| The Linnan region, located in the north of Xiaokou fault and the south of Yingzijiefault, is the favorable migration and accumulation district in Linnan sag. The totalexploration area is approximately 1000km2. With the development of exploration, thelower part of the third member of Paleogene Shahejie Formation is gradually becomingthe key point. In this article we focus on the study of the sequence stratigraphy,sedimentary facies and reservoir characteristics of the lower part of the third member ofPaleogene Shahejie Formation based on cores, well-logs, and formation test dataincluding the thin sections and cast thin sections, observation of scanning electronmicroscope (SEM), pressured-mercury testing and X-ray diffraction analysis of clayminerals.The stratum of the lower part of the third member of Paleogene Shahejie Formationcan be divided into two sequences. Sequence one can be further divided into threesystems tracts: the lowstand systems tracts composed of three parasequence sets, thetransgressive systems tracts composed of two parasequence sets and the highstandsystems tracts composed of four parasequence sets. Sequence two only has the lowstandsystems tracts which consist of five parasequence sets in the target layer. Within thesequence stratigraphic framework, the sedimentary facies are studied. Sequence one, thelake was in the initial development stage and the water body was unstable. Theflood-overlake depositional system, involving the mud flat, sand flat, mixing flat and theflood channel mainly developed. Sequence two, the lake basin became more stable, thesedimentary facies changed to the delta front and incised valley in which containedmicrofacies of the underwater distributary channel, the channel mouth bar, the distal bar,the interdistributary estuary, the incised valley channel, the channel levee and the channeloverflowing. The favorable sand mainly deposited in microfacies of the sand flat and theflood channel in sequence one and the underwater distributary channel, the channelmouth bar and the distal bar in delta front and incised valley channel in sequence two. Onthe contrary with the isolated channel sand strips, the sand body deposited in sand flatand delta front displayed good continuous distribution. The reservoir characters and its controlling factors were also researched using thinsections, SEM, mercury intrusion and so on. Lithic feldspathic and feldspathicsandstones are chief rock types in the study area. The main cementation types are theporous cementation and mosaic cementation and the diagenesis had a magnificent impacton reservoir properties. Eight pore types including primary intergranular pores, theintragranular dissolved pores, the intergranular dissolved pores, the molded pores, thecement dissolved pores, the overgrowth quartz intergranular pores, the gaps along theparticles and microfractures are identified in the target layer. The secondary pores are themain pore type. By analyzing physical materials, it can be seen that the porosity andpermeability had strong heterogeneity. In general, reservoir physical properties are underthe control of the microfacies and the diagenesis. The influence of the sedimentarymicrofacies primarily reflected on the controlling of the lithological type, involving thefine-grained clastic sediments and the coarse-grained clastic deposition. For thefine-grained clastic reservoir, it is mainly controlled by the diagenesis. The calcareouscementation of the sandstone's top and bottom result the reservoir heterogeneity andreduce the porosity and permeability. Whereas the dissolution can increase the reservoirporosity and make reservoir properties improved. For the coarse-grained clastic reservoir,the matrix content is the main controlling factors. The matrix-supported channelsandstones display bad properties, and the grain-supported sandstones are better. All inall, the whole research has an important theoretical and guiding significance for thefurther exploration and development of the study area.
|
PDF Full Text Request