4D SEISMIC AND ROCK PHYSICS MODELING RESPONSES TO RESERVOIR STEAM FLOOD

摘要

Time Lapse (4D) seismic and Rock Physics model was constructed in Melati oil field on central Sumatra Basin to monitoring and tracking steam flood and production related changes in the reservoir. A model of the reservoir steam flood was constructed for a pattern steam flood in Area X of the field. The model was based on a geostatistical geological model and populated with temperature and porosity. Pressure and saturation properties were added to provide the necessary input for seismic modeling. Through a rock physics model based on the core analysis of the field, the elastic properties (Vp, Vs and density) were determined from the reservoir properties. These elastic properties were used to determine the seismic response of the model with and without steam. The results indicated that from the rock physics modeling using Gassmann equation, steam injection decreases the V_p by an average of 20-25% in the reservoir sands. Rock physics analysis also show that shear velocities are also sensitive to steam injection, with an average decrease of 12%. However, the Gassmann calculation results show that V_s is insensitive to steam injection. This discrepancy is probably caused by Gassmann's assumptions that no chemico-physical interactions exist between the rocks and pore fluids. Time shifts in seismic modeling events provided an indication of the presence of steam in the overlying reservoir. The relationship between time shift and steam thickness was strong for thick steam, but it was not possible to distinguish thin steam zones from thick hot oil zones solely on the basis of time shift. At the same time, tuning betweenrnthe steams related and geologically related seismic events influenced seismic amplitudes. It appears that a combination of attributes is necessary to resolve the effects of steam on the 4D seismic data acquired over the field.