Dongying Depression. Complex Fault Zone, Shallow Oil And Gas Migration And Accumulation Mode

The shallow layers in Dongying sag were drilled through by many wells but with low degree of understanding. The shallow layers were tectonically crushed and sedimentation is complex. Petroleum came from the third and the fourth member of Shahejie Formation with long migration distance, complex migration path, multiple migration pattern and unclear reservoir forming rules. Based on multiple means such as geology, geophysics and laboratory techniques, under the direction of sedimentology, sequence stratigraphy, structural geology, petroleum geology, and especially the new born "meshwork-carpet"type reservoir forming theory for shallow layers, the paper studied characteristics of reservoir forming in shallow layers in Dongying sag and discussed meshwork layer that communicated with oil source, storage layer and accumulation meshwork layer from aspects of properties, types, configuration, their combination and influence on petroleum migration and accumulation. Study defined petroleum migration path, migration pattern, migration procedure and then established two migration-accumulation models with one model controlled by vertical faultage, and the other controlled by lateral sand body. The former were mainly developed in complex faulted belt in central anticlinal zone, and reservoir is featured by prolific multiple layers with convergence migration-accumulation pattern; the latter were mainly developed in slope belt, counted from the low lying area to the edge of the sag, reservoir types were in turn of low relief anticline, faulted block-faulted nose, draping structure, and unconformity with divergence migration-accumulation pattern. In a word, took shallow layer as target, by means of geology, geophysics and numerical simulation, the paper endeavored to describe precisely the complex fault belt and identify oil bearing layers thereby summed up corresponding techniques for petroleum exploration.