil at 2013’. The inversion of both the 1988 and 2013 data sets was considered excellent, the sand vs shale facies distribution defining the complex reservoir architecture of the Forties Field as proved by some 350 well penetrations. The new inversion technology has resulted in valuable new insights to distribution of remaining hydrocarbons. In this case study it has provided another evaluation tool to be integrated into the Forties bypassed pay target methodology along with other datasets: 4D seismic, existing inversion results, production history and well log data integrated into detailed structural and stratigraphic analysis.