Seismic Fault Preserving Diffusion

This paper focuses on the denoising and enhancing of 3-D reflection seismic data. We propose a pre-processing step based on a non linear diffusion filtering leading to a better detection of seismic faults. The non linear diffusion approaches are based on the definition of a partial differential equation that allows us to simplify the images without blurring relevant details or discontinuities. Computing the structure tensor which provides information on the local orientation of the geological layers, we propose to drive the diffusion along these layers using a new approach called SFPD (Seismic Fault Preserving Diffusion). In SFPD, the eigenvalues of the tensor are fixed according to a confidence measure that takes into account the regularity of the local seismic structure. Results on both synthesized and real 3-D blocks show the efficiency of the proposed approach.Comment: 10 page

Identification of Regional Shale Gas Sweet Spots and Unconventional Reservoirs Using Well Logs and Seismic Data

To enable the oil and gas industry conduct exploration and identify potential shale gas sweet spots in a fast and cost-effective manner, the study developed a novel method for predicting in situ rock elastic properties. Specifically, taking the Canning Basin as a case study, correlation equations between static and dynamic rock elastic properties were developed. Such correlation equations can be used to accurately predict the actual in situ rock elastic properties, including the brittleness index

Seismic methods applied to structural interpretation

Seismic modeling and seismic attribute assisted interpretation are conducted to illustrate the use of seismic methods in structural interpretation. Pre-stack time migration (PSTM) seismic modeling is used to study common pitfalls and artifacts associated with the pre-stack time migrated seismic data in common fold-thrust structures. Fault-bend fold models are well imaged but with gentle “pull-ups” due to the lateral velocity variance. Fault -propagation folds exhibit significant footwall “pull-ups” and poor imaging of the steep front limbs. The maximum slip (S) on the fault plays an important role on the dip of the front limbs of trishear fault-propagation folds, and therefore the imaging quality of the front limbs. The fault propagation to slip ratio (P/S ratio) has a lesser influence on the signature of the fault and front limbs. Lateral thickness changes in the high velocity salt or low velocity mobile shale substrate associated with detachment and faulted-detachment folds cause “pull-ups”, “push-downs” and other artifacts. The structures seen on the seismic are also sensitive to the accuracy of the root-mean-square (RMS) velocity used for migration, whereby errors in velocity analysis cause distortion in the resulting geometry of the structures. We also conducted seismic attribute analysis using advanced fault probability attribute on a 3D seismic survey in the Great South Basin, New Zealand. The attribute sharpens the discontinuities associated with polygonal faults which are difficult to interpret due to their complex planiform geometry. Four separate polygonal fault patterns are recognized based on the mechanism of formation and the slope of the faulted units at the time of formation. The formation of the polygonal fault systems in the Great South Basin is related to volume reduction and shear failure due to the opal-A to opal-CT transition within the sediments

Seismic amplitude vs. offset and attribute analyses for mine planning at the Hannukainen Fe-Cu-Au mine site

A seismic reflection survey was carried out at the Hannukainen-Rautuvaara Iron (Fe), Copper (Cu), and Gold (Au) deposits as part of the HIRE (High Resolution Reflection Seismics for Ore Exploration, 2007-2010) project. The main discovery from this survey was a regional structure showing three reflective layers dipping to the southwest. The top of this package of reflectors is currently planned to be mined at Hannukainen. The deeper parts of this package may have potential continuation of the economically viable deposits seen at shallow depths. In this work, a target-specific, amplitude-preserving workflow for profiles E1 and V5 of the Hannukainen-Rautuvaara HIRE seismic data will be formulated and applied. Then seismic amplitude vs. offset (AVO) and attribute analyses will be used to analyse the reflective layers and identify potential areas of interest for further study. This is a burgeoning area of seismic research, AVO analysis is typically used in hydrocarbon exploration and has only been sparsely used in hard rock settings for mineral exploration. Attribute analysis is more common in hard rock environments, but still underutilised. The seismic reflection data were re-processed focusing on retaining the high-frequency content of the seismic signal, this is key for further analysis. The results of the AVO analysis consist of determining the AVO class of the responses seen across the CMPs of two selected AVO horizons. AVO product and Poisson’s ratio change across the horizons were calculated, and an area of interest was identified from the correlation of these parameters. Attribute analysis was done using the seismic attributes envelope, first derivative envelope, Hilbert Transform, relative impedance, phase, weighted instantaneous frequency and dip. The amplitude attributes (envelope, first derivative envelope, Hilbert Transform, relative impedance) were useful in determining the areas of the reflector package that showed the strongest amplitudes and selecting horizons on the uppermost reflector for AVO analysis. Phase and weighted instantaneous frequency helped determine the continuity of the reflector package which revealed a clear four-layer signature, differing form the earlier three-layer interpretation. The dip attribute showed vertical anomalies, some of which correlated with mapped faulting in the area. Detailed interpretation of the geophysical results requires better borehole coverage, and petrophysical work, to tie in the seismic data results to the alteration and mineralisation. With open pit mine planning ongoing in the study area, the identification of deep-seated mineral deposits will have direct impact on the planning of the mine and the future of exploration in Hannukainen-Rautuvaara

Depth-registration of 9-component 3-dimensional seismic data in Stephens County, Oklahoma

textMulticomponent seismic imaging techniques improve geological interpretation by providing crucial information about subsurface characteristics. These techniques deliver different images of the same subsurface using multiple waveforms. Compressional (P) and shear (S) waves respond to lithology and fluid variations differently, providing independent measurements of rock and fluid properties. Joint interpretation of multicomponent images requires P-wave and S-wave events to be aligned in depth. The process of identifying P and S events from the same reflector is called depth-registration. The purpose of this investigation is to illustrate procedures for depth-registering P and S seismic data when the most fundamental information needed for depth-registration – reliable velocity data – are not available. This work will focus on the depth-registration of a 9-component 3-dimensional seismic dataset targeting the Sycamore formation in Stephens County, Oklahoma. The survey area – 16 square miles – is located in Sho-Vel-Tum oilfield. Processed P-P, SV-SV, and SH-SH wave data are available for post-stack analysis. However, the SV-data volume will not be interpreted because of its inferior data-quality compared to the SH-data volume. Velocity data are essential in most depth-registration techniques: they can be used to convert the seismic data from the time domain to the depth domain. However, velocity data are not available within the boundaries of the 9C/3D seismic survey. The data are located in a complex area that is folded and faulted in the northwest part of the Ardmore basin, between the eastern Arbuckle Mountains and the western Wichita Mountains. Large hydrocarbon volumes are produced from stratigraphic traps, fault closures, anticlines, and combination traps. Sho-Vel-Tum was ranked 31st in terms of proved oil reserves among U.S. oil fields by a 2009 survey. I will interpret different depth-registered horizons on the P-wave and S-wave seismic data volumes. Then, I will present several methods to verify the accuracy of event-registration. Seven depth-registered horizons are mapped through the P-P and SH-SH seismic data. These horizons show the structural complexity that imposes serious challenges on well drilling within the Sho-Vel-Tum oil field. Interval Vp/Vs – a seismic attribute often used as lithological indicator – was mapped to constrain horizon picking and to characterize lateral stratigraphic variations.Geological Science

Tracking 3D seismic horizons with a new, hybrid tracking algorithm

We introduce a new algorithm for tracking 3D seismic horizons. The algorithm combines an inversion-based, seismic-dip flattening technique with conventional, similarity-based auto-tracking. The inversion part of the algorithm aims to minimize the error between horizon dips and computed seismic dips. After each cycle in the inversion loop, more seeds are added to the horizon by the similarity-based auto-tracker. In the example data set, the algorithm is first used to quickly track a set of framework horizons, each guided by a small set of user-picked seed positions. Next, the intervals bounded by the framework horizons are infilled to generate a dense set of horizons, a.k.a. HorizonCube. This is done under supervision of a human interpreter in a similar manner. The results show that the algorithm behaves better than unconstrained flattening techniques in intervals with trackable events. Inversion-based algorithms generate continuous horizons with no holes to be filled post-tracking with a gridding algorithm and no loop-skips (jumping to the wrong event) that need to be edited as is standard practice with auto-trackers. As editing is a time-consuming process, creating horizons with inversion-based algorithms tends to be faster than conventional auto-tracking. Horizons created with the proposed algorithm follow seismic events more closely than horizons generated with the inversion-only algorithm and fault crossings are sharper

3D Seismic Depth Imaging and Velocity Model Building in Anisotropic Media: Serri Oil and Gas Field, Saudi Arabia

Seismic imaging is a significant element in hydrocarbon exploration to locate drilling prospects and it relies mainly on an accurate velocity model. Prestack depth migration (PreSDM) versus traditional post-stack time migration has become a common method for seismic velocity model building and imaging. This methodology accounts for seismic velocity anisotropy of the propagating waves in the subsurface with a higher level of accuracy in positioning the seismic events in their true positions in the subsurface. In this thesis, we examine a 303 km2 of 3D seismic data acquired by Saudi Aramco in the Serri field of North-West Saudi Arabia. The dataset is diagnosed to be of extremely poor reflective quality likely due to seismic anisotropic effects caused by shale deposits. Our main goal was to produce an enhanced and better focused seismic image that is geologically accurate and interpretable This study develops a practical method for building an anisotropic velocity model to be further used in the anisotropic PreSDM. Based on this study, three main approaches have made a significant impact on the improvement of seismic imaging: (1) analysis of elastic reflection coefficients characterizing heterogeneities in the subsurface, (2) study of the variation of the reflection coefficients with the angle of incidence, and (3) a detailed characterization of the P-wave propagation velocity field. The seismic imaging results showed that PreSDM provided a significant improvement of the seismic image quality. Moreover, the anisotropic PreSDM provided more continuous and brighter reflections than the isotropic PreSDM

Geometric and depositional responses of carbonate build-ups to Miocene sea level and regional tectonics offshore northwest Australia

The geometric and depositional responses of isolated carbonate build-ups to Miocene sea-level change and regional tectonics was investigated using a combination of 3D seismic and borehole data from the Browse Basin, North West Australia, and outcrop information from the Cariatiz Reef, southeast Spain. The interpreted seismic volume documents five (5) Miocene sequence boundaries and five (5) main seismic facies. Seismic attribute analyses proved a highly effective tool for interpreting carbonate facies but, when compared with outcrop information from southeast Spain, data are limited to large-scale features of scales beyond 16.4 m vertically and 18.75 m horizontally. Hence, this work clearly shows that estimations of reservoir potential are significantly underestimated if based on seismic data alone. As a corollary of the structural analysis in this work, growth patterns suggest Messinian structural partitioning across the Browse Basin, with deformation associated with plate collision focused in preferentially orientated faults - thus only influencing carbonate build-up evolution at a local scale

3D seismic data interpretation of Boonsville Field, Texas

The Boonsville field is one of the largest gas fields in the US located in the Fort Worth Basin, north central Texas. The highest potential reservoirs reside in the Bend Conglomerate deposited during the Pennsylvanian. The Boonsville data set is prepared by the Bureau of Economic Geology at the University of Texas, Austin, as part of the secondary gas recovery program. The Boonsville field seismic data set covers an area of 5.5 mi². It includes 38 wells data. The Bend Conglomerate is deposited in fluvio-deltaic transaction. It is subdivided into many genetic sequences which include depositions of sandy conglomerate representing the potential reserves in the Boonsville field. The geologic structure of the Boonsville field subsurface are visualized by constructing structure maps of Caddo, Davis, Runaway, Beans Cr, Vineyard, and Wade. The mapping includes time structure, depth structure, horizon slice, velocity maps, and isopach maps. Many anticlines and folds are illustrated. Karst collapse features are indicated specially in the lower Atoka. Dipping direction of the Bend Conglomerate horizons are changing from dipping toward north at the top to dipping toward east at the bottom. Stratigraphic interpretation of the Runaway Formation and the Vineyard Formation using well logs and seismic data integration showed presence of fluvial dominated channels, point bars, and a mouth bar. RMS amplitude maps are generated and used as direct hydrocarbon indicator for the targeted formations. As a result, bright spots are indicated and used to identify potential reservoirs. Petrophysical analysis is conducted to obtain gross, net pay, NGR, water saturation, shale volume, porosity, and gas formation factor. Volumetric calculations estimated 989.44 MMSCF as the recoverable original gas in-place for a prospect in the Runaway and 3.32 BSCF for a prospect in the Vineyard Formation --Abstract, page iii