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3rd EAGE North African/Mediterranean Petroleum and Geosciences Conference and Exhibition
- Conference date: 26 Feb 2007 - 28 Feb 2007
- Location: Tripoli, Libya
- ISBN: 978-90-73781-42-9
- Published: 26 February 2007
41 - 60 of 100 results
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Mapping Offshore Facies and Structures Using CSEM
Authors L.J. Srnka and L.A. WahrmundMarine controlled-source electromagnetics (CSEM) has grown into a useful method for oil and gas exploration, with many surveys acquired worldwide since 2000 by industry including ExxonMobil. Pre-drill prediction success rates are encouraging. The technology is geophysically sound, but needs more development to be useful across the full Upstream. CSEM data interpretation is improved significantly by integration with other data including seismic. An example from deepwater Brazil shows the ability of CSEM to map facies. Extension of the technology to offshore deepwater Libya poses new challenges, including resistive non-reservoir facies and deep targets.
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Gravity and Magnetic Data Interpretation in the Sirte Basin
More Lesshas been created from the available well, seismic and published map data, the gravity effect has been forward modeled and subtracted from the observed gravity. The remaining gravity field has been inverted to derive a first basement depth map. The results of this work will be used in basin-SR charge modeling which should further our understanding of the Sirte basin’s petroleum system.
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HFVS Optimzation for Land Operations - Shake and Go
Authors M.L. Johnson and C.E. KrohnA new vibroseis acquisition technique, which uses HFVS (High Fidelity Vibrator Seismic) separation with continuous sweeping, results in unsurpassed production rates and at the same time excellent data quality. With Continuous HFVS, there is no waiting for between sweep listening times or for between vibrator slip times. All vibrators sweep simultaneously using a long segmented sweep and then move to the next shot points. Calculated production rates are as great or greater than other high productivity methods, particularly with multi-fleet flip-flop operations. In processing, each long data record is parsed into individual segments and separated with the HFVS technique. Separation with C-HFVS is as good as standard HFVS separation. Cross contamination of signal from the vibrator points being acquired simultaneously is not observable in the output records. As long as the sweep segment length is greater than 1.5 times the listening time, the noise quality is comparable to that of HFVS, since harmonic interference noise from sweeping during the listening time is limited to times near the end of the sweep segment.
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“Sparse 3D” Acquisition – An Efficient Exploration Technique
Authors C. Webb, M. Millington, H. Crook and R. HeathWith the seismic and rig markets being very tight in Libya, and in light of the 5 year EPSA-IV licence period, any chance to fast-track the work programme should be examined. For BG Libya, the ‘sparse’ 3D acquisition design discussed in this paper should allow acquisition of high quality 3D data, whilst retaining an efficient survey acquisition schedule and pricing. Use of the existing 2D data and acquisition of a test line ahead of the survey design was a great advantage in the design optimisation, and should be considered as best practice in ‘sparse’ 3D design.
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Desert Sparse 3D as an Alternative to 2D Exploration
Authors B. Pagliccia and P.L. PichonClassically, the first step in exploration corresponds to shooting of 2D seismic, in order to obtain a preliminary image of the subsurface. Through interpretation of these initial data, sub-areas are defined with good exploration potential. Thereof the most prospective areas are then covered with 2D infill layouts. This classical strategy is now challenged by recent acquisition systems with high-channel capacities which, with an adapted sparse design, allow to acquire 3D seismic in a cost effective way compared to 2D. Furthermore, this “Sparse 3D” approach gives a better definition of the prospective areas. A sparse 3D has been acquired by Total E&P Libya on the NC192 concession, with a design optimization derived from decimation test performed on conventional 3D. This sparse 3D has documented a major progress in imagery compared to pre-existing 2D acquired in 1992 by previous operators. Based on the new images, major elements of the structural framework had to be revised, which in term resulted in an optimized definition of new prospects. When surface and subsurface conditions are favourable for sparse 3D acquisition, it has to be considered as a serious alternative to conventional 2D. Then this method may improve significantly the geological understanding of the subsurface under reasonable costs.
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Fit-for-Purpose Seismic Technology - A Case Study in the Use of Point-Receiver Recording for Exploration in the Western Desert of Egypt
Authors P.V. Baaren and J. QuigleySeismic survey design balances the complex interaction of many factors against the objective of delivering a cost-effective and fit-for-purpose dataset, on time, to the seismic interpreter. The availability of new technology allows reevaluation of this balance of factors to best realize the value the technology can provide. Traditional assumptions in terms of fold requirements and source and receiver effort can be revisited. A case history is presented from a 2000-km2 3D Vibroseis survey in the Western Desert of Egypt. Availability of a high-channel-count point-receiver acquisition system and associated source and processing technology allowed a significant rebalancing of the field acquisition parameterization relative to an existing, successful, conventional technique. The resulting dataset, though acquired with a reduced field effort, compares favorably with the existing data both geophysically and economically.
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Environmental Impact Limitation during Exploration Activities in a Highly Sensitive Environment
More LessLimitation of the environmental footprint caused by exploration activities is achievable, especially through applying control measures at the time the operations take place. The current GIS project is an example of the additional benefits that can be created, as a by-product of the implementation of operational procedures.
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Enhanced Understanding of the Krechba Field, Algeria by Using Modern Processing and Depth Conversion Techniques
Authors C. Reiser, J. Sinden, A. Castoro, H. Sognnes, S. Omri, S. Brown, A.M. Malik, D. Abdelouafi and M. FrenchKrechba is one of eight fields in the In Salah Gas Development in Central Algeria, operated jointly by BP, Sonatrach and Statoil. The field is in the northern part of the acreage retained for development, and consists of reservoirs in the Carboniferous and Devonian. The Carboniferous, Tournasian C10.2 sands are the main contributor to the gas production to date, being developed for first gas in 2004. The original field discovery made in 1957 was based on 2D seismic. Due to uncertainty on the top reservoir and the thin reservoir, a 3D seismic dataset of approximately 600 km2 was acquired in 1997. Seismic amplitudes were used to define accurately the presence and quality of the estuarine sands very well developed over the field. This reservoir consists of several stacked thinner sands, at depths ranging from 2800 m to 3400 m. With this challenging task, to improve the seismic resolution and the seismic quality lead to reprocessing of the 3D volume which was finalized in 2006. This paper reviews the main steps of the seismic depth conversion process with the use of seismic velocity on this field using the reprocessed seismic, and draws some conclusions regarding the future development of the field.
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Formation Evaluation and Reservoir Monitoring behind Dual Casings - A First Libya’s Case Study
Authors R.G. Gauchet, C.R. Robert, M.A. Attayeb and L.W. WihardjoThe success of Formation Evaluation and Reservoir with modern tools, provided proper planning & Monitoring behind dual casings can be achieved logging preparation. The casing ex-centralization and well deviation are key factors that provide tool orientation and make it possible to record a stronger formation signal. The quantitative water saturation comparison (between open and cased hole evaluation) has indicated significant remaining oil left at the Dahra formation. The current oil water contact has been positively identified.
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Opportunities and Challenges for Improved Oil Recovery
Authors G.F. Teletzke, J.R. Wilkinson and K.C. KingA worldwide look at long-term trends reveals that new discoveries of conventional oil fields are declining while demand for oil is estimated to increase approximately 1.5% per year from the current levels of approximately 85 million bopd. A portion of the increased demand will be met by increasing supplies from non-conventional deposits but the majority will need to come from improved rates and recovery in conventional oil fields. Industry experience and performance to date indicates that while considerable opportunities exist, there will also be fundamental challenges facing our ability to increase light oil recovery. This means increasing attention on fundamental parameters driving increased field offtake rates and recovery factors. This paper will discuss both basic technical parameters that need to be addressed and the IOR/EOR technologies that can be deployed (or developed) to meet this challenge. It also covers the pros and cons of various types of enhanced oil recovery injection fluids. Attributes of enhanced recovery cost elements that need to be considered in fiscal regimes that are mutually beneficial to both host governments and the international partners will also be summarized.
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IOR/EOR in Hydro
Authors H. Tonne and R. NygaardIn this paper Hydro’s historic IOR achievements are reviewed. Key technologies for future IOR opportunities are identified. Improved reservoir control and well technology will continue to add new reserves to our portfolio of fields. Seismic monitoring, integrated operations, wired drill pipe, expandable metal and autonomous down-hole inflow valves will be important elements of our future IOR effort.
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Integrated Processing and F3 Reservoir Sand Interpretation Study, Wafa Field, Onshore Libya
Authors A.N. Fogg, T.H. Larsen, D.R. Sallis, H. Fares, F. Ghrouda, H. Zbeda, C. Pazzi and J. MartinThis paper describes the interpretation, seismic inversion and associated petrophysical analysis of an 868km2 full fold (1100km2 total) 3D seismic dataset over the Wafa field in Concession Block NC 169A, Ghadames Basin, Libya. The data was acquired for EniGAS BV. Seismic processing was carried out by Veritas DGC Limited during 2005 and the interpretation and seismic inversion was carried out in Veritas’ Crawley (UK) office from February 2005 to November 2005 by the VHR (Veritas Hampson-Russell) division.
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Characterization and Modelling of a Reservoir with Multiple Scales of Fracturing
Authors F. Gouth, A. Toublanc and M. MresahAn integrated fracture study from characterization to modelling on a carbonate field is described. This oil and gas accumulation is produced through 6 horizontal wells. Outcrop data allowed us to understand the spatial organisation of fractures seen on well imagery and to identify the main fractures scales: bed confined (BCF) in tight layers, highly persistent (HPF) and conductive faults. Two orientations have been identified at both BCF and HPF scales: axial N70 fractures related to the folding and N150 fractures uniformly distributed throughout the reservoir. Mud losses have been used to rank the conductivity of the different scales encountered at the well and PLTs have shown a clear relationship between fractures and productivity. A correlation between KH from PBU and N70 FF has emphasized the key dynamic impact of the HPFs. The fracture modelling has been performed using a DFN and has focused on HPFs. A fracture permeability grid data has been processed by the DFN and was used as an input for a double porosity model. The shape factor derived from well imagery data was lowered to match the historical GOR. This is thought to be due to the heterogeneity in dynamic properties of the HPF set.
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Well Test Analysis and Modeling of a Multi-Scale Fractured Reservoir – The in Amenas Field, Algeria
Authors R. Basquet, O.P. Wennberg, H.H. Veire, P. Ingsøy and A. DraouThe In Amenas in East Algeria is operated by a joint venture between Statoil, BP and Sonatrach. In this study we focus on the gas condensate production of the Cambrian and Ordovician reservoir Units of Tiguentourine field. A study to develop a methodology for a fracture model has been based on the available static data, i.e. borehole images, cores and seismic. The objectives are 1) to validate the structural image proposed by the geological and geophysical analysis, and 2) to characterize the hydrodynamical properties of this complex multi-scale fractured reservoir from dynamic data such as well test measurement. One well with both FMI interpretation and well test data have been analyzed. Firstly, a conventional well test interpretation was used. However, such a tool does not capture all the heterogeneities of the fracture system. Therefore, analyze was completed using a methodology based on fluid flow simulation within the actual fracture system. The applied FRACA model preserves the fracture distribution along the wellbore according the FMI interpretation. Despite the number of unknown parameters and the large uncertainties on the other characteristics, it was possible to match the well test signature fixing all the parameters with realistic values.
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Fracture Network Modeling and Dual Permeability Simulation of Carbonate Reservoirs
Authors J.M. DeGraff, M.E. Meurer, L.H. Landis and S. Lyonselement models to compute effective matrix permeability; 3) analysis of fracture data from core, image logs, and outcrop; and 4) integration of field performance, structure, stratigraphy, and lithology. Directional equivalent fracture permeability, porosity, and matrix block dimensions are estimated using discrete fracture network (DFN) and 3D geologic models, while effective matrix permeability is derived using proprietary technology (patent pending). Fracture analysis consists of identifying structural and stratigraphic controls on fracture data from available sources, and then using this knowledge to derive a set of rules to populate a DFN model. Dual-porosity / permeability reservoir simulation models are built in EMpower™ using a similar grid geometry and cell size, effective matrix properties, and DFN-generated fracture properties. Simulation results show a better history match with less iteration than previous models when compared with multiphase production history. In test cases, dual-porosity / permeability models more accurately capture the impact of fractures on fluid flow than do single-medium models.
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Rock-Fabric Facies and Diagenetic Controls on Carbonate Reservoirs
More LessA Case Study from the Early Eocene El Garia Formation, Tunisia.
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Effective Simulation of Thick Carbonate Reservoirs
Authors C.E. Shuchart and I.S. Abou-SayedWorldwide, substantial oil and gas resources are contained in low permeability sandstone reservoirs and variable permeability carbonate reservoirs. Matrix or fracture stimulation treatments are typically required to effectively and optimally produce these resources. Many of the larger resources are characterized by thick intervals and/or multiple reservoir targets. ExxonMobil has undertaken multi-disciplinary approaches to the development and integration of technologies for design, implementation, and evaluation of acid and fracture stimulation treatments for these reservoirs. Specifically for matrix stimulation of thick carbonate reservoirs, acid placement and diversion are extremely important and challenging. Additional challenges associated with stimulating thick reservoirs include increased rock heterogeneity, development of differential reservoir pressures, and impact of the hydrostatic pressure of the fluid in the wellbore. Successful stimulation of moderate thickness intervals (100-500 ft) has been achieved through a combination of high-rate injection, viscous diversion, and selective perforating. However, for thicker reservoirs these methods may not be sufficient. ExxonMobil continues to advance the development of mechanical, chemical, and engineering methods to improve acid placement in very thick reservoirs (500+ ft).
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Physics Limit Drilling
Authors S.R. Keller and F.E. DupriestThis extended abstract describes the use of a physics-based approach to well construction. First, physics-based drilling models and limit states are integrated in a quantitative risk analysis framework to help plan the well. Then, during drillng operations, a physics-based, energy approach is used to maximize penetration rates.
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Acid's Behavior and Performance on the Matrix with Time - Hassi R'mel Field, Algeria
Authors M. Boussa, D. Bencherif and M. KhodjaSandstone matrix stimulation has been the subject of extensive investigations for over 40 years and extensive experimental work has been conducted to investigate the reactions of various mud acid systems with damaging and formation materials[1-2-3]. Theoretical analysis and modelling of the stimulation process have also been studied by some investigators[4-5-6]. Another experiment of acidizing was realised in Hassi-R'Mel field with 3 types of acid. This field is a gas condensate reservoir with a superposition of three layers having very good petrophysic characteristics. A decrease in production of the wells was observed in the various zones. Build up tests realised on those wells showed significant skin, which is due primarily to the excessive invasion of the mud used during drilling and Work Overs. For that, a stimulation by acidizing was decided to optimise and to improve the potential of these wells which is less than that hoped within sight of their petrophysic characteristics. In order to study the effects of stimulation, PLT’s were realised before and after the acidizing. Before stimulation, studies were undertaken to see and analyze each acid's behavior on the matrix and to draw the conclusions on the capacities and disadvantages of each one of them on the reservoir. The analyses carried out before, during the acidizing and several years after us made it possible to make a technical and economic study which will enable to see and to understand acid's behavior with time and its impacts on the reservoir , on the wells's equipment and investment costs. The purpose of this presentation is to show: -various methods of acidizing used and the concentrations used. -acid's behavior and performance on matrix with time -the advantages and disadvantages from this stimulation campaign. -the ratio of the profit on the capital costs after the operation of acidizing
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Porosity and Permeability from Drill Cuttings
Authors R. Lenormand, P. Egermann and J. BouillotThe early determination of rock petrophysical properties is one of the main concerns during the reservoir characterization process because it impacts directly the reserves (porosity, saturation) and also the well deliverability (permeability). Logs generally provide a good estimate of porosity and saturations along the well, but permeability is more difficult to obtain especially in carbonates. Drill cuttings can provide additional information on the petrophysical properties of the reservoir. In this paper, we have described a method for measuring permeability on drill cuttings with the following capabilities: size of cuttings down to 1 mm diameter,volume of cuttings around 1 cm3 (2-3 grams of dry cuttings),permeability from the microDarcy to around 100 mDarcy. The main constrain of the method is to need consolidated cuttings with a porosity larger than 4% in order to have a minimum volume of air trapped during the spontaneous imbibition. Porosity is difficult to measure on small cuttings. The more accurate method is based on NMR relaxometry with an apparatus dedicated to the measurement of small volumes.
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