bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Method to Assess the Value of Intelligent Wells
Authors: Gai H. 
Published: December 2007

Abstract
This paper articulates the understanding of the value of the Intelligent Well (IW) technology, and presents a systematic method to quantify the value of IW technology in specific applications.
Assessing the value of a project is often a prerequisite for its start and success. Without a clear understanding of the potential value of the technology, progress would be haphazard at best. The status of the technology is discussed. It is argued that understanding the value is a key for the industry to decide where to take the IW technology, which in turn will govern where to take the industry in terms of value addition.
The attributes of value determine the level of complexity of the task. Some efforts are made to show that a myriad of factors both affect the value and prevent a reliable or even a meaningful assessment being carried out.
The method described is a collection of common sense approaches, leading to a recommendation for the applications, based on the value and other considerations. Step-by-step explanation is presented. An example is also given. It has been shown that rigorous value assessment for a specific project could lead to new insight into aspects that unstructured analysis may not provide. The option with the highest NPV may not be the one that is recommended.
The mechanisms used in the method are not limited to IW value assessment.
Slimhole Completion Experience in Java Sea, Indonesia: A Look Back on Performance of the First 40 Slimhole Wells
Authors: Susilo Yoliandri , Wibowo Wahju , Dewi Devialina P. , Dwibhakti Kristyawan 
Published: December 2007

Abstract
Slimhole completions have been applied worldwide for years. The aim of this type of completion is to reduce well costs (drilling and completion) and therefore improve project economics. This paper presents the results of applying slimhole completions into oil and gas wells in the Offshore North West Java (ONWJ) Field, Indonesia. In looking back at the performances of previous wells, this paper focuses on problems associated with slimhole wells during completion time and their post-production compared with potential cost savings and future well intervention benefits.
To date, more than 40 slimhole wells have been drilled in ONWJ fields. Typically, the wells were completed in 3-1/2" or 2-7/8" monobore. Cost savings were achieved through these completions. However, additional problems seem to have arisen during completion time that could reduce the economics of the project. The most frequent problem during completion was due to cement obstruction (22.2% from total cemented wells) in the liner section after the cementing job, caused by poor cement displacement. This commonly occurred on relatively deep and deviated wells. From previous experience, drilling practice has improved, resulting in fewer operational problems during completion time.
The overall results show the problems associated with slimhole are still within an acceptable range compared with the potential cost savings and benefits. In our case, production rates from slimhole-monobore wells have not been much different from conventional wells. This paper also shares some operational practice improvements made to reduce problems associated with slimhole-monobore wells.
Temperatures Induced by High Power Lasers: Effects on Reservoir Rock Strength and Mechanical Properties
Authors: Graves Ramona M. , Batarseh Samih , Parker Richard A. , Gahan Brian C. 
Published: December 2007

Abstract
The temperature effects of high power lasers on rock strength and mechanical properties are presented. It was found that the high temperature induced by lasers drilling through rock enhances porosity and permeability and reduces strength. High temperature causes microcracks, vaporizes cementation, and dehydrates clays.
Microcracks were monitored using thin sections and SEM analyses. Representative samples were cut for thin section analyses before and after lasing. For the SEM test, a small fragment of the sample was removed and coated with gold for better electron conductivity, thus allowing fracture imaging in three dimensions.
Phase changes also affect rock properties such as permeability, porosity and strength. The effect depends on the temperature distribution and gradient as well as the mineralogy. At each temperature, different reactions take place. For example, at 550°C smectite clay will collapse and dehydrate. This mechanism results in increasing void space in the rock sample. At the same temperature, quartz grains will expand by 1.75%1 and when the grains cool, microcracks are created, which also increases the void space. This increase in void space may or may not change permeability, but it does decrease the acoustic velocities that in turn change the calculated porosity and elastic moduli.
Results show in all cases, the Young's modulus, shear modulus, bulk modulus, and combined modulus near the lased portion, were reduced when compared to the unlased portion.
In sandstones, the decrease was 50% or more. A bulk modulus decreased of 50% causes the compressibility near the wellbore to increase by 50%. Depending on the lithology, Poisson's ratio decreased or increased slightly. For limestones and shales, the differences between the moduli of lased and unlased samples were less significant than in sandstone.
Ekofisk Field Well Log Decompaction
Authors: Gauer P. R. , Sylte J. E. , Nagel N. B. 
Published: December 2007

AbstractThe Ekofisk Field is a large oil reservoir located in the Norwegian sector of the North Sea. About 8.2 meters of seafloor subsidence has occurred above this thick, high porosity chalk reservoir since production started in 1971. The seafloor subsidence is a result of reservoir compaction in the chalk, driven primarily by pressure depletion early in the field life and water weakening at later stages.Reservoir compaction monitoring via radioactive marker bullets has established a clear association between compaction and changes in water saturation and reservoir pressure. These data have also confirmed the mechanical behavior of the chalk observed during laboratory tests. The compaction of high porosity chalk is a result of both net effective stress increases linked to pore pressure depletion and water weakening induced by water injection. Field compaction data from a compaction monitoring well located in the crestal part of the field also suggest a vertical compaction to subsidence ratio of 1.20 to 1.25.Owing to compaction-related issues, many wells have been redrilled over the life time of the field. The new wells have yielded new data, such as porosity, water saturation, and layer pressure, spanning the entire field production period. These data, however, have been affected by compaction and, consequently, have introduced biases when used as hard data to build a geological description of the reservoir. A porosity loss of as much as 10 p.u., for example, can be predicted for high porosity, crestal chalk which has undergone a total reservoir compaction approaching 40 feet over a 30-year production life.More than 200 wells have been drilled since 1971 at Ekofisk, with only 42 of them being considered representative of the initial geological state of the field. In order to utilize the data from all 200-plus wells, a software program was developed to handle the complex decompaction and forward compaction logic needed to correct the well logs for compaction effects. Using the decompaction and forward compaction capabilities of the developed software, data from all 200-plus wells were used to evaluate the total reservoir compaction volume and shape. This was, in-turn, compared to 4D seismic-based compaction results as well as compaction results from geomechanical simulations.The developed software and evaluations have made it possible to now build a geological model of the Ekofisk reservoir using data from the 200-plus wells drilled on the field, each representing the initial state of the reservoir prior to production in 1971. Ultimately, this is expected to improve the flow simulations of the reservoir leading to better estimates of production and reserves.
Probabilistic Analysis of Wellbore Stability During Drilling
Authors: de Fontoura Sergio A.B. , Holzberg Bruno B. , Teixeira Édson C. , Frydman Marcelo 
Published: December 2007

Abstract
The current paper presents three analytical methods for evaluating the influence of parameter uncertainties in the wellbore failure process: FOSM (First Order Second Moment), FORM (First Order Reliability Model) and SEAM (Statistical Error Analysis Method). Results generated by Monte Carlo method are used as reference. These methods evaluate the probability of failure based upon reliability indexes. The paper also presents the results of a sensitivity study to establish the most important parameters that control wellbore instability. This is necessary in order to limit the number of calculations before establishing the probability of failure. The results demonstrate the importance of reducing uncertainties associated with the relevant parameters by means of careful testing procedures.
Using Flow Induced Stresses for Steering of Injection Fractures
Authors: Jørgensen Ole 
Published: December 2007

Abstract
Both horizontal and vertical rock stress magnitudes are substantially affected by pore pressure gradients generated by production from and water injection into low permeable chalk fields. This is confirmed by solid mechanics stress analyses and by observing fracture propagation in developed fields. Stress changes generated around horizontal injectors placed centrally between two parallel horizontal producers are considered in detail in this paper. It is shown that overburden and sideburden stresses may be altered and controlled to confine propagation of fracturing along the length of a central openhole horizontal injection well. It thereby becomes possible to establish a line drive development based on injection of water at fracturing conditions at reduced risk of premature water breakthrough (patent pending).
Estimating Fluid Pressures That Can Induce Reservoir Failure During Hydrocarbon Depletion
Authors: Streit J. E. , Hillis R. R. 
Published: December 2007

Abstract
A Mohr-Coulomb failure criterion is applied to estimate fluid pressures that may cause fault reactivation during the depletion of hydrocarbon reservoirs. The estimates incorporate the decline in total minimum horizontal stress that accompanies fluid pressure depletion in hydrocarbon reservoirs. Such pore pressure/stress coupling must be incorporated in predictions of depletion-induced failure because it significantly influences the fluid pressures at which faulting occurs. A new algorithm for failure incorporating the coupled decrease in pore pressure and stress is derived to calculate the fluid pressures that can cause slip on normal faults during ongoing production. The algorithm is applied to the Ekofisk reservoir, Norway, using various friction coefficients for chalk and incorporating the observation that the minimum horizontal stress decreased at 80% the rate of pore pressure depletion in the field. A friction coefficient of 0.6 yields realistic results when modelling the depletion period 1975 to 1990. A fluid pressure decrease from the initial 45 MPa to 38 MPa is required to activate optimally oriented faults with dip angles of approximately 60°. This fluid pressure level (38 MPa) was attained in 1978-1980 and marks the onset of significant subsidence in the Ekofisk field. Ongoing fluid pressure depletion from 38 MPa to the present level of approximately 25 MPa is sufficient for sliding on faults with dip angles of 48° to 73°. Preexisting fractures in the Ekofisk reservoir fall in this range, as they exhibit predominantly steep dip angles (65°). Slip events recorded during seismic monitoring that was conducted in 1994, are likely to represent the reactivation of such steeply dipping faults and possibly the formation of new fractures. The modelling technique presented for predicting induced reservoir and fault failure is an essential requirement for the long-term planning of hydrocarbon field depletion.
Evaluating Stress-Induced Anisotropy and Mechanical Damage From Cross-Dipole Sonic Data Using Dispersion Analysis
Authors: Plona T. J. , Kane M. R. , Sinha B. , Walsh J. 
Published: December 2007

Abstract
Advanced sonic characterization of near-wellbore mechanical damage and formation anisotropy yields important new information for drilling and completion engineering as well as for geophysics. Damage in shales is a precursor to wellbore stability problems. Stress-induced mechanical damage in weak reservoirs indicates zones where selective vertical perforation can reduce the risk of sanding. Identifying stress-induced anisotropy enables orienting perforations consistent with the stress direction to minimize sanding problems and optimize production; and in the case of hydraulic fracturing, to minimize near-wellbore tortuosity. Proper well placement to maximize oil recovery from hydrofracing requires knowledge of the stress directions.
Sonic cross-dipole logging with advanced frequency-domain processing provides the unique capability to characterize the mechanical state of the formation around the borehole. Traditional processing is performed in the time domain and identifies whether the formation is isotropic or anisotropic. Recently, we showed that frequency-domain processing of cross-dipole data (i.e., slowness-frequency analysis or dispersion analysis) distinguishes intrinsic from stress-induced anisotropy. The unique identification of stress-induced anisotropy also yields the stress direction. Further processing can lead to estimates of stress magnitudes. These results are obtained even in the absence of breakouts or drilling-induced fracturing, the traditional borehole stress indicators.
The near-wellbore region can be significantly perturbed by the drilling process and the associated borehole stress concentrations, resulting in radial variation of the shear slowness. Slowness-frequency analysis of cross-dipole data shows that low frequencies sample at a distance into the formation that is equal to two to three borehole diameters, sensing the unaltered rock. High frequencies penetrate a distance equal to one borehole radius, probing the mechanically damaged zone. Deviation from the homogeneous model at high frequencies indicates damage. Analysis of dipole dispersion curves yields an estimate of the depth of the mechanical damaged zone.
Worldwide (Middle East, Africa, Gulf of Mexico, Southeast Asia) field examples in both overburden shales and reservoir rocks (sands and carbonates) highlight the additional information derived from cross-dipole dispersion curves. Dispersion analysis of these data sets enables identification of: 1) stress-induced anisotropy, stress direction, and stress magnitudes; and 2) near-wellbore mechanical damage in both sands and shales.
The key to this new understanding is the combination of wide-band acquisition of crossed dipole sonic data, advanced frequency-domain processing techniques, and good knowledge of acoustic wave propagation in boreholes.
Dual-porosity Approach for Directional Boreholes
Authors: Zhang Jincai , Roegiers Jean-Claude 
Published: December 2007

Abstract
Naturally fractured reservoirs can be treated as dual-porosity media consisting of a primary rock matrix system as well as fractures. These dual-porosity formulations coupling matrix and fracture deformations as well as fluid flow in both systems are first presented. The finite element solution for any directional wellbore drilled in a dual-porosity medium is given. Mud weight considerations are presented for both permeable and impermeable boundary conditions. A case study for inclined wellbore problems was also conducted. The effects of single- and dual-porosity, time, and mud weight are parametrically studied allowing for a better understanding of the physical characteristics governing borehole problems.
Uncertainties in the Pore Pressure Evaluation in Deepwater: a Statistical Approach
Authors: Falcao José L. 
Published: December 2007

Abstract
The Pore Pressure is a critical point of any drilling project, once it influences the definition of the mud weight, casing setting depths, casing design, riser safety margin (RSM), etc. During the design stage of offshore and shallow water wells, safety factors (ranging normally from 0.5 to 1.0 ppg) are introduced to compensate the lack of accuracy in pore pressure evaluation. However, this may impose a limit in deepwater drilling operations. In such environment, as the water depth increases, the formations tend to show lower fracture gradients, which makes the difference between the pore pressure and the fracture gradient curves quite small, complicating the project.
In this work the methods employed by Petrobras to evaluate the formation pressure are reviewed. Next, a procedure, employing statistical analysis, to evaluate the uncertainty in the pore pressure determination in the offshore portion of Campos Basin - Brazil, is presented. For that, a DST (drill stem test) and RFT (repeat formation test) database collected along the years in this area is employed. As a result, the safety factor applied over the Pore Pressure could be reduced, simplifying deepwater well projects.
A New High-Resolution Electronic Memory Gauge Improves Reservoir Characterization
Authors: Azari M. , Kool H. , Soliman M. Y. 
Published: December 2007

Abstract
A new quartz electronic memory gauge that has been introduced to the oil industry will be presented in this paper. This gauge can record data with more precision than existing gauges, and thus, can establish more accurate flowing and shut-in pressure with higher resolution. In addition to describing the gauge design, this paper will also discuss the advantages of improved gauge resolution in the analysis of well test data and in determination of the hydrocarbons in place. The impact of using a higher resolution gauge on well testing is illustrated through analysis of field data.
Field Trial of a Downhole, Fiber Optic, Two-phase Flowmeter in PDO's Nimr Field
Authors: Kragas Tor K. , van der Spek Alex , Al Hashmi Khalid M. 
Published: December 2007

Abstract
A field trial was conducted in June, 2001, of a downhole fiber optic two-phase flowmeter in two wells at PDO's Nimr field in Oman. The fiber optic flowmeter provides real-time measurements of volumetric flow rate and water cut. The purpose of the field trial was to evaluate the performance of the flowmeter for potential application at Nimr. Specifically, objectives were to determine the deployability of the flowmeter at Nimr, to determine the ability to operate with heavy, viscous Nimr crude, and to determine the ability of the flowmeter to distinguish between high water cut legs in dual lateral completions with artificial lift. Accuracy goals for the flowmeter were ±3% on water cut and ±10% on total volumetric flow rate.
The fiber optic flowmeter was successfully installed in two wells at Nimr. In one of the wells the meter was installed in the completion string just below an electrical submersible pump (ESP) and in the other well it was installed just below a beam pump. A surface Coriolis mass flow meter served as a reference for the two-week field trial. In the beam-pumped well it was found the noise environment is not compatible with the physical measurement principle of the optical flowmeter, and a comparison against the surface-measured rates was not possible. In the ESP-pumped well, comparison of the flow rates and water cut measured by the fiber optic flowmeter and the Coriolis meter were better than expected, -1% to +2% on water cut and -1% to +3% on total rate, and well within specifications.
Application of Silicone Microemulsion for Restriction of Water Production in Gas Wells
Authors: Lakatos I. , Tóth J. , Lakatos-Szabó J. , Kosztin B. , Palásthy Gy. , Wöltje H. 
Published: December 2007

Abstract
A novel method based on injection of silicone microemulsion was developed for restriction of water production in gas wells. The treating solution was a surfactant stabilized siloxane emulsion which was driven into the formation by water and nitrogen. According to the laboratory studies disproportional permeability modification is in the background of the water retention. The phenomena is attributed to inversion of microemulsion to macroemulsion initiated by spontaneous dilution by water and then entrapping of formed siloxane droplets by the pores. The method was tested at the largest Hungarian gas field (Algyő field, Hungary). Evaluation of the pilot test has definitely proved the beneficial effect of silicone injection on gas production and gas/water ratio: the gas production tripled and lasted for at least a half year. The encouraging results urged the operator to continue both the laboratory and the field tests with the aim at developing a method which might be used routinely in low permeable, tough gas fields and underground gas storage.
New One-Trip Multi-Zone Frac Pack System with Positive Positioning
Authors: Vickery E. Harold , Bayne Christian F. 
Published: December 2007

Abstract
Effective fracture stimulation of multiple pay zones usually requires multiple fracture treatments with multiple trips in and out of the wellbore for perforating and placing frac pack equipment. An additional concern is positive positioning of downhole equipment, particularly when performing high-pressure treatments in deviated wellbores or from a floating platform or drilling rig.
A system is presented that allows stimulation of multiple pay intervals using several independent fracture treatments to be accomplished with a single trip into the wellbore to place packers, screens and gravel pack tools. The system also keeps the equipment in proper positioning for each treatment, thereby minimizing the risks associated with treating multiple zones.
Treatment parameters are discussed to assist in designing the independent stimulations. We will also discuss several equipment issues important to eliminating risk associated with pumping these treatments.
An example is presented to illustrate how this system can be used to treat a long production interval with high laminated sands.
Detection of Asphaltenes Flocculation Onset in a Gas Condensate System
Authors: Thou S. , Ruthammer G. , Potsch K. 
Published: December 2007

AbstractAsphaltene plugging is one of the most frequent causes of production depletion in medium and light crude oil reservoirs, especially when the pressure declines due to its exploitation. Other physicochemical phenomena, like intrinsic instability of the produced crude oil, incompatibility between "commingled" produced oils, between streams entering the flow stations, as well as inadequate stimulation procedure, can be responsible for asphaltene deposition during crude oil production and transportation, going from the reservoir to surface facilities.Asphaltenes precipitation is one of the major operational problems affecting production in the Höflein field northwest Vienna. The deposits were responsible for plugging the coalescing filters, which are designed to dehydrate down to 5 ppm of suspended water. Asphaltene deposition is also blamed for prolonging the annual summer stopover, which is proposed for general maintenance on Korneuburg facilities.The purpose of this work is to show the application of a systematic technique for detecting the onset of asphaltene flocculation under various pressure and temperature conditions as well as for selection and evaluation of chemical inhibitors in the field Höflein. The results allowed defining the asphaltene deposition envelope (ADE) as well as selecting the best inhibitor evaluated under production facility conditions. In addition, the characteristics of this phenomenon as well as the problems associated with it have been highlighted.