bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of Numerical Simulations and Laboratory Waterfloods in Fractured Carbonates
Authors: Haugen Åsmund , Fernø Martin A. , Graue Arne 
Published: December 2007

Abstract
Recovery mechanisms in fractured carbonate rocks have been investigated by comparing laboratory experiments with numerical simulations. The experimental data include waterfloods in blocks of carbonate rock with 2D, in-situ fluid saturation of the advancing waterfronts. The waterfloods were initially performed on the whole block, and then repeated on the same block with a fracture network containing both closed and open fractures to isolate the effect from fractures.
The primary objective for the experiments was to investigate how the presence of fractures altered the dynamics of the propagating waterfront. A numerical, grid based model of the block was created and a sensitivity study of the representation of fractures was carried out. Especially the impact of the degree of capillary contact over fractures was studied. Matrix capillary pressure and relative permeability curves were determined by history matching both average oil production and the in-situ fluid saturation profiles from the unfractured block experiment. These were in turn used as input for the matrix properties in the fractured block simulations.
The results show how the degree of capillary contact between matrix blocks controlled fluid saturation development and influenced the waterflood oil recovery in fractured limestone. Sensitivity studies on the degree of capillary contact over fractures showed this to be the most significant parameter for the frontal propagation during waterfloods. Numerical simulations together with experimental data gave increased understanding of the waterflood oil recovery mechanisms in fractured carbonate rock.
Value of Information in the Oil and Gas Industry: Past, Present, and Future
Authors: Bratvold Reidar B. , Bickel J. Eric , Lohne Hans Petter 
Published: December 2007

Abstract
An important task that petroleum engineers and geoscientists undertake is to produce decision-relevant information. Some of the most important decisions we make concern what type and what quality of information to produce. When decisions are fraught with geologic and market uncertainties, this information gathering may take the form of seismic surveys, core and well test analyses, reservoir simulations, market analyses, price forecasts, etc., on which the industry spends billions of dollars each year. Yet, considerably less time and resources are expended on assessing the profitability or value of this information. Why is that?
This paper addresses how to make value-of-information (VOI) analysis more accessible and useful, by discussing its past, present, and future. Based on a survey of SPE publications, we provide an overview of the use of VOI in the oil and gas industry, with a focus on how the analysis was carried out and for which types of decisions VOI analysis has been performed. We highlight areas where VOI methods have been used successfully and identify important challenges.
We then identify and discuss the possible causes for the limited use of VOI methods and suggest ways to increase the use of this powerful analysis tool.
Cement Sheath Evaluation in Nonconventional Environment—Case History
Authors: De Paula J. L. , Rodrigues V. F. , Vicente R. 
Published: December 2007

Abstract
Sonic and ultrasonic tools have been widely used for cement sheath evaluation along the last decades. The evaluation main goal is the definition of the presence of cement in the annulus and its ability of promoting hydraulic isolation among different permeable zones, regardless of its density, compressive strength or even quality of the slurry. The challenges interpreting those logs are enormous because the influence of many variables in the acoustic signal. The difficulties increase dramatically if the well configuration is not conventional. In those cases, huge mistakes can occur requiring from the interpreter experience, understanding of the tools and acoustic principles, and detailed information about the well, casing, cement, and so on. The paper describes in detail three well documented cases histories where non-conventional conditions in the wellbore prevailed and required extreme care and experience to obtain the correct log interpretation. The first case reports the evaluation of an annulus with cement between two concentric casings; the disturbances caused by reflections from the second interface in the CBL signal are discussed and recommendations presented to bypass this obstacle. In the second case, the challenges to evaluate the cement sheath in a fiber glass casing are presented; usually in this case, the first signals arriving at the receiver do not come from the casing. Finally, the last case history describes the difficulties to come up with the right evaluation logging a liner cemented with lightweight slurry. For all cases, guidelines and recommendations are suggested to avoid misinterpretations and assure correct decisions about cement sheath evaluation.
Evaluating Crystallization Risks in Liquefied-Natural-Gas (LNG) Production
Authors: Ayala H. Luis F. , Fernández L. Juan Emilio 
Published: December 2007

Abstract
Liquefied Natural Gas (LNG) is anticipated to dominate world energy trade and fill the gap between production and energy demands in few years, especially in the US. LNG is the liquefied version of dry natural gases at ultralow temperatures (about -160 C or -260 F at atmospheric pressure), which aims at minimizing storage volume requirements needed for overseas transportation. Within this context, it is clear that technology must continue to be developed in order to optimize the thermodynamic processes involved in the compression, liquefaction and re-vaporization of LNG and associated operational challenges. One key challenge during the production of LNG is that the presence of trace amounts of heavy components in the gas feed composition is known to induce the precipitation of a solid phase during the cooling process, which presents the risk of equipment plugging and associated hazards. However, there are very few general thermodynamic tools available for the prediction of solid-liquid equilibrium for very low temperature conditions (&lt; -200 F). In this study, available thermodynamic predictive tools are evaluated for the determination of LNG crystallization conditions. Previously presented crystallization prediction models are examined and potential pitfalls identified. The results from this study are expected to provide a better understanding of the thermodynamics of Liquefied Natural Gas (LNG) processes and provide a framework for subsequent work in the analysis of LNG refrigeration and liquefaction processes—which are typically considered the key elements of any LNG project.
A Phenomenological Approach to Analysis of Barite Sag in Drilling Muds
Authors: Paslay P. R. , Sathuvalli U. B. , Payne M. L. 
Published: December 2007

Abstract
Barite sag is the undesirable fluctuation in drilling mud density that occurs due to downhole settling of the weighting agent. Barite sag causes problems such as differential sticking, lost circulation, and can lead to serious well control events.
This paper describes a fundamental theoretical effort to describe dynamic sag in drilling muds by considering the behavior of a system of particles in a non-Newtonian Bingham fluid. A continuum mechanics based model of dynamic sag in an inclined annulus is presented in terms of the fluid and particle properties. The results of the model are used to understand the influence of typical oilfield variables in precipitating sag. The analysis presented in this paper represents one of the first modeling/computational efforts to predict sag using phenomenological models (rather than empirical correlations or observational rules of thumb).
Success of SAG Foam Processes in Heterogeneous Reservoirs
Authors: Renkema W. J. , Rossen W. R. 
Published: December 2007

Abstract
In principle, miscible gas injection can displace nearly all of the oil from the portions of a reservoir swept by gas. However, reservoir heterogeneity, low gas density and high gas mobility reduce sweep efficiency and drastically decrease recovery. Fortunately, the use of foam can reduce gas mobility and the effect of heterogeneity and therefore increase sweep efficiency. Based on the work of Shan and Rossen, an optimal design strategy is proposed here for surfactant-alternating-gas (SAG) foam processes and tested in a homogeneous reservoir and in two layered rectangular reservoirs. Fractional-flow theory, Stone's and Jenkins' model for gravity segregation, and an idealized model developed by Shan and Rossen are used design the process and interpret the results.
In the homogeneous reservoir, fixed-pressure SAG processes result in better sweep efficiency than fixed-rate SAG processes. A one-cycle SAG process, where one big slug of surfactant is followed by one big slug of gas, gives better sweep than multiple-cycle SAG processes; sweep efficiency is higher and the process proceeds faster. Adsorption can be dealt with by adjusting the size of the first surfactant slug. The optimal SAG process gives much better sweep efficiency than a WAG process without foam. Simulations reveal factors not accounted for in Shan and Rossen's idealized model for a single-cycle SAG process; nonetheless the model accurately predicts the rate of advance of the foam front at the top of the reservoir and qualitatively predicts the shape of the foam front. A ten-cycle SAG process performs somewhat better than predicted by Stone's model for continuous injection.
In heterogeneous reservoirs, a maximum-fixed-pressure SAG process also gives best results. The surfactant slug sized for a homogeneous reservoir is much too large in this case, however, and much of the surfactant wasted. Again, a one-cycle process SAG performs better than multiple, smaller cycles, but sweep is not as good as in a homogeneous reservoir. A high-permeability layer at the top of the reservoir leads to better sweep efficiency at gas breakthrough than when the reservoir has a low-permeability layer at the top. A low-permeability layer at the top allows early gas breakthrough once gas in high-permeability layers below it reaches the edge of the surfactant bank above. Compared to WAG processes, the optimal SAG process shows much better sweep efficiency.
Straining of Fine Particles in Gaps in Porous Media
Authors: Rodriguez Elena , Bryant Steven L. 
Published: December 2007

Abstract
This paper presents an extension of the theory of retention of fine particles in formations. The mechanism of interest is straining, which depends only on the shape and distribution of constrictions in pore space. To quantify the geometry of constrictions, we used computer-generated dense random packs of spheres as model porous media. A characteristic feature of dense packings is a pair of neighboring grains that do not quite touch. We refer to the void space between pairs of such spheres as gaps. Gaps are smaller than pore throats, which are the void space between three spheres. Geometric analysis of throats and gaps was combined with a new methodology to compute flow rates in gaps. The results were input to an existent straining theory to study the dependence of straining rate on fines size. Only the flow of a single fluid phase is considered.
Numerous experiments show evidence of straining of particles smaller than the smallest pore throat in the column, under conditions that exclude the possibility of filtration. The simplest test of a theory is whether it can account for these anomalous observations. Existing theories that consider pore throats as the constrictions cannot explain these observations, whereas including gaps in the set of pore space constrictions correctly predicts the observations.
A more stringent test of straining theory is to predict the dependence of particle straining rate in a column flow experiment upon the size of the particles. Classical pore-throat-based theories make the physically reasonable assumption that once a particle enters a small constriction, it is guaranteed to be trapped there. Thus the probability of trapping is proportional to the flow rate through the constriction. These theories significantly overestimate the influence of particle size for small particles. We argue that the probability of particle retention in a gap need not be 100% even if the particle enters the gap. The particle may rebound from the grain(s) rather than become wedged in the gap. If this happens, the particle may eventually be swept around the gap.
We therefore extend the theory by postulating retention probability to be proportional to flow rate through the gap and inversely proportional to the momentum or to the kinetic energy of the carrier fluid. The extensions bracket the scaling behavior reported in experiments.
Our analysis of particle straining in gaps explained a longstanding set of observations for which previous theories could not account. These results suggest that a more detailed study of particle/grain collisions is needed to explain fully the straining rates observed in experiments.
Learning Curve Benefits Resulting from the Use of a Unique BHA Directional Behaviour Drilling Performances Post-Analysis
Authors: Studer Regis , Simon Christophe , Genevois Jean-Michel , Menand Stéphane 
Published: December 2007

Abstract
With the current market's high prices for drilling units and sophisticated directional and formation assessment services, low systems reliability or poor directional performance in the execution of complex wells (ERD, HPHT, Deep Water applications) can spell costly Non Productive Time (NPT) for operators. Over the past two decades, many Bottom Hole Assembly (BHA) models have been developed to address the directional performance issue, but their application in an operational environment has generally failed for lack of strong associated BHA analysis methodologies.
This paper presents a unique automated methodology for Post Analysis of BHA directional behaviour. It is based on modern 3D analytical models, combining BHA, BIT and formation effects with highly flexible data management. Implemented in user-friendly BHA management software, it can be used to define a BHA run segmentation and to determine the influence of the BHA settings in particular geological formation blocks. The Post Analysis clearly displays the final results of the BHA (objectives and performances versus prediction window), highlighting any problematic intervals drilled.
Already, the methodology has solved challenging directional performances issues, generating significant savings and optimising the learning curve process. The field applications referred to in the paper have demonstrated that, without a proper methodology, a model offers little added value.
The examples discussed here from Total E&P affiliates deal respectively with Rotary, Rotary Steerable System (RSS) and Steerable Motor (SM) directional BHAs. Case studies have led to BHA and bit design modifications. The results were well beyond expectations, ensuring good well positioning through the reservoir by improving BHA stability and manoeuvrability. Efficient drilling (reduced sliding, improved hole quality) was also achieved with a single SM BHA in 17 1/2" applications during kick-off, and successive build-up and slant drilling intervals.
The methodology and its associated BHA Management® software have proved an undeniably valuable tool for the drilling community. The model is also run at the well Pre Engineering stage to check BHA design proposals by making multiple sensitivity analyses and by fine-tuning solutions to the operational context. Finally, in an industry with high personnel turnover, the software's global data management system ensures good capitalization of know-how and ongoing learning curve benefits.
Simulation Study Investigating Gas Cap Contamination Caused by Miscible CO2-WAG
Authors: Janssen P. H. , Lackner A. S. , Stensen J. Å. , Haugse V. 
Published: December 2007

Abstract
The gas cap contamination level and mechanisms caused by CO2-EOR operations in an oil field have been investigated by compositional reservoir simulations on a sector model of the Upper Tilje reservoir. The impact of different EOR and gas cap drawdown operational parameters on the contaminated gas volumes has been determined.
The results show that the contaminated part of the produced gas from the gas cap, with more than 2.5% CO2, can be correlated to the final position of the CO2 front during the EOR-period. Massive CO2-breakthrough on the other hand, which is responsible for the contaminated part of the produced gas with more than 7.5% CO2, is a nearly linear function of the stored CO2 mass. This implies that EOR-operations which both increase oil recovery and CO2 storage, such as SWAG-injection, short-cycle WAG or oil producer gas shut-off will significantly increase gas cap contamination.
Gas cap contamination however can be reduced by well-positioned horizontal gas producers and large gas blowdown flow rates.
Physics-Driven Interface Modeling for Drainage and Imbibition in Fractures
Authors: Prodanovic Maša , Bryant Steven L. 
Published: December 2007

Abstract
The geometric distribution of immiscible fluid phases in fractures is not readily accessible experimentally, so aperture-scale simulations of drainage and imbibition in realistic fractures can provide valuable insight. We implement a level set method for computing the location within a fracture of the interface between two fluids controlled by capillary forces. The movement of the interface in response to changes in capillary pressure is approximated as quasi-static displacement. Fluid interfaces are thus constant mean curvature surfaces, satisfying the Young Laplace equation. We apply a progressive-quasistatic (PQS) algorithm to determine when spontaneous pore-level events occur during fluid displacement. The algorithm captures reversible and irreversible behavior. We illustrate the approach in two types of rough-walled fractures. One type is a 3D crack between irregular, impermeable surfaces; the other type is a gap between irregular 2D and 3D grain packs. We focus on the disconnected (defending) fluid volumes and (advancing) fluid main pathway as the geometric properties of the fracture are varied, notably aperture and the number of contact points between the upper and lower fracture surfaces. The curvature of the fluid-fluid interface in the plane of the fracture is often ignored by invasion percolation simulation techniques, yet it is known to influence strongly the fluid cluster properties. Our simulations establish the exact position and shape of the interface in realistic fracture geometries, from which fluid volumes, contact areas and interface curvatures can be obtained. This establishes a new, mechanistic basis for predicting relative permeabilities in fractures and for evaluating transfer functions in dual-porosity flow models.
Openhole Gravel Packing With Zonal Isolation
Authors: Barry M. D. , Hecker M. T. , Haeberle D. C. , Blacklock J. , Yeh C. S. 
Published: December 2007

Abstract
Many current deepwater and high rate wells are being completed in an openhole environment as openhole completions provide the greatest opportunity to maximize reservoir flow potential. Current technology, however, lacks the subsurface control necessary to effectively manage the reservoir in situations where sand control is required. ExxonMobil is pioneering technologies to model well performance more accurately and to provide subsurface control during completion and production operations. The first hardware developments within this initiative build on the success of Alternate Path® and NAFPacSM gravel packing technologies and address water or gas breakthrough in openhole, multi-zone gravel pack completions. ExxonMobil affiliates collaborated with third party suppliers to design and qualify new hardware to facilitate zonal isolation, extend gravel pack reach, and simplify rig site operations. This process included engineering design, component testing, and full-scale prototype evaluation. First application of this technology is targeted for early 2008.
This paper discusses newly developed sand control screen hardware that is enabling technology to perform openhole gravel packs with true zonal isolation. The equipment provides the ability to seal off bottom water, selectively complete or gravel pack targeted intervals, perform a stacked openhole completion, or isolate a gas/water-bearing sand following production. Application of the technology is expected to extend well life and ultimately increase volumes and reserves capture.
Integrated Wellbore/Reservoir Model Predicts Flow Transients in Liquid-Loaded Gas Wells
Authors: Chupin Gaël , Hu Bin , Haugset Tor , Sagen Jan , Claudel Magali 
Published: December 2007

Abstract
An integrated transient wellbore/reservoir model is described and applied to investigate the liquid loading in a gas well. The well produces from a storage reservoir with water coning from its aquifer.
The integrated model shows that the water cone causes the gas flow rate from each gas layer to decrease and the liquid holdup in the wellbore to increase. Depending on reservoir conditions, the well may enter into a mode of unsteady production during which the gas flow rate cycles over a period of several days. The reason for this unsteady flow is uncovered by the simulation.
Simulation results are compared with operational experience and full field reservoir simulations. The integrated model provides more realistic results compared to methods where the reservoir and the wellbore are modeled separately.
Field Validation of Drillpipe Rotation Effects on Equivalent Circulating Density
Authors: Hemphill Terry , Bern Peter , Rojas Juan Carlos , Ravi Krishna 
Published: December 2007

Abstract
It is important to predict the Equivalent Circulating Density (ECD) of fluids as closely as possible for safe drilling and completion of wells. This is especially true for those challenging wells where the margin between hole collapse and formation fracturing is very narrow. These characteristics of narrow safe drilling windows are commonly seen in extended-reach drilling (ERD) and deepwater wells, and pose significant drilling and cementing challenges.
Over recent years, the changes in ECD caused by fluid compressibility, downhole fluid rheology, drillpipe eccentricity, and rate of penetration have been widely studied. In contrast, work on the modeling of drillpipe rotation effects on pressure drop and ECD have received relatively little attention. Early studies have looked at the relationship between circulating pressure drop, especially in slimhole drilling configurations, and at very high drillpipe rotational speeds. More recently the predicted effects of rotation on ECD in concentric and eccentric wellbore geometries have been studied and model improvements have been made. These technical approaches are summarized in this paper.
The effect of drillpipe rotational speed on the predicted ECD for different drillstring combinations are presented and discussed. The calculated effects of drillpipe rotation on pressure drop and ECD are compared to actual field measurements using downhole annular pressure gauges.
From the results discussed in this paper, the reader can gauge the accuracy of the current calculation methods. The changes in ECD with drillpipe rotation can now be better predicted, something especially important for those wells whose safe drilling window is narrow. Ultimately this reduces drilling and completions risk and helps assure safe and efficient well construction.