Tight oil accumulation of the redeposited carbonates in the continental rift basin:A case study from Member 3 of Shahejie Formation in Shulu sag of Jizhong depression,North China

Tight oil in the redeposited carbonates was mainly distributed in the Lower Submember of Member 3 of Shahejie Formation in Shulu sag of Jizhong depression,North China.Through high-resolution 3D seismic data,well logging data and drilling data,the Lower Submember of Member 3 of Shahejie Formation was divided into 5 third-order sequences and 15 parasequence sets.The redeposited marl and rudstone were major reserving horizons of tight oil,and ten reserving space types were developed and could be classified into two main categories,i.e.,pores and fractures.Two types of tight oil reservoirs were established,i.e.,the marl hydrocarbon reservoir of the source-reservoir integration and the rudstone hydrocarbon reservoirs of the source-reservoir paragenesis.The assemblage relationship among the high-quality source rocks,system tracts with the source-reservoir configuration was the major control factor for tight oil accumulation in the redeposited carbonates.The lacustrine transgressive system tracts and highstand systems tracts in SQ1 to SQ5 were the favorable horizons for development of the marl hydrocarbon reservoir,the lowstand system tracts in SQ1 to SQ3 were the favorable horizons for development of the rudstone hydrocarbon reservoir.

Space-Time Evolution and Controlling Factor of Fine-Grained Sediments in the Upper Fourth Member of Shahejie Formation, Dongying Depression

Fine-grained rocks（FGR） are the important source rocks and reservoirs of shale hydrocarbon which is the prospect hotspot at present. Widely distributed fine-grained sediments（FGS） of the upper fourth member of Shahejie Formation in Dongying depression are taken as an example to study the space-time evolution and controlling factor of FGS in this paper. Based on the analysis of well cores, thin sections, inorganic and organic geochemistry indicators, FGR are divided into 7 types of lithofacies. Through the study of ‘point-line-plane＇, this study shows that FGS has the characteristics of rhythum, diversity and succession. The first stage is characterized by clayey FGS（massive claystone）. The second stage is characterized by carbonate FGS（low-TOC laminated limestone） and dolomitic FGS（dolomitic-silty shale） formed by transgression. The third stage is characterized by organic-rich carbonate FGS（middle/high-TOC laminated limestone） distributed in cycle. The fourth stage is characterized by FGS mixed carbonate and siliciclastic sediments（calcareous-silty shale）. A variety of space-time evolution of FGS are controlled by multiple factors including tectonism, climate and lake conditions.

Syndepositional Fault Controlling on Depositional Filling of the Third Member of Shahejie Formation in Beitang Sag

In the continental lake basin whose structures were extraordinarily active, tectonism is an important factor in controlling the sequence and the depositional filling of the basin. This article reports the assemble patterns of syndepositional fault in the third member of Shahejie （沙河街） Formation in Beitang （北塘） sag. The results show that the comb-shape fracture system and the fracture transformation zone were developed in Beitang sag. These assemble patterns obviously controlled the sand-body and spatial distribution of sedimentary system. However, the steep slope belt of fault terrace, the multistage slope belt and the low uplift gentle slope belt controlled the development of sequence styles. Analyses of the spatial-temporal relationship of the assemble pattern of syndepositional faults and the sedimentary system help predict the favorable exploration zone.

The important turning points during evolution of Cenozoic basin offshore the Bohai Sea:Evidence and regional dynamics analysis

The Cenozoic basin offshore the Bohai Sea underwent a multicycle-rifting during its evolutionary process, which resulted in the multiple unconformities in the strata. The tectonic activities shown by these unconformities have different manifestations and influences on the basin evolution. The authors systematically analyze the tectonic evolution characteristics of the sags off-shore the Bohai Sea with a large set of hydrocarbon exploration data. The analysis reveals that two phases of tectonic activities during the late depositional stage of the third member of Shahejie Formation (about 38 Ma) and the late depositional stage of Dongying Formation (about 24 Ma) reflect the significant changes in the basin's features and structural framework before and after these tectonic activities. As a result, the two phases of tectonic activities are recognized as important turning points (i.e., tectonic transitions) of Cenozoic basin evolution. The regional dynamic backgrounds of the two phases of tectonic transitions are also discussed. It is suggested that the early tectonic transition occurred at about 38 Ma under such regional dynamic back- ground that a huge kinematics adjustment happened between Eurasian Plate and its neighboring plates, i.e., Pacific Plate and Indian Plate. Meanwhile, the Tan-Lu Fault's slip reversed from left lateral to right lateral. The late tectonic transition occurred in late Paleogene (about 24 Ma) and reflected the Himalayan orogeny's influence on the Chinese continent and even the Asian continent; at the same time, the stress field produced by the escape tectonics was related to the Himalayan orogeny, superposed on the pre-existing stress field, and then enhanced the right lateral slip activity of the Tan-Lu Fault.