- Home
- A-Z Publications
- Petroleum Geoscience
- Previous Issues
- Volume 14, Issue 1, 2008
Petroleum Geoscience - Volume 14, Issue 1, 2008
Volume 14, Issue 1, 2008
-
-
Sensitivity of the impact of geological uncertainty on production from faulted and unfaulted shallow-marine oil reservoirs: objectives and methods
Authors T. Manzocchi, J. N. Carter, A. Skorstad, B. Fjellvoll, K. D. Stephen, J. A. Howell, J. D. Matthews, J. J. Walsh, M. Nepveu, C. Bos, J. Cole, P. Egberts, S. Flint, C. Hern, L. Holden, H. Hovland, H. Jackson, O. Kolbjørnsen, A. MacDonald, P. A. R. Nell, K. Onyeagoro, J. Strand, A. R. Syversveen, A. Tchistiakov, C. Yang, G. Yielding and R. W. ZimmermanEstimates of recovery from oil fields are often found to be significantly in error, and the multidisciplinary SAIGUP modelling project has focused on the problem by assessing the influence of geological factors on production in a large suite of synthetic shallow-marine reservoir models. Over 400 progradational shallow-marine reservoirs, ranging from comparatively simple, parallel, wave-dominated shorelines through to laterally heterogeneous, lobate, river-dominated systems with abundant low-angle clinoforms, were generated as a function of sedimentological input conditioned to natural data. These sedimentological models were combined with structural models sharing a common overall form but consisting of three different fault systems with variable fault density and fault permeability characteristics and a common unfaulted end-member. Different sets of relative permeability functions applied on a facies-by-facies basis were calculated as a function of different lamina-scale properties and upscaling algorithms to establish the uncertainty in production introduced through the upscaling process. Different fault-related upscaling assumptions were also included in some models. A waterflood production mechanism was simulated using up to five different sets of well locations, resulting in simulated production behaviour for over 35 000 full-field reservoir models. The model reservoirs are typical of many North Sea examples, with total production ranging from c. 15×106 m3 to 35×106 m3, and recovery factors of between 30% and 55%. A variety of analytical methods were applied. Formal statistical methods quantified the relative influences of individual input parameters and parameter combinations on production measures. Various measures of reservoir heterogeneity were tested for their ability to discriminate reservoir performance. This paper gives a summary of the modelling and analyses described in more detail in the remainder of this thematic set of papers.
-
-
-
Sedimentological parameterization of shallow-marine reservoirs
The key causes of heterogeneity within progradational shallow-marine reservoirs have been defined as: shoreline type (wave vs. fluvial dominated); shoreline trajectory; the presence of permeability contrasts associated with dipping clinoform surfaces within the shoreface or delta front; the presence of cemented barriers between parasequences; and the progradation direction of the shoreline (described with respect to the main waterflood direction in the simulated reservoir). These parameters were recorded from a series of 56 modern and ancient depositional systems from a variety of climatic and tectonic settings. These data were then used to build the 408 synthetic sedimentological models that formed the basis for the SAIGUP study.
-
-
-
Assessing the effect of geological uncertainty on recovery estimates in shallow-marine reservoirs: the application of reservoir engineering to the SAIGUP project
Reservoir management is a balancing act between making timely operational decisions and the need to obtain data on which such decisions can be made. There is a further problem: estimates of recovery for prospective development plans are subject to uncertainty because of the uncertainty of the geological description within the simulation model.
The SAIGUP project was designed to analyse the sensitivity of estimates of recovery due to geological uncertainty in a suite of shallow-marine reservoir models. However, although it was generic, it had the hallmarks of active reservoir management, because those members of the team responsible for deriving the notional development plans for individual models via reservoir simulation, and computing the recoveries, had to work in parallel with others under time and budget constraints.
This paper describes the way the reservoir engineering was carried out to achieve these objectives, the assumptions made, the reasoning behind them, and how the principles could be used in other studies. Sample results are also presented, although the bulk of the results are presented in other papers in the project series. One surprising result was that faults that impede flow can improve recovery. The underlying physical explanation for this behaviour is provided.
-
-
-
Combined effects of structural, stratigraphic and well controls on production variability in faulted shallow-marine reservoirs
Authors A. Skorstad, O. Kolbjørnsen, T. Manzocchi, J. N. Carter and J. A. HowellSeveral key parameters that describe a prograding shallow-marine reservoir are investigated for their relative importance on hydrocarbon production variability. Sedimentological parameters are aggradation angle, progradation direction relative to the waterflood, continuity of cemented surfaces and shoreline curvature. Structural parameters are the fault pattern, the density (throw) of the faults and the fault-rock permeability. The last component investigated is the effect of well placements. Having three distinct levels for all sedimentological and structural parameters in addition to a non-faulted case gives a dataset of 2268 reservoir models. Four different sets of well locations produce 9072 production datasets.
The variability of the production data is decomposed into its explanatory factors in order to see the relative importance of the chosen parameters. The production data include the total production, the discounted production and the recovery factor. The sedimentological parameters dominate both the production and the discounted production variability, especially the aggradation angle and progradation direction, whereas the fault pattern is equally significant for the recovery factor. Continuity of sedimentological barriers were found to contribute less than expected to the production variability for these reservoir models, and the well placements also showed a low effect.
-
-
-
A study of the structural controls on oil recovery from shallow-marine reservoirs
Authors T. Manzocchi, J. D. Matthews, J. A. Strand, J. N. Carter, A. Skorstad, J. A. Howell, K. D. Stephen and J. J. WalshThe differences in oil production are examined for a simulated waterflood of faulted and unfaulted versions of synthetic shallow-marine reservoir models with a range of structural and sedimentological characteristics. Fault juxtaposition can reduce the economic value of the reservoirs by up to 30%, with the greatest losses observed in models with lower sedimentological aggradation angles and faults striking parallel to waterflood direction. Fault rock has a greater effect than fault juxtaposition on lowering the economic value of the reservoir models in the compartmentalized cases only – and only when the fault rock permeability model is based on the least permeable published laboratory data. Moderately sealing faults can increase the economic value of reservoirs except when the main flow direction is parallel to the faults. These results arise from the dependence of economic value on both sweep efficiency and production rate. Simple predictors of fault juxtaposition and fault-rock heterogeneity have been established and combined with two-dimensional considerations from streamline theory in an attempt to capture quantitatively the change in economic reservoir value arising from faults. Despite limitations associated with the three-dimensional role of juxtaposition, the results are encouraging and represent a step towards establishing a rapid transportable predictor of the effects of faults on production.
-
-
-
Upscaling uncertainty analysis in a shallow-marine environment
Authors Karl D. Stephen, Canghu Yang, Jonathan N. Carter, John A. Howell, Tom Manzocchi and Arne SkorstadGeological models are often created at a scale finer than is suitable for flow simulation and also ignore the effects of sub-cellular heterogeneities. Upscaling of static and dynamic reservoir properties is an important process that captures the impact of smaller scales, ensuring that both heterogeneity and the flow physics are represented more accurately. A Geopseudo upscaling approach for shallow-marine reservoirs is presented, which captures the essential flow characteristics across a range of scales from laminae to the simulation grid. Starting with a base-case set of minimum assumptions enables generation of one set of pseudo-relative permeability and capillary pressure curves per facies. This is then expanded to investigate the limitations of these assumptions and compare their impact against variations in large-scale geological and structural parameters. For the analysis, two-level full factorial experimental design is used to determine important parameters. A comparison of upscaling effects is also performed.
The most important upscaling and fine-scale parameters identified by the analysis are the shape of the capillary pressure curve, lamina-scale permeability variation and upscaling flow speed. Of similar importance are the sedimentological parameters for shoreline aggradation angle and curvature. Fault direction (perpendicular and parallel to the shoreline) and the fine-scale upscaling method are of moderate to low importance. The shallow-marine parameter for clinoform barrier strength and the direction of flow considered when upscaling are unimportant. Analysis of upscaling effects suggests that the algorithm used at the intermediate scale is not important, while the assumed flow speed is very important, typically resulting in a 10% maximum variation in cumulative recovery. Fine-scale properties and upscaling methods affect recovery mostly due to increased initial water saturations but also because of early breakthrough.
-
-
-
Optimization of a reservoir development plan using a parallel genetic algorithm
Authors Jonathan N. Carter and John D. MatthewsA parallel genetic algorithm has been applied successfully to design a production plan that is substantially superior to that obtained using a conventional engineering approach. The reservoir, a dipping structure, was expected to yield optimum production using a rolling line drive from downdip to updip positions. The simulation allowed for 3800 positions for each of 11 wells, giving a total of 1.3×1031 options. The genetic algorithm sampled 1650 of these and was able to identify seven solutions that would increase production by over 30% compared with the rolling line drive. In contrast, a random search using 850 samples managed to find only two plans that improved production; in each of these cases the improvement was less than 1%.
-
-
-
Faults in conventional flow simulation models: a consideration of representational assumptions and geological uncertainties
Authors T. Manzocchi, A. E. Heath, B. Palananthakumar, C. Childs and J. J. WalshEven when geologically based methods are used to determine fault rock permeabilities and thicknesses for input into flow simulators, a wide range of simplifying assumptions regarding fault structure and content are still present. Many of these assumptions are addressed by defining quantitative and flexible methods for realistic parameterization of fault-related uncertainties, and by defining automated methods for including these effects routinely in full-field flow simulation modelling. The fault effects considered include: the two-phase properties of fault rocks; the spatial distributions of naturally variable or uncertain single-phase fault rock properties and fault throws; and the frequencies and properties of sub-resolution fault system or fault zone complexities, including sub-seismic faults, normal drag and damage zones, paired slip surfaces and fault relay zones. Innovative two-phase or geometrical upscaling approaches implemented in a reservoir simulator pre-processor provide transmissibility solutions incorporating the effect, but represented within the geometrical framework of the full-field flow simulation model. The solutions and flexible workflows are applied and discussed within the context of a sensitivity study carried out on two faulted versions of the same full-field flow simulation model. Significant influence of some of these generally neglected fault-related assumptions and uncertainties is revealed.
-
Volumes & issues
-
Volume 30 (2024)
-
Volume 29 (2023)
-
Volume 28 (2022)
-
Volume 27 (2021)
-
Volume 26 (2020)
-
Volume 25 (2019)
-
Volume 24 (2018)
-
Volume 23 (2017)
-
Volume 22 (2016)
-
Volume 21 (2015)
-
Volume 20 (2014)
-
Volume 19 (2013)
-
Volume 18 (2012)
-
Volume 17 (2011)
-
Volume 16 (2010)
-
Volume 15 (2009)
-
Volume 14 (2008)
-
Volume 13 (2007)
-
Volume 12 (2006)
-
Volume 11 (2005)
-
Volume 10 (2004)
-
Volume 9 (2003)
-
Volume 8 (2002)
-
Volume 7 (2001)
-
Volume 6 (2000)
-
Volume 5 (1999)
-
Volume 4 (1998)
-
Volume 3 (1997)
-
Volume 2 (1996)
-
Volume 1 (1995)