Small Normal Faults Research Articles

Three-dimensional structural models, evolution and petroleum geological significances of transtensional faults in the Ziyang area, central Sichuan Basin, SW China

With drilling and seismic data of Transtensional (strike-slip) Fault System in the Ziyang area of the central Sichuan Basin, SW China plane-section integrated structural interpretation, 3-D fault framework model building, fault throw analyzing, and balanced profile restoration, it is pointed out that the transtensional fault system in the Ziyang 3-D seismic survey consists of the northeast-trending FI19 and FI20 fault zones dominated by extensional deformation, as well as 3 sets of northwest-trending en echelon normal faults experienced dextral shear deformation. Among them, the FI19 and FI20 fault zones cut through the Neoproterozoic to Lower Triassic Jialingjiang Formation, presenting a 3-D structure of an “S”-shaped ribbon. And before Permian and during the Early Triassic, the FI19 and FI20 fault zones underwent at least two periods of structural superimposition. Besides, the 3 sets of northwest-trending en echelon normal faults are composed of small normal faults arranged in pairs, with opposite dip directions and partially left-stepped arrangement. And before Permian, they had formed almost, restricting the eastward growth and propagation of the FI19 fault zone. The FI19 and FI20 fault zones communicate multiple sets of source rocks and reservoirs from deep to shallow, and the timing of fault activity matches well with oil and gas generation peaks. If there were favorable Cambrian–Triassic sedimentary facies and reservoirs developing on the local anticlinal belts of both sides of the FI19 and FI20 fault zones, the major reservoirs in this area are expected to achieve breakthroughs in oil and gas exploration.

Integrated geophysical methods to constrain subsurface structures of Tulu Moye-Bora-Berecha axial volcanic complex, main Ethiopia rift: Implications for geothermal resources

The Main Ethiopian Rift (MER) is a well-known continental rift whose axial sector is characterized by the occurrence of regularly spaced silicic caldera complexes and central stratovolcanoes, interspersed with large fields of fissural basalts, small mafic scoria cones and numerous young normal faults and fissures. The Tulu Moye-Bora-Berecha volcanic complex is found in the central portion of the MER and includes the Tulu Moye geothermal prospect area. A combination of gravity and magnetic methods was used to better constrain the subsurface volcanic stratigraphy and tectonic structures. Regional and residual anomaly maps were produced from the gravity data and the magnetic data were corrected to produce anomaly and enhanced maps. A complete Bouguer anomaly contour map was produced after the necessary reduction was applied to the gravity data. Due to the geomagnetic field's dipolar nature and since the study area is in the equatorial region (<15°), the reduced-to-equator (RTE) technique was used to minimize external effects and correct the data as if the body had been laid at the magnetic equator. The anomalous source's depth was calculated using a Euler depth solution and spectral analysis approach. Joint 2D forward models on three profiles were developed using GM-SYS of Oasis Montaj software. From the interpretation of the geophysical results, the following conclusions have been reached: (1) the crystalline basement is more raised around Salen ridge and west of it; (2) the main heat source of the geothermal system appears to be a central region of the studied area near Salen ridge and is estimated to be at 4–5 km depth, (3) under Gnaro obsidian dome, the basaltic and silicic volcanic horizon is thin, and the deep-seated regional fault serves as the main conduit for the passage of hot fluid to the surface and (4) the gravity and magnetic anomaly plots, regional-residual maps and enhanced data plots all indicate towards the existence of a major geological feature-a large caldera-comprising of Tulu Moye, Bora and Berecha volcanic centers.

Imaging small geological structure in coal mines based on reflected acoustic logging of underground cross-seam boreholes

Accurate identification of small geological structures is the key and difficult point in coal mine geological survey. The reflected acoustic logging technology has the advantages of large detection range and high imaging resolution, and can realize the accurate investigation of small structural interfaces. Therefore, the idea of identifying small geological structures in coal mines by using cross-seam boreholes reflected acoustic logging is proposed. By placing acoustic logging tools in underground cross-seam boreholes, waveforms generated at coal-rock interfaces around the borehole are collected. The reflection wave information is then inverted to obtain interface images of small structures. First, COMSOL Multiphysics software is utilized to build finite element models for reflected acoustic logging in coal-bearing formations containing coal seam fractures, small normal faults, and coal seam thinning zones, respectively. Then forward modeling is conducted to analyze the spatiotemporal variation patterns of the full waveform signals and velocity snapshots. Finally, the reflected acoustic logging data is inverted to realize the offset imaging of small structures in coal mines. The forward modeling results show that: the arrival times of reflected waves varying with the source longitudinal coordinates exhibit good consistency with the interface morphology of borehole vicinity small structures. The inversion results show that: when fractures exist in the coal seam, the imaged dip angle of the fracture is 54.14°, with an error rate of 2.07% compared to the analytical model, and the imaged fracture length is 15.32 m, with an error rate of 4.57%. When small faults exist in the coal seam, the imaged dip angle of the fault plane is 70.63°, with an error rate of 1.41% compared to the analytical model, and the imaged fault plane length is 13.75 m, with an error rate of 3.03%. When thinning zones exist in the coal seam, the imaged dip angles of the upper and lower interfaces of the thinning zone are 44.61° and 57.80°, with error rates of 0.31% and 0.40% respectively compared to the analytical model. The imaged lengths of the upper and lower interfaces are 9.32 m and 18.73 m respectively, with error rates of 0.32% and 1.08% respectively. Acoustic reflection logging technology can effectively invert the locations and morphological characteristics of small structures in coal mines. This study can provide fundamental theoretical support for the application of acoustic reflection logging technology in cross-seam boreholes for identification of small structures in coal seams.

Dynamic Response of Tunnels with a Rubber-Sand Isolation Layer under Normal Fault Creep-Slip and Subsequent Seismic Shaking: Shaking Table Testing and Numerical Simulation

Tunnels may suffer severe damage when passing through an active fault in high-intensity earthquake zones. The present study aims to investigate the performance of an isolation layer composed of a rubber-sand mixture, an emerging trend in low-cost seismic mitigation studies. Based on the Ngong tunnel in the Nairobi-Malaba Railroad in Kenya, Africa, the effect of the rubber-sand isolation layer on the acceleration and strain of the tunnel lining was investigated through a shaking table test under small normal fault creep-slip and subsequent seismic shaking. The influences of the length of the isolation layer and the rubber content in the mixture were analyzed by numerical simulation. The results indicate that the isolation layer slightly reduces the acceleration response of the tunnel lining within the fault and obviously reduces the permanent strain of the invert and crown within the fault under small normal fault creep-slip and subsequent seismic excitation. The mitigation effect of the isolation layer is related to the length of the isolation layer and the rubber content in the mixture. In the case of this study, the length of the isolation layer is triple the fault width (influence range of the fault) and the appropriate enhancement of the rubber content of the isolation layer offers favorable conditions for mitigation effect, respectively.

Numerical models of normal faulting at the St. Malo anticline, deepwater Gulf of Mexico, USA

Two-dimensional, plane-strain finite element numerical models produce small normal faults similar to those formed during the Oligocene to Miocene of the salt-cored St. Malo anticline in the deepwater Gulf of Mexico. The mechanical stratigraphy used in the models was derived from well data and a rate-independent, elastic-plastic constitutive model with a non-associated flow rule was used to represent the behavior of weak, over-consolidated rocks. Motion of salt is modeled by displacing the base of the overburden from an initially flat configuration to the observed present-day geometry. Model results using dominantly vertical displacement with minor extension (2%) are consistent with observed faulting at St. Malo. Small amounts of contraction (2–5%) in the numerical model suppress normal faulting whereas 2% extension best reproduces the observed structural style. The normal faults develop during elastic-plastic bending and evolve from sub-vertical, plastic mode-I failure zones to dominantly inclined normal faults. Throws of normal faults produced by the numerical models range from 11 m to 123 m. By comparison, the throws observed in the crest of the St. Malo anticline range from 30 m to 300 m. Models only using vertical displacement develop normal faults with ≤50 m throws due to bending; these are below seismic resolution. Only models with ≥2% extension develop normal faults that would be detectible (i.e., throws ≥50 m). A constraint of all the models is that the top of the salt is not faulted. The maximum depth of normal faulting in the models is ca. 900 m below the top of the reservoir. The maximum throws at the top of the reservoir in the models are ca. 30–65 m. Initiation of the normal faults as plastic mode-I failure zones in the numerical models suggests a mechanism that could facilitate early seal breach, even without juxtaposition of stratal leak points.

Gas Hydrate Accumulation Related to Pockmarks and Faults in the Zhongjiannan Basin, South China Sea

The amplitude and coherence attributes of three-dimensional (3D) seismic data are used to confirm gas hydrate occurrence and to delineate its distribution in the Zhongjiannan basin, South China Sea. High amplitude anomalies (HAAs) are distributed above or below the regional base of gas hydrate stability zone (BGHSZ), which intersect with the bottom simulating reflectors (BSRs) or are interrupted by different types of pockmarks. The maximum amplitude attribute extracted along T1 (5.5 Ma) horizon is controlled by the widely distributed faults. The layer-bound polygonal faults (PFs) show networks of small normal faults, and the dominant orientations of PFs are similar or orthogonal to the regional tectonic faults, which provide the fluid migration pathways for gas and fluids to form HAAs. BSR shows the strong amplitude and continuous reflection where the faults or PFs can reach the BGHSZ without the influence of the pockmarks. Most of the pockmarks are related to the reactivation of faults and magmation, and some pockmarks are caused by the dissociation of gas hydrate. Around the matured pockmark, the BSR is discontinuous, and HAAs locally appear within the pockmarks. The inverted acoustic impedance profile shows obviously high values of HAAs except in pockmark zones. Partial HAAs occur above BGHSZ, and the continuity is interrupted by the pockmarks with only high values around the pockmarks. We propose that BSR, HAAs, pockmarks, and different types of faults are closely related to the occurrence and distribution of gas hydrates in the study area. This work allows us to understand the relationship between gas hydrate occurrence and accumulation with pockmarks, faults, and magmatic activities.

Geochemical Analysis of a Multi-Layer Hydrocarbon Reservoir in the Wuerhe Area, Junggar Basin

From 5000 m underground to the surface, there is a multi-layer hydrocarbon reservoir under the Wuerhe nose uplift in the Junggar Basin. Light oil, heavy oil, oil sand, and solid bitumen are found in Permian to Cretaceous strata. The normal crude oil present under heavy oil and solid bitumen reservoir can easily ignored by explorers. To effectively exploit the petroleum and bitumen mineral resources in the Junggar Basin, geochemical characteristics of crude oils in the different layers were analyzed. It is concluded that the crude oils and bitumen minerals came from Permian source rocks of alkaline lacustrine facies. Combined with tectonic movement analysis, two stages of accumulation occurred in research area. During the Indosinian Tectonic movement, the crude oil generated from Permian source rocks first migrated upwards along large faults and then accumulated in the Permian, Triassic, and Jurassic reservoirs. The crude oil of the Jurassic reservoir was seriously biodegraded and a high abundance of 25-norhopane was detected. At the end of the Yanshan movement, small normal faults were developed to connect the oil in the Triassic reservoirs to the surface. The light components of the oil in the fault system quickly volatilized and left solid bitumen minerals in the faults. Due to the plugging effect of “bitumen plug”, the oil and gas in the lower part cannot migrate upward and be damaged. Therefore, light oil-heavy oil–oil sand and bitumen minerals were formed from the bottom to the top. The research result will also have a guiding significance for oil and gas exploration in the northwest margin of the Junggar Basin.

Burial wedges—Evidence for prolonged progressive burial of the Paradox Basin salt walls—With a detailed example from Gypsum Valley, Colorado

AbstractMany Paradox Basin passive salt diapirs underwent a prolonged history (&gt;65 my) of progressive burial during the Early Triassic to Jurassic. Burial is recorded by a series of geographically limited wedge‐shaped stratal panels of diapiric roof, termed ‘burial wedges’, which partly covered the diapirs, thereby gradually narrowing them. Tectonostratigraphic analysis of the Triassic Chinle Fm. burial wedge developed on the Gypsum Valley diapir illustrates the typical features and processes associated with burial wedges. Burial wedges represent the first description of the geometry and deposition of strata deposited on a partially buried diapir. Recognition of burial wedges allows reinterpretation of Paradox Basin diapirs where large areas of the roof strata were syndepositionally folded rather than deformed in the Neogene. The observations and concepts can also be applied to the terminal histories of passive salt diapirs in other salt basins. Preserved burial wedges cover 97 km2, or 64% of the original Gypsum Valley diapir and overlie regional unconformities. Onlapping strata stack into wedge halokinetic sequences (HS). Caprock‐clast conglomerates indicate deposition on exposed diapirs. Syndepositional deformation of burial wedge strata formed small synclinal ‘microbasins’ and contractional chevron folds trending subparallel to the diapir margin. A four‐stage burial wedge model includes the following: (1) erosion of the diapir roof during formation of regional unconformities; (2) onlap and partial burial of the diapir; (3) local dissolution and possible concomitant gravity‐driven folding and (4) ongoing rotation during deposition, forming wedge HS signifying continued inflation of the top of the diapir. Post formation, the burial wedges were deformed in ways that obscure their original geometry. The most common deformation is downwarping of the burial wedge into the diapir due to dissolution or lateral movement of salt, creating an anticlinal fold that overlies the underlying diapir margin. These anticlines may be offset on small normal faults subparallel to the diapir margin. Burial wedges were faulted during later diapir breaching and solution collapse.

Mechanical Stratigraphy Controls Normal Fault Growth and Dimensions, Outer Kwanza Basin, Offshore Angola

AbstractMechanical stratigraphy controls the growth patterns and dimensions of relatively small normal faults, yet how it influences the development of much larger structures remains unclear. Here, we use 3D seismic reflection data from the Outer Kwanza Basin, offshore Angola to constrain the geometry and kinematics of several normal faults formed in a deep‐water clastic succession. The faults are up to 6.3‐km long and 1.9‐km tall and have up to 44 m of throw. Aspect ratios and lower‐tip throw gradients are greater for faults that terminate downward at a c. 100 m thick, mass‐transport complex (MTC; up to 5.2 and 0.12) than for those that offset it (up to 2.7 and 0.01). Faults that offset the MTC invariably have &gt;30 m of throw. Based on their geometric properties and throw patterns, we interpret that the faults nucleated above the MTC and propagated down toward it. Upon encountering this unit, which we infer behaved in a more ductile manner than encasing strata, tip propagation was halted until tip stresses were sufficiently high (corresponding to minimum throw of c. 30 m) to breach it. Faults with smaller throw were unable to breach the MTC. We argue that using only geometric criteria to determine fault growth patterns can mask the significant control mechanical stratigraphy has on fault kinematics. Mechanical stratigraphy is therefore a key control on the growth of large, seismic‐scale normal faults, in a similar way to that observed for far smaller structures.

Architectural characteristics and evolution sequences of different types of faults in extensional basins—evidence collected from cores in the Dongying Depression

Drilling cores taken from faults in the Bohai Bay extensional basin are investigated to identify the architectural characteristics and tectonic evolution of different types of faults in the clastic strata. Growth and normal faults divided by the diagenetic stage and fault throw exhibit varied structural characteristics. Regardless of the size of growth faults, the fault cores and damage zones are visible. Meanwhile, small normal faults primarily comprise damage zones with slip surfaces (including fractures and deformation bands). The breccias in the fault core of the growth fault rotate under the lubrication of an unconsolidated mudstone, resulting in a mudstone-wrapped state. However, the normal fault is formed in the consolidated stage of the mudstone layer, and the number of its structural breccias are mainly reduced by small faults or fractures lacking mudstone lubrication. The deformation mode directly determines the type of fault architecture and the propagation mode of the fault core. These normal faults (including vertical, flower, and conjugate fault zones) are the products of pure shear, wherein the σ1 principal stress axis is basically vertical, and they constitute a series of fractures or deformation bands without a unified main slip surface. These growth faults can form a complete fault architecture under simple shear, in which the σ1 principal stress axis is gradually inclined to a certain extent with an increase in the fault width. The difference between the two types of faults is essentially attributed to the fault core being easier to propagate under simple shear than under pure shear. In terms of structural evolution, the growth fault evolves from the original fault core with hanging-wall damage zone into a complete fault structure with a fault core and two damage zones. The normal fault is composed of the large conjugate fracture system or multiple single slip surfaces, which may form the fault core when pure shear changes to simple shear or when the displacement is large. The differences in the structural characteristics, deformation modes, and tectonic evolution of growth faults and normal faults would inevitably affect later fluid migration.

The role of tectonic inheritance in the development of a fold-thrust belt and superimposed rift: An example from the São Francisco basin, eastern Brazil

The São Francisco intracratonic basin, eastern Brazil, hosts multiple sedimentary successions younger than 1.8Ga that witnessed major plate reorganizations since its generation. During the Brasiliano/Pan-African Gondwana amalgamation, in the Ediacaran-Cambrian boundary, the western half of the basin was involved in the Brasília foreland fold-thrust belt, which propagated eastwards deforming its Proterozoic-Paleozoic strata. Lately, as the South Atlantic rift evolved giving rise to the Brazilian continental margin, the basin was affected by extensional tectonism leading to the development of the Cretaceous Abaeté half-graben. During this episode, elements related to a prominent structure of the Brasília foreland fold-thrust belt, the João Pinheiro fault, were reactivated controlling the graben architecture. Aiming to unravel the evolutionary history of the fault zone since its nucleation until its Cretaceous extensional reactivation, we conducted a structural investigation based on field, well-tied 2D seismic data, and paleostress analysis. Our study revealed that the fault represents an emergent ramp of the basal detachment of the Brasilia foreland fold-thrust belt. Formed under EW-oriented shortening, the structure exhibits a gentle recces-salient geometry in map view, which reflects variations in the detachment depth influenced by pre-orogenic rift structures. Trains of NS-trending chevron folds are abundant and their high symmetry and dominance are expressions of the control exerted by mechanical stratigraphy and low-friction basal detachment. The superposed Abaeté half-graben developed under an extensional regime with a NE-trending maximum extension. Under this condition, a stratigraphic interface along the João Pinheiro fault zone was reactivated giving rise to the graben border fault. NS- to NW-oriented preexisting bedding planes were activated as small normal faults. Although newly-formed faults are present, reactivation is the most effective mechanism of extension accommodation. Therefore, this study provides insights on the influence of tectonic inheritance on the architecture, deformation pattern, strain/stress partitioning and evolution of both extensional and compressional intracontinental systems.

Modelo geológico evolutivo e deposicional do paleocânion de Regência, região onshore da Bacia do Espírito Santo, Cretáceo ao Eoceno

O paleocânion de Regência, reconhecido em subsuperfície na Bacia do Espírito Santo, foi originado no Cretáceo e preenchido até o Mesoeoceno. Dados de 31 seções sísmicas, 29 poços e marcadores bioestratigráficos substanciaram a elaboração de modelos geológicos que aprimoram o conhecimento sobre a evolução e a morfologia do paleocânion. Os resultados incluem correlações estratigráficas, interpretações de feições estruturais e das principais superfícies estratigráficas (topos das formações Mariricu, São Mateus, Regência e Urucutuca), mapas de contorno estrutural dos topos litoestratigráficos e seções esquemáticas. Desde seu início, o paleocânion foi estruturado por falhas no embasamento. Próximo ao topo da Formação Mariricu, de idade aptiana, já há indícios de geometria de extensa calha rasa. O paleocânion é dividido pela Zona de Charneira Cedro-Rio Doce (ZCCRD), sistema de falhas normais de direção N-S. A morfologia do paleocânion também foi controlada por diversas falhas normais nos blocos proximal e distal à ZCCRD, originadas no embasamento, ainda ativas quase até o final do preenchimento do paleocânion, com direção NE-SO. Falhas normais também tiveram papel determinante na origem de um canal secundário de grande porte a sudoeste, assim como outros menores ao longo da margem norte. Na porção proximal, depósitos neocretácicos foram preservados devido a abatimento e rotação de blocos por falhas normais. Pode-se inferir que o preenchimento eoeocênico proximal foi por sedimentos da mesma fonte que aqueles acumulados no depocentro do paleocânion. Refletores sísmicos sugerem a presença de abundantes canais escavados e preenchidos na porção inferior do cânion e transição cânion acima para canais dispersos. O conjunto de interpretações é sintetizado esquematicamente por meio de um modelo geológico evolutivo e deposicional.

Paleostress field reconstruction in the western Dharwar craton, south India: Evidence from brittle faults and associated structures of younger granites

We present new fault slip data to decipher the tectonic stress regime in younger granites (2.61 Ga) of western Dharwar craton (WDC), south India. The study is based on paleostress reconstruction of the terrain using fault-slip data from the small scale oblique slip normal faults of Chitradurga granite. Paleostress analysis using Right Dihedron and Rotational Optimization methods reveal that these faults have developed under NNE-SSW directed extension. Similar results are also obtained when left-lateral and right-lateral oblique-slip normal faults are treated as separate entities. It is envisaged that all faults in Chitradurga granite have developed under a single tectonic event and are considered to be extensional shear fractures. We interpret that the oblique-slip normal faults in granite oriented along NNW-SSE to N-S (P shear), NW-SE (R shear), NE-SW (R′ shear), and WNW-ESE (T) are defined as the respective shear components of the regional riedel shear system. It developed due to sinistral movement along the Chitradurga Shear Zone (CSZ) during late D3 deformation at shallow crustal level. The fault planes act as primary or secondary shear planes, depending on their proximity to the CSZ and kinematically fit well with regional far-field compression. The present study addresses the formation of oblique slip normal faults in the Chitradurga granite and its implication in reconstructing the paleostress field in the Precambrian south Indian shield.

Extensional Structures in the Ophiolites from Cuba and China: New Constraints to Slowly‐Spreading Ancient Oceanic Lithosphere

AbstractA group of low‐angle normal faults developed in banded gabbro of Moa Ophiolite, Cuba. The dark gabbro was cut into puddings by several normal faults, while light gabbro was just swelling in layer thickness. In Hongliuhe ophiolite at eastern segment of South Tien Shan Suture Zone in China, the extensional deformation concentrates on fine cumulus gabbro which is typically mylonitized. Abundant structural features were discovered in HLH ophiolite such as S‐C foliation, C’ foliation, extensional crenulation cleavage, small toughness normal fault, low‐angle normal faults and high‐angle normal faults. According to the above tectonic phenomenon from the ophiolite belts in Cuba and China, we will get the conclusion: the maximum principal compressive stress (b1) is vertical to cumulus bedding, and the maximum tensile stress (b3) is paralleling to cumulus bedding. Considering of the above evidence, the extensional tectonic event should developed at mid‐ocean ridge. Due to seafloor spreading, the maximum tensile stress is paralleling to cumulus layer, and extensional tectonic is kept in cumulus gabbro. In this way, normal faults developed in dark gabbro, while brittle‐ductile extensional developed in light gabbro. A large number of domes, folds paralleling to ocean ridge and detachment faults represented by low angle normal fault were discovered near ocean ridge in Indian Ocean and Atlantic Ocean. In this way, materials from deep oceanic lithosphere (e.g. gabbro, mantle peridotite) outcrop at the crust surface of ocean basin. The above evidences from China and Cuba are consistent with extensional tectonic and metamorphic core complex from slowly and super‐slowly spreading Indian Ocean and Atlantic Oceanic lithosphere based on ODP. Therefore, extensional deformation in the ophiolite belt is of significant meaning for clarifying the formation process and mechanism of ancient oceanic basin.

Structure styles and tectonic evolution of the Abrolhos Sub-Basin, Perth Basin, Western Australia

Based on examination and re-interpretation of 2D seismic and well data, three groups of faults were recognized in the Abrolhos Sub-basin: a) major normal faults transecting the Permian, Triassic and Jurassic, b) small normal faults developed in the Early Permian, and c) small normal faults developed in the Triassic and Jurassic.

The evolution of a Late Cretaceous–Cenozoic intraplate basin (Duaringa Basin), eastern Australia: evidence for the negative inversion of a pre-existing fold–thrust belt

The Duaringa Basin in eastern Australia is a Late Cretaceous?–early Cenozoic sedimentary basin that developed simultaneously with the opening of the Tasman and Coral Seas. The basin occurs on the top of an earlier (Permian–Triassic) fold–thrust belt, but the negative inversion of this fold–thrust belt, and its contribution to the development of the Duaringa Basin, are not well understood. Here, we present geophysical datasets, including recently surveyed 2D seismic reflection lines, aeromagnetic and Bouguer gravity data. These data provide new insights into the structural style in the Duaringa Basin, showing that the NNW-striking, NE-dipping, deep-seated Duaringa Fault is the main boundary fault that controlled sedimentation in the Duaringa Basin. The major activity of the Duaringa Fault is observed in the southern part of the basin, where it has undergone the highest amount of displacement, resulting in the deepest and oldest depocentre. The results reveal that the Duaringa Basin developed in response to the partial negative inversion of the pre-existing Permian–Triassic fold–thrust belt, which has similar orientation to the extensional faults. The Duaringa Fault is the negative inverted part of a single Triassic thrust, known as the Banana Thrust. Furthermore, small syn-depositional normal faults at the base of the basin likely developed due to the reactivation of pre-existing foliations, accommodation faults, and joints associated with Permian–Triassic folds. In contrast to equivalent offshore basins, the Duaringa Basin lacks a complex structural style and thick syn-rift sediments, possibly because of the weakening of extensional stresses away from the developing Tasman Sea.

Application of analytical diffusion models to outcrop observations: Implications for mass transport by fluid flow through fractures

AbstractA pavement outcrop with excellent exposure of spatial relationships among joints, veins, small offset normal faults, and associated alteration halos (redox fronts) provided an opportunity to compare predictions of analytical models for reaction front propagation in a fracture‐matrix system with a real‐field situation. The results have important implications for fluid flow and pollutant transport through a fractured medium. The alteration halos observed suggest that all joints of different sets and most small faults are conductive to meteoric water at shallow depth. On the other hand, veins are local barriers to mass transport by diffusion. By using petrologic and petrophysical data, analytical modeling, and the width of the alteration halos, it was possible to estimate when the fracture network was open to fluid flow. The inferred time for fluid flow and diffusion through the fracture network is sensitive to the porosity n of the rock matrix used in the analytical solutions: 2200 ± 500 years with n = 0.08, 4600 ± 900 years with n = 0.05, and 16,000 ± 4000 with n = 0.02. The second and third age determinations are consistent with the landscape evolution of the area since the end of the last Wűrmian ice age and with the timing required to fill the fractures observed in outcrop. We suggest that analytical modeling is an important tool for the determination of transport and reaction time scales in fractured formations where it is constrained by a robust petrophysical and chemical properties data set.

Fault zone architecture within Miocene–Pliocene syn-rift sediments, Northwestern Red Sea, Egypt

The present study focusses on field description of small normal fault zones in Upper Miocene–Pliocene sedimentary rocks on the northwestern side of the Red Sea, Egypt. The trend of these fault zones is mainly NW–SE. Paleostress analysis of 17 fault planes and slickenlines indicate that the tension direction is NE–SW. The minimum (σ3) and intermediate (σ2) paleostress axes are generally sub-horizontal and the maximum paleostress axis (σ1) is sub-vertical. The fault zones are composed of damage zones and fault core. The damage zone is characterized by subsidiary faults and fractures that are asymmetrically developed on the hanging wall and footwall of the main fault. The width of the damage zone varies for each fault depending on the lithology, amount of displacement and irregularity of the fault trace. The average ratio between the hanging wall and the footwall damage zones width is about 3:1. The fault core consists of fault gouge and breccia. It is generally concentrated in a narrow zone of ∼0.5 to ∼8 cm width. The overall pattern of the fault core indicates that the width increases with increasing displacement. The faults with displacement < 1 m have fault cores ranging from 0.5 to 4.0 cm, while the faults with displacements of > 2 m have fault cores ranging from 4.0 to 8.0 cm. The fault zones are associated with sliver fault blocks, clay smear, segmented faults and fault lenses’ structural features. These features are mechanically related to the growth and linkage of the fault arrays. The structural features may represent a neotectonic and indicate that the architecture of the fault zones is developed as several tectonic phases.

Neogene-Quaternary evolution of the Tefenni basin on the Fethiye-Burdur fault zone, SW Anatolia-Turkey

The Fethiye-Burdur fault zone (FBFZ) is a complex belt of major break in the southwestern Anatolia. A number of basins occur within the FBFZ. The Tefenni basin is one of the NE-SW trending basins located in the central part of the FBFZ. The basin is 10–20 km wide and 60 km long. It contains two infills of fluvial, lacustrine and alluvial fan deposits from late Miocene to Recent. The older and folded infill rests on the pre-middle Miocene basement rocks with an angular unconformity and consists of fluvial and lacustrine sediments. The younger and undeformed Plio-Quaternary basin fill unconformably overlies the older basin fill and is composed predominantly of conglomerate, mudstone, silt, clay and recent basin floor sediments. The Tefenni basin is controlled by a series of NE-SW trending left lateral oblique-slip normal faults along its margins. The Tefenni and Mürseller faults bound the northwestern margin of the basin and the Kemer fault bounds the southeastern margin of the basin. The basin is also cut by NE-SW striking major and NW-SE, N-S and E-W striking small scale normal faults. Structural analyses in the basin show that NE-SW-trending contraction stress regime ended by Pliocene and was followed by NE-SW-trending extension from Pliocene onward.

Optimization of Upper Burgan Reservoir Multilateral Well With Inflow-Control Device

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 175227, “Optimize Development Strategy of Upper Burgan Reservoir Through Multilateral Well With Inflow-Control Device in Raudhatain Field, North Kuwait,” by Sankar Chowdhuri, Peter Cameron, Tarek A. Gawwad, Mohammad R. Madar, Siddhartha Sankar Sharma, Moute’a Dughaim AlMutairi, Vijay Shankar Rajagopalan, Suresh Chellappan, and Moudi Fahad Al-Ajmi, Kuwait Oil Company, prepared for the 2015 SPE Kuwait Oil &amp; Gas Show and Conference, Mishref, Kuwait, 11–14 October. The paper has not been peer reviewed. In coning situations, such as in the production of oil reservoirs with a bottom aquifer, multilateral wells reduce the coning effect and, hence, prove to be more cost-effective. This paper discusses the first multilateral well with a Level-4 junction combined with an inflow-control device (ICD) planned, designed, and drilled in the Upper Burgan reservoir of Raudhatain field, north Kuwait. The paper covers the main challenges of well placement during geosteering to ensure the best quality of reservoir rock in structurally and depositionally complex settings with smart-completion design. Introduction The Raudhatain oilfield structure is one of several developed along a prominent anticlinal ridge that plunges gently north of Kuwait. These individual highs, in which the principal oil accumulations of the area are localized, tend to be of large areal extent and substantial structural relief. The Raudhatain structure exhibits a quasiradial pattern of small normal faults of limited throw. This geometry suggests a primary origin by uplift. The Raudhatain structure is a faulted anticlinal dome with 65 to 90 ft of topographical relief. The 3D seismic has defined the major faulting in the northern part of Raudhatain as northwest trending, whereas in the southwestern part of the field the faults trend northwest. Fault throws are highly variable and range from less than 30 ft to as much as 150 ft. Stratigraphy of Upper Burgan Reservoir The Burgan formation is a major reservoir unit. It unconformably overlies the carbonate Shuaiba formation and underlies the Mauddud carbonates with locally unconformable contact. The thickness of Burgan is approximately 950 ft of soft, clean, porous, well-sorted quartz sandstones of littoral to possibly deltaic aspect, interbedded with siltstones and dark shales. The Burgan formation at Raudhatain has been divided informally into three members, termed the Upper Sand, Middle Shale, and Lower Sand.