A New Methodology To Determine The Pre-Consolidation Stress For Evaluating The Compaction Drive In Unconsolidated Heavy Oil Reservoirs

摘要

Compaction Drive consists in the expulsion of oil due to the reduction of pore volume. Generally, unconsolidated sands display an elasto-plastic behaviour during depletion. The limit between the elastic and the plastic behaviour is called the preconsolidation stress and referred to as Pc0. As long as the effective stress is less than Pc0, the rock behaves elastically and the pore compressibility is low. If ever the effective stress exceeds Pc0, the compressibility increases significantly. In heavy oil fields of unconsolidated sand, the additional recovery due to compaction drive may be estimated between 0.5 and 1 % if the rock remains elastic during the field life and to more than 3% if the plasticity threshold is reached early. Experience has shown that it is almost impossible to determine Pc0 from laboratory tests on sand samples, mainly because of cores disturbance. TOTAL has been investigating other methods to determine this parameter. The method presented in this paper is based on : ? Laboratory tests on preserved intra-reservoir shales ? A shale compaction model derived from the critical state theory of Cam-Clay and calibrated on a normal compaction trend for shales ? Geological description of the deposition-erosion history on a basin scale.