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- Volume 35, Issue 4, 2017
First Break - Volume 35, Issue 4, 2017
Volume 35, Issue 4, 2017
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Detecting microseismicity using distributed vibration
Authors Daniele Molteni, Michael John Williams and Colin WilsonDistributed acoustic sensing (DAS) and, more generally, distributed vibration sensing (DVS) offer new approaches to the detection of seismic waves, based on interrogation of a fibre-optic cable. We investigated the detection of microseismic events using a heterodyne distributed vibration sensor (hDVS), comparing to a pair of borehole geophone arrays co-located in the monitoring well. The aim was to establish the current performance level of hDVS for microseismic monitoring and to understand any differences between geophone and hDVS responses. We compared the microseismic events detected simultaneously on both systems. Under the assumption that hDVS measures strain in the fibre, the comparison to geophone particle velocity was made in the strain-rate domain. We supported these observations with modelling work. We found the hDVS measurements directly comparable to the geophones, indicating a potentially true amplitude response from hDVS. An anomaly in the hDVS frequency response was a function of apparent phase velocity. Modelling verified the observed effect as consistent with the filtering effect of the light pulse used in fibre interrogation. We find that hDVS detects microseismicity but is not yet a replacement for the borehole array. However, improved microseismic response might be achieved with shorter pulse-length systems in the next generation of fibre interrogators. The heterodyne distributed vibration sensor (hDVS), together with other forms of distributed acoustic sensing (DAS), have been reported as observation techniques for microseismic monitoring (Webster et al., 2013; Li et al., 2015; Molteni et al., 2016). We present further results from the study described by Molteni et al. (2016) and extend the discussion on the differences between observation with a borehole array of geophones and observation on a laser-interrogated fibre-optic cable that is cemented behind casing.
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How microseismic can help to improve our understanding of refracturing
More LessThe rapid drop in production rate from horizontal wells in unconventional reservoirs requires adding new wells to maintain an economically viable production level from the reservoir. The main goal of drilling new wells is to access unproduced hydrocarbons and unlock the full potential of the asset. Alternatively, bypassed hydrocarbons can be accessed by restimulation of depleted wells through refracturing. The latter offers significant cost savings because it eliminates the costs associated with drilling and completing new wells. However, the final economic viability of refracturing is a matter of the balance between the post-refracturing production increase gain and the treatment cost. The reported results on the efficiency of refracturing are very mixed so far, even for the wells within the same formation (Kashikar and Jbeili, 2015). While some operators reported satisfactory post-refracturing production uplift, some have reported no significant production gain, indicating the high level of uncertainty and unpredictability.
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Will your surface microseismic hydraulic fracture monitoring project be successful?
Authors David E. Diller and Ted ShuckThe benefits of microseismic monitoring of hydraulic fracturing are well understood, and continue to grow as acquisition, processing, and interpretation methods improve. Most surveys are conducted using downhole receivers placed close to the reservoir zone. However, for some surveys, a surface monitoring operation can produce good results and provide certain advantages compared to a downhole survey including: • No need for an observation well. • No problems with high reservoir temperatures. • Typically more accurate spatial locations (x,y) of events. • No spatial bias (or distance-to-observation-well bias), which is especially important for large multi-well projects. • Better cost scalability to multi-well projects, and probably lower overall costs for multi-well projects. • More robust source mechanism determination, especially compared to single observation well downhole monitoring. The disadvantages of a surface survey compared to a downhole survey include: • Less precise depth locations of events. • Typically higher costs for a single well project. • Lower sensitivity, and higher risk of failure. The risk of failure, especially in a new area or a new formation, probably deters people from using surface monitoring. Microseismic geophysicists who work for operators describe their discomfort in being unable to answer the question when asked by their management, ‘Will a surface project be successful?’ We present a summary of our experiences with successful and failed projects, we establish a set of metrics for the purposes of comparison, and we provide guidelines for planning successful projects.
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The influence of bedding-parallel fractures in hydraulic fracture containment
Authors Elahe P. Ardakani, Ted Urbancic, Adam M. Baig and Gisela ViegasThe Middle Devonian Marcellus Shale Formation in the Appalachian Basin, which encompasses more than 3.3 trillion tonnes of organic matter, has low permeability (0.1 to 10 μd) and requires extensive fracture stimulation before the reservoir will yield gas in commercial volumes (de Witt, 1986). Since 2004, the application of horizontal drilling, combined with multi-staged hydraulic fracturing to create permeable flow paths from the shale units into wellbores, has resulted in a drilling boom for the Marcellus Formation (Engelder et al., 2009). These lateral wells are usually completed from the toe to the heel over a number of stages using a plug-and-perf method, or if a multiple well pad is being stimulated, after a zipper-frac style (Baig, et al., 2012). Effective hydraulic fracturing in unconventional shale reservoirs requires an understanding of the pre-existing discontinuities (impermeable/not effectively connected natural fractures) state and an assessment of whether at any point of the stimulation it is energetically favourable to move fluids within the reservoir. The dynamic nature of the local stress regime owing to hydraulic fracturing leads to stimulation of different fracture sets which could include bedding-parallel fractures and bedding planes. Describing the progression of the fracturing into the formation and ancillary issues of how far into the reservoir the rock has been stimulated and the stimulation containment provides the opportunity for operators to potentially control fracture behaviour and improve completion designs.
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3D shear wave velocity structure delineation using ambient noise automatic analysis
Authors D. Giannopoulos, C. Orfanos, K. Leontarakis, A. Lois and N. MartakisPassive Seismic Interferometry (PSI) is considered as a revolutionary method characterized by a rapid development especially during the last decade. The method was initially based on the theory that the cross-correlation (CC) of random wave fields of ambient seismic noise recorded on two locations (stations) on the Earth’s surface yields an approximation of the Green’s function (GF) of the medium between the two locations. The retrieved empirical GF represents an approximation of the seismic response as if one of the two stations was acting as an impulsive source of surface waves (e.g. Claerbout, 1968; Lobkis and Weaver, 2001; Campillo and Paul, 2003; Shapiro and Campillo, 2004; Wapenaar, 2004; Cutris et al., 2006). Since the retrieved GF carries the signature of the velocity structure between the stations, the inter-station travel-times for surface- waves on multiple paths within a seismic network can be used in a tomographic inversion to image the seismic velocity perturbations, by performing the commonly called Ambient Noise Tomography (ANT).
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Is it worth trying to evaluate aircraft landings via passive seismic? The starting points and constraints
Authors Jan Mestan, Radek Smeja, Jeena Yohannan and Jan Frantisek KotekThis paper discusses the difficulties related to aircraft landing evaluation as a result of pairing of data collected on board and the determination of plane-runway touches. Today’s on-board sensors provide data that is hard to connect with exact landing styles and resulting deformations. Passive seismic can provide valuable tools, because it has the ability to measure the runway vibrations that are proportional to the plane deformations. Even the style of the landing (symmetrical v. asymmetrical) can be caught by distributing more sensors along each side of the runway. Although it is an available and widely used method, it seems that passive seismic has only a small value for a plane landing evaluation today. The difficulties are resulting from the requirement on the runway homogeneity, a frequent runway calibration or noisy effects that will particularly affect the quality of soft landing seismograms. For passive seismic to become a valuable tool, five stages of its implementation are proposed. Aircraft landing is a critical part of every flight (Figure 1). A hard landing can lead to hidden damage that can put the people on board in danger in the following flights. The question is whether it would be useful to evaluate the quality of landings via runway vibrations instead of sensors on board and invest money in long-term tests. The use of seismic sensors in various branches of industry has been spreading over the past decades. They are used for measuring vibrations of bridges, highways or buildings. They are often used in vibroseis trucks for geophysical measurement. The shape of their sweep vibrations is controlled (Tellier et al., 2015). This paper deals with a reverse problem. The vibrations generated by aircraft landings cannot always be controlled. Thus the runway seismic properties have to be well known. There exist recent patents on real-time road or runway conditions monitoring (Friedlander and Kraemer, 2014; Hagelin et al., 2014). Other issues such as the use of residual vibration energy from air wake for production of electricity have been discussed (Agarwal and Ali, 2013). This paper is intended to provoke a discussion about the entry of real-time passive seismic monitoring to the field of airports.
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Ranking velocity models for depth conversion, closure confidence and volumetrics
More LessThis paper discusses the question of closure confidence, as it applies to the size of a field. The procedure is demonstrated with reference to a particular case study. After introducing the field in question, the size of the field on the time map is examined and compared with a couple of simple depth maps. This leads to the general questions of how to decide which of several possible structure maps is best, and what ‘best’ means in the context of a depth map of an oil field. The approach used in this paper to solve this problem is to create many thousands of depth maps, and use the technique of cross-validation to choose the best depth map(s). The variation of size and extent within these different depth maps is examined, and a statistical attempt made to determine how large the field is, and what the volume uncertainty is. It is concluded that no individual map can be regarded as ‘best’, as the map that predicts the most likely depth at each point on the oil field does not correspond to the most likely volume of oil. A second objective of this paper is to raise awareness of the public domain freeware software http://xval.sf.net that was used to generate these results.
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Rough sea surface implications on receiver deghosting
Efficient removal of ghost events is the key to achieving broadband seismic data. On the receiver-side, accurate ghost removal can be performed when both pressure and vertical particle velocity information is available. However, deghosting pressure-only measurements by spectral division with a flat sea surface or a statistical ghost function is still commonly applied. In this paper, we evaluate the performance of wavefield separation and deghosting with a flat sea surface (or statistical) ghost function for a rough weather marine seismic data acquisition. The behaviour of the pressure ghost function under rough sea conditions is analysed in comparison to the flat and the statistical pressure ghost functions. The three pressure ghost functions (i.e., true, flat, and statistical) converge to the same amplitude and phase values for the lower frequencies, but they diverge from each other for higher frequencies. The error created by wavefield separation and deghosting by spectral division is quantified, using synthetic and real seismic data. Wavefield separation provides deterministic and full receiver-side deghosted up-going wavefields, while both flat and statistical deghosting methods result in significant errors with implications in pre- and post-stack evaluation.
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Volumes & issues
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Volume 42 (2024)
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Volume 41 (2023)
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Volume 40 (2022)
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Volume 39 (2021)
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Volume 38 (2020)
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Volume 37 (2019)
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Volume 36 (2018)
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Volume 35 (2017)
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Volume 34 (2016)
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Volume 33 (2015)
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Volume 32 (2014)
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Volume 31 (2013)
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Volume 30 (2012)
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Volume 29 (2011)
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Volume 28 (2010)
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Volume 27 (2009)
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Volume 26 (2008)
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Volume 25 (2007)
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Volume 24 (2006)
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Volume 23 (2005)
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Volume 22 (2004)
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Volume 21 (2003)
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Volume 20 (2002)
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Volume 19 (2001)
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Volume 18 (2000)
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Volume 17 (1999)
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Volume 16 (1998)
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Volume 15 (1997)
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Volume 14 (1996)
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Volume 13 (1995)
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Volume 12 (1994)
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Volume 11 (1993)
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Volume 10 (1992)
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Volume 9 (1991)
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Volume 8 (1990)
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Volume 7 (1989)
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Volume 6 (1988)
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Volume 5 (1987)
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Volume 4 (1986)
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Volume 3 (1985)
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Volume 2 (1984)
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Volume 1 (1983)