bluuebunny/crossref_metadata_2025_split huggingface dataset:
Slickwater Fracturing: Food for Thought
Authors: Palisch T.T.. T. , Vincent M.C.. C. , Handren P.J.. J. 
Published: August 2010

Summary
The evolution of fracturing technology has provided the industry with numerous advances, ranging from sophisticated fluid systems to tip-screenout designs to propagation modeling. Interestingly, these advances typically have focused on conventional designs that use a crosslinked-fluid system. However, as the development of unconventional (e.g., tight gas, shales, coalbed methane) or underpressured reservoirs has increased, so has the demand for innovative hydraulic-fracture designs. The most recent of these design changes has been the popular method of placing proppant with slickwater, linear gel, or hybrid treatments.
Although our industry has significant expertise in fracture design, most of our experience has been in conventional crosslinked-fluid systems. However, there are many aspects of crosslinked-fluid design that either do not apply to slickwater treatments or, in some cases, are contrary to the requirements of slickwater treatments.
This paper will begin by reviewing the motivation, benefits, and concerns with slickwater fracturing and discuss why this seemingly old method has regained popularity over conventional crosslinked designs in many reservoirs. In addition, the authors will detail some of the important theories related to slickwater fracturing, including fracture width and complexity, proppant transport and settling, and conductivity requirements. In each scenario, emphasis will be placed on the different strategy employed compared to crosslinked-fluid designs, and the mistakes or misunderstandings that are frequently made will be highlighted.
Where appropriate, laboratory testing, field measurements, reference material, and other resources are presented to support the observations made by the authors. This paper will serve as a resource to any engineer or technician who is designing/pumping slickwater fracs, or who is considering this technology for potential application. By applying the concepts presented in this paper, engineers will be able to appropriately evaluate the potential benefits of using this technique in their completions, as well as draw on the experiences of others to take full advantage of this technology.
Dynamic Pore-Network Simulator for Modeling Buoyancy-Driven Migration During Depressurization of Oil-Saturated Systems
Authors: Ezeuko C.C.. C. , McDougall S.R.. R. , Bondino I.. , Hamon G.. 
Published: August 2010

Summary
A number of vertically oriented heavy- and light-oil-depletion experiments have been conducted in recent years in an attempt to investigate the effect of gravitational forces on gas evolution during solution-gas drive. Although some experimental results indirectly suggest the occurrence of gas migration during these tests (especially at slow depletion rates), a major limitation of such an interpretation is the difficulty in visualizing the process in reservoir-rock samples. In contrast, experimental observations using transparent glass models have proved invaluable in this context and provide a sound physical basis for modeling gravitational gas migration in gas/oil systems. However, the experimental observations often exhibit somewhat contradictory trends—some studies showing dispersed gas migration, while others describe fingered, channelized flow—and, to date, there appears to have been little systematic effort toward modeling the wide range of behaviors seen in or inferred from laboratory tests.
To this end, we present a new pore-network simulator that is capable of modeling the time-dependent migration of growing gas structures. Multiple pore-filling events are modeled dynamically with interface tracking allowing the full range of migratory behaviors to be reproduced, including braided migration (i.e., discontinuous flow of gas through narrow channels) and discontinuous dispersed flow. Simulation results are compared with experiments and are found to be in excellent agreement. Moreover, simulation results clearly show that a number of network and fluid parameters interact in a rather complex manner and, as a consequence, the competition between capillarity and buoyancy produces different gas-evolution patterns during pressure depletion. The implications of evolution regime on recovery from gas/oil systems undergoing depressurization are discussed extensively.
Effects of Friction on Post-Buckling Behavior and Axial Load Transfer in a Horizontal Well
Authors: Gao Guohua , Miska Stefan 
Published: August 2010

Summary
In this paper, the buckling equation and natural boundary conditions are derived with the aid of calculus of variations. The natural and geometric boundary conditions are used to determine the proper solution that represents the post-buckling configuration. Effects of friction and boundary conditions on the critical load of helical buckling are investigated. Theoretical results show that the effect of boundary conditions on helical buckling becomes negligible for a long pipe with dimensionless length greater than 5π Velocity analysis shows that lateral friction becomes dominant at the instant of buckling initiation. Thus, friction can increase the critical load of helical buckling significantly. However, once buckling is initiated, axial velocity becomes dominant again and lateral friction becomes negligible for post-buckling behavior and axial-load-transfer analysis. Consequently, it is possible to seek an analytical solution for the buckling equation. Analytical solutions for both sinusoidal and helical post-buckling configurations are derived, and a practical procedure for modeling of axial load transfer is proposed. To verify the proposed model and analytical results, the authors also conducted experimental studies. Experimental results support the proposed solutions.
Transport of CO2-Foaming Agents During CO2-Foam Processes in Fractured Chalk Rock
Authors: Zuta John , Fjelde Ingebret 
Published: August 2010

Summary
The coinjection of carbon dioxide (CO2) and a CO2-foaming agent to form stable CO2 foam has been found to improve the sweep efficiency during CO2-foam processes in carbonate reservoirs. However, only a few studies of CO2-foam transport in fractured rock have been reported. In fractured chalk reservoirs with low matrix permeability, the aqueous CO2-foaming-agent solution will flow mainly through the fractures. The total retention of the CO2-foaming agent in the reservoir will depend on how much of the matrix is contacted by the CO2-foaming-agent solution during the project period and, therefore, on its transport rate into the matrix.
This paper presents results from a series of static and flowthrough experiments carried out to investigate the transport and retention phenomena of CO2-foaming agents in fractured chalk models at 55°C. Fractured chalk models with 100% water-saturation and residual-oil saturation after waterflooding were used. In the static experiments, the fractured model was created by transferring core plugs with different diameters into steel cells with an annulus space around the plugs. The fracture volume was filled with foaming-agent solutions with different initial concentrations. The experiments were carried out in parallel, with liquid samples regularly taken out from the fracture above the plugs and analyzed for the foaming-agent concentration. The experiments were monitored until the concentrations in the fractures reached a plateau.
At specific and constant concentrations of the foaming agent in the fractures, the plugs were demounted and samples drilled out along the whole lengths of the plugs from the outer, middle, and center portions. These samples were analyzed for foaming-agent concentration to determine how much of it had penetrated the matrix.
Results indicate that the transport of the foaming-agent decreases toward the center of the plugs with 100% water-saturation and residual-oil saturation after waterflooding. Modeling of the static experiments using the Computer Modelling Group (CMG)'s commercial reservoir simulator STARS was also carried out to determine the transport rate for the foaming agent. A good history match between experimental and modeling results was obtained. In the flow-through experiments, the fractured model was created by drilling a concentric hole through the center of the plug. The hole, simulating an artificial fracture, was filled with glass beads of different dimensions. Fractured models with different effective permeability were flooded with equal volumes of the foaming-agent solution. Results show that the transport of CO2-foaming agent into the matrix is slower in the fractured models than in the homogeneous models with viscous flooding of the rock.
Streamline-Based Simulation of Non-Newtonian Polymer Flooding
Authors: AlSofi Abdulkareem M. , Blunt Martin J. 
Published: August 2010

SummaryCurrent commercial simulators for polymer flooding often make physical assumptions that are not consistent with available experimental data and pore-scale modeling predictions. This may lead to overly optimistic recovery predictions for shear-thinning polymers, while the potential advantages of reducing flow rate or using shearthickening agents are overlooked.We develop a streamline-based simulator that overcomes these limitations and demonstrate how it can be used to design polymerflooding projects. The simulator implements an iterative approach to solve the pressure field because the pressure depends on the aqueous-phase viscosity, which, in turn for non-Newtonian fluids, depends on shear stress and, hence, the pressure gradients. This is in contrast to the common approach in commercial simulators where this viscosity/pressure interdependence is ignored, leading to overestimation of sweep efficiency. Furthermore, in the simulator, non-Newtonian viscosities are defined to be cell-centered while current simulators use a face-centered approach, thereby overpredicting viscosities and the stability of the displacing fronts. In addition, we use a physically based rheological model where non-Newtonian viscosities in two-phase flow are taken at actual effective stresses instead of single-phase equivalents.To validate the simulator, we construct 1D analytical solutions for waterflooding with a non-Newtonian fluid. We then compare our results to those from commercial simulators. We discuss the significance of current assumptions to demonstrate the effect of non-Newtonian behavior on sweep efficiency and recovery.
Structural Surface Uncertainty Modeling and Updating Using the Ensemble Kalman Filter
Authors: Seiler A.. , Aanonsen S.I.. I. , Evensen G.. , Rivenæs J.C.. C. 
Published: August 2010

Summary
Although typically large uncertainties are associated with reservoir structure, the reservoir geometry is usually fixed to a single interpretation in history-matching workflows, and focus is on the estimation of geological properties such as facies location, porosity, and permeability fields. Structural uncertainties can have significant effects on the bulk reservoir volume, well planning, and predictions of future production.
In this paper, we consider an integrated reservoir-characterization workflow for structural-uncertainty assessment and continuous updating of the structural reservoir model by assimilation of production data. We address some of the challenges linked to structural-surface updating with the ensemble Kalman filter (EnKF).
An ensemble of reservoir models, expressing explicitly the uncertainty resulting from seismic interpretation and time-to-depth conversion, is created. The top and bottom reservoir-horizon uncertainties are considered as a parameter for assisted history matching and are updated by sequential assimilation of production data using the EnKF. To avoid modifications in the grid architecture and thus to ensure a fixed dimension of the state vector, an elastic-grid approach is proposed. The geometry of a base-case simulation grid is deformed to match the realizations of the top and bottom reservoir horizons.
The method is applied to a synthetic example, and promising results are obtained. The result is an ensemble of history-matched structural models with reduced and quantified uncertainty. The updated ensemble of structures provides a more reliable characterization of the reservoir architecture and a better estimate of the field oil in place.
Potential for Polymer Flooding Reservoirs with Viscous Oils
Authors: Seright R.S.. S. 
Published: August 2010

Summary
This paper examines the potential of polymer flooding to recover viscous oils, especially in reservoirs that preclude the application of thermal methods. A reconsideration of enhanced-oil-recovery (EOR) screening criteria revealed that higher oil prices, modest polymer prices, increased use of horizontal wells, and controlled injection above the formation parting pressure all help considerably to extend the applicability of polymer flooding in reservoirs with viscous oils. Fractional-flow calculations demonstrated that the high mobile-oil saturation, degree of heterogeneity, and relatively free potential for crossflow in our target North Slope reservoirs also promote the potential for polymer flooding. For existing EOR polymers, viscosity increases roughly with the square of polymer concentration—a fact that aids the economics for polymer flooding of viscous oils. A simple benefit analysis suggested that reduced injectivity may be a greater limitation for polymer flooding of viscous oils than the cost of chemicals. For practical conditions during polymer floods, the vertical sweep efficiency using shear-thinning fluids is not expected to be dramatically different from that for Newtonian or shear-thickening fluids. The overall viscosity (resistance factor) of the polymer solution is of far greater relevance than the rheology.
Equivalent Wellblock Radius for Partially Perforated Vertical Wells—Part I: Anisotropic Reservoirs With Uniform Grids
Authors: Dogru Ali H. 
Published: August 2010

Summary
The well index in a numerical reservoir simulator relates the flow rate to the difference between well flowing pressure and simulator gridblock pressure. The standard method for computing well index, Peaceman's formula (Peaceman 1978), requires an equivalent wellblock radius at which the gridblock pressure is equal to the pressure from an analytical solution for steady-state single-phase flow. Although Peaceman's formula is accurate for fully penetrating vertical wells, it fails to account for the effect of vertical flow in partially penetrating wells.
In this paper, we present a new analytical expression for the equivalent wellblock radius in a homogeneous, anisotropic reservoir with a uniform square grid around the well path. The new equation has the same structure as Peaceman's equation but adds one new parameter to account for partial penetration and for vertical flow. The new formula reduces to Peaceman's formula when the well is fully penetrating. Model simulation study showed that the new method reduced the error in the calculated flow rates from 30% to less than 1% at minimal cost.
A USD 100 Million "Rock": Bitumen in the Deepwater Gulf of Mexico
Authors: Han Gang , Osmond Jerry , Zambonini Michael 
Published: August 2010

Summary
Bitumen encounters in the deepwater Gulf of Mexico (GOM) are not unusual. In many cases, bitumen presence delayed or prevented reaching programmed total depth and adversely affected rig schedule and development planning. The cost from these events could be as high as USD 100 million. On the basis of a series of laboratory tests that investigate the effect of temperature, pressure, and drilling fluids on bitumen mechanical behaviors, this paper attempts to address four questions: (1) What is bitumen and what are its properties, especially at in-situ conditions (18,000-psi stress and 185°F temperature); (2) where is it found, in pore space or fracture; (3) what are the shapes of the in-situ accumulation; and (4) what drives it into the borehole? It has been found that the bitumen encountered at various depths may be significantly different. The bitumen adjacent to salt formation is likely to be stable and could accumulate in a large horizontal spread. The bitumen at the greater depth has to be close to vertical to survive in-situ stresses. For the horizontal bitumen spread, there is a potential to successfully drill through with a liner, and manipulating mud weight may also help. However, for the vertical-column bitumen, increasing mud weight may not be efficient, and sidetracking to avoid further encounter may be more practical. These findings are consistent with the drilling experience in the field and may help to develop a strategy to manage future bitumen encounters in the deepwater GOM.
Assessment of CO2 Storage in DF1-1 Gas Field South China Sea for a CCS Demonstration
Authors: Zhang Liang , Niu Baolun , Ren Shaoran , Zhang Yin , Yi Ping , Mi Honggang , Ma Yongxin 
Published: August 2010

Summary
DF1-1 gas field is located in the west of the South China Sea, which is associated with high concentration of CO2. Currently CO2 separated from the natural gas stream is emitted into the atmosphere. In this study, a demonstration project of CO2 capture and storage (CCS) is considered, proposing to inject CO2 separated on the platform back into the original gas reservoir. The CO2 storage site considered is a nearly abandoned gas block in the DF1-1 gas field, which was reassessed for the safety of CO2 storage. Membrane separation technique will be installed on the platform for the separation. CO2 is compressed at a super-critical state and injected through a single well (used to be a producer) into the gas formation. A new platform auxiliary to the main platform will be built to accommodate the compressor and separation equipment. CO2 will be injected at the rate of 0.14 million Sm ³ for 10 years over the field development period. At the end of the project, the pressure of the CO2 storage reservoir will be increased to its original pressure. Scoping economic analysis shows that the CO2 storage cost of the project is around US$20 per ton CO2, in which the auxiliary platform is the main cost factor.
Analysis of the Storage Capacity for CO2 Sequestration of a Depleted Gas Condensate Reservoir and a Saline Aquifer
Authors: Barrufet Maria A. , Bacquet Alexandre , Falcone Gioia 
Published: August 2010

Summary
Among the three types of geological CO2 sequestration (mature oil and gas fields, unminable coalbeds and deep saline formations), depleted gas condensate reservoirs are particularly interesting. First, because of the high-compressibility of gas, these reservoirs have larger storage capacity than oil reservoirs or aquifers. Second, the condensate that has dropped out from the gas phase during natural depletion will re-vaporize because of re-pressurization of the reservoir and by miscibility with the injected CO2. This condensate can be recovered from producing wells and leaves more pore volume for available storage of CO2.
The objective of this study is to investigate the CO2 storage capacity in different formation types, for different levels of CO2 purity and different injection schedules. To this aim, we analyzed the injection of a CO2-based stream into a depleted gas condensate reservoir and into a saline aquifer using a compositional reservoir simulation model.
The dynamics of the reservoir impose a minimum period of injection that is required in order for the storage scheme to benefit from 100% of the reservoir storage capacity. Hence, over and above a certain CO2 injection rate, it becomes meaningless to invest in bigger compressors to increase this rate to reduce the time of injection.
When the CO2 stream contains impurities, such as N2 or methane, the storage capacity of the reservoir decreases proportionally to the impure stream's compressibility factor and its concentration of impurities. This finding suggests that an economic optimum between the costs of separation, compression and injection can be determined.
Finally, the mass of CO2 sequestrated per pore volume in the equivalent aquifer model is approximately 13 times lower that of the depleted gas condensate reservoir model. This confirms that, because of their low overall compressibility, aquifers offer a far lower ratio of CO2 stored per pore volume than depleted gas condensate reservoirs. However, aquifers tend to have a far larger extent, which often compensates somewhat for this lower ratio and therefore provides storage for significant volumes of CO2.
A Practical Way Out of the GHG Emissions Problem
Authors: Gupta Subodh C. 
Published: August 2010

Summary
Ever-increasing global demand for energy, and the world's supply predominantly being fossil-based, implies continued growth of emissions. Efficiency improvements and employment of non-fossil energy will definitely help mitigate the problem, but it is generally recognized that "pure carbon offsets" will have to play a major role if the problem has to be combated in a timely fashion. Discussion on pure offsets employing geological storage [namely, carbon capture and storage (CCS)] is advancing rapidly. However, major issues with this approach are its high cost and the long-term post operation liability. The author has previously proposed an alternate approach of pure offset-charcoal sequestration (CS), which essentially employs conversion of dead plant material into inert solid carbon. CS promises to be both less expensive and a better option as far as the operational and post-operation liability is concerned. Among the numerous advantages of the charcoal approach is its easier reversibility, both in terms of liability and costs. Although implementation of this approach at a scale where it can make a significant impact on global CO2 concentration needs to be preceded by a substantial information dissemination and public preparedness, a practical way to introduce it is through using municipal solid waste (MSW) as the feed biomass for CS. This will not only allow time for public acceptance to evolve, and evaluation of potential associated risks, but immediately help mitigate the growing problem of space requirement for waste landfills, waste transport costs and emission of methane from the rotting municipal waste associated with the continued urban sprawl. This paper, aside from describing the carbon sequestration from waste (CSW) method, estimates the cost of carbon offset with this and other competing approaches, such as the use of MSW for conversion to bio-alcohol and for power generation. It highlights the difference between carbon credits associated with mobile energy needs (pure offsets) and stationary energy needs and makes a case for price duality of carbon credits. It also compares the global potential of CSW in combating the greenhouse gas (GHG) problem, making more than two Socolow wedges with use of charcoal for soil enhancement and other purposes amounting to less than 0.04 such wedges. In this work, the cost of carbon offset with CSW is estimated to be as low as CAD 2.6/tonne CO2 equivalent (CO2e).