The characteristics and hydrocarbon-generation model of Paleogene–Neogene System saline lacustrine facies source rocks in the Western Qaidam Basin, China

Abstract

To further understand the characteristics and hydrocarbon-generation model of Paleogene-Neogene System salt-lake facies source rocks in the Western Qaidam Basin, selecting argillaceous source rock samples from the Lower Ganchaigou Formation, the Upper Ganchaigou Formation, and the Upper Youshashan Formation in the Western Qaidam Basin, relevant experimental studies have been carried out, including pyrolysis of rocks, analysis of soluble components, and simulation of hydrocarbon generation and expulsion. According to the analysis of the experimental results, the selected sample thermal evolution degree stays in the low-mature-immature stage and shows good hydrocarbon-generation ability. There was a positive correlation between chloroform bitumen "A," moderate salt content and carbonate content, and cumulative liquid hydrocarbon production. The hydrocarbon-generation peaks of the Paleogene-Neogene salt-lake facies source rocks in the Western Qaidam Basin are significantly advanced compared to the traditional model. The result clearly defines the hydrocarbon-generation model of Paleogene-Neogene salt-lake facies source rocks in the study area, which is important to direct the oil and gas exploration in the Western Qaidam Basin.

Multistage Hydrocarbon Generation of Saline Lacustrine Source Rocks in Hydrous Pyrolysis: Insights from Clay Mineral–Organic Matter Interactions

“…31,53,57 However, to our knowledge, few pyrolysis experiments have reproduced bimodal features similar to those of natural sections. 72,73 Our experimental results are consistent with the bimodal hydrocarbon generation in nature, and the SARA fractions of liquid hydrocarbons have similar evolution to that of SOM in source rocks (Figures 2 and 13), indicating that mineral−OM interactions can well explain the multistage hydrocarbon generation of saline lacustrine source rocks. In previous pyrolysis of saline lacustrine source rocks, 72,73 deionized water or anhydrous environments cannot provide the conditions for mineral transformation, and thus could not induce the SOM desorption at low temperatures.…”

“…After considering mineral–OM interactions in hydrous pyrolysis, our experiments demonstrate a multistage hydrocarbon generation model that is different from the traditional theory of kerogen degradation, especially the formation of low-mature oils at low temperatures. In the last few decades, many low-mature oils from saline lacustrine source rocks have been found in China’s eastern and western basins. ,,− As shown in Figure , chloroform A of saline lacustrine source rocks usually shows a bimodal feature with increasing depth, including a low-mature oil peak and a mature oil peak. ,, In previous studies, the formation of low-mature oils is mainly attributed to the early degradation of kerogen with low activation energy , or the significant contribution of primary SOM. ,, However, to our knowledge, few pyrolysis experiments have reproduced bimodal features similar to those of natural sections. , Our experimental results are consistent with the bimodal hydrocarbon generation in nature, and the SARA fractions of liquid hydrocarbons have similar evolution to that of SOM in source rocks (Figures and ), indicating that mineral–OM interactions can well explain the multistage hydrocarbon generation of saline lacustrine source rocks. In previous pyrolysis of saline lacustrine source rocks, , deionized water or anhydrous environments cannot provide the conditions for mineral transformation, and thus could not induce the SOM desorption at low temperatures.…”

“…The parent material of hydrocarbon generation is different at different stages. Stage I is the conversion of mineral-bound SOM to low-mature oils, which is not found in most pyrolysis experiments. , Stage II includes a sequential reaction from kerogen through polar compounds to mature oils. Stage III is the conversion of liquid hydrocarbons and residual kerogen to gaseous hydrocarbons and pyrobitumen.…”

Natural gas potential of Neogene source rocks in the Yiliping area, Qaidam Basin: Using an improved hydrocarbon generation and expulsion model based on least‐squares Monte Carlo

“…The parameter distributions of GPI o and HI o were determined according to the HI classification criteria of kerogen. Due to the similar depositional environment, the parameter distributions of θ 2 , β 2 , θ 1 and β 1 were determined by analogy with the thermal simulation analysis data of the Tertiary source rocks in western Qaidam Basin (Chen & Zhang, 2019; Song, Cao, et al, 2021; Song, Wang, et al, 2021; Xu et al, 2019). After 6000 simulations, the change in model parameters appears to be stable as the simulation time increases, indicating that the simulation results are reliable (Table 3).…”

Microbial Communities and Sulfur Isotopes of the Cenozoic Sulfurous Oil Reservoirs in the Southwestern Qaidam Basin, Western China

“…It can be structurally divided into the northern fault block, the western depression and the eastern depression. Huge natural gas resource potential has been discovered in the Qaidam Basin (Chen et al, 2020b;Guo et al, 2022;He et al, 2021;Ma et al, 2018), including the Jurassic coal-type gas at the northern margin, the Paleogene-Neogene oil-type gas in the southwest, and the Triassic biological gas in the Sanhu area (Chen et al, 2019b;Guo et al, 2018b;Li et al, 2021b;Liu et al, 2021a;Shao et al, 2022;Wang et al, 2022;Yin et al, 2021a). The natural gas in the southwest was mainly originated from four sources: oil-associated gas from sapropel-type kerogen (type I kerogen), mixed oil-associated gas, coal-type gas and mixed gas (Guo et al, 2020;Liu et al, 2013;Zeng et al, 2022).…”