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75th EAGE Conference & Exhibition - Workshops
- Conference date: 10 Jun 2013 - 13 Jun 2013
- Location: London, UK
- ISBN: 978-90-73834-49-1
- Published: 10 June 2013
21 - 40 of 138 results
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Multicomponent Seismic for Gas Hydrate Monitoring
Authors E. Asakawa, T. Hayashi, H. Tsukahara and H. TakahashiThe first offshore methane hydrate production test will be conducted by METI and JOGMEC/MH21 in early 2013 in the eastern Nankai Trough, Japan. The test aims to prove the applicability of the depressurization technique for MH production. The flow test intervals will be at shallow sediment depths but at deep water depths. JOGMEC plans to carry out a multi-component seismic survey to monitor the dissociation of MH by the depressurization technique in the flow test scheduled in early 2013. JGI, Inc. has developed deep-water OBC system (Deep-sea Seismic System, DSS) with OCC Corp. and deployed the DSS close to the production test well in August 2012. After deployment, the DSS system was buried by ROV. Then we carried out the baseline 2D/3D multicomponent seismic survey. The results show the good quality to delineate the methane hydrate concentrated zone. After the baseline survey, we have left the DSS on seafloor and remains there until the monitoring surveys scheduled in April and August 2013, because the fixed location of the sensors is crucial for time-lapse monitoring survey.
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A New Approach for Quantification of Gas-hydrates in Fracture Shale in KG basin, India from MCS Data
More LessThe coring of NGHP has recovered gas-hydrates in fracture shale in KG basin, India. Higher resistivity and sonic logs at site 10 indicate gas-hydrates between 30 to 150 mbsf. The simple Archie's formula to resistivity log overestimates gas-hydrates when compared to pressure core measurements. This is due to its isotropic assumption, as fractures cause anisotropy. Considering gas-hydrates as part of matrix and brine in pores, we establish a relation between normalized resistivity (NR) and velocity of sediments with and without gas-hydrates respectively from log data, and estimate gas-hydrates by modified Archie's formula to NR with the saturation exponent (n) that matches with pressure core measurement by incorporating effect of anisotropy. We derive seismic velocities from MCS data along 6 in-lines and 6 cross-lines (each of 8 km long) around the drilling site in KG basin covering an area of ~14.7 sq km. The modified Archie's formula to velocity-resistivity transformed data show gas-hydrates between 5 to 50% along different lines. Average volume saturation is calculated as 12.28% using 60% average porosity observed in density-porosity log. Total volume of gas within 168 m average thickness (indicated by high velocity anomaly) of hydrate-bearing sediments is calculated as 51.5 BCM in the study area.
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Sources Methane and Gas Hydrate in Okhotsk Sea
By A. ObzhirovMultidisciplinary surveys were conducted to investigate gas seepage and gas hydrate accumulation on the Northeastern Sakhalin Continental Slope (NSCS), Sea of Okhotsk, during joint Korean–Russian–Japanese expeditions conducted from 2003 to 2012 (CHAOS and SSGH projects). About 500 gas seeps were detected in a 2,000 km2 area of the NESS (between 53º45'N and 54º45'N). Active gas seeps in the gas hydrate system on the NSCS were evident from features in the water column, on the seafloor, and in the subsurface: well- defined hydroacoustic anomalies (gas flares), side-scan sonar structures with high backscatter intensity (seepage structures), bathymetric structures (pockmarks and mounds), gas- and gas-hydrate-related seismic features (bottom-simulating reflectors, gas chimneys, high-amplitude reflectors, and acoustic blanking), high methane concentrations in seawater (10-20mkl/l), and gas hydrates in sediment near the seafloor.
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Conversion of Natural Gas Hydrate into CO2 Hydrate – A Win-win Situation
By B. KvammeInjection of carbon dioxide into in situ natural gas hydrate sediments will lead to an exchange in which carbon dioxide will primarily occupy the large cavities of structure I under the release of the original methane in these cavities. The exchange can go directly as a solid state exchange or it can be a result of a hydrate formation dissociation sequence. In the latter case new hydrate from injected carbon dioxide will release heat for dissociation of the in situ methane hydrate. In this case the heat transport is fast and the rate controlling mass transport is liquid transport and as such orders of magnitude faster than the slow solid state mechanism. The conversion is discussed in detail in terms of state of the art multi scale modelling and experimental work. The role of entropy changes in driving the exchange process is discussed in detail. Some highlights of results from a recent pilot plant test of the concept in Prudoe Bay Alaska are also discussed. Finally some remaining challenges, and possible strategies, for the future development of hydrate as an energy resource are discussed.
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A Common Framework to Calculate Uncertainties of Microseismic Events from Downhole and Surface Recordings
By U. ZimmerThe results of microseismic surveys are almost exclusively presented as “dots” in three-dimensional space. Although it is well known that each of these microseismic event locations has an individual level of accuracy, the location accuracy is rarely quantified. In cases where the location uncertainty is represented by bars around the “dot”, they often represent only the precision, i.e. repeatability, of the event location. For the purpose of interpretation it is much more useful to specify the accuracy, i.e. the difference between the calculated and the true location. By using a methodology based on probability density functions (PDFs) it is possible to calculate meaningful confidence intervals around the most probable solution, i.e. the “dot”, which are much more representative of the overall location accuracy. In addition, this methodology allows similar calculations for the two main types of localization algorithms used throughout the industry, i.e. migration-type algorithms and algorithms requiring explicit arrival time picks. This allows creating a common framework that can be applied equally well to recordings from surface and downhole arrays. With this approach it is possible to include the individual location uncertainties in the overall interpretation of the microseismic map.
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Simulation of Microseismic Deformation During Hydraulic Fracturing
Authors S. Maxwell and X. WengModeled geomechanical deformation associated with hydraulic fracture stimulation of a complex hydraulic fracture provides context for interpretation of microseismic deformation. Partitioning of modeled strains into shear and dilatational components allows relative comparison of the appropriate displacement mode with observed cumulative microseismic moments. A workflow is described where the input parameters of the simulation are varied to match both the footprint and deformation of the microseismicity, which then results in an estimate of the complete fracture network volume and proppant placement. In this way the effective stimulated volume can be assessed and used as input to a reservoir simulation to investigate well performance and reservoir drainage.
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Characterization of Unconventional Reservoirs Through the Use of an Integrated Rock Quality Index
More LessUnconventional reservoirs require hydraulic stimulation to be commercially productive. Recently, distinctions have been made between reservoir quality vs. completion quality (Cipolla et al. 2012), emphasizing the importance of both elements for production. There are many sources of variability in reservoir quality; in this paper I examine several fundamental reservoir properties in detail and combine them in a new way: the Rock Quality Index (RQI). Through the definition of a geomechanical model and corresponding mechanical stratigraphy, those factors having a substantial effect on reservoir quality became apparent. Two fundamental categories; compositional variation and fabric variation, are used to characterize overall reservoir variation. Burial, compaction, hydrocarbon generation, diagenesis, and tectonics all affect the mechanical character and in-situ stress state of the reservoir. The Rock Quality Index (RQI) is an effort to understand how composition and fabric relate to stress anisotropy, fracturing, and rock properties, and ultimately aid in defining the best zones for exploitation. Therefore, this Rock Quality Index (RQI) is vital for the defining the second element of unconventional reservoir success; completion quality. Without a reservoir framework to drive the completion design, high completion quality will be harder to achieve.
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Nonlinear diffusion-based Interpretation of Hydraulic Fracturing Induced Seismicity
Authors S.A. Shapiro and N. HummelWe present a microseismicity-based approach to characterise the hydraulic transport during borehole fluid injections. This approach allows to reconstruct the enhanced permeability evolution inside of the stimulated rock. We apply our approach to seismicity recorded during a hydraulic fracturing treatment in the Barnett Shale. The spatio-temporal analysis of induced events reveals a significant nonlinear fluid-rock interaction. To explain this, we consider an effective poroelastic medium representation. We suppose a nonlinear diffusional relaxation of the pore-pressure perturbation with a power-law pressure-dependence of permeability. We generate synthetic seismicity distributions whose spatio-temporal features are similar to the ones which we observe in Barnett Shale. Our results indicate that the fluid transport during the hydraulic fracturing treatment can be described by a nonlinear diffusion based on a power-law dependent permeability.
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Microseismic Monitoring of Reservoir Stimulation: Case Studies and Implications for Improved Geomechanical Characterization
Authors M. Bohnhoff, G. Kwiatek, P. Martinez-Garcon and G. DresenMicroseismic monitoring is a well-established but still widely underestimated technique to characterize reservoir geomechanical parameters and processes related to stimulation using fluid injection. We present two case studies in which we applied state of the art seismological methods investigating data sets of induced seismicity. Physical processes occurring in the reservoir during massive fluid injection can be determined with substantially refined resolution if appropriate effort is undertaken to acquire high-quality microseismic recordings. While the presented results were obtained for geothermal reservoirs the techniques can be applied to any type of geo reservoir.
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Strategies for Field Evaluation: How Proper Instrumentation Deployment Is the Key to Unlocking the Limitless Value of Microseismic Data
Authors A. Baig, T. Urbancic and E. von LunenMicroseismic data are traditionally restricted to locations of hypocentres and have been of great utility in outlining the geometries of the stimulated regions for hydraulic fracturing and other injection programs. However, there is much more information to be gained from careful analysis of the microseismic data, the key to unlocking this potential rests not only in careful analysis, but also in recording the data from properly calibrated arrays, with a heterogeneous distribution of sensors to allow for wideband recording, and with geometries that enable such higher-order processing techniques. The wideband recording ensures that the magnitude range can be accurately calculated for the large magnitude events that potentially saturate the 10 or 15 Hz instruments normally deployed for microseismic monitoring. By recording the seismic waveforms from a number of azimuths, techniques like seismic moment tensor inversion (SMTI) can be employed to gain an understanding of the fracture network that is being activated during these treatments, and the fracture modes (tensile, shear, shear-tensile) for each event, giving a clear picture of the dynamics of the discrete fracture network during hydraulic stimulations.
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Seismic Hazard Associated with Shale-Gas-Fracking? The Bowland Shale Case Study
By S. BaischThe phenomenon of micro-earthquakes occurring in the course of shale gas fracking is well known and has been extensively used for fracture mapping. The aspect of a potential seismic hazard resulting from these earthquakes is fairly new and there exist only few documented cases of fracking induced seismicity strong enough to be perceptible on the Earth’s surface. Recent examples are two felt micro-earthquakes induced by fracking operations in the Bowland Shale (UK). Here we present the results of a geomechanical study explaining the circumstances under which such exceptionally strong earthquakes may occur. From observation data we find evidence that the treatment well in the Bowland Shale intersects a critically stressed (natural) fault or similar plane of weakness. Micro-earthquakes are induced on the existing fracture plane by fluid pressure diffusion and co-seismic stress redistribution. Based on these physical processes we have developed a numerical model of the induced seismicity yielding results which are consistent with observation data. Using the numerical model we estimate the maximum magnitude that could potentially occur by similar hydraulic treatment operations in the Bowland Shale. The resulting magnitude is considered to be too small to cause damage at the Earth’s surface. To account for parameter uncertainties, we have developed an additional traffic light system for controlling future fracking operations.
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Bowland Basin Shale Operations Past and Present, Micro-seismic Monitoring and Induced Seismicity Mitigation Protocol
By H. ClarkeShale gas exploration commenced in the Bowland basin of NW England with the Preese Hall 1 discovery well in August 2010. Two more vertical wells and a 100km2 3D seismic have since been completed and an OGIP resource estimate of 200 TCF. Following the drilling of Preese Hall-1 a multistage hydraulic fracture program commenced in spring 2011. Associated with this fracturing activity, two felt seismic tremors occurred on April 1st (ML=2.3) and May 27 (ML=1.5). Hydraulic fracturing operations were paused and a detailed geomechanical study concluded that seismicity at Preese Hall-1 was induced by injection of fluid into a fault zone within the proximity of the well bore.
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Shale Rock Properties - Extending the Scope of Rock Physics
By F. KetsTraditionally, the emphasis of rock physics in the Petroleum Industry has been on the elastic properties of rocks, with the major area of application in the description and characterisation of reservoirs. The search for unconventional resources does not only lead to an extension of the discipline to the description of less porous and quite often anisotropic media, but also to a reconsideration of inelastic properties which are critical for the deliverability of the reservoir. Questions arise whether experimental techniques proven useful in rock physics calibration can be applied with equal confidence in unconventional reservoirs.
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Monitoring Fracture Network Stimulation Using Micoseismic Data
Authors M. Kendall, J.P. Verdon, A.F. Baird, A. Stork and P. UsherThe successful exploitation of many reservoirs requires fracture networks, sometimes naturally occurring, often hydraulically stimulated. Microseismic data acquired in such environments hold great promise for characterising such fractures or sweet spots. The loci of seismic events delineate active faults and reveal fracture development in response to stimulation. However, a great deal more can be extracted from these microseismic data. Inversions of shear-wave splitting data provide a robust means of mapping fracture densities and preferred orientations, useful information for drilling programs. They can also be used to track temporal variations in fracture compliances, which are indicative of fluid flow and enhanced permeability in response to stimulation. Furthermore, the frequency-dependent nature of shear-wave splitting is very sensitive to size of fractures and their fluid-fill composition. Here we discuss a range of methods for extracting spatial and temporal variations in sub-seismic scale fractures.
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Modifying the Seismic Source Array Spectrum to Reduce the Risk of Injury to Marine Mammals
By R. LawsAcoustic injury criteria for marine mammals are well defined and they are applicable to seismic sources. Several studies have suggested that marine seismic sources emit more high-frequency energy than is required for imaging. I show how the extent of the injury zone can be reduced by using a source array with an output spectrum that is partially attenuated at higher frequencies while probably not compromising image quality.
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Does Seismic Surveys Impact Fish and Fisheries
By I. GauslandThe presentation will discuss studies on impact of seismic operations on fish and fisheries, and review some shortcomings in studies frequently used in Environmental Impact Assessments and as a basis for governmental regulations of seismic operations. The difference of opinion between the parties may lead to unnecessary conflict and significant increased cost for all operations.
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Monitoring and Mitigating Bioacoustic Impacts from Seismic Surveys - The Australian Perspective
By C. ErbeIn Australia, proponents of seismic surveys and other operations emitting underwater noise have to prepare an Environmental Plan (EP) for approval by the regulator before operations can commence. In support of the EP, large amounts of data are often collected, such as baseline data on the marine soundscape, the physical and biological environment, operational noise characteristics etc. More data (on underwater noise, animal abundance and behaviour etc.) is sometimes collected during operations as part of monitoring and mitigation plans. Australia’s offshore oil & gas industry has recently come together to share data from bioacoustic environmental impact assessments, yielding charts of baseline soundscape characteristics, catalogues of anthropogenic source characteristics, improved models for sound field prediction, and growing databases of animal behaviour, abundance and migration. This data sharing will ultimately help to streamline the environmental approval process.
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Mitigating the Potential Effects of Underwater Sound on Marine Mammals - A Global Overview
By R. ComptonConcerns regarding the potential impacts of underwater sound upon marine species such as whales, dolphins and porpoises has led to the implementation of mitigation measures during marine seismic operations. These measures include the use of personnel and passive acoustic equipment to monitor for species within a given safety zone around the source, delay and shutdown to the source during operations. These procedures have become a common part of marine seismic surveys and represent best practice with regard to environmental responsibility.
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The Perceived Impacts of Seismic Surveys on Marine Life - Are They Really a “Big Issue” or Simply “Big Business”?
By J. HughesIn keeping with the title of this workshop, I have chosen my title to be even more provocative! I will summarise the main concerns put forward as being representative of this “big issue,” such as “the increasing levels of sound discharged in the oceans (by the petroleum industry) may prevent cetaceans communicating (masking effect) and hence have a negative impact on their life functions” or even “the oil industry’s activities may have a very significant impact in harming and even killing cetaceans and fish in the marine environment. It could even lead to their extinction!” Note the devious use of the words “may” or “could” in these claims made by those who most vocally express opposition to seismic surveys. In parallel, I will outline the facts and observations that surely point to such claims being conjecture (I provocatively call them “myths!”). Finally, I will explore what I consider to be the most likely motives that a variety of generic organisations (such as environmental NGOs, political parties, various levels of government and even sections of the petroleum industry) have for ignoring the facts, making the claims, spreading the misinformation and propagating the myths in order to make this issue “big business.”
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24/7 Automatic Detection of Whales Near Seismic Vessels Using Thermography
Authors O. Boebel and D.P. ZitterbartDetecting whales at sea by visual observation for mitigation purposes is inherently difficult and personal intensive while restricted to daylight hours. These caveats are overcome by the system described herein, which employs a state-of-the-art thermographic infrared scanner in conjunction with a learning computer algorithm to automatically and reliably detect whale blows. The stand-alone system provides detection, verification and documentation of each ship-whale encounter, allowing a retrospective review of every mitigation decision taken aboard. The system has been developed over the course of 5 years and was thoroughly tested in polar waters during 7 expeditions to the Arctic and Antarctic, accumulating 5871 hours of operation. Of these, 3472 hours, were analyzed with various learning automatic detection algorithms, which discovered about 4500 whale blows in this data. Direct comparisons of auto-detections with concurrent whale sightings by visual observers (double blind setup) confirm a very high degree of detection reliability within 2-3 nautical miles from the ship in subpolar and polar environments. The system, when used as a an “assistant”, allows a single marine mammal observer to efficiently monitor the ships entire surroundings and to take instantly and retrospectively verifiable decisions regarding the use of airguns, as all relevant data is automatically stored.
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