Seismic reflection imaging of karst in the Persian Gulf: Implications for the characterization of carbonate reservoirs

Abstract

16Karstification positively and negatively impacts the quality of carbonate reservoirs; for example, 17 dissolution and brecciation can increase porosity and permeability, whereas cavern collapse or 18 cementation driven by post-karstification fluid flow may occlude porosity and reduce permeability. Karst 19 may also pose challenges to drilling due to the unpredictable and highly variable porosity and 20 permeability structure of the rock, and the corresponding difficulty in predicting drilling mud-weight. 21When combined, outcrop, petrographic and geochemical data can constrain the style, distribution and 22 origin of seismic-scale karst, which may provide an improved understanding of carbonate reservoir 23 architecture and allow development of safer drilling programs. However, relatively few studies have 24 utilized seismic reflection data to characterize the regional development of seismic-scale karst features. 25In this study we use time-migrated 2D seismic reflection data to determine the distribution, scale and 26 genesis of karst in a 3 km (9800 ft) thick, Jurassic-Miocene carbonate-dominated succession in the 27 Persian Gulf. We map 43 seismic-scale karst features, which are expressed as vertical pipes columns of 28 2 chaotic reflections capped by downward-deflected depressions that are onlapped by overlying strata. 29The columns are up to 2 km (6500 ft) tall, spanning the Upper Jurassic to Upper Cretaceous succession, 30 and are up to 5.5 km (18,000 ft) in diameter. We interpret these pipes formed in response to hypogene 31 karstification by fluids focused along pre-existing faults, with hypogene-generated depressions 32 enhanced by epigene processes during key intervals of exposure. Our study indicates that seismic 33 reflection data can and should be used in conjunction with petrographic and geochemical techniques to 34 determine the presence of hypogene karst plays, and to help improve the characterization of carbonate 35 reservoirs and associated drilling hazards. 36 37 Introduction 38

Seismic Characterization of Hypogenic Karst Systems Associated with Deep Hydrothermal Fluids in the Middle-Lower Ordovician Yingshan Formation of the Shunnan Area, Tarim Basin, NW China

“…Paleokarst seismic facies are extremely complex. Previously published studies provide valuable insights into seismic evidence of paleokarst facies (e.g., [23,24,37,38]). Key seismic parameters include reflection amplitude, continuity of seismic events, apparent frequency, external form, and internal reflection configuration.…”

“…Investigations of hypogenic karst systems predominantly focus on the section-or planar-view delineation of a lateral stratiform hypogenic karst system and the relevant fault system zone individually (e.g., [38,[43][44][45][46][47]). Recently acquired 3D seismic data, covering the entire study area, make it possible to investigate the seismic facies and distributions of hypogenic karst systems [23,24].…”

Three-Dimensional Geophysical Characterization of Deeply Buried Paleokarst System in the Tahe Oilfield, Tarim Basin, China

“…The underground paleokarst system can serve as an effective reservoir or oil and gas accumulation, forming some world-class oil and gas fields. Existence of examples of such fields have been reported in the Middle East [12], North America [13], and China [14][15][16][17]. Among them, the Tahe Oilfield is dominated by Ordovician carbonate karst reservoirs at a depth of more than 5500 m [18].…”

Deep Electrical Resistivity Tomography for the Hydrogeological Setting of Muro Lucano Mounts Aquifer (Basilicata, Southern Italy)

“…Seismic methods are the most suitable to delineate geological boundaries and the external geometry of the aquifer. Gravity can be used to identify large voids, such as potential sinkholes, as well as caves and major karst conduits [9][10][11][12][13][14][15]. Moreover, geoelectrical and electromagnetic methods, by determining lateral and vertical variations in subsurface electrical resistivity, are useful to identify geological and hydrogeological features, such as caves, fractures, and sinkholes, and are particularly sensitive to the presence of subsurface water [16][17][18][19][20][21].…”