Abstract
The alkaline lake source rocks of the Fengcheng Formation are developed in the Mahu Sag of the Junggar Basin. Different from traditional continental fresh water and saltwater lake source rocks, alkaline lake source rocks lack targeted evaluation criteria, and it is unknown whether their hydrocarbon generation models are consistent with traditional models. Therefore, in the present study, evaluation standards and hydrocarbon generation models of alkaline lake source rocks are discussed based on geological and organic geochemical data and a systematic summary of the geochemical characteristics of the Fengcheng Formation source rocks. The Fengcheng Formation source rocks are mainly diamictite with mixed argillaceous rock and dolomite; most total organic carbon (TOC) values range from 0.2–1.4%; and the kerogen is primarily oil-prone type II, reaching low- to high-maturity stages. Based on the types of organic matter in source rocks and the relationships between organic matter abundance parameters, the evaluation standard of alkaline lake source rocks is proposed. The Fengcheng Formation is mainly composed of good to excellent source rocks (55.5%) with high hydrocarbon generation potential. The single-peak hydrocarbon generation model of the Fengcheng Formation is similar to that of traditional freshwater or saltwater lakes, with a high hydrocarbon generation rate, two to five times that of the traditional model; its main particularity is in the formation of naphthenic crude oil from the kerogen of bacteria and algae. A new understanding of the hydrocarbon generation potential and model of alkaline lake source rocks in the Fengcheng Formation can provide support for tight oil and shale oil exploration in the Mahu Sag.
Highlights
An alkaline lake is a special type of high-salinity saline lake that contains hydrochemical lake-water carbonate
Melack et al [1] statistically analysed the biological yield of multiple alkaline lakes near the Rift Valley in Africa and found that the biological yield of alkaline lakes was 2.0–12.6 times that of rivers and freshwater lakes
The main reason for the high organic matter yield in Qinghai Lake is that water with a high pH value can take in more atmospheric CO2, can store more inorganic carbon, and can dissolve more phosphorus and other nutrients, promoting the mass reproduction of plankton [4,5]
Summary
An alkaline lake is a special type of high-salinity saline lake that contains hydrochemical lake-water carbonate. Qinghai Lake in China is an alkaline lake with a pH value of 9.1–9.4 and a high organic matter yield [3]. The main reason for the high organic matter yield in Qinghai Lake is that water with a high pH value can take in more atmospheric CO2, can store more inorganic carbon, and can dissolve more phosphorus and other nutrients, promoting the mass reproduction of plankton [4,5]. In the alkaline lake source rocks of the Green River Formation in the Ewing Basin, USA, the organic carbon distribution ranges from 0.2% to 29.6% and the common values range from 3% to 5% [2]. High-quality source rocks are developed in the Hetaoyuan Formation [7,8,9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
