Paleoenvironment and organic matter enrichment of the Carboniferous volcanic-related source rocks in the Malang Sag, Santanghu Basin, NW China

Abstract

Volcanic activity was quite frequent during the deposition of the Late Carboniferous Ha’erjiawu Formation in the Santanghu Basin. The petrology and organic and inorganic geochemical indicators were used to investigate hydrocarbon potential, paleoenvironmental conditions and organic matter enrichment of the mudstones. The results show that the oil generation capacity of the Ha’erjiawu Formation mudstones, which has abundant oil-prone organic matter (Type II kerogen with hydrogen index values mainly ranging from 250 to 550 mg HC/g TOC) in mature stage (Tmax values mainly ranging from 435 to 450 °C), is considerable. The Ha’erjiawu Formation was deposited in a dysoxic, freshwater-mildly brackish, and warm-humid environment. During its deposition, the Ha’erjiawu Formation received hydrothermal inputs. The volcanic hydrothermal activities played an important role in the organic matter enrichment. In addition, the total organic carbon (TOC) is significantly positively correlated with the felsic mineral content, but it is negatively correlated with the carbonate mineral content and C27/C29 ratios, indicating that terrigenous organic matter input also contributed to the primary productivity in the surface water. Therefore, the formation of the high-quality source rocks in the Ha’erjiawu Formation was jointly affected by the hydrothermal activity and the terrigenous organic matter input.

Variational Reservoir Characteristics of the Wufeng–Longmaxi Formation from Different Sedimentary Region and Its Implications in Southeastern Sichuan Basin, China

“…Rock-Eval pyrolysis analysis was conducted on a Rock-Eval VI instrument, in which the shale samples were heated in a helium environment. Therein, when the pyrolysis temperature is less than 572 K, the peak area represents the free hydrocarbon S 1 (mg HC/g Rock) and the pyrolysis hydrocarbon S 2 (mg HC/g Rock) is represented by the peak area at pyrolysis temperatures around 572–1112 K during the pyrolysis process. , …”

“…Therein, when the pyrolysis temperature is less than 572 K, the peak area represents the free hydrocarbon S 1 (mg HC/g Rock) and the pyrolysis hydrocarbon S 2 (mg HC/g Rock) is represented by the peak area at pyrolysis temperatures around 572−1112 K during the pyrolysis process. 34,35 In order to identify the type of the organic matter, δ 13 C values were analyzed using a MAT 253 IRMS instrument. Additionally, an optical microscope with transmitted light and reflected fluorescence was used to identify the kerogen maceral compositions in sedimentary rocks.…”

“…Before the analysis by ICP-MS, hydrofluoric acid (HF) and HNO 3 were used in a two-step digestion method to leave the volatile elements in the solution. 34 For this methodology, calibration of analytical results was performed using duplicate analyses and standard samples with a <2% analytical error. 42 Additionally, scanning electron microscopy (SEM) was used to identify the distribution of mineral composition, by which the sample chips were set as 1 cm × 1 cm × 2 mm.…”

Influence of Water Injection Pressure and Method on Oil Recovery of Water Injection Huff and Puff in Tight Volcanic Oil Reservoirs

“…The Santanghu Basin is an important petroleum-bearing basin in Northwest China. According to the current exploration and development results, several oil-bearing formations and various reservoir types have been developed in the basin, tight volcanic oil reservoir (TVOR) is one of them. − In 2006, the Tuha Oilfield discovered the TVOR in the Carboniferous Karagang Formation in the Malang Sag of the Santanghu Basin through drilling . Since then, the Tuha Oilfield has adopted various measures to increase the production of TVOR.…”

“…At present, there are very few reports on the research and efficient development of TVOR and even fewer studies on the WIHP of TVOR. (5) The research on the WIHP in TVOR mainly focuses on constant-pressure WIHP (CWIHP), and there are few studies on other efficient WIMs. Therefore, it is of great significance to study the WIHP oil recovery characteristics and the optimization of WIMs in TVOR by using the combined full-diameter cores that are closer to the actual reservoir and assisted by the NMR monitoring technology.…”