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- Volume 34, Issue 2, 2016
First Break - Volume 34, Issue 2, 2016
Volume 34, Issue 2, 2016
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The characterization of unconventional reservoirs in the Bowland sequence using onshore 3D seismic data, Cleveland Basin, UK
The Lambda-Mu-Rho (LMR) approach of characterizing reservoir intervals in seismic data is a useful tool for efficient well placement and completion. The successful exploitation of unconventional hydrocarbons in the UK could play a fundamental role in helping to satisfy the growing energy demand. To achieve this, it has been proved necessary to differentiate the more brittle from ductile rocks to maximize reservoir recovery. Economic gas production in unconventional plays requires hydraulic fracture stimulation. This study utilizes the impedance, density and the Lame parameters (Lambda, λ and Mu, μ) logs derived from the Amplitude Variation with Offset (AVO) inversion to compute the more seismically intuitive LMR logs and the elastic properties Poisson’s Ratio and Young’s Modulus. The optimal Carboniferous tight sandstone reservoir intervals at Kirby Misperton in the Cleveland Basin were successfully characterized using the LMR crossplot method. Tight gas-filled sandstones are characterized by a low λρ and a high μρ value as a result of their low incompressibility, high rigidity and intrinsic brittleness. The analysis confirmed that the Lower Bowland sequence is prospective from an unconventional perspective due to its high quartz content and therefore is likely to respond positively to hydraulic fracturing. Unconventional resources currently account for 43% of US gas production with gas consumption expected to increase between 2010 and 2030 (Rogers, 2011). Tight gas sandstones represent approximately 70% of all global unconventional gas production and reserves that are yet to be developed (Khlaifat et al., 2011). Although commercial exploration and production of unconventional gas in the UK is in its infancy, it offers significant potential for future gas production growth and will become increasingly important as the easily exploitable conventional gas reserves are exhausted (Law and Curtis, 2002). Most tight gas reservoirs are often characterized by a multi-layered reservoir system that are often hydraulically fractured to enhance recovery rates from the reservoir intervals (Meckel and Thomasson, 2008).
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Interpretation of wrench faulting and faultrelated pressure compartmentalization, Wattenberg Field, Denver Basin Colorado
Authors Abdullah Nurhasan and Thomas L. DavisA structural interpretation of a 128 km2 3D seismic data set from Wattenberg Field, Colorado indicates a northeast-trending step-over fault system in the Niobrara Formation. These step-over faults are the product of a fault block rotation that is caused by two large-scale dextral wrench faults: the Longmont and the Lafayette wrench fault zones. An investigation into different fault orientations between the Niobrara and the overlying Pierre Shale indicates that a rotation of the maximum horizontal stress has occurred during the Laramide Orogeny. The step-over faults and stress rotation result in reservoir compartmentalization in the Niobrara. Seismic inversion shows the different stress field compartmentalization. Low impedance occurs in a lower effective stress environment caused by high pore pressure. These compartments may constitute ‘sweet spots’ in exploration and production in the Niobrara Formation. The Niobrara Formation is a major hydrocarbon reservoir deposited during the Late Cretaceous (Figure 1a). This formation consists of the Smoky Hill Member and Fort Hays Limestone. The Smoky Hill member consists of A, B, and C chalks, and A, B, and C marls. Bratton (unpublished work, 2015) indicates that the overpressure regime extends into the overlying Sharon Springs Member of the Lower Pierre Formation. Figure 1B shows the geologic events of the Late Cretaceous Petroleum System (Higley and Cox, 2007). The Laramide Orogeny occurred during the Late Cretaceous and Early Tertiary (between 70-50 ma.). This event is thought to be responsible for the structural features in the study area (Higley and Cox, 2007). The products of this movement include several wrench fault zones located in the area mapped by Weimer (1996).
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An unsettling science, or poor marketing?
By Paolo SudiroT he debate on whether global warming is a threat to humankind, if human activity has been its cause, and what actions should or could be taken to confront it has exceeded the borders of academic dispute to become a public and political issue. Any action taken in response to global warming, from business as usual to drastic CO2 emissions reduction, will have severe consequences for the environment and the global economy. Therefore, appropriate political decisions should be taken based on the best scientific evidence available. Unfortunately, the debate on climate change has been hampered by systematic distortion of the available facts, and reciprocal accusations of misconduct between the polarized fields of pro-AGW adherents and AGW-denialists which have had the effect of undermining the credibility of science itself. Bob Heath’s article on climate change/global warming published in First Break November (Heath, 2015) reminded me of similar papers published a few years ago by different authors and in a different journal, strikingly similar in their approach to the issue of climate change. The papers’ audience was very similar of First Break’s public, addressed to a general audience of geologists belonging to different disciplines of the earth sciences, not necessarily experts in climate science but with an understanding of the science and its problems. Those papers were also disputing the validity of AGW, using more or less the same arguments that Heath uses, mixing together technical data to disprove AGW and rhetorical tools to discredit the scientists supporting the opposite position. I am not going to address here the validity of Heath’s claims about the reality, origin, amplitude, and impact of climate change: maybe global warming is not happening, or if it is happening it could be natural, and even if it is anthropogenic there is nothing we can do to stop it, and it may be that a warmer planet is better. Moreover, the climate change debate seems to be more a subject for anthropologists or social scientists, and individual positions on the matter appear to be mainly motivated by personal cultural prejudice, regardless of the science behind (Boykoff, 2008; Kahan et al., 2010; Lewandowsky et al., 2013a, 2013b). The bottom line is that, even using the best science available, there is no way in which a pro-AGW reader or an AGW-skeptic will change their minds.
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Advanced cuttings analysis provides improved completion design, efficiency and well production
R ecent case studies of lateral well completions have highlighted the apparent ineffectiveness of geometric stage performance with regards to fracture initiation and stimulated reservoir volume (Far et al., 2015; Ashton et al., 2013; Ganguly and Cipolla, 2012). It has been observed that poor stage performance can be attributed to varying rock type compositions along the borehole, due to lateral facies changes and/or wellbore porpoising. The inefficiencies linked to non or poor performing stages can result in higher costs, associated with equipment and materials, and limit the production potential of wells. This case study highlights how the application of an optimized hydraulic fracture stimulation plan, by honouring lateral well geological heterogeneities, improved completion efficiency and well production within the Cleveland Sandstone formation, Oklahoma, USA. Optimized completions Designing optimized hydraulic fracture stimulation in a lateral well requires an understanding of the near-well bore geomechanical properties and the near-well bore and farfield stresses along the entire lateral. Such reservoir characterization is normally developed from geomechanical and petrophysical analyses using wireline or logging-while-drilling (LWD) services that include acoustic and borehole- image logs. Unfortunately, economic considerations can often inhibit or prohibit the use of logging techniques and hence the complete characterization of the reservoir, especially in the current low oil and gas price environment. A practical and convenient alternative for reservoir characterization is to use the commonly available cuttings samples to provide gross characterization of a vertical or lateral well. Utilizing Automated Mineralogy (AM) techniques, such as CGG’s RoqSCANTM, (Ashton et al., 2013) provides comprehensive data from these cuttings which includes mineralogy, texture and rock properties throughout the entire length of the well. RoqSCAN analysis can be performed either in the laboratory or at the well site to provide near-real-time reservoir navigation and data to optimize the design of completions that will be performed soon after the well reaches total depth (TD).
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High-resolution imaging and characterization of a CO2 layer at the Sleipner CO2 storage operation, North Sea using time-lapse seismics
Authors R.A. Chadwick, G.A. Williams and J.C. WhiteL arge-scale underground storage of industrially produced carbon dioxide is the most effective way of keeping cumulative man-made emissions of greenhouse gases within safe limits (IPCC, 2005). The CO2 injection operation at Sleipner, in the central North Sea between the UK and Norway, commenced in 1996 and is the world’s longest-running industrial-scale storage project. It is also the first example of underground CO2 storage arising as a direct response to environmental legislation (Baklid et al., 1996). CO2 separated from natural gas produced at the Sleipner field is being injected into the Utsira Sand, a regional saline aquifer of late Cenozoic age, in excess of 200 m thick in the Sleipner area (Figure 1a). The aquifer comprises mostly clean unconsolidated sand of high porosity (> 0.3) and high permeability (> 1 Darcy). A number of thin intra-reservoir mudstones, typically 1-2 m thick, are evident from geophysical logs acquired in wells around Sleipner (Figure 1b). The CO2 is injected in a dense phase via a deviated well at a depth of 1012 m below sea level, approximately 200 m beneath the top of the reservoir. Injection commenced in 1996 at a roughly constant rate, with around 16 million tonnes of CO2 stored by 2015. A comprehensive deepfocused monitoring programme has been deployed of which time-lapse seismic has proven to be the key tool (Arts et al., 2008). A baseline 3D survey was acquired in 1994, with repeat surveys in 1999, 2001, 2004, 2006, 2008, 2010 and 2012. The plume is imaged on the seismic data as a tiered structure some 200 m high comprising a number of bright sub-horizontal reflections (Figure 2a). These are interpreted as reflections from thin layers of CO2 trapped beneath the intra-reservoir mudstones which are partially but not wholly sealing. The reflective layering had formed by 1999 with each individual reflection traceable on all of the subsequent surveys. As a general rule the middle and upper reflections in the plume have increased in amplitude and lateral extent on successive time-lapse surveys, whereas the lower layers have ceased growing, in some cases shrinking and dimming. A key objective of the monitoring at Sleipner is to demonstrate that geological storage of CO2 is a safe and viable technology. One aspect of this is to quantitatively verify or constrain predictive flow simulations of plume development. However, because the injection well is near-horizontal, no wellbore penetrates either the CO2 plume or the exact stratigraphy that the plume now occupies, and quantitative analysis is challenging.
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Zohr – A newborn carbonate play in the Levantine Basin, East-Mediterranean
Authors Paolo Esestime, Ashleigh Hewitt and Neil HodgsonThe Levantine Basin in the East-Mediterranean is proven as a prolific hydrocarbon province, with numerous gas fields and discoveries, including several of giant reserve size extending from the over-explored Nile Delta of Egypt and offshore Israel in the south to underexplored Cyprus and Lebanon to the north and east. Many of the gas discoveries to the east are biogenic in origin, although a thermogenic source underlies the Nile Delta, as evidenced by minor oil discoveries and, especially in the pre- Pliocene, ubiquitous gas condensate discoveries (Figure 1). Historically, exploration of the Nile Delta targeted siliciclastic plays since AGIP (now ENI) made the groundbreaking discovery of the Abu Madi Field in the Nile Delta of Egypt in 1967. The Abu Madi gas condensate play was followed offshore with the Baltim discoveries and throughout the 1970s and 1980s this play was exploited, following Miocene channel deposits, broadly deposited during the Mediterranean drawdown of the Messinian Salinity crisis, located in shallow water. IEOC (an ENI subsidiary) drilled deeper targets in the 1980s and found over-pressured gas in Middle Miocene sands in the El Temsah field discovery. In the 1990s exploration in the Delta moved on to target Pliocene turbidite play-fairways in ever deeper water (eg discoveries of Ha’py (Amoco) and Rosetta (BG)), and more recently Early Miocene and Oligocene targets have yielded good results in the Nile Delta for BP (Raven Field) and others. Early Miocene clastics have proved prolific offshore Israel, where, in water depths greater than 1500 m, Early Miocene deep water turbidites provide the reservoirs for more than 30TCF in Noble’s Tamar and Leviathan gas discoveries alone.
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The future of oil exploration
Authors Karyna Rodriguez, Neil Hodgson and Ashleigh HewittThe outbreak of hostilities between new unconventional oil supply and giant legacy oil production represents a violent threat to the sustainability of the conventional oil exploration industry. Coruscations from this battle starkly illuminate the explorer’s paradox: an imperative to focus on plays that have low risk and huge potential, whilst having to seek these within mature basins on well explored continental shelves. Where can we find sufficient prospects with dramatic enough scale to compete in the unconventional vs legacy giant wars? Using 2D seismic acquired in the last two years on the Atlantic margins, we will examine the play systematics that manifest in Ultra-Deep Water (UDW) low risk prospects on a scale hitherto unimagined that will ultimately win conventional’s fight back to be the futures energy supplier of choice.
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Dealing with spatial sampling sparseness and irregularity in 3D OBC seismic data offshore Abu Dhabi
Authors Shotaro Nakayama, Mark Allen Benson, Tarek Materid, Kamal Belaid and Dmitriy ZarubovDue mainly to commercial and operational constraints, seismic data are often sparsely and irregularly sampled, leading to several challenges in processing of 3D OBC seismic data offshore Abu Dhabi. Conventional linear noise attenuation techniques based on multi-channel filters are not effective with Scholte waves as they are usually aliased with typical sampling intervals in 3D OBC seismic data (e.g., 25 m source and receiver point intervals), and sometimes scattered because of near-surface heterogeneity. To address them, we apply model-based surface wave attenuation, Surface Wave Analysis Modelling and Inversion (SWAMI), which enables an estimate of local near-surface properties by analysing dispersion curves. Thus, both direct and scattered Scholte waves are effectively modelled and attenuated without suffering from under-sampling. A data interpolation and regularization technique called Matching Pursuit Fourier Interpolation (MPFI) is then applied to enhance spatial sampling. MPFI employs an anti-aliasing capability so optimum data reconstruction can be performed for any frequency range. In addition to the regularization aspect, MPFI with a 5D implementation (4 spatial coordinates and time) is targeted to densify receiver line interval and extend source lines, which consequently enhances fold, offset and azimuth distributions of the data.The implementation of the two techniques successfully addresses processing challenges in sparsely and irregularly sampled OBC seismic data.
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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)