Abstract:

The Tahe and Shunbei oil and gas fields， discovered by SINOPEC， are recognized as two major oil and gas fields in the Tabei non-foreland area of the Tarim Basin （also referred to as the study area）. Both fields exhibit contiguous hydrocarbon distribution and accumulation of multilayer systems， boasting the largest areas and the highest degrees of hydrocarbon enrichment in the study area. Focusing on the Ordovician hydrocarbon reservoirs in these two oil and gas fields， we investigate their hydrocarbon properties， multiple hydrocarbon phases， hydrocarbon accumulation patterns， differential hydrocarbon enrichment， production performance， and differential fault activity. Accordingly， we explore the orderly distribution of the Ordovician hydrocarbon systems in the study area. The results indicate that the orderly distributions of hydrocarbon properties and phases in the study area are jointly controlled by the multi-source and multi-stage hydrocarbon generation and expulsion， differential thermal evolution of source rocks， long-term stable evolution of paleo-uplifts and -slopes， and the formation and evolution of reservoirs. The major hydrocarbon accumulation periods of gas and ultra-heavy oil reservoirs， orderly distribution of hydrocarbon reservoir types， and the degree of hydrocarbon enrichment in the study area are governed by multi-stage structural adjustments and corresponding multi-stage hydrocarbon accumulation. In the Shunbei area， the hydrocarbon accumulation pattern is characterized by vertical hydrocarbon transport along faults and lateral transport via lithologic carrier beds and unconformities in the eastern part of the study area， determining that hydrocarbon accumulation in this area is predominantly driven by in-situ hydrocarbon charging， exhibiting great oil column heights. The differential hydrocarbon enrichment in this area is controlled by lateral hydrocarbon adjustments and the scale of source rock-rooted fault zones under certain slope gradient. The distribution of primary hydrocarbon reservoir， principally formed during the Late Hercynian and the Yanshanian， is governed by the evolutionary characteristics of source rocks in the area. In contrast， the Tahe area manifests a hydrocarbon accumulation pattern dominated by lateral hydrocarbon transport along faults， unconformities， and fracture-cavity karst bodies. The Tahe oil and gas field largely exhibits multi-stage hydrocarbon accumulation in vertically layered and laterally contiguous reservoirs， resulting in differential hydrocarbon accumulation governed by deep-seated fault zones and paleo-uplifts and -slopes. Against the backdrop of the overall orderly hydrocarbon accumulation in the hydrocarbon-rich zones， the source rock-rooted strike-slip fault zone functions to control hydrocarbon storage， accumulation and enrichment in an orderly manner， with hydrocarbons being trapped and enriched around the migration pathways around the deep-seated strike-slip fault zone. Given the orderly distribution of the Ordovician hydrocarbon system in the study area， it can be inferred that the potential areas for reserve and production increase via all-round exploration include the circum-western margin of the Manjiaer Depression， circum-Luntai fault zone， and the circum-Awati north slope.

Key words: enrichment pattern, orderly distribution, hydrocarbon reservoir, Ordovician, Shunbei area, Tahe area, Tabei non-foreland area, Tarim Basin