Major and trace element compositions of 83 fine-grained sedimentary rocks (including 14 fine-grained sandstones, 24 siltstones and 45 mudstones) from the Zhanhua Sag of Jiyang basin in the North China Block were analyzed to investigate the effects of sedimentary processes (e.g., source provenance, mineral assemblage, grain size and chemical weathering etc.) on the bulk chemical compositions. Compared with the average upper continental crust (UCC), these rocks have higher TiO 2 , Al 2 O 3 , Fe 2 O 3 , Ba, Th, U, Nb, Ta, Zr, Hf, Y and REE, but lower SiO 2 , MnO, MgO, CaO, K 2 O, Na 2 O, P 2 O 5 , Cr, Co, Ni and Sr. From sandstones, siltstones to mudstones, there exist systematic increase in Rb, Cs, V, Cr, Co, Ni, Nb, Ta, Th, U and REE, and decrease in SiO 2 , K 2 O, Na 2 O and Ba. Such variation trends reflect a predominant role of grain size effect on the geochemistry of these sediments. K 2 O, Na 2 O, Ba, Zr and Hf positively correlate with SiO 2 and negatively correlate with Al 2 O 3 , whereas other elements generally show negative correlations with SiO 2 and positive correlations with Al 2 O 3 , suggesting that clay minerals are major hosts for most elements, while quartz and feldspar exert a dilution effect. The accessory heavy minerals exert a minor control on the bulk REE composition of the sediments, e.g., the contribution of heavy minerals (apatite, zircon, sphene, monazite etc.) to the bulk REE concentrations is less than 20%. Our results show that grain size and clay minerals are the two most important factors to control the bulk chemical compositions of the Zhanhua Sag sediments, and probably terrestrial fine-grained sediments in general.

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The main pay of Guantao Formation in GudaoField is a large-scale thick positive-rhythm channel sand oil layer. At the extra high water-cut stage, the thick oil layer is waterflooded seriously, but the top remaining oil is still enrichment due to influence of reservoir heterogeneity. The research shows that the development effectiveness of tapping the potential with vertical well is bad and the economic benefit is low [1] . If horizontal well is used, the producing degree and the recovery of the remaining reserve can be improved effectively. Among various factors of affecting development effectiveness of horizontal well, the influence of intraformational bed development is much more important. The development of intraformational bed and its control on remaining oil distribution should be understood first, then the technology policy research of tapping the potential with horizontal well was conducted in order to ensure the good development effectiveness with horizontal well. In this paper, the remaining oil distribution features under the different developmental conditions of intraformational bed are expounded in detail, the intraformational bed was divided into two kinds, developed and undeveloped; according to its developmental conditions, the technology policies of horizontal well were studied respectively, and the commensurate design criteria of horizontal well was proposed. The application of the achievements in tapping the potential of remaining oil in thick positive-rhythm oil layer during the extra-high water cut period has achieved preferable effectiveness, which provides reference for that in the same type of reservoir.

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Coarse clastic rocks of the upper Sha 4 Member in the northern Bonan Sag of the Bohai Bay Basin in eastern China are important hydrocarbon reservoirs. The deposits are tight reservoirs owing to the low porosity (less than 10%) and low permeability (less than 1 mD). Because of the strong heterogeneity, although the reserve in the northern Bonan Sag is remarkable, only 4.9% of the reserves are recovered. We have studied these tight reservoirs by linking diagenesis to sedimentary facies to help predict the distribution of high-quality tight reservoirs. Petrographic analysis is undertaken based on cores, thin sections, X-ray diffraction and scanning electron microscope, helpful to understand the impacts on tight reservoirs of sedimentary factors and diagenesis factors. Sedimentary microfacies, lithologic characteristics, reservoir property, diagenesis, and diagenetic minerals are studied. Coarse clastic rocks are deposited mainly in nearshore subaqueous fans and fan deltas. The multistage sandstones are the valid reservoirs of coarse clastic rocks and dominated by feldspathic litharenite, lithic arkose, and arkose. The reservoir property is poor principally owing to the strong compaction and cementation. Pores are composed of secondary pores and primary pores. The secondary pore, generated in the dissolution of detrital minerals and/or cements, is the major type of pores and important to porosity improvement. By linking diagenesis to sedimentary facies, it can be concluded that high-quality tight reservoirs of coarse clastic rocks of the upper Sha 4 Member in the northern Bonan Sag of Bohai Bay Basin in eastern China are associated with medium to coarse-grain sandstones, found in the middle part of underwater distributary channel deposits in fan deltas and in the middle part of underwater channel deposits in nearshore subaqueous fans, with abundant secondary porosity but low cement contents, vertically at depths ranging from 3500 to 4100 m.