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76th EAGE Conference and Exhibition - Workshops
- Conference date: 16 Jun 2014 - 19 Jun 2014
- Location: Amsterdam, Netherlands
- ISBN: 978-90-73834-90-3
- Published: 16 June 2014
61 - 80 of 142 results
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Experimental Studies of Stress Dependence, Static vs Dynamic Behaviour and Mechanical Anisotropies of Shale
Authors R.M. Holt, A. Bakk, A. Bauer, E. Fjær and J.F. StenebråtenLaboratory data from controlled rock mechanical tests with various shales have been used to understand and quantify stress effects on wave velocities of relevance for 4D seismics, and to quantify the difference between static and dynamic mechanical properties and their anisotropies.
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The Effect of Shale Mineralogy on Anisotropy in Unconventional Resources Settings - A Rock Physics Modeling Study
By R. BachrachRock physics modeling provides a mathematical framework that links rock volumetric and microstructural parameters to effective elastic properties. Shales, which are elastically anisotropic, provide a special challenge for rock physics modeling due to the complex nature of their fabric and pore space and the large variations in depositional and diagenetic settings that affect the mineralogical composition, porosity and fabric of the rock.
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3D Relocation Errors of Microseismic Events by Surface and Borehole Receivers for Shale Gas Stimulation
Authors H. Alsahfy, A.L. Vesnaver, M. Jervis and H. KuleliMicroseismic monitoring and mapping of induced hydraulic fractures (frac) is an important tool in unconventional oil and gas exploitation. It is a key technology for completion evaluation which allows for continuous improved frac design, frac effectiveness, and ultimate resources recovery estimation and development. Formation evaluation tools provide accurate measurements of the target formation’s petrophysical and mechanical properties proximal to the borehole only, distal to the borehole though, Microseismic monitoring can be a useful tool to monitor the formation’s response to the frac. Shale response to hydraulic stimulation can be estimated mainly by the local density and pattern of hypocentres. Linear trends of microseismic event and their associated focal mechanisms may highlight the reactivation of faults due to hydraulic stimulation, while the location of events outside the target formation may suggest a need for future Improvements to the completion/ stimulation plan, and in some cases, re-stimulation. However, errors in the hypocentre locations may convert clear trends into “fuzzy” clouds, hampering our understanding of how the simulation interacted with the formation. The accuracy of hypocentral coordinates of micro-earthquakes is critical for understanding and proper planning for the hydraulic stimulation jobs of a shale play.
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The Role of Geomechanics in Reservoir Stimulation Design Procedure
Authors M.M. Slota-Valim and H.B. Jedrzejowska-TyczkowskaHydraulic fracturing treatment preceded with reliable geomechanical analysis of the reservoir, whether carried out immediately after well completion or during late stages of the reservoir lifetime (refracturing among others), helps to avoid near-wellbore area damage and the hydrocarbons production increase, through the creation of the artificial fracture network and therefore enabling free flow of the gas from the unconventional formation into the wellbore. The practice of stimulation treatment by fracturing the geologic formation reaches 1947, but the early application of hydraulic fracturing was not successful due to the problems with diagnosis of the complications and selection of wells that were about to be subjected to the treatment. Over the last two decades numerous cases of successful secondary fracturing were recorded in the hydrocarbons reservoirs in North America, Russia, China, Brazil and Algeria. Obviously the potential for production increase have hydrocarbon deposits around the world, especially those at advanced stage of exploitation. In most of the cases the use of such treatments is much more economical than determining optimal location, well design, drilling and completion of new well.
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Model-based Workflows for Optimal Long-term Reservoir Mangement
Authors O. Leeuwenburgh, P. Egberts, A. Chitu and F. WilschutLife-cycle optimization is the process of finding field operation strategies that aim to optimize recovery or economic value with a long-term (years to decades) horizon. A reservoir simulation model is therefore generally appropriate and sufficient to explore the impact of different recovery scenarios. A number of challenges arise when trying to determining the optimal recovery strategy. We describe a practically feasible model-based optimization workflow that addresses complications associated with computational effort, large numbers of decision variables (controls), and the uncertainty in the properties of the reservoir. A software tool has been developed, in cooperation with industry partners, and applied to several synthetic and real field cases to demonstrate the value and potential benefits of this workflow, such as optimal well operating strategies for multiple wells that increase recovery or economic value, improved well design, and reservoir understanding.
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Marine CSEM - Where Do We Stand and Where Can We Go?
More LessAlthough most of the early problems that plagued commercial marine CSEM data have been addressed, the market for marine CSEM data is shrinking. Reasons include a lack of integration with the rest of the exploration workflow, high cost of data acquisition, and lack of diversity in the marketplace. Small companies are discouraged from competing because of the threat of patent lawsuits, and large companies appear to be looking for a larger commercial opportunity than marine EM currently provides. Data show that the marine CSEM method works, and that very few commercially viable hydrocarbon targets lack a detectable resistivity signature. The existence of the large number of dry wells that support this assertion demonstrates that the method is not being used to best advantage.
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CSEM - Where Do We Stand and Where Can We Go?
More LessCSEM was established as an industry 12 years ago by several service companies that offered 2D CSEM commercially. The presentation will focus on how CSEM has developed as a commercial tool since the first commercial introduction 12 years ago and look into the future. The technology has gone through a significant development. The most important step was from 2D to 3D wide azimuth data enabled by improvements in equipment, operations, inversion and streamlined processing of large data volumes. Both horizontal and vertical resistivity cubes are now inverted, enabling mapping of anisotropy and CSEM is no longer limited to deep-water applications. Wide-azimuth 3D surveys will most likely be the main way to acquire CSEM data also in the future. In future processing and inversion, magnetic field data will be used more to improve imaging, especially in shallow water. In general MT data will also be used more which implies stationary seafloor receivers with both electric and magnetic sensors (Ex, Ey, Hx and Hy). CSEM will see deeper (stronger sources), get better resolution and improved data will be processed jointly with seismic, resulting in improved imaging. Moreover, the data will be used as an important part in the oil companies workflow.
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Increasing Transmitter Current and Reducing Ambient Noise Levels – What Are the Limitations?
Authors R. Mittet, J.P. Morten and H.R. JensenThe marine controlled-source electromagnetic method (CSEM) can detect subsurface hydrocarbon reservoirs because they represent resistors in a conductive medium, i.e. brine-saturated rocks. The limitations on the applicability of the technology are given by target burial depth, lateral extent, and the net pay thickness. Improvements to the acquisition instrumentation can extend the applicability and increase the resolution. However, several factors affect the accuracy of the measured data. To achieve a significant improvement it is important to understand the experimental error contribution from each hardware component in relation to the target effect on the data. We present error propagation analysis for CSEM acquisition, which reveals feasible limitations for target detection. Further, we show how equipment can be optimally improved to extend applicability of the technology.
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Rotate your Dipoles by 90 Degree - the Vertical CSEM Approach
Authors S.L. Helwig, J.M. Børven, K. Eide, Ø. Frafjord, T. Holten and A.W. El KaffasThe acronym CSEM has widely become synonymous for frequency domain Controlled Source ElectroMagnetics with seabed nodes and horizontal towed dipole transmitters. While this incarnation of marine CSEM is certainly the best known CSEM variant, it is not necessarily always the best option for acquisition over a certain prospect. Based on numerical modelling the differences between horizontal FD CSEM and vertical TD CSEM for given models were explored. The results show that time domain CSEM with vertical transmitter and vertical receiver dipoles is a viable alternative that provides high sensitivity, high depth of penetration as well as low disturbance by air wave and 3D structures. It's much smaller transmitter receiver distance creates an advantage in lateral resolution as well as in the detection of narrower or smaller structures. Case studies with comparisons between inverted vertical-vertical CSEM data and well log results show the real world usefulness of the method as well as the necessity for close integration of the results with other geophysical data. We argue that the marine CSEM landscape will become more divers and that acquisition layout and methodology for a given target needs to be evaluated on a case by case basis to achieve optimum results.
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Investigations on Small Scale Targets with Sputnik, a Two Polarization Transmitter System
Authors S. Hölz, A. Swidinsky, M. Sommer and M. JegenSputnik is a novel CSEM transmitter system, which is used for small scale investigations. The system is special in the sense that it can excite two perpendicular TX polarizations at each TX location. It can be shown that this generally increases the sensitivity of measurements to the resistivity structure of the seafloor. This style of experiment requires new approaches for a first pass data interpretation, for which we have adapted the concept of rotational invariants to the marine case. Rotational invariants allow a display of measured data in terms of apparent resistivity sections. They can also be used in the inversion of data. Additionally - using the skew invariant - a dimensionality analysis of the underlying resistivity structure is possible directly from the measured data. Within the past two years the system has been used in three successful experiments for the investigation of methane hydrates and free gas. First results prove that the system is a useful tool for investigations on small targets.
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Anisotropic Inversion of Towed Streamer EM Data in Shallow Waters
By J. MattssonTowed streamer electromagnetic (EM) data along a survey line at the Alvheim Boa oil field in the North Sea has been inverted using an open-source 2.5D inversion code. The electric field data was acquired in 4 kn with a single vessel using a horizontal bipole source at 10 m depth and densely populated electrode pair receivers housed in a towed streamer towed at 50 m depth in water depths between 110 and 125 m. The inversion algorithm is based on a parallel adaptive 2.5D finite element algorithm and uses a regularized variant of a Gauss-Newton minimization algorithm. This inversion method has proven to be fast and efficient for and suitable for towed streamer EM data. In this case, the resulting anisotropic resistivity cross section corresponds well with the high resistive part of the sand layer in the vicinity of the reservoir depocenter. The low noise in the frequency response data and the low navigation and measurement uncertainties made it possible to obtain a final misfit as low as 2 %. The towed streamer EM technology has proven to be a robust and useful CSEM method in shallow waters. The densely sampled frequency response data is suitable for anisotropic inversion.
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Towards Real Earth Models - Computational Geophysics on Unstructured Tetrahedral Meshes?
Authors C.G. Farquharson, P.G. Lelièvre, S. Ansari and H. JahandariUsing unstructured tetrahedral meshes to specify 3D geophysical Earth models has a numer of advantages. Such meshes can conform exactly to the triangularly tessellated wireframe surfaces in the 3D Earth models used by geologists. This offers up the possibility of both geophysicists and geologists working with a single unified Earth model. Unstructured tetrahedral meshes are extremely flexible, and so can accurately mimic arbitrarily complicated subsurface structures and topography. Also, in the context of electromagnetic methods, unstructured tetrahedral meshes can be very finely discretized around sources and yet can transition to a coarse discretization in the extremities of the solution domain without, in principle, affecting the quality of the mesh. However, using unstructured tetrahedral meshes for geophysical Earth models has its challenges. The tessellated surfaces in wireframe geological models are often not immediately suitable for computational techniques as they can contain intersecting facets and facets with extreme aspect ratios. Generating tetrahedral meshes that are of sufficient quality from real wireframe geological models can therefore be difficult. This presentation will aim to discuss the pros and cons of using unstructured tetrahedral meshes for geophysical Earth models, keeping in mind the complexities of the real subsurface that we are ultimately trying to represent.
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Advanced Modeling and Inversion Tools for Controlled Source EM
By E. HaberModeling and invasion of CSEM data is a challenging problem. In this work we present a combination of methodologies that allows for the solution of such problem using reduced in a computational efficient way. Our framework is composed from three main parts 1. An adaptive mesh, that is adapted to the sources and receivers, that decreases the size of each linear system to be solved. 2. A multiscale approach that allows us to use large cells far away from the sources and receivers and correctly average or upscale the conductivity. 3. A stochastic programming approach that allows for the reduction of the number of forward modeling at each step of the inverse problem
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New Advances for a Joint 3D Inversion of Multiple EM Methods
More LessElectromagnetic (EM) methods are routinely applied to image the subsurface from shallow to regional structures. EM methods differ in their sensitivities towards resistive and conductive structures as well as in their exploration depths. Joint 3D inversion of multiple EM data result in significantly better resolution of subsurface structures than the individual inversions. Proper weighting between different EM data is essential, however. We present a recently developed weighting algorithm to combine magnetotelluric (MT), controlled source EM (CSEM) and DC-geoelectric (DC) data. It is known that MT data are mostly sensible to regional conductive structures, whereas, CSEM and DC data are suitable to recover more shallow and resistive structures. Our new scheme is based on weighting individual components of the total data gradient after each model update. Norms of each data residual are used to assess how much weight individual components of the total gradient must have to achieve an equal contribution of all data in the inverse model. A numerically efficient way to search for appropriate weighting factors could be established by applying a bi-diagonalization to the sensitivity matrix. Thereby, the original inverse problem can be projected onto a smaller dimension in which the search of weighting factors is numerically cheap.
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Estimation of the Petrophysical Model through the Joint Inversion of Seismic and EM Attributes
Authors F. Miotti, I. Guerra, F. Ceci, A. Lovatini, M. Paydayesh, G. Milne, M. Leathard and A. SharmaReservoir characterization objectives are to estimate the petrophysical properties of the prospective hydrocarbon traps and to reduce the uncertainty of the interpretation. In this framework, we present a workflow for petrophysical joint inversion (PJI) of seismic and EM attributes to estimate the petrophysical model in terms of porosity and water saturation. This study realizes the joint inversion within the probabilistic structure provided by the Bayesian theory. 3D volumes of estimated porosity and saturation show how the joint inversion of acoustic impedance and electrical resistivity can provide a quantitative description of the reservoir properties and with it a measure of uncertainty, which is consistent with the petrophysical model and observations.
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Joint CSEM–seismic Evaluation of Risky Drilling Task
More LessDue to the complex surface and subsurface exploration conditions, hydrocarbon reservoir distribution is controlled by many unknown factors, such as structure reservoir, lithologic trap reservoir, stratigraphic trap reservoir, and changes of exploration target, etc., any single geophysical exploration method has higher risk to predict and evaluate the hydrocarbon reservoir. Explorationists have high expectation to identify hydrocarbon target using CSEM method, but its wide applications have been limited due to its low resolution and poor accuracy. Recent years, CSEM and seismic constrained or joint inversion has achieved higher accuracy for electrical anomaly target exploration. Based on this trend, we have developed a new exploration method of the joint TFEM (Time and Frequency domain EM) – Seismic evaluation of risky drilling task. When an exploration area not only has confirmed seismic structure trap and reliable AVO anomaly, but also has matched induced polarization (IP) and resistivity anomaly (R) on the potential exploration target, it will have much lower drilling risk. The wide application of this new exploration method in the west of China has significantly improved the drilling success rate through the using the joint TFEM – Seismic method to predict and evaluate the potential hydrocarbon target.
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Marine CSEM for Gas Hydrate Exploration Using a Seafloor-towed Multi-receiver System
Authors K. Schwalenberg, M. Engels, D. Rippe and C. SchollIn the past years BGR – the German Federal Institute for Geosciences and Natural Resources has been developing unique marine CSEM systems to explore the electrical attributes of the shallow seafloor. CSEM data are sensitive to the presence of resistive gas and gas hydrate in the sediment, and provide complementary volume information which, if used in connection with seismic and other exploration methods, e.g. drilling, allow for a better evaluation of the gas or gas hydrate resource potential. The gas hydrate setting differs from the exploration of conventional offshore oil and gas reservoirs as typical gas hydrate deposits are smaller in scale und at shallower depths below the seafloor. Therefore instrumentation and survey configurations need to be adapted. HYDRA, the seafloor-towed, multi-receiver system has been recently refined with a new signal generator and receiver units which both allow for online communication and data transfer. 1D and 2D inversions of CSEM data collected offshore New Zealand result in highly anomalous resistivities over several methane seep sites within the gas hydrate stability field which are believed to be caused by concentrated gas hydrates below the seeps.
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Overview of Marine Controlled-Source Electromagnetic Interferometry by Multidimensional Deconvolution
Authors J.W. Hunziker, E. Slob and K. WapenaarInterferometry by multidimensional deconvolution for marine Controlled-Source Electromagnetics can suppress the direct field and the airwave in order to increase the detectability of the reservoir. For monitoring, interferometry by multidimensional deconvolution can increase the source repeatability. We give an overview over the method and discuss a possible path of research for the future.
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Recent Developments for Land-based Controlled-source Electromagnetic Surveying
Authors K. Tietze, A. Grayver, R. Streich and O. RitterControlled-source electromagnetic (CSEM) surveying has been in use for more than ten years and has become a well-established tool for hydrocarbon exploration in marine environments. On land, however, CSEM methods are rarely applied in a similar manner, since challenges are greater for a range of technical, logistical, and numerical aspects. Over the last five years, the Geo-Electromagnetics working group at the German Research Centre for Geosciences Potsdam (GFZ) has been developing the CSEM method for land-based applications, including a three-phase current transmitter allowing for arbitrary source polarizations, new robust data processing concepts, and 1D to 3D modelling and inversion software. The CSEM hardware and software has been successfully applied in a series of surveys on different targets. We show examples from case studies, including 3D inversion results from the Ketzin CO2 injection test site in Northern Germany.
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Advances in Electromagnetic Survey Instrumentation and the Use of a Cased Borehole for Imaging a Deep Formations
Authors A.D. Hibbs, T.R. Petrov, J. Pendleton, A. Agundes, S. Kouba, T. Hall, D. Boyle, T. Martin, C. Schenkel and H.F. MorrisonElectromagnetic (EM) resistivity imaging methods have the potential to map subsurface fluid distribution in applications ranging from derisking potential prospects to quantifying the propagation of hydrofractures in unconventional reservoirs. However, to date EM surveys have been limited to reservoirs too shallow or too large to be of general applicability in the oil industry. The critical technology issues in extending EM methods are: a) generating an adequate subsurface electrical current, and b) the sensitivity and stability of the EM resistivity measurement apparatus. A borehole provides a physical means to contact to deep hydrocarbon formations. To date boreholes have been exploited by lowering a current injection electrode to the depth of interest and completing the electrical circuit with a counter electrode at the surface. This borehole to surface EM method has been successfully used to image oil-to-water contact in an oil reservoir but has the disadvantage that the well must be opened, and, for a producing reservoir, taken off-line. We have now demonstrated a new approach that uses the borehole casing as a current injection electrode. In addition, we have developed the first capacitive sensors for geophysical use and have adapted them for use with commercial seismic data recorders.
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