Improving reservoir models of Cretaceous carbonates with digital outcrop modelling (Jabal Madmar, Oman): static modelling and simulating clinoforms
30
Citation
70
Reference
10
Related Paper
Citation Trend
Abstract:
ABSTRACT In Jabal Madmar in the Sultanate of Oman, Cretaceous epeiric carbonate platform architectures were characterized by employing a digital outcrop modelling workflow. A framework model for Natih Sequence I (Natih E member) was established, which embeds a meticulously studied platform-top incision and shoal complex. Outcrop-scale clinoforms are recognized in these shoals by hectometre-scale (100 m long) medium to high-angle (1–5°) inclined stratal surfaces comprising texture-based facies transitions. These clinoforms are usually beneath the resolution of seismic data and as such are not easily recognized and correlated between wells. Geologically realistic clinoform models were built using a well-defined stratigraphic model that incorporated inclined surfaces in the model grid and if available, data on lateral facies transitions. Waterflood simulations demonstrated improved sweep efficiency in these models. In contrast, simple models without clinoform heterogeneities resulted in less efficient piston-like patterns of sweep. The study presented in this paper demonstrates an outcome contrary to previous studies, as in this study, barriers to flow are absent. Complex clinoform models must be considered in reservoir modelling workflows to correctly derive static and dynamic rock properties. This is because outcrop-scale clinoforms have a potential impact on reservoir behaviour under secondary and tertiary recovery mechanisms.Keywords:
Outcrop
Geobiology
Environmental geology
Gemology
Palaeogeography
Lucy MacGregor1 and Richard Cooper suggest that for marine controlled source electromagnetic survey methods to achieve more general adoption in the E&P industry, the applications need to be refocused with more emphasis on prospect appraisal and reservoir monitoring rather than exploration.
Economic geology
Environmental geology
Geobiology
Gemology
Palaeogeography
Igneous petrology
Value (mathematics)
Glaciology
Cite
Citations (3)
The current model describing the sealing mechanism of high-pressure hydrocarbon traps and the ensuing methodology for predicting top seal integrity and capacity in high-pressure plays assumes that the caprock, defined as the low matrix permeability formation immediately overlying the reservoir, is the seal. This study challenges this assumption and proposes the existence within the caprock of a fluid waste zone consisting of a system of fractures cutting from the reservoir upwards into the caprock and, therefore, charged with reservoir fluids. Because of the waste zone fractures the reservoir fluids are not sealed at the base of the caprock. Instead the seal coincides with the fracture waste zone tip point, which occurs at an important stress and stratigraphic boundary termed the ultimate seal. Six case studies demonstrate that in the UK Central Graben the top seal for Mesozoic high pressure hydrocarbon accumulations lies between the Base Cretaceous Unconformity and the base of the Chalk Group and that the Jurassic Kimmeridge Clay Formation is not necessarily the seal for these traps. The data used for the construction of structural and stress models for the case studies include pore pressure measurements, formation integrity measurements, well logs and reflection seismic profiles. An important conclusion of this study is that the shorter the waste zone the higher the chance of finding a hydrocarbon column in the reservoir.
Environmental geology
Igneous petrology
Geobiology
Gemology
Economic geology
Palaeogeography
Cite
Citations (7)
The Draugen Field is an elongate, low relief, anticline containing mainly multi-Darcy sandstones. Oil initially in-place (STOOIP) is 182 x 10 6 Sm 3 . The 1987 Plan for Development and Operation (PDO) assumed a central cluster of 6 deviated production wells and 3 subsea water injectors at each end of the field. In addition two subsea wells would provide early production. Unsteady state relative permeability data indicate a residual oil saturation of 35%. In the full field simulation model this was increased to 40% to account for small-scale heterogeneity. The model yielded a recovery of some 67 x 10 6 Sm 3 . Modern steady state and centrifuge techniques have since demonstrated a long tail of very low oil relative permeability before reaching a residual oil saturation of some 15%. Fine grid simulations translated this into a gravity segregation process behind the displacement front. Other fine grid models reveal that horizontal wells will yield a slower build up of water cut than vertical wells. The increased productivity of the horizontal wells reduced the required number of platform producers from 6 to 5. Pseudo-relative permeabilities were developed to represent fine grid model performance in a new sophisticated full field model. This model predicted an ultimate recovery of 94 x 10 6 Sm 3 (40% increase). The additional predicted recovery is attributed to a reduction of the effective residual saturation and delayed water production associated with horizontal wells. In October 1993 Draugen started production from one horizontal subsea well, which has since demonstrated a better than expected coning performance. Production from platform wells was initiated in June 1994 with initial well rates up to 8000 Sm 3 per day, confirming the expected high productivity of horizontal wells. Optimization and tuning of facilities has since allowed the peak production rate for the field to be increased from the planned 17 500 Sm 3 per day to a present actual level of 24 600 Sm 3 per day. Further de-bottlenecking is ongoing with the aim of increasing process capacity.
Environmental geology
Gemology
Geobiology
Igneous petrology
Economic geology
Palaeogeography
Cite
Citations (0)
In this work we present a methodology for optimal management of brownfields that is illustrated on a real field. The approach does not depend on the particular reservoir flow simulator used, although streamline-derived information is leveraged to accelerate the optimization. The method allows one to include (non-linear) constraints (e.g. a recovery factor larger than a given baseline value), which are very often challenging to address with optimization tools. We rely on derivative-free optimization coupled with the filter method for non-linear constraints, although the methodology can also be combined with approaches that utilize exact/approximate gradients. Performance in terms of wall-clock time can be improved further if distributed-computing resources are available (the method is amenable to parallel implementation). The methodology is showcased using a real field in west Siberia where net present value (NPV) is maximized subject to a constraint for the recovery factor. The optimization variables represent a discrete time series for well bottom-hole pressure over a fraction of the production time frame. An increase in NPV of 7.9% is obtained with respect to an existing baseline. The optimization methods studied include local optimization algorithms (e.g. generalized pattern search) and global search procedures (e.g. particle swarm optimization). The controls for one injection well in the real field were actually modified according to the solution determined in this work. The results obtained suggest improvement for most economic scenarios.
Brownfield
Environmental geology
Economic geology
Geobiology
Igneous petrology
Palaeogeography
Gemology
Cite
Citations (9)
Reservoir compartmentalization can seriously compromise a project’s economics if left undetected during appraisal. Its early identification is made more likely if maximum use is made of available fluid appraisal data. This involves making a critical comparison of time-scales for various fluid properties to equilibrate compared with the actual time since those properties were initially disturbed. Spatially varying fluid properties indicate compartmentalization if they have existed for longer than the time needed for them to equilibrate. Here we use data from appraisal wells and reservoir mixing time-scales to investigate vertical and horizontal compartmentalization in the Horn Mountain Field (Gulf of Mexico) and to quantify the properties of the baffles/barriers identified. We compare our results with earlier work using time-lapse geochemistry and mud gas isotope logging. Present fluid compositional variations in the field are shown not to be diagnostic of horizontal compartmentalization as the mixing time-scales by molecular diffusion are longer than the time since the reservoir filled. In contrast, pressure shifts and density differences are diagnostic. They indicate that faults within the Horn Mountain Field are relatively impermeable and would act as barriers during oil production. They also confirm that a shale-filled channel acts as a barrier to vertical flow.
Compartmentalization (fire protection)
Environmental geology
Gemology
Geobiology
Igneous petrology
Economic geology
Palaeogeography
Cite
Citations (6)
Exhumation in the Eromanga Basin of South Australia and Queensland has been quantified using compaction methodology. All methods of estimating exhumation utilize rock properties that are affected by, and retain a memory of, burial in excess of that presently observed. The tool used for estimating the exhumation in this study is analysis of the degree of overcompaction of rock units. Since porosity describes compaction state, the sonic log, controlled strongly by the amount of porosity, is an appropriate indicator of compaction and, hence, is used for quantifying exhumation from compaction. The standard method of estimating exhumation based on the degree of overcompaction of a single shale unit has been modified, and seven units, predominantly shales ranging in age from the Cretaceous to the Jurassic, have been analysed. All units yield similar results. Burial at depth greater than currently observed is the most likely cause of overcompaction since it is unlikely that sedimentological and/or diagenetic processes are responsible for similar amounts of overcompaction in different lithologies. The results of the compaction analysis reveal that Late Cretaceous–Tertiary exhumation increases eastwards from the Patchawarra Trough, through the Gidgealpa–Merrimelia–Innamincka Trend and Nappamerri Trough into the Queensland sector of the basins. This study has major implications for hydrocarbon exploration. Predicted maturation of source rocks will be greater for any given geothermal history if exhumation is incorporated in maturation modelling. The exhumation study helps to quantify velocity anomalies associated with overcompaction. Exhumation values can also be used to improve porosity predictions of reservoir units in undrilled targets.
Geobiology
Environmental geology
Economic geology
Palaeogeography
Hydrocarbon exploration
Gemology
Igneous petrology
Glaciology
Cite
Citations (31)
Outcrops are valuable for analogous subsurface reservoirs in supplying knowledge of fine-scale spatial heterogeneity pattern and stratification types, which are difficult to obtain from subsurface reservoir cores, well logs or seismic data. For petrophysical properties in a domain where the variations are relatively continuous and not dominated by abrupt contrasts, the spatial heterogeneity pattern can be characterized by a semivariogram model. The outcrop information therefore has the potential to constrain the semivariogram for subsurface reservoir modelling, even though it represents different locations and depths, and the petrophysical properties may differ in magnitude or variance. However, the use of outcrop-derived spatial correlation information for petrophysical property modelling in practice has been challenged by the scale difference between the small support volume of the property measurements from outcrops and the typically much larger grid cells used in reservoir models. With an example of modelling the porosity of an outcrop chalk unit in eastern Denmark, this paper illustrates how the fine-scale spatial correlation information obtained from the sampling of outcrops can be transferred to coarser-scale models of analogue rocks. The workflow can be applied to subsurface reservoirs and ultimately improves the representation of geological patterns in reservoir models.
Outcrop
Environmental geology
Geobiology
Gemology
Igneous petrology
Economic geology
Palaeogeography
Cite
Citations (4)
As part of an effort to try to halt the decline in onshore oil production and accelerate production from onshore fields in Azerbaijan, a World Bank-sponsored study of four fields was carried out: the Bibi-Eybat, Kala, Buzovni-Mashtagi and Zirya fields. The study integrated geoscience, engineering, economics and environmental issues. This paper concentrates on the determination of methods for increasing production rates and recovery. The characteristics of the subject fields are summarized and their current status described. Methods for improving oil production rates in the fields include: mechanical work-overs, artificial lift optimization, sand-control and changes to well completion practices. Our work indicates that production rates could be raised between two-and ten-fold through the application of modern oil-field practices, but financial constraints have prevented their widespread use. Well intervention techniques form the basis of several outline field development plans, described with the associated production forecasts. A brief review is made of possible exploration plays which exist in and around the subject fields.
Igneous petrology
Environmental geology
Geobiology
Palaeogeography
Economic geology
Gemology
Oil Production
Cite
Citations (21)
In western Kazakhstan there are several world class hydrocarbon fields, including the onshore Karachaganak Field. The geological setting is very challenging for the seismic imaging techniques where deep carbonate platform targets underlie a complex overburden including diapiric and detached salt structures. Furthermore, the extensive oil field infrastructure generates a noisy environment for seismic acquisition and reduced access for vibroseis trucks. KPO conducted an extensive integrated feasibility study for a new survey, complemented by a seismic acquisition test in 2008 which confirmed the need for dense source and receiver coverage, long offsets and wide azimuths to optimize imaging of the pre-salt targets. The survey was acquired in 2009 and survey execution exceeded local and international standards. It was the highest channel survey acquired in Kazakhstan and when fully depth image processed it will yield a high spatially sampled seismic volume, with improved resolution and structural definition. The application of the latest technology and techniques will enable better characterization of this complex carbonate reservoir, adding future value by better placement of wells and reducing overall costs for the ongoing development of the field.
Gemology
Economic geology
Environmental geology
Igneous petrology
Geobiology
Palaeogeography
Cite
Citations (0)