Early Palaeozoic carbonate reservoirs from the Yingshan Formation of Well block ZG-43 in Tazhong Low Rise, Central Uplift, Tarim Basin, NW China: geological features and controlling factors

Abstract

Marine carbonate reservoirs, as a focus of petroleum exploration and development in China, are involved with high exploration risk and prediction difficulty owing to high heterogeneity and diversity of reservoir beds. In the Tarim Basin, NW China, carbonate reservoirs host about 38% of the whole basin's hydrocarbon resources in a large prospecting area mainly distributed in the Cambrian and Ordovician rocks in central (Tazhong) and northern (Tabei) Tarim. Recently, a better understanding has been made of the karsted weathering crust at the top of the Lower Ordovician Yingshan Formation in the northern slope area of the Tazhong Low Rise, Central Uplift, Tarim Basin. As a new frontier of exploration, oil/gas distribution and controlling factors of carbonate reservoirs in the Yingshan Formation are not clearly understood. In this work, we investigated the reservoir beds and oil/gas properties in 13 wells in Well block ZG‐43 on the No. 10 structural belt in the Tazhong Low Rise, and studied hydrocarbon accumulation characteristics with seismic and geochemical data. The Yingshan Formation in Well block ZG‐43 is mainly composed of calcarenite, dolomitic limestone, dolomite, cryptite, as low porosity and low permeability reservoir beds, with fracture‐void porosity constituting the main reservoir pore space. Oil/gas is quasi‐layer distributed beneath the unconformity between the Yingshan and Lianglitag formations to a depth of 140 m. The oil in Well block ZG‐43 is condensate with low density, low viscosity, low sulphur, low resin, low asphaltene, and high wax. The gas is 87.3% methane, generally containing H2S. The oil/gas distribution pattern is oil in the east and gas in the west, and H2S content in the west is lower than that in the east. The controlling factors for hydrocarbon are multi‐source supply and multi‐phase charging, interstratal karstification, hydrothermal activity, structural location and sealing condition. A structural–lithological trap is the main type of oil/gas accumulation. Oil/gas distribution was clearly affected by strike–slip faults. Oil/gas with multi‐source supply and multi‐phase charging was controlled by favourable local palaeo‐highs, and affected by later karsting and hydrothermal activity, as well as gas invasion in the Himalayan (Cenozoic) period. Under the caprock of compact limestone in the third to fifth members of the Lianglitag Formation, oil/gas migrated up along the strike–slip fault planes, and moved laterally to both sides in a ‘T’ shape, and formed large‐scale quasi‐layer condensate gas reservoirs controlled by reservoir bed quality. Copyright © 2013 John Wiley & Sons, Ltd.

Ordovician Hydrocarbon Migration along the Tazhong No. 10 Fault Belt in the Tazhong Uplift, Tarim Basin, Northwest China

“…The early formed 10FB and 1FB have been divided into several blocks by the striking faults, i.e., ZG441, ZG46, ZG43, and ZG51 from west to east (Figure ). The NE strike–slip faults also extended down to the Proterozoic basement. ,, …”

“…There are six kinds of microfacies developing in the study area: mound, reef, slope, restricted platform, beach, and interbank sea facies . Excellent reservoir belts with grain beach and organic reef facies have been developed in the north slope of the Tazhong Uplift, which is also the best area with the advantage for hydrocarbon resources exploration potentiality of the Ordovician carbonate. ,− Due to sea-level fluctuation, nine sedimentary cycles have been developed, and the overall thickness reached about 100–300 m . The 10FB is located on the carbonate platform inner area and mainly developed organic reef and grain beach systems that are composed of oolites, intraclast limestones, and most bioclast limestones .…”

“…Faults have always been widely considered a difficult and disputed topic in petroleum geology because they influence the essence features of petroleum systems, especially the petroleum-migration process. − The Tazhong Uplift, one of the most prolific petroliferous areas in the Tarim Basin, is located in the central part of the basin . The uplift is formed with multi-episode structural movements and develops complex faults. , Faults in the uplift can be divided into two subfault systems: (1) NW-trending thrust fault system mainly includes the Tazhong no. 10 fault, the Tazhong no.…”

“…Yang et al (2012), Zhou et al (2013), Pang et al (2013a,b), and Lan et al (2014, 2015) indicated that strike-slip faults might be additional pathways for hydrocarbon migration in the Tazhong Uplift, based on the study of nitrogen-bearing organic compounds, crude oil trace elements, and carbon isotope ratios of natural gas, and suggested that the hydrocarbon charged into the Ordovician of the uplift though the intersection zones of strike-slip faults and the Tazhong no. 1 fault. ,,− …”

Hydrocarbon migration along fault intersection zone - A case study on Ordovician carbonate reservoirs in Tazhong area, Tarim Basin, NW China

“…For example, oil accumulated in the west, while gas predominated in the east. Whether large-scale lateral migration from west to east exists is still uncertain (Guo et al, 2008;Lan et al, 2014). Based on the geological setting and reservoir distribution characteristics' analyses, hydrocarbon migration process and mechanisms in the Ordovician strata of the Tazhong area were investigated by integrating geological, geophysical, and geochemical parameters.…”