- Home
- A-Z Publications
- First Break
- Previous Issues
- Volume 35, Issue 3, 2017
First Break - Volume 35, Issue 3, 2017
Volume 35, Issue 3, 2017
-
-
Delineating fractures in the sub-seismic domain through seismic and image log analysis: a North Sea case study
Authors Ryan M. Williams, Enric Pascual-Cebrian, Jon C. Gutmanis and Gaynor S. PatonFault and fracture studies for fractured reservoir characterization have been an essential stage of prospect generation and field development from seismic data and well data. Fracture characterization studies often utilize cores and image logs to map fracture intensity and orientation (e.g., Trice, 1999). These results are then scaled up and applied on a reservoir scale. A similar process is applied to faults in seismic data, which are downscaled in an attempt to identify fracture networks for future well planning. Upscaling and downscaling fractures and faults is an attempt to bridge the seismic-to-well data gap (e.g., Barr et al., 2007; Fossen and Hesthammer, 2000). The biggest ambiguity with either of these processes relates to scale. The trends seen at the centimetre scale within cores and image logs may or may not be similar to regional fault patterns identified by surface seismic (e.g., Emsley et al., 2007). Outcrop analogues may help to bridge the gap between well and seismic observations. However, suitable outcrop analogues are not always available or adequate to build fracture models. Furthermore, comparisons between outcrops and subsurface reservoirs should consider differences between tectonic histories, subsidence and stress conditions. Fractures may play an important role in estimating the amount of recoverable reserves for a prospect/field in terms of porosity and permeability, alternatively the presence of fractures may act as baffles to fluid flow. Therefore, the aim of this publication is to show a methodology to improve understanding of fracture trends between well and seismic data, and secondarily to improve fracture pattern identification and delineation in the gas field E17a, offshore Netherlands (Block E), Southern North Sea (Figure 1). Two independent studies were performed; a well driven fracture and fault analysis and a seismic driven fault analysis, and the two results were compared. The seismic fault study was undertaken using Cognitive Interpretation workflows to illustrate the potential of small-scale faulting and fracture lineaments. The well study was focused on interpreting image logs to identify fracture orientation and intensity, and in situ stress conditions. The two sets of results were analysed together to see whether there is overlap in the faults/fractures being identified and to identify whether modern seismic acquisition and interpretation techniques are able to bridge the well-to-seismic scale gap.
-
-
-
The Graneros-Greenhorn petroleum system, a possible new resource play, Rocky Mountain region, USA
Authors Stephen A. Sonnenberg, Hannah M. Durkee and Craig A. KaiserThe Graneros-Greenhorn Petroleum System is a widespread unit in the Denver Basin. Organic-rich source rocks are found in both the Graneros and Greenhorn formations (Kaiser, 2012; Durkee, 2016). Reservoir rocks are found in the Greenhorn Limestone. This petroleum system is age equivalent to the Eagle Ford Formation of the Gulf Coast region. Numerous hydrocarbon shows and some vertical well production suggest the high potential for this petroleum system in the Denver Basin (Kaiser, 2013; Durkee, 2016). Horizontal drilling and multi-stage hydraulic fracture stimulation may be keys to future production from this interval. The Graneros and Greenhorn were deposited during the Cenomanian and lower Turonian stages of the Cretaceous (~ 92.1 to 97.2 Ma, Kauffman et al., 1993) (Figures 1, 2). Paleoenvironmental reconstruction for Greenhorn time is shown by Figure 2. This paper illustrates the potential of the Greenhorn to become a resource play and some of the similarities between the Greenhorn and the existing resource play of the Niobrara Formation. The term resource play implies widespread production (continuous accumulation) with somewhat predictable, repeatable results.
-
-
-
Petroleum systems modelling as an exploration tool: from surface seismic acquisition to basin modelling: a case study from a periplatform basin in Northern Adriatic
Authors Gabriele Busanello, Anna Del Ben and Michele PipanThe Adriatic Sea hosts important historically explored hydrocarbon provinces. In the northern areas, the main sources of hydrocarbon productivity are from biogenic gas reservoirs located in Quaternary thick deltaic depositional systems related to the Apennine and Dinaric foreland domain. In addition, Mesozoic thermogenic oil plays were identified and exploited in the Southern areas. Herein, we use basin and petroleum systems modelling (BPSM) techniques to investigate the still unproved thermogenic hydrocarbon potential of deep Mesozoic basins in the North Adriatic Sea and to correlate the results with the sedimentary evolution of proven petroleum systems in the Central and South Adriatic, both in the Italian and Croatian offshore areas. We used the regional CROP-M16 marine seismic profile in the eastern segment of the study area, where it cuts the western margin of the Dinaric carbonate platform and reaches the pelagic domain of the Umbria-Marche basin intersecting the Barbara isolated platform (Figure 1). We reprocessed the 2D seismic data set to obtain the correct dips and depths of the geological structures from a depth-migrated profile. During the interpretation phase, we integrated the information from profile CROP-M16 with the orthogonal CROP-M17B and C profiles that are intersecting the Alessandra-001 exploration well. The interpretation allowed a detailed analysis of the main lithological discontinuities and of the fault system. We used the interpreted features together with the petrophysical parameters inferred by the available wells in the area and by literature, for 2D petroleum systems modelling. Our simulation integrated the available information to produce a set of possible scenarios of basin development, with the objective to understand the maturation and migration of hydrocarbons.
-
-
-
Applying full-azimuth angle domain imaging to study carbonate reefs at great depths
The main goal of the seismic surveys conducted in the target area in Kazakhstan was to image and detect a major Devonian carbonate barrier reef and to characterize the density and orientation of its main fracture zones. This area is unique in that the carbonate layers occur at great depths, from 5700 to 8500 m, with a complex structure of overburden layers of interbedded clay, sandstone, salt and others (Table 1). These different lithology plays and morphology rocks create strong vertical and lateral velocity variations, resulting in a complex seismic wave phenomenon. In addition, the target carbonate structures contain heterogeneous objects and require high-quality processing of the recorded data. Under such conditions, it is crucial to use full-azimuth, long-offset and dense (high fold) acquisition patterns. Advanced processing sequence tools and high-end depth migrations are required to handle both strong heterogeneity and azimuthal anisotropy effects. Traditional Kirchhoff migrations, even the most accurate ones (wavefront reconstruction, beam), have not been able to provide the required image quality and level of detail required at the target zones (Figure 1). Conventional Kirchhoff migrations generate surface offset-azimuth/offset domain common image gathers (CIG). In this particularly complex area, the correlation between the surface offset-azimuths and the actual, in situ, subsurface slowness-azimuths (azimuth of the incidence/reflected ray pairs at the image points) is relatively poor, leading to significant errors in the estimation of fracture orientation. Additionally, Kirchhoff migrations do not account for multi-pathing (multi-wave path solutions between image points and surface source/receiver locations), which is essential when imaging in areas involving complex wave phenomena. Kirchhoff beam migrations map surface beams with given directions backward to the subsurface. Since they account for the multi-pathing, they provide better results. However, they normally generate the same type of surface offset-azimuth/offset CIGs and therefore cannot be accurately used for azimuthal studies. They also cannot ensure sufficient subsurface illumination, especially at the complex target subsurface regions.
-
-
-
Utilizing a novel quantitative interpretation workflow to derisk shallow hydrocarbon prospects — a Barents Sea case study
More LessLarge areas of the Barents Sea, such as the formerly disputed zone between Norway and Russia in the eastern Barents, are still undrilled. An exploration licence was recently awarded over the Haapet Dome (PL859) to operators with a prime interest in shallow Jurassic reservoirs (Reiser et al., 2016). Multiple oil and gas discoveries made farther west, such as Goliat and Norvarg, make this part of the world a highly prospective area for hydrocarbons. Traditionally the combination of a hard seabed with relatively shallow water depths has prevented the recording of near offset reflection data for the shallowest sediments. It is therefore not surprising that the presence of shallow hydrocarbons in this area has only recently been revealed thanks to imaging techniques that use the energy from sea-surface reflections which provide the missing near angle information for reliable AVA analysis. This paper describes a regional rock physics study of the Barents Sea and a quantitative interpretation workflow using Separated Wavefield Imaging (SWIM) and Full Waveform Inversion (FWI) to identify leads over the Haapet Dome in absence of direct well information.
-
-
-
Shelf stability and mantle convection on Africa’s passive margins (Part 1)
Authors Neil Hodgson and Karyna RodriguezMany clastic wedges prograding from the coast in Africa’s passive margin basins display extraordinary gravity-driven collapse structures described variously as gravity-driven linked systems, fold and thrust belts or megaslides (Butler and Turner, 2010, Scarselli et al 2016). These features form relatively slowly and are distinct from instantaneous collapse submarine landslides or Mass-Transport Complexes (MTC) that reflect sudden catastrophic shelf collapse in response to seismicity, gas hydrate destabilization or high sedimentation rates. Megaslides occur on giant scales from hundreds to thousands of square kilometres in extent, and are characterized by up-dip listric growth fault rollover systems in extensional zones, and a corresponding down-dip shortened section comprising multiple imbricate toe thrust faults and duplexes often referred to as foldand thrust belts (FTB’s). Separating the structured material from largely undeformed coherently bedded strata below, is a zone of planar, sub-horizontal detachment, or décollement. One model that seeks to explain the induced instability that initiates these features infers that the décollement surface comprises a layer that is organic-rich. Sediments prograding out over this layer eventually bury this unit to a temperature and pressure that induces early hydrocarbon generation. This increases the inter-grain pore pressure and reduces the strength of the unit, so that previously stable sediments, in a stable angle of repose begin to slide under gravity basin-ward above this décollement surface.
-
-
-
Tutorial: RTM image enhancement; bad models and mad physics
Authors Ian Jones, Marcin Kobylarski and John BrittanThe final stage of a shot-based migration process is usually the imaging condition, which brings together elements of the upcoming and downgoing wavefield for each shot gather in order to form an image contribution. This procedure suffers limitations owing to the approximations made in representing the physics of the system, and in addition to that, the final summation of all shot contributions necessarily assumes that the subsurface parameter model was perfect, such that all image contributions align perfectly for summation (within a Fresnel zone), as well as ideally having recorded data that are noise free and adequately sampled. In this work, we assess the effect of unresolvable velocity error on the final image, and present a case study example of a technique for compensating for these errors via a localized phase alignment of each of the many thousands of elemental traces that can contribute to the final image.
-
-
-
HRS 3D data — a fundamental change in site survey geohazard interpretation
Authors K.P. Games and E. SelfDespite improvements in acquisition, processing and interpretation techniques over the last 30 years, it appears that our ability to unambiguously identify the presence of shallow gas has not improved at the same rate. The industry sets high standards and has endeavoured to raise these standards by issuing up-to-date guidelines for conducting drilling hazard site surveys. The most recent advances have been in the acquisition of HRS 3D and pseudo 3D data. Over the last three years, we have successfully acquired and processed nine HRS 3D datasets in the North Sea. There is an expected improvement in the quality of the data due to the enhanced horizontal resolution and the understanding of the geology which can be derived from the 3D perspective. However, what we did not expect to see was the degree to which anomalies indicative of the presence of shallow gas can be identified on the HRS 3D data but cannot be interpreted from the HRS 2D data. We believe that in certain situations this fundamentally alters the approach we should take in assessing shallow gas hazards from HRS 2D data alone.
-
Volumes & issues
-
Volume 42 (2024)
-
Volume 41 (2023)
-
Volume 40 (2022)
-
Volume 39 (2021)
-
Volume 38 (2020)
-
Volume 37 (2019)
-
Volume 36 (2018)
-
Volume 35 (2017)
-
Volume 34 (2016)
-
Volume 33 (2015)
-
Volume 32 (2014)
-
Volume 31 (2013)
-
Volume 30 (2012)
-
Volume 29 (2011)
-
Volume 28 (2010)
-
Volume 27 (2009)
-
Volume 26 (2008)
-
Volume 25 (2007)
-
Volume 24 (2006)
-
Volume 23 (2005)
-
Volume 22 (2004)
-
Volume 21 (2003)
-
Volume 20 (2002)
-
Volume 19 (2001)
-
Volume 18 (2000)
-
Volume 17 (1999)
-
Volume 16 (1998)
-
Volume 15 (1997)
-
Volume 14 (1996)
-
Volume 13 (1995)
-
Volume 12 (1994)
-
Volume 11 (1993)
-
Volume 10 (1992)
-
Volume 9 (1991)
-
Volume 8 (1990)
-
Volume 7 (1989)
-
Volume 6 (1988)
-
Volume 5 (1987)
-
Volume 4 (1986)
-
Volume 3 (1985)
-
Volume 2 (1984)
-
Volume 1 (1983)