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Petroleum Geoscience    [7 followers]  Follow    
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1354-0793 - ISSN (Online) 2041-496X
     Published by Geological Society of London Homepage  [10 journals]   [SJR: 0.837]   [H-I: 31]
  • Role of forced regression in controlling Brent Group reservoir
           architecture and prospectivity in the northern North Sea
    • Authors: Went, D. J; Hamilton, R. V, Platt, N. H, Underhill, J. R.
      Pages: 307 - 328
      Abstract: The Middle Jurassic Brent Group of the northern North Sea presents a mature and highly productive reservoir play fairway where a combination of effective facies analysis and depositional sequence stratigraphy offers real potential to optimize exploitation. The north of the Brent province differs from classically studied southern areas in being dominated by marginal-marine delta-front facies. A core- and log-based study of 37 wells around the Don fields was performed to establish a sequence stratigraphic framework, map facies and thereby describe facies architecture. The results demonstrate that reservoir quality and productivity are regionally and locally controlled by facies. Of particular interest are intervals of fluvio-estuarine channel to sharp-based shoreface sandstone that formed during sea-level lowstands, since it is these packages that boost well productivity but, conversely, also increase the risk of early water breakthrough on production. Analogy with the Saloum Delta of Senegal highlights the importance of rapid and continuous barrier migration and destruction in controlling the deflection and switching of fluvio-estuarine channels, explaining also the preferential preservation of channel-floor deposits over continuously eroded barrier and delta-top facies. Interpretations suggest that deposition in the study area was dominated by punctuated progradation of the Brent Delta, as periods of delta plain incision alternated with episodes of base-level rise and delta aggradation/progradation. A model of regression for the Brent Delta is presented, where the Rannoch, Etive and Ness formations are an amalgam of highstand, falling stage and lowstand systems tract deposits, and the Tarbert Formation is a transgressive systems tract deposit, with the delta responding to regional relative sea-level changes driven by uplift and deflation of the mid North Sea dome. The prograding Brent Delta is characterized as a succession of attached shorefaces formed by alternating periods of normal and forced regression. Significantly, this explains the long distance (>200 km) build out of the Brent Delta and the continued presence of coarse-sandstone packages, as well as the potential for high-quality reservoirs even in the distal reaches of the system. It also suggests that there is limited potential for lowstand fan plays beyond the northernmost tip of the delta.
      PubDate: 2013-11-28T04:07:07-08:00
      DOI: 10.1144/petgeo2013-028|hwp:master-id:petgeo;petgeo2013-028
      Issue No: Vol. 19, No. 4 (2013)
  • Repeated inversion and collapse in the Late Cretaceous-Cenozoic northern
           Voring Basin, offshore Norway
    • Authors: Lundin, E. R; Dore, A. G, Ronning, K, Kyrkjebo, R.
      Pages: 329 - 341
      Abstract: The Norwegian Atlantic margin, although frequently described as passive, has seen several significant and highly variable deformation events prior to and after early Cenozoic break-up. This chronology is strongly exemplified in the northern Vøring Basin, where deformation resulted in significant vertical motions, including deep erosion and sediment reworking. Post-break-up compressional deformation is well documented in the NE Atlantic margins, and is represented in the north Vøring Basin by the Vema and Naglfar domes. A prominent Maastrichtian–Paleocene pre-break-up phase of compression inverted the northern prolongation of the latest Turonian Vigrid Syncline. This syncline was the fairway for the approximately 1 km-thick Santonian–Campanian Nise Formation sandstone, shed from NE Greenland and/or the western Barents Sea margin. The inversion focused on the Vigrid Syncline axis, forming an anticline here referred to as the Vema–Nyk Anticline. The anticline may have been a major trap but was breached by erosion prior to collapse due to Late Paleocene extension. The remnant eastern half of the anticline is the Nyk High. The associated flanking syncline, the Någrind Syncline, also remains preserved. The collapsed side of the anticline is the Hel Graben, which itself was inverted in the Middle Miocene time forming the Naglfar and Vema domes. More speculatively, the development of the Vigrid Syncline and its bounding structural highs, the Gjallar Ridge and Utgard High, may also represent folds, marking the onset of compressional buckling in the mid-Norwegian–NE Greenland rift system. The repeated compressional deformation, as well as the extensional collapse, was focused on the area subjected to Early Cretaceous hyperextension. Compressional buckling under relatively low stress levels is proposed to have been due to significant lithosphere weakening caused by the hyperextension, whereby both high attenuation of the crystalline crust and serpentinization of the upper mantle contribute to the weakening. The Late Cenozoic compression post-dated the hyperextension by approximately 110 Ma, which suggests that the weakening is long-lived and that lithosphere has not been strengthened significantly through time.
      PubDate: 2013-11-28T04:07:07-08:00
      DOI: 10.1144/petgeo2012-022|hwp:master-id:petgeo;petgeo2012-022
      Issue No: Vol. 19, No. 4 (2013)
  • Fracture modelling based on the stochastic extended finite element method
    • Authors: Mingming, T; Jinliang, Z, Huifang, M, Shuangfanga, L.
      Pages: 343 - 355
      Abstract: Because a large number of oil and gas reservoirs are naturally fractured, they play an important role in hydrocarbon exploration and production. To fully extract and model the fracture system features of reservoirs, a new fracture modelling method, called the stochastic extended finite element (SEFE) method, is presented in this paper. This method couples fracture mechanics and the kriging method with a multi-field trend in an attempt to benefit from the advantages of each method: compliance with fracture mechanics equations and the reproduction of the fracture’s observed data, respectively. Based on the SEFE simulation method, we wrote a fracture modelling system software and built a fracture propagation model and a fracture distribution model of the Upper Cretaceous Formation in the Daqingzi region. A parallel study was performed to verify the fracture propagation pattern and boundary conditions in the proposed model based on a geomechanical analogue experiment. The results of these studies demonstrate that fracture modelling based on the SEFE method may improve the precise characterization of fractured reservoirs.
      PubDate: 2013-11-28T04:07:07-08:00
      DOI: 10.1144/petgeo2011-062|hwp:master-id:petgeo;petgeo2011-062
      Issue No: Vol. 19, No. 4 (2013)
  • Assessing the seismic AVA detectability of CO2 storage sites using novel
           time-lapse attributes
    • Authors: Jafargandomi, A; Curtis, A.
      Pages: 357 - 374
      Abstract: Monitoring of stored carbon dioxide (CO2) in subsurface reservoirs is fundamental to operation and management of the storage site, and is a requirement of some national and international legislation. As a consequence, effectiveness of monitorability (the ability to observe the evolving location of subsurface CO2) for any given level of investment in monitoring technology is a significant investment uncertainty that must be assessed along other components of the storage-site selection criteria (e.g. capacity, injectivity and storage economies). We develop a workflow to assess the time-lapse seismic detectability of changes in subsurface aquifer reservoirs by analysing expected changes in seismic amplitude variation with angle (AVA) in the field. Laboratory measurements are used to calculate the seismic response of the reservoir at different saturations and pressures. We include the scattering effect of material above and below the reservoir by using a finite-difference, full-waveform modelling approach AVA analysis then assimilates local site effects into the detectability assessment. We show that performing waveform modelling which includes local geological heterogeneities above and below the reservoir interval is essential to assess the storage site monitroability. In order to quantify expected time-lapse changes in the seismic response, we introduce a new set of robust time-lapse attributes based on time–frequency decomposition. The attributes effectively separate amplitude and phase changes (time-shifts) of time-lapse seismic records, and allow us to quantify their repeatability against the background noise. Furthermore, the frequency-dependent nature of the attributes provides a quantification of the frequency–domain effects of time-lapse changes. The approach is employed to assess the detectability of supercritical CO2 in two analogue storage sites in the near-shore UK North Sea. Analysis of laboratory measurements and AVA responses indicate the contrasting monitorability of the two sites, which helps decision making about further site investigation and development. Application of the approach to hydrocarbon reservoir monitoring is straightforward.
      PubDate: 2013-11-28T04:07:07-08:00
      DOI: 10.1144/petgeo2012-043|hwp:master-id:petgeo;petgeo2012-043
      Issue No: Vol. 19, No. 4 (2013)
  • Investigating reservoir pressure transmission for three types of coalbed
           methane reservoirs in the Qinshui Basin in Shan'xi Province, China
    • Authors: Zou, M; Wei, C, Fu, X, Bao, Y, Cai, Z.
      Pages: 375 - 383
      Abstract: Based on the characteristics of seven representative coalbed reservoirs in the Qinshui Basin in Shan’xi Province, China, the reservoirs were classified as gas pressure reservoirs, water pressure reservoirs or hybrid pressure reservoirs. Reservoir modelling technology was adopted to study the 1000 day recoverability and reservoir pressure transmission process of three typical coalbed methane (CBM) wells, each of which represents one of the three coalbed reservoir classifications identified. The results indicate that the three reservoirs are quite different in terms of their drainage performance. For gas pressure reservoirs, reservoir pressure changes in a very small region around the well bore. The gas production of this type of reservoir is very low; hence, integrated coal and gas mining may be appropriate to enhance its recovery. Reservoir pressure propagates further in water pressure reservoirs but declines gradually. The gas recoverability in water pressure reservoirs is also low, which indicates that effective water drainage is the key technology for improving it. The pressure in hybrid pressure reservoirs propagates moderately in the whole effective region. This type of reservoir has the strongest gas recoverability and is suitable for CBM exploitation using surface to reservoir boreholes.
      PubDate: 2013-11-28T04:07:07-08:00
      DOI: 10.1144/petgeo2011-083|hwp:master-id:petgeo;petgeo2011-083
      Issue No: Vol. 19, No. 4 (2013)
  • Comparison of scaling relationships of extensional fault cores in tight
           carbonate and porous sandstone reservoirs
    • Authors: Bastesen, E; Braathen, A, Skar, T.
      Pages: 385 - 398
      Abstract: This paper presents a comparative analysis of the thicknesses–displacement relationships of fault cores in non-/low-porous carbonate and porous sandstone reservoirs. Fault thickness data were collected from extensional faults in mainly Cretaceous continental sandstones and Late Cretaceous–Paleogene marine carbonates exposed along the eastern flank of the Suez Rift, Egypt. The dataset consists of 730 thickness measurements, of which 313 are from 68 faults in carbonate rocks, and 417 are from 120 deformation band/microfaults and faults in sandstones. These data show that the increase in fault core thickness with displacement for the two lithologies is, overall, similar in log–log space, consistent with a power-law trend with an exponent of 0.5. However, for smaller faults, cores in carbonates are generally thicker than those in sandstones. The observation of nearly equal core thickness–displacement relationships for larger faults (>10 m displacement) suggests that increased displacement reduces the geomechanical influence of lithology. In a statistical analysis of bins of fault displacement, small displacement faults seem to follow a skewed distribution towards smaller fault core thicknesses, moderate displacement faults have a normal distribution, while large displacement faults have a distribution skewed towards large core thicknesses. Each thickness distribution can be estimated with a mean and standard deviation. Fault core thickness variations are caused by interplaying factors such as fault geometric development, spatial and temporal positioning of shear and volumetric strains, and rheological changes. The variability in core thickness and intrinsic architecture of fault cores for any given location will cause significant variation in across-fault fluid flow, even for the same juxtaposition style.
      PubDate: 2013-11-28T04:07:07-08:00
      DOI: 10.1144/petgeo2011-020|hwp:master-id:petgeo;petgeo2011-020
      Issue No: Vol. 19, No. 4 (2013)
  • Integration of spectral gamma-ray and geochemical analyses for the
           characterization of the upper Jurassic Arab-D carbonate reservoir: outcrop
           analogue approach, central Saudi Arabia
    • Authors: Eltom, H; Abdullatif, O, Makkawi, M, Yasin, M.
      Pages: 399 - 415
      Abstract: Investigation by spectral gamma-ray (SGR) and inductively coupled plasma-mass spectrometry (ICP-MS) geochemical analyses of the Upper Jurassic Arab-D reservoir analogue (central Saudi Arabia) revealed a strong correlation between the SGR response of the outcrop lithofacies and their elemental content. The two units of the reservoir (the Upper Jubaila Member of the Jubaila Formation and the Arab-D Member of the Arab Formation) showed distinctive SGR log profiles controlled mainly by their lithofacies associations. The geochemical analysis revealed four groups of chemical associations. Group 1 includes SiO2, Al3O2, Fe2O3, K2O, TiO2, Zr and Zn. This group has a strong relationship with the radioactive elements U, K and Th (Group 4). The reservoir facies exhibit high concentrations of chemicals from these two clusters. Group 2 includes CaO and Sr. A high concentration of chemicals from this group indicates a tendency towards pure carbonate facies and fewer siliciclastic impurities. A high concentration of MgO, the only chemical included in Group 3, marks dolomitic zones. Group 4 contains the radioactive elements. The boundary between the Upper Jubaila Member and the Arab-D Member is clearly defined from vertical SGR log profiles, vertical geochemical data logging and cross-plots of Group 1 chemicals with the radioactive elements in Group 4. The geochemical data for the Upper Jubaila Member show a very low concentration of U, K and Th. Consequently, the SGR response of the lithofacies was very low. All of the reservoir lithofacies showed high concentration of Group 1 and Group 4 components compared with the non-reservoir lithofacies. The Th/U ratio indicates a general shoaling upwards following the same trend of the outcrop lithofacies. A high Th/U ratio characterizes reservoir lithofacies, whereas a low ratio characterizes non-reservoir lithofacies. The lithofacies and the SGR log motifs were related in the measured sections. This study provides a method for predicting lithofacies from SGR log motifs within a high-resolution stratigraphic framework integrated with the geochemical data analysis. Here, we introduce an exploration guide for subsurface reservoir zonation and the identification of formation tops.
      PubDate: 2013-11-28T04:07:07-08:00
      DOI: 10.1144/petgeo2012-001|hwp:master-id:petgeo;petgeo2012-001
      Issue No: Vol. 19, No. 4 (2013)
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