Achieving Marine Like 4D Repeatability Onshore: an example from a Heavy Oil Field in South Oman

A. Al-Maamari¹, A. Wulff¹, K. Hunt¹, S. Busaidi¹, and R. Adawi¹

Abstract

Enhanced Oil Recovery (EOR) developments in the form of steam injection within a heavy oil field in south Oman have resulted in a requirement to closely monitor steam/oil mobility throughout production. Initial modelling suggested that reservoir saturation changes would likely generate a 4D signal, representative of steam front advancement, if acquisition and processing were performed as meticulously as possible. The Surface Seismic 4D project was therefore conducted with the objectives of: gaining a greater understanding of the applicability of surface seismic time-lapse to PDO assets onshore; and assisting in the optimisation of future steam injection and production well plans within the field. The Surface Seismic 4D project comprises a baseline survey from 2006 along with a dedicated monitor survey acquired in 2012. The acquisition parameters were carefully repeated wherever possible, given the significant alterations to the surface conditions between 2006 and 2012, resulting in 92% of the source and receivers repeatable within 3 meters. The detailed acquisition effort was followed by similar processing efforts that resulted in a high repeatability (NRMS < 0.1); in areas where no surface changes took place. Unfortunately in the project’s main area of interest the resultant NRMS values were greater than 0.4, predominantly due to significant infrastructure development that took place after the acquisition of the base survey. Specific 4D signal deterioration resulted from: significant alteration to surface facilities precluded occupation of many coincident shot and receiver points; the additional facilities introduced production noise variability between the two surveys; near surface (topography) changes between the two surveys. The objectives of this onshore time lapse project were partially achieved. Very good, marine like, repeatability was accomplished in part. However surface changes within the steam injection area of interest were so determinate and destroyed any 4D signal. Valuable lessons have been learnt and will be taken into consideration during the planning of future 4D surveys.

AAPG Search and Discovery Article #90188 ©GEO-2014, 11th Middle East Geosciences Conference and Exhibition, 10-12 March 2014, Manama, Bahrain