bluuebunny/crossref_metadata_2025 huggingface dataset:
50/50 Oil/Water Ratio Invert Oil Emulsion Mud – A Useful Tool or a Sales Gimmick?
Authors: Daynes R , Pratt S , Coates J
Published: December 2007

It is proposed within this paper that the use of Less Toxic Oil Based mud (LTOBM) with an oil to water (o/w) ratio of 50/50 (as opposed to the more conventional 75/25 o/w ratio) significantly reduces mud costs and may also reduce the volume of oil retained on cuttings and hence reduce the volume of oil dumped into the sea along with the cuttings.

Mud properties from two Field Trials of the 50/50 LTOBM in the UK sector of the North Sea are presented and the oil on cuttings retention figures are discussed theoretically.

Techniques suitable for investigating water in oil emulsions (to see what physical changes are brought about by varying the oil/water ratio and other parameters) are reviewed, and Optical Microscopy, Laser Light Scattering and Electron Microscopy results are presented.
Down Hole Safety Valve for Concentric Completion
Authors: Geyelin J. L.
Published: December 2007

Gas lift is a widespread method of artificial lift. However, on wells where there is no provision for Side Pocket Mandrels one way to avoid a heavy work over, is to run a macaroni string inside the existing tubing; gas can be injected via the macaroni and the lifted fluid flowed through the tubing-macaroni annulus.

On offshore wells, regulations or Company policy may impose the use of Surface Controlled Subsurface Safety Valve. This paper describes a new type of SC-SSV, run as an integral part of the macaroni string, which will close the macaroni string and the tubing-macaroni annulus. Associated equipment to set the SC-SSV in place and to seal the macaroni string system in the Chrismas-tree is also covered in the paper. In addition, field experience on over 30 offshore wells equipped with such a system is related.
Control of Scale in Sea Water Applications by Magnetic Treatment of Fluids
Authors: Donaldson J. D. , Grimes S. M.
Published: December 2007

The effects of magnetic fields on precipitates obtained from fluids that have been passed through the fields are studied for some potentially scale forming materials. The effect of the field is shown to vary with the material and with the method used to achieve precipitation. The changes that can be observed include changes in particle size, crystal morphology, crystal phase, solubility and rate of precipitation. Results from both laboratory and industrial case studies are presented. The data are interpreted in terms of the interaction between the applied magnetic field and the highly charged crystallisation nuclei being the major effect responsible for the changes.
Engineered Solutions to the Hazards of Oil Based Muds
Authors: Sweetsur A
Published: December 2007

In the drilling process, mud performs a number of functions requiring different physical and chemical properties and it is useful to consider how these are affected by the use of an oil based fluid.

The first function of the mud is to transport cuttings to the surface, which in general requires a velocity of around 100-200 ft/min and a viscosity of 30-50 secs/qt. The mud should have sufficient viscosity and gel strength to ensure that the cuttings are transported from the cutting surface and that they do not sink back to the bottom should circulation be interrupted. Secondly, the mud also works as a cutting fluid to lubricate and cool the bit and to ensure that it is working on a clean formation, and to assist cutting via the energy of the fluid jets from the bit nozzles.

The third essential function of the mud is as a primary means of pressure control. The hydrostatic head of the column of mud serves to counter-balance the formation pressure at any depth and must be amenable to adjustment to compensate for variations in pressure. Also, by measuring flow rates in and out of the hole, the volume of mud in the tanks and by monitoring whether the mud contains gas, fluids or hydrocarbons, a large amount of information about what is happening at the bit can be obtained.
End of Field Life Economics in the North Sea
Authors: Kellas G. K. , Kemp A. G. , Rose D.
Published: December 2007

With many North Sea oil fields now well into the decline phase of their production profiles, interest is now being shown in the management of a field in its latter years of production. The realisation that reservoirs have a finite limit and that this limit is approaching prompts two questions:

What determines how much of the remaining oil reserves can be produced and how can this be maximised while retaining economic efficiency? What determines when a field should be abandoned and what constraints are there on the decision to abandon?
Prediction of Drilling Trajectory in Directional Wells Via a New Rock-Bit Interaction Model
Authors: Ho H.-S.
Published: December 2007

This paper presents the basic concepts and methodologies of a new general rock-bit interaction model useful in predicting drilling trajectories in directional (and deep vertical) wells. This model is a generalization of existing similar models. It accounts for the anisotropic drilling characteristics of both the formation and the bit. The model is developed in a 3-D geometry. Therefore, it is capable of predicting the walk tendency and the build/drop tendency of a given BHA (bottomhole assembly) under any drilling condition. The model can be used as follows: in the forward mode to predict the drilling direction; in the inverse mode to generate the rock and bit anisot ropy indices; in the log-generation mode to generate drilling logs, such as a drilling dip log. Examples of the first two uses are shown.

The drilling directions predicted using various practices and theories are compared to those using this general theory in parametric form. Significant differences can be seen, not only in the predicted walk tendency, which is often missed, but also in the predicted build/drop tendency of the BHA.

This paper also shows why a 3-D analysis is essential to properly predict the drilling direction. A 2-D analysis not only completely ignores the walk tendency of the BHA, it also incorrectly predicts the build/drop tendency.
Drilling a 2,000-ft Horizontal Well in the Devonian Shale
Authors: Yost A. B. , Overbey W. K. , Carden R. S.
Published: December 2007

This paper discusses drilling a 2,000-foot horizontal well in the Devonian Shale, Wayne County, West Virginia, to test the concept that multiple hydraulic fractures from a horizontal wellbore can increase gas recovery efficiency over vertical stimulated boreholes. Discussion focuses on the air/mist drilling, wireline probes, and bottomhole assemblies that were used to drill the well. The target was a 50-foot zone located at a depth of 3,400 feet. Total hole length was 6,020 feet. The angle-building section was achieved using a 4.25°/100-foot design to reduce the risks associated with casing installation in the horizontal section. Directional control methods proved to be unreliable in an air-drilling environment. Bottomhole assembly performance was heavily dependent on motor life and lithologic type. The completion program for the well consisted of installation of 4 1/2-inch casing with external casing packers and port collars. This completion string was installed in 2,000 feet of open hole section that was air drilled. Both geophysical well logs and a borehole television camera survey were used to design the casing string so that shale intervals could be isolated for testing and evaluation before and after stimulation.
Oil Displacement Experiments in Heterogeneous Cores: Analysis of Recovery Mechanisms
Authors: Sorbie K. S. , Wat R. M. S. , Rowe T. C.
Published: December 2007

In a previous paper, we reported on an extensive series of single phase stable displacement experiments in a heterogeneous core system consisting of a cylinder of sandstone with a central core removed and filled with high permeability unconsolidated material; this is referred to as a cored core [1]. These experiments were designed to show some of the main viscous cross flow mechanisms which occur in processes such as polymer flooding in stratified systems. In this work, we extend these results in the cored core system by reporting on a series of oil displacement experiments. The objective of this work is to establish how the recovery mechanisms observed in the single phase experiments in the dual permeability core are modified when there is two phase flow with changing mobility in the aqueous phase. Qualitatively, the viscous cross flow recovery mechanisms seen in the single phase experiments, are also observed here although they are modified to some extent by two phase (relative permeability) effects. As in our previous work, numerical simulation is used in order to interpret and model the main experimental observations. Good agreement is obtained between experiment and theory in that observed cumulative oil curves, watercuts, layer flow rates and tracer profiles are well reproduced by the calculations. The simulation results lead to a clear interpretation of the two phase displacement experiments in terms of effects associated with relative permeabilities and the presence of the glycerol viscosifier.
East Vacuum Grayburg-San Andres Unit CO2 Injection Project: Development and Results to Date
Authors: Brownlee M. H. , Sugg L. A.
Published: December 2007

The East Vacuum Grayburg-San Andres Unit, operated by Phillips Petroleum Company, is the site of the first full scale miscible carbon dioxide injection project in the State of New Mexico. Since unitization in December, 1978, the unit has undergone infill drilling, repressurization by water injection, and is now in its second WAG (water-alternating-gas) cycle of CO2 injection. Early engineering efforts, based on the high fluid conductivity of the reservoir, prescribed the use of larger than normal downhole equipment in conjunction with the choice of an injection pattern with a high producer to injector ratio. This effort made possible the very short transition time between late primary production and early tertiary development. Due to over thirty years of primary production, reservoir pressure in the unit had fallen well below minimum misciblility pressure. Reservoir repressurization, accomplished with water injection, was conducted prior to the initiation of CO2 injection in September, 1985. During this time, the injection scheme was also determined, contracts for the purchase and delivery of the CO2 were negotiated, and design and construction of the CO2 injection system and produced gas gathering system were completed. Handling of the CO2 contaminated hydrocarbon gas production was also considered, resulting in the design and construction of a dehydration and reinjection facility. Treatment of the produced gas for the recovery of hydrocarbons is still under investigation.

Results have been encouraging with a large percentage of the wells exhibiting no CO2 breakthrough to date. However, isolated cases of CO2 breakthrough have been observed in a small number of wells in the more heterogeneous section of the tertiary project area. Future plans for the project include continued monitoring of reservoir performance, the evaluation of a proposed ten acre infill pilot project, and optimization of the CO2 reinjection facility.
Sensitivity of Steam Displacement Predictions to Three-Phase Relative Permeability Models
Authors: Sato K. , Aziz K.
Published: December 2007

Users of thermal simulators usually provide data in terms of two sets of two phase relative permeability functions: (1) krow and krw in a water-oil system, and (2) krog and krg in an oil-gas system. Within the thermal simulator two-phase relative permeabilities are used to predict effective permeability of each phase when all three phases are flowing simultaneously in a block. The most frequently used models for making these predictions are due to Stone (Model I and Model II) and their modifications. The literature does not provide clear guidance on the selection of a relative permeability model for a given problem. In this paper we present theoretical and numerical analyses of three-phase relative permeability models for steamflood problems.

Our analysis shows that relatively high krw and krg (from two-phase data) lead to higher kro from Model I than Model II, and the reverse is true when krw and krg are relatively low. The differences in predicted kro by the two models are greatest in the range of low oil saturations.

We have selected three sets of relative permeability data from the literature that have been previously used for the modelling of steamfloods. Data Sets 1, 2 and 3 are characterized by moderate, low and high values of krw and krg, respectively. The oil relative permeability (kro) predicted for Data Set 1 by the Stone's two models is about the same. As expected from our theoretical analysis, Stone's two models yield quite different kro's for Data Sets 2 and 3. However, oil production predictions with Model I and Model II for Data Set 3 are not too different, but these two models show significant differences in the simulation results for Data Set 2. Investigation of saturation profiles near production and injection wells show that low krw and krg values (Data Set 2) tend to drive saturations into the range where Stone's two models give different results, and high krw and krg values (Data Set 3) tend to keep saturations in the range where the two models give similar results.

The results of this study should be of value in selecting three-phase relative permeability models for steamflood simulations.
In-Situ Combustion With Oxygen-Enriched Air
Authors: Petit H. J. M.
Published: December 2007

To evaluate the field of application of in—situ combustion with oxygen, research was performed on the specific characteristics of in—situ combustion with oxygen-enriched air as compared to conventional combustion with air using two oils having different specific gravities (0.90 and 0.96).

The equipment is made up of an outer cell and an inner tube, equipped with heating collars. Since extensive safety precautions must be taken when using high oxygen concentrations, special attention was devoted to the choice of materials and equipment when the device was being designed. The device is combined with a computerized control system (flowrates, pressures, heat losses control) as well as data acquisition and processing of the experimental results.

The effects of total pressure, oxygen partial pressure and injected oxygen flux were studied. When the total injected flux (N2+O2) is constant and oxygen partial pressure increases, there is a less than proportional increase of the combustion front velocity no matter what pressure and oil are considered. This result is due to insufficient residence time of the oxygen in the reaction zone when the oxygen flux becomes very high. The results obtained at low pressure (1 MPa, 145 psi) at a constant oxygen flux show that the fuel availability and the air requirement at front are slightly affected by the oxygen partial pressure. Indeed, a slight increase in these parameters is found with oxygen enrichment for the heavier oil, and the opposite effect for the lighter oil. When the oxygen concentration increases at higher total pressure (7 – 10 MPa, i.e. 1015–1450 psi) and at constant oxygen flux, the characteristics of combustion are hardly affected for the heavier oil, whereas a reduction of about 40% is observed for the oxygen requirement at front for the lighter oil. These results can be explained by heat–exchange and mass –transfer phenomena. Combustion tests performed in sand packs that had first been swept by carbon dioxide, so as to simulate its effect in the zones downstream from the oxygen combustion front, revealed the influence of this gas on the process.

This laboratory study allowed us to compare the performances of combustion with enriched air in relation to those of conventional combustion with air. The results showed, in some cases, the advantage that can be obtained by using a gas richer in oxygen than air.
A Focused Current Resistivity Logging System for MWD
Authors: Evans H. B. , Brooks A. G. , Meisner J. E. , Squire R. E.
Published: December 2007

An MWD focused current resistivity system has been developed for well conditions under which neither the short normal nor the electromagnetic device operates well; that is, in wells where highly conductive drilling fluids are used, where relatively high formation resistivities are encountered, and where large resistivity contrasts are expected. The focused current system employs a guarded electrode design; the dynamic measurement range is 0.1 to 1000 ohm-m at ±5 percent of the resistivity value. The response characteristics of the MWD focused current device compare well to some published responses for equivalent wireline systems.

The focused current system offers superior performance in logging high-angle holes where excellent thin-bed resolution is required, in high-salinity muds where other systems do not perform well, and in fresh muds where the short normal is typically run. It provides exceptional resistivity measurements in all conductive borehole fluids.

A limited number of MWD focused current logs, the system correction charts and comparisons of focused current log responses to wireline log responses in the same wells are shown.
Interference Pressure Behavior in Multilayered Composite Reservoirs
Authors: Hatzignatiou D. G. , Ogbe D. O. , Dehghani K. , Economides M. J.
Published: December 2007

Analytical solutions are presented for studying the interference pressure behavior in a multi-layered, composite reservoir. The model considers an infinitely large reservoir with two partially or fully completed wells. Fluid interlayer crossflow is included. Each layer consists of two concentric zones, an inner and an outer region of uniform reservoir rock and fluid properties, separated by a mobility discontinuity.

The solutions are validated by comparison with the results obtained from several limiting models for interference testing, specifically the homogeneous single layer reservoir, the single layer composite system, and the two-layered systems with and without crossflow.

A sensitivity study is presented to examine the influence on pressure response of wellbore storage and skin effects at the active well, inter-layer crossflow, diffusivity ratio, mobility ratio, and permeability ratio.

Dimensionless pressure type curves are developed for estimating valuable formation characteristics of transmissibility and storativity from interference test data.
Pressure Drawdown in a Layered Reservoir With Linear Boundaries
Authors: Chen T.
Published: December 2007

An analysis of pressure drawdown has been conducted for a layered reservoir in which each layer is pinched-out by a linear boundary. It was found that if all the pinch-out distances were finite, then the bottom-hole pressure behavior of such a system could not be distinguished from that of a single-layered reservoir with an equivalent pinch-out distance. Consequently, only a single distance can be estimated from a drawdown or a buildup test. If, however, one of the layers is infinite in extent, then there is sufficient character in the pressure response to enable the use of the test data for estimating the pinch-out distance of the finite layer as well as the transmissibilities of each layer.
High-Resolution Logging: The Key to Accurate Formation Evaluation
Authors: McCall D. C. , Allen D. F. , Culbertson J. S.
Published: December 2007

Homogeneous geological zones, even 1-ft thick, are rarely seen in nature. The wireline logs that are used to evaluate reservoirs typically have bed resolutions ranging from 2 to 10 ft and cannot detect sudden changes in porosity, lithology or saturation. Now, however, log analysts can accurately evaluate formations that are less than 1-ft thick through new wireline measurements and enhancements of older measurements.
The Sources of Errors in Slowness Measurements and an Evaluation of Full Waveform Compensation Techniques
Authors: Liu O. Y.
Published: December 2007

The sources of errors in slowness, or ∆t, measurements are analyzed in this paper. Using synthetic waveforms generated by the finite difference method and a scaled model, the slownesses of compressional, shear and Stoneley waves are evaluated for examples of bedding, cave-in, fractured formation, eccentered and tilted tools. The depth-derived borehole compensation (DDBHC) and other means of improving the accuracy of slowness estimation are applied to the full waveform slowness estimation.

The effect of washouts on slowness estimates is extremely large if borehole compensation is not applied. Bed boundaries cause moderate error in slowness measurements and can be minimized by compensation. Simulation shows that the tool eccentering and tilting have only minor effect on compressional and shear slownesses, and no effect on the Stoneley wave. The shear slowness is disturbed more by discontinuities than compressional and Stoneley waves. The slowness is most affected when the receiver array is straddling the discontinuity and relatively more affected after the array passes the discontinuity than before entering it.

The conventional DDBHC method produces fairly good results for full waveform slowness estimation. Better results can be obtained, especially for shear slowness estimates, if some preprocessing is done on the waveforms and if the weighting on the receiver and transmitter slownesses used in the conventional DDBHC method is modified according to the results of model simulations and earlier studies. For borehole washouts, more scaled model and simulation work is needed for developing better compensation algorithms.
Behavior of Wells With Low-Conductivity Vertical Fractures
Authors: Cinco-Ley H. , Ramey H. J. , Samaniego F. , Rodriguez F.
Published: December 2007

This paper presents the transient pressure behavior for a well with a low conductivity vertical fracture, (kfbf)D ≤ 0.1; these cases include low kfbf fractures, long fractures or wells in relatively high permeability formations.

It appears that this type of systems exhibits two flow periods only: bilinear flow and pseudo-radial flow. It is demonstrated that for these fracture conductivities the effective wellbore radius is given by rw′=0.28(kfbf/k); that means that there is a maximum value of the effective wellbore radius achieved by hydraulic fracturing for a given value of (kfbf/k).

A new single line type curve is presented for analysis of pressure transient tests.
A Unified Type Curve Approach for Pressure Transient Analysis of Naturally Fractured Reservoirs
Authors: Jalali Younes , Ershaghi Iraj
Published: December 2007

A comprehensive treatment of pressure transient analysis of naturally fractured reservoirs is presented. Parameter estimation is based on pattern recognition, type curve matching, and auxiliary correlations. Pattern recognition verifies the amenability of data to analysis as well as the applicability of the model to observed behavior. Conditions under which a variety of pressure response patterns develop, are rigorously established. For each pattern, the applicable analysis procedure is specified.

A type curve is developed that incorporates interporosity flow response ranging from unsteady state to pseudo-steady state. Thus, type curve analysis determines the governing mode of interporosity flow and yields the reservoir parameters accordingly.

Auxiliary correlations are based on a thorough analysis of the transition curve. The correlations independently determine the reservoir parameters and thereby assist type curve analysis. In certain cases, the correlations can determine the proportion of matrix that contributes under "restricted" and "unrestricted" conditions.

The developed procedure is readily amenable to computer aided analysis of pressure transient data in naturally fractured reservoirs.
Acquisition Techniques in Cross-Hole Seismic Surveys
Authors: Delvaux J. , Nicoletis L. , Noual G. , Dutzer J. F.
Published: December 2007

The key to cross-hole seismic measurements is actually to dispose of appropriate sources and receivers. Most of the cross-hole seismic experiments have been done with hydrophone receivers and air gun or sparker types of sources. We have experimented these tools and compared them to other solutions like a coupled weight drop source and 3 component geophones. These equipments have been tested on a same site, a shallow reservoir in the Paris Basin. The hydrophone streamer enables a fast collection of the data but requires an energetic source (around 10 000 Joules) in order to counterbalance the lack of preamplifiers in the streamer, and to increase signal/noise ratio. The conventional 3 component borehole tool is more sensitive but does not record the full spectrum transmitted by the source (currently up to 500 Hz). Our results corroborate theoretical investigation on the radiation pattern of down-hole sources.
Electrochemical Origin of Conduction in Shaly Formations
Authors: Sen P. N.
Published: December 2007

Solving equations of motions for cations and anions in the presence of a double layer we show that rock conductivity σ is a nonlinear function of water conductivity σw. Both the observed bend for low salinity and the simple linear form at high salinity, similar to the empirical rules of Waxman – Smits (W-S) or Dual Water (D-W) model of Clavier et. al., are obtained. This provides a fundamental basis for these widely and repeatedly used empirical rules. We find additional geometrical factors multiplying the "clay" term which can explain the experimentally observed variation of conductivity intercept, from sample to sample, as a function of charge Qv. Most importantly, we show that the conductivity depends on the micro-geometry and a key dimensionless parameter ξ = Ω+r+/(N0a). The surface ion number density is Ω+, r+ is the ratio of average diffusion coefficient of the counter ions in the double layer divided by that outside, N0 is the bulk ion density far from the double layer and the particle radius is a. Dependence on r+ explains why exchanging with less mobile ions like Ca++ reduces the conductivity.
Closed Chamber Testing: The Effects of Wellbore Friction and Fluids Compression
Authors: Salas B. , Sageev A.
Published: December 2007

Closed chamber tests are commonly performed as back surge perforation cleaning in wells where high surface pressures are not desired. Typical of closed chamber tests are high fluid velocities in the wellbore, and a variable wellbore storage caused by the rapid gas compression as the liquid column approaches the upper surge assembly. In this paper, we examine the effects of wellbore friction and variable wellbore storage including liquid and vapor compressibilities on pressure responses on closed chamber tests.

The bottom hole pressure builds up more rapidly at early time when frictional effects are present. This rapid build up is associated with high liquid velocities in the wellbore. However, at late time the liquid velocity decreases, and frictional effects diminish. Wellbore frictional effects are dampened significantly in the presence of positive wellbore skin.

The effects of liquid and gas compressibilities in the wellbore on the pressure build up during a closed chamber test are significant. Allowing the liquid to expand in the wellbore causes the rapid gas compression to occur earlier, but results in a slower final build up. This delay in the final build up is caused by the additional late time wellbore storage that depends on the compressibility of the liquid and the vapor columns. The final wellbore storage is a combination of a large volume of a low compressibility liquid, and a small volume of a high compressibility gas.

The closed chamber tests responses including frictional effects and wellbore fluids compression were generated by coupling a superposition reservoir model with a wellbore fluid flow model.
Petroleum Engineering: An Emerging Discipline for the 21st Century
Authors: Miller M. A. , Pope G. A.
Published: December 2007

Petroleum engineering as a discipline has historically been intimately allied with a single industry. As such, the discipline is often viewed as being more of a technical specialty than as a fundamental discipline in the same sense as chemical, civil, electrical, or mechanical engineering. However, there are distinctive factors that make petroleum engineering fundamentally different from other engineering disciplines, much in the same way that mechanical engineering is different from chemical engineering. These differences make petroleum engineers best qualified to deal with the general class of engineering problems involving fluid movement within the earth, even in such non-energy related areas as hydrology and underground waste disposal. In addition to the need for petroleum engineers for hydrocarbon extraction, it is likely that as we move into the next century, many natural resource problems will require increasing reliance on technical expertise that can and should be supplied by what are currently called petroleum engineers.

Nomenclature has forced petroleum engineering into being a narrowly-perceived discipline, when in reality it possesses as much or more breadth as any other engineering discipline. The time is at hand for the discipline of petroleum engineering to stake out a claim to address all engineering problems involving fluid transport in the earth. No other engineering discipline provides a more appropriate base of knowledge and methodology. An example undergraduate curriculum is proposed for the education of petroleum engineers for the 21 st century. It is further proposed that the term "petroleum engineering" may not be entirely appropriate to fully describe this more fundamental emerging discipline.
The Effects of Current Low Drilling Levels on Lower 48 Oil and Gas Production
Authors: Woods T. J.
Published: December 2007

The severe drop in oil and gas drilling activity since 1985 has led to growing concerns about the near-term oil and gas production outlook in the lower-48 states. The Gas Research Institute has developed a detailed representation of the lower-48 oil and gas resource base and the activities necessary to explore and develop that resource base. Combined with a highly detailed assessment of gas well completions, the analysis indicates that lower-48 oil and gas production could be maintained at their 1986–87 levels through the year 2000 without a return to the peak drilling activity levels of the 1981–85 period and with little increase in real oil prices above the 1985 level. The development of new technology and improved production practices to improve the recovery of hydrocarbons-in-place in known oil and gas fields will play a critical role in sustaining lower-48 oil and gas production at their 1986–87 levels through the year 2000.
Unique Subsea Completions in the Kepiting Field, Indonesia
Authors: Coates R. L. , Kadi I.
Published: December 2007

The Kepiting Field development demonstrates an economical way of producing marginal reservoirs using a floating production facility and seafloor completed wells.

Unique to the Kepiting completions is a method for re-entering the wells to perform wireline operations. The system consists of steel tubular risers permanently connected to the seafloor trees which are terminated at the top by tensioning buoys located approximately 50 feet below the water. A buoyed platform/ginpole structure that extends the riser to the surface is temporarily attached to the top of the riser buoy and provides a dry working area from which to support operations using a wireline unit mounted on a workboat.

The success of the Kepiting project, which presently is used as a testing model for future deepwater projects, has increased Conoco's interest in developing marginal reservoirs using similar production/completion systems.
Economic Evaluation of Thermal Recovery Projects
Authors: Ramage W. E. , Castanier L. M. , Ramey H. J.
Published: December 2007

This paper presents a technique of economic evaluation of enhanced oil recovery projects for steam injection and in-situ combustion. In 1980, Williams and Ramey1 presented a model for the economic evaluation of steamfloods and in-situ combustion projects. Our study revises and updates then-work.

The oil recovery schedules for steam injection were generated using a modified Marx and Langenheim2 model and the recovery for in-situ combustion was computed using the Gates and Ramey3 technique. These models allow the determination of oil recovery versus fluid injected for a given reservoir or pilot providing that the main reservoir parameters such as porosity, thickness and saturations are known.

Some of the parameters needed for economic evaluation are not well known, and other parameters such as the recent price of oil may vary rapidly. A classic economic analysis is bound to be uncertain at best. In order to partially alleviate this problem our economic evaluation method includes a spreadsheet approach and a Monte Carlo simulation. A discounted net present value was obtained for each of the processes at different injection rates, and pattern sizes. The results are presented as a probability for a given net present value instead of a single value.

An example using published data from the Belridge field is shown. For this field both in-situ combustion and steam injection were found to be economically competitive.

The above mentioned technique can easily be modified for application to other fields or even other enhanced oil recovery processes. The models and economic calculations can easily be run on a microcomputer (IBM PC in our case).
The Tax Reform Act of 1986: Impact on Oil and Gas Tax
Authors: Kells R. B.
Published: December 2007

The Tax Reform Act of 1986 has created numerous changes in the tax laws which affect oil and gas investors, producers, royalty owners and the oil and gas industry in general.

Tax changes have been implemented with respect to intangible drilling costs, prepayment of intangible drilling costs, depletion, depreciation of oil, and gas equipment, the investment tax credit and the alternative minimum tax.
An Analysis of Field Development Strategies for Methane Production From Coal Seams
Authors: Sung W. , Ertekin T.
Published: December 2007

Natural gas production from conventional gas reservoirs and methane production from coal seams are different not only because of the different physical characteristics of the producing horizons but also because of the existence of different gas storage mechanisms. In the design of an optimum development plan for a coal seam degasification process, as it is the case in conventional reservoirs, it will be necessary to have a good knowledge of the field parameters such as total reserves, well productivity and formation characteristics. One of the more significant planning concerns in the development of a coal seam is the determination of the most efficient geometric arrangement of drainage wells for the purpose of establishing a uniform pressure decline throughout the coal seam. Since most of the methane gas in the coal seams is in the adsorbed stage, achievement of a uniform pressure distribution will assure the continuity of the free gas phase in the system. Existence of a pronounced permeability contrast in two principal directions coupled with the sorption characteristics necessitates the identification of certain criteria that will infer the optimum pattern configuration for coal seams.

In this paper we present the results of a series of numerical exercises targeted for a better understanding of the effectiveness of several drainage patterns. Along these lines, the effects of coal seam properties such as porosity, permeability, and permeability contrast have been isolated to understand the role of each individual parameter in the selection of optimum vertical and horizontal drainage well configurations. In the case of sparsely drilled well configurations, several infill drilling scenarios have been considered in an effort to maximize the ultimate recovery.
Evolution of Prudhoe Bay Automation
Authors: Davis Guy E.
Published: December 2007

The Standard Alaska Production Company (SAPC) was faced with a need to upgrade four major digital control systems used for oil production at Prudhoe Bay, Alaska. This equipment directly controls production of a 850,000 BPD facility. The changes were necessitated because of continuing plant expansions and resolution of control system debottlenecking problems. This paper describes the distributed control systems, methods used, technical complexity of the work, team organization, scheduling, installation coordination and duration of plant shutdown to perform the actual cutovers. The bottom line—the job of replacing four major computer systems was completed using a six-day outage for each facility. Impact to production was held to a minimum through advanced personnel training. Control system availability and plant operation improved considerably when the work was completed.

As production facility equipment ages, these techniques will become more important to other plant owners.
Diagnosis and Removal of Microbial/Fines Plugging in Water Injection Wells
Authors: Cusack F. , McKinley V. L. , Lappin-Scott H. M. , Brown D. R. , Clementz D. M. , Costerton J. W.
Published: December 2007

Because bacteria are naturally present in the water12 used in water injection for secondary oil recovery, these organisms adhere to available surfaces and produce biofilms3 just as they do in all aquatic ecosystems examined to date4. The bacterial biofilms in individual water injection wells develop to an extent dependent on the nutrient supply in the injection water. Organic contaminants are converted to bacterial biomass, and to bacterial exopolysaccharide slimes. Some organic compounds (notably lactate and acetate) are oxidized by anaerobic bacteria that use sulphur compounds as hydrogen acceptors and produce H2S. This souring process is dependent on the input of organic nutrients and it is the function of a heterotrophic bacterial population that is concentrated very close (<3 meters) to the well bore. The generation of H2S in the bulk of the water-flooded formation is severely limited by the very low levels of available bacterial nutrients in these areas and most H2S production is limited to the immediate viscinity of water injection and production wells. Injection well back flow data12 and injection well cleaning data2 both demonstrate, unequivocally, that heterotrophic bacterial growth in a waterflood operation is limited to areas very close to injection and production well bore holes. These areas are readily accessible to biocide treatment.

Bacterial biofilms develop very rapidly on the extensive surfaces of artificial and natural rock cores14, and these slime-enclosed adherent bacterial populations can reduce permeability by direct plugging. Treatment with 5-12% sodium hypochlorite (bleach) is sufficient to remove these bacterial accretions in both field2 and laboratory5 experiments, and treatment with sufficient bleach (3-4 tubing volumes) is regularly used to clean injection wells plugged by bacterial growth. We have recently shown6 that the bleach concentration used to remove bacterial biofilms can be reduced to ±1% without loss of efficacy. Bacterial biofilms trap particulate material8 and injection wells in systems with large amounts of particulate material in the injection water become plugged with biofilms impregnated with these particles. Bleach alone is not effective in cleaning these microbial/fines plugged wells but a combination of bleach and acid (in that order, with a water "spacer") is very effective5 because bleach removes the biofilm and allows access of acid to acid-soluble fines. Our developing general understanding of the nature of injection well plugging allows us to custom-design a cleaning protocol to remove this damaging material and restore original levels of water injectivity.
Rheology of Fracturing Fluids at Low-Shear Conditions
Authors: Acharya A. , Deysarkar A. K.
Published: December 2007

The rheological evaluation of cross-linked and uncross-linked fracturing fluids has drawn considerable attention in the recent years. These fluids are widely used in massive hydraulic fracturing jobs where they have to endure long hours of exposure to the reservoir temperature. They are also used in deep (>10,000 feet) formations which are significantly hotter than normal shallow reservoirs. Such demand on the stability of fracturing fluids at elevated temperatures for long hours has motivated researchers to study the rheology of fracturing fluids in detail.

Research efforts have been made to understand (i) the effect of in-line mixing of polymer gel and cross-linker, (ii) the effect of wall slip, and (iii) the effect of breaker (oxidizer) type and concentration at reservoir temperature on rheology of fracturing fluids. Considerations have been given to include the effect of pressure for compressive fluids like foam fracturing fluids. The effect of viscoelasticity and molecular structure of cross-linked fracturing fluids on proppant transport are also being studied.

An important aspect of fracturing fluid rheology that remained almost unattended is the low shear and zero-shear rheological characteristics of the commonly used fracturing fluids. In a typical fracturing job, the fluid experiences low shear in various locations of the fracture. Also, the proppant exerts very low shear to the fluid while settling in the fracture. Therefore, a good knowledge of the rheological characteristics of the fracturing fluids at low shear is very important.

The purpose of this paper is to evaluate rheology of commonly used fracturing fluids at low shear rates. The low shear rheology will include measurement of low shear viscosity and yield stress. The low shear rheological data was gathered from Rheometrics pressure rheometer (RPR) and a mini rotary viscometer (MRV). The MRV is commonly used in the low temperature characterization of automotive lubricants. This paper will compare the low shear rheological data obtained from RPR and MRV with those calculated from a typical Fann 50 viscometer. The final part of this paper will discuss the importance of the presence of yield stress on proppant transport for cross-linked CMHPG and guar fracturing fluids.
Determination of Interaction Coefficients and Critical Properties of Heavy Fractions for Equation of State Computations: An Automated Algorithmic Approach
Authors: Obut S. T. , Ertekin T.
Published: December 2007

Equations of state are widely used in compositional simulation to predict phase distribution and composition, which in turn facilitates prediction of compositionally dependent properties such as density, viscosity, interfacial tension, and enthalpy. A well-known problem confronted with naturally occuring hydrocarbon systems is characterization of the high molecular weight fraction (usually C7 +). The high molecular weight fraction must be split into an optimum number of pseudo-components each having a prescribed set of critical properties and interaction coefficients. Since procedures for doing this are largely empirical, typical equation of state packages must be tuned to available experimental data.

Often available experimental data are limited in scope, or the ultimate simulation involves significant changes in temperature, pressure or composition. In each situation, tuned pseudo-component critical properties and/ or interaction parameters will manifest important temperature, pressure, and composition dependencies. Thus, a versatile phase description can effectively be ensured if tuning is automated internally within the equation of state package.

In this paper, a methodology for achieving this task is described. First, the heavy fraction is split into a defined number of pseudo-components and starting values of binary interaction parameters and critical properties are obtained by using readily available correlations in the literature and/or mixing rules. Then, a linear optimization technique (two-phase method) is adopted for non-linear applications by using iterative techniques (iterative variables being pseudo-component binary interaction coefficients with CH4 and pseudo-component critical properties). Tuned sets of binary interaction parameters and critical properties of pseudo-components for a cubic equation of state are generated by using experimental depletion curves.

As the computation progresses the tuned set replaces the default set to achieve further improvements. The success of this linear optimization routine is demonstrated for different reservoir oils.
Investigation of Gas/Oil Relative Permeabilities: High-Permeability Oil Reservoir Application
Authors: Delclaud J. , Rochon J. , Nectoux A.
Published: December 2007

Gravity drainage can result in a high recovery efficiency for high permeability oil reservoirs with low viscosity oil and low interfacial tension.

In order to make reliable field wide performance predictions of this production mechanism, it is necessary to obtain accurate determination of gas-oil relative permeabilities and residual oil saturation.

Gas-oil relative permeabilities have been extensively investigated, by performing: –displacement experiments in various conditions (differential pressure, interfacial tension, connate water or not, short or long core, room or reservoir conditions).–dynamic capillary desorption experiments.

Special emphasis has been given to the actual physical meaning of the residual oil saturation and the way it is reached.

The main results are: –Gas-oil displacement experiments performed in laboratory conditions (high interfacial tension) with various pressure drops give the same relative permeability if interpreted taking capillary effect into account. The final experimental oil saturation, which depends on the maximum acceptable injection pressure (turbulent flow problems) is different from the "true" ROS (corresponding to kro = 0).–Capillary desorption experiments in lab conditions with numerical interpretation of the transient production, may be used to determine ROS and oil relative permeability at high gas saturation.–Interfacial tension (in the range 0.6 – 30 mN/m) has little influence on the relative permeabilities.–Presence of connate water has little influence: oil and water behave as a single liquid phase.–Relative permeabilities obtained from laboratory conditions (short core) and reservoir conditions (long core) experiments are very close.–The final desaturation (ROS around 5 %PV) is reached very slowly, due to the very low level of oil relative permeability (about 10−5).

A reliable method to determine relative permeabilities in laboratory conditions has been established, by performing both displacement and capillary desorption experiments.
Scale Inhibitor Precipitation Squeeze for Non-Carbonate Reservoirs
Authors: Carlberg B. L.
Published: December 2007

There has been evidence of a need for scale inhibitor precipitation squeeze treatment in sandstone as well as in carbonate reservoirs. The Mixed Chelate process was designed to meet that need with the injection of a single solution. Success in the laboratory has been verified with numerous experiments. Success has also been evidenced in a field test initiated in late 1986.