Seismic Horizons Research Articles

ПРИМЕНЕНИЕ МЕТОДА СЕЙСМИЧЕСКОЙ ИНВЕРСИИ ДЛЯ ОЦЕНКИ ФИЗИЧЕСКИХ ПАРАМЕТРОВ НЕФТЕГАЗОНОСНЫХ ПЛАСТОВ

The article is devoted to a modern seismic inversion model. The spatial distribution of impedance is simulated using a synthetic well tie. A low-frequency background model is built as well as an acoustic impedance cube. Density and sonic log data are balanced. The study conducted both an analysis of petroelastic properties and a dynamic analysis. Guidelines for drilling locations are given. The method used takes into account the geological data based on a structural model for seismic horizons.

Geological structure, history of development and prospects of oil content of the Paleozoic complex of sediments of the Medynskoye-sea

The study of the geological structure, the history of the development of the Medynskoye-Sea field by reference seismic horizons corresponding to the boundaries of the Paleozoic stratigraphic complex; identification of the features of the structure and distribution of petroleum horizons identified by drilling and logging of exploration wells. Keywords: Pechora Sea; Medynskoye-sea; paleozoic; reservoir; oil capacity; shelf; hydrocarbon reserves; productive horizon.

Automatic velocity picking based on optimal key points tracking algorithm

Picking velocities from semblances manually is laborious and necessitates experience. Although various methods for automatic velocity picking have been developed, there remains a challenge in efficiently incorporating information from nearby gathers to ensure picked velocity aligns with seismic horizons while also improving picking accuracy. The conventional method of velocity picking from a semblance volume is computationally demanding, highlighting a need for a more efficient strategy. In this study, we introduce a novel method for automatic velocity picking based on multi-object tracking. This dynamic tracking process across different semblance panels can integrate information from nearby gathers effectively while maintaining computational efficiency. First, we employ accelerated density clustering on the velocity spectrum to discern cluster centers without the requirement for prior knowledge regarding the number of clusters. These cluster centers embody the maximum likelihood velocities of the main subsurface structures. Second, our proposed method tracks key points within the semblance volume. Kalman filter is adopted to adjust the tracking process, followed by interpolation on these tracked points to construct the final velocity model. Our synthetic data example demonstrates that our proposed algorithm can effectively rectify the picking errors of the clustering algorithm. We further compare the performances of the clustering method (CM), the proposed tracking method (TM), and the variational method (VM) on a field dataset from the Gulf of Mexico. The results attest that our method offers superior accuracy than CM, achieves comparable accuracy with VM, and benefits from a reduced computational cost.

Performance assessment of an iterative ensemble smoother with local analysis to assimilate big 4D seismic datasets applied to a complex pre-salt-like benchmark case

Abstract The use of 4D seismic (4DS) (or time-lapse seismic, TLS) in data assimilation (DA) makes the process more complex due to the higher amount of data to be assimilated, requiring more robust methods and better computational resources (processing capacity and memory). The development and application of permanent seismic monitoring technologies have increased in recent years, improving the overall 4D seismic quality in terms of signal resolution and repeatability. However, a massive amount of data is generated from the multiple monitors, making the incorporation of 4DS data in the DA process more complex. Therefore, robust DA methods capable of dealing with huge amount of data effectively and efficiently are essential. This paper aims to assess the performance of an iterative ensemble smoother method, named subspace ensemble randomized maximum likelihood with a local analysis, to assimilate a big dataset. The method was applied in a challenging pre-salt-like benchmark case with eight seismic surveys, one base, and seven monitors. The 4DS data are the impedance ratios (between two consecutive monitors) in 15 seismic horizons, totaling 105 maps to be assimilated. To our best knowledge, this is state of the art in terms of practical applications in DA. It was possible to assimilate all the data simultaneously: the 105 horizons for the 4DS data and the wells’ production and pressure data. The DA was successful in terms of results quality and method performance. We also ran a case assimilating only well data for comparison purposes.

Late Devensian to Holocene environmental change, Loch Lomond, UK: A seismic sedimentary record of deglaciation, paraglacial and postglacial landscape evolution

We present an interpretation of two-dimensional sub-bottom profiling data from Loch Lomond, Scotland, UK. Sediments deposited during and following the last glacier advance have been investigated for decades around the shores of Loch Lomond. For the first time, this study presents an interpretation of the subsurface providing a window into the late Quaternary and Holocene history of Loch Lomond and its surrounding. The seismic stratigraphy records the infill of the loch during the final stages of the Loch Lomond Stadial (LLS, 12.9–11.7 ka BP), through the Holocene and into the present day. Results reveal the presence of distinct seismic facies (SF) identifying four principal seismic horizons; SF-I, SF-II, SF-III, and SF-IV. The SF-I horizon represents the glaciated surface, interpreted as subglacial till (locally forming drumlins), glacial moraines or bedrock. Ice retreat was accompanied by glaciolacustrine sedimentation in a proglacial lake setting, depositing up to 44 m of laminated sediments and ice marginal fans (SF-IIa, b). A period of landscape instability followed with extensive deposition of mass transport deposits (SF-III). These deposits, characterised by chaotic seismic facies with an erosional basal surface, are up to 43 m thick and may represent up to 50 % of the sediment fill. SF-IV comprises finely laminated sediments deposited during the Holocene and highlights slower sedimentation rates in comparison to earlier phases of sedimentation. This study reveals new insights into the deglaciation of Loch Lomond, including previously unrecognised extensive mass transport deposits buried in the subsurface, associated with a period of paraglacial adjustment.

Horizon extraction using absolute seismic phase obtained by unwrapping techniques

Automatic detection of horizons and other geological structures of interest is often employed as a preliminary step in seismic interpretation. Although necessary, the identification and extraction of horizons can be a laborious and time-consuming step for the interpreter. Therefore, we present a semi-automatic horizon extraction algorithm based on the absolute phase of seismic data obtained through phase unwrapping techniques. We assess the algorithm accuracy and robustness in several examples, including noisy data sets. In addition, we present comparative results between two phase unwrapping methods, showing their robustness when associated with seismic horizon extraction. We compare the results obtained by our methods with the results obtained by seismic horizon extraction algorithms available in the literature.

Bayesian geophysical basin modeling with seismic kinematic metrics to quantify uncertainty for pore pressure prediction

Bayesian geophysical basin modeling (BGBM) methodology is an interdisciplinary workflow that incorporates data, geologic expertise, and physical processes through Bayesian inference in sedimentary basin models. Its application culminates in subsurface models and properties that integrate the geohistory of a basin, rock-physics definitions, well-log and drilling data, and seismic information. Monte Carlo basin modeling realizations are performed by sampling from prior probability distributions on facies parameters and basin boundary conditions. After the data assimilation, the accepted set of posterior subsurface models yields an uncertainty quantification of subsurface properties. This procedure is especially suitable for pore pressure prediction in a predrill stage. However, the high computational cost of seismic data assimilation decreases the practicality of the workflow. Therefore, we introduce and investigate seismic traveltime criteria as computationally faster proxies for analyzing the seismic data likelihood when using BGBM. Our surrogate schemes weigh the prior basin model results with the available seismic data with no need to perform expensive seismic depth-migration procedures for each Monte Carlo realization. Furthermore, we apply BGBM in a real field case from the Gulf of Mexico using a 2D section for pore pressure prediction considering different kinematic criteria. The workflow implementation with the novel seismic data assimilation proxies is compared with the complete computationally expensive benchmark approach, which uses a global analysis of the residual moveout in depth-migrated seismic image samples. Moreover, we validate and compare the outcomes for predicted pore pressure with mudweight data from a blind well. The fast proxy for analyzing the depth positioning of seismic horizons developed in this work yields similar uncertainty quantification results in pore pressure prediction compared with the computationally expensive benchmark. Our fast proxies make the BGBM methodology efficient and practical.

Incised valleys on the Algarve inner shelf, northern Gulf of Cadiz margin: Stratigraphic architecture and controlling factors in a low fluvial supply setting

A network of cross-shelf paleovalleys has been recognized over the paleo-inner shelf off the Gilão-Almargem Estuary, a small fluvial drainage system that presently receives minor sediment supply in the eastern Algarve shelf, northern margin of the Gulf of Cadiz (SW Iberian Peninsula). This study is aimed at determining the driving controls that triggered substantially different paleohydrological conditions and sedimentary dynamics of ancient fluvial systems in this margin. We focus on evidences of secondary controls on valley genesis and evolution, superimposed to primary glacio-eustatic control such as antecedent geology, low fluvial supply and changing hydrodynamic regimes. The architecture and spatial distribution of these paleovalleys were interpreted based on a grid of seismic profiles with different resolutions. Likewise, a sediment core obtained in a distal position of the paleovalley system provided information about sedimentary processes during the most recent stage of valley infilling. The chronostratigraphic framework was constructed based on regional seismic horizons defined in previous studies and complemented with two AMS 14C dates obtained from bivalve shells.The inner shelf paleovalley system is composed of several incised valley features which exhibit a remarkable similar internal architecture. These inner valley features exhibit two major incision phases (from oldest to youngest; IP 2 and IP 1) that are thought to constitute a simple paleovalley system formed during the last glacial cycle. The origins of the incision are considered to be different. The older one is related to fluvial incision during the sea-level fall leading into the Last Glacial Maximum, whereas the recent one is interpreted as the result of tidal scour during the postglacial transgression. Their corresponding infillings are interpreted, respectively, as estuarine bay-fill deposits and estuary-mouth sands. Overlying the paleovalley infilling, a distinctive reflective unit is in agreement with the generation of coastal barriers and related depositional systems.The formation of the paleo-inner-shelf paleovalley system was strongly conditioned by antecedent geology, which strongly limited the generation of wide incised valleys and determined the amount of incision landward of a well-defined break of slope. Its postglacial infilling was mainly estuarine in nature, likely involving the development of a dendritic system, with numerous barriers interrupted by tidal inlets and channels in a mixed estuarine system with low fluvial supply.

Automatic horizon tracking algorithm with curvature constraint

Seismic horizon tracing is a key step in seismic data interpretation. At present, it mainly relies on manual interpretation to mark the layers within the region. The deficiency of manual interpretation lies in its low precision and efficiency, and it relies heavily on the experience of the interpreter. Aiming at the above problems, the author proposes an automatic horizon tracking algorithm with curvature constraint. The algorithm firstly determines the initial seed points of horizon tracking based on logging data, and then generates all seed points by tracing the direction of crossline. According to the seed point, track the horizon by the direction of the inline. The curvature of each horizon point is calculated in the direction of the crossline according to the tracked results. For the layer point that do not meet the ruling curvature threshold, they are traced again in the direction of the crossline, and finally the corrected tracking results are obtained. Through the test of actual data, this method has achieved good results.

Processing and interpretation of seismic reflection data from the Los Humeros super-hot geothermal system

The Los Humeros volcanic complex is a geothermal field in Mexico that is now being further investigated as a candidate for the development of a super-hot geothermal system, as it has a temperature of over 350 ∘C. The European Horizon 2020 project GEMex (2016–2020) worked in this context aiming to characterize the geological and geophysical aspects of the area to assess the feasibility of a super-hot geothermal system. We describe the results of time and depth processing and interpretation of legacy 2D reflection seismic lines acquired in 1998 to study the deep structures of the caldera in the Trans-Mexican Volcanic Belt. The study is relevant for the geophysical characterization of the subsurface in this area, where no vertical seismic profiles are available but only two short sonic well logs. The interpretation of selected seismic horizons in the seismic depth profiles was first determined by the local geological model of the curved caldera and then calibrated by the stratigraphy of the boreholes and the matching of the 2D seismic lines crossing points. The processing outcomes are depth-migrated profiles, the corresponding P-wave velocities and the updated geological models. The main results are the representation of the basement and the identification of the structural make-up of the main units with some of the main faults of the collapsed caldera. Our results provide new insights into the subsurface geometry of volcanic collapses and the geothermal field contained within them at the caldera scale.

Geoelectrical model of the Earth’s crust along the Shu-Sarysu geotraverse according to magnetotelluric soundings

Purpose. To study and assess the possibility of effective application of electrical prospecting by magnetotelluric sounding (MT-sounding) and to determine the range of geological problems to be solved in the geoelectric conditions of the Shu-Sarysu geotraverse. Methodology. The issues of methodology of modern technologies of field observations, peculiarities of processing and interpretation of MT-sounding data are considered, which showed that modern instrumental and methodical electrical survey technologies of MT-sounding allow obtaining results of field measurements of increased reliability, due to their accuracy, productivity, mobility, noise immunity, level of automation. To identify the main features of the geoelectric structure of the Earth’s crust and the upper mantle, the modern technique of interpreting MT data allows for 1, 2D inversion of the effective curves of apparent resistivity and impedance phase. Findings. Based on MT-sounding data, a geoelectric section of the Shu-Sarysu geotraverse was constructed, characterizing the position and morphology of five geoelectric boundaries in the crustal section in the 0–40 km depth interval. The identified five geoelectric horizons show good coincidence with the conventional seismic horizons and confidently correlate with the geological references established by GIS data. Originality. On the basis of MT-sounding studies, the geological interpretation of the structure of suprasalt and subsalt structural-formation complexes is presented; the geological efficiency of MT-sounding electrical prospecting in revealing the complex structures in the conditions of the Shu-Sarysu geotraverse is shown. On the basis of model constructions of the geoelectric section, new data on the deep geological structure of the Shu-Sarysu geotraverse were obtained: new data on the structure of Mesozoic terrigenous-sedimentary rock complexes and the Paleozoic part of the section with the allocation of the supposed faults; on the basis of MT-sounding results, recommendations for further detailed geological exploration work were given. Practical value. A comprehensive interpretation is recommended of the obtained MT-sounding data together with the results of geological and geophysical research on the regional profile in order to establish search criteria for the discovery of mineral deposits and the prospects of gas content in the area.

Superimposed structure in the southern periphery of Abu Gharadig Basin, Egypt: Implication to petroleum system

South West Abu-Sennan (SWS) area near the southern periphery of the Abu-Gharadig petroliferous basin in the Egyptian Northern Western Desert is an important hydrocarbon field characterized by being a multi-reservoir with a complex structural architecture. Therefore, in this study, we illustrated the regional structural role that facilitated having Jurassic mature source rocks (Masajid and Khatatba formations) through surgical seismic interpretation and observed the controlling petroleum system of the study area using a set of 20 seismic lines and 4 wells data. The study resulted in having the SWS oil field controlled by a strike-slip movement that occurred during the Upper Cretaceous time accompanying the African Plate movement against the Eurasian Plate superimposing an ENE–WSW strike-slip fault zone in the region and a strong pattern of NW–SE-oriented faults due to numerous phases of extension. The associated structures include horsts, normal fault propagation folds, and strike-slip-related anticlines. The strike-slip tectonics played a major role in forming entrapment for the Jurassic expelled hydrocarbons. The seismic horizons flattening exercise performed on AR/G member and Khoman Formation demonstrated that the main reason for not having hydrocarbon accumulations in the Jurassic levels in the study area is that the trap configuration was ready to accumulate hydrocarbon but after the hydrocarbon generation and migration time. The study concluded that the hydrocarbons migrated along the faults which cut deeply to the source rocks and entrapped in the possible cretaceous reservoirs during the late cretaceous time. The conducted workflow in this study can be utilized to better explore and develop cretaceous reservoirs in the study and neighbouring areas.

Palynology, palaeoclimate and chronology from the Saalian Glacial to Saint-Germain II interstadial from two long cores at the limit between the Mediterranean and Euxinian regions

The Marmara region (NW Turkey) has a transitional vegetation and climate between the Mediterranean one and the Euxinian one. For the last Interglacial period or Eemian and following the two Saint-Germain Interstadials (i.e. c. MIS 5), as well and the previous glacial, the Saalian, no vegetation or climate information is available yet. Here we provide the results of the pollen analysis of two sediment cores taken from the Sea of Marmara. We focus on the period below a major erosion horizon, i.e. the red-H1 seismic horizon, which corresponds to the last Interglacial and a large part of the previous glacial period. A palaeoclimatic reconstruction inferred from pollen assemblages is also proposed here.Based on geochemistry that allows inter-core comparison and on a succession of warm and cold phases derived by pollen analysis, a nearly complete sequence from the Saalian Glacial period (c. MIS 6) to the Saint-Germain II Interstadial (MIS 5a) was obtained, despite the occurrence of hiatuses corresponding often to lowstands.The Pterocarya extinction has been traced from MIS 7 in Italy to Saint-Germain I Interstadial (c. MIS 5c) in the eastern Sea of Marmara, showing a progressive retreat from west to east until the Black Sea region, where it is still present nowadays.The climatic changes reconstructed for the Eemian Interglacial (or c. MIS 5e) are characterised by warmer temperature and a slightly drier climate than at present, at its peak. This pattern is in agreement with the Ohrid climate pattern, in the Balkans. In the Marmara region, this is reflecting a shift of the Mediterranean climate towards the NE and a reduction of the Euxinian vegetation.

Chapter 6. Seismic expression of North Sea Jurassic sequences

Abstract Many of the stratigraphic sequences recognized in North Sea Jurassic well sections correspond to mappable surfaces on seismic sections. Typically, however, sequences are only mappable seismically within individual sub-basins, and seismic correlation between sub-basins, or across highs, is generally impossible without independent control from wells. Particularly prominent seismic sequence boundaries occur at near-base J54 in the Inner Moray Firth (‘Intra-Oxfordian Event’) the Viking Graben (‘Top Heather’ in this area), base J62 (‘Top Heather’, Moray Firth), base J66 (‘Top Lower Hot Shale’, Inner and Outer Moray Firth), base J71 (East Shetland Platform), base J73 (‘Top Siltstone Member’, Moray Firth) and top J70/base K10 (‘Base Cretaceous Unconformity’ (BCU), basin-wide). The BCU is the most frequently mapped seismic horizon in the North Sea Basin in Jurassic–basal Cretaceous studies. This surface, at the base of the Cromer Knoll Group, separates synrift sediments from post-rift successions above and marks a major shift in the tectonic evolution of the North Sea Basin.

Reconciling the onshore/offshore stratigraphy of the Canning Basin and implications for petroleum prospectivity

The Canning Basin is a prospective hydrocarbon frontier basin and is unusual for having limited offshore seismic and well data in comparison with its onshore extent. In this study, seismic mapping was conducted to better resolve the continuity of 13 key stratigraphic units from onshore to offshore to delineate prospective offshore hydrocarbon-bearing units, and better understand the distribution of mafic igneous units that can compartmentalise migration pathways and influence heat flow. The offshore Canning Basin strata are poorly constrained in six wells with limited seismic coverage; hence data availability was bolstered by integrating data from the onshore portion of the basin and adjacent basins into a single 3D seismic stratigraphic model. This model integrates over 10 000 km of historical 2D seismic data and 23 exploration wells to allow mapping of key stratal surfaces. Mapped seismic horizons were used to construct isochores and regional cross-sections. Seven of the 13 units were mapped offshore for the first time, revealing that the onshore and offshore stratigraphy are similar, albeit with some minor differences, and mafic igneous units are more interconnected than previously documented whereby they may constitute a mafic magmatic province. These basin-scale maps provide a framework for future research and resource exploration in the Canning Basin. To better understand the basin’s geological evolution, tectonic history and petroleum prospectivity, additional well data are needed in the offshore Canning Basin where Ordovician strata have yet to be sampled.

Fluvial reservoir characterization through channel belt dimension and petrophysical analysis

The dimensions and connectivity of fluvial reservoirs vary greatly, making it challenging to characterize them using conventional approaches. In this study integrated channel belt dimension analysis from seismic geomorphology and empirical equations, well log facies, and petrophysical analysis were performed to characterize the fluvial reservoirs. The study interval consists of fluvial deposits and is divided into three reservoir zones, which are defined by four key regional markers (B, D, K, O). In these intervals, six (6) fluvial facies have been identified. Based on the log facies proportions and their stacking relationships, it is interpreted that the reservoirs in Zone 1 (B to D) were deposited in a proximal reach of a meandering system, Zone 2 (D to K) in a marginal marine setting, and Zone 3 (K) in a distal reach of a meandering system. The dimensions of fluvial channels and channel belts were determined using empirical equations. The results were compared with the observed dimensions of fluvial channels and channel belts from the seismic horizon and stratal slices of the same intervals. Zone 1 and 3 are characterized by broad meander belts (1000–4000 m) compared to zone 2 (600–1300m). Petrophysical analysis showed zone 1 and 3 have the better petrophysical properties compared to zone 2. Though zone 3 has the most well-developed sand bodies the best reservoir interval is zone 1 because of its higher porosity. Although channel belt dimensions have a significant influence on reservoir connectivity, they do not seem to have control on reservoir properties. The channel belt dimensions obtained from the empirical equations and interpreted from the seismic geomorphology analysis were found to be strikingly similar. Since three-dimensional seismic data is not available everywhere and seismic imaging quality decreases with depth, empirical equations can be used to analyze fluvial reservoir parameters and their connectivity at greater depths.

A Data Science Approach to Uncertainty Evaluation in Fault-Seal Analysis for Exploration Applications in Siliciclastic Reservoirs

Summary Fault-seal analysis is used to understand the risk of hydrocarbons leaking out of a trap across bounding faults. There is a broad standard industry workflow for this analysis in clastic rocks, involving building a structural framework of the key seismic horizons and faults, estimating the clay content of the stratigraphy, predicting fault clay content using an algorithm such as shale gouge ratio (SGR), converting the predicted clay content to capillary threshold pressure, and calculating sealing capacity using the reservoir fluid properties. The inputs to the analysis are typically subject to considerable uncertainty that is difficult to understand and evaluate. One approach is to create “end member” scenarios to evaluate the impact of the key uncertainties, but this gives an incomplete picture and only a limited number of scenarios can be run and analyzed in the time typically available. The approach outlined here instead uses an automated workflow that runs hundreds of scenarios with stochastically varying input parameters. Data-science techniques combining domain expertise, mathematics and statistics, and computer coding are used to analyze and build models of the results. The advantages of the approach over a traditional fault-seal analysis workflow are that a wider range of input uncertainties can be considered, and that the results of a large number of realizations can be consolidated and visualized in ways that are specific to the problem being addressed and useful to the geologist undertaking the analysis. A key advantage is that the uncertainty inherent in this type of analysis can be explicitly incorporated, and the impact of the uncertainty clearly understood and communicated to decision-makers. Similar techniques could be applied to other geological analyses where uncertainty is an issue.

Sequence-constrained multitask horizon tracking

Deep learning-based automatic horizon tracking has achieved promising results but still faces serious cross-horizon phenomena. Therefore, based on multitask learning, seismic data characteristics, and the seismic horizon sequence (or position) relationship, we have developed a sequence-constrained multitask horizon tracking (SMHT) method for high-precision automatic horizon tracking. SMHT contains the horizon label automatic enrichment, the multitask horizon tracking network (MHTN), and the horizon sequence-constrained loss function. Horizon label automatic enrichment aims to automatically generate the upper and lower auxiliary horizon labels of the target horizon label, and then the horizon region labels corresponding to the auxiliary and target horizon labels for MHTN. MHTN contains the shared layer, the auxiliary task, the main task, and the horizon sequence-constrained horizon correction. In MHTN, the shared layer generates multiscale feature maps of the input seismic data. The auxiliary task uses the concept of object detection to extract the horizon region (or probability), and the main task extracts the high-precision horizon within the extracted horizon region. The horizon sequence-constrained horizon correction with the horizon sequence-constrained loss function aims to avoid the cross-horizon phenomenon and finally obtain precise horizon tracking results. Application of MHTN to two field 3D seismic data sets finds that SMHT performs well in automatic horizon tracking.

Integration of recent drill results with multichannel seismic reflection data: New inferences on the subsurface configuration and sedimentary history of the northwestern Bay of Bengal

The study pertains to the use of two industry wells and one IODP drill site in conjunction with high quality multichannel seismic reflection data in the northwestern Bay of Bengal. The industry wells provide subsurface information from Early Cretaceous period while the IODP drill site U1444 gives information about deposition younger to Miocene. Their locations over the seismic profiles facilitated the assignment of ages to the prominent seismic horizons thereby yielding a revised seismic stratigraphy of the northwestern Bay of Bengal.The ages of the oldest seismic horizons are in agreement with the recently published ages of the underlying oceanic crust. The sediments up to Late Cretaceous time are thick west of 85°E Ridge, while to its east, they are thin. The sediments up to Paleocene time thin towards offshore, implying that they are land derived (from East Coast of India). Fan sedimentation commenced in the Eocene time and was excessive since Miocene. The transparent sequence between the Late Pleistocene and Pliocene unconformities is thin over the 85°E Ridge. The western extents of the Quaternary subfans above the Late Pleistocene unconformity are demarcated in the study area.Further, the study suggests that the emplacement of the 85°E Ridge took place in the Middle Cretaceous period. Faulting/folding at the continental rise occurred around Miocene time and maybe linked to intraplate deformation that occurred in the Central Indian Ocean Basin. Thus, the inferences drawn from this study help to provide a reliable sedimentary history of the northwestern Bay of Bengal forming an updated base for future investigations.

Fault reactivation potential in a carbonate field in Brazil based on geomechanical analysis

The reactivation of faults may directly modify their permeability and the integrity of the petroleum system seal. Thus, this understanding is fundamental for decision-making in the petroleum industry at different levels while developing, for example, hydraulic fracturing projects, fracture networking, Enhanced Hydrocarbon Recovery (EOR), and CO2 storage. The identification of the stress field based on elastic properties, failure criterion, rock strength, and in-situ principal stresses allow to understand the geomechanical behavior of stratigraphic units. This process becomes complex in carbonate reservoirs because they present high geomechanical variability related to the sedimentary and diagenetic processes they undergo. In this context, the present work aims to study the potential for fault reactivation in the pre-salt Barra Velha and Itapema Formations and in the Camboriu Formation in the study area, Santos Basin, Brazil, based on geomechanical modeling. Data from 28 wells with basic geophysical well-logs and wellbore image logs, absorption and formation pressure tests, and 3D pre-stack seismic data were used. The results indicate an abnormally high fluid pore pressure (9.49 ppg) concerning hydrostatic pressure (8.34 ppg). Three structural compartments delimited by interpreted seismic horizons and faults were defined. Three fault regimes were defined based on minimum and maximum horizontal stresses gradients: a double normal-transcurrent regime for the Barra Velha and Itapema Formations; a normal regime for the Piçarras Formation; and a double transcurrent-inverse regime for the Camboriu Formation. Finally, based on the stress polygon, scenarios of fault reactivation in the structural compartments were estimated. With increases between 16% and 28.1% of the pore pressure by fluid injection, the transcurrent movement of the faults can be generated. The reverse faults of a shallower structural compartment have the highest probability of reactivation and movement.