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- Volume 35, Issue 7, 2017
First Break - Volume 35, Issue 7, 2017
Volume 35, Issue 7, 2017
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Rock property prediction for integrated exploration and development, Vaca Muerta formation, Neuquén Basin, Argentina
Authors Carlos Convers, Thomas L. Davis, Christian Hanitzsch and David CuriaOil companies have been testing different characteristics related to shale plays in an effort to identify the best zones for a good productive well. Total organic carbon (TOC), pore pressure, natural fractures, thickness, mineralogical composition and geomechanical parameters are used to define those zones. The vertical and lateral heterogeneity of rock properties are critical factors that impact production. The integration of 3D seismic and well data is necessary for the prediction of rock properties and identifies their distribution within the rock, which can also be related to the mechanical response of the rock. This study uses TOC and carbonate content as part of the mineralogical composition of the Vaca Muerta (VM) Formation to identify the best zones with hydrocarbon presence (sweet spots) and rock with brittle characteristics based on carbonate content. For this purpose, the study includes a 3D seismic survey and several vertical wells with full log suites in each well to complete the analysis. The well logs are used to compute a model-based inversion which uses pre-stack seismic data to estimate rock property volumes. An inverse relationship between P-impedance and TOC is observed and quantified. Likewise, a direct relationship between P-impedance and volume of carbonate is identified. Neural network is then used to predict the lateral and vertical heterogeneity of rock properties. TOC behaves as an adequate indicator of possible zones with high potential of hydrocarbon presence. Meanwhile, the carbonate content in the VM Formation is a valid indicator of brittle-ductile rock. The analysis detected zones that have a good presence of hydrocarbons and brittle rock. This model presents a more complete understanding of the reservoir, which can be used as an aid in future exploration and development of the VM Formation.
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Quantitative prediction of injected CO2 at Sleipner using wave-equation based AVO
In the context of carbon capture and storage (CCS), quantitative estimation of injected CO2 is of vital importance to verify if the process occurs without any leakage. From a geophysical perspective this is challenging as a CO2 plume has a severe imprint on seismic data. While this makes delineation of the plume rather straightforward, for quantitative interpretation a technique is required that takes complex wave propagation, including multiple scattering and mode conversions into account. In this contribution to the Special Topic, a wave-equation based AVO technique is discussed and successfully demonstrated on a seismic dataset from the Sleipner site. The technique solves the exact wave-equation which means that all complex wave propagation effects mentioned above are properly modelled. The scheme naturally inverts for compressibility and shear compliance and these parameters are more closely related to saturation, porosity and lithology than the conventional impedances. From compressibility the CO2 saturation can be found and the total amount of injected CO2 is calculated by integration over the plume. The result obtained was found to be in good agreement with the known value at the time when the data was acquired.
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Geomechanical modelling using poro-elasticity to prevent frac hits and well interferences
Authors A. Ouenes, A. Bachir, A. Khodabakhshnejad and Y. AimeneModelling unconventional reservoirs requires a continuum multi-scale approach to represent the dominant physics occurring at each scale (Figure 1). In the most common far field studies (thousands of feet around the wellbore), geophysics used in conjunction with processes such as facies constrained extended seismic elastic inversion (Kiche et al., 2016) provide dynamic geomechanical properties throughout the entire reservoir volume – properties, which are critical to the optimal selection of landing zones and completions of unconventional wells. It is also in the far field that the combination of geomechanical properties with continuous natural fracture models (Jenkins et al., 2009) are used as input in a robust reservoir geomechanics workflow (Aimene and Ouenes, 2015) that is able to simulate the interaction between the regional stresses and the three major sources of stress gradients affecting hydraulic fracturing: variable geomechanical properties, geologic discontinuities, and pore pressure variability. The resultant locally varying differential stress distribution provides the initial reservoir stress conditions before fracking and the correct input for the estimation of strain during and after hydraulic fracturing, which should be validated with a predicted microseismicity (Aimene and Ouenes, 2015). This strain provides coupling between the far and mid-field studies and creates the unique opportunity to constrain the mid-field frac design (Paryani et al., 2016) and reduce the uncertainties of multiple frack design parameters by constraining lateral stress gradients and imposing the symmetric frac lengths that the earth will allow. The behaviour of the mid-field hydraulic fracturing is also affected by multiple near field effects such as type of completion (Peterson et al., 2017) and its effects on the near wellbore geomechanics. The near field effects could be estimated at any well using surface drilling data (Jacques et al., 2017) which could provide the necessary information required in the mid and far fields in the inverse design and validation process in situations where there is lack of data.
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Experiences from continuous microseismic monitoring for industrial-scale CO2 storage
Authors V. Oye, R. Bauer, S. Greenberg, A. Braathen and B. Goertz-AllmannOne way to make large-scale geological storage of CO2 a publicly more accepted practice is to develop more convincing methodologies for monitoring verification and accounting (MVA). Passive seismic data has a large potential to enhance this current lack of credibility in MVA. Presented here are three case studies, where passive seismic data were analysed in innovative ways to provide relevant information on the CO2 and its behaviour in the subsurface. We briefly describe the applied analysis methods and the added value in the cases of In Salah (Algeria), Decatur (Illinois, U.S.) and the Longyearbyen CO2Lab (Svalbard). We also describe the differences in deployment of sensors for passive seismic data acquisition, and the resulting difficulties in unified data analysis workflows. Finally, we provide an overview on recent CO2 storage sites and the generally increased acceptance for the importance of passive seismic data acquisition. To avoid further catastrophic global warming, a drastic and immediate reduction of greenhouse gas emissions is necessary. A whole range of international organizations have realized this for a long time, including the Intergovernmental Panel on Climate Change (IPCC), the International Energy Agency (IEA), and the United Nations Framework Convention Climate Change (UNFCCC). On 4 November, 2016 the Paris Agreement finally entered into force with most of the world’s political leaders showing that they are ready to take immediate action. Among many greenhouse gas reduction strategies, Carbon Capture and Storage (CCS) is an important technology, because it can generate net negative CO2 emissions, mostly with regards to bio-energy CCS (BECCS). Advancement of renewable energy sources is vital to reducing reliance on fossil fuels. However, regardless of the speed in the advancement in renewable energy sources, CCS can reduce the CO2 footprint from ‘dirty’, greenhouse gas-producing, industrial and agricultural processes, which cannot be replaced by renewable energies.
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Fractured basement — an overlooked play type with significant potential from a global seismic database
Authors Karyna Rodriquez, Anongporn Intawong, Neil Hodgson, Douglas Paton and Philip BirchFractured basement reservoirs are most commonly defined as metamorphic and igneous rocks unconformably overlain by a sedimentary sequence, where faulting has led to the creation of a natural fracture network where hydrocarbons can accumulate. Here, we also consider basement rocks to include those of sedimentary origin with little or no matrix porosity (North, 1990), such as the Cambro-Ordovician quartzitic sandstones of the Table Mountain group in South Africa. Fractured quartzites and granites are generally considered to be the optimum reservoirs (Koning, 2013). Basement reservoirs have been recognized for decades but are still often disregarded – with wells barely penetrating them – as many oil companies stop drilling as soon as basement rocks are intersected. Where basement has been penetrated to a sufficient depth (approximately 300 m), significant volumes of undiscovered hydrocarbons may still have been missed by a failure to intersect the fracture systems (Aguilera, 1996). Despite inadequate exploration, fractured basement rocks are important oil and gas reservoirs around the globe (Figure 1). Though many were originally found by chance, the large discoveries made in Vietnam and more recently in the UK are now paving the way for an exploration strategy of this unconventional highly prospective play type.
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From geology to production: a completion optimization case study from Cleveland Sand, Oklahoma
Authors Vivek Swami, Graham Spence, Theophile Gentilhomme, Bob Bachman, Mark Letizia and Casey LippOil companies seldom acquire the necessary data to help them understand subsurface heterogeneity when they design multi- stage completions for lateral wells. In particular, well logs are rarely run in the lateral section. In the absence of such subsurface information, operators generally adhere to ‘geometric’ completion designs or equally spaced stages in the lateral section. While this approach seems reasonable and follows industry norms, it may not be very effective for heterogeneous rock (Far et al., 2015; Ashton et al., 2013; Ganguly and Cipolla, 2012). The geometric completion design may result in a limited stimulated reservoir volume (SRV) and lower well production than could be achieved with an optimized design based on subsurface information. Geoscientists, completion engineers and reservoir engineers focus on different aspects of the complex problem of fracture spacing in a horizontal well. In the comprehensive study presented in this article, the authors have developed an integrated reservoir model combining reservoir characterization, petrophysical, geophysical, drilling and completion data. A fully coupled reservoir/geomechanical simulation model was built to capture the variation in rock properties in the lateral section, and to assess the impact of this variation on the simulation of injection and production processes. This single model was used to simulate both the injection and production times for the well.
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Shale gas reservoir characterization and sweet spot prediction in China
Authors Gang Yu, Yusheng Zhang, Ximing Wang, Xing Liang, Wei Liu, Riu Guo, Uwe Strecker and Maggie SmithAn integrated study of the well Zhao-104 and surrounding wide-azimuth 3D seismic data volume within the shale gas reservoir in South China has been conducted with the objective of generating shale formation properties related to fracture orientation and intensity in the area and deriving such reservoir rock properties as data quality allows. Well data, structural seismic information and prestack inversion products were combined in an integrated interpretation. Seismic gather conditioning improved seismic data quality prior to pre-stack inversion by improving signal/noise ratio, removing NMO stretch and aligning reflection events. Velocities from residual moveout (RMO) analysis on individual sectors were used as input to detection of fracture orientation and anisotropy. Fracture strike and P-wave anisotropy were calculated using the RMO updated sector velocity fields in elliptical velocity inversion, while inversion for P and S impedance and derivative attributes produced volumes that relate to rock properties such as brittleness and rigidity that are likely to impact fracturing. Measured logging curves were edited and missing curves estimated for the entire wellbore for geophysical purposes. Porosity, mineralogy and saturation were also estimated and elastic attributes were examined in crossplot space to find discrimination in properties of interest. Matrix modelling and synthetic seismograms were studied in order to understand likely seismic signatures and AVA behaviour. A set of post-stack volumetric attributes that are indicative of the presence of faults and fractures were derived and fed into an unsupervised neural network to perform fracture facies classification. In addition, seismically resolvable faults and discontinuities were automatically generated from fault sensitive attributes. At the end, information from all parts of the project were combined to assess structural characteristics and identify areas of high fracturing and stress direction that are important for the placement of horizontal wells and likely high total organic content (TOC) zones, necessary as a source of hydrocarbons or ‘sweet spot’.
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Lateral changes in reservoir properties of the Stø Sandstone in the Snøhvit field, SW Barents Sea
Authors Md Jamilur Rahman and Nazmul Haque MondolThe Stø sandstone being the main reservoir in the Barents Sea area is moderate to well sorted and mineralogically mature. This formation is thickest in the southwestern part of the Snøhvit field and gradually thinning eastward. The main objective of this study is to find out this variation using rock physics analysis. Two wells (7120/6-2S and 7121/5-1) from the field were used in this study to investigate lateral rock property variation within the Stø sandstone reservoir. Stress-dependent mechanical compaction varies because of mineralogy and textural difference from east to west despite similar effective stress regime during burial. Chemical compaction also plays a significant role which depends on the dissolution of quartz grains at stylolites and pressure solution of grain-to-grain contact and available specific surface area to precipitate quartz cement. More stylolites generated in shalye sandstone in the east compared to clean sandstone in the west suggested higher cementation in the eastern wells compared to the west. It can be concluded that both mechanical and chemical compaction processes resulted in rock property variations in the same reservoir rock within the field.
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Reducing the risk of hydrocarbon exploration and lithology characterization — using a neural network approach in the West Delta Deep Marine Concession Area, Offshore Nile Delta, Egypt
Authors N. Abd-Elfattah and R.M. FahmyThere are many approaches and concepts for the exploration and development of hydrocarbon reservoirs. In this study, we develop both a lithology classification and a gas chimney prediction workflow. We classify the entire seismic volume into its most likely facies domains and transform the seismic cube into a gas chimney probability cube. Both these approaches utilize a neural network algorithm, which we find is an efficient method to integrate the multiple input attributes required to extract the target log, or to isolate target features from the seismic background data. A combination of a set of seismic attributes (obtained from multilinear regression) with the nonlinearity of the artificial neural network technique is used to develop effective workflows to classify and explore the reservoirs. Analysis of the results helps to quantify the chance of success of the exploration prospects and also, in conjunction with the petroleum system of the prospects, leads to a reduced risk of the hydrocarbon exploration and development wells.
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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)