Evaluation of the Oil-Bearing Properties of Shale and Shale Oil Mobility in the Fengcheng Formation in the Mahu Sag, Junggar Basin, Northwest China: A Case Study of Well Maye-1

Abstract

Due to an increasing energy demand and the depletion of conventional oil, there is ever increasing demand for unconventional shale oil and gas resources. As the most hydrocarbon-rich sag in the Junggar Basin, the development prospects for shale oil in the Mahu Sag have become a focus of research. However, so far, there have been few studies of the oil-bearing properties of shale and shale oil mobility in the sag. This paper redresses this using a range of methods, such as pyrolysis and multi-temperature step pyrolysis. The results show that the Fengcheng Formation shales are generally good quality source rocks. The main body of the shale is low mature-mature, and the type of organic matter is mostly Type II kerogen. In the depth intervals at 4616.45~4640.30 m, 4661.25~4695.20 m, 4728.30~4759.80 m, 4787.60~4812.30 m, and 4876.70~4940.25 m, the oil-bearing properties of the shale and shale oil mobility are good, with an average S 1 of more than 1.5 mg/g, OSI of more than 100 mg/g.TOC-1, a ratio of free/adsorbed oil ( S 1 − 1 + S 1 − 2 / S 2 − 1 ) of more than 3, and a ratio of free/total oil ( S 1 − 1 + S 1 − 2 / S 1 − 1 + S 1 − 2 + S 2 − 1 ) of more than 80%. The second member (P1f2) and the lower part of the first member (P1f1) of the formation offer the most promising commercial prospects. Shale oil mobility in the formation is greatly affected by the abundance of organic matter. The higher the TOC value, the greater the hydrocarbon generation capacity, and the better its adsorption capability in the shale. The Fengcheng Formation shale is mature, and shale oil mobility is good. Impacted by the main reservoir space, the felsic shale in the formation has optimal shale oil mobility, with the shale oil being characterized by self-generation and self-storage, and accumulation in adjacent layers.

Distribution characteristics of organic matter in the Fengcheng Formation in Mahu Sag, Junggar Basin: implications for hydrocarbon generation model in alkaline lacustrine deposition

“…Based on the results summarized from previous studies (Chen et al, 2016;Gao et al, 2018;Xiao et al, 2021;He et al, 2022;Hou et al, 2022), the TOC content of the source rocks in the Fengcheng Formation ranges from 0.03% to 4.17%, with an average of 0.96%. The S 1 +S 2 values of the source rocks range from 0.15 mg/g to 29.56 mg/g, with an average of 5.63 mg/g.…”

“…(B) Classification of organic matter types in the Fengcheng Formation. (Data are sourced fromChen et al, 2016;Gao et al, 2018;He et al, 2022;Xiao et al, 2021).…”

Occurrence Mechanisms of Laminated-Type and Sandwich-Type Shale Oil in the Fengcheng Formation of Mahu Sag, Junggar Basin

“…NMR can obtain the relaxation time spectrum of fluids in different pores, whereas the reliability of identifying different occurrence states must be further verified. Meanwhile, micro-nano CT scan visually presents the three-dimensional occurrence states of fluids, but the fluid identification standard is somewhat empirical. , Multitemperature pyrolysis experiments reveal shale oil occurrence states, but the calculation of free oil content must consider the loss of light hydrocarbons, which is difficult to accurately recover …”

“…34,35 Multitemperature pyrolysis experiments reveal shale oil occurrence states, but the calculation of free oil content must consider the loss of light hydrocarbons, which is difficult to accurately recover. 36 Overall, direct characterization methods can directly show the occurrence characteristics of shale oil, but their applications in quantitative characterization are limited. In comparison, indirect characterization methods can quantitatively characterize but cannot intuitively show the distribution characteristics of shale oil.…”