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Fourth EAGE Borehole Geology Workshop
- Conference date: September 27-29, 2021
- Location: Online
- Published: 27 September 2021
1 - 20 of 22 results
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WBI Analytics: Porosity Spectrum Analytics predict areas of High Quality Properties in Middle East Carbonate Reservoir
Authors G. Burmester, A.S. Almehrzi and M.I. SusantoSummaryCarbonate reservoirs in UAE are characterized by vertical and lateral heterogeneity which impacts production performance. Moving fields into water injection and EOR phases of the development, a robust description of this variability is critical. In an integrated multi-well reservoir characterization study, Abu Dhabi Offshore Company and OMV worked together to evaluate 12 wells with WBI data using the methods of determining porosity spectrum, porosity texture and fracture aperture/porosity analytics in a probabilistic approach. The study demonstrates the value of WBI data to the reservoir model, in predicting effective porosity, quantifying fracture contributions, and identifying high quality rock classes. The rock classes were integrated into the reservoir model and are proven to be aligned with principal component analysis (PCA) that come from other measurements (e.g. bed thickness trend, permeability, etc). This enables 3D distribution of the classes in the reservoir model. The rock class scheme, which consist of 6 classes, is aligned with PCA existing in the reservoir model confirming the robustness of the scheme.
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A Dispersion-based Approach for Monopole Slowness Estimation and its Implications for Borehole Geology
Authors X. Sun and C. AyadiunoSummaryMonopole acoustic logging is one of the most common approaches to evaluate borehole geology conditions. It is recognized that overlapped waves or wave interferences in monopole waveforms can pose a practical challenge to reasonable geological interpretations. To mitigate this situation, this paper presents a method to extract and reconstruct the waveforms of interest (i.e., compressional, shear and Stoneley wave) from the original waveform data by using Radon transform. In particular, an adaptive muting scheme is employed to overcome the severely diffused energies caused by the limited receiver samplings, which is an intrinsic issue of borehole acoustic logging. Then, a new slowness spectrum is formulated via a dispersive perspective to upgrade the accuracy of slowness estimation. In practice, the entire workflow is demonstrated by a high- frequency monopole example, and the derived results suggest that wave separation is a critical step to reveal true kinematic and dynamic behaviours of each wave mode prior to interpretation. Moreover, it is shown that using the adopted dispersive measure to analyse borehole compressional and shear waves can remarkably enhance the accuracy of slowness estimation with respect to borehole geology.
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Unraveling the Mystery of Conglomerate Reservoir by Comprehensive Formation Evaluation in Liaohe Depression, Bohai bay Basin
More LessSummaryIt is necessary to integrate various advanced measurements to gain in-depth understandings of coarse- grained sediments which have complex mineral composition, variable grain size and rock texture. Geochemical element log helps to calculate the complex mineral composition. FMI image shows the grain size of the gravel, the size of grain to support gravels, rock texture and natural fractures. NMR log characterizes the porosity and pore size structure. Dipole sonic data reflects the permeability and fracture effectiveness. The TOC from geochemical element log, the separation between density porosity and NMR total porosity indicate the fluid property. In this case, the upper is conglomerate with parent rock being mainly clastic, and the lower is breccia with parent rock being metamorphic. Breccia has lower porosity and more fractures than conglomerate. For both, the lithofacies with more coarse grains, proper grain sorting, and coarse grain supported pattern has higher porosity and better pore size structure, they contribute higher production. Effective natural fractures improve the bulk permeability and production. Fine grains, poor sorting, and calcareous cementation harm the reservoir rock properties.
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Successful use of image logs for sidewall core orientation from field to laboratory
Authors R. Berto, G. Volonte, A. Bersani, R. Cerri and F. PinelliSummaryThe presented e-SWCG (SideWall Core Goniometry) workflow is dedicated to deliver a complete a posteriori orientation of the rotary sidewall cores (RSWC), allowing several applications, such as geomechanical tests, permeability anisotropy and natural fracture evaluation, previously reserved to larger size samples taken from bottom hole cores. The method is based on the identification of geological features recognizable on 360° unrolled X-Ray CT image and at the well scale on the image logs. This approach is currently adopted in Eni for different geological environments and requires several scenarios of log planning strategy, operational solutions and post-coring procedures, in order to maximize the quality of the subsequent analyses. The presented case studies involve two wells very different in terms of lithology, borehole environment and, more importantly, a priori knowledge of the RSWC orientation. Particularly, one case history on carbonates shows the reliability of the procedure even with limited available data. On the other hand, the other case on a clastic reservoir emphasizes the advantages of using coring tools to achieve greater control on RSWC positioning. Both case histories successfully provided the correct parameters to orient the physical rock samples.
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A novel two-stage segmentation technique for unsupervised textural facies recognition
Authors M.T. Galli, R. Berto, C. Onzaca and F. RicciutiSummaryA new automatic textural facies recognition model in borehole images has been developed. The novelties of the approach rely on the creation of a fast and unsupervised method customized on the geometrical characteristics of image log data. The circularity of borehole images is exploited, the scale of analysis can be changed, and previous interpretations of the image log can improve the overall results providing an initial segmentation, such as manual picking of beddings. The workflow is based on a two-stage segmentation algorithm, designed for textural facies recognition in wellbore images: in the first stage, the image is divided into different regions, while, in the second stage, groups of regions are clustered according to their similarity of textural information and spatial coherence of pixel values. The workflow has been tested in both clastic and carbonate reservoirs, and the results were promising; the recognized facies mapping was consistent from the geological point of view, honouring the main lithological and structural framework. The recognition of textures from borehole images is an important step in the analysis of well data; the outcomes of the new methodology highlighted the added value of an automatic approach in terms of objectivity and robustness of the interpretation.
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Borehole Image Interpretations during ongoing operations – a workflow from a scientific drilling campaign in Switzerland
Authors B. Roters, M. Habermüller, N. Levi and R. GarrardSummaryThe National Cooperative for the Disposal of Radioactive Waste (Nagra) currently pursues a multi- well scientific data gathering program in northeastern Switzerland to find the best suitable site for construction of a radioactive waste disposal. The target is the Opalinus Clay, a thick claystone formation of Lower Dogger age. During the program boreholes are drilled and borehole image logs are acquired among other measurements. Also, MHF and GTPT test are done in the open-hole
boreholes. Results of MHF testing are reviewed again with BHI, which are compared with the pre- MHF BHI runs. The image logs are run during ongoing drilling, testing and workover operations; this means acquisition, and also processing, QC and interpretation of BHI are performed under time and cost pressure. NiMBUC Geoscience developed a workflow for this project to deliver processed and QC’ed, highly accurate, hand-picked image interpretations within the required 12 hours to Nagra and
other vendors. This allows smooth and cost-efficient operations at the drill site. The high-quality interpretations are also the foundation for more detailed analyses and comparisons of and between the boreholes at a later stage. This is a good practice example of fitting BHI interpretations into ongoing drilling operations.
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Characterization of the Stress Field at the Alpine Thrust Front (Eastern Alps, Austria)
Authors N. Levi and M. HabermuellerSummaryThe stress field near the Alpine thrust front was studied in the Austrian Molasse Basin, based on geophysical data of over 70 wells drilled in both the undeformed foreland and the thrust belt. Stress orientations were inferred from the orientation of borehole breakouts and drilling induced tensile fractures on image logs. The resulting SHmax orientation is constantly oriented close to N-S (perpendicular to the belt front), with little variations only in the Eastern part of the study area.
Stress perturbations along the borehole were observed only in two neighboring wells in the eastern sector, indicating active out-of-sequence thrusting along the alpine front thrust. Integration with 3D seismic and Quaternary outcrop data highlight very recent fault activities. In particular, displaced Pleistocene conglomerates and stress field rotations in the boreholes indicate active faulting at the eastern closure of the Molasse Basin.
1D geomechanical models indicate a strike-slip regime in the western and central sector, with high stress gradients in the internal zone of the belt, whereas moderate gradients occur in the foreland. In the eastern sector, where active out-of-sequence faulting was observed, the 1d models indicate a thrust regime in the allochthonous units, whereas the basement is governed by a strike-slip regime.
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Formation evaluation through single casing from ultrasonic oblique incidence logging
More LessSummaryWell integrity evaluation has a central role for current and future projects which utilizes boreholes to achieve the applications proposes (e.g. oil and gas, injection projects, CCS, geothermal, waste disposal, water management, etc.). This abstract reveal strong incentives for further evaluation of the data collected in the case holes with scope of harmonizing of integration of information and knowledge between the geology and well structure itself. We present background theory, brief numerical simulations for oblique incidence ultrasonic logging focused on single casing integrity evaluation followed by relevant examples for information integration between cased hole third interface echoes (TIE) standard image products and open hole logging while drilling imaging. We conclude that when downhole physical condition for TIE analyze are met, the stratigraphical image analyze is possible directly from specific ultrasonic cased hole logging.
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Deepening the Understanding of Reef Limestone Reservoir Heterogeneity with Technology Advances in Borehole Imaging
More LessSummaryCarbonate reservoirs in UAE are characterized by vertical and lateral heterogeneity which impacts production performance. Moving fields into water injection and EOR phases of the development, a robust description of this variability is critical. In an integrated multi-well reservoir characterization study, Abu Dhabi Offshore Company and OMV worked together to evaluate 12 wells with WBI data using the methods of determining porosity spectrum, porosity texture and fracture aperture/porosity analytics in a probabilistic approach. The study demonstrates the value of WBI data to the reservoir model, in predicting effective porosity, quantifying fracture contributions, and identifying high quality rock classes. The rock classes were integrated into the reservoir model and are proven to be aligned with principal component analysis (PCA) that come from other measurements (e.g. bed thickness trend, permeability, etc). This enables 3D distribution of the classes in the reservoir model. The rock class scheme, which consist of 6 classes, is aligned with PCA existing in the reservoir model confirming the robustness of the scheme.
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Integrated Sub-surface Approach for Narrow Margin Drilling in Duva Region: A Case Study from North Sea
Authors D. Kumar, J.P. Castagnoli, S. Clerc, R. Aleixo, S. Ferrari and M. DammSummaryLost circulation in Lower Kyrre and Tryggvason formations and shear failure in Rødby and Åsgard formations is a well-known challenge in the Duva region (southern part of North Sea). Covering above mentioned formations in one 12 ¼” section was the chosen concept, to deliver the challenging well trajectories. The pre-planning included a geomechanical forecasting of the drilling window for the planned trajectory.
Integrated approach of drilling event analysis with recently acquired image data in drilled offset geo-pilot well from the Lower Kyrre and Tryggvason formation provided valuable information on fractures and drilling events in the region. Core test results used to create empirical correlation to estimate rock strength properties of the formations. Correlations available in public domain for North Sea (Fuller correlation for static rock properties and internal friction angle from gamma ray) used to estimate mechanical properties. Poro-elastic approach with strain terms derived from the available leak-off test data and lost circulation events provided the realistic horizontal stress profile. A final drilling window was prepared using Modified Lade failure criterion. Integrated geomechanics support in real-time and equivalent circulating density management helped successful drilling in the region.
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Geo-mechanical Electro-facies Analysis Using High-resolution Unconfined Compressive Strength Derived from High-res Mechanical Property Image
More LessSummaryAdvancements in integrated, high-resolution reservoir characterization can be applied to enhance efficiencies in the unconventional reservoirs’ completion strategies. Sonic-derived mechanical property outputs do not adequately resolve thin beds and therefore do not provide a representative characterization of the reservoir. A novel workflow is proposed to address this challenge, with the integration of high-resolution borehole image data & geo-mechanical logs using SOM data analytics model, as applied to the Eagle Ford shale unconventional reservoir. The Eagle-ford shale has highly laminated thin beds, nodular facies as clear from the resistivity image data, which can’t be resolved from conventional logs and geo-mechanical outputs. The SOM model (Model1), based on conventional resolution petrophysical and acoustic logs, does not accurately represent the reservoir properties. The image-based high resolution UCS data helped in achieving a high-resolution geo-mechanical SOM based electro-facies model (Model 2) where high-resolution-UCS reduced the uncertainty of the earlier model. The resolution difference of Model 1 and 2 shows the second has better capability to resolve the intricate changes in the reservoir. Core-like SOM facies with optimized UCS are a unique solution in terms of geo-mechanical aspect of Shale oil/gas reservoirs. Which helped in further field development studies of Eagle Ford formation in USA.
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Have We Reached Fullwave Sonic P&S Wireline-Immunity Through LWD Advantages?
Authors J. Haugestaul, I. Nagy-Korodi, Á. Spitzmüller, A. Kallhovd and B. RuehlickeSummaryLWD as well as wireline (WL) Fullwave Sonic data were acquired over the same 8.5” reservoir section of a wellbore in the Norwegian continental shelf. Processing methodologies for Monopole and Quadrupole/Dipole are discussed including SFA, STC and dispersion. Compressional as well as shear sloweness results from both tools are shown in LWD-WL comparison plots. Challenges with the LWD data are discussed. Real-time pore pressure prediction using the real-time sonic results were performed and estimates vs. actual presented for Åsgard and Mandal formations.
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Real-time geosteering integration, a substantial element to achieve and exceed the production in Culebra Field
Authors A. Paladines, I. Reyes Campos, I. Hernández Martínez, D. Llanos Dimas, M. Garcia and P. DelgadoSummaryReaching and exceeding production is a key objective in the development plan of Culebra Field. In order to meet such goal, two main strategies were taken into consideration, the implementation of water flooding, and the drilling of horizontal wells, to improve the recovery factor of the reservoir. After a detailed analysis of the reservoir characterization, it was observed that the quality of the rock had an impact on production. However, due to the geological characteristics of the field, one of the main uncertainties is how to insure the landing and geosteering in the area with the best properties. To address the challenges, we reviewing the lessons learned, and analysing how we could optimize the measurements in real-time to meet the objectives. For the landing, we used Gamma Rays, X-ray diffraction, and analysis of the fluid during drilling, which integration classify the type of rock and fluid content, optimizing the landing point. For the horizontal section, the incorporation of measurements from different sources, such as real time bed boundary mapping, density, neutron, X- ray diffraction, and Mass Spectrometer allowed us take proactive decisions, leading to position the wellbore in the reservoir zone with good quality of rock type, confirming the presence of hydrocarbon fluid.
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Data acquisition and evaluation from the Eos well (31/5-7), Northern Lights CCS project, Norway
Authors R. Meneguolo, S. Kassold, V. Høigjelle and Z. VeselovskySummaryThe goal of the forerunning CCS project in Europe and worldwide, named Longship, is building a high-capacity, robust and safe storage site.
The site is within Exploitation License EL001 in the Norwegian North Sea, with the Storage Complex defined by the lower Jurassic Dunlin Group, a dipping saline aquifer.
Exploration well 31/5-7 was drilled in late 2019 with the goal of acquiring the necessary information to reach final investment decision, and to address the CCS-specific issues storage resource evaluation, injectivity and storage integrity.
Each dataset of the taylor-made data acquisition contributed to several aspects of the subsurface understanding. Standard log suite was used for large-scale correlation and identification of large-scale heterogeneities and connectivity, subsequently strengthened by the ESP DST results. Standalone FMI provided detailed information on structural evolution and on storage integrity. Integrated sedimentological core observations and FMI defined the depositional setting, and the meso-scale heterogeneities crucial for the estimation of the storage resource. Pressure measurements in the storage unit and in the overburden, coupled with an XLOT in the cap rock, provided the crucial evidence of the cap rock integrity and sealing capability.
Altogether, the information confirmed the assessment of storage capacity and strengthened confidence in storage safety.
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Automatic Borehole Image Reconstruction, Augmenting Robust Geological Interpretation: A Machine Learning Approach
More LessSummaryImages from the oil-based mud (OBM) imager comprise impedivity amplitude and phase data, with the raw phase angle measurements being often affected, in certain environments. Altered phase angle measurements introduce image artefacts, which impact the interpretability of the processed borehole image. This paper describes the process of training a regression model, used as a part of the preprocessing workflow to reconstruct affected phase-angle measurements. This leads to a clear post-processed image, thus enabling robust geological interpretation.
The regression model used is a customized ensemble learner. Each base model in the collection is trained using a controlled stochastic approach. The prediction power of an individual Base Model was determined using a supervised validation technique. Weights are assigned to the models based on prediction power and finally, the weighted mean used for aggregation.
The current ML-based approach focuses on repairing raw measurements, even before processing. Once these raw measurements are corrected, image processing further sharpens the constituent features, making them visible on the image. This approach improves image quality with minimal human intervention.
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Modeling Open Fracture Response in Non-Conductive Mud with LWD Dual Imager
Authors A. Alexandre, T. Brill, N. Bize-Forest, C. Shrivastava and C. BusserSummaryFracture classification into open vs. closed with borehole images in non-conductive mud has always been challenging, due to established workflows seeking leakage of current into fractures in wells drilled with conductive mud system. Often there are questions raised regarding open fracture classification with resistivity imagers in non-conductive mud. A dual-physics logging-while-drilling imager that utilizes resistivity and ultrasonic measurement principles collocated on a single collar provides complementary information to classify fractures.
The high-resolution electromagnetic waves are sent through the mud at optimal frequencies. The impedivity images are a function of the distance between the sensors and the borehole wall, thereby allowing a standoff image to help interpretation of open features. With mud acoustic slowness knowledge, high-resolution ultrasonic pulse-echo images deliver also standoffs information.
Modelling and laboratory experiments with both physics were performed for different resistivity and acoustic contrast against variable standoff. The results suggested that detection limit of open fractures is way finer than the image resolution. Based on detection limit and available contrast of feature against the host matrix; features manifested themselves on different frequencies distinctly. It can be concluded that the fine-aperture fractures present in the subsurface can be detected and characterized to a large extent.
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Initiative for Standards for Borehole Image Derived Deliverables
Authors C. Rambousek, W. Derschowitz, S. Schlöpke and R. ReinmillerSummaryIn 2020 the initiative to establish a standardization for borehole image log related data has been established by several geoscience consultancies, geoscience specialists from O&G operators who are involved with BHI Data, software companies and service companies. Borehole image logs (BHI) are one of the key sources for determining structural models, depositional environments, and flow units. Their ability to record bedding and fracture geometries along with stress and petrophysical properties make BHI a unique data source for a variety of disciplines. Currently, a lack of data processing and reporting standards limits the usefulness of many expensive and complex BHI logging records. Valuable information can be lost in transferring between data formats. This paper presents an example of how such BHI standardization could benefit the community by improving the deliverables of BHI analyses. This abstract is designed to gauge interest for this initiative and add new members to the consortium to work on a timeline for definitions of non-proprietary, cross-industry standards. This presentation is designed to build the awareness of the issue of BHI data standards and to attract a diverse group of professionals developing, interpreting, and applying BHI data.
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Chalk reservoir depositional cycles and their hardgrounds. An integrated approach using microresistivity
Authors G. Rizzi, G. Aplin, C. Buchan, B. Callaghan and A. BoylanSummaryNorth Sea Chalk cycles were determined from microresistivity images. Three image facies (and their sub-types) were defined
- Stratified
- Mottled
- Other
Image facies are arranged into cycles. Basal thinly stratified image facies are overlain by mottled image facies. They reflect an upwards transition from ecologically stressed deposition, decreasing sedimentation rates and colonisation by a burrowing fauna.
Conventional core analysis data was not available. However, data from adjacent reservoirs indicates that chalk cycles may exert a control upon reservoir potential. Lower helium porosity and permeability values are associated with stratified cycle bases; relatively higher porosity and permeability corresponds to cycle tops.
Some cycles contain centimetre-scale irregular surfaces or hardgrounds. Their occurrence is corroborated by observations from near-by cored intervals.
The distribution of depositional cycles have enabled four image facies associations to be determined;
- Shelf top.
- Crestal.
- Slope /flank.
- Basinal / intra-shelf basin.
Oversteep (>10°) bedding indicate that local palaeoslopes were striking NW-SE during deposition. Slopes were also facing NNE and SSW; consistent with seismic cross-sections.
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Improving the Image of Injectites
Authors C. Buchan, R. McGarva and B. CallaghanSummaryNo summary.
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