Tracing Hydrocarbons Migration Pathway in Carbonate Rock in Lunnan-Tahe Oilfield

Abstract

Tracing hydrocarbons migration pathway is of great significance in studying hydrocarbon accumulation process and predicting hydrocarbon bearing potential of exploration targets, but it is very difficult to trace the hydrocarbons migration pathway in ancient carbonate formations due to strong heterogeneity. In this paper, a combination of geological and geochemical methods is used to discuss the hydrocarbons migration pathway in Ordovician carbonate rock of the Lunnan-Tahe Oilfield in the Tarim Basin. Deep faults and karst unconformity constitute the hydrocarbons passage framework in this area. High angle fractures caused by tectonic stress, pores and cavities formed by karstification played an important role in the connectivity and continuity of this network system. Core observation and thin-section identification revealed that the karsted holes communicating with fractures in the geologic history were the effective pathway for hydrocarbons migration in carbonate formation. The marks of hydrocarbon migration were left in these kinds of fractures and cavities, which were the direct evidence of hydrocarbon migration. The regularities of geochemical parameters of crude oil and hydrocarbon inclusion could effectively indicate the direction of hydrocarbon migration. It could be seen from the section analysis results in this paper that the features of vertical migration in a single well are apparent due to fracture communication; while in the lateral direction, the network system in which fractures and cavities are interconnected constitutes the main lateral pathway for hydrocarbons migration. Analysis results of such wells as Lunnan 63, Jiefang 127, Lunnan 39 and Lunnan 44 indicate that hydrocarbons migration direction was from bottom to top in the vertical direction and from south to north and from east to west in the lateral direction.

Distribution and Implication of Adamantane in Crude Oils in Lunnan Area, Tarim Basin in China

“…The reservoir ages involved Ordovician, Carboniferous and Triassic (Zhang et al, 2000a;2000b;Zhou et al, 2010) (Fig. 1).…”

Accumulation Mechanism of Complicated Deep Carbonate Reservoir in the Tazhong Area, Tarim Basin

“…It has become a key area for the oil and gas exploration and development in the Tarim Basin (Zhou et al, 2006). Besides, a large number of faulting types and characteristics different from those shown by 2D seismic data are discovered (Zhou et al, 2010), and the fault is closely related to the complexity of oil and gas. In the Cambrian -Early Ordovician, Tazhong uplift and north depression were an integrated carbonate platform, the Tazhong area contained semi-restricted ~ open platform facies, and large sets of platform facies carbonate rocks developed in the Lower Ordovician Yingshan formation.…”

“…The Tazhong area of the Tarim Basin, an inherited palaeohigh zone, is situated at a favorable destination of oil and gas migration, where abundant hydrocarbon resources are contained. Because several sets of source rocks developed in the Tarim Basin (Zhang et al, 2005), multiple stages of hydrocarbon charge processes occurred, and frequent adjustment, reformation or even destruction took place at late stage, the phase of marine hydrocarbons in the platform basin zone of the Tarim Basin is diverse and its genesis is complex (Han et al, 2007;Lü et al, 2009;Yang et al, 2007;Zhao et al, 2009;Zhu et al, 2011b;Zhang et al, 2007;2011c;Zhou et al, 2010;Yang et al, 2010;Gao et al, 2012). Bitumen, extra heavy oil, heavy oil, light oil, condensate oil and natural gas coexist, leading to the mixed color of crude oil (Zhu et al, 2012d).…”

Characteristics and Enrichment Factors of Supergiant Lower Cambrian Longwangmiao Gas Reservoir in Anyue Gas Field: The Oldest and Largest Single Monoblock Gas Reservoir in China

“…In the Precambrian in the Javier-Chroust of southern Oman, a total of 9 carbonate oil reservoirs have been discovered, with a cumulative proved natural gas recoverable reserves of 7000 × 10 8 m 3 and oil in place (OIP) of 3.5 × 10 8 m 3 (Cozzi et al, 2012;Liang et al, 2014). China has made a great effort in the exploration of Proterozoic-Lower Cambrian oil or gas and has discovered more than 2.28 × 10 8 t possible reserves of oil in Tazhong and 7.5 × 10 11 m 3 reserves of gas in Kuche (Zhou et al, 2010;Lu et al, 2009Lu et al, , 2011Lu et al, , 2012Jiao et al, 2013). Although a total of 138 bituminous veins as thick as 15.3 m had been discovered in the Sinian-Lower Cambrian strata in the Longmenshan area in the Sichuan Basin, showing a good hydrocarbon potential (Wang et al, 2011).…”