Page 588 - Petrophysics

STATIC STRESS-STRAIN RELATION 555

-.
CASINO
RVE SRPS To REsEIIW3lR -ACTION N40 CASINO FAJLURE:
1. RL~LRVOIR FWRE PRESSURE DCCREAS= WE m mowcnow.
2 EPECTMT LOM ON RESER- ROCK WJCRWES.
a RESERVOIR ROCK IS COMPACIZD BY THE wm INCRME.
4. RADIAL STRESS INCREASES CMSINQ WEUORE INST#EIuTy.
6. CASING FAILURE WILL OCCUR UNLESS EFRCTIM STRESS (-e) IS DECREASED.
Figure 9.1. Illustration of casing failure resulting from compaction of reservoir rock.

from two different sources:

(1) laboratory measurements, which allow for direct measurements of
strength parameters and static elastic behavior with recovered core
material from discrete depths; and
(2) downhole measurements through wireline logging, which allow
the determination of dynamic elastic constants from the continuous
measurement of compressional and shear velocities.

However, it is important to remember that, because reservoir rocks
are often layered, fractured, faulted and jointed, rock masses some-
times may be controlled more in their reactions to applied loads by
the heterogeneous nature of the overall rock mass than by the micro-
scopic properties of the rock matrix. Consequently, the mechanical
properties obtained from laboratory core tests may be slightly to
considerably different from those existing in-situ. Core alteration during
and after drilling also may influence the results. Nevertheless, mechanical
properties determined under laboratory test conditions are a source of
valuable information for most projects in rock mechanics because knowl-
edge of deformational characteristics of rock is essential in locating and
extracting mineral resources, and in the design and construction of any
structure in the rock [5].

STATIC STRESS~TRAIN RELATION

Poulos and Davis developed the following analytical model of the
evaluation of the static stress-strain relation [7]. Consider a cubic rock