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Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Seismic Characterization for Stochastic Modeling of Fractures in Na_SJ Reservoirs of UG Field, West Kuwait
(1) NFD, WK, Kuwait Oil Company, Ahmadi, Kuwait.
In the context of oil recovery optimization in naturally fractured carbonate reservoirs of West Kuwait, fracture detection along with lithological distinction offers a great added value as it helps in characterizing the wells productivity.
This paper describes a seismic workflow for characterizing reservoirs affected by fracture corridors as well as small scale diffuse fractures. The method is based on the parallel use of two approaches: (1) seismic attributes analysis performed on post-stack data, and (2) lithology prediction using pre-stack inversion and characterization.
A multi-variate attribute classification technique is applied to generate zonation maps that highlight sub-seismic fractured corridors. Statistical cluster analysis is used to identify the seismic classes, and then to group traces having the same characteristics.
At the end of the process, the interpretation highlights discontinuous zones affected by large-scale fractures. Ranking of so called “fractured seismic facies” in terms of probability of fracture occurrence allows generating an index map for the large scale fracture (swarms/corridors). The 3D stochastic fracture model eventually incorporates this large scale fracture prediction.
Modelling of sub-seismic scale fractures can also be guided by seismic data. Higher fracture density is, in this reservoir, related to cleaner limestone units. Hence, lithological discrimination based on pre-stack attributes (P and S impedances) was performed to predict the lithological changes impacting on fracture density.
This method associates shaliness at wells with impedance variations. Based on (Ip,Is) crossplots, discrimination between lime stones and shales was made possible in 3D at the seismic scale. Volumes and derived maps of shale occurrence were generated to provide guidelines for the simulation of shaly rock-types in the geological model. This 3D facies model was then used to model the network of small scale factures.
From this workflow, two types of deliverables based on seismic data and calibrated at wells provide robust guidelines for 3D stochastic fracture model building within the whole Umm Gudair field area.