Search Results (3)

In recent years, the successful application of gravity-flow deposit theory in major petroliferous basins in China had attracted extensive attention in the field of sedimentology and had become a key research frontier. This study utilized core, drilling, logging, and microphotograph data, along with low-temperature nitrogen adsorption and high-pressure mercury injection experiments. It discussed the characteristics of gravity-flow deposits, sedimentary microfacies, sedimentary models, and the significance of gravity-flow deposits to pore heterogeneity in shale reservoirs, focusing on the first submember of the Dongyuemiao Member (referred to as the Dong 1 Member) in the Fuling area of the Sichuan Basin. The results indicated the development of four types of mudrock in the Dong 1 Member: massive to planar laminated shell mudrock (F1), planar laminated bioclastic mudrock (F2), planar laminated silty mudrock (F3), and massive mudrock (F4). These corresponded to debris flow deposits (F1, F2), turbidite deposits (F3), and suspension deposits (F4). According to the characteristics of lithofacies combinations and sedimentary features, four sedimentary microfacies were identified: gravity-flow channel, tongue-shaped, lobate, and semi-deep lake mud. The Shell Banks were disturbed by earthquakes, tides, storms, and other activities. Silt, clay, fossil fragments, plant debris, and other materials were deposited under the influence of gravity, mixing with surrounding water to form an unbalanced and unstable fluid. When pore pressure exceeded viscous resistance, the mixed fluid became unbalanced, and gravity flow began to migrate from the slope to the center of the lake basin. A sedimentary unit of gravity-flow channel-tongue-shaped-lobate was developed in the Fuling area. The Fuling area’s gravity-flow depositional system resulted in distinct microfacies within the Dongyuemiao Member, each exhibiting characteristic lithofacies associations. Notably, lobate deposits preferentially developed lithofacies F3, which is distinguished by significantly higher clay mineral content (60.8–69.1 wt%) and elevated TOC levels (1.53–2.45 wt%). These reservoir properties demonstrate statistically significant positive correlations, with clay mineral content strongly influencing total pore volume and TOC content specifically enhancing mesopore development (2–50 nm pores). Consequently, the F3 lithofacies within lobe deposits emerges as the most prospective shale gas reservoir unit in the study area, combining optimal geochemical characteristics with favorable pore-structure attributes. Full article

The turbidite lobe is a significant reservoir type formed by gravity flow. Analyzing the architecture of this reservoir holds great importance for deep-water oil and gas development. The main producing zone in Z Oilfield develops a set of turbidite lobes. After more than 60 years of development, the well spacing has become dense, providing favorable conditions for detailed research on reservoir architecture of this kind. Based on seismic data, core data, and logging data, combined with the results of reservoir numerical simulation, this paper studies the reservoir architecture of turbidite lobes, displays the distribution of remaining oil in the turbidite lobes, and proposes development policies suitable for turbidite lobe reservoirs. The results show that the turbidite lobes can be classified into four sedimentary microfacies: lobe off-axis, lobe fringe, interlobe facies, and feeder channel facies. The study area is mainly characterized by multiple sets of lobes. There are feeder channels running through the south to the north. Due to the imperfect well pattern, the remaining oil is concentrated near the lobe fringe facies and the gas–oil contact. It is recommended to tap the potential of the turbidite lobes by adopting the “production at the off-axis lobes facies and injection at the lobe fringe facies (POIF)”. The study on the reservoir architecture and remaining oil of turbidite lobes has crucial guiding significance for the efficient development of Z Oilfield and can also provide some reference for developing deep-water oilfields with similar sedimentary backgrounds. Full article

Gravity-flow deposits form the northern part of the Crocker Formation (Oligocene–Early Miocene), with the most significant interpretation as a sand-rich system in the proximal and a mud-rich system in the distal area of the deep-water turbidite depositional setting. Seven outcrop localities in the northern-part area were selected for mapping and sampling, starting from Kota Kinabalu up to the Telipok area to evaluate the sedimentary sequence. This study used mapping, field observation, and log sketches in the field, as well as extensive analysis and interpretation of sedimentological methods to investigate the sequence of sediment outcrops in the Crocker Formation area of northwest Sabah. During the fieldwork, five main facies were found, namely, massive sandstone facies (f1), graded sandstone facies (f2), laminated sandstone facies (f3), interbedded sandstone and mudstone facies (f4), and mudstone facies (f5). These northern-part outcrops are interpreted as being deposited from the highest to the lowest turbidity currents and the actuality of pelagic mudstone deposition, based on their fining-coarsening-upward pattern. The five geometrical bodies were proposed as laterally contiguous depositional environments, namely, (1) inner fan channel, (2) inner fan channel–levee complex, (3) mid-fan channelized lobes, (4) non-channelized lobes/distal lobes, and (5) basin plains. The facies interpretation shows that the study area consists of lobes, channel–levee complexes, and levees formed in a fan of a deep-water basin setting, with the basinal plain enveloped by thick mudstone deposits. This northern part of the Crocker Formation is interpreted as a multiple-sourced sediment, shelf-fed, Type II, low-efficiency, and sand-rich turbidite depositional system. Full article