Search Results (3)

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 Xiaoerbulake Formation in the Tarim Basin is considered one of the most important deep to ultradeep hydrocarbon reservoirs in the world. The objective of the present study is to analyze the facies, depositional environment and reservoir quality of the Early Cambrian Xiaoerbulake Formation in the Tarim Basin through integrated analysis of 120 m of cores, 3240 m of well cuttings, wireline logs and over 1100 thin sections from 17 exploration wells. Early Cambrian Xiaoerbulake Formation deposits in the Tarim Basin were deposited on a ramp setting. The ramp was occupied by seven facies associations and ten facies types ranging from the inner ramp to the outer ramp. These facies associations include tidal flat, lagoon, high-energy shoal, sabkha, inter-shoal, low-energy shoal and open shelf. Their distribution was controlled by paleogeographic patterns, sea level changes and the paleoclimate. Reservoir quality is considerably affected by facies together with diagenetic processes, including dolomitization and anhydrite cementation. High-quality reservoirs are found in the dolograinstone of high-energy shoal environments, which are favorable exploration facies in the carbonate ramp. Their pore space types consist of interparticle pores, intraparticle pores, intercrystalline pores, vuggy pores and moldic pores, with a porosity of 1.4%–7.5%. This study will help with our understanding of the stratigraphic framework, sedimentary-facies evolution and high-quality reservoir distribution of the Early Cambrian carbonate ramp in the Tarim Basin, facilitating exploration and the production of hydrocarbons from the Xiaoerbulake Formation. Full article

Lower Cambrian Xiaoerblak Formation is one of the major exploration targets in Cambrian pre-salt Tarim Basin; however, the exploration breakthrough is restricted by insufficient understanding of its sedimentary evolution and reservoir genesis. In this paper, based on a systematic description of the outcrop in the Xiaoerblak section, northwestern Tarim Basin, some samples were selected for tests of stable carbon and oxygen isotopic compositions, strontium isotopic composition, order degree, trace and rare earth elements, U-Pb isotopic age and clumped isotope. It is found that the Xiaoerblak Formation mainly develops nine types of dolomites, i.e., laminated microbial dolomite, thrombolite dolomite, stromatolite dolomite, foamy microbial dolomite, grain dolomite, etc. According to the lithofacies associations, it can be divided into three members: Xi 1, Xi 2, and Xi 3, of which member Xi 2 is subdivided into three submembers. The characteristics of lithofacies assemblage formed bottom to top indicate that it can be described as a third-order sequence. The Xiaoerblak Formation was deposited in a nearshore shallow seawater environment characterized by high water salinity and temperature under a warm and humid climate during the Early Cambrian, giving rise to the sedimentary sequence of inner ramp lagoon, subtidal microbial mound shoal and tidal flat in the carbonate ramp setting from bottom to top. Its dolomitization occurred in the penecontemporaneous–shallow burial period when the temperature was relatively low and high-salinity seawater acted as the main dolomitizaiton fluid. The reservoir space mainly comprises primary microbial framework pores and vugs formed by the atmospheric freshwater dissolution. Reservoirs were controlled by lithofacies, high-frequency sequence boundary and early dolomitization. The research results are of great significance for presalt Cambrian lithofacies paleogeographic mapping and reservoir prediction. Full article