Study On Fine Description And Remaining Oil Distribution Of Tide Dominated Delta Reservoir

The study target Zone Tarapoa is a mature oil-field put into the production in the 1970's, characterized by tide-dominated delta reservoir, lower amplitude structure, multiplex water drive mode and high water cut, in which remianing oil distribution is very complex. Detailed reservoir desription and reservoir simulation study is a key to solve the above problems.The study adopts sequence stratigrapy theory, intergrated seismic and drilling data processing, fine reservoir description techonolgy to depict the 3D distribution of the reservoir and strata as a whole. By combination of the data of the reservoir and strata, and production performance, oil-water contact relationship has been researched, and a 3D geooloical model has been built for further dynamic numerical reservoir simulation to characterize the residual oil distribution and features. The main siginificant achievements and conclusions of the study are presented as below.1. The study indicates that both micro-amplitude anticline and lateral reservoir variation control the trap formation and oil-water distribution in this region. Based on the fine stratifigraphic classification and correlation, the micro-structure and its role in remaining oil distribution have been studied.2. The study summarizes three tide-dominated delta estuarine depositional systems, including mixed-load tidal-river point bars; laterally accreting sinuous tidal channels and associated point bars; and estuarine mouth, wave-dominated, laterally accreting tidal inlets and shoals.3. The study shows that the distribution of remaining oil is controlled by the sedimentary microfacie devided from core data based on logging facies analyses. Formation M1 belongs to delta estuarine depositional model, with mirofacies of river channel, tidal channel and debouch bar, and generally characterized by normal deposition rythem. Different sedimentary microfacies have different distribution models of remaining oil. For fluvial-dominated channel sand, the remaining oil saturation is high in the main body of the river channel; and the edge of the channel is characterized with stronger water flooding and lower remaining oil saturation due to the washout of bottom-edge water. Fortide-dominated channel depositional body, the main body of the tidal channel has high remaining oil saturaton despite of high oil recovery in the region; and however, the edge of the tidal channel has been totally waterflooded. The region near the debouch bar, with higher remaining oil distribution, is the main potential zone.4. The reservoir watered-out degree depends on specific water drive mode. Based on reservoir property characterization evaluation, the logging interpretation chart of porosity, permeability, saturation and shale content for sandy conglomerate reservoir has been established. The 3D geological model, based on the concept model is built for further reservoir numerical simulation. The simulation indicates that the waterflooded degree is normally lower in the interwell region for the bottom-water dominated reservoir, and there exists lower oil-water contact interface regions; for the layered bottom- edge water reservoir, almost the whole reservoir has been waterflooded, especially in the edge and bottom region, and the interwell region also with higher waterflooded degree.5. The differential relationship equation of oil-water displacement potential with reservoir force field and saturation has been derived, which indicates the dynamic variation of the reservoir hydrodynamics system depends on reservoir drive mode, and different drive modes form different fluid potential, and the fluid potential difference controls the direction of oil-water displacement and the distribution of the remaining oil.