- Home
- Conferences
- Conference Proceedings
- Conferences
Second EAGE Workshop on Borehole Geophysics
- Conference date: 21 Apr 2013 - 24 Apr 2013
- Location: St Julian's , Malta
- ISBN: 978-90-73834-46-0
- Published: 21 April 2013
21 - 40 of 42 results
-
-
VSP While Drilling: A Deepwater Case Study Offshore West Africa
Authors J. Kemper, A. Jervis, M. Richards, J.-C. Puech and N. KelsallRank wildcat wells in deepwater represent some of the greatest opportunities for operators today but also present major challenges. 3D surface seismic velocity data without nearby well calibration has significant uncertainty from the conversion of two-way time to horizon depths, which further induces risk in the predrill pore pressure model created from limited available data. This case study is about a deepwater exploration well drilled offshore West Africa where seismic while drilling technology was used extensively to reduce depth uncertainties and drilling risks from spudding to total depth of the well. This allowed for the target depth uncertainty to be reduced by more than 90% along the three consecutive drilled sections, from greater than +/-100 meters to less than +/-5 meters. Furthermore it allowed this 2D well trajectory to avoid accidental penetration of the first target, avoiding a kick and placing the 13 3/8” casing shoe safely above the first target, 80 meters shallower than predicted, and just 20 meters from the top formation. Placing the 13 3/8” casing shoe as deep as possible increased the mud weight window for the 12 1/4” hole section, and contributed towards saving a casing string close to the bottom of the well.
-
-
-
Landing a Horizontal Well with the Assistance of 2D VSP
Authors S. Berman, V. Lesnikov, T. Duncan and R. WilliamsThis paper describes the uncertainties associated with determining an appropriate dip to geosteer a well towards the landing zone and along the well trajectory, and how a 2D VSP helped. Various methods of pre-drill dip estimation are discussed and compared to the 2D VSP and to LWD measurements.
-
-
-
Advanced Borehole Seismic Imaging of Transition-Zone Subsurface Structures
Authors T. Radford, M. Karrenbach and F. YustianaTransition zone seismic surveys collected over a subsurface reef structure present significant subsurface imaging challenges in producing reliable interpretations for reservoir assessment. In order to aid the reservoir description, the complete vertical and horizontal borehole trajectory was instrumented with 3C receivers, while simultaneously recording 3C receivers in shallow vertical wells. Even with a limited source layout, such a source and receiver geometry allows us to extract a multitude of information about the near surface and deeper subsurface. While traditional standard imaging is challenging with this geometry, interferometric processing, imaging and analysis allows us to obtain valuable reservoir information. In the following we briefly introduce the geologic setting and data acquisition aspects, and focus on the results obtained by using advanced processing flows, such 3D velocity model construction using nonlinear travel-time tomography, interferometric seismic gather generation and depth imaging, as well as elastic full wave form forward modelling to help in the interpretation, analysis and uncertainty estimates.
-
-
-
Simulation and Proposed Processing Workflow of Simultaneous Source 3DVSP Data
Authors M. Atif Nawaz and W.H. BorlandSimultaneous source acquisition is a method that is currently being accepted as the way of reducing the acquisition time and hence related cost, for both surface and borehole seismic (3DVSP). It is critically important for 3DVSP because of high cost of offshore rigs. Two or more sources can be used with a predifined firing delay. The delay time of firings is chosen as a random function from shot to shot. The data thus acquired as the blended respose of multiple sources. Surface seismic data acquired with simultaneous sources can exploit random delays to separate the respose of multiple sources in receiver domain. In borehole seismic, receiver domain separation, however, poses other challenges like separation of downgoing and upgoing wavefields. New methods are proposed to separate simultaneous sources response in the source domain. The methods prove successfull and open new frontiers for efficient and cost-wise feasible acquisition and processing of 3DVSP data.
-
-
-
Kirchhoff Prestack Depth Migration of 3D VSP Data in Offset and Angle Domains
By L. HuShallow unconsolidated sediments, irregular refractors, rapid surface elevation changes and hidden karsts are geologic features in the Middle East that can significantly degrade the quality of recorded seismic data. Accurate handling of these complexities is critical for seismic interpretation as low relief structures, stratigraphic traps and fractures have become important exploration targets. Vertical Seismic Profiling (VSP) not only generates higher fidelity data when compared with surface seismic surveys, but VSP data can also be analyzed for reservoir properties via imaging, modeling and inversion for various seismic attributes. This paper describes a Kirchhoff prestack depth migration (PSDM) technique for 3D VSP data to produce common image gathers (CIGs) in both offset and angle domains. The offset domain CIGs are for use in migration velocity analysis (MVA) and the angle domain CIGs (ADCIGs) are for use in modeling and elastic inversion for reservoir properties. This extended Kirchhoff PSDM technique was applied for both synthetic and real data examples and the initial results are promising.
-
-
-
Improving the Low-Frequency Content of Land VSP Data Acquired using a Vibroseis Source
Authors M. Puckett, T. Dean, J. Quigley, D. Lane and J. TulettThe targets for VSP surveys are becoming more challenging, being deeper and overlain by more complex sub-surface formations. Coupled with this is a move to more complex acquisition methodologies, 3D VSPs in particular, and a desire for wider bandwidth data, in particular enhanced low-frequency content. As the preferred source for land VSP surveys is the seismic vibrator there is a requirement for vibrators to be able to emit lower frequencies than has previously been possible. Emitting such frequencies requires a sweep design methodology that takes into account the mechanical, hydraulic and control electronics limitations of the vibrator. Through measurements made both at the vibrator and downhole we show that Maximum Displacement Sweeps can be successfully employed to considerably increase bandwidth.
-
-
-
Portable Airgun Tank - A New Approach to Land BHS using Airguns
More LessThe Portable Airgun Tank (PAT) is a new approach to land Borehole Seismic surveys when using airguns. The PAT is a water filled surface mounted flexible tank which is fully portable and reusable with different sizes available to suit particular applications. Once water filled an airgun source is deployed and centred in the tank. The PAT offer a very constant source signature on every shot.
-
-
-
Drill-Bit Seismic While Drilling by Downhole Wired Pipe Telemetry
Authors F. Poletto, F. Miranda, P. Corubolo, A. Schleifer and P. ComelliDrill-bit seismic while drilling provides reverse VSP, makes it possible to predict the formation changes ahead of the bit, and to image 2D and 3D structures without interference with drilling activity. When the pilot signals used for crosscorrelation with the seismic signals are recorded at the surface, an issue in the application of this methodology may be the loss of the drill-bit-vibration signal during its propagation from the bottom to the surface through the drill string. With PDC bits, as well as during drilling by sliding condition without pipe rotation, and in highly deviated or horizontal wells, the pilot signal recorded at the surface may be weak and consequently the SWD results poor. A solution is to use near-bit downhole tools to get good-quality measurements of the pilot signal. Literature reports examples of SWD with the use of downhole memory systems, from which the data are downloaded after the bit retrieval at the surface. In this paper we present the new results obtained using a drill pipe equipped with a wireline communication system from bottom hole to the surface. The results demonstrate the applicability of this method providing good-quality RVSP data, in terms of S/N and frequency content.
-
-
-
New Moveout Approximation for Walkaway VSP Geometry in a 3D Anisotropic Model
By E. BliasI introduce a new explicit form of vertical seismic profile (VSP) traveltime approximation for a 3D model with non-horizontal boundaries and anisotropic layers. The goal of the new approximation is to dramatically decrease cost of time calculations by reducing the number of calculated rays in a complex multi-layered anisotropic model for VSP walkaway data with many sources. This traveltime approximation extends the generalized moveout approximation proposed by Fomel and Stovas. The new equation is designed for borehole seismic geometry where the receivers are placed in a well while the sources are on the surface. Testing this new approximation for the 3D anisotropic model with dipping boundaries shows its very high accuracy for offsets up to three depths. The new approximation can be used for 3D anisotropic models with tilted symmetry axes for practical VSP geometry calculations. The new explicit approximation eliminates the need of massive raytracing in a complicated velocity model for multi-source VSP surveys.
-
-
-
The Theory and Application of Layer Q Inversion Based on VSP Data
More LessAccording to the compensation principle of surface energy consistency, this paper described a method to eliminate the difference of the excitation energy in zero-offset VSP data, and then use the FK method to separate the down-going wavefield with amplitude preserved processing. Through the analyzing of the difference of amplitude spectra between selected down-going wavefield and monitoring wavelet, we removed the variation of source wavelet in the Q inversion results. After combined with the analytical method, we obtained reasonable equivalent Q values. Based on the relationship between layer Q and equivalent Q, we achieved the stable layer Q values. By working through the contrast between the estimated layer Q and interval velocity, and the results of inverse Q filtered to VSP and near-well surface seismic data for amplitude compensation, we have achieved following improvements: (1) the inversed layer Q and layer velocity are very similar; (2) inverse Q filtering broadened the data spectrum, enhanced the dominant frequency, and improved the seismic resolution greatly; (3) the real data examples showed that this layer Q inversion method is reasonable, effective and stable.
-
-
-
Long offset walkaway and circle VSP in Nankai trough seismogenic zone
Authors Y. Sanada, R. Hino, M. Kinoshita, J.O. Park, E. Araki, G. Moore, N. Bangs, R. von Huene, T. Tsuji and S. KodairaThe purpose of this VSP surveys is to illuminate deep plate boundary and mega-splay faults with high resolution imaging, and to build Vp and Vs model in this area. The seismic data were successfully acquired with the 53.4km walkaway VSP and the circular VSP with 3.5km radius with 16 three-component wireline borehole seismic tools in the cased hole. Zero offset VSP were carried out as well. The long offset survey like this long distance and deep target was first-ever carried out in academia and industrial field. Preliminary P-P reflection image shows high resolution reflections from splay faults. Anisotropy results using direct arrival time from circle VSP indicate anisotropy and its orientation is consistent with the orientation of Philippine plate subduction and the stress orientation from bore hole image. We are planning 3D spiral VSP in 2013.
-
-
-
A High-Resolution Seismic Investigation of the Borehole Surrounding with the Seismic Directional SPWD-Method
More LessIn borehole seismics several methods are in use while drilling. In the case of small layer structures, for instance thin layers or faults, the resolution of surface seismic methods is often not sufficient to determine and locate these structures for exploration. Combining a seismic source and receiver in a common device in the drill string would increase the seismic resolution. In the project SPWD such a prototype of a device has been designed, manufactured and tested. The used source signal frequencies are up to 5000 Hz, which allows a resolution of up to one metre. The resolution is therefore significantly higher than for VSP and SWD. With a penetration depth of about 100 metres an exploration of the borehole surrounding is possible. By applying this method while drilling the risks and costs of drilling can be minimized because of the possibility of adjusting the drill path and locating small sought-after structures.
-
-
-
Equipment Testing and Optimization for Borehole Seismic Monitoring
Authors I.M. Geldmacher, A. Marr, J. Rangel and B. DyerWith the advent of strong interests everywhere into unconventional – speak “shale” – reservoirs, the discipline of borehole geophysics is experiencing a remarkable renaissance. Particularly the fields of microseismic (MS) and vertical seismic profiling (VSP) are showing strong activities worldwide. Regardless whether one looks at MS or VSP, in order to properly interpret these borehole seismic data, one needs to rely on an optimal performance of the recording unit. While some parameters, such as sensor orientation or system noise levels, can be site dependent, there are a number of parameters the operator can influence to achieve a superior data record; laying the ground work for a more accurate event location or velocity model. In this work we present the results of a survey comparing a number of different downhole sensor arrays, excitation mechanisms and operational mechanics, with the goal to identify superior and inferior areas for the tools. The test was set up using a three well set up. The center well was used as a control well to obtain measurements that allowed us to use comparisons from consistent source readings. Those consistent source readings were compared with respect to the various arrays tested.
-
-
-
4D Passive and Aggressive Monitoring of Air Injection into Top Water Overlaying Bitumen Telephone Lake, Alberta
Authors R.D. Pearcy and L. MayoAs part of an air injection monitoring exercise in Telephone Lake area of Northern Alberta, a high resolution simultaneous surface 3D and downhole survey was acquired to map the extent of the water displacement with in the bitumen zone.
-
-
-
Acoustic Impedance Inversion of VSP data
More LessDuring the drilling stage, VSP plays an important role in predicting the depth of target strata and the lithologic characteristics of the deep strata ahead of the drill bit. Therefore, using VSP data to predict ahead of the drill bit has become a popular topic. Highly precised acoustic impedance inversion is a key technique for ahead of drill bit prediction using VSP data. In this paper, we have proposed a method of predicting the acoustic impedance in the formation ahead of the drill bit using VSP data. First, the nonlinear iterative inversion is adopted to invert for acoustic impedance using the VSP corridor stack. Then, by modifying the damping factor in the iteration and using the preconditioned conjugate gradient method to solve the equations, the stability and convergence of the inversion results can be significantly enhanced. The results from theoretical models and real data demonstrate that the method is very useful and effective for ahead of drill bit prediction using VSP data.
-
-
-
A High Resolution VSP in the Oil Sands for Improved Reservoir Characterization
Authors M.H.L. Morrish and L.M. Weston BellmanThis is a case study that looks at the application of a high resolution multi-component VSP acquired in the Athabasca Oil Sands Region of Canada. The 2D Walkaway VSP was the first to be acquired using a new type of downhole array capable of over 2,000 channels of 3-component data per borehole. The HDVSP™ array is based on the VectorSeis® MEMS sensors, which are deployed at either 1 or 2-metre intervals from the surface to the bottom of the well. For this case study, 141 3C sensors were deployed in the well at 2m intervals. The Athabasca oil sands region is an area with complex reservoirs, complex fluid distributions and unconventional rock property behavior. High quality shallow multi-component seismic data contributes to the conditions required for unprecedented detail in reservoir characterization, enabling accurate predictions of both lithology and fluids. The incorporation of converted-wave data shows how an under-utilized dimension of seismic data can increase the quality of the solution. The VSP data was used to improve the seismic reservoir characterization by enabling high-quality calibration and integration of the converted shear (PS) data with the conventional P-wave (PP) data obtained from the multi-component 3D surface seismic.
-
-
-
3D Spectral Element Method in Anisotropic Viscoelastic Media for Borehole Seismic
Authors M. Charara, D. Sabitov and G. PekarWe present an efficient and accurate numerical algorithm for the simulation of borehole seismic experiments. The basis of the approach is a heterogeneous spectral element method implemented on multi-GPU applied to elastic wave equation. The approach was designed to simulate wave propagation in 3D arbitrary anisotropic elastic media with attenuation for a constant via standard linear solid using the method. Due to the use of an unstructured grid, the spectral element algorithm enables handling geological models of big complexity.
-
-
-
3D-VSP Design Acquisition for Monitoring In Situ Combustion. A Case Study: Llanos Basin Colombia
More LessIn order to monitoring the combustion in-situ in a field, we decide to use the 3D-VSP technique such that it could be repeated several times during the field development. The selection was based on (1) area target extension, (2) monitoring wells distribution, (3) thickness target affected by air injection and (4) vertical and horizontal resolution required. The goal of this work is select the parameters which allow both, right target illumination and repeatability. The 3D-VSP design strategy was analyzing the sensibility of the acquisition parameter and performs geophysical modeling by ray tracing. During sensibility analysis the source distribution (geometry) and the number and depth levels were perturbed. The depth level is a critical parameter for repeatability; because of the possible damage induced by combustion to the formation. Additionally, ray tracing was performed on the structural model to quantify the optimal source distribution and the optimal source density. Variability of parameters was evaluated as a function of the homogeneity coverage. Finally the optimized acquisition geometry includes results from sensibility analysis and geophysical modeling processes
-
-
-
Ray-Based Approaches to 3D VSP Modelling for Survey Planning and Interpretation
Authors L. Zühlsdorff and Å. DrottningAdvanced seismic modelling is the key to survey evaluation and design. Two different but complementary ray-based methods are presented: (1) the classic ray-tracing approach with a focus on illumination mapping and attribute filtering, and (2) simulation of depth migrated seismic images of the reservoir as based on illumination vectors. Combining these methods, shot and receiver positions can be optimized, fold and amplitude at target level can be verified, both lateral and vertical resolution can be estimated, and final seismic (depth migrated) images can be simulated and compared for a given survey setup and various overburden properties. Examples are shown for a 3D VSP case and an ocean bottom cable reference case.
-
-
-
3D PSDM Model Building in a Well-Rich Environment
Authors D.C. Weber and V. LesnikovThe paper describes velocity-depth model building for a marine 3D VSP survey in the Arabian Gulf. OBC seismic data exists but is of poor S/N and contaminated with multiples. We construct a P-wave velocity-depth model using only VSP checkshots and well tops from wireline. The checkshots provide P-wave velocity control and the well tops define the depth intervals. First, well tops are gridded in 3D to extrapolate continuous surfaces over the depth volume. Then time-depth information from checkshots is converted to interval velocity functions at each well. Finally, interval velocity is gridded and smoothed in 3D. The composition of all the layers yield the P-wave model. The P-wave model was used to perform pre-stack depth migration on P-wave gathers from a 3D VSP survey. Model accuracy was verified by QC of common image point gathers. We then use wireline Vp/Vs ratio from area wells as a scaler to convert the P-wave model to S-wave. A Vp/Vs volume was built using 3D kriging of the Vp/Vs ratio logs from available wells. The Vp/Vs volume was then divided into the P-wave volume to yield the S-Wave volume. PSDM results using the S-wave model on S-wave gathers are not currently available.
-