Sandstone Characteristics And Assessment Of Palaeocene In Lishui Sag

After years of exploration of Lishui Sag, it has been testified that this sag ownsgood potential for oil and gas resources. Currently, the storage of oil and gas that hasbeen discovered is still little. The exploration of oil and gas is also not verysuccessfully. Inspected from geology of Li-shui Sag, before the maximum floodingsurface period of the E1m, controlled by Lingfeng fault, the Yandang and Linanmovement, there are many different sizes mountains in Lishui sag, and the topographyis complex. The complex topography makes the deposition varied, hence, makesreservoir evaluation and favorable reservoir prediction difficult. Previously, manyresearches, such as structure, deposition, sequence, reservoir characteristics,diagenesis, hydrocarbon accumulation and so on, have been carried out. Although, asthe geology of the study area is complex, the results are not uniform, and itsapplicability can not fit the whole study, the previous studies provide many resources,which help me to research the reservoir characteristics and evaluation of Lishui Sag.The studied layer is Paleocene strata of Lishui Sag. During the research, manyresources have been used, such as geology resources, well logs and seismic data, thinsection, X-ray diffractions, petrophysical parameters and intrusive mercury curves,supplementing the casting thin section and scanning electron microscopy observing.First, I carried out assaying reservoir characteristics, pore structures and diagenesis.Second, I analyzed the factors that affect the quality of reservoirs. Then, I executedreservoir classification and evaluation. Last, I predicted areas of favorable reservoir.From this paper, conclusions as followed can be drawn:(1)The stratigraphic sequence can be divided as follows: the Paleocene is dividedinto5third sequences, from bottom up are SⅢ1, SⅢ2, SⅢ3, S Ⅲ4, S Ⅲ5in sequence.These sequences are subdivided into11system tracts, in which S Ⅲ4is subdividedinto3system tracts, the rest are subdivided into2system tracts respectively.(2)The whole pattern of Lishui sag is a process of evolution that the inland rift lake basin changes to intra-continental rift basin, then changes to inland lake basin. Interms of the sedimentary systems, in the west of the study area, which sedimentarysources are supplied by the Zhemin uplift, always deposits delta beach bars. And inthe east of the study area, which sedimentary sources are supplied by the Linfengburied hill and Yandang bulge, always deposits slope aprons and delta fans.(3)The maturity of sandstones of Lishui sag is low. And the sandstone maturityof reservoirs of E1m is higher than that of E1l and E1y. The sandstones of the westarea of Lishui sag are mainly made of medium and fine sandstones. Especially,sandstones are mainly of feldspar lithic sandstone and lithic sandstone. Andsandstones of the east area are mainly made of fine sandstone. The types ofsandstones are decentralized and the composition of debris is complex.(4)Diagenesis strongly controls the reservoir properties of the studied area,especially the compaction diagenesis and carbonate cements. Hence, the strength ofthe compaction of the west is stronger than the one of the east. The erosion iscommon the feldspar, lithic dissolution. The reservoirs’ diagenetic stages of thePaleocene are mainly in the middle diagenetic A stage, where part of the shallowdepth are still in the early diagenetic B stage.(5)The porosity and permeability of reservoirs are low, the porosity is small, thethroat is thin, and the physical property is bad. The pores are consisted of original andsecondary pores. And the remaining original pores are the mainly pores. The physicalproperty of the Lishui western reservoirs is better than one of the Lishui easternreservoirs. Reservoirs of the lower E1m group are of a good physical property.(6)The classification standard of reservoirs has been established, whichsubdivides the reservoirs into I, II, III three categories. The sandstones with goodqualities mainly develop in E1m1-HST、E1m2-HST、E1m2-LST, which are alwaysdeposited in meandering sands, shoreface, shoreface beach and bar and slope apron.