Geochemistry and Organic Petrology of Middle Permian Source Rocks in Taibei Sag, Turpan-Hami Basin, China: Implication for Organic Matter Enrichment

Abstract

The Taodonggou group of Middle Permian is an important source rock in Taibei sag of Turpan-Hami basin. Due to its deep burial, drilling has only been revealed in recent years. Based on organic petrology and organic geochemistry experiments, this paper studies the organic petrology, organic geochemistry, sedimentary environment, and hydrocarbon generation potential of source rocks in Taibei sag, Turpan-Hami basin, and reveals the influence of the sedimentary environment on the organic matter abundance of source rocks. The results are as follows: (1) The organic matter of the Middle Permian source rocks in Taibei sag of Turpan-Hami basin is mainly sapropelite and exinite. The vitrinite is mainly vitrodetrinite, and the exinite is mainly lamalginiite. (2) The total organic carbon content value is 0.55–6.08 wt %, and the average value is 2.58 wt %. The PG value ranges from 0.78 mg HC/g to 30.86 mg HC/g, and the average value is 4.88 mg HC/g. Chloroform asphalt “A” is 0.046–0.8767 wt %, and the average value is 0.285 wt %. The types of organic matter are mainly III and II–III, and the R o value is 0.628–1.49 wt % (average = 0.988 wt %). The T max distribution is 329–465 °C. The average temperature is 434.7 °C, which is in the mature stage (oil window stage). The Middle Permian source rocks are mainly very good to excellent source rocks with a good hydrocarbon generation potential. (3) The source rocks are deposited in a semihumid and semiarid climate. Organic matter is input as a mixed source. The early and late stages is dominated by terrestrial higher plants. The middle stage is dominated by lower aquatic organisms, and the sedimentary environment consists of weak reduction and weak oxidation environments. (4) In the study area, the abundance of organic matter has a weak negative correlation with CPI and a positive correlation with Pr/Ph and ∑C21–/∑C22+. Under the coaction of paleoclimate, organic matter input, and redox environment, the enrichment model of organic matter with high productivity and weak oxidation environment characteristics can also form excellent source rocks. This study is of great significance and provides theoretical guidance for the exploration of deep oil and gas resources.

Mineralogical and elemental geochemical characteristics of Taodonggou Group in Taibei Sag , Turpan-Hami Basin: Implication for Source sink system and evolution history of lake basin

“…Based on the above analysis, Taodonggou Group mudstone in the study area were deposited in a warm, humid and hot paleoclimate. This result is consistent with Miao's indicator result using the biomarker parameter CPI (Miao et al, 2021),…”

“…The Turpan-Hami Basin has undergone four stages: extensional rift basin development stage, compressional foreland basin development stage, extensional faulted basin development stage, and compressional regenerated foreland basin development stage, and finally formed the current pattern of Mesozoic Cenozoic superimposed composite inland basin (Zhu et al, 2009;Jiang et al, 2015;Wartes et al, 2002;Greene et al, 2005). According to the tectonic evolution characteristics of the Turpan-Hami Basin, the Turpan-Hami Basin can be divided into three primary tectonic units from east to west: Hami Depression, Liaodun Uplift and Turpan Depression (Miao et al,2021;Fig. 1a).…”

“…According to Fig. 14 studies on organic matter input of Taodonggou Group mudstone (Miao et al, 2021), the lake basin evolution of Taodonggou Group mudstone can be classified into three stages.…”

“…In addition, the sedimentary water body is deep at this time, which is a deep lake environment of brackish water and dyoxic. Furthermore, the content of low aquatic organisms in the lake basin at this stage is low, and the input of organic matter is mainly from terrestrial higher plants (Miao et al, 2021). For this reason, a set of high-quality hydrocarbon source rocks with organic matter type III have been deposited (Fig.…”

Strata Uplift Controlled Deep Shale Gas Accumulation Modes: A Case Study from the Weiyuan Block, Sichuan Basin

“…The deep (>3500 m), ultradeep (>5000 m), and unconventional oil and gas resources can be considered important alternatives to the energy supply in China. Deep shale gas is one of the important replacement fields of growth in oil and gas reserves and production in China in the future. − When compared with shallow shale gas, the occurrence pattern of deep shale gas presents an obvious difference, and the accumulation mechanism is relatively complex. − These characteristics lead to significant differential enrichment of Longmaxi Formation shale gas, seriously restricting large-scale exploration and the next stage of deep shale gas development.…”