Hydrocarbon reservoir development in reef and shoal complexes of the Lower Ordovician carbonate successions in the Tazhong Uplift in central Tarim basin, NW China: constraints from microfacies characteristics and sequence stratigraphy

Abstract

The analyses of hydrocarbon reservoirs in the high-frequency reef and shoal facies of the Lower Ordovician carbonate successions in the Penglaiba Formation (O1P) and Yingshan Formation (O1–2Y) in the Tazhong (Katake) Uplift in central Tarim basin showed three types of hydrocarbon reservoirs: type 1 associated with synsedimentary facies, type 2 developed by hot active basinal dissolution fluids [mesogenetic fluids, geothermal/hydrothermal fluids and thermochemical sulfate reduction-related fluids] and tectonic activity, and type 3 are hypogenic–epigenetic karst reservoirs formed by meteoric and mesogenetic dissolution fluids. Porosity and permeability development in the reef and shoal facies in the highstand system tracts (HST) of the third-order sequence cycles (SQ1–SQ3) correlates well with regression peaks in O1P and O1–2Y, mostly related to multiphase tectonic activity, long-term exposure, denudation and dissolution in near-surface to shallow burial settings. The carbonate successions in the O1P and O1–2Y are composed of seventeen microfacies (MF-1 to MF-17) deposited on a shallow marine platform. Six main groups of microfacies associations (MFA-1 to MFA-6) were recognized, with each microfacies association corresponding to the transgressive system tracts and HST of SQ1–SQ4 in O1P and O1–2Y. The microfacies represent specific sedimentary environment including platform interior and platform margin deposited under particular hydrodynamic conditions. Tectonics and frequent relative sea-level fluctuation associated with rapid transgression and slow regression favored the deposition of the large-scale vertical stacking, high-frequency reef and shoal facies across the carbonate platforms in this uplift. The hydrocarbon reservoirs in this study have relatively moderate porosity and low permeability, and are somewhat potential reservoirs for hydrocarbon exploration in the Tazhong Uplift.

Carbonate Platform Reef-Shoal Reservoir Architecture Study and Characteristic Evaluation: A Case of S Field in Turkmenistan

“…Various methods for architecture analysis were used, including field outcrops measurements of modern sediments, indoor simulation experiments, and ground penetrating radar measurements [26][27][28][29][30]. However, since the morphological characteristics of the sedimentary facies architecture in the underground could not be observed directly, the core analysis, logging data interpretation, comparison of the small layers of the well profile-combined with the analysis of the prediction results of seismic data-were used to indirectly judge the architectural features of the sedimentary body [31,32].…”

Sedimentological, Diagenetic, and Sequence Stratigraphic Controls on the Shallow to Marginal Marine Carbonates of the Middle Jurassic Samana Suk Formation, North Pakistan

“…The presence of MF-1, characterized by non-laminated, unfossiliferous mudstone with dolomitized lime mud matrix, calcite-filled evaporative molds, and absence of marine biota, suggests a low-energy hypersaline deposition in a supratidal environment, possibly mudflats or tidal ponds [22]. MF-2, which comprises alternating grainstone and mudstone layers, is typically found along the edges of shoals where frequent energy shifts occur [63]. MF-3, with diagenetic dolomite rhombs and low faunal content, suggests deposition on tidal flats.…”