Jw. Dudley et al., MEASURING COMPACTION AND COMPRESSIBILITIES IN UNCONSOLIDATED RESERVOIR MATERIALS BY TIME-SCALING CREEP, SPE RESERVOIR EVALUATION & ENGINEERING, 1(5), 1998, pp. 430-437
A testing procedure and analysis method is proposed that gives compact
ion and compressibility data that are independent of test duration for
unconsolidated sands. Compaction data on unconsolidated sand material
[including several Gulf of Mexico (GOM) reservoirs] derived from this
method are presented. Tests on twin plugs give essentially the same s
tress-strain data for test durations from one day to three months. Thi
s occurs because of a fundamental time-scaling property of these uncon
solidated materials. The creep behavior is modeled with a fractional p
ower law dependence with time, which represents the Voigt material mod
el having an extremely broad distribution of relaxation times. This an
alysis indicates that the characteristic relaxation times of these mat
erials are measured in decades or longer. Creep equilibrated tests are
, therefore, impractical and not relevant to a reservoir that will be
depleted in one or two decades. Analysis of the power law creep parame
ters indicates the creep behavior is consistent at higher stresses amo
ng the materials tested. The creep parameters scale with stress and pr
ovide a means of decoupling the time-dependent behavior from the stres
s-strain behavior.