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3rd EAGE Workshop on Borehole Geophysics
- Conference date: 19 Apr 2015 - 22 Apr 2015
- Location: Athens, Greece
- ISBN: 978-94-6282-144-6
- Published: 19 April 2015
21 - 40 of 40 results
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Processing 8 Wells DAS 3D VSP from South of Oman
By S.S. AlabriIn 2012 Petroleum Development Oman (PDO) tested acquiring a 2D walkway VSP in South Oman using fibre optics (DAS). The results from that test were encouraging such that PDO embarked on acquiring a full field 3D VSP survey using 8 wells in 2014. The aim of this survey is to serve as a base line survey for a 4D repeatability exercise to monitor steam injection in a heavy oil field. The survey was shot using 2 vibrators per single location and repeated 4 times to enhance the signal to noise ratio. Over 5000 shot locations were acquired in duration of 24 days covering a circular area of about 1km radius. The data was recorded simultaneously in 8 wells This paper present the processing annd merging of the 8 wells.
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3D Joint Full Wavefield Imaging of Surface and VSP Data
Authors B. El-Marhfoul and D.J. VerschuurSurface seismic data can provide an image over an extended area. However, due to the involved two-way travel paths – including twice propagating through a possibly unconsolidated near-surface area– the resolution usually is quite limited. Borehole-related seismic data has a broader frequency band and better quality, resulting in a higher-resolution image. The main disadvantage of VSP data is the non-uniform fold distribution, which rapidly decreases while moving away from the well. This makes the areal extent of the final image very limited. In practice, VSP and surface seismic data are processed separately and the VSP image is spliced into the surface seismic data image. This workflow does not guarantee a perfect tie of the two images. In this paper we propose to employ both surface seismic and 3D VSP data simultaneously in one imaging process, such that – at least within an area around the well location – an optimum high-resolution image is obtained and the lateral continuity and consistency is guaranteed. Furthermore, by including all multiple scattering in a closed-loop imaging process – as proposed by the full wavefield migration process – a true amplitude reflectivity image will be obtained with high resolution and maximum lateral extent.
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Detect Water Velocity Variations with Direct Arrivals and Water Bottom Multiples from 3D Subsurface Seismic OBN/DAS-VSP
More LessNodes (OBN) survey geometry is similar to that of the Vertical Seismic Profile (VSP), except no sensors in a borehole. Thus, VSP 3C analysis methods are applicable to 4C OBN. Li and Hewett (2013) developed a time-angle diagnosis method to quantify velocity uncertainties in a model using the VSP first arrival times (FAT) and first arrival angles (FAA). We applied this method to FAT/FAA from a 2012 OBN survey in the Gulf of Mexico to diagnose water velocity models and to detect spatial variations in the water velocity. Arrival times and angles of water bottom multiple (WBM), which was typically treated as “noise” to be eliminated, were used to characterize the water velocity uncertainties. We also investigated feasibility to use FAT and WBM from DAS-VSP concurrently acquired with the 2012 OBN to constrain the water velocity models. Diagnoses with OBN FAT indicate that the maximum RM of water velocity is -0.7% with a maximum 2-way time misfit up to ~12 ms, while OBN WBM analyses reveal lateral variation of water velocity is about +/-1%. A joint tomography using FAT/WBM from OBN/DAS/VSP is expected to be feasible for revealing details of spatial/time-variations of the water velocity.
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Integrated Prestack Depth Migration of VSP and OBS Data in Angle Domain
By L. HuVertical Seismic Profiling (VSP) surveys not only generate higher fidelity data when compared with ocean bottom sensors (OBS), but VSP data can also be analyzed for reservoir properties via imaging and inversion for seismic attributes. This paper describes a Kirchhoff prestack depth migration (PSDM) technique for both VSP and OBS data using a common velocity model to produce angle domain common image gathers (ADCIGs) on a unified grid. Further processing of ADCIGs in a post-migration step is demonstrated to be an effective means of integrating partial images migrated for VSP and OBS data, and has produced results superior to the conventional workflow.
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Use of VSP for Improving Drilling Decisions in the Bolivian Foothills
Authors V. Lesnikov, M. Verliac, J.F. Ballard and J.M. FleuryThe paper demonstrates successful application of the borehole seismic technology for subsurface imaging in the borehole vicinity and ahead of the bit to de-risk the sidetrack trajectory of the development well in the complex foothills environment. The VSP data acquired from the rig source and two fixed offset sources were rush processed and the processing results of a good quality became available for the interpretation within 24 hours from acquisition for each of three profiles. As a result of the borehole seismic data interpretation, the sidetrack has been drilled successfully reaching the Devonian fractured sandstone reservoir around predicted depth.
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VSP Measurements used as a Tool in Sub Salt Field Development
Authors T. Bartels, M. Gelhaus and M. HumphriesMany of the Rotliegend low permeability dry gas fields in the Southern Permian Basin in northern Germany are covered by salt dome structures that lead to imaging problems in subsalt reservoir between 4000 m to 5000 m depth. As compartmentalization is the key challenge in field development high resolution seismic is essential for well planning. Only a vintage 3D seismic from 1993/94 with limited quality exists. Acquisition of new 3D seismic is not possible due to permitting restrictions and public resistance. Therefore the focus is on the acquisition of 2D VSPs in every new drilled well. The VSP measurements give local insights. With a general structural understanding and production history in mind those local insights can be merged into the overall picture and generate immense value for the understanding of the field.
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3D VSP Benefits in Heavy Oil Field in South Oman
Authors F. Al-Kindi, J. Al Aamri, M. Al Amri, A. Al Aamri and S. BurnsOccidental conducted a program to test geophysical methods for reservoir surveillance and monitoring in a steam injection operation at a heavy oil field in Oman. This field is a Permian age Gharif reservoir. It consists of three stacked reservoirs with porosity range from 25-33%. The heavy oil is heated by steam to reduce its viscosity and to increase its mobility. Based upon forward modelling of the reservoirs, Occidental thought that the steam injection operations would induce changes in the reservoir properties that could be detectable by geophysical methods. Monitoring steam is believed to be a vital element in managing the steam injection to reduce cost and increase recovery factor. Feasibility studies done on well log data and core measurements showed that the compressional velocity decreases by 10-15 % due to steam injection. In 2005 a pilot geophysical monitoring program was started to test techniques with potential to detect the changes in the reservoir properties due to steam injection. A list of methods containing surface seismic, borehole seismic, passive seismic and geomechanical deformation methods was proposed. From 2005 to 2010 this intense program was conducted by doing three 2D offset VSPs, a tiltmeter survey, microseismic, six cross well tomography profiles and surface 4D seismic, as well as modelling and feasibility work. All of these techniques were tested over an active area of steam injection to maximize the possibility of observing reservoir changes. Results from each geophysical technique were correlated with other geophysical techniques results and with other surveillance results. An ambitious forward plan has been drawn based on the conclusions from this pilot monitoring program. This plan consists of applying the two geophysical techniques that showed encouraging results from pilot mode to implementation mode. Both VSP and cross well tomography showed that there is a change in reservoir properties matching the modelled response in magnitude and correlating very well with other surveillance measurements From 2011 to 2013 Oxy implemented a 3D VSP program aiming to evaluate the technical and operational difficulties that might be faced when using 3D VSP in optimizing steam injection and heavy oil production in this field. There are many uses of the 3D VSP so far. The data is being used to understand the steam distribution in the reservoir. This helped to identify injectors that could cause steam break through or hot fluids break through. This technology helped the engineers to identify the locations of cold areas and helped the planning of infill wells that would assist them draining these areas for better recovery.
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Improving the Low-frequency Content of Borehole Seismic Data Acquired Using an Air-gun Source
Authors J. Tulett, R. Hearn, J.F. Hopperstad and T. DeanAbstract: The targets for offshore borehole seismic (BHS) surveys are becoming more challenging because they are deeper and overlain by more complex subsurface formations. Coupled with this is a move to more advanced acquisition methodologies such as 3D vertical seismic profile (VSP) surveys, as well as a desire for more powerful seismic sources that are also capable of generating wider-bandwidth data, in particular with increased low-frequency content. Low frequencies have a variety of benefits including overcoming the high-frequency attenuating effects of the Earth, improving vertical resolution, enhancing inversion results, and improving velocity analysis. A new BHS air-gun source array design has been introduced that significantly improves the low-frequency signal level but is a compact size that enhances the safety of deployment and towing.
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Validation and Calibration of the SPWD-wireline Prototype for High-resolution Directional Seismic Imaging in Deep Borehole
Authors K. Jaksch, R. Giese, M. Groh, A. Jurczyk and K. KrügerThe project SPWD - Seismic Prediction While Drilling intends the development of a borehole prototype which combines seismic sources and receivers in one device to improve the seismic resolution and exploration depth by the application of a phased array technique for its magnetostrictive actuator sources. Within SPWD a wireline prototype has been designed, manufactured and tested. In May and September 2013 the pressure-tightness and the hydraulic system for coupling of the SPWD-prototype were proofed successfully at the KTB Deep Crustal Lab in Windischeschenbach (Germany) up to a depth of 2100 m. In 2014 3D-seismic measurements to calibrate the prototype have been carried out in the GFZ-Underground-Lab in Freiberg. The measurements applying different wavefield amplification directions show clearly dipping reflective structures depending on the amplified direction.
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Land Seismic While Drilling: Guided Drilling to Reduce Depth Uncertainties. First in China
The Seismic While Driling technology is mainly for offshore use due seismic source limitation. In order to have fully syncronized acquisition of Checkshots, similar seismic source is required as in the offshore environment i.e Air Gun. The land operations puts more chalenges as compared to offshore operations. With good pre-job planning and collabration with different segments, the first land Seismic while drilling operation went successfully in two deep wells in Tarim basin, Noth West of China. Good quality Checkshots were obtained with both real-time and memory data, with excellent repeatibility. The quality of real-time data enabled to reduce the waiting time for model update and remigration of the data, which further reduce the turn around time for results delivery to driller to adjust the well trajectory in time and drill to the target safely.
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Defining the Bandwidth of Vibroseis Sweep Data at the Target, not at the Source
Authors T. Dean, J. Tulett, D. Lane and M. PuckettHydraulic seismic vibrators are the preferred source for land vertical seismic profile (VSP) surveys. The introduction of new, more powerful vibrators wogether with the use of Maximum Displacement (MD) sweeps has resulted in the extension of the bandwidth from less than three octaves to nearly seven. One of the advantages of the design procedure for MD sweeps is that the spectrum of the resulting sweep is an input to, rather than a result of, the design process. This enables the design of sweeps where the spectrum contains sections of the bandwidth that have been enhanced. The data presented in this paper shows that the bandwidth of the data received downhole can be successfully adjusted by varying the power spectrum of the transmitted sweep. Even in highly attenuated terrains this enables us to transmit high frequency energy to significant depth.
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VSP to Delineate Magmatic Bodies, Supercritical Fluids, Superheated Steam within Krafla Geothermal Field, NE-Iceland
Authors F. Kästner, S. Halldórsdóttir, G.P. Hersir, S. Planke, R. Giese, K. Gunnarsson, A. Gudmundsson, E. Juliusson and Ó.G. FlóvenzA VSP test experiment at the high temperature geothermal field Krafla in Iceland has been carried out. In two boreholes a zero-, far- and moving-source VSP has been applied to delineate subsurface fracture sets, zones of supercritical fluids, superheated steam and zones of magma with the background of a magmatic, high temperature and high attenuating basement. A careful preparation and evaluation of the survey is needed in order to provide a high resolution image of the surrounding subsurface. Under such special conditions high-quality three component data have been recorded and will grant a good basis for further processing and imaging techniques. It can be assumed that VSP techniques will provide a good alternative and addition to hitherto only applied surface seismic, teleseismic or microseismic procedures.
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Wavenumber Response of Data Recorded Using Distributed Fibre-optic Systems
More LessDue to their ease of use, relative low cost, and excellent spatial sampling, distributed fibre-optic- based seismic acquisition systems are gaining increased attention, particularly in vertical seismic profile (VSP) surveys. Data recorded using such systems clearly exhibit a radiation pattern effect whose characteristics depend on the effective length of the section of fibre being used for sampling. The use of long gauge lengths results in the attenuation of high frequencies and high wavenumber whereas the use of short gauge lengths results in the attenuation of low frequencies and low wavenumbers. One solution to this problem would be to process data with a variety of different gauge lengths and merge the data at a later time. Unfortunately many of the systems currently available cannot offer this option because the length is fixed either by the hardware or within the initial processing.
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1D Anisotropic Velocity Model Inversion from Multi-offset VSP Data Sets (Conventional Array and Optical Cable)
Authors P. Bettinelli and B. FrignetOptical seismic acquisition with distributed vibration sensing has been recently proposed to improve seismic acquisition efficiency (Hartog et al. 2013). An experimental multi-offset VSP data set has been acquired with both conventional and optical technologies in a 620-m-deep cased vertical well (Frignet and Hartog 2014). The 1D isotropic ray trace modelling times cannot be matched with picked transit times. It is necessary to introduce some VTI anisotropy to reconcile modelled and measured times at all offsets. Both conventional and optical VSP times were satisfactorily modelled with a 1D anisotropic model. Conventional multi-offset VSPs are not often acquired. In addition to the successful Thomsen anisotropic parameters inversion, an optical VSP acquisition is an order of magnitude faster than conventional acquisition. Therefore, multi-offset optical VSP could be routinely acquired in less time than conventional zero-offset VSP. Multi-offset VSP is a cost-effective technology for investigating velocity anisotropy in horizontally layered environments
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Joint Study of 3D-VSP and Surface Full-azimuth Seismic in Northeast China
More LessGreat progress have been made on VSP techniques in recent years, especially the improvement of downhole geophone manufacture and VSP data processing methods. In XJWZ area of Daqing oil field, the reservoir is mainly formed by volcanic and its distribution is complex due to many periods of volcanic overlap in this area. Before this project is conducted, seismic surveys are mainly 2D and narrow azimuth 3D which are not suitable for anisotropy analysis and fracture identification. Therefore, a joint survey of 3D-VSP and full-azimuth surface seismic was implemented. This project tries to combine the advantages of VSP and surface seismic by 3D-VSP and full-azimuth surface seismic simultaneous survey. Q factor and anisotropy parameter estimated from VSP are applied to 3D seismic processing. Reservoir characterization and gas saturation prediction with final images shown encouraging results. Suggested well has been drilled and wet gas has been founded, so the validity of this method has been proved.
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Reducing Velocity Model Uncertainty and Improving Microseismic Event Location Accuracy: Crosswell Seismic Tomography Using a Repeatable Sparker Source
More LessVelocity model errors are a major source of uncertainty in microseismic event location – a source of uncertainty that often goes unaddressed. This paper demonstrates how a commercial downhole sparker source can be used to produce crosswell tomography surveys that result in much improved velocity profiles. The combination of improved velocity model and more accurate event time picking deliver a much more constrained error distribution of micro seismic event location. This paper will outline a description of a repeatable and broadband downhole source, and the expected improvement to event location accuracy which is likely to be achieved, along with suggestions on how this may be applied to future monitoring surveys.
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Remaining Gas Prediction with Walkaround VSP Data: A Case Study from Junggar Basin, China
Authors Y.H. Wang, Q.H. Zhang, Z.D. Cai, C.W. Liu and C. WangTwo VSP surveys were acquired around DX10 well in Junggar basin in 2004 and 2013, respectively. This study analyzed kinds of time-frequency attributes sensitive to gas reservoir from zero offset time-lapsed VSP data and walkaround VSP data. Reasonable estimation of the remaining gas distribution was derived with the hydrocarbon detection attributes, which is helpful for sidetrack well planning.
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Traveltime Inversion of Walkaway VSP Data for a Model with Dipping TI Layers
By E. BliasWalkaway vertical seismic profiling (VSP) data potentially provides the most reliable anisotropy estimates. In many cases, a 1D model is not quite adequate for real data. If walkaway first break function is not symmetrical with respect to the well, then we need a velocity model with dipping/curvilinear boundaries. In this paper, I present a traveltime inversion approach for transverse isotropy (TI) parameter estimation that takes into account lateral velocity changes in the overburden. I describe these changes with dipping boundaries above the shallowest receiver. Dipping boundaries, interval velocities and anisotropic TI parameters in the overburden are included, together with simultaneous estimations of anisotropic parameters within the receiver array depth interval. Tests on model data show reliable anisotropy estimates. This approach was applied to multi-azimuthal walkaway data.
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Orientation of 3 Component Rig-Source VSPs
Authors C. Naville, R. Tavernetti, M. Sweeney and K. KazemiAbout 75% of commercial borehole seismic operations are zero-offset VSPs, or “Rig-VSPs”. They are recorded before total completion in low deviated holes, with a deep open hole interval and a single casing, then multiple casing depth intervals above. Three components of geophones are recorded, with excellent mechanical tool coupling to the borehole wall, but usually the VSP tool cannot be oriented into geographical coordinates. Therefore only the Z-axis component is processed, or a near vertical component computed from the 3 recorded components, resulting in a reduction of the geological information derived from rig-VSPs. APS and IFPEN propose to implement current and future generations of VSP tools with cost effective fluxgates and inclinometers to improve the present situation.
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3D 3C Walkaway to Calibrate Surface Seismic
Authors C. Naville, M. Denis, L. Nicoletis, P. Ricarte and E. SuaudeauImproved processing tools enable a new approach of complex land 3D VSP analysis. The first aim is to extract information useful for processing and interpretation of 3D surface data, the second one to obtain elastic wave fields (PP, P-SV, SV-SV, SH-SH) ready for imaging, from VSP data in 3 Components.
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