Integration of Well-Test Deconvolution Analysis and Detailed Reservoir Modelling in 3D-Seismic Data Interpretation: A Case Study

Abstract

This paper demonstrates how a combination of seismic data interpretation, advanced well test deconvolution analysis and detailed reservoir modeling helped address the concern of reservoir compartmentalization in the E-M field located offshore South Africa and thus significantly improve the history match. The reservoir is heavily faulted and many of the faults have no throw across them suggesting possible communication throughout the reservoir. Several simulation efforts in the past have failed to reconcile the connected hydrocarbons initially in-place estimated from material balance and those calculated volumetrically leading to unsubstantiated assumptions in order to attain a reasonable history match. The paper draws on the strength of an integrated petroleum engineering study that included detailed fault mapping on the re-processed 3D seismic dataset. The latter was guided by the outcomes of recent deconvolution well test analyses and a revised geological model over the entire field. As a result of this study, a new structural and stratigraphic model that satisfactorily explained the historical production performance of the reservoir was proposed. The field is located on a large tilted fault block, dominated by extensional structures with top reservoir locally truncated by the lower cretaceous synrift unconformity (1At1). The primary reservoir is synrift (pre-1At1) shallow marine and fluvio-deltaic sandstone within an upper shallow marine interval (USM). The new stratigraphic model recommends that, in addition to the extensive faulting, the reservoir stratigraphy may also be compartmentalised by field wide horizontal shale barriers. These shale barriers have prevented access to all the hydrocarbons by the existing production wells and presents opportunities for infill drilling in the reservoir. Introduction The E-M field is situated approximately 100 km offshore South Africa in Block 9 of the Bredasdorp basin (Figure 1). The development scheme for the entire basin is underpinned by the requirement to supply about 200 MMscf/d of gas feedstock to an onshore processing plant in Mossel Bay. The E-M field is the main field in the E-M area group of fields, which consist of the E-M, E-H, E-BF, F-AD, and F-BE fields. The E-M, E-H and E-BF fields are located approximately 50 km away from the F-A gas processing platform which exports gas and condensates to the gas-to-liquid (GTL) refinery at Mossel Bay. The wells are connected back to the F-A platform by an 18″ flowline, which picks up production from the F-AD and F-BE fields on the way (Figure 2). These latter two fields are relatively close to the F-A field, being 7 km and 5 km away respectively. All these fields are sub-sea developments, with the distant ones being controlled via a control-buoy tethered above the field. The buoy acts as an interface between the F-A platform and the sub-sea control and measurement equipment. Communication between the buoy and the F-A platform is by radio, thus eliminating the need for a long, complex control umbilical.