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<jats:p> 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. </jats:p>

<jats:p> Faults play a key role in reservoirs by enhancing or restricting fluid flow. A fault zone can be divided into a fault core that accommodates most of the displacement and a surrounding damage zone. Interpretation of seismic data is a key method for studying subsurface features, but the internal structure and properties of fault zones are often at the limit of seismic resolution. We have investigated the seismic response of a vertical fault zone model in sandstone, populated with fault facies based on deformation band distributions. Deformation bands reduce the porosity of the sandstone, and they condition its elastic properties. We generate synthetic seismic cubes of the fault facies model for several wave frequencies and under realistic conditions of reservoir burial and seismic acquisition. Seismic image quality and fault zone definition are highly dependent on wave frequency. At a low wave frequency (e.g., 10 Hz), the fault zone is broader and no information about its fault facies distribution can be extracted. At higher wave frequencies (e.g., 30 and 60 Hz), seismic attributes, such as tensor and envelope, can be used to characterize the fault volume and its internal structure. Based on these attributes, we can subdivide the fault zone into several seismic facies from the core to the damage zone. Statistical analyses indicate a correlation between the seismic attributes and the fault internal structure, although seismic facies, due to their coarser resolution, cannot be matched to individual fault facies. The seismic facies can be used as input for reservoir models as spatial conditioning parameters for fault facies distributions inside the fault zone. However, relying only on the information provided by seismic analyses might not be enough to create high-resolution fault reservoir models. </jats:p>

<jats:p> Seismic data in fold and thrust belts (FTBs), especially in onshore areas, are often difficult to interpret due to poor imaging of complex structures. Outcrops, either in the same area as the seismic or in FTBs with similar stratigraphy, provide direct and essentially unfiltered views of structures that can form in this structural style. In addition, physical and mathematical analog models can provide insights on the development of compressional structures and the parameters that most strongly influence their shape. The task of seismic interpretation in FTBs can be aided substantially by using well-exposed outcrops and analog models of compressional structures as templates. </jats:p>

<jats:p> Subsurface structural maps are stored as spatially referenced numeric grids. The spatial sampling density of these grids is a critical parameter in the mapping process because the sampling and aliasing that occurs when transforming from original data sources during the gridding process controls the information content and aesthetics of the final map. New results from upscaling experiments and sampling theory indicate that it is possible to specify gridding parameters that remove noise while retaining key geologic structure — an optimized generalization procedure. Furthermore, geologic structure may exist at multiple scales. Sampling theory can again be applied, in a multiscale curvature analysis, to yield structure at a range of scales via decomposition of a gridded surface. These products can be analyzed further for indications of short-wavelength, high-curvature features that may correspond to fault or fracture zones, and long-wavelength, prospect, and field-scale structure. These results combine to inform a discussion on sampling, smoothing, and geologic information, as well as provide a quantitative alternative to rules of thumb for grid sampling that balance signal and noise in standard mapping schemes. </jats:p>

<jats:p> Cores drilled from wells are significant resources for understanding the geologic characteristics of petroleum reservoirs. However, due to the high cost and long rig time involved, it is impossible to obtain cores from the entire sedimentary formation in a drilling well. Furthermore, core breakage limits the amount of information that can be obtained in the vertical deposition environment of deep-buried formations. Therefore, we have used ultrahigh-resolution and high-quality borehole electrical images obtained by a borehole electrical imaging tool, High-Definition Formation MicroImager (FMI-HD), to supplement “core” information and characterize the petrologic features, such as grain size and sedimentary structure, of conglomeratic formations in the Permian Upper Urho Formation at well JL42, Zhongguai Uplift, Junggar Basin, China. We have observed conglomeratic cores at 95.92 m in well JL42 and recorded various petrologic features of the core cylinders. In the cored interval, the FMI-HD images were compared with core photos in detail; grain size results from the FMI-HD images and cores were very similar. However, there were major differences in the structural results due to core interruption. In addition, the high-resolution depositional facies of the Upper Urho Formation at well JL42 were dissected in terms of the distributive fluvial system, not the fan-delta system, using vertical grain size features derived from FMI-HD images. Boulders, cobbles, coarse pebbles, and fine pebbles were developed in thick gravelly channels in the lower proximal facies, whereas fine pebbles and granules were developed in thin channels in the upper medial facies. Therefore, FMI-HD images can be efficiently used to supplement cores and sedimentary information, which provides important insights on the paleogeology of conglomeratic formations and in turn on the exploration potential of petroleum systems. </jats:p>

<jats:p> Subtle fault detection plays a vital role in reservoir development studies because faults may form baffles or conduits that significantly control how a petroleum reservoir is swept. Small-throw faults are often overlooked in interpreting seismic amplitude data. However, seismic attributes can aid in mapping small faults. Over the years, dozens of seismic attributes have been developed that offer additional features for interpreters with associated caveats. Using the Maui 3D seismic data acquired in the Offshore Taranaki Basin, New Zealand, we have generated seismic attributes that are typically useful for fault detection. We find that multiattribute analysis provides greater geologic information than would be obtained by the analysis of individual attribute volumes. We extract the geologic content of multiple attributes in two ways: interactive corendering of different seismic attributes and the unsupervised machine learning algorithm self-organizing maps (SOM). Corendering seismic attributes that are mathematically independent but geologically interrelated provides a well-integrated structural image. We suggest eight combinations of 16 various attributes useful for a human interpreter with interest in fault and fracture detection. Current interpretation display capabilities constrain corendering to only four attribute volumes. Therefore, we use principal component analysis and SOM techniques to efficiently integrate the geologic information contained within many attributes. This approach gathers the data into one classification volume based on the interrelationships between seismic attributes. We show that our resulting SOM classification volume better highlights small faults that are difficult to image using conventional seismic interpretation techniques. We find that SOM works best when a fault exhibits anomalous features for multiple attributes within the same voxel. However, human interpreters are more adept at recognizing spatial patterns within various attributes and can place them in an appropriate geologic context. </jats:p>

<jats:p> The Delaware Basin of Texas and New Mexico is experiencing elevated levels of seismicity. There have been more than 130 earthquakes with moment magnitudes of at least 3.0 recorded between 2017 and 2021, with earthquakes occurring in spatiotemporally isolated and diffuse clusters. Many of these events have been linked to oilfield operations such as hydraulic fracturing and wastewater disposal at multiple subsurface levels; however, the identification and characterization of earthquake-hosting faults have remained elusive. There are two distinct levels of faulting in the central region of the basin where most earthquakes have been measured. These fault systems include a contractional basement-rooted fault system and a shallow extensional fault system. Shallow faults trend parallel to and rotate along with, the azimuth of S<jats:sub> HMAX</jats:sub>, are vertically decoupled from the basement-rooted faults, accommodate dominantly dip-slip motion, and are the product of more recent processes including regional exhumation and anthropogenic influences. The shallow fault system is composed of northwest–southeast-striking, high angle, and parallel trending faults which delineate a series of elongate, narrow, and extensional graben. Although most apparent in 3D seismic reflection data, these narrow elongate graben features also are observed from interferometric synthetic aperture radar (InSAR) surface deformation measurements and can be delineated using well-located earthquakes. In contrast to the basin-compartmentalizing basement-rooted fault system, shallow faults do not display any shear movement indicators, and they have small throw displacement given their mapped length, producing an anomalous mean throw-to-length ratio of 1:1000. These characteristics indicate that these features are more segmented than can be mapped with conventional subsurface data. Much of the recent seismicity in the south-central Delaware Basin is associated with these faults and InSAR surface deformation observations find that these faults also may be slipping aseismically. </jats:p>

<jats:p> Multi-component seismic exploration provides more valuable information for the prediction of underground structure, lithology, fluids and fractures. Most studies on lithology estimation and fluid description using PP- and PS-wave seismic data are mainly focusing on relatively shallow targets with high porosity. Focusing on the deep carbonate (dolomite) reservoirs with low porosity (generally less than 5%), we first analyze characteristics of seismic response difference between PP-wave and PS-wave, and then we combine logging data and seismic forward modeling to implement the identification of fluids using amplitude difference between PP and PS waves. Datasets are acquired over grain beach dolomite reservoirs in the Cambrian Longwangmiao (LWM) formation, the central Sichuan Basin, Western China. The reservoirs are filled with different types of fluids (e.g. gas, water, bitumen, etc.). Based on comparisons between seismic responses of PP-wave and PS-wave, we observe that at the location of the gas-bearing layer, PP-wave amplitude exhibits strong peaks and PS-wave amplitude shows relatively weak peaks, which is different from that obtained for the case of the water-saturated layer. However, at the location of bitumen-filled reservoirs, both PP- and PS-wave amplitudes exhibit strong peaks, and the reflection amplitude of PP-wave is stronger than that of PS-wave. Therefore, the amplitude difference of PP and PS waves provides a valuable information and feasibility for fluid identification. We verify that the maximum peak amplitude attribute of PS-wave may better characterize the distribution of porous dolomite reservoirs than that of PP-wave, and using the attribute of maximum peak amplitude difference between PP and PS waves, we may distinguish gas-bearing and water-saturated layers. Comparing with actual drilling results, we conclude that the proposed PP/PS interpretation technique is feasible for the fluid identification in deep carbonate reservoirs. </jats:p>