oa Seismic Characterization for Stochastic Modeling of Fractures in Na_SJ Reservoirs of UG Field, West Kuwait

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