Influence of Ordovician carbonate reservoir beds in Tarim Basin by faulting

Abstract

The quality of the Ordovician carbonate reservoir beds in the Tarim Basin is closely related to the development of secondary pores, fractures and cavities. Karstification is important in improving the properties of reservoir beds, and karstification related to unconformity has caught wide attention. Compared with the recent research on the unconformity karst reservoir bed improvement, this paper shows a new way of carbonate reservoir bed transformation. Based on field survey, core and slices observation, transformation of Ordovician carbonate reservoir beds by faulting can be classified into three types: (1) Secondary faults and fracturs generated by faulting improved carbonate reservoir bed properties, which were named the Lunnan or Tazhong82 model; (2) upflow of deep geothermal fluids caused by faulting, with some components metasomatizing with carbonate and forming some secondary deposit, such as fluorite. It can improve carbonate reservoir bed properties obviously and is named the Tazhong 82 model; and (3) the faulting extending up to the surface increased the depth of supergene karstification and the thickness of reservoir bed. It is named the Hetianhe model. Transformation effect of carbonate reservoir beds by faulting was very significant, mainly distributed on the slopes or on the edge or plunging end of the uplift.

Fluid mixing induced by hydrothermal activity in the ordovician carbonates in Tarim Basin, China

“…Both deep‐seated faults and up‐reaching faults have been formed during the hydrothermal event (Lü et al . ), which may have brought deeper high saline water and meteoric water into the Ordovician strata in the Tarim Basin, resulted in fluid mixing and hydrothermal mineral precipitation. Fluorite and calcite samples, associated with the hydrothermal calcite, dolomite, anhydrite, and barite, show relatively lower homogenization temperatures (<120°C) with salinities much lower than the coexisting hydrothermal minerals in the NW Tarim area (Fig.…”

“…), as well as an increase in the depth of karstification (Lü et al . ). Thus, fluid mixing during the Permian hydrothermal activity in Tarim Basin was a complicated chemical and physical process, which not only altered the hydrocarbon properties (Xing & Li ) but also significantly affected the reservoir porosity (Lü et al .…”

Depositional architecture of the late Ordovician drowned carbonate platform margin and its responses to sea-level fluctuation in the northern slope of the Tazhong region, Tarim Basin

“…The large-scale architecture of carbonate platforms and shelves is controlled by the interplay between the relative sea-level change and the growth rate of carbonate rocks (Eberli et al, 2004). Repeated exposure and the associated diagenetic changes of carbonate platforms have a major impact on porosity evolution and reservoir quality (Vahrenkamp et al, 2004;Lü et al, 2008;Zhang and Liu, 2009).…”

Simulation of 3D karst conduits with an object-distance based method integrating geological knowledge

“…These networks actually play a major role in the flow regime of most carbonate aquifers and reservoirs [e.g., Lü et al, 2008, Chaojun et al, 2010: their conduits act as preferential flow paths and concentrate the fluids. As conduit shapes result from a complex dissolution process [e.g., Ford and Williams, 2007], a straightforward modelling approach of fluid flows would represent karstic conduits as equivalent to cylindrical tubes.…”