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74th EAGE Conference and Exhibition - Workshops
- Conference date: 04 Jun 2012 - 07 Jun 2012
- Location: Copenhagen, Denmark
- ISBN: 978-90-73834-28-6
- Published: 04 July 2012
61 - 80 of 156 results
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Tight Chalk Reservoir Stimulation as a Field Development Tool
Authors Franz Marketz, Maryvan Domelen, Sara Kofoed and Simon WherityFor the development of very tight chalk reservoir in the Danish Sector of the North Sea stimulation is a key value driver. Stimulation and Completion techniques have therefore been screened as early as the “Assess” and “Select” phases the hydrocarbon maturation process. In this way a well concept tailored to the reservoir has been developed and tested before executing full field development.
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Cemented, Multi-stage Ball Drop Completion Field Trial in the North Sea
More LessStimulation is a necessity for optimum production in many fields. This is becoming more and more important in order to make certain projects economically feasible. There are many stimulation techniques and technologies available. The challenge is to find the optimal stimulation solution that matches the drilling/completion design (casing size, zonal isolation type etc.) and does not drastically extend the stimulation time. One success story can be seen through the experience of one North Sea operator. They have been through an evolution on stimulation techniques on their long producing chalk field. Initial stimulation technique was traditional perforation in clusters throughout the entire reservoir section bullheading with 28% HCL. Post production analysis showed that this resulted in poor acid distribution and uneven production. Liner deformation around the clusters also resulted in costly operations.
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Practicalities of Stimulation in Tight Gas Reservoir
More LessRemaining development opportunities in the Southern Gas Basin of the North Sea are mostly confined to lower permeability sandstones and pose significant technical execution challenges and cost hurdles. Field operators have increasingly had to rely upon the adoption of multiple fractured, horizontal wells to achieve commercial rates, deploying completion practises that historically evolved in chalk oil fields in Denmark and Norway and materials honed in the recent technology-enabled opening up of shale plays across North America. The presentation will summarise activities of the most active operator in recent years in the Southern Gas Basin.
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Shale Developments: Use of Modern Data Mining Methods to Interpret Similarities and Differences Between Gas and Oil Completion/Stimulation Strategies
Authors Randy La Follette and William D. HolcombThe presentation and discussion will focus on results of statistical analysis of Barnett Shale gas and Bakken Shale oil production result drivers. Large data sets including key reservoir parameter proxies, well architecture information, completion variables, and stimulation data were compiled, quality controlled, and analyzed to identify key production influences. The analysis and interpretation took into account both controllable influences on well productivity, e.g., well length, azimuth, completion type, stimulation size and materials, along with uncontrollable influences, e.g., fracture bounding bed presence / absence, fracturing into unknown Geohazards. The most obvious production driver is well location, a fair proxy for reservoir quality in the “shale” plays. Well architecture, including azimuth, length, and drift angle may or may not be a major determinant of productivity. It is apparent from both the Barnett and Bakken data sets that longer well lengths do not produce proportionately more hydrocarbons. Specific completion and stimulation parameters, e.g., use of coarse-mesh proppants are also important productivity drivers in certain circumstances.
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Monitoring and Modelling Hydraulic Fracture Stimulation: Future Directions
Authors Quentin J. Fisher, J- M. Kendall, J. P. Verdon and A. Baird and M. HudsonMultiple hydraulic fracturing along horizontal wells has proved to be a game changer that has led to the economic recovery of a vast amount of natural gas from shale resource plays in the USA. Optimization of hydraulic fracture stimulations has generally been achieved using a trial-and-error approach; although the microseismic monitoring of event locations has over the last decade proved to be a key enabling technology. Reductions in gas price, combined with the push to exploit resource plays in highly populated areas without a well-developed supply chain, mean that there is increasing pressure to optimize hydraulic fracture stimulations. Use and integration of advanced microseismic monitoring and geomechanical modelling offers the potential to make a step change in the optimization of hydraulic fracture stimulation. In particular, interpretation of microseismic attributes such as the magnitude and frequency dependence of shear wave splitting can be used to track temporal and spatial changes in fracture density, compliance and potentially size. Geomechanical modelling of the stress distributions prior to and following fracture stimulation can potentially help optimize the spacing and sequencing of individual stages of a fracture treatment as well as identifying the optimal time to conduct workovers (i.e. refracturing).
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Interpretation and Application of Microseismic Images
More LessMicroseismic monitoring (MSM) of hydraulic fracture treatments is routine in North America and has added significantly to our understanding of fracture growth. The interpretation of microseismic images is advancing steadily, extracting more information from event patterns, temporal evolution, and acoustic waveforms. The increasing amount of information from MSM provides significant opportunities to improve stimulation designs, completion strategies, and field development. However, the applications of microseismic interpretations are many times ill-defined, overlooked, or not applied properly. The integration of microseismic images, fracture modeling and reservoir simulation is required to determine the effective stimulated volume. One of the most common misapplications of microseismic interpretations is the assumption that larger stimulated volume (SV) will automatically result in increased well productivity. Characterizing propped and un-propped regions of the hydraulic fracture is critical when evaluating well performance and estimating drainage area and hydrocarbon recovery. This abstract highlights the interpretation and application of microseismic images using excerpts from SPE 152165 (Cipolla et al 2011a).
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New Deterministic Calculation Regime for the Estimation and Characterization of the Stimulated Reservoir Volume (SRV)
More LessA new deterministic calculation regime for the estimation and characterization of the Stimulated Reservoir Volume (SRV) exists. It is based upon a combination of ultra-fine-scaled measurements of induced surface deformation morphology (on the micrometer scale) and a new, two-pass, geomechanical inversion technique. The approach overcomes instabilities and questions of uniqueness with inverted solutions of reservoir strain distributions. The technique was deployed concurrently with the more conventional, High-node-count, highfrequency, downhole, offset microseismic mapping in an exploratory horizontal completion located in an Eagle Ford horizon where low deviatoric stresses made dual and tri-modal complex fracture networks likely. Passive microseismics and microdeformation techniques respond to fundamentally different mechanical processes associated with hydraulic fracturing. This pilot application merged the results from these two mapping diagnostics to explore the potential for integrated geophysical/geomechanical information to facilitate a more accurate and comprehensive understanding of treatment performance.
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Advanced Drilling and Completion Solutions for Unconventional Shale Gas
More LessNatural gas and oil production from shale reservoirs has reshaped the petroleum industry in North America and is posed to have a major impact in other locations around the world. Traditionally shale has been seen as a source rock, a trap or a drilling hazard within the petroleum industry. Today, however, many of these source rocks have proven to yield commercial production of hydrocarbons when the correct technologies are applied to understand the reservoir potential of a given formation and proper drilling and completion techniques are used. This presentation will examine some of the basic geological requirements that need to be assessed to determine if a particular shale reservoir has good production potential. It will then look at drilling and completion solutions have proven successful in different shale reservoirs. Guidelines to optimize the completion design based on specific reservoir properties will be discussed. New validation technologies, including microseismic fracture mapping will be discussed showing their significance in maximizing the productive capacity from a given well and improving our understanding in the production mechanisms. New technology in the area of stimulation fluids and equipment development will also be discussed.
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Completion Based Stimulation Technology; When Fracturing Just Doesnt Fit
Authors Thomas Jrgensen and Rune FreyerReservoir stimulation is required for efficient production in many fields. But traditional fracturing requires much preparation and design. Rock mechanics in small fields require significant data capture and it is not possible to develop as good understanding by trail and error like in the large North American plays where hundreds or even thousands of wells are stimulated before “cracking the code”. Challenges in small fields can be to understand stress fields, water or gas intervals, formation damage or other field specific issues.
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Surveillance Field Trial to Identify Thief Zones in MFF-09B, a well with a Controlled Acid Jetting (CAJ) Liner
Authors Hansvan Dongen, John Davies, Kerem Yuksel and Edo BoekholtzThe Controlled Acid Jetting (CAJ) well design was developed by Maersk Oil for the development of relatively thin but aerially very extensive oil accumulations in low-permeability Chalk formations in the North Sea. These relatively low-cost long horizontal wells (up to 30,000 ft Total Depth) enabled the development of the Dan West Flank and Halfdan oil fields, which would otherwise have been uneconomic. Building on the favourable experience from the North Sea, Maersk Oil has also applied CAJ wells for the cost-effective development of the Al Shaheen oil field in Qatar. The initial development decision for CAJ wells to develop these waterflooded oil fields has effectively resulted in a zero (below Coil Tubing reach) well intervention policy in terms of inflow/outflow profile surveillance and subsequent treatment of any thief zones and/or high-skin intervals encountered. The initial field developments have met expectations with respect to development costs and initial oil production rates. A significant number of waterflood patterns now show faster than forecasted watercut development, which indicates the presence of non-conformances (i.e. natural and/or induced fractures acting as thief zones). When thief zones are present in water floods, oil ultimate recovery is lower than forecasted, which has triggered the need to develop new CAJ well intervention technologies for inflow/outflow profile surveillance and subsequent treatment of thief zones. A dedicated Long Wells Conformance Control (LWCC) team was set up in 2010 to accelerate the development and implementation of such new technologies for the North Sea and Qatar oil fields.
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Temperature Dependence of Ultrasonic Velocities in Shales – Can We Use It For Interpreting Time-lapse Seismic?
Authors Andreas Bauer, Rune Holt, Audun Bakk, Erling Fjr and Jrn StenebrtenThe temperature dependence of ultrasonic velocities in shales show significantly larger temperature sensitivities than predicted by the Gassmann fluid-substitution model, which can be attributed to temperature dependent velocity dispersion. We expect the temperature dependence of velocities to be frequency dependent, resulting in different temperature sensitivities at seismic, sonic and ultrasonic frequencies.
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A Study of Geomechanical Effects on Time-lapse Seismics
Authors Giorgio Cassiani, A. Brovelli G. Vignoli and B. PlischkeTime-lapse seismics is known to be a very effective monitoring technique for the subsurface fluid movement and saturation changes, as well as for geomechanical phenomena [Snieder et al., 2007]. The integration of seismic and reservoir engineering is now becoming state-of-theart [Boutte, 2007] while the number of applications is steadily increasing [Staples et al., 2006]. Among the future challenges to the use of time-lapse seismics is the integration with geomechanics [Landrø, 2006]. The improvement of time-lapse seismic technology [e.g. Tang et al., 2007, Aarre et al., 2007] allows for better and more accurate data acquisition, that in turn allows to “see” effects previously difficult to detect. The effects of geomechanics on time-lapse seismic data have been described in detail by a number of publications [Hatchell and Bourne, 2005; Sayers and Schutjens, 2007; Cox and Hatchell, 2008; Kristiansen and Plischke, 2010]. The overall impact of reservoir exploitation on the changes in seismic response includes the following aspects: (1) Fluid saturation effects, that are based upon: (a) dependence of density on fluid saturation; and (b) dependence of bulk moduli on fluid saturation (Gassmann, 1951). This is the key effect sought in time-lapse seismics, as it allows remote monitoring of the fluid migration in the reservoir. Mainly, two effects are sought in data hopefully depending on the above saturation changes, i.e.: - time shifts, i.e. changes in reflector location in time as a consequence of changes in velocity, and mainly: - impedance changes, i.e. reflectivity changes, as impedance is the product of velocity and density, both changing with fluid content. (2) Pressure (effective stress) effect: this is the first, well known geomechanical effect, often referred to in the literature as pressure effect, but it is actually a dependence on effective stress. It is generally observed that the velocity decrease is very strong in presence of effective stress decrease (expansion), while velocity increase is relatively mild under stress increase (compaction) [e.g. Hatchell and Bourne, 2005]. This asymmetric behaviour is often explained in terms of crack opening under stress release conditions.
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Drilling in Depleted Fields - From Surprises to Surprises?
More LessAs a result of depletion, the reservoir rock generally compacts and thus leads to stress changes both within the reservoir and in its overburden. In turn these changes affect drilling operations. The presentation will describe those changes and introduce a series of field cases illustrating their impact on drilling. Most of these field cases are based upon the analysis of tens of wells and all of them showed behaviours, which surprised the authors at the time of their study. A brief overview of each case is given below. A few years ago, Geomec analysed the stress changes due to depletion – i.e. reservoir stresspath – for a series of over thirty fields, as part of a large Joint Industry Project (Figure 1). The presentation will give a brief overview of the project’s results, insisting on those, which were not expected at its onset.
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Workflow for Coupled Geomechanical and Reservoir Problems – Recent Experiences
More LessDevelopment of unconventional resources requires solving difficult reservoir engineering problems, many of which have some geomechanical component of the analysis. Geomechanics is coupled with the reservoir problem to varying degrees, ranging from problems that can be solved sequentially to those requiring full coupling. In an overall workflow of solving such problems, the selection of the method to solve them, and the degree of coupling which they demand, are some of the most important decision points. The use of the coupled flow and geomechanical models has become more commonplace in recent years, but there are still somewhat specialized, and the best (and most efficicent) workflow for coupled simulation depends critically on the type of the problem being investigated. In this presentation, we will give a survey of this part of the workflow and discuss several examples that demonstrate the differences of the possible approaches.
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Solutions for 3D Coupled Geomechanical and HF Modelling in UG Reservoirs
More LessWith growing worldwide activity in exploration and development of ultra-low permeability unconventional reservoirs the O&G industry has become increasingly dependent on efficient and effective horizontal wells drilling as well as hydraulic fracture completions to increase surface area and promote gas migration. Integrated geomechanical workflow allows encompassing rigorous 3D stress modelling provided by VISAGE* system, hydraulic fracture modelling by P3D model, near wellbore analyses and drillling optimization techniques. Solutions span from data screening, throughout data integration and analysis and finally to well design support covering various scales. They rely on a more accurate 3D stress field characterization, reflecting the structure, heterogeneity/anisotropy, pressure, temperature effects from well to reservoir scale.
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An Acquisition System Using Complementary Components to Achieve Robust Broadband Seismic
Authors Stian Hegna and Gregg ParkesIn a conventional marine acquisition system there are several components that have limitations in terms of bandwidth. However it is possible to re-design or re-arrange several of these components to produce complementary responses providing broadband seismic. The basic components of an acquisition system consist of sources and receivers. On the receiver side the main limitations are related to the sea surface reflection (receiver ‘ghost’). On the source side the limitations are related to the sea surface reflection and the responses of the airgun arrays. The induced responses of these effects are all known or can be measured, so why can’t they simply be removed? The problem arises because most of these responses contain deep notches, which make their removal very unstable in any practical sense. Now all these effects can be related to specific components of the acquisition system. It is then possible to re-design the parameters of those components to produce complementary responses that negate the effect of the notches. Once these components are in place the seismic data can be corrected in a very robust way to produce optimal broadband seismic.
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Deep Interpolated Streamer Coverage - Broadband Seismic Data Offshore South Africa
More LessDeep interpolated streamer coverage is a seismic acquisition technique based on 3D over/under towed-streamer acquisition (Kragh et al. 2009). The technique is designed to provide broadband seismic data and deploys two receiver spreads: a shallow spread primarily for high-frequency information and a deep spread for low-frequency information. The cable separation between over cables is chosen for high temporal and spatial resolution and is typically 50 - 100 m. The cable separation for the deep spread is designed to record the low-frequency component and is much coarser, typically 300 m. In the processing phase, data from the deep (under) cables are interpolated to match the crossline sampling of the shallow (over) cables. Wavefield separation is then used to combine the high-frequency response of the upper cables and the low-frequency response of the interpolated lower cable data set to give a broadband seismic data set that is suitable for detailed structural interpretation and amplitude inversion. In addition to the technical benefit of improved low-frequency response, there is also an operational advantage. The deep cables that provide most of the low-frequency component are towed in a seismically quieter environment than the shallow cables, and hence, are less susceptible to swell noise. This operational advantage is particularly important in areas such as offshore southern South Africa, which has a short season for seismic acquisition and is notorious for high levels of swell in both good and bad weather.
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What to Expect from Variable-Depth Streamer Data
Authors Dechun Lin, Yves Lafet and Ronan SablonVariable-depth streamer acquisition is emerging as a key technique for providing wide-bandwidth seismic data. This technique allows us to obtain a usable bandwidth from 2.5 Hz up to the source notch. It has consistently produced high-quality images in terms of seismic resolution, layer stratigraphy and low-frequency penetration. Seismic interpretation and inversion becomes easier and more robust.
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Increasing Spatial and Temporal Bandwidth with Multi-component Streamer Data
Increasing bandwidth is not only about temporal frequencies but also about spatial wavenumbers, in particular those which are poorly sampled in the cross-line direction with streamer separations of 16 to 24 times the inline sampling interval. In this talk, we present results from a test with a mini-3D array of prototype 4C marine streamers in which we use, in addition to the pressure, the vertical and crossline gradients of the pressure wavefield in order to reconstruct and 3D deghost the wavefield at arbitrary points within the aperture. From the experimental 3D survey, we show examples of spatial and temporal enhancement of wavefields reconstructed using a generalised matching pursuit algorithm, comparing pressure-only and multi-component reconstructions. We find that multicomponent reconstruction is able to de-alias high wavenumber diffractions, that are completely missed by a pressure-only matching pursuit algorithm with priors, and generate broad-band unmigrated timeslices with excellent resolution.
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Increased Temporal Bandwidth Using Hydrophone Only Recording and Conventional Airgun Arrays – Why Not?
More LessUsable bandwidth is determined by the signal to noise ratio rather than just signal. Modern streamers have superior noise performance compared to older versions and this reduction in noise seems to have been overlooked in the search for greater temporal bandwidth. Above approximately 2Hz the noise floor is determined by environmental issues such as swell noise and cable jerk rather than noise inherent to the equipment. Tests show that a usable temporal bandwidth of at least 3-90Hz can be obtained using a conventional airgun array and modern hydrophone only recording when a) the sea surface is not a perfect mirror and b) the streamer is towed in a deep, quiet environment.
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