MEASURING COMPACTION AND COMPRESSIBILITIES IN UNCONSOLIDATED RESERVOIR MATERIALS BY TIME-SCALING CREEP

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.