Добірка наукової літератури з теми "Inverted fault zones"

“Triangle zone” geometry is well established in thrust tectonics, where the leading edge of a frontal thrust branches backward onto a hinterland-directed roof thrust, and the triangle zone thus formed defines the thrust system’s leading edge. Similar geometries occur in extension and inversion settings, where a triangle zone can form between a deep-seated master fault and a roof fault or backthrust located in a hanging-wall detachment. In basement-controlled extension, triangle zone development can occur when the shear strength of the master fault plane in the zone above a hanging-wall detachment cutoff exceeds that of a new or reactivated antithetic fault detaching on the hanging-wall dip slope. This structural style is characterized by pronounced hanging-wall synclines linked to detached extensional faults higher up the hanging-wall dip slopes. The same principles apply during early phases of inversion tectonics. The part of the master fault that is above the hanging-wall detachment cutoff may constitute a buttress that causes displacement to backthrust along any available detachment into accommodation structures such as emergent ramps. This structural style is characterized by compressional structures within the graben while there is minor or even no sign of inversion on the graben margin faults. These geometries could be accounted for by other processes, for example, localized deep-seated fault-controlled structures within graben, or salt redistribution. However, fieldwork and analog models demonstrate the admissibility of triangle zone kinematics across a range of tectonic settings in the presence of detachment layers that are thin relative to the overall stratigraphy — typically tens to hundreds of meters in thickness. These models can guide seismic interpretation of unusual fold structures in extensional and inverted graben. Seismic interpretation examples were evaluated from the North Sea and Saudi Arabia.

The Great Sumatran Fault (GSF) is a 1900-km-long fault extending from Lampung, Indonesia, to India's Andaman Islands. The fault location is not only on the land but also in the marine area. Previous studies were only focused on the land area of Sumatra and Andaman Islands even though the marine fault has also impacted earthquakes and tsunamis such as in 2004. As an effort to disaster risk mitigation, this study used the gravity method to map and study the continuity of the GSF in the marine area from the Aceh Province, Indonesia, to the Andaman Islands, India. The gravity data were obtained from Topex with a resolution of 1.85 km/px. Based on the Bouguer data, the subduction zone in the western part of the Indian Ocean is observed with the anomaly of 500–700 mGal, while the residual structure of GSF, relative to the subduction zone, only comes to clarity through a horizontal derivative transformation with anomaly 130-250 mGal. To delineate the fault's geometry, the data were inverted by GRABLOX 1.6 using Singular Value Decomposition and Occam methods. The 3D modeling results also clearly show the contrast density between regional faults such as subduction zones on the Westside of the West Andaman Fault (WAF). The GSF faults can also be well demonstrated at 50 km depth. Based on these results, the gravity Topex is potentially used as a preliminary study of the GSF activity in the marine area.

ABSTRACT Recent earthquakes off the northeastern Kamchatka coast reveal that this region is seismically active, although details of the locations and complexity of the fault system are lacking. The northern part of Kamchatka has poor coverage by permanent seismic stations and ground geodetic instruments. Here, we exploit the Differential Interferometric Synthetic Aperture Radar (DInSAR) technique to characterize the fault geometry and kinematics associated with the 29 March 2017 Mw 6.6 Yuzhno-Ozernovskoe earthquake. The aim is to contribute to identifying the active fault branches and to better understanding the complex tectonic regime in this region using the DInSAR technique, which has never before been applied to the analysis of coseismic offsets in Kamchatka. We produced coseismic deformation maps using Advanced Land Observation Satellite-2 ascending and descending and Sentinel-1A descending Synthetic Aperture Radar (SAR) scenes and detected a predominant uplift up to 20 cm and a westward motion of approximately 7 cm near the shoreline. We jointly inverted the three geodetic datasets using elastic half-space fault modeling to retrieve source geometry and fault kinematics. The best-fit solution for the nonlinear inversion suggests a north–west-dipping oblique reverse fault with right-lateral rupture. The model fault geometry is not only generally consistent with the seismic data but also reveals that a hitherto unknown fault was ruptured. The identified fault structure is interpreted as the northern extension of the east Kamchatka fault zone, implying that the region is more complex than previously thought. Important implications arise for the presence of unknown faults at the edges of subduction zones that can generate earthquakes with magnitudes greater than Mw 6.

To understand the oil and gas accumulation rules and main controlling factors of H Basin at different phases, approaches such as reservoir dissection and analysis on the spatial allocation of reservoir accumulation conditions are adopted to divide the reservoir of the main fault depression zones of central H Basin into early and late phases. The widely-spread oil and gas at early phase are obviously more than that of the late phase. The main controlling factors of reservoir accumulation at early phase include source rocks area, antithetic faults - tilted upheavals and sand body of fan delta front subfacies while that of the late phase include sources rocks area, inverted structure and long-term developed fractures. The achievement of the study expounded in this paper is significantly important to correctly understand the oil and gas accumulation rules of complicated faulted-block fields and guide the oil and gas exploration activities.

Abstract. The crustal-scale west-vergent San Ramón thrust fault system at the foot of the main Andean Cordillera in central Chile is a geologically active structure with Quaternary manifestations of complex surface rupture along fault segments in the eastern border of Santiago city. From the comparison of geophysical and geological observations, we assessed the subsurface structure pattern affecting sedimentary cover and rock-substratum topography across fault scarps, which is critic for evaluating structural modeling and associated seismic hazard along this kind of faults. We performed seismic profiles with an average length of 250 m, using an array of twenty-four geophones (GEODE), and 25 shots per profile, supporting high-resolution seismic tomography for interpreting impedance changes associated to deformed sedimentary cover. The recorded traveltime refractions and reflections were jointly inverted by using a 2-D tomographic approach, which resulted in variations across the scarp axis in both velocities and reflections interpreted as the sedimentary cover-rock substratum topography. Seismic anisotropy observed from tomographic profiles is consistent with sediment deformation triggered by west-vergent thrust tectonics along the fault. Electrical soundings crossing two fault scarps supported subsurface resistivity tomographic profiles, which revealed systematic differences between lower resistivity values in the hanging wall with respect to the footwall of the geological structure, clearly limited by well-defined east-dipping resistivity boundaries. The latter can be interpreted in terms of structurally driven fluid content-change between the hanging wall and the footwall of a permeability boundary associated with the San Ramón fault. The overall results are consistent with a west-vergent thrust structure dipping ∼55° E at subsurface levels in piedmont sediments, with local complexities being probably associated to fault surface rupture propagation, fault-splay and fault segment transfer zones.

Abstract. The crustal-scale west-vergent San Ramón thrust fault system, which lies at the foot of the main Andean Cordillera in central Chile, is a geologically active structure with manifestations of late Quaternary complex surface rupture on fault segments along the eastern border of the city of Santiago. From the comparison of geophysical and geological observations, we assessed the subsurface structural pattern that affects the sedimentary cover and rock-substratum topography across fault scarps, which is critical for evaluating structural models and associated seismic hazard along the related faults. We performed seismic profiles with an average length of 250 m, using an array of 24 geophones (Geode), with 25 shots per profile, to produce high-resolution seismic tomography to aid in interpreting impedance changes associated with the deformed sedimentary cover. The recorded travel-time refractions and reflections were jointly inverted by using a 2-D tomographic approach, which resulted in variations across the scarp axis in both the velocities and the reflections that are interpreted as the sedimentary cover-rock substratum topography. Seismic anisotropy observed from tomographic profiles is consistent with sediment deformation triggered by west-vergent thrust tectonics along the fault. Electrical soundings crossing two fault scarps were used to construct subsurface resistivity tomographic profiles, which reveal systematic differences between lower resistivity values in the hanging wall with respect to the footwall of the geological structure, and clearly show well-defined east-dipping resistivity boundaries. These boundaries can be interpreted in terms of structurally driven fluid content change between the hanging wall and the footwall of the San Ramón fault. The overall results are consistent with a west-vergent thrust structure dipping ~55° E in the subsurface beneath the piedmont sediments, with local complexities likely associated with variations in fault surface rupture propagation, fault splays and fault segment transfer zones.

Microseismicity is recorded during an underground mine development by a network of seven boreholes. After an initial preprocessing, 488 events are identified with a minimum of 12 P-wave arrival-time picks per event. We have developed a three-step approach for P-wave passive seismic tomography: (1) a probabilistic grid search algorithm for locating the events, (2) joint inversion for a 1D velocity model and event locations using absolute arrival times, and (3) double-difference tomography using reliable differential arrival times obtained from waveform crosscorrelation. The originally diffusive microseismic-event cloud tightens after tomography between depths of 0.45 and 0.5 km toward the center of the tunnel network. The geometry of the event clusters suggests occurrence on a planar geologic fault. The best-fitting plane has a strike of 164.7° north and dip angle of 55.0° toward the west. The study region has known faults striking in the north-northwest–south-southeast direction with a dip angle of 60°, but the relocated event clusters do not fall along any mapped fault. Based on the cluster geometry and the waveform similarity, we hypothesize that the microseismic events occur due to slips along an unmapped fault facilitated by the mining activity. The 3D velocity model we obtained from double-difference tomography indicates lateral velocity contrasts between depths of 0.4 and 0.5 km. We interpret the lateral velocity contrasts in terms of the altered rock types due to ore deposition. The known geotechnical zones in the mine indicate a good correlation with the inverted velocities. Thus, we conclude that passive seismic tomography using microseismic data could provide information beyond the excavation damaged zones and can act as an effective tool to complement geotechnical evaluations.

In two companion papers we report the detailed geological and mineralogical study of two emblematic serpentinized ultramafic bodies of the western North Pyrenean Zone (NPZ), the Urdach massif (paper 1) and the Saraillé massif (this paper). The peridotites have been uplifted to lower crustal levels during the Cretaceous rifting period in the future NPZ. They are associated with Mesozoic pre-rift metamorphic sediments and small units of thinned Paleozoic basement that were deformed during the mantle exhumation event. In the Saraillé massif, both the pre-rift cover and the thin Paleozoic crustal lenses are involved in a Pyrenean recumbent fold having the serpentinized peridotites in its core. Based on detailed geological cross-sections microscopic observations and microprobe mineralogical analyses, we describe the lithology of the two major extensional fault zones that accommodated: (i) the progressive uplift of the lherzolites upward the Cretaceous basin axis, (ii) the lateral extraction of the continental crust beneath the rift margins and, (iii) the decoupling of the pre-rift cover along the Upper Triassic (Keuper) evaporites and clays, allowing its gliding and conservation in the basin center. These two fault zones are the (lower) crust-mantle detachment and the (upper) cover décollement located respectively at the crust-mantle boundary and at the base to the detached pre-rift cover. The Saraillé peridotites were never exposed to the seafloor of the Cretaceous NPZ basins and always remained under a thin layer of crustal mylonites. Field constraints allow to reconstruct the strain pattern of the mantle rocks in the crust-mantle detachment. A 20–50 m thick layer of serpentinized lherzolites tectonic lenses separated by anastomosed shear zones is capped by a thin upper damage zone made up of strongly sheared talc-chlorite schists invaded by pyrite crystallization. The cover décollement is a few decameter-thick fault zone resulting from the brecciation of Upper Triassic layers. It underwent strong metasomatic alteration in the greenschist facies, by multi-component fluids leading to the crystallization of quartz, dolomite, talc, Cr-rich chlorite, amphiboles, magnesite and pyrite. These data collectively allow to propose a reconstruction of the architecture and fluid-rock interaction history of the distal domain of the upper Cretaceous northern Iberia margin now inverted in the NPZ.

In the mining process of working face, the additional stress generated by the fault changes the law of roadway deformation and failure as well as the law of overburden failure. Aiming at the influence of the fault in the mining process of working face, this study introduced the geological strength index (GSI) to analyze the stress distribution in the elastic-plastic zone of the surrounding rock of the roadway. And similar experiments under different engineering backgrounds were combined to study the characteristics of overburden movement and stress evolution. Based on the conclusions obtained, the roadway support scheme was designed. This study shows that, compared with ordinary mining, through-the-fault mining causes slippage and dislocation of the fault, the load of the overburden is transferred to both sides of the fault, and the stress near the fault accumulates abnormally. The “three zones” characteristics of the overburden movement disappear, the subsidence pattern is changed from "trapezoid" to "inverted triangle", and the influence distance of the advanced mining stress on the working face is extended from 20m to 30m. The instability range of roadway surrounding rock is exponentially correlated with the rupture degree of the surrounding rock. Through the introduction of GSI, the critical instability range of roadway surrounding rock is deduced to be 2.32m. According to the conclusion, the bolt length and roadway reinforced support length are redesigned. Engineering application shows that the deformation rate of the roadway within 60 days is controlled below 0.1~0.5mm/d, the deformation amount is controlled within 150mm, and the roadway deformation is controlled, which generally meets the requirements of use. The research results provide guidance and reference for similar roadway support.

It is widely recognised that inverted fault zones form economically significant structures for subsurface fluid exploration and production. Inverted fault zones are formed by the contractional reactivation and reversal of pre-existing extensional fault zones. Recognising the reverse-reactivation of normal faults in sedimentary basins is fundamental, as the reconfiguration of fault geometries has implications for overall basin geometry, sediment accommodation and supply, and fluid flow pathways. This is particularly important for understanding the modification or creation of petroleum system elements through time, which in turn allows for increased targeted exploration. Notwithstanding the broad economic relevance of inverted fault zones, integrated multi-scale (from micrometre-scale to outcrop-scale) studies on the structural, petrophysical, and geochemical properties of inverted fault zones within porous reservoir rocks are limited. This thesis characterises the structural, petrophysical, and geochemical properties of inverted fault zones from two localities, the Otway Basin (Australia) and Bristol Channel Basin (United Kingdom), in order to understand how inverted faults influence fluid flow at a range of scales. To address this, this thesis has two main topics of focus: (1) identify the influence of inverted faults on surrounding lithology by assessing the relationship between faults, damage zones around faults, and fractures related to fault growth; and (2) identify how subsurface fluids flow, interact, and modify their surrounds by assessing the geochemistry of fluids in fractures and thereby constraining the source, evolution, and migration of fluids preserved in fractures. An integrated, multi-scale approach is crucial for improving the prediction of subsurface fluid flow beyond the wellbore. In order to understand the influence of inverted faults on surrounding lithology, an inverted fault (Castle Cove Fault) in the Otway Basin, southeast Australia, is the focus of the first two chapters of this thesis. The geometries and relative chronologies of natural fractures adjacent to the Castle Cove Fault are investigated. Structural mapping in the hanging wall damage zone reveals three sets of shear fractures that are geometrically related to the Castle Cove Fault. Inversion of the Castle Cove Fault has resulted in the development of an extensive network of fractures and complex fold structures, and inversion would have subsequently improved the outcrop-scale permeability structure of the damage zone for fluid migration. At the micrometre-scale, the permeability structure has also been influenced by fault inversion. Petrophysical and petrographical analyses in the hanging wall damage zone show that microstructural changes due to faulting have enhanced the micrometre-scale permeability structure of the Eumeralla Formation. These microstructural changes have been attributed to the formation of microfractures and destruction of original pore-lining chlorite morphology as a result of fault deformation. Consequently, inversion has subsequently improved the micrometre-scale permeability structure of the damage zone adjacent to the Castle Cove fault plane. Characterisation of the permeability structure adjacent to reverse-reactivated faults at a range of scales will aid with predicting fluid flow associated with inversion structures. Structural and geochemical analyses in the next two chapters of this thesis aim to understand how subsurface fluids flow and characterise the source, evolution, and migration pathways of fluids preserved in inverted fault zones. The geochemical evolution of fluids precipitated as calcite and siderite-cemented concretions and fractures throughout the eastern Otway Basin have been investigated. Pore fluids were sourced from both meteoric water and sea water during the deposition of the Eumeralla Formation and pore fluid evolution was strongly influenced by diagenetic reactions and increased temperature during burial. Using a similar analytical approach, the geochemical evolution of fluids precipitated as calcite and gypsum-cemented fractures throughout the eastern Bristol Channel Basin have vibeen investigated. The main source of fluids were connate pore waters, which were altered by diagenetic reactions within their host lithologies and subsequently redistributed through migration along faults and their associated damage zones. Knowledge of the source, evolution, and migration pathways of these fluids provides valuable insights for understanding the development of inverted sedimentary basins through time. Consequently, integrated studies on the multi-scaled permeability structure of inverted fault zones and the fluids preserved within them will ultimately improve fluid exploration and monitoring strategies in sedimentary basins.
Thesis (Ph.D.) -- University of Adelaide, Australian School of Petroleum (ASP), 2019

The steam injection process is one of the most effective thermal recovery processes for heavy oil reservoirs. Common challenges with this method are unexpected faults, heat transfer efficiency, and less exposure between oil and steam. The existence of an unexpected fault causes steam to escape from the target zone to the untargeted zone and poses a hazard on the surface. This condition has made the steam injection activity very restricted in faulted reservoirs. The application of hydraulic fracturing known as the fracturing-assisted steam flooding process is a new promising technique for increasing oil recovery by creating a path between injection wells and producing wells. This paper evaluates the effect of a faulted reservoir and accommodates a hydraulically fractured reservoir simulation in the steam injection process using a commercial simulator. The focus of the hydraulic fractures implementation in this study is to increase the exposure between steam and oil. The effect of the injection pattern using an inverted five-spot pattern is also evaluated in this paper. Two reservoir model scenarios are used to illustrate the proposed method: the faulted reservoir model and hydraulically fractured reservoir model. A new development plan is proposed to overcome the faulted reservoirs in the steam injection process with a 20-25% increase in oil recovery compared to the traditional approach. It was observed that the presence of hydraulic fractures in the steam injection process significantly increased the oil recovery by 25-40%. The sensitivity results indicate that parameters such as the fracture schedule and permeability multiplier in the fracture zone affect the increment in oil recovery during the fracture-assisted steam flooding process. This study proves an improvement in the effectiveness of the steam injection process in faulted reservoirs and presents a unique approach to improve steam-oil exposures. This paper introduces a new development plan to overcome faulted reservoirs in the steam injection process. We also introduce an alternative approach to the application of fracture-assisted flooding in the steam injection process. Both methods will greatly impact to increase.

Abstract An Ultra-Deep Directional Electromagnetic LWD Resistivity (UDDE) tool was deployed in a mature Lower Cretaceous carbonate reservoir to map injection water movement. These thick carbonate reservoirs experience injection water preferentially travelling laterally at the top of the reservoir. The water held above oil by negative capillary forces slumps quickly, leading to increasing water cut, eventually killing the natural lift horizontal producing well. Real time 3D and 1D inversions provided important accurate mapping of the non-uniform water fronts and reservoir boundaries, providing insights into reservoir architecture and water movement. The candidate well is located in an area of significant uncertainty regarding fluid distribution and structural elements like sub-seismic faults etc. Pre-well 1D inversion results indicated that the water slumping front away from wellbore can be mapped within a vertical radius of 60-100 ft TVD. However, 1D inversion is not accurate where steeply dipping or discontinuous formations exist due to the presence of faults and is expected to impact well placement, mapping water fronts / formation boundaries and long-term oil recovery. Therefore in the real time, full 3D and 1D inversions of the Ultra-Deep EM data were run to provide high quality reservoir imaging in this complex geometrical setting and deliver improved reservoir fluid distribution and structure mapping. The pre-well inversion modeling optimized the frequency and transmitter-receiver spacing of the UDDE tool. The bottom hole assembly (BHA) configuration also included conventional LWD tools such as Neutron-Density, propagation Resistivity and Gamma Ray. Multiple 3D inversion datasets were processed in real-time using different depths of inversion ranging from 50 ft up to 120 ft depth. The 3D inversion results during the real-time drilling operation detected the non-uniform waterfront boundaries and water slumping up to 80 ft TVD above the wellbore using a slimhole (4¾″) tool. An interpreted sub-seismic down-thrown fault was mapped which controlled the non-uniform slumping fluid distribution, causing the water front to approach closest to the wellbore in this location. This suggests that the fault zone is open and provides a degree of increased permeability around the plane of the fault. The real-time 3D inversion, 1D shallow and 1D deep inversion results showed comparable structural imaging despite being inverted independently of each other. These results permitted updates to the static / dynamic reservoir models and an optimization of the completion design, to delay the water influx and thereby sustain oil production for a longer period of time. Field wide implementation of the UDDE tool and its advanced technology with improved 1D and 3D inversion results will enhance the quality of realtime geosteering, mapping and updating of reservoir models which have challenging water slumping fronts and structural variations. This will enable improvment in well locations, their spacing and finally allowing the proactive design of smart completions for enhanced oil production and improved recovery factors.

In highly deviated/horizontal wells, understanding the downhole water entry points and the effectiveness of the completion barriers are paramount challenges for a proper production management and for a prospective water shut-off design. The integration of hybrid cable with a mono-conductor and optical fiber (Distributed Temperature/Acoustic Sensing, or DTS/DAS), pulsed neutron-based Water Flow Log (WFL) and Production Logging (PL) can provide information about the downhole flow profiling, the water producing zones and the failures of the completion hydraulic seals. This paper discusses an optimized data acquisition and interpretation workflow tailored for such highly complex well scenarios. The reference case study is Well A, an onshore horizontal oil producer intercepting a naturally fractured carbonate reservoir. The horizontal drain was completed with slotted liners in front of faults and fractures identified as the main oil entry points. Fast asphaltenes deposition makes this environment challenging for tool stuck risks, hence conventional PL tool strings are not usable during production. After initial outstanding performances, Well A started to suffer from a huge water-cut with consequent impact on production and surface facilities. The acquisition and the interpretation of a combo DTS and WFL conveyed via coiled tubing provided a clear picture of the downhole flow profile highlighting a strong water production in the shallower part of the drain. The horizontal drain was then temporary excluded with a bridge plug and a batch of specific sealant polymer in order to hydraulically isolate inside and behind the pipe. A new interval was then opened to production with through-tubing perforations. Unfortunately, at the well restart, the production performance was similar to pre-isolation and perforation, still with an important water contribution. Hence, a spinner-based PL string, combined with an inverted WFL, was utilized to investigate the new perforated interval and the isolation of the bottom of completion. The log acquisition was performed during brine injection to overcome the risk of tool stuck due to the asphaltene deposition during production. It is well-known that collecting reliable data is the starting point for the design of a proper operation aimed at excluding hydraulic communication with an abandoned drain. This experience confirmed the possibility to acquire strategic information in challenging producer wells during brine injection and using a combo PL-WFL for fluid path discrimination inside and outside the completion environment. Auxiliary pulsed neutron log outcomes, such as the Compton ratios, can be used to define the actual region of the communication behind casing.