No abstract

The micro-nano pore structure of conglomerate in the Lower Karamay Formation of the Xinjiang Oilfield, Junggar Basin, northern China is characterized to predict its impact on fluid reserves and seepage. Authigenic clay minerals are mainly kaolinite (67%), followed by an illite/smectite mixed layer (18%), illite (10%), and chlorite (5%). For kaolinite, pore throats between 0-200 nm are dominant, accounting for 90% of the total pore throats. For illite/smectite mixed layer, pore throats also between 0-200 nm account for nearly 80%, while pore throats between 200-500 nm only account for 15%. For illite, pore throats below 100 nm account for about 80%, while pore throats in the range of 100-500 nm only account for 20%. For chlorite, most throats are below 200 nm. The pore roundness of illite is the highest, while the pore roundness of chlorite is relatively lower. The lower limits of the dynamic and static pore throat radii are 42.128 nm and 72.42 nm, respectively. The theoretical contribution rates of the illite/smectite mixed layer, kaolinite, illite and chlorite to storage/ seepage are 60%/45.86%, 52.72%/38.18%, 37.07%/28.78% and 32.97%/26.3%, respectively. Therefore, the contribution rates of clay minerals in the study area are as follows: illite/smectite mixed layer, kaolinite, illite and chlorite.

The Yinggen‐Ejinaqi Basin (YEB) is located in the central‐southern part of the Central Asian Orogenic Belt (CAOB). Tectonically, the basin is situated at the intersection between the eastern and western CAOB, where Late Palaeozoic strata were well exposed. Hence, it offers a great opportunity to study the deep strata of the eastern CAOB. In this paper, based on extensive studies of Upper Palaeozoic field outcrops and reanalysis of associated geochemical and geochronological data in previous research, the local stratigraphic correlation is established, and the tectonic evolution, sedimentary filling, sedimentary characteristics, and petroleum system of the YEB are discussed. It is revealed that: (a) The filling characteristics of the Upper Palaeozoic strata in YEB are closely related to the closure of the Paleo‐Asian Ocean (PAO). YEB underwent subduction‐related compression during the initial extensional phase of the fore‐arc basin from the Viséan to the Serpukhovian (late Early Carboniferous). During the Bashkirian–Sakmarian interval (Late Carboniferous to Early Permian), it was in subduction‐related fore‐arc and postarc rifting phases. During the Artinskian–Capitanian (Early‐Middle Permian) times, it was in an intracontinental rifting‐depression phase. During the Wuchapingian (Late Permian), it was in an intracontinental compressional phase. Tectonostratigraphy, tectonic evolution, and hydrocarbon potential assessments of the study area show that the Zhusileng Hangwula‐Tost Ul tectonic zone (ZHTUTZ) and southwestern part of Querrshan‐Atasbogd tectonic zone (QATZ) are identified as the main prospective areas for the exploration in the YEB. (b) According to the tectonostratigraphic analysis, tectonic evolution and hydrocarbon system of Carboniferous–Permian in the YEB, the YEB has similar attributes to the basin province in western CAOB (e.g., Santanghu and Junggar basins) and eastern CAOB (Erlian, Songliao Basin). To explore commercial oil and gas in the deeper strata (Carboniferous–Permian) of the eastern CAOB basins, further tectonostratigraphic analyses and comprehensive assessment on hydrocarbon potentials are necessitated in the near future.