bluuebunny/crossref_metadata_2025 huggingface dataset:
An Adaptive-Implicit Switching Criterion Based on Numerical Stability Analysis
Authors: Fung Larry S-K. , Collins David A. , Nghiem Long X.
Published: December 2007

A new switching criterion for adaptive-implicit reservoir simulation, based on the numerical stability of the local amplification matrix, is discussed. Adaptive-implicit methods can be used to achieve substantial savings in computing time and storage. The success of their application, however, depends critically on an appropriate switching criterion. The standard criterion discussed in the literature is the application of threshold changes in the primary variables, which are usually determined by some preliminary testing and chosen conservatively because of their empirical nature. Further, backward switching (implicit to explicit) is not normally feasible. With the switching criterion discussed in this paper, these disadvantages are eliminated. The method has been applied to a variety of black-oil reservoir simulation problems, including the first and second SPE Comparative Solution Projects and a water-injection problem. In all cases tested, the new criterion is shown to perform satisfactorily. For the waterflood problem in particular, the new criterion with backward switching was found to decrease computing time and storage significantly compared with the standard switching criterion. This criterion can easily be extended to other types of reservoir simulators.
High-Resolution Simulation of Unstable Flows in Porous Media
Authors: Christie M. A.
Published: December 2007

This paper describes accurate numerical methods used to solve equations governing two-phase, three-component flow on a fine grid to obtain predictions of fingering behavior for both miscible and immiscible flows. The reasons for the choice of finite-difference scheme are discussed. Results are presented that show almost complete stabilization of fingering for illustrative line-drive and quarter five-spot configurations when water and solvent are injected simultaneously at the optimum water-alternating-gas (WAG) ratio.
Discontinuous and Mixed Finite Elements for Two-Phase Incompressible Flow
Authors: Chavent Guy , Cohen Gary , Jaffré Jérôme , Eymard Robert , Guérillot Dominique R. , Weill Luce
Published: December 2007

The simulation of multiphase flow presents several difficulties, including (1) the occurrence of sharp moving fronts when convection is dominating, (2) the need for a good approximation of velocities to calculate the convective terms of the equation, and (3) flow singularities around wells. To handle the first difficulty, we propose a Godunov-type higher-order scheme based on a piecewise linear approximation of the saturation associated with a multidimensional slope limiter. With respect to the second, the pressure equation is approximated by means of a mixed-hybrid formulation equivalent to the classic mixed formulation but yielding a positive-definite linear system. To solve the third difficulty, we introduce macroelements around wells. Numerical experiments illustrate the capabilities of the method.
Implementation of an Improved Adaptive-Implicit Method in a Thermal Compositional Simulator
Authors: Tan T. B.
Published: December 2007

A multicomponent thermal simulator with an adaptive-implicit-method (AIM) formulation/inexact-adaptive-Newton (IAN) method is presented. The final coefficient matrix retains the original banded structure so that conventional iterative methods can be used. Various methods for selection of the eliminated unknowns are tested. AIM/IAN method has a lower work count per Newtonian iteration than fully implicit methods, but a wrong choice of unknowns will result in excessive Newtonian iterations.

For the problems tested, the residual-error method described in the paper for selecting implicit unknowns, together with the IAN method, had an improvement of up to 28% of the CPU time over the fully implicit method.
Simulation off Fluid Flow in Hydraulic Fracturing: Implications for 3D Propagation
Authors: Ben Naceur Kamel , Thiercelin Marc , Touboul Eric
Published: December 2007

A formulation for simulating arbitrarily shaped 3D fractures is presented. The technique extends previous variational techniques and provides a stable solution with a minimum number of elements. The model is used to assess the applicability of simplified height-growth models. Issues related to the treatment of 2D convection fields, associated with the fluid-flow equations, are also addressed.
Stability of Highly Inclined Boreholes
Authors: Aadnoy B. S. , Chenevert M. E.
Published: December 2007

Hole inclination produces alterations in the stress state around the borehole and in the physical properties of the rock. Depending on specific conditions, such effects may lead to collapse of the borehole or a reduction in the fracture-initiation pressure. This paper shows how to determine such effects through the application of stress analysis and rock mechanics.
Ultrasonic Inspection of Rotary-Shouldered Connections
Authors: Chapman Paul W.
Published: December 2007

This paper presents the results of a research project that combined laboratory investigation and field data to identify the parameters that affect the sensitivity and reliability of an ultrasonic system of inspection for rotary-shouldered connections. Variations of the parameters were introduced in a controlled environment so that the type and magnitude of their effect could be determined and quantified.
Drillstring Fatigue Performance
Authors: Chen Wen-Ching
Published: December 2007

The life-prediction technique of a whole-life fatigue model was applied to drillstring components. Good agreement existed between the life predictions and the experimental data of drill collars. These life predictions were then used to study the effects of material properties and commonly used thread profiles on the fatigue life of drillstring components. Results of the study indicate that the newly developed microalloying technology and thermomechanical-processing technology in steel metallurgy can significantly benefit the fatigue life of drillstring components. The sensitivity studies on the effect of thread profile on fatigue performance of drillstring components indicate that fatigue life could be enhanced by an improved thread-profile design.
Surface-Casing Strain Capacity for North Slope Operations
Authors: Hirshberg A. J. , Moyer M. C. , Rickenbach R. M.
Published: December 2007

Thaw subsidence during the production life of wells drilled through the permafrost can transfer very high axial compressive loads to the surface casing. Improved techniques were required to define the compressive strain capacity of surface casing for North Slope operations. These techniques were used to identify cost-effective surface-casing designs capable of withstanding the axial compressive strains imposed by permafrost thaw.

Plans to drill North Slope development wells on closer surface spacing resulted in predicted permafrost thaw loads on the surface casing that exceed current operating practices. In addition, development of lower-productivity wells has resulted in completions with smaller-diameter tubulars. Both of these considerations have led to a reassessment of the surface-casing programs for these new wells.

The results presented are based on two parallel and complementary investigations: full-scale physical testing and nonlinear finite-element analysis. The physical tests provided information about the performance of the casing and connections under high compressive loads. Data were used to verify the accuracy of corresponding finite-element models with three different criteria: strain-gauge data from the coupling and pin surfaces, failure mode comparison, and failure load comparison. An excellent match was achieved between the strain-gauge data and the analytical strain results, the actual vs. modeled failure mode (i.e., compressive bulging in the pipe body), and the actual vs. modeled failure load. Once verified, the models were used to investigate the effects of field-related parameters that were not tested. These included variations in makeup condition, pipe-wall thickness, thread taper angle, and casing length. Finally, these results enabled the selection of suitable surface-casing materials and connections for arctic operations.
Improved Interpretation of Casing Logs for Casing Failure
Authors: Wooley G. R. , Hatcher M.
Published: December 2007

Casing inspection logs may be used to interpret the nature of a casing failure downhole. This paper provides data to improve interpretation for casing failures and presents results of laboratory tests of four commercially available tools. The tools are tested in five casing specimens, corresponding to five types of failures.

Results indicate that although standard casing inspection logs can detect the existence of a casing failure in a well and define its location, interpretation of additional details with regard to the type of failure requires special efforts. Calibration procedures and interpretation techniques that are not commonly practiced in the field are presented to allow distinction between a split and a part and to define details of the split or part. Also, recommendations are made with regard to running speeds and sensitivity settings.
A Practical Approach to Jarring Analysis
Authors: Wang Jaw-Kuang , Kalsl Manmohan S. , Chapelle René A. , Beasley Thomas R.
Published: December 2007

To fulfill the practical needs of drilling personnel routinely involved in jar selection and use, a computer program based on stress-wave theory was developed. This approach provides an accurate, fast, and simple-to-use method for jar selection and optimization. It eliminates the need for large computational facilities, long solution times, and a high level of engineering expertise that are commonly associated with state-of-the-art transient dynamic finite-element methods (FEM's).

The program's accuracy was verified through comparisons with FEM results. The program produces a large matrix of results over the specified range of jarring variables within a few seconds of processing on a personal computer. The results provide an insight into the interaction between jarring variables and guidance in the optimum jar placement. Some application results are presented to show its usefulness in assisting drilling personnel in jar selection and placement. Typical results for the bottomhole assemblies (BHA's) containing heavyweight drillpipe (HWDP) show some interesting and not-so-obvious problems in such assemblies.
Dynamic Surge/Swab Pressure Predictions
Authors: Mitchell R. F.
Published: December 2007

It is generally accepted that the pulling and running of pipe causes pressure surges. The prediction of pressure surges is of economic importance in wells where the pressure must be maintained within narrow limits to prevent lost circulation and formation-fluid influx. For these wells, the drilling engineer needs the best possible method of calculating surge pressures to drill wells with a minimum of trouble.

This paper presents a dynamic surge/swab model that extends existing technology with the following features: (1) pipe and annulus pressures are coupled through the pipe elasticity; (2) longitudinal pipe elasticity and fluid viscous forces determine pipe displacement; (3) fluid properties vary as a function of temperature and pressure; and (4) formation elasticity, pipe elasticity, and cement elasticity are all used to determine the composite elastic response of the wellbore.

Comparisons between the model and field data demonstrate good agreement. Data matches have been made for both water- and oil-based muds in both shallow and deep wells. Furthermore, the model matches data that had not been previously matched by other models.
Modifications To and Experience With Air-Percussion Drilling
Authors: Pratt C. A.
Published: December 2007

Shell Canada Ltd. has air-percussion drilled 48 wells since Fall 1983. The industrial hammer was used predominantly, but the older oilfield hammer was used occasionally. A total of 117 solid-head bits were run. Experiences with the industrial percussion hammer indicated that tool modifications were required to reduce hole spiraling and the tendency of bits to go undergauge. High penetration rates (ROP's) with the new hammer required excessive blowing on connections, leading to the modification of a computer program for air-volume requirements. Because minor equipment failures were causing lost time, modifications were made to the jet system, sample catcher, and downhole floats.
Interpretation of Pressure Decline for Minifracture Treatments Initiated at the Interface of Two Formations
Authors: Moschovidls Z. A.
Published: December 2007

This paper extends the classic pressure-decline analysis to the more complex case where the minifracture is initiated near the interface of two formations and penetrates two or more formation layers of different leakoff characteristics. The development shows that the classic analysis is still valid, but it gives an effective or average leakoff coefficient that depends on the areal extent of the minifracture at the end of pumping in each individual layer. Examples demonstrate how to estimate individual layer leakoff coefficients with this theory, minifracture pressure-decline field data, and the fracture geometry predicted by a 3D fracturing simulator. Finally, the results obtained are used to explain field fracturing observations.
A Study of the Methods for Preventing Rod-Wear Tubing Leaks in Sucker-Rod Pumping Wells
Authors: McCaslin K. P.
Published: December 2007

Because of the high cost associated with tubing replacement, rod-wear tubing leaks are one of the most costly types of subsurface failures on sucker-rod-pumped wells. While severe hole deviation is most often blamed for rod-wear tubing leaks, case studies show that most rod-wear leaks are caused by accelerated corrosion, which is the result of the removal of a protective corrosion scale from the inside of the tubing. For this reason, the key to eliminating rod-wear tubing leaks economically is correctly identifying the problem as either mechanical wear or corrosion wear and then implementing the appropriate corrective measures.

Four case histories involving a total of 90 problem wells are presented to illustrate the methods used to differentiate between corrosion wear and mechanical wear. In these fields, tubing leaks were reduced by as much as 80% by proper identification of the cause of the leaks.
Use of Single-Well Simulators and Economic Performance Criteria To Optimize Fracturing Treatment Design
Authors: Anderson Robert W. , Phillips Alice M.
Published: December 2007

Low-permeability reservoirs are currently being propped with sand, resin-coated sand, intermediate-density proppants, and bauxite. This wide range of proppant cost and performance has resulted in the proliferation of proppant selection models. Initially, a rather vague relationship between well depth and proppant strength dictated the choice of proppant. More recently, computerized models of varying complexity that use net-present-value (NPV) calculations have become available. The input is based on the operator's performance goals for each well and specific reservoir properties. Simpler, noncomputerized approaches include cost/performance comparisons and nomographs. Each type of model, including several of the computerized models, is examined here. By use of these models and NPV calculations, optimum fracturing treatment designs have been developed for such low-permeability reservoirs as the Prue in Oklahoma. Typical well conditions are used in each of the selection models, and the results are compared. The computerized models allow the operator to determine before fracturing how changes in proppant type, size, and quantity will affect postfracture production over time periods ranging from several months to many years. Thus, the operator can choose the fracturing treatment design that best satisfies the economic performance goals for a particular well, whether those goals are long or short term.
Flow of Clay Suspensions Through Porous Media
Authors: Baghdikian Serge Y. , Sharma Mukul M. , Handy Lyman L.
Published: December 2007

This study was undertaken to investigate the transient behavior of particulate plugging of porous media. The objectives of the experiments were to study in detail a well-characterized system and to check the validity of theoretical predictions. Experiments included injection of clay suspensions under different conditions into sandpacks, measurement of pore-size distribution, and monitoring of permeability and effluent particle concentrations.
Kinetics of Crude-Oil Coke Combustion
Authors: Vossoughi Shapour , El-Shoubary Youssef
Published: December 2007

Coke is a solid or semiliquid material that deposits on the sand-grain surface area and is eventually burned as a fuel during an in-situ combustion process. Its combustion is the main source of energy to sustain the fire front. This study investigates the effects of different variables—such as specific surface area, oxygen partial pressure, and oil content—on the coke combustion by thermogravi-metric analysis (TGA). Each variable was varied while the others were kept constant. The TGA and the derivative thermogravimetric (DTG) curves were subjected to kinetic analysis. The rate equation produced indicated that the rate of coke combustion was proportional to the coke content yet to be burned, oxygen partial pressure, and sand-grain specific surface area. The rate constant followed an Arrhenius-type equation for the temperature dependency. The rate equation was tested for the range of specific surface areas of 0.126 to 24.3 m2/g [615 to 119,000 ft2/lbm], oil content of 10 to 58 wt%, and oxygen partial pressure of 5 to 50 kPa [0.05 to 0.50 atm]. The model's validity was tested for various crude oils from different geographical locations in the U.S., Canada, and Latin America.
Designing and Selecting Demulsifiers for Optimum Field Performance on the Basis of Production Fluid Characteristics
Authors: Berger P. D. , Hsu C. , Arendell J. P.
Published: December 2007

A method for characterizing and predicting the performance of emulsion breakers has been developed that involves the relationship between the preferred alkane carbon number (PACN) of the demulsifier and the equivalent alkane carbon number (EACN) of the crude oil and the salinity of the emulsified aqueous phase. This procedure can be used both to choose the proper demulsifier for field use and to develop effective new compounds by determining the effect of changes in molecular architecture and interfacial properties on performance. Parameters studied include chemical type, molecular weight, degree of branching, partition coefficient between the water and oil phases, interfacial-tension (IFT) reduction, and interfacial-viscosity changes. The importance of each of these properties to performance is discussed.
Use of Water-Vapor Desorption Data in the Determination of Capillary Pressures at Low Water Saturations
Authors: Melrose J. C.
Published: December 2007

The equilibrium conditions applicable to a single liquid phase held by capillary forces within the pore space of a reservoir rock sample are reviewed. It is shown that if the conditions for both chemical and capillary equilibrium are satisfied, an extended form of the classic Kelvin equation is obtained. With available thermodynamic data, it is also shown that the classic form of the Kelvin equation can be used to compute air/brine capillary pressures for core-plug samples. Experimentally, it is only necessary to allow such samples to reach equilibrium in a constant-vapor-pressure environment. Thus the conventional methods for determining capillary pressures can be usefully supplemented by vapor-phase desorption experiments. Although such experiments require relatively long equilibration time, they are simple to perform and are free from the difficulties common to other methods. A convenient way to establish a constant-vapor-pressure environment is to use saturated solutions of such salts as BaCl2, KNO3, and K2SO4. The available vapor-pressure data for these solutions are reviewed and tabulated. From these data, Kelvin capillary pressures are calculated for a range of NaCl brine compositions and temperatures. Some preliminary data obtained by this technique are reported for a pair of matched Berea core plugs of about 10 cm3 PV.
When Is a Reservoir Limit Test Applicable?
Authors: Matthews C.S.
Published: December 2007

Technology Today Series articles provide useful summary information on both classic and emerging concepts in petroleum engineering.Purpose:To provide the general reader with a basic understanding of a significant concept, technique, or development within a specific area of technology.

As discussed in an earlier paper in this series (" Transient, Semisteady-State, and Steady-State Flow," April 1986 JPT, Pages 385–86). after an extended time of production at constant rate in a bounded reservoir, the pressure decrease becomes proportional to time. The period in which this occurs is called semisteady state and is illustrated in Fig. 1.

The contributory pore volume, Vp, of the reservoir may be calculated from the slope of the production curve after it reaches semisteady state. For this reason, the constant-rate production test has been called a reservoir limit test. The applicable equation follows.
A Comprehensive Application of a Composite Reservoir Model to Pressure-Transient Analysis
Authors: Olarewaju J. S. , Lee John W.
Published: December 2007

This paper presents analytical solutions for interpreting pressure-transient tests for wells producing from a finite composite reservoir system. The paper also includes rate solutions and methods for analyzing long-term production data and forecasting production of oil or gas in a finite composite reservoir.
Density off Crude Oil Saturated With CO2
Authors: Marra R. Kendall , Poettmann Fred H. , Thompson Robert S.
Published: December 2007

A correlation for determining the density of CO2/crude-oil mixtures with engineering accuracy was developed. The correlation is based on the ideal-solution principle. Apparent liquid densities for CO2 were correlated as a function of pseudoliquid system density and CO2 concentration. In the final working correlation, the pseudoliquid system density is expressed as a function of pseudoliquid hydrocarbon density and CO2 concentration. The pseudodensities are then corrected to reservoir conditions. The correlation is presented in both graphic and equation form and is easily adaptable to computer or hand-held calculator applications.

The mean error for the 154 data points used to develop the correlation is +1.39%, the average absolute error is 4.46%, and the standard deviation is 5.25%. An error analysis of the experimental data indicated that when the 20 points with the greatest deviation are removed, the mean error is +0.06%, the average absolute error is 2.8%, and the standard deviation is 2.44%.

The correlation presented provides a simple method for calculating the density of CO2/crude-oil mixtures with engineering accuracy. The densities are used for calculating FVF and swelling and in other reservoir engineering calculations.
An Analytical Simulator for Drillstem Test Interpretation
Authors: Hegeman Peter , Abbaszadeh Maghsood
Published: December 2007

An analytical drillstem test (DST) simulator has been developed that can be used to verify the interpretation of DST's that have insufficient or poor-quality flow-rate data. The DST is modeled as a sequence of alternating pressure-specified buildup periods. With field data, it is shown that this simulator can be used to enhance the interpretation of nonsurface flowing DST's.
Hydraulic Fracturing Model Based on a Three-Dimensional Closed Form: Tests and Analysis of Fracture Geometry and Containment
Authors: Boutéca M. J.
Published: December 2007

The numerical model described in this paper was designed to provide a realistic three-dimensional (3D) solution for fracture propagation in minimal computation time. Comparisons with available results show good concordance for a wide range of data. The results of a parametric study are compared with the Nolte analysis of the propagation pressure.
Automatic Type-Curve Matching for Well Test Analysis
Authors: Abbaszadeh Maghsood , Kamal Medhat M.
Published: December 2007

This paper presents a general method for automatic well test interpretation. The method matches the field data with theoretical reservoir models using a constrained, nonlinear, least-squares regression technique coupled with numerical Laplace inversion of pressure-drawdown equations. Pressure gradients are computed by forward finite-difference approximations. Hence, reservoir models whose pressure gradients are difficult to obtain analytically can be readily included. Only equations for drawdown type curves of reservoir models are needed. Simulated pressure tests and actual field data are analyzed to illustrate the application of the method. The method reduces the time required to perform well test analysis and minimizes the subjectivity of interpretation.
Criteria for Gas-Lift Stability
Authors: Asheim Harald
Published: December 2007

Severe flow instability (heading or annulus heading) is known from operations of gas-lift systems. Here, two simple stability criteria are developed and compared with reported field data. The stability problems experienced for the cases examined would have been identified with these criteria and corrected at the design stage.

Introduction

The currently used principles for gas-lift design were established during the early 1950's. They provide relations betweengas injection pressure and the most efficient point of injection andgas injection rate and the production rate to be expected.

From these relations, standardized procedures for gas-lift design have been worked out. Works on application and optimization of the procedures have provided further insight into the interrelations between gas-lift design and economic performance.

Often-unstated assumptions of gas-lift design are that it will be possible to inject gas at a constant downhole rate and that the resultant production rate will be stable. This is not necessarily true; severe flow instability is well known in the actual operation of gas-lift systems.

Variations in pressure and flow rate are observed in all multiphase flow systems, even in pumping wells, because of redistribution of gas and liquids. They cause relatively small short-duration pressure and flow changes. Alone, this has little effect on the continuity of production. In a gas-lift system, however, it may trigger system instabilities.

API recommends that, for the sizing of pipes receiving gas-lifted production, a "surge factor" of 40 to 50% should be added to the estimated steady-state flow rate, compared with 20% for naturally flowing wells. Intended as guidelines for cases where more definite information is lacking, these numbers may indicate something about the uncertainties concerning the flow instabilities during gas lift.

Bertuzzi et al. observed that when the lift-gas input rate was reduced below a certain minimum, violent heading would occur and the liquid production would eventually cease. They postulated that "a sudden drop in pressure in the tubing brought about a sudden surge of gas into the tubing. The volume of gas surging into the tubing is dependent on the pressure and volume of gas in the annular space. If the pressure in the annular space dropped too much, gas ceased to flow into the tubing." More recently, gas-lift insta-bilities have led to shutdowns of wells in the Claymore field. This was amended by replacement of the downhole injection valve by a fixed orifice.

Flow instabilities have also been observed and analyzed for simple air-lift pumps. This is related to gas-lift instability. However, the inflow mechanisms of a gas-lift system are considerably more complicated than for an air-lift pump. Besides, the friction dampening will be much larger in a gas-lift system because of order-of-magnitude-larger flow length. Thus, the dominating mechanisms of instability will be quite different.
Simulation of PVT Experiments
Authors: Bouett L. W. , Grader A. S. , Orr F. M.
Published: December 2007

An interactive program (PVTLAB) was written to simulate PVT experiments with a microcomputer. The simulator is a real-time representation of an actual PVT laboratory. Operations typically performed in the laboratory may also be performed with the simulator. The Peng-Robinson equation of state (PR-EOS) is used to calculate phase behavior, and the results of the calculations are displayed in color on the microcomputer monitor. The monitor graphically represents the condition of all the physical components of the PVT laboratory, including pressures, fluid levels in vessels, and the status of valves and pumps. A printed record of every action taken during a run is kept if desired. A simulated experimental error results in an appropriate termination of the run. Program structure and operation are described, and examples of simulated PVT experiments are given.
Reperforation of North Sea Electric-Submersible-Pump Wells With an ESP/Y-Tool/TCP System
Authors: Dudley R. W.
Published: December 2007

As a result of the increasing emphasis on reducing operating costs and minimizing deferred production, a new system was designed for the reperforation of wells lifted with electric submersible pumps (ESP's). This paper describes an alternative method that can be used when a tubing-conveyed-perforating (TCP) system is required for the underbalanced reperforation of an ESP well. The method, which uses a combined ESP/Y-Tool/TCP assembly, can save about 24 hours in rig time over conventional methods. Use of the method can avoid substantial deferred or lost production, particularly when other wells requiring workovers are awaiting use of a rig at considerable cost. The system can also be used for the completion of new wells where an ESP is required from the outset and, under certain conditions, has an application during drillstem tests (DST's).
Refurbishment of the Ballast-Water System of the Gravity-Based Structure Beryl Alpha
Authors: Seume Klaus , Gilchrist James M.
Published: December 2007

In Sept. 1985, the Beryl Alpha platform in the North Sea experienced a leak in its ballast-water system in the utility shaft 328 ft [100 m] below sea level. The importance of the ballast-water system for platform operations and the particular location of the leak led to the development and implementation of unique and extensive repair procedures. This experience may be of interest to design engineers and repair contractors. The total repair program took more than 3 years and has cost $6.5 million [£10 million*].
Formation Pressure Prediction With Seismic Data From the Gulf of Mexico
Authors: Martinez Ruben D. , Schroeder Joyce D. , King Geoffrey A.
Published: December 2007

In this study, we derive seismic formation-pressure logs using seismic data from offshore Louisiana to delineate the distribution of overpressured zones in the subsurface. The seismic-data processing consists of velocity modeling, wavelet processing, and seismic inversion. From the acoustic impedances produced by seismic inversion, we derive seismic velocity and density logs at every seismic trace location using a relationship between sonic velocities and acoustic impedances. We use these logs to compute the seismic formation-pressure logs vs. depth. Formation-pressure logs are calculated with the assumption that compressional velocity, mean density, and depth are proportional to formation pressure. These logs are constrained at every depth by estimated matrix and fluid compressional velocities (vmax and vmin). vmax and vmin are derived from porosity and sonic well-log information.

Results include profiles of seismic-velocity, seismic-density, and formation-pressure logs for two intersecting seismic lines from offshore Louisiana. Logs from one well are used to constrain the data processing. The seismic formation-pressure sections delineate a large region of overpressured shales in the subsurface.
Experimental Study of a New type of Oil Production Platform
Authors: Kobayashi H. , Hirakawa S. , Suzuki T.
Published: December 2007

A hybrid-type guyed tower platform composed of a steel-framed tower and a concrete caisson with oil-storage space inside and a petalous pedestal on top has been proposed. Computer analyses, laboratory tests, and an experiment at sea were performed to verify its design and construction.
A Study of Slip/Stick Motion of the Bit
Authors: Kyllingstad Å. , Halsey G. W.
Published: December 2007

This paper deals with torsional oscillations caused by slip/stick motion of the drill-collar section. This phenomenon is associated with a large-amplitude, saw-tooth-like variation in the applied torque. "Slip/stick motion" refers to the belief that the amplitude of the torsional oscillations becomes so large that the drill-collar section periodically comes to a complete stop and does not come free until enough torque is built up in the drillstring to overcome the static friction.

A mathematical model of slip/stick motion is presented. This model includes parameters describing downhole friction effects and a simplified description of the drillstring. The effects of damping, finite rotary-table inertia, and the rotary-speed control system are discussed. Theoretical predictions are compared with measured torque signals recorded during field drilling.

This kind of drilling performance is likely to be less effective than normal drilling and may also lead to fatigue problems. This paper discusses ways to avoid severe torsional oscillations by using a more sophisticated feedback system to control the rotary speed.
Displacement of a Rich Gas Condensate by Nitrogen: Laboratory Corefloods and Numerical Simulations
Authors: Renner T. A. , Metcalfe R. S. , Yellig W. F. , Spencer M. F.
Published: December 2007

A unique laboratory study of displacement of a rich gas condensate (from an Overthrust Belt reservoir in the western U.S.) by nitrogen and buffer gas (nitrogen plus separator gas) was conducted in slim tubes and long Berea sandstone cores at 215°F [375 K] over the pressure range 4,500 to 5,700 psia [31.0 to 39.3 MPa]. Innovative modifications and adaptations of laboratory flow equipment were required to complete this study under the severe test conditions used. Unit displacement efficiency was higher for buffer-gas injections than for nitrogen alone.

A generalized compositional model, which incorporates a modified Redlich-Kwong equation of state (EOS) for the fluid properties, was used to simulate the laboratory corefloods described above. With an appropriate estimate of the number of gridblocks required to mimic mixing effects in the cores, good matches of all measured parameters were obtained, although calculated gas breakthrough times were consistently later than observed. Compositional profiles were generally well-matched, with the largest deviations occurring for the methane and C7 + fractions. This simulator can be used for reservoir engineering studies of the fluid systems described.
New Insights Into Enriched-Air In-Situ Combustion
Authors: Moore R.G. , Bennion D.W. , Belgrave J.D.M. , Gie D.N. , Ursenbach M.G.
Published: December 2007

This paper presents the results of 10 enriched-air in-situ combustion-tube tests performed on core from the Athabasca oil sands deposit. The tests show that at high pressures, the use of oxygen-enriched air results in increased low-temperature reactions between the oxygen and the oil, resulting in an increased fuel load and decreased burn stability. Although water injection may enhance the performance of oxygen combustion, it may also lead to increased oxygen storage in the swept zone.

Introduction

In-situ combustion, or fireflooding, is a thermal recovery technique that offers a high theoretical efficiency and uses relatively simple surface equipment. Although the process has been extensively studied in the laboratory and the field, operational problems associated with field projects, combined with the success of steam-based processes in a wide variety of reservoirs, have retarded the large-scale application of this technology.

Enriched-air injection is a modification of standard in-situ combustion technology with the potential to overcome a number of the problems that have hindered widespread field application of the process. In their excellent review of oxygen fireflooding literature, Garon et al. concluded that oxygen offers many process and operational advantages over normal air in-situ combustion. Fairfield and White discussed the advantages of using oxygen in the heavy-oil reservoirs of Saskatchewan, where field operations were hampered by severe sanding and gas locking of the production wells and by the formation of tight, difficult-to-treat emulsions. They concluded that removal of the large nitrogen volumes from the reservoir by injection of oxygen rather than normal air would not only reduce the sanding and gas-locking problems, but the greater allowable rates of oxygen injection would result in accelerated recovery schedules.

It is now generally accepted that in-situ combustion should be a follow-up process to steam stimulation if it is to be applied in cold, viscous reservoirs, such as those of northern Alberta. BP Resources Canada Ltd., in conjunction with the Alberta Oil Sands Technology and Research Authority (AOSTRA), has successfully piloted oxygen injection following steam stimulation of the Cold Lake reservoir. The application of in-situ combustion as an alternative to steam flooding has considerable merit because of its significantly higher thermal and displacement efficiencies.

This paper discusses enriched-air (95% oxygen) in-situ combustion tests conducted for AOSTRA on the Athabasca Oil Sands reservoir by the U. of Calgary In Situ Combustion Laboratory. The original objective of these tests was to evaluate the burning characteristics of enriched air at pressures up to 5520 kPa [800 psi]. The definite pressure effects noted during the initial test program, however, prompted an extension of the pressure range to 10 300 kPa [1,500 psi].
Thermal Recovery Well Test Design and Interpretation
Authors: Ambastha A. K. , Ramey H. J.
Published: December 2007

Because a reservoir undergoing a thermal recovery process is typically idealized as a composite reservoir, this study develops new design and interpretation equations by investigating pressure-derivative behavior of a well in a two-zone, radial, infinite or finite composite reservoir. Accurate design equations help establish the test duration required to observe a particular feature in well test data and thus the applicability of an interpretation method to determine front radius, or swept volume.

This study shows that the dimensionless time to the end of the first semilog line (deviation time) based on front radius is a constant. The deviation-time method may be used if wellbore storage does not mask the first semilog line. Design equations for the time of the beginning of the second semilog line and the time to observe outer-boundary effects show that the intersection-time method is not suitable for thermal recovery well test analysis. Correlations developed for the end of pseudosteady-state behavior of the swept region should help select the correct Cartesian line to calculate swept volume. This paper also presents derivative type curves applicable for all front radii, with mobility and storativity ratios as parameters for infinitely large composite reservoirs. For closed and constant-pressure outer boundaries, the ratio of outer boundary to front radius is the third parameter.
Assigning Effective Values to Simulator Gridblock Parameters for Heterogeneous Reservoirs
Authors: Begg S. H. , Carter R. R. , Dranfield P.
Published: December 2007

Characterization of heterogeneous reservoirs for simulation studies by use of a statistical component to the reservoir description combined with calculation of effective permeabilities is discussed through a case study of a fluvial reservoir. Inspection of whole core and logs from the Sherwood reservoir revealed that it is extremely heterogeneous, containing short shales embedded in a mixture of sands and silts. A statistical approach was used to quantify the distribution of core-plug porosity and permeability measurements to discriminate between significantly different rock types. A successive rescaling procedure was then adopted in which we first calculated effective values for each rock type from the core-plug data. These results were combined with statistics on the spatial distribution of the rock types to calculate effective values for the nonshale part of each layer. Finally, the effect of the shales on the vertical permeability was incorporated. The resulting anisotropy ratios, on the order of 10-3, were used successfully in black-oil model studies, a good match between the simulator predictions and observed production data being achieved with minimal fine tuning of the model parameters.
Effect of Borehole Size, Mudcake, and Standoff on the Photoelectric Absorption Index Measurement
Authors: Gearhart D. A.
Published: December 2007

The photoelectric absorption index, IPe, is accepted as an accurate measurement for the description of formation lithology. The measured IPe has been shown to deviate slightly for a given lithology because of the effects of porosity. Properly calibrated and measured IPe's, however, have been observed to deviate from predicted values in practice, even considering the influence of porosity. Such departures were traced to variations in borehole size and tool standoff.

The nature of the physical method of recording an IPe does not ensure independence from the influence of the borehole environment. A series of laboratory experiments has been conducted in test formations to verify and to characterize the influence of borehole size, mudcake, and standoff on IPe measurement. A set of nomographs has been constructed that allows correction of IPe measurements for the influence of the borehole environment. With these nomographs, a more accurate interpretation of IPe can be performed.
Geochemical Logging With Spectrometry Tools
Authors: Hertzog R. , Colson L. , Seeman B. , O'Brien M. , Scott H. , McKeon D. , Wraight P. , Grau J. , Ellis D. , Schweitzer J. , Herron M.
Published: December 2007

A geochemical logging tool (GLTSM) string, measuring natural, activation, and prompt neutron-capture gamma rays, produces logs of the most abundant and a few trace inorganic element concentrations. Direct measurements of Al concentrations are provided. A geochemically based closure model is used to derive Si, Ca, Fe, S, Gd, and Ti concentrations. The only significant spectroscopically undetermined element, Mg, is inferred by comparing measured with derived photoelectric factor. Analysis algorithms, demonstrations of accuracy and precision, and applications of geochemically derived formation properties are discussed.
A Perspective Look at Fracture Porosity
Authors: Hensel W. M.
Published: December 2007

Because overly optimistic estimates of hydrocarbons associated with reservoir fractures may lead to economic disasters, it is important that fracture porosity values, assigned by whatever means, be examined critically. Some basic fracture models together with documented examples of fracture width and frequency tend to suggest an upper limit for fracture porosity.
A New Set of Type Curves for Well-Test Interpretation With the Pressure/Pressure-Derivative Ratio
Authors: Duong Anh N.
Published: December 2007

This paper presents a new set of type curves used in well-test analysis for homogeneous reservoirs with wellbore storage and skin effects. When the pressure/pressure-derivative ratio (PDR) is used as a parameter in constructing the type curves, the vertical scales on both type-curve and field-data plots are identical. This automatic alignment of the vertical scale makes the new type curves easier to match and, subsequently, easier to use in the computer-aided analysis. The paper concludes that use of the new type curves reduces the uniqueness problem in pressure-transient type-curve matching, identifies the flow regimes effectively, and gives greater confidence in the results. A new method to correct the pressure buildup when drawdown type curves are used in radial-flow wells is also proposed. Two example applications, one with a long producing time and one with a short producing time before shut-in, are included to demonstrate the use of these type curves.
Analysis of Geothermal Wells With Simultaneous Logging Instruments
Authors: Davarzani J. , Sloan M. L.
Published: December 2007

A new series of instruments has been developed for applications in geothermal wells. These instruments provide simultaneous acquisition of spinner-flowmeter, pressure, and temperature data. The hardware and the calculation methods used to determine various wellbore steam properties are described briefly and a geothermal field example with details and analysis methods is presented.
Thermal Effects in Cyclic Operation of Storage Reservoirs
Authors: Batesole Elizabeth C. , Wilkes James O.
Published: December 2007

This paper addresses the long-term temperature and pressure variations of natural gas that is stored cyclically in underground reservoirs to avoid the formation of gas hydrates. A detailed examination of the well and near-well reservoir emphasizes the cumulative importance of the Joule-Thomson effect over many years.
Hydrate Equilibria for Binary and Ternary Mixtures of Methane, Propane, Isobutane, and n-Butane: Effect of Salinity
Authors: Paranjpe S. G. , Patil S. L. , Kamath V. A. , Godbole S. P.
Published: December 2007

This paper provides new experimental data on the phase behavior of gas hydrates for several binary and ternary mixtures of methane, propane, isobutane, and n-butane. After the molecular Kihara parameters for n-butane in the thermodynamic model were tuned, the predictions were in good agreement with the experimental data. The role of n-butane in hydrate formation is explained, and the effect of salinity on the phase behavior of binary mixtures of propane/n-butane is determined.
Production Optimization in the Provincia Field, Colombia
Authors: Blann Jack , Jacobson Laurie , Faber Christian
Published: December 2007

Designing or redesigning production facilities for optimum operation usually results in the generation of maximum profit from an installation. But in older fields, or fields where a short life is expected, design changes may not be a viable option. In such cases, obtaining maximum production within the limits of existing facilities, thereby minimizing new investments, may be an attractive option.

This paper discusses application of the latter technique in the Provincia field, Colombia, to optimize oil and gas production within constraints imposed by periodic temporary gas-compression-capacity restrictions and by the configuration of existing oil and gas facilities. The multistep optimization program used at Provincia included improvement of individual well performance, optimization of individual well facilities, fieldwide optimization of surface facilities, and optimization of the field production scheme.
Perforating a High-Pressure Gas Well Overbalanced in Mud: Is It Really That Bad?
Authors: Bundy Thomas E. , Elmer Matthew J.
Published: December 2007

This paper presents a case study of four high-pressure gas wells that were perforated overbalanced in heavyweight mud and then evaluated with pressure-transient tests. The surprising result of these tests was the minimal amount of completion damage. The average skin damage calculated from the test data was 2.6, which is much lower than the 12.6 predicted from data available in the literature. The information from this case study gives the completion engineer additional data on which to base decisions when designing perforation operations in high-pressure gas wells. This case study also raises the possibility that completion damage from overbalanced perforating practices decreases as reservoir pressure increases.