Characterization of paleo-karst reservoir and faulted karst reservoir in Tahe Oilfield, Tarim Basin, China

Abstract

The Ordovician carbonate reservoir is the most productive deep-earth reservoir in Tahe Oilfield and other oilfields in Tarim Basin. Exploration and production successes in recent years reveal a new reservoir type, namely faulted karst reservoirs, which is closely related to regional strike-slip faults and very different from the well-recognized paleo-karst reservoir. The paleo-karst reservoirs distribute mainly in weathering crust regions in the northern Tahe Oilfield. Their primary reservoir spaces are meter-scale caves and the fluid conduits are predominantly the unconformable surfaces. In production, paleo-karst reservoirs always have sufficient energy, therefore high productivity. The faulted karst reservoirs mainly develop in southern Tahe Oilfield, controlled by the different ordered strike slip faults and related dissolutions. Their reservoir space is smaller than which of paleo-karst reservoirs. The predominant fluid conduits in these reservoirs are the faults. In production, reservoirs along major strike-slip faults have sufficient energy, high productivity and slow watercut increase like paleo-karst reservoirs. While in areas with less strong energy, faulted karst reservoir exhibits weak productivityand rapid watercut increase, implying a rule of "big fault big reservoir, small fault small reservoir, no fault no reservoir. A comprehensive understanding of the geophysical features, distribution characteristics, reservoir property, and production behaviors of the two reservoir types will assist further exploration and production in Tahe Oilfield and other basins containing such reservoirs.

Transitions of Dissolution Patterns in Rough Fractures

“…These dissolution patterns determine how the dissolved region develops and how the permeability increases (Roded et al., 2018; Wang & Cardenas, 2017). Understanding and quantifying the dissolution patterns in rough fractures is fundamental to many natural settings and engineering applications, including the evolution of karst hydrology (Hanna & Rajaram, 1998; Kaufmann & Braun, 2000; Li et al., 2020; Lu et al., 2020; White, 2002), weathering and diagenesis of fractured rocks (Iyer et al., 2008; Wang & Al‐Aasm, 2002), dissolving pre‐existing fractures by acid‐brine in CO 2 sequestration (Elkhoury et al., 2013, 2015; Pruess, 2008; Snippe et al., 2020), and hydraulic fracturing of shales by acidizing (Morsy et al., 2013; Vengosh et al., 2014).…”

Pore Structure Characteristics and Permeability Prediction Model in a Cretaceous Carbonate Reservoir, North Persian Gulf Basin

“…Factors of Pore Structure. In general, diagenesis will continue to transform the original pore throat structure that was formed during the sedimentary period [74,75]. Because of the active nature of the minerals in carbonate rocks, the pores in the reservoir rocks can be completely changed [5].…”

New Method for Characterizing Internal Structure of Fault-Karst Reservoirs and Analysis on Acidizing Fracturing Effect: A Case Study in HLHT Oilfield, Tarim Basin, NW China

“…The concept of "fault-karst reservoir" is a great breakthrough in geological theory of fracturecave reservoirs, which provides new ideas for exploration and exploitation in marine carbonates. The concept is more and more accepted now, leading to several successful exploration [10][11][12][13][14][15]. In actual practice, the fault-karst reservoirs are divided into different types of trap for oil production.…”