Main constrains and dynamic process of Ordovician hydrocarbon accumulation, central and western Tahe Oil Field, Tarim Basin

Abstract

Diversified types of oil and gas resources have been discovered in the Ordovician strata of central and western parts of the Tahe Oil Field, Tarim Basin. The formation contains oil in the vertical direction as a whole, and its accumulation process appeared to be extremely complicated. The dynamic process of oil and gas accumulation in the central and western parts of Tahe Oil Field were re-studied on the basis of combination of approaches including perspective of multiple reservoir-forming factors and their temporal and spatial dynamic configuration relationships, the discussion of typical reservoir profiles, thermal evolution of source rocks and consequent hydrocarbon generation history, paleo-structural evolution, hydrocarbon accumulation period and transport system, thus, a model of compound accumulation was established following an idea that paleo-structures and strike-slip faults together constrained reservoir formation and hydrocarbon generation as well as accumulation. Studies have shown that the main constrains for hydrocarbon accumulation in the study area includes the long-term hydrocarbon generation and expulsion from source rocks, multi-stage charging and accumulation and mixing transformation, paleo-structural controlling the migration and accumulation direction, vertical conduction and lateral adjustment by strike-slip faults, and multiple types of fractures and caves. The dynamic process of hydrocarbon accumulation has the characteristics of "vertical transportation, lateral accumulation, paleo-uplift controlling enrichment" in the early stage, and "in-situ hydrocarbon source, vertical migration and accumulation, and fault controlling enrichment" in the late stage. The mixed accumulation of oil and gas of different stages and different properties has created the present complex oil and gas appearance of the Ordovician strata. The heavy oil area was dominated by early accumulation, which was related to the high paleo-structures in the middle and late Caledonian periods, and the later charging was relatively weaker. The light oil area was dominated by late accumulation, mainly constrained by the vertical transport and short-range lateral adjustment of strike-slip faults. It is most developed in the NNE-trending fault zone and the intersection with the NNW-trending fault.

Keywords

• hydrocarbon accumulation period
• hydrocarbon accumulation model
• dynamic accumulation process
• ordovician
• central and western parts of tahe oil field
• tarim basin