Summary
This paper presents an innovative and promising, multidisciplinary approach
that includes geology (borehole images, cores, and wireline logs); geophysics
(seismic facies analysis), and reservoir engineering data (production data,
PLT, and well test) that were combined to identify the main types of fractures,
to predict their occurrence in the reservoir, and to determine the hydraulic
properties of the different fractures sets.
The Najmah-Sargelu of west Kuwait is an oil-bearing reservoir made of tight
carbonates where porosity and permeability are provided mainly by the fracture
network. In this paper, we first introduce the method used to identify and
predict the two main scales of fractures: joints and large-scale fractures
(faults and fracture swarms). The shale content (Vshale) and mechanical-beds
thickness were found to be the two main geological drivers on joints
occurrence. The thickness of individual beds was recorded from borehole
acoustic images, which enabled us to measure a fracture spacing/bed thickness
(S/T) ratio for each fracture set and for different shaliness. Second, we used
an innovative solution to deliver an accurate map of the location of
large-scale fractures. This approach concurrently uses a set of relevant
attributes per selected fracture in a multivariable statistical process called
seismic facies analysis (SFA).
A 3D-stochastic fracture model was then generated, incorporating the two
scales of fractures and this model was constrained by the shaliness of the
reservoir, the S/T ratio, and the seismic facies map. In this approach, the two
scales of fractures are modeled independently. The model of large-scale
fractures is conditioned by the picking of lineaments on the SFA map and
validated at wells, whereas small-scale fractures are modelled according to
geological driven statistics on fracture density and fracture orientation. The
calibration of the hydraulic properties of the fractures was achieved through
the second innovation presented in this paper: the simulation of a synthetic
well test using the 3D-fracture model and matched with the real data. This
resulted in the calibration of effective hydraulic conductivity for each
fracture type. These values were combined with the 3D-stochastic fracture model
to produce 3D-fracture-properties models (porosity, permeability, and block
size) for the Najmah-Sargelu.
Introduction
A detailed geological and hydraulic characterization of the fracture network
occurring within the Upper Jurassic Najmah-Sargelu reservoir was planned in
2003 and 2004 by Kuwait Oil Company (KOC) in consultation with Beicip-Franlab.
The objective of the study was to identify the main geological drivers on
natural fractures occurrence; to measure their hydraulic properties; and
eventually, using the discrete-fracture-modeling (DFN) approach, to compute the
equivalent fracture properties (porosity, permeability, and block sizes)
required for the reservoir simulation. This was achieved through a close
integration of geological, geophysical, petrophysical, and dynamic data carried
out using workflows and methods implemented in a fracture analysis and modeling
software (Bourbiaux et al. 2002).
The main tasks performed during the project and presented in this paper are
the following:
- Fracture analysis from cores
- Fracture analysis from BHI logs
- Integration of 3D-seismic data set
- 3D fracture modeling
- Hydraulic characterization of the fracture network
- Computation of the fracture properties in the reservoir grid.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
18 January 2005
- Meeting paper published:
12 March 2005
- Revised manuscript received:
10 November 2006
- Manuscript approved:
3 May 2007
- Version of record:
20 December 2007
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