Subsurface temperature anomalies reveal blind geothermal systems: A case study from the Aryskum Depression, South Torgai Basin, Kazakhstan

Abstract

The petroliferous Aryskum Depression, located within the South Torgai Basin, Kazakhstan, comprises several grabens up to 6 km deep, separated by horsts with more than 4 km of structural relief. Spatial analysis of reported reservoir and measured bottomhole temperatures from oil and gas wells revealed elevated geothermal gradients, ranging from 29 to 45 °C/km. An underlying active mantle plume is the main source of this anomalous heat flux. Higher gradients (>35 °C/km) are likely related to additional factors, including radiogenic heat production from granites in the basement, high thermal conductivity of the crust (including intrusive bodies), and convective heat transfer by hydrothermal fluids circulating through open faults within the highly fractured basement and sedimentary basin-fill. The overlay of basement lithotypes, faults, and reservoir-quality sands allowed for robust delineation of isotherms and prediction of geothermal reservoirs. Favorable conditions exist across the basin for both direct electricity generation with temperatures of ∼150 °C at depths of ∼4.3 km, and direct heat utilization from shallower aquifers. The study demonstrates how integration of data from various sources, in a structural and sedimentological framework, can advance exploration for blind geothermal systems in analogous basins worldwide.

English abstract from the publisher’s record of the article. The authors’ abstract, reproduced under CC BY 4.0.

Keywords

• geothermal gradient
• blind geothermal systems
• bottomhole temperature
• sedimentary basin
• Kazakhstan

In plain English

The Aryskum Depression is an oil-bearing part of the South Torgai Basin in Kazakhstan. It is made of several grabens up to 6 km deep, separated by horsts with more than 4 km of structural relief. The authors analysed reported reservoir temperatures and measured bottomhole temperatures from oil and gas wells and found elevated geothermal gradients of 29 to 45 °C/km.

They interpret an active mantle plume beneath the basin as the main source of the high heat flow. Gradients above 35 °C/km, in their view, also reflect radiogenic heat from granites in the basement, the high thermal conductivity of the crust, including intrusive bodies, and convective heat transfer by hydrothermal fluids moving along open faults in the fractured basement and basin fill.

By overlaying basement rock types, faults and reservoir-quality sands, the authors drew isotherms and predicted where geothermal reservoirs lie. They conclude that conditions across the basin favour both electricity generation, with temperatures of about 150 °C at depths of about 4.3 km, and direct use of heat from shallower aquifers.

How to cite

Milovan Fustic, Ashirgul Kozhagulova, Kamal Regmi, Dias Kadirbek, Assel Zhalgasbayeva, Mahmoud Leila, Galymzhan Yensepbayev, Yerlibek Bolat, Aidos Temirkhassov and Stephen E. Grasby (2026). Subsurface temperature anomalies reveal blind geothermal systems: A case study from the Aryskum Depression, South Torgai Basin, Kazakhstan. Energy Reports, vol. 16, 109636 (December 2026). https://doi.org/10.1016/j.egyr.2026.109636