The Shoal Reservoir Characteristics And The Effect Of Simulated Reservoir Volume (SRV)

The study of tight shoal reservoirs provides insides for future exploration and exploitation towards this type of petroleum play.Simulated reservoir volume(SRV)is a new reconstruction method of tight sandstone reservoir.It is very important to apply the SRV technology for the exploitation of the tight carbonate shoal reservoir in theory and practical exploitation.In this paper,the characteristics of tight shoal reservoirs were described from the micro and macro levels and the factors affecting the developing of tight shoal reservoirs were summarized.The large-size true triaxial hydraulic fracturing simulation experiments on tight shoal reservoir samples were carried out to analyze the feasibility of SRV and to reveal the regularity on crack propagation.The heterogeneity of the tight shoal reservoirs is high.Macroscopically,the lateral distribution of the tight shoal reservoirs was affected by the reefs while the vertical superimposition of which was controlled by the sea level.Microscopically,the shoal reservoirs in Bachu and Tazhong area have poor property with low porosity and low permeability,the reservoir space are mainly pore,dissolved caves and fractures,the types of throat mainly include pore-shrinking throat,sheet throat and networked throat.The development of the shoal reservoirs was influenced by microfacie,sequence stratigraphy and diagenesis.The favorable reservoirs mainly developed in lowstand system tracts(LST),highstand system tracts(HST)and the top of meter-scale cycles.The dissolution,silication and dolomitization are the chiefly constructive diagenesis while the cementation and compaction-pressure solution the main destructive diagenesis of the reservoir in Tazhong area.The bioclast intraclast grainstone is the favorable sedimentary facies.The large-size true triaxial hydraulic fracturing simulation experiments on tight shoal reservoir samples were carried out.and fracture networks were formed after fracturing,demonstrating that the tight intra-platform shoal reservoirs have good fracturing capability.Low-field NMR analyses were conducted before and after hydraulic fracturing on samples collected at the same location;spectral lines showed that micro-fractures were more developed after hydraulic fracturing.The effect of SRV on tight shoal reservoirs depends on the coupling function of natural fractures and ground stress: fracture networks consist of vertical main fractures and horizontal branch cracks formed under the background of tectonic stress and a vertical principal stress slightly smaller than the maximum principal stress in the horizontal direction.Stylolite structures and calcite veins are widely distributed in tight shoal reservoirs.The experimental results indicate that both stylolite structures and calcite veins belong to the dominant fracture surface,which can be activated by hydraulic fracturing.