Online Journal for E&P Geoscientists

Al Kindy, Mohammed ^*1; Warrlich, Georg ¹
(1) Petroleum Development Oman, Muscat, Oman.

The fracture network is frequently one of the highest ranking subsurface risk uncertainties in terms of impact to reservoir development. Its appropriate characterization and modelling are essential for optimal development strategy selection. Limited reservoir penetration and inconclusive well and dynamic data often advocate the use of regional analogues and large scale seismic data. In this study we have compared the important properties of outcrop fracture pattern with subsurface fracture data from a number of EOR carbonate fields in North Oman that have different amounts and types of data sets. We have also explored the limitation of using seismic attributes to map fracture clusters in subsurface at various scales.

The outcrop data sets include mapping structural lineaments from SAT images, analyzing fracture-cluster properties and reconstructing the structural evolution history of the selected surface structures. The outcrop data collection was done in Jebel Madar, Jebel Madmar, Jebel Qusaibah and few domal structures in the Huqf area. Seismic structural lineament mapping was done in 3D seismic cubes that were either acquired close to the outcrops or in the North Oman field regions where the subsurface fracture data come from. This allows the comparison of seismic attributes extracted from these cubes with both the outcrops and the reservoir BHI and dynamic data. Surface and subsurface fracture data are compared to different extractions of seismic attributes to explore the reliability of these attributes to map the fracture corridors.

Results show the importance of understanding the evolution and burial history of structures in order to make comparison between surface and subsurface fracture pattern. Fracture corridors need to be classified according to their origin. Fractures that have the same orientation can be related to different stress regimes and therefore have different distribution. Moreover, the dimensions and cementation of fractures are strongly related to the tectonic regime and the burial and uplift history of the structure. Although seismic attributes are useful for mapping fracture-corridor lineaments, choosing the appropriate attribute type and setting is substantial to make suitable representation of different sets of fractures. In overall, all analogues and large scale data sets should be compared with dynamic well data (e.g. interference tests and mudlosses). The key risks and uncertainty ranges of fracture modelling should be well captured during fracture scenario development.