bluuebunny/crossref_metadata_2025_split huggingface dataset:
Composite Bridge Plug Technique for Multizone Commingled Gas Wells
Authors: Garfield Garry 
Published: December 2007

Abstract
Composite bridge plugs save operator time and money by enabling quick and easy installation and removal. While easily deployed on either standard electric line or coiled tubing equipment, composite bridge plugs (CBPs) can be removed in one-fourth the time required to mill traditional cast iron bridge plugs and with reduced formation damage. CBPs can be installed under pressure in multi-zone, commingled gas wells without expensive formation kill-weight fluids. After remedial operations, CBPs are removed with coiled-tubing-conveyed milling equipment using low viscosity milling fluids that minimize formation damage and easily remove composite cuttings from the wellbore. This is especially important because of the low annular velocities characteristic of coiled tubing operations. The wellbore is left cleaner than those using cast iron bridge plugs in similar operations.
CBPs can withstand high pressures for up to 10 days without compromising their pressure integrity and without the need for a cement barrier on top of the CBP. Initial field runs have demonstrated that CBPs can be milled as quickly as 30 minutes compared to 2 hours for milling conventional cast iron bridge plugs. Multi-zone, commingled gas wells using as many as 7 CBPs have been brought back on production after taking only 12 hours to remove all CBPs, including rig-up and rig-down of the coiled tubing unit. Field runs also indicate CBPs can be milled quickly when set at depths exceeding 19,000 feet.
Experimental Studies Of Low Ift Displacement By CO2 Injection
Authors: Rosman A. 
Published: December 2007

Abstract
An experimental technique is described for isolating the influence of low interfacial tension (IFT) from the influence of other CO2 displacement mechanisms. Also, the capillary number concept was extended to correlate the displacement efficiencies of the CO2-oil systems. Experimental results indicate that low IFT displacement by CO2 is an effective recovery mechanism.

Introduction
The use of CO2 as an enhanced oil recovery agent in petroleum reservoirs has been investigated both in the laboratory and in the field. Several recovery mechanisms were identified among which those most often considered were: swelling, viscosity reduction, and vaporization and extraction of portions of oil. A CO2 displacement may be either immiscible or miscible portions of oil. A CO2 displacement may be either immiscible or miscible depending on injection gas composition, reservoir oil composition, reservoir temperature, and pressure.
The concept of low IFT flooding has been extensively studied for surfactant and micellar enhanced oil recovery processes; however, the literature shows no investigations of the influence of low IFT on CO2 displacement efficiency.
During CO2 flooding, low IFT occurs simultaneously with vaporization, swelling, and viscosity reduction, making its influence difficult to isolate. In this paper we discuss an experimental technique designed to isolate low IFT effects.

EXPERIMENTAL TECHNIQUE
The following procedure was used to isolate the effect of IFT on CO2 displacement efficiency from other CO2 displacement mechanisms:CO2 and reservoir oil were mixed at the desired temperature, pressure, and CO2-to-oil mole ratio.The mixture was brought to equilibrium.Compositions, densities, and viscosities of the equilibrated oil and gas, as well as the IFT between phases were measured. IFT measurements used the pendant drop method.The core was saturated with the equilibrated oil as described below.The equilibrated oil was displaced from the core with equilibrated gas.
As the displacing gas and reservoir oil were preequilibrated, their compositions and physical properties, including IFT, remained constant during displacement. Injection rate was also constant. The pressure drop across the core was kept at a minimum to preserve the equilibrium between the displacing gas and the displaced liquid.
Each experiment consisted of three stages:Bringing the core to the experimental stage. This included the following operations:saturating the core with brine,measuring permeability to brine, anddisplacing the brine with several volumes of equilibrated oil to a specified irreducible water saturation, Swi.Performing the displacement. The equilibrated gas was injected at a constant rate, and the pressure drop across the core was continuously recorded.
Improved Prediction of Waterflood Sweep Efficiency Using Multi-Exponent Matrix-to-Fracture Transfer Functions
Authors: Civan Faruk , Rasmussen Maurice L. 
Published: December 2007

SummaryA generalized methodology is presented that obtains analytical solutions for imbibition waterfloods in naturally fractured oil reservoirs undergoing multi-step matrix-to-fracture transfer processes. The phenomenological representation of the oil transfer from matrix to fracture is based on a three-exponential matrix-to-fracture transfer function, the necessity for which is seen by examination of experimental data. The resulting in-tego-differential equation is converted to a fourth-order partial differential equation, linearized by invoking the unit end-point mobility ratio approximation, and then solved analytically by asymptotic means. It is shown that the asymptotic-approximation approach significantly reduces the complexity of the solution process and yields adequate solutions for longtime evaluation of waterfloods in naturally fractured reservoirs. The solution is not only computationally advantageous, but it also provides a physically meaningful interpretation of the propagation speed and diffusive spreading of the progressing wave front, which could not be readily obtained from the usual type of solution methods, such as the direct application and inversion of the Laplace transformation.
Water Sensitivity and Swelling Characteristics of Petroleum-Bearing Formations: Kinetics and Correlation
Authors: Civan Faruk 
Published: December 2007

AbstractFrequently, the composition of petroleum-bearing formations includes certain minerals and clays, the swelling of which in contact with water-based drilling and completion fluids, may cause formation damage and adversely affect the wellbore stability. This paper presents a kinetic model for correlation and prediction of the water sensitivity and swelling characteristics of petroleum-bearing formations and its verification by experimental data.The swelling of petroleum-bearing formations is perceived to occur via the absorption of water by a water-exposed surface hindered diffusion mechanism. Hence, a theory of swelling and alteration of petroleum-bearing clayey formations is developed and applied for correlation of various properties of practical importance, including water content, permeability, volume expansion or porosity, and basal spacing of clay. An analytical solution is derived and reformulated for convenient straight-line plotting of experimental data. It is demonstrated that this model accurately represents the swelling characteristics of petroleum-bearing formations, successfully correlates various experimental data, and allows for accurate determination of the swelling rate parameters.The theoretical treatment provides insights into the mechanism of the swelling of petroleum-bearing formations and leads to the development of a practical and theoretically rigorous method for accurate straight-line correlation of experimental data and determination of the swelling rate parameters. This model can be used for accurate description of the swelling characteristics of petroleum-bearing formations, prediction of conditions causing wellbore stability problems, and development of optimal strategies for effective mitigation of the undesirable consequences of swelling in petroleum reservoirs.
Accurate Measurement of Gas Diffusivity in Oil and Brine Under Reservoir Conditions
Authors: Civan Faruk , Rasmussen Maurice L. 
Published: December 2007

SummaryThis paper presents a physically and mathematically rigorous transient-state non-equilibrium diffusion model for accurate determination of the gas diffusion coefficient from experimental measurements of the gas pressure decline in a closed tank by dissolution of gas in a liquid (oil and brine). The short- and long-time solutions of this model for equilibrium and nonequilibrium transfer processes are derived analytically. These solutions are reformulated to enable direct determination of the best estimate of the diffusion coefficient by regression of the resultant analytical expressions to experimental data. These analytic expressions are also facilitated to develop a set of charts, similar to the type-curves used in well testing for routine applications in the laboratory. The experimental data given by previous researchers are analyzed by means of the present improved methods and the diffusion coefficients obtained are compared with the previous studies. The accuracy of the present results are confirmed by comparing their values to those measured and reported at the gas saturation conditions of the liquid phase, which are accurately known, because the saturation is a well defined state, at which state the amount of dissolved gas attains a maximum. This model can be used for determining gas diffusivity in oil, brine, as well as drilling mud and completion fluids.
Underbalanced Drilling: Real Time Data Interpretation and Decision Support
Authors: Lorentzen Rolf J. , Fjelde Kjell Kåre , Frøyen Johnny , Lage Antonio C. V. M. , Nævdal Geir , Vefring Erlend H. 
Published: December 2007

Abstract
The accurate prediction of the downhole pressures and the returning flow rates in low-head drilling (LHD) and underbalanced drilling operations (UBD) is a major concern in the oil industry. The present work shows an original formulation of a dynamic two-phase flow model based on the classic drift-flux set of conservation equations. However, different from the traditional approach, the closure of the system is obtained by using measured data acquired during the execution of the operation. The innovative concept consists of formulating simple closure relations that are dependent on unknown parameters, which are calculated and updated from time to time to minimize the differences between model predictions and measured data.
The potential of this new approach is discussed by presenting some transient examples of application. The current study represents a first step on the development of a methodology for the introduction of a learning while drilling process in the hydraulic design and follow-up of LHD and UBD operations.
Conductorless Concept for Offshore ‘Disposable’ Exploration Wells
Authors: Hoving P. G. 
Published: December 2007

Abstract
The first offshore ‘disposable’ exploration well in NAM (G14-1) proved the technical viability of the conductorless concept. The concept can be applied to any offshore exploration well in an area with a stable seabed. Cost savings can be achieved (20" conductor or 10¾" casing)
From a study aimed at reducing offshore exploration well costs it was concluded that Mudline Suspension (MLS) systems could in future be omitted from all wells. As a consequence these wells will always be abandoned. This design approach further allows for conductor elimination. The first casing string would then be subjected to the environmental load imposed by the sea.
Two wells were identified to trial this concept, both initially designed with a 95/8" surface casing.
The conductorless concept was technically proven on the first well. Learning's could not be transferred to the next well due to significant problems encountered in top-hole drilling. The conductorless trial for this well was cancelled. Concept application to all future wells will depend largely on finding an effective method for drilling the near seabed formations.
Downhole Flow Control Optimization in the Worlds 1st Extended Reach Multilateral Well at Wytch Farm
Authors: Gai H. 
Published: December 2007

Abstract
This paper introduces an optimization method for multi-zone or multi-lateral flow control completions. This is developed around a real application, in the world first Extended Reach Multilateral well at Wytch Farm.
The flow control completion is described before the theoretical framework is set out against the background of the specific Wytch Farm well. Then the optimization plan is sketched, with detailed graphical explanation of how the optimization is performed and the assumptions and analytical relationships described. Some Wytch Farm data is presented and analyzed, showing that more work is still needed to complete this important work which is attempting to fill up a gap left by the fast development in flow control hardware over the past 5 years.
The key issues in optimization are discussed along with the lessons learnt. In the closing remarks the authors state that the main objective of this paper is more to push the industry to put some much needed effort in this area than to develop a reliable tool first time round.
Rheological Properties of Drilling Muds in Deep Offshore Conditions
Authors: Herzhaft Benjamin , Peysson Yannick , Isambourg Patrick , Delepoulle Amaury , Toure Abdoulaye 
Published: December 2007

Abstract
The development of deep and ultra-deep offshore operations brings new and more complex technical challenges due to the harsh conditions encountered at these water depths. In particular, temperature around 2°C and pressure up to 400 Bars are not uncommon at the mud line. The drilling fluid, while flowing through the well, will experience temperatures from 0°C to 150°C and must keep its properties for this whole range of temperatures. The mud rheological properties will strongly depend on the temperature and pressure variations, and also on mud formulations.
This work is an experimental study of the influence of temperature and pressure variations on various muds rheology. Rheological characterizations were performed with laboratory rheometers down to temperatures as low as 0 °C. Various oil based muds were investigated. Rheological properties of the base oil were measured and correlated with the mud properties. This was used to determine the influence of the nature of the based oil and of the type of additives present in the formulation. Gelation phenomena occurrence was evidenced for some formulations, and the kinetic of gelation was quantified by using specific experimental setup. Mathematical laws were established to characterize and predict the temperature and pressure dependency of oil based mud rheology. The influence of the mud rheology temperature and pressure dependency on down-hole pressures prediction was demonstrated by comparing simulations to field data.
Brent In-Fill Drilling Programme: Lost Circulation Associated With Drilling Depleted Reservoirs
Authors: Addis M. A. , Cauley M. B. , Kuyken C. 
Published: December 2007

Abstract
Drilling in the Brent field began to experience severe lost circulation problems after the start of depressurisation in 1998. The losses occur in the reservoir sections which are penetrated by extended reach and near-horizontal wells. In contrast, wells drilled before the onset of depressurisation experienced few losses.
The lost circulation problems result from a narrowing of the drilling operating window as reservoir depletion gradually reduces the fracture gradient. Numerous interbedded reservoir shales, which are sub-seismic in thickness, require a minimum mud weight to maintain stability especially in the sub-horizontal sections. Problems become acute when the fracture gradient is reduced to a level below the equivalent circulating density required to successfully drill the shales.
The rate of decline in the fracture gradient has been much lower than would have been predicted from a conventional geomechanics estimation, and this has extended the duration of the Brent drilling programme during depressurisation.
The Brent in-fill drilling programme continues very successfully, through accurately estimating the fracture gradient decline which accompanies depletion using the field validated depletion constant model, and through a team wide Equivalent Circulating Density (ECD) management approach to drilling. The key objectives of this paper are, a) to explain several of the Brent mud loss incidents which accompany depletion, and b) to outline the approach used to develop a reliable depletion constant model in support of continuing drilling operations and the enhanced ECD management strategy.
Computing the Danger of Hydrate Formation Using a Modified Dynamic Kick Simulator
Authors: Petersen Johnny , Bjørkevoll Knut S. , Lekvam Knut 
Published: December 2007

Abstract
Planning offshore wells in deep water depths needs special tools to optimize operation and safety procedures. One of the many technical problems in deep-water operations is the possible formation of hydrates in the BOP or Kill/Choke line. Hydrates are ice type substances consisting of frozen mixtures of water and hydrocarbons which may plug the BOP stack and well circulation path and will be very difficult and time consuming to remove.
An advanced dynamic kick simulator, developed at Rogaland Research, has recently been expanded to include the determination of the potential for hydrate formation. Using dynamic temperature simulation, detailed PVT computations of the hydrocarbon influx on the component level, and an advanced hydrate formation program it is possible to obtain the ‘distance’ in temperature from hydrate formation throughout the well at any time during a simulated operation.
The simulator includes code that takes into consideration the effect of hydrate inhibitor chemicals such as salts and alcohols. Thus it is possible to make several trial runs with differently inhibited muds to compare the danger of running into hydrates.
The paper briefly discusses the physical and chemical models used, and points out how to circulate in a way to minimize the chance of hydrate formation.
Simulating kick with hydrate formation is a novel and significant contribution. This will enable the industry to perform planning and engineering of complicated well control situations. In particular it will allow the planning engineer to evaluate the risk of hydrate formation versus the cost of mud inhibition – this will be very useful for low mud weight situations where providing hydrate inhibition is very expensive.
Real-Time Well Construction Monitoring – A Case History of Sincor's Heavy Oil Project
Authors: Branch A. J. , Andersen K. , Lavillonniere J. L. , Larsen T. , Kremer Y. , Capacho G. A. 
Published: December 2007

Abstract
Sincor, an operating company owned by TotalFinaElf/ PDVSA/Statoil is utilizing real-time well construction monitoring technology for its field development program in the Zuata area of Eastern Venezuela. From each rig site, real-time Logging-While-Drilling (LWD) and surface drilling parameter data are transmitted via satellite, 300 km to Sincor’s headquarters in Caracas.
The survey information (inclination and azimuth), along with the gamma ray and resistivity LWD data are for the first time directly and automatically loaded into a Landmark Graphics Openworks™ database. The well trajectory (with LWD curves) can then be viewed on the seismic profile. The seismic profile is automatically posted to the Sincor intranet allowing viewing either by the rig site team members or by Caracas team members from their offices or homes, thus ensuring 24-hour coverage. Multiple wells are monitored simultaneously. With this information, the geo-science and drilling engineering teams both in Caracas and at the rig sites can immediately make better-informed decisions, such as redefining the well trajectory.
This paper will discuss the processes involved from the initial well design on the seismic section through to the real-time acquisition of data while drilling and its subsequent transfer to Caracas. There, the actual well trajectories and the LWD curves can be viewed in real time against the seismic sections and proposed well paths.
Shallow Casing Shoe Integrity Interpretation Technique
Authors: Wojtanowicz A. K. , Zhou D. 
Published: December 2007

Abstract
In contrast to leak-off testing in deep wells, leak-of plots from the shallow well sections subsea, exemplified in the paper, are inconclusive because there is no obvious point of deflection from the initial linear section of the plot. In the paper, simultaneous effects of geo-mechanical factors and fluid loss mechanism have been combined to explain and analyze the tests in shallow marine sediments SMS.
Based on theoretical analysis, three main stages of leak-off plot from SMS, pressure buldup, stabilization and fall-off are identified and explained. Non-linearity of the pressure buildup and mechanisms controlling pressure stabilization are explained and used to develop a method to analyze LOT.
The presented interpretation procedure considers separately the pressure stabilization and the pressure builup and fall-off sections of the LOT plot. The procedure combines well data with pressure testing record. Well data includes overburden pressure – calculated from correlations specific for SMS, and the maximum cementing pressure at the time of slurry placement.
The stabilized LOT pressure analysis identifies the maximum strength of the casing shoe controlled by the rock stress (overburden pressure) and the failure by rock fracturing. Also presented is a graphical procedure for comparing the plots of actual and equivalent pressure fall-off. The graphical procedure provides a pattern-recognition method to distinguish the mechanism of cement-rock parting from the fluid loss mechanism.
A Practical Method for Evaluating Effects of Fracture Charging and/or Ballooning When Drilling High Pressure, High Temperature (HPHT) Wells
Authors: Helstrup Ole A. , Rahman M. K. , Hossain M. M. , Rahman Sheik S. 
Published: December 2007

Abstract
Fluctuations in the returned mud volume have often been observed when drilling HPHT wells. There are several contributing factors for this, out of which increased wellbore volume due to elastic deformation and mud taken by natural fractures are considered in this paper. These effects are significant in HPHT wells as a result of the high mud pressure required to control the well. This, however, can give the driller the misimpression that the extra mud volume is lost to the formation due to wellbore breakout and/or fractures. When the mud weight is reduced to prevent such a suspected mud loss, the formation quickly regains its original volume and the "lost" mud is returned. This might again be misunderstood as a kick and the mud weight is increased immediately to prevent the suspected kick. The repetition of this process a few times might eventually lead to an actual wellbore failure.
This paper presents a method to estimate the volumetric expansion of wellbores as a function of wellbore pressure. The wellbore near-breakout/fracture pressure, which is of interest for this analysis, is established by considering different failure modes including helical shear, elongated shear and tensile fracture. The increases in wellbore volume are estimated at this pressure as a limit below which the driller should not be fooled by the suspected breakout/kick situation and thus avoid it leading to wellbore failure.
The method to estimate the volumetric expansion is based on analytical and numerical approaches. Analyses show that the diametric expansion of the wellbore may be in the range of centimetres at a critical pressure, and thus a deep well may consume a significant number of extra mud barrels before actual breakout occurs. This might be alarming enough to lead the driller to suspect breakout/fracturing in the absence of any analytical guidance. Thus, the paper has presented a novel approach to analyse such a suspected situation during well drilling at HPHT conditions, and the information presented will assist engineers to avoid confusion and manage the well efficiently in such a situation.