Search Results (5)

The Late Paleozoic strata on the northwestern margin of the Tarim Block provide valuable insights into the subduction and collision processes that formed the Southwest Tianshan Orogenic Belt. This study integrates detrital zircon U-Pb dating and sandstone geochemical analysis of the Balikelike and Kalundaer formations to examine sedimentary provenance and tectonic settings during the Cisuralian–Guadalupian Epoch in the Keping area on the northwestern margin of the Tarim Block. Three of five Precambrian detrital zircon U-Pb age populations, 2500–2300 and 2000–1800 Ma and 900–600 Ma, are likely related to the fragmentation of the Columbia supercontinent and Rodinia’s assembly, respectively. Two Paleozoic detrital zircons, 500–380 Ma, are associated with Paleozoic magmatism. Among them, ~295 Ma zircons are associated with post-collisional extension and emplacement of the Tarim Large Igneous Province. Geochemical analysis of sandstones, coupled with tectonic reconstruction, indicates a passive continental margin setting in the northwestern margin of the Tarim Block during the Silurian Period, later transitioned to a foreland basin from the Pennsylvanian to the Guadalupian Epochs. The crustal transformation from the Middle-late Devonian to Early Mississippian marked the closure of the South Tianshan Ocean (STO), involving a soft collision and significant uplift, with major orogenesis occurring in the Late Guadalupian. Five key stages are identified in the evolution of the foreland basin: (1) Middle-late Devonian to Early Mississippian initiation (remnant ocean basin stage); (2) Late Mississippian to Early Pennsylvanian early stage; (3) Late Pennsylvanian to Early Cisuralian middle stage; (4) the Late Cisuralian stage; and (5) the terminal Guadalupian stage. These findings provide new constraints on when STO closed and propose an innovative foreland basin evolution model during the late post-collisional phase from the Late Mississippian to Guadalupian. Collectively, the data advance our understanding of the tectonic processes that shaped the northwestern Tarim Block, with broader implications for Paleozoic geodynamics. Full article

The carbonate rock of the Qiulitage Formation is a significant stratum for oil and gas exploration in the Tarim Basin. To elucidate its environmental characteristics, we conducted tests and analyses of trace elements, carbon, and oxygen isotopes of the carbonate rocks of the Qiulitage Formation in the Kekeqigankake section of the Keping area. The results reveal that δ¹³C values range between −1.7‰ and 4.3‰, with an average value of 1.645‰. δ¹⁸O values fluctuate from −11.4‰ to −6‰, with an average value of −8.2475‰. Z values (paleosalinity) vary from 120.33 to 131.67, significantly exceeding 120 with an average value of 126.52, indicating a marine sedimentary environment. Paleotemperature values (T) range from 12.75 to 29.09 °C, with an average value of 21.36 °C, suggesting warm climate conditions. The Sr/Ba (3.42~24.39) and Sr/Cu (57.5~560) ratios are elevated, while Th/U (<1.32) and V/Cr (0.989~1.70) ratios are reduced, suggesting that the Qiulitage Formation was deposited in an oxygen-rich, warm marine sedimentary environment with relatively high salinity. Full article

The genesis of deep-to-ultra-deep dolomite reservoirs in the Tarim Basin is crucial for exploration and development. The Cambrian subsalt dolomite reservoirs in the Tarim Basin are widely distributed, marking significant prospects for ultra-deep reservoir exploration. Based on big data methodologies, this study collects and analyzes porosity and permeability data of carbonate reservoirs in the western Tarim Basin, specifically targeting the Cambrian deep-oil and gas-reservoir research. Through an examination of the sedimentary evolution and distribution of carbonate–evaporite sequences, and considering sedimentary facies, stratigraphic sediment thickness, fault zone distribution, and source-reservoir assemblages as primary reference factors, the study explores the macro-distribution patterns of porosity and permeability, categorizing three favorable reservoir zones. The controlling factors for the development of Cambrian carbonate reservoirs on the western part of the Tarim Basin are analyzed from the perspectives of sedimentary and diagenetic periods. Factors such as tectonic activity, depositional environment, microbial activity, and pressure dissolution are analyzed to understand the main causes of differences in porosity and permeability distribution. Comprehensive analysis reveals that the porosity and permeability of the Series2 carbonate reservoirs are notably high, with extensive distribution areas, particularly in the Bachu–Tazhong and Keping regions. The geological pattern of “Three Paleo-uplifts and Two Depressions” facilitated the formation of inner-ramp and intra-platform shoals, creating conducive conditions for the emergence of high-porosity reservoirs. The characteristics of reservoir development are predominantly influenced by diagenetic and tectonic activities. The Miaolingian is chiefly affected by diagenesis, featuring high permeability but lower porosity and smaller distribution range; dolomitization, dissolution, and filling processes under a dry and hot paleoclimate significantly contribute to the formation and preservation of reservoir spaces. In the Furongian, the Keping and Bachu areas display elevated porosity and permeability levels, along with substantial sedimentary thickness. The conservation and development of porosity within thick dolomite sequences are mainly governed by high-energy-particulate shallow-shoal sedimentary facies and various dissolution actions during diagenesis, potentially indicating larger reserves. Full article

The uplift–depression framework controls the source–reservoir assemblage. However, the exploration breakthrough is restricted by an insufficient understanding of the uplift–depression differentiation framework in the Early Cambrian Keping–Wensu area. In this paper, based on field outcrops evaluations, thin section analysis, logging data, drilling data, and 3D seismic data, Wensu low paleo-uplift was discovered in the northern Tarim Basin, and the planar distribution was demonstrated in detail, generally shown as a SW–NE trending nose structure, extending roughly 114 km in length to the southwest, about 35 km in width to the northeast, and with the overall characteristic of being high in the west and low in the east. During the Early Cambrian, the Tabei paleo-uplift evolved into the Wensu low paleo-uplift and largely died out by the Middle Cambrian, with the development of ramps and rimmed carbonate platforms. The tectonic-sedimentary evolution of the uplift–depression framework controlled the development of a set of main source rocks and two sets of large-scale effective reservoir rocks in the Lower Cambrian, constituting two sets of effective hydrocarbon accumulation in the upper and lower stratigraphic parts of the basin. Among them, the upper assemblage holds more potential for hydrocarbon exploration, and is expected to be a next strategic target area for hydrocarbon exploration of Cambrian subsalt in the Keping–Wensu area. Full article

The Lower Paleozoic carbonate reservoir in the Tarim Basin is a hotspot area for deep oil and gas exploration in China. Although the Lower Cambrian of the Bachu Uplift has not encountered industrial oil flow, rich bitumen has been found there. As the most direct trace of petroleum migration, the effective identification of bitumen is the key to studying the hydrocarbon transportation path. In this study, the Adobe Photoshop quantification (PSQ) method is used to identify the bitumen content in the Xiaoerblak Formation in Well Shutan 1, and, combined with the bitumen characteristics of the Shihuiyao section, a high-quality petroleum transverse transport layer is determined. The results indicate the following: (1) In Well Shutan 1, bitumen is mainly concentrated in the middle and upper parts of the Xiaoerblak Formation with high porosity and high permeability. (2) The shale of the Yuertus Formation in the Shihuiyao section has low hydrocarbon generation potential. However, the overlying Xiaoerblak Formation has developed multistage bituminous veins and bitumen-encapsulated gravels, which is the result of multiple instances of horizontal hydrocarbon migration. (3) After combining the bitumen characteristics of Well Shutan 1 and the Shihuiyao section, it is confirmed that there are high-quality lateral transport conductors in the middle and upper parts of the Xiaoerblak Formation, and the Subsalt Cambrian dolomite reservoir has great exploration potential. Full article