Synthetic Faults Research Articles

Rheological Controls on Asperity Weakening During Earthquake Slip

AbstractEvolution of fault strength during the initial stages of seismic slip plays an important role in the onset of velocity‐induced weakening, which in turn, leads to larger earthquake events. A key dynamic weakening mechanism during the early stages of slip is flash heating, where stress concentrations at contacts on the interface lead to the rapid generation of heat. Although potential weakening from flash heating has been extensively modeled, there is little recorded microstructural evidence of its physical manifestations. We present results of a series of triaxial experiments on synthetic faults in quartz sandstone. Samples were subjected to a variety of normal stresses and ambient temperatures, to induce a range of slip event sizes and sliding velocities. We show the microstructural evolution of asperity interactions from the onset of flash heating through to the formation of grain‐scale areas of sheared melt. Using microstructural observations and mechanical data from the experiments, we model temperature and the viscoelastic behavior of the glass. Results suggest that, in the earliest stages of slip asperity contacts melt, but temperatures remain too low for viscous shear to occur within the melt layer. Instead melted asperities behave as glassy solids, facilitating continued frictional heating. With further slip, increased asperity temperatures allow the transition to viscous shear within the melt layer, facilitating weakening. These results highlight the dynamic evolution of the viscoelastic properties of the melt and resulting effects on asperity strength. Such complexity has, to‐date, not been fully addressed in modeling of flash heating.

Synrift evaporite deposition and structural characterization of the onshore Alagoas subbasin

The Sergipe-Alagoas Basin, situated in the north-east Brazilian margin, has a long tradition of oil and gas production and the presence and distribution of evaporites play an important role in petroleum systems in the basin. However, little research has focused on the structural evolution of the older, synrift evaporitic sections of the basin. We have focused explicitly in the detailed subsurface structural characterization of the rift in the Alagoas subbasin and the distribution of the Early Aptian evaporites. To accomplish this objective, we interpreted selected 2D and 3D seismic and well data located in two areas known as the Varela Low (VL) and Fazenda Guindaste Low (FGL). We identified diverse deformation styles in those two basin depocenters. Our interpretation indicates that VL consists of a half-graben with a significant rollover structure, controlled by two listric northeast–southwest border faults. The deformation in the hanging wall is also accommodated by release faults and minor antithetic faults. In this depocenter, we mapped in the seismic and the well data an older evaporitic sequence within the Coqueiro Seco Fm., known as Horizonte Salt. This evaporitic section occurs in the internal part of the VL half graben, where it is limited by release and antithetic faults. Significant salt strata growing toward the antithetic fault is observed. Whereas, the FGL represents a graben elongated along the north-east direction and is controlled by several types of structures. We recognized normal synthetic and antithetic faults, transfer zones, release faults, and rollover anticlines in the seismic throughout this depocenter. We mapped an evaporitic section within the Maceió Fm., known as Paripueira Salt, which consists of disconnected salt bodies, restricted to the hanging walls of synrift faults.

Reservoir Characterization of Buma Field Reservoirs, Niger Delta using Seismic and Well Log Data

The reservoir characterization of Buma Field, Niger Delta using seismic and well log data is the focus of this research. Seismic data in SEG-Y format and suites of well logs have been used to achieve the aim and objectives of the research. Methodologies used in this work are standard methods used in this kind of research. Results of the analysis seismic data shows fifteen faults have been identified, nine trend NW-SE and are antithetic faults whereas the six trend NESW and are synthetic faults. These faults formed closures and could act as trapping mechanisms for hydrocarbon in the identified horizons/reservoirs. Two hydrocarbon bearing horizons D and F have been mapped on the seismic and analysis of the well logs showed that sand and shale are major lithologies in the studied wells. Well correlation showed similarities in geological properties such as lithology, reservoir tops and petrophysical properties. Volumetric estimation carried out on the two reservoirs showed Reservoir D having average thickness of 26.73 ft., area of 3784.89 acres, bulk volume of 4407x106 ft3 , net volume of 4226x106 ft3 , pore volume of 216 x106 RB, hydrocarbon pore volume (oil) of 143x106 RB and STOIIP of 77 MMSTB. Reservoir F has an average thickness of 41.55 ft., area of 2790.63 acres, bulk volume of 5051x106 ft3, net volume of 4769x10106 ft3 , pore volume of 248x10106 RB, hydrocarbon pore volume (oil) of 167x10106 RB and STOIIP of 88 MMSTB. Integrating results of structural interpretation, well log analysis, petrophysical properties and volumetric estimation it is evident that both reservoirs have very good porosities and excellent permeability, good thicknesses of productive sand and reduced water saturation as to aid storage and easy flow of hydrocarbon pore fluids. Therefore, the two Buma Field Reservoirs D and F are prolific with hydrocarbon pore fluids (oil) which can be exploited economically

Experimental and numerical study on isolated simply-supported bridges subjected to a fault rupture

To investigate the effects of fault crossing on the seismically isolated bridges, shake table testing was conducted on a 1/10 scaled two-span simply-supported bridge model isolated by lead rubber bearings (LRBs). A synthetic fault rupture, consisting of low- and high-frequency simulations, was used to excite the test model from low to high amplitude. Test results revealed that lead rubber bearings are effective in protecting the girders and the piers of the bridge subject to fault rupture, but at the cost of large peak and residual bearing deformation or even the failure of LRBs. The bearings at near fault (NF) span are more susceptible to fault rupture than the crossing fault (CF) span because the participation of longitudinal response compensates the transverse seismic demand of the bearings at CF span. Two numerical models were constructed with differing modeling consideration of LRBs: a sophisticated one using Bouc-wen model and a simplified one using Bilinear model. Both numerical models were able to predict the behavior of test model equally well before the failure of the bearings, validating that the existing nonlinear analytical techniques are adequate to estimate the seismic response of bridges subjected to a fault rupture.

22‐kyr‐Long Record of Surface Faulting Along the Source of the 30 October 2016 Earthquake (Central Apennines, Italy), From Integrated Paleoseismic Data Sets

AbstractWe integrate paleoseismic data sets along the Mt. Vettore‐Mt. Bove normal fault system rupturing at the surface in the 30 October 2016 Norcia earthquake. Through the analysis of new trenches from this work and a review of the preexisting data, we correlate events among trench sites along antithetic and synthetic fault splays. We recognize seven M 6.5, 2016 Norcia‐type (or larger) surface‐faulting events in the last ~22 kyr, including 2016. Before 2016, one event occurred in the past two millennia (260–575 CE) and possibly corresponds to the event damaging Rome in 443 or 484/508 CE. Three previous events occurred between 10590 and 415 BCE, whereas the two oldest ones date between 19820 and 16540 BCE. The average recurrence time is 3,360–3,640 years for the last ~22 kyr and 1,220–1,970 years for the last ~4 kyr. We infer a minimum dip‐slip rate of 0.26–0.38 mm/year on the master fault in the central portion of the Mt. Vettore–Mt. Bove normal fault system and a dip‐slip rate of at least 0.10 mm/year on the southernmost portion. We infer a Middle–Late Pleistocene inception of the long‐term scarp of the investigated splays. The along‐strike variation of slip rates well reproduces the trend of the 2016 surface slip; thus, the time window exposed in the trenches is representative for the present fault activity. Based on trenching data, different earthquake rupture scenarios should be also considered for local hazard assessment.

A Small-Sample Wind Turbine Fault Detection Method With Synthetic Fault Data Using Generative Adversarial Nets

The limited fault information caused by small fault data samples is a major problem in wind turbine (WT) fault detection. This paper proposes a small-sample WT fault detection method with the synthetic fault data using generative adversarial nets (GANs). First, based on prior knowledge, a rough fault data generation process is developed to transform the normal data to the rough fault data. Second, a rough fault data refiner is developed by GANs to make the rough fault data more similar with the real fault data. Moreover, to make the generated data better suited to the WT conditions, GANs are improved in both the generative model and the discriminative model. Third, artificial intelligence (AI)-based WT fault detection models can be well trained by using only the generated data in the condition of small fault data sample. Finally, three groups of generated data evaluation experiments and four groups of WT fault detection comparative experiments are conducted using real WT data collected from a wind farm in northern China. The results indicate that the method proposed in this paper is effective.

Evaluation of hydrocarbon reserves using integrated petrophysical analysis and seismic interpretation: A case study of TIM field at southwestern offshore Niger Delta oil Province, Nigeria

This study presents the log analysis results of a log suite comprising gamma ray (GR), resistivity (LLD), neutron (PHIN), density (RHOB) logs and a 3D seismic interpretation of TIM field located in the southwestern offshore of Niger Delta, Nigeria. This study focuses essentially on reserves evaluation of hydrocarbon-bearing sands. Well data were used in the identification of reservoirs as well as hydrocarbon presence and determination of petrophysical parameters. Three horizons that corresponded to selected sands tops (sand D, sand E, and sand F) were mapped after well-to-seismic tie. The three horizons marked the tops of reservoir sands and provide the structures for hydrocarbon accumulation. Structural depth maps were created from the mapped horizons. The structural style is dominated by widely spaced simple rollover anticline bounded by growth faults, and this includes down-to-basin faults, antithetic faults and synthetic faults. The petrophysical values – the porosity, net-to-gross, water saturation, hydrocarbon saturation that were calculated yielded an average porosity value of 0.23, water saturation value of 0.32 and an average net-to-gross value of 0.62. Hydrocarbon in-place was evaluated. The total hydrocarbon proven reserves for the mapped horizons (sand D, sand E, and sand F) were evaluated to be 39.04MMBO of oil, and 166.13BCF of gas for sand E.

Major structural elements and petrophysical properties of the miocene section, “XYZ Field”, western shallow Offshore Depobelt, Niger Delta

R1, R2, R3, and F. reservoir units were identified in the XYZ Field. The reservoirs are within the Oil proven fault block and F reservoir is located on the footwall structure of the second synthetic fault with similar structural characteristics. The faulting in the XYZ field resulted in a downward movement of the XYZ Discovery relative to the XYZ prospects. The structural development process of the field was a syn-sedimentary. This explains why the XYZ-1 penetration in the footwall of the synthetic found oil-in F sand. However, petrophysical results show that the reservoirs of interests have good petrophysical properties with minimum porosity of 0.1 and maximum water saturation of 0.7. The discoveries by the XYZ-1 well prove the existence of a working hydrocarbon source and charge system. However the distribution pattern of the discovered hydrocarbons is not yet understood. Â

Faulting processes during early-stage rifting: seismic and geodetic analysis of the 2009–2010 Northern Malawi earthquake sequence

SUMMARYIn December, 2009, a rare sequence of earthquakes initiated within the weakly extended Western Rift of the East African Rift system in the Karonga province of northern Malawi, providing a unique opportunity to characterize active deformation associated with intrabasinal faults in an early-stage rift. We combine teleseismic and regional seismic recordings of the largest events, InSAR imagery of the primary sequence, and recordings of aftershocks from a temporary (4-month) local network of six seismometers to delineate the extent and geometry of faulting. The locations of ∼1900 aftershocks recorded between January and May 2010 are largely consistent with a west-dipping normal fault directly beneath Karonga as constrained by InSAR and CMT fault solutions. However, a substantial number of epicentres cluster in an east-dipping geometry in the central part of the study area, and additional west-dipping clusters can be discerned near the shore of Lake Malawi, particularly in the southern part of the study area. Given the extensive network of hanging wall faults mapped in the Karonga region on the surface and in seismic reflection images, the distribution of events is strongly suggestive of multiple faults interacting to produce the observed deformation, and the InSAR data permit this but do not require it. We propose that fault interaction contributed to the seismic moment release as a series of Mw 5-to-6 events instead of a normal main shock–aftershock sequence. We find the depth of fault slip during the main shocks constrained by InSAR peaks at less than 6 km, while the majority of recorded aftershocks are deeper than 6 km. This depth discrepancy appears to be robust and may be explained by fault interaction. Structural complexities associated with fault interaction may have limited the extent of coseismic slip during the main shocks, which increased stress deeper than the coseismic slip zone on the primary fault and synthetic faults to the east, causing the energetic aftershock series. There is no evidence of deformation at the Rungwe volcanic province ∼50 km north of the earthquake sequence between 2007 and 2010, consistent with previous interpretations of no significant magmatic contribution during the sequence.

Hydrocarbon Reservoir Evaluation: a case study of Tymot field at southwestern offshore Niger Delta Oil Province, Nigeria

Abstract: Aim: This study presents the log analysis results of a log suite comprising gamma ray (GR), resistivity (LLD), neutron (PHIN), density (RHOB) logs and a 3D seismic interpretation of Tymot field located in the southwestern offshore of Niger delta. This study focuses essentially on reserves estimation of hydrocarbon bearing sands. Well data were used in the identification of reservoirs and determination of petrophysical parameters and hydrocarbon presence. Three horizons that corresponded to selected well tops were mapped after well-to-seismic tie. Structural depth maps were created from the mapped horizons. The structural style is dominated by widely spaced simple rollover anticline bounded by growth faults, and this includes down-to-basin faults, antithetic faults and synthetic faults. The petrophysical values – the porosity, net-to-gross, water saturation, hydrocarbon saturation that were calculated yielding an average porosity value of 0.23, water saturation of 0.32 and an average net-to-gross value of 0.62. Three horizons H1, H2 and H3 were mapped. The three horizons marked the tops of reservoir sands and provide the structures for hydrocarbon accumulation. Hydrocarbon in-place was estimated. The total hydrocarbon proven reserves for the mapped horizons H1, H2, and H3 were estimated to be 39.04MMBO of oil and 166.13BCF for sand E.

Bimodal or quadrimodal? Statistical tests for the shape of fault patterns

Abstract. Natural fault patterns formed in response to a single tectonic event often display significant variation in their orientation distribution. The cause of this variation is the subject of some debate: it could be noise on underlying conjugate (or bimodal) fault patterns or it could be intrinsic signal from an underlying polymodal (e.g. quadrimodal) pattern. In this contribution, we present new statistical tests to assess the probability of a fault pattern having two (bimodal, or conjugate) or four (quadrimodal) underlying modes and orthorhombic symmetry. We use the eigenvalues of the second- and fourth-rank orientation tensors, derived from the direction cosines of the poles to the fault planes, as the basis for our tests. Using a combination of the existing fabric eigenvalue (or modified Flinn) plot and our new tests, we can discriminate reliably between bimodal (conjugate) and quadrimodal fault patterns. We validate our tests using synthetic fault orientation datasets constructed from multimodal Watson distributions and then assess six natural fault datasets from outcrops and earthquake focal plane solutions. We show that five out of six of these natural datasets are probably quadrimodal and orthorhombic. The tests have been implemented in the R language and a link is given to the authors' source code.

Reservoir characterization and volumetric estimation of Orok Field, Niger Delta hydrocarbon province

Geophysical analysis was undertaken on the available suit of well logs, 3D seismic and checkshot data from the field in a view to carrying out reservoir characterization and volumetric estimation of Orok Field Niger Delta Province. Lithology delineation and Petrophysical evaluation including porosity, water saturation and net-to-gross were undertaken. Well to seismic tie, structural interpretation and horizon mapping were carried out. Time and depth maps were generated and volumetric estimation of the reservoirs were carried out. Four gas-bearing reservoir (A001, B001, C001 and D001) of variable thickness and depth from the subsurface were identified. Their effective porosity ranges from 19% for A001, 20% for B001, 20% for C002 and 18% for the basal D001 respectively. Water saturation estimated from the reservoir sands ranges from 23% for A001, B001 20%, C001 12% and 10% for D001. The hydrocarbon saturation of the reservoirs stood at 77%, 80%, 82%, 90% for A001, B001, C001 and D001 respectively. Only sand A001 and sand B001 had good seismic tie and were able to be mapped through the seismic. Three synthetic structural building listric faults were interpreted across the inlines intercepting the top of reservoir Sand A001 and B001. The volumetric estimation reveals that A001 and B001 have an area of 813.708 acres and 813.693 acres and volume of 151 billion cu.ft and 286 billion cu.ft of gas respectively. Three synthetic structural building listric faults (F1, F2 and F3) intercept the top of sandstones A001 and B001. The structural trapping mechanism in both sandstones resulted from synthetic fault assisting structures i.e rollover anticlines. The modeled faults trends approximately northwest to southeast direction and dip in the southwest direction.

Friction of foliated fault gouge with a biotite interlayer at hydrothermal conditions

To investigate the influence of foliation and structure within fault zones, synthetic fault gouges of quartz containing various thin layers of biotite were sheared in a triaxial testing system at hydrothermal conditions to acquire the faulting behaviour, along with quartz-biotite mixtures tested for comparison. First, in Series-1 experiments, gouges were sheared at a temperature of 100 °C, with effective confining pressure of 200 MPa, pore pressure of 30 MPa and loading rate of 1.22 μm/s. The results revealed that strength of quartz-biotite mixture weakened linearly with increasing biotite proportion, whereas the gouges with a biotite interlayer weakened much more significantly even for biotite content as little as ~5 wt%. Series-2 experiments were performed on simulated gouge with 15 wt% biotite interlayer at temperatures of 25–600 °C, effective normal stress of 200–230 MPa and pore pressure of 30 MPa, with stepped shear rates of 0.0488 to 1.22 μm/s. At effective normal stress of 200 MPa, the simulated foliate gouge showed a transition from velocity strengthening to velocity weakening around 200 °C, which persisted up to 600 °C. Stick-slips above 400 °C were associated with minor a–b averagely of ~−0.0006 and submicron dc values. At effective normal stress of 230 MPa and temperature of 600 °C, stick-slip motions evolved with slip distance to viscous-like behaviour at a displacement of ~3 mm. Microstructural observation on deformed samples revealed that shear deformation mainly occurred within the biotite interlayer in most cases, with surrounding quartz gouge only slightly deformed but increasingly compacted as temperature increased. Viscous-like behaviour corresponded to migration of dominant shear deformation to the quartz gouge, as indicated by the development of Riedel shears therein. Our results may help constrain fault strength and depth range of seismogenesis within fault zones associated with biotite in form of foliations and/or interconnected networks.

The controls of geomorphology and sediment supply on sequence stratigraphic architecture and sediment partitioning of the lacustrine rift basin in the Es3 of Liuzan area, Nanpu Sag, Bohai Bay Basin, China

ABSTRACTAn important hydrocarbon reservoir is hosted by the third member of the Shahejie Formation (Es3) in the Liuzan area, Nanpu Sag, Bohai Bay Basin, China. The Es3 can be divided into five third-order sequences (from base to top: Sq1, Sq2, Sq3, Sq4 and Sq5). Utilising well logs, cores and high-resolution 3-D seismic data, this study investigates the development characteristics and styles of sediment transport pathways in the steep-slope zone of the lacustrine rift basin. Two styles of sediment transport pathway are identified in the study area, including the faulted trough and fault slope-break zone. The faulted trough is divided into a single faulted trough, synthetic faulted trough and antithetic faulted trough. The fault slope-break zone is composed of synthetic fault slope-break zone and antithetic fault slope-break zone. The fan-delta plain and fan-delta front are recognised in the study area. The different styles of delivery conduits control depositional facies types and the spatial and temporal evolution of fan-delta depositional systems from Sq3 to Sq5. Based on paleo-geomorphological reconstruction, the dispersal pattern of the steep-slope zone system divided into a northern steep-slope system and an eastern steep-slope system is established. In Sq3, the northern steep-slope system develops large-scale mixed sandy–muddy fan-delta deposits derived from the NW. The eastern steep-slope system feeds the medium-scale gravel-rich fan-delta sediments. In Sq4, the large-scale mixed sandy–muddy fan-delta deposits develop from the NNE direction in the northern steep-slope system. The small-scale sand-rich fan-delta sediments are transported from the eastern steep-slope system. In Sq5, the large-scale mixed sand–mud fan-delta deposits are fed by both the northern steep-slope system and eastern steep-slope system. The strata stacking pattern exhibits a seesaw mode in the study area. Based on the analysis of the channel-belt thickness and the fan-scales, the paleogeomorphology of the drainage area in Sq3 and Sq4 and sediment supply in Sq5 alternatively control the sequence stratigraphic architecture and sediment partitioning in the sink area. The model proposed in this study may aid in the prediction of favourable reservoirs and good source–reservoir–seal development in lacustrine rift basin.

Analyzing the Storage Defects From the Perspective of Synthetic Fault Injection

In the era of digital media where users create multimedia, and the size and number of media files increase, the importance of robustness of storage devices is also increasing. Even a fault in storage may lead to not only damage of a file but also cause fatal errors that affect the system. To prevent the storage systems from such errors, it needs to be tested for physical errors and analyze their failure behaviors to take appropriate actions to prevent them. SOAR is an independent fault injection system with an SATA multiplexer to inject faults to not only storages used by desktop applications but also CE devices. SOAR runs real-time on top of Linux. SOAR injects both physical and logical errors on storage devices or device driver layer depending on the type of errors user wants to generate, respectively. Along with SOAR, we designed three test frameworks for multimedia players, file system benchmark tools, and file system. As the case study of the usage of proposed fault injection system, we tested and verified five multimedia players with a CE device, two file system benchmark tools, and four file systems

Research on fault diagnosis system of hall for workshop of meta-synthetic engineering based on information fusion

By analyzing multi-sensor information fusion system and hall for workshop of meta-synthetic engineering (HWME) essentially, a universal information fusion system of HWME based on multi-sensor is put forward. Analyzing the fault diagnosis framework of complex system based on information fusion technique, together with the research on the general process of information fusion synthesis fault diagnosis, a fault diagnosis system framework of HWME based on information fusion is set up, which is all-purposed and runs through the whole process of synthetic fault diagnosis. By this method, a new approach to multi-sensor information fusion synthesis fault diagnosis has been found.

Sequence stratigraphic approach to hydrocarbon exploration: a case study of Chiadu field at eastern onshore Niger Delta Basin, Nigeria

This study integrated lithofacies, foraminifera and seismic data to develop a sequence stratigraphic approach to hydrocarbon exploration for Chiadu field. The application of lithostratigraphic approach led to correlation of diachronous lithofacies and wrongly defined an approximately accurate extent of the reservoirs. This study necessitated the use of sequence stratigraphic framework for the purpose of establishing chronostratigraphic concept and facies prediction. The genetic sequence model of Galloway was adopted for sequence stratigraphic interpretation of the field. The structural style is dominated by closely spaced simple rollover anticline bounded by growth faults, and this includes down-to-basin listric faults, collapsed crest structures, antithetic and synthetic faults. Result of foraminifera analysis showed that the analyzed interval is very rich in calcareous benthic but decreased in planktic and arenaceous benthic foraminifera. Lithofacies analysis shows that the continental lithofacies is made up of dominantly sand with thin bands of shales, while Agbada lithofacies is made up of alternating intervals of sandstones and shales to very thick shale unit in the lower section. The facies identified using log motifs and their stacking patterns include braided fluvial, crevasse splay, fluvial point bar, distributary/tidal channels, intertidal, subtidal and storm-dominated shelf facies. The presence of water depth indicator fossils confirmed the water depths of coastal deltaic, shallow inner neritic, inner neritic, middle neritic and outer neritic were based largely on the presence of environmentally restricted benthic foraminifera species. Integration of lithofacies and biofacies data suggests depositional environments ranging from coastal deltaic to outer neritic environment. Sequence stratigraphic analysis identified three complete sequences with accompanying system tracts over the interval 7922.3–14,856.34 ft. The transgressive system tracts (TSTs) within these sequences are dominated by marine shales and thin sands. Reservoir quality sands are found in highstand system tract and shelfal lowstand system tract, while the shales of TSTs and HSTs form potential source and seal units. The delineation and correlation of sequence stratigraphic surfaces enable us to build an approximate chronostratigraphic framework, which is essential for determining facies relationships. Reacquisition and/or processing should be done to improve seismic data quality for better imaging and interpretation/mapping, especially hydrocarbon prospect at deeper horizon.

Seismic imaging of fault damaged zone and its scaling relation with displacement

We have studied seismically resolved damaged zone of normal faults in siliciclastic rocks of the Norwegian continental shelf. The workflow we have developed reveals structural details of the fault damaged zone and in particular, the subsidiary synthetic faults, horsetail at the main lateral fault tips at different depths and fault bend. These subsidiary or small fault segments form an area that can be clearly followed laterally and vertically. We call this area fault damaged zone. The studied damaged zone on seismic data comprises the fault core and the fault damage zone, as defined in outcrop studies. Spectral decomposition (short-time Fourier transform for time-frequency resolution and continuous wavelet transform) was performed on the data centered around faulted intervals. The magnitude of higher frequencies was used to generate coherence attribute volumes. Coherence attributes were filtered to enhance fault images. This integrated workflow improves fault images on reflection seismic data. Our approach reveals details of damaged zone geometry and morphology, which are comparable with the outcrop studies of similar examples conducted by previous researchers or us. We have extracted the fault geometry data including the segment length, displacement, and damaged zone width at different depths. Our results show that subsidiary faults, fault bends, linkage of fault segments, and branching in the fault tip (horsetail structure or process zone) all affect the width of the damaged zone and the distribution of displacement. We have seen a distinct increase in the fault damaged zone width near the fault bend locations. The fault segment length decreases with depth toward the lower fault tip, which is below the base Cretaceous unconformity. In addition, the displacement increases below the unconformity. In general, there is a positive correlation between fault displacement and the corresponding damaged zone width measured in this study, which is in agreement with previous studies.

Seismic interpretation and petrophysical evaluation of SH field, Niger Delta

Three out of the 14 hydrocarbon-bearing sands (A, B and I) in the ‘SH’ field onshore Niger Delta which contain bulk of the hydrocarbon reserves in the field were considered as development candidates. Seismic interpretation and petrophysical evaluation of logs of 13 wells were integrated with the aim of verifying and ascertaining the hydrocarbon reserves prior to field development which involves enormous financial commitment. Results show that the field is structurally controlled by sets of northwest–southeast-trending synthetic faults which dip southwest. Hydrocarbon traps at the three sand levels are rollover anticlinal closures that are generally sealed by a major listric fault that demarcated the field into northwest and southeast blocks. The southern fault block is hydrocarbon bearing; wells drilled in the field targeted these closures and encountered a number of stacked hydrocarbon-bearing sand levels. Reservoir-A developed a hanging-wall rollover anticlinal structure sealed by a major listric fault forming a trap with oil–water contact (OWC) of 1222 m TVDSS. Reservoir-B also shows similar structure as reservoir-A, but it is partitioned into two hydrocarbon compartments by a sealing fault; these two compartments have different OWCs. Reservoir-I exhibits similar structure to reservoir-A. The evaluation of the petrophysical characteristics revealed that the reservoirs are of good quality with average net to gross, porosities, water saturation and hydrocarbon saturation ranging from 0.774 to 0.980, 0.220–0.339, 0.133–0.367 and 0.633–0.867, respectively. Variation in the petrophysical parameters and the uncertainty in the reservoir structure of the three reservoirs were considered in calculating range of values of gross rock volume and in-place volume. The study shows oil-in-place volume in the range of 243.83–357.90 MMstb in reservoir-I, whereas reservoir-A contains 148.98–241.14 MMstb, reservoir-B1 31.31–50.36 MMstb and reservoir-B2 67.79–108.98 MMstb of oil. Conclusively, this study has further confirmed the high productivity and commercial viability of the wells within the field of study to be able to adequately compensate for the cost of development.

Comparison of upwards splaying and upwards merging segmented normal faults

A common model for normal fault growth involves a single fault at depth splaying upwards into a series of en-echelon segments. This model is applied to faults as well as a range of extension fractures, including veins, joints and igneous dykes. Examples of splaying growth fault systems in the Columbus Basin, offshore Trinidad, are presented. They include the commonly described upwards splaying type, but also one fault zone with an upward change from disconnected overlapping synthetic faults to a continuous fault. One fault zone with high-displacement fault segments is separated by a relay ramp at depth, becomes breached higher up, developing into a continuous fault at its upper part, where displacements are least. This example suggests that whilst kinematic linkage typically precedes geometric linkage in the evolution of relay ramps, low-displacement parts of a fault system may be geometrically linked whereas higher displacement areas are only kinematically linked.