bluuebunny/crossref_metadata_2025_split huggingface dataset:
Casing- and Screen-Failure Analysis in Highly Compacting Sandstone Fields
Authors: Furui K.. , Fuh G.F.. F. , Morita N.. 
Published: November 2012

Summary
Many casing- and screen-damage incidents have been reported in deepwater oil and gas fields in the Gulf of Mexico and other locations around the world. We reviewed historical casing/well failure events in a highly compacting sandstone field and performed a comprehensive geomechanics analysis of various casing-damage mechanisms (tension, axial compression, shear, and bending) related to large reservoir depletion. Among five wells that experienced mechanical well-integrity issues, two of them showed casing restrictions in the caprock at intervals approximately 1,000- to 1,600-ft true vertical depth (TVD) above the top of the depleting (main) reservoir. A multi-finger caliper log obtained from one of the wells indicates that the overburden casing failure occurred at a highly geopressured, thin sand layer approximately 1,100-ft TVD above the top of the compacting reservoir. The remaining casing-failure events occurred near (less than 200-ft TVD) or within the compacting reservoir interval.
A 3D nonlinear finite-element-method (FEM) model has been developed for simulating stress changes in the overburden and the reservoir intervals and evaluating the effect of lithological anomalies on casing stability. The simulation results indicate that large tensile and shear strains could develop within a thin, weak-strength layer in the overburden and at the interface between cap-rock and the depleting reservoir interval. Casing damage by bending/shear could also occur at these thin-layered sands saturated with overpressured gas.
In the reservoir interval, shear stresses acting on the screens can be relatively high because of the difference of the movements between the internal base pipe and the external shroud and gravel. Screen failure may also occur at the welded points. If casing failure occurs in the unperforated sand layer just above the compacting reservoir, it induces localized high-velocity flow on the upper part of the screen, causing potential screen erosion. Casing failure caused by fault slip near the reservoir occurs only if a fault has sealing capability while maintaining a large pressure differential across the fault plane.
The numerical-analysis results presented in this work help engineers understand possible casing- and screen-deformation and -failure mechanisms experienced in highly compacting sandstone fields. On the basis of the study findings, we also present some completion-design guidelines to avoid or mitigate compaction-induced casing damage in both the overburden and reservoir intervals.
An Alternative to Streamlines for Flow Diagnostics on Structured and Unstructured Grids
Authors: Shahvali M.. , Mallison B.. , Wei K.. , Gross H.. 
Published: November 2012

SummaryStreamline-based methods can be used as effective post-processing tools for assessing flow patterns and well allocation factors in reservoir simulation. This type of diagnostic information can be useful for a number of applications, including visualization, model ranking, upscaling validation, and optimization of well placement or injection allocation. In this paper, we investigate finite-volume methods as an alternative to streamlines for obtaining flow diagnostic information. Given a computed flux field, we solve the stationary transport equations for tracer and time of flight by use of either single-point upstream (SPU) weighting or a truly multidimensional upstream (MDU) weighting scheme. We use tracer solutions to partition the reservoir into volumes associated with injector/producer pairs and to calculate fluxes (well allocation factors) associated with each volume. The heterogeneity of the reservoir is assessed with time of flight to construct flow-capacity/storage-capacity (F-vs.-Φ) diagrams that can be used to estimate sweep efficiency. We compare the results of our approach with streamline-based calculations for several numerical examples, and we demonstrate that finite-volume methods are a viable alternative. The primary advantages of finite-volume methods are the applicability to unstructured grids and the ease of implementation for general-purpose simulation formulations. The main disadvantage is numerical diffusion, but we show that a MDU weighting scheme is able to reduce these errors.
Computation of Productivity Index With Capillary Pressure Included and Its Application in Interpreting Production Data From Low-Permeability Oil Reservoirs
Authors: Li Kewen , Chen Zengwei 
Published: November 2012

SummaryCapillary pressure might be ignored in high-permeability rocks, but it cannot be neglected in low-permeability rocks. To study the effect of capillary pressure on production performance in low-permeability oil wells or reservoirs, the formulas for calculating water cut and dimensionless total and oil productivity indices (PIs) were derived by considering capillary pressure. PI and water-cut data were computed using the new models with capillary pressure included. The results proved that PI increases with water cut in high-permeability rocks but decreases with the increase in water cut within a specific range in low-permeability rocks. Waterflooding experiments were then conducted in core samples with low and high permeabilities. The experimental waterflooding data demonstrated the same relationship between PI and water cut that was proved in the new PI model. Finally, the PI data were calculated using production data from oil wells, and the results were compared with the experimental data of the PI determined from coreflooding tests. The curves of PI vs. water cut, obtained from the production data of oil producers, were consistent with those inferred from waterflooding data in core samples. Note that the core plugs were sampled from the same oil wells. The new PI model was used to explain the difference in production performance between high- and low-permeability oil wells.
An Investigation Into Optimal Solvent Use and the Nature of Vapor/Liquid Interface in Solvent-Aided SAGD Process With a Semianalytical Approach
Authors: Gupta Subodh , Gittins Simon 
Published: November 2012

Summary
The steam-assisted gravity-drainage (SAGD) process is used widely to recover heavy oil and bitumen from formations in which no other recovery method has proved to be economical. It is an energy-intensive process, and because of economic and environmental reasons, solvents as additives to the injected steam are being explored currently to reduce the energy and emissions intensity of SAGD. The solvent-aided process (SAP), tested in the field and described in the literature, is one such attempt.
In the SAP, a small amount of hydrocarbon solvent is introduced as an additive to the injected steam. Thus, the viscosity of the oil is also reduced because of solvent dilution in addition to heating. The SAP can improve the energy efficiency of SAGD significantly, thus reducing the heat requirement, as shown in field trials discussed elsewhere. However, on the use of the right amount of solvent that can result in best overall performance, there is very little discussion in the literature. Because of the high cost of such solvents, there is incentive to optimize their use in SAGD. Recently, various authors have attempted to address the subject with, for example, arbitrary time-dependent schemes of solvent injections, assessing their impact on results or by treating the internal reservoir dynamics as a black box and using optimization methods, such as genetic algorithms (GAs), to estimate the optimal amount of solvent. While these approaches orient us to the problem in a context-specific manner, it is believed a generalized treatment to estimate optimal use of solvent requires a mechanism-based understanding.
The approach presented in this paper is aimed at estimating the optimal solvent in the context of SAGD. It combines the existing Butler's oil-drainage analytical models (Butler 1985, 1988, 1994) for SAGD and vapor extraction (VAPEX), which deal with heating effect and solvent-dilution effect one at a time, into one. Then, it calculates the time-dependent steam rates to maintain the predicted oil rates in conjuction with solvent rates and, thus, estimates the solvent/steam ratio (SSR) and the steam/oil ratio (SOR). The results are discussed for a few light-alkane solvents. In the process of this exercise, it is discovered that to obtain reasonable SSR and SOR, a significant amount of oil has to drain from a diffuse layer, which has a varying temperature, solvent concentration, and gas saturation (from maximaum gas saturation at the injection end to zero at the vapor/liquid interface).
Stability Analysis of Pipe With Connectors in Horizontal Wells
Authors: Gao Guohua , Di Qinfeng , Miska Stefan , Wang Wenchang 
Published: November 2012

Summary
Except for coiled tubing, most tubular goods used for downhole operations (such as drillpipe and sucker rod) have connectors. Because a connector and the pipe body have different outer radii, the deformation and buckling behavior of a pipe with connectors constrained in a wellbore is much more complicated. However, most buckling models were established by neglecting the existence and effects of connectors.
In this paper, buckling equations of a pipe with connectors in horizontal wells were derived with application of elastic-beam theory. The axis of an unbuckled pipe is a 2D curve in the vertical plane and has three configurations—no contact, point contact, and wrap contact. We derived the two critical distances between connectors, Lc1 and Lc2, beyond which a pipe changes its configuration from one to another. The authors proposed an algorithm to determine the critical force (Fcrs) of buckling by numerically solving the buckling equations using the fourth-order Ronge-Kuta method.
Both the distance between two adjacent connectors (Lc) and the radius difference between a connector and the pipe body (∆rc) have significant impact on the critical force, in addition to net clearance between a pipe and wellbore (r0), bending stiffness (EI), and weight per unit length (w) of pipe. When Lc is small, radial deflection is negligible. Fcrs increases as ∆rc increases. However, when Lc is close to Lc1, effects of radial displacement become significant, and Fcrs decreases dramatically as ∆rc increases. Fcrs decreases as Lc increases when Lc Lc1, and it reaches its minimum at Lc=Lc1. When Lc &gt; Lc1, Fcrs fluctuates as Lc increases. Some curves of Lc1, Lc2, and Fcrs, all in dimensionless forms, were calculated and presented in this paper for practical applications.
Our numerical results show that the critical force may reduce by 20 to 60% for commonly used drillpipes and sucker rods with centralizers, which indicates that a pipe string designed without considering the effects of connectors may be risky. The results presented in this paper may provide some practical guidance for optimal design of centralizers for sucker-rod strings, or may avoid some risks because of improper design of drillpipe strings.
Effect of Discontinuous Microfractures on Ultratight Matrix Permeability of a Dual-Porosity Medium
Authors: Apaydin O.G.. G. , Ozkan E.. , Raghavan R.. 
Published: November 2012

Summary
This paper examines the effects of matrix microfractures on the effective matrix permeability of a dual-porosity medium. An analytical model is presented, with composite matrix blocks consisting of a core in which unconnected microfractures do not contribute considerably to flow capacity and a surface layer where the microfractures connected to the matrix surface (resembling wormholes) cause a stimulation effect. The composite matrix flow is coupled with the flow in a network of macrofractures, as in the conventional dual-porosity idealizations of fractured media. This paper investigates the effect of matrix-surface stimulation and demonstrates improved fluid transfer from the matrix medium to the fracture network because of matrix microfractures. It is shown that matrix microfractures accelerate production by providing earlier and more-effective contribution of the matrix into flow rates. This contribution of the matrix because of microfractures cannot be simulated by enhanced matrix permeability because the microfractured surface layer of the matrix causes flow characteristics different from those of a homogeneous (unfractured) matrix. The effect of the microfractured surface layer of the matrix cannot be taken into account by a triple-porosity model used to incorporate two sets of connected natural fractures or connected fractures and vugs.
Theoretical and Experimental Modeling of Residual Gel Filter-Cake Displacement in Propped Fractures
Authors: Ouyang L.. , Yango T.. , Zhu D.. , Hill A. D. 
Published: November 2012

Summary
Fracture fluid damage caused by residual polymer gel in propped fractures results in low fracture conductivity and short effective fracture length, sometimes severely reducing the productivity of a hydraulically fractured well. The residual gels are concentrated in the filter cakes built on the fracture walls and have much higher polymer concentration than the original gel. The residual gel exhibits a higher yield stress and is difficult to remove after fracture closure.
In this work we studied polymer gel behavior theoretically and experimentally in hydraulic fracturing. We developed a model to describe the flow behavior of residual polymer gel being displaced by gas in parallel plates. We developed analytical models for gas/ liquid two-phase stratified flow of Newtonian gas and non-Newtonian residual gel to investigate gel cleanup under different conditions. The concentrated gel in the filter cake was modeled as a Herschel-Bulkley fluid, a shear-thinning fluid following a power law relationship, but also having a yield stress.
The model developed shows that three flow regimes may exist in a slot, depending on the gas flow rate and the filter-cake yield stress. At low gas velocities, the filter cake will be completely immobile. At higher gas velocity, the shear at the fracture wall exceeds the yield stress of the filter cake, and the gel is mobile, but with a plug flow region of constant velocity near the gas/gel interface. Finally, at high enough gas velocity, a fully developed velocity field in the gel is created.
The parameters for the gel displacement model were evaluated by experiments. We examined the filter-cake formation by pumping the fracture fluid through a conductivity cell, allowing leakoff to build the filter cake, measuring the cake thickness, and flowing gas through the cell to simulate the cleanup process. The results show that the yield stress of the residual gel plays a critical role in gel cleanup.
Quantification of Drillstring-Integrity-Failure Risk Using Real-Time Vibration Measurements
Authors: Arevalo Yezid , Fernandes Ashley 
Published: November 2012

Summary
Vibration measurements have traditionally targeted the improvement of downhole-tool reliability. This paper targets the effects of vibration on the complete drillstring. Failures associated with drillstring vibration continue to happen despite the sophistication of today's measurements. These failures represent a very significant amount of lost time, which we target to improve.
The industry has a very limited database for evaluating indices to manage or quantify risks of vibration to the complete drillstring. This fact makes the use of the methods in the field heavily depend on the past experience of the drillers and on the rig types. Operators are faced with an unknown quantification of the risk severity when attempting to mitigate vibration. By quantifying the risk, this work demonstrates how the prevention of incidents can be achieved. These incidents include but are not limited to, twistoffs, backoffs, and bottomhole-assembly (BHA) component failures.
The proposed solution is based on real-time measurements of drillstring vibration to estimate an ongoing drillstring-integrity risk, which is used as a guideline to improve decisions while drilling the well. This solution has been developed through use of advanced vibration sensors to discriminate between different types of vibration. This was critical to estimating realistic cumulative damage to the drillstring, which is highly dependent on the type of vibration suffered by the assembly and the onset of vibration-mode coupling.
This paper shows that approximately 80% of drillstring-integrity failures analyzed can be identified and prevented through use of the proposed risk-quantification solution. This result has been obtained despite unknown fatigue or wear of drillstring components before a run, and vibration sensors were located at a single position in the drillstring. This indicates that the primary contributor to drillstring failures is the drilling conditions for any given run.
Effect of Methane Co-Injection in SAGD--Analytical and Simulation Study
Authors: Sharma Jyotsna , Moore R. Gordon , Mehta Sudarshan A. 
Published: November 2012

Summary
Steam-assisted gravity drainage (SAGD) is a commercially viable recovery method for oil sands of Athabasca used where other methods have been unsuccessful. In one variation of SAGD, a small amount of a noncondensable gas is added to the injected steam to maintain pressure in the chamber while using the energy in place, reducing steam consumption and providing thermal insulation from overburden heat losses. The role of gas during steam-gas co-injection processes, in terms of its effects on chamber development, bitumen flow rates, and heat losses, is not fully understood, and therefore is the main focus of this work.
A new analytical model for gas injection in SAGD is derived, taking into account the three-phase flow of gas, oil, and water in the reservoir. The analytical theory is used to predict the fluid flow rates as well as phase mobility, relative permeability, and saturation profiles in the mobile oil region. The theoretical results are replicated by fine-grid numerical simulations. Methane was used as the noncondensable gas for the purpose of this study because it is the main solution gas in most reservoirs. It is, however, believed that the findings of this study are equally applicable to other noncondensable gases such as nitrogen, air, helium, and others. Fine-grid numerical simulations were performed to gain a visual understanding of gas distribution in a SAGD chamber and its effect on in-situ steam quality, overburden heat losses, phase saturations, and fluid-flow rates. The simulation results support the predictions of the mathematical theory.
The results of the analytical and numerical study reveal that methane co-injection with steam is in general unfavorable in a SAGD operation. The injected methane tends to accumulate at the steam condensation front, which lowers the heat transfer rate of steam to the adjacent oil, resulting in lower oil production rates and slower growth of the chamber.
Accurate Modeling of Faults by Multipoint, Mimetic, and Mixed Methods
Authors: Nilsen Halvor M. , Lie K.-A.. -A. , Natvig Jostein R. 
Published: November 2012

Summary
The predominant way of modeling faults in industry-standard flow simulators is to introduce so-called transmissibility multipliers in the underlying two-point discretization. Although this approach provides adequate accuracy in many practical cases, two-point discretizations are only consistent for K-orthogonal grids and may introduce significant discretization errors for grids that severely depart from being K-orthogonal. Such grid-distortion errors can be avoided by lateral or vertical stair-stepping of deviated faults at the expense of errors in the geometrical fault description. In other words, modelers have the choice of either making (geometrical) errors by adapting faults to a grid that is almost K-orthogonal, or introducing discretization errors because of the lack of K-orthogonality if the grid is adapted to deviated faults.
We propose a method for accurate description of faults in solvers based on a hybridized mixed or mimetic discretization, which also includes the MPFA-O method. The key idea is to represent faults as internal boundaries and calculate fault transmissibilities directly instead of using multipliers to modify grid-dependent transmissibilities. The resulting method is geology-driven and consistent for cells with planar surfaces and thereby avoids the grid errors inherent in the two-point method. We also propose a method to translate fault transmissibility multipliers into fault transmissibilities. This makes our method readily applicable to reservoir models that contain fault multipliers.
A Comprehensive Theoretical and Experimental Study on Fluid Displacement for Oilwell-Cementing Operations
Authors: Aranha Pedro Esteves , de Miranda Cristiane Richard , Cardoso Walter F. , Campos Gilson , Martins André Leibsohn , Gomes Frederico C. , de Araujo Simone Bochner , Carvalho Marcio S. 
Published: November 2012

Summary
Displacing fluids in downhole conditions and for long distances is a complex task, affecting several steps of well construction. Cementing gains relevance the moment that fluid contamination compromises cement-sheath integrity and consequently zonal isolation.
Density and rheology design for all the fluids involved is essential to achieve operational success. Properties hierarchy and preferred flow regimes have been empirically defined and tend to provide reasonable generic results. Challenging operations, including ultradeep waters and their narrow operational-window scenario, require further knowledge of the physics involved to prevent undesirable events.
This paper presents the in-house development of software for annular miscible fluid displacement that analyzes fluid displacement in typical vertical and directional offshore wells, for Newtonian and non-Newtonian liquids and laminar- and turbulent-flow regimes. The formulation proposed provides accurate results for a wide range of input parameters, including the cases in which the ratio of the inner radious to the outer radius of the annulus is small.
The computational work is validated by unique results obtained from an experimental test rig where detailed displacement tests were conducted. Contamination degrees were measured after the displacement of a sequence of fluids through 1192 m of vertical well. Effect of fluid-density and rheology hierarchy, flow regimes, and displacement concepts was investigated. The results provide relevant information for the industry and fundamental understanding on displacement of Newtonian and non-Newtonian liquids through annular sections.