On-line Optimization-Based Simulators for Fractured and Non-fractured Reservoirs Page: 76 of 188
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considered as a rupture in reservoir rocks. Two of the most common types of
fractures are faults and joints. A fault is a fracture along which one side has
moved relative to the other . A fracture is regarded as a joint when there is no
noticeable displacement along the fracture . Two dimensional representations
of a fault and joints are shown in Figure 5.1 and Figure 5.2, respectively.
Two common causes of fractures are overburden pressure and tectonic forces.
Figure 5.3 shows a fracture created by overbuden prssure and Figure 5.4 shows a
pair of conjugated fractures created by tectonic forces.
Direct evaluation of fractures includes outcrop observation in the field and
core examination in the laboratory . Fracture opening (fracture width), frac-
true filling and fracture orientation can be measured during the direct evaluation
process. Indirect methods include well logs and seismic data. There are many
well logging methods for the evaluation of fractures, for example, induction logs,
the combination of sonic, neutron and density logs, gamma ray and borehole tele-
5.2 Fracture Information from the Field
Before the discussion of fractured reservoir simulation, it is necessary to under-
stand what types of fracture information are available and are given to simulator
developers. For simplicity, consider two-dimensional applications. The fracture
information of an oil field given by geologists or reservoir engineers are in terms
of straignt line segments. The permeability of each fracture is given or estimated
from its width. It is not uncommon that the width of fractures are never known.
An example data set of a fractured domain Q is given as follows. The domain
with fractures is shown in Figure 5.5. The matrix permeability tensor is given as
a function of the location, that is
km = km(x) (5.1)
where m stands for rock matrix or simply matrix and x E Q. Fracture properties
are given in Table 5.1. The location and orientation of each fracture is defined
Figure 5.1: Cross-section view of a fault.
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Deo, Milind D. On-line Optimization-Based Simulators for Fractured and Non-fractured Reservoirs, report, August 31, 2005; Utah. (https://digital.library.unt.edu/ark:/67531/metadc877059/m1/76/: accessed May 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.