Shiyou shiyan dizhi (May 2022)
Influence of geothermal field on ultra-deep Ordovician oil and gas in Shunbei field, Tarim Basin: a case study of Shunbei No. 5 strike-slip fault
Abstract
The types and properties of the ultra-deep Ordovician oil and gas resources in the strike-slip fault zone of the Shunbei oil and gas field in the Tarim Basin show regular changes. The main controlling factors of oil and gas distributional characters are unclear, which restricts the evaluation of resource types and exploration sequences. To study the consequences of the thermal field on oil and gas, the statistical analyses of the current measured temperature of the Shunbei No. 5 fault zone, the restoration of the thermal history[JP] of the key accumulation period, the thermal evolution of the source rocks, and the Ordovician oil and gas properties and maturity are carried out. Results show that present geothermal field in the Shunbei area has a vertical gradient gradually decreasing from shallow to deep, and the present geothermal temperature as well as the paleotemperature of key accumulation period of the source rocks of the Cambrian Yuertus Formation gradually increase from north to south. With the background of ultra-deep low geothermal gradient, the temperature of the Shunbei Ordovician ultra-deep reservoir did not reach the cracking temperature point for large amounts of crude oil, which provided favorable conditions for the preservation of liquid oil. In the critical accumulation period, the late Hercynian, the thermal evolution degree of the local Cambrian Yuertus Formation source rocks gradually increases from north to south. Since high pressure inhibited the evolution of hydrocarbon generation, the northern and middle segments of the Shunbei No. 5 fault zone are mainly oil-generating, while the southern segment is condensate-gas-generating. The evolution products are in good consistency with the current Ordovician ultra-deep oil and gas reservoir types, crude oil density, natural gas drying coefficient, production gas/oil ratio, and the plane distribution characteristics of oil and gas thermal evolution degree, indicating that the thermal evolution difference of source rocks under the control of geothermal field is the main factor affecting the distribution of resource types and oil and gas properties.
Keywords
