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- Volume 33, Issue 3, 2015
First Break - Volume 33, Issue 3, 2015
Volume 33, Issue 3, 2015
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Grey level co-occurrence matrix and its application to seismic data
Christoph Georg Eichkitz, John Davies, Johannes Amtmann, Marcellus Gregor Schreilechner and Paul de Groot demonstrate how grey level co-occurrence matrix can be adapted to work on 3D imaging of seismic data. Texture analysis is the extraction of textural features from images (Tuceryan and Jain, 1998). The meaning of texture varies, depending on the area of science in which it is used. In general, texture refers to the physical character of an object or the appearance of an image. In image analysis, texture is defined as a function of the spatial variation in intensities of pixels (Tuceryan and Jain, 1998). Seismic texture refers to the magnitude and variability of neighbouring amplitudes at sample locations and is physically related to the distribution of scattering objects (geological texture) within a small volume at the corresponding subsurface location (Gao, 2008). Four principal methods have been developed for the analysis of seismic texture (Figure 1). These are texture classification, segmentation, synthesis, and shape.
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Interpretation of geophysical data using structural principles to build geological models
Authors Jenny Ellis and Norman ArmstrongJenny Ellis and Norman Armstrong present new tools for 3D kinematic modelling that address the challenges with geological interpretation of geophysical data, and have the added benefit of revealing the timing of geological events important for understanding the petroleum system. Geophysical and geological interpretation typically forms the foundation for the construction of geological models in the petroleum industry. It is unusual to be able to interpret these datasets with one definitive model (Figure 1). Multiple interpretations are often possible from the same dataset, as the data is a representation or subsample of reality. Economic decisions in the exploration and drilling of conventional and unconventional hydrocarbon resources are based on the geological model constructed from data subsamples. It is therefore essential that the geoscientist carrying out the interpretation is critical and open minded in order to understand and address uncertainty with the modelled interpretation.
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Developing an integrated structural modelling workflow
Authors Emma Howley and Randi Sundt MeyerEmma Howley and Randi Sundt Meyer present a workflow and tools that integrate fault and horizon uncertainty modelling with structural modelling and 3D gridding to enable users to quantify uncertainty more effectively. A fundamental problem in reservoir modelling today is the ability to create models – based on limited input data – that accurately represent the reality. Structural modelling is a key means of achieving this and yet, while a critical component of the reservoir modelling workflow accounting for the greatest uncertainty in terms of in-place reserves, it faces a variety of challenges and limitations. Chief among these is the rise in more geologically complex reservoirs that often come with poor quality data and the inability of today’s interpretation solutions to create a spatially accurate analysis of the field. Other challenges include the inability to input the inherent uncertainty of such fields directly into the interpretation and structural model for quantified risk analysis and improved decisionmaking. The result is that decisions are often made with limited models and only best-case estimates of faults and horizons, with the interpreter having a weak understanding of potential errors or uncertainty in the interpretation. The result is an underestimating of the actual uncertainty in reservoir volumes. This article aims to address these challenges and limitations through a new workflow and set of structural modelling tools. The workflow and tools integrate fault and horizon uncertainty modelling with structural modelling and 3D gridding to enable users to quantify uncertainty more effectively and acknowledge realistic uncertainties in the data via the building of geologically realistic scenarios. The new workflow and tools will enable users to quantify uncertainty in their structural modelling and increase their confidence when it comes to crucial decisions on where to drill, what production strategies to adopt, and how to maximize oil and gas recovery. At a time of low oil prices, this is vital.
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Unconventional seismic attributes for fracture characterization
Authors Hardeep Jaglan, Farrukh Qayyum and Huck HélèneHardeep Jaglan, Farrukh Qayyum and Hélène Huck introduce several new geometrical attributes that help in characterizing fault networks, fractures density and their connectivity. Faults and fractures are generally represented as discontinuous reflection patterns on seismic data and mostly appear as linear, sub-linear or curvilinear features in three dimensions. In seismic interpretation faults are routinely detected through multi-trace seismic attributes such as coherency, similarity, semblance, variance, curvature, dip, azimuth, etc. These attributes are often grouped as geometrical attributes because they mostly help in defining the geometrical nature of seismic reflections. The objective of this paper is to introduce several new geometrical attributes that help in characterizing fault networks, fractures density and their connectivity. The proposed attributes are derived after specialized workflows based on a precomputed dip-azimuth volume. These attributes are referred as unconventional fracture attributes because they are new and not routinely applied to fault detection and characterization.
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Improved stratigraphic interpretation using broadband processing – Sergipe Basin, Brazil
Authors Mike Saunders, Laurie Geiger, Dan Negri, Jaime A. Stein, T. Altay Sansal and John SpringmanMike Saunders, Laurie Geiger, Dan Negri, Jaime A. Stein, T. Altay Sansal and John Springman demonstrate that de-ghosting and bandwidth extension using the Continuous Wavelet Transform (CWT) technique can produce broadband data that allows for improved identification and mapping of thinner potential hydrocarbon reservoirs. The Sergipe Basin originated in the Early Cretaceous and is a relatively mature hydrocarbon province on the northeast coast of Brazil, comprising 44,370 km² both onshore and offshore. The onshore portion of the basin (12,620 km²) is considered mature, with more than 2 billion bbls in place and 816 wells drilled since 1935. The offshore Sergipe Basin is gaining prominence as Petrobras has made several discoveries since 2010, including the 2010 Barra well (1-SES-158) and the subsequent Barra 1 appraisal well (3-SES-165). These wells targeted oil and gas charged Maastrichtian sandstones that display readily identifiable AVO anomalies on 2D seismic profiles. Approximately 16,000 km of long offset 2D seismic data was acquired in 2014 using a flat streamer towed at a depth of 15 m. The data was processed through pre-stack time migration using conventional techniques, and through prestack depth migration including conventional and broadband processing techniques. The broadband processing included proprietary pre-migration de-ghosting and bandwidth extension phases. The application of these two technologies resulted in seismic data with a vertical resolution as fine as 5 m to 10 m. Improvements in the resolution can be quantified by analysing the sequence stratigraphic interpretation which was done on both the conventionally processed data set and a broadband data set.
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Imaging complex geology through challenging surface terrain – a case study from West China
Authors Huiwen Xie, Chao Wu, Caiming Luo, WenSheng Duan, Yingjie Zhao, Xin Ji, Sherman Yang, Xioalong yao, Dingxue Wang, Zhengguo Jia and Qinglin LiuHuiwen Xie, Chao Wu, Caiming Luo, WenSheng Duan,Yingjie Zhao, Xin Ji, Sherman Yang, Xiaolong Yao, Dingxue Wang, Zhengguo Jia and Qinglin Liu describe a reprocessing project combining four 3D datasets that improved the imaging of a deep subsalt thrustfaulted target in an area of variable topography and complex near-surface conditions. Oil and gas exploration is moving into areas of increasingly complex geology, where depth imaging – along with the associated need to build accurate velocity models – is becoming an ever more important tool in efficiently finding and developing oilfields. This article presents a case study of structural imaging from an area where both the subsurface geology and surface conditions are extremely complex. The project combined several vintages of land 3D seismic data from the Dabei block, located in the Kuche foreland basin area of the northern Tarim Basin, West China. Several previous attempts had been made to reprocess these datasets, but the results were all considered inadequate to meet the imaging quality and accuracy required for reliable well placement. The goal of the new reprocessing project was to deliver accurate imaging of hydrocarbon-bearing strata beneath a large anticline in subsalt thrust-fault blocks at depths of around 7000 m. Tomographic static correction using carefully picked first breaks outperformed previous field static solutions based on upholes. A multi-domain noise attenuation sequence included a newly developed method that uses true shot and receiver coordinates, thereby handling irregularities in acquisition geometry. A tilted transverse isotropic (TTI) velocity model was built using a combination of diving wave tomography (DWT) in the shallow part; geologically constrained reflection tomography in the remainder of the overburden; and multi-azimuthal tomography in the offset vector tile (OVT) domain in the salt and target zone. In areas of thick high-velocity conglomerate deposits, a seismic joint inversion (SJI) model building technique was applied to include information from non-seismic data to better define strong lateral velocity changes.
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High resolution seismic undershooting of platforms – stretching the limits
Authors K.A. Games, A.J. Pretty, I.A. Stennett, N.D. Wakefield and D.S. MannUndershooting, a technique for acquisition of seismic data beneath areas that are difficult to access at the surface of the Earth, has long been practised in the field of 3D seismic exploration. The publication of new guidelines by the OGP for the Conduct of Offshore Drilling Hazard Site Surveys specifies that seismic data greater than ten years old are no longer valid for this application. Hence, there is a need to be able to use the undershoot technique in the evaluation of shallow sub-sea hazards beneath existing structures such as Production Platforms if new wells are planned to be drilled from these structures. This paper outlines the approach taken using two multi-role site survey vessels to acquire a high-resolution undershoot dataset, with the emphasis being to ensure that this was suitable for shallow geohazard evaluation. We describe the techniques and equipment, including specifically designed in-house navigation software routines, the trials undertaken, and the successful acquisition of a useable dataset. Examples are provided that demonstrate the high quality of the seismic dataset acquired. It was only possible to achieve this using a 3D approach for the binning and processing of the seismic data.
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Directionless fracture stability assessment based on a 4D geomechanical model of a SAGD scenario
By Marc HollandIn SAGD operations the injection of steam leads to thermally induced stresses and pore pressure changes in the subsurface. Although the pressure and temperature can be modelled with reservoir simulators, the change of the stress field in relation to these properties can impact the stability of faults and fractures, which in turn have effects on the fluid transport properties. To assess the potential for fault and fracture (re-)activation we create a model of a SAGD operation by coupling the outcome of a reservoir simulation to a 4D geomechanical finite-element model. The model reveals the bounding faults to have critically stressed. A second, more conservative, approach uses a directionless assessment without the need of discrete fractures. It shows extensive critically-stressed regions above and below the injection at much earlier stages, which extend far into the cap-rock. The model shows the importance of creating integrated 3D or 4D models honouring overburden stiffness and vertical load in the same way as the locally induced stresses. A challenge remains in quantifying the input rock parameters for the entire vertical column. The outcome of the model stresses the need for a detailed discussion of the cap rock thickness and the impact of potential of fractures.
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Volumes & issues
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Volume 42 (2024)
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Volume 41 (2023)
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Volume 40 (2022)
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Volume 39 (2021)
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Volume 38 (2020)
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Volume 37 (2019)
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Volume 36 (2018)
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Volume 35 (2017)
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Volume 34 (2016)
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Volume 33 (2015)
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Volume 32 (2014)
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Volume 31 (2013)
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Volume 30 (2012)
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Volume 29 (2011)
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Volume 28 (2010)
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Volume 27 (2009)
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Volume 26 (2008)
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Volume 25 (2007)
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Volume 24 (2006)
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Volume 23 (2005)
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Volume 22 (2004)
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Volume 21 (2003)
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Volume 20 (2002)
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Volume 19 (2001)
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Volume 18 (2000)
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Volume 17 (1999)
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Volume 16 (1998)
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Volume 15 (1997)
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Volume 14 (1996)
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Volume 13 (1995)
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Volume 12 (1994)
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Volume 11 (1993)
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Volume 10 (1992)
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Volume 9 (1991)
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Volume 8 (1990)
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Volume 7 (1989)
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Volume 6 (1988)
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Volume 5 (1987)
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Volume 4 (1986)
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Volume 3 (1985)
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Volume 2 (1984)
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Volume 1 (1983)