bluuebunny/crossref_metadata_2025 huggingface dataset:
A General Study of Asphaltene Flocculation Prediction at Field Conditions
Authors: Gharfeh Samir , Singh Probjot , Kraiwattanawong Kriangkrai , Blumer David
Published: December 2007

A large set of field data have been collected during the last decade related to various facets of asphaltene instability problems at our production facilities. These problems include compatibility of heavy oil with hydrocarbon diluents in a Venezuelan operation, commingling of live oil and condensate in a North Sea production facility, compatibility of drilling mud-base oil, and miscible injectants with reservoir fluids in Alaskan operations. In each of the field cases, significant lab data were generated by titrating the neat dead crude oil, and oil-solvent blends with n-alkanes. The solvents used to study the asphaltene issue were toluene, condensate, and base oil. We have applied available asphaltene prediction techniques (Heithaus 1960, 1962; Wiehe and Kennedy 2000ab; Wiehe et al. 2001; Andersen 1999; Wang and Buckley 2001; Wang et al. 2003, 2004; Leontaritis 1998) to explain the field data. None of the models has been found comprehensive enough to explain flocculation at all the conditions, including the flocculation that occurs at ambient conditions in the presence of paraffinic diluents; stability enhancement that occurs upon addition of aromatic solvents; and the instability that occurs in a live fluid because of changes in composition, pressure, and temperature. To handle a complex crude oil system, these models made some simplifying assumptions that enabled them to make the problem manageable. In doing so, they lose some predictive capability. We found there are two forces that need to be accurately captured— dynamics of the alteration of solubility parameter of the hydrocarbon matrix, and change in entropy of mixing—to model the asphaltene behavior. The latter has been either empirically estimated by extrapolating the ambient titration data or neglected in many of the previous models. The basic parameters for our model can be calculated from lab data generated by titrating the dead crude oil, or oil solvent blends with n-alkanes, at different temperatures. So far, this model has been applied to various field conditions in production facilities and has been found successful in matching the field data.
Hydrate Remediation in Deepwater Gulf of Mexico Dry-Tree Wells: Lessons Learned
Authors: Harun A. F. , Krawietz T. E. , Erdogmus M.
Published: December 2007

Hydrate plugs were formed above the mudline in two dry tree oil wells in the Gulf of Mexico. The plugs were formed when trying to open the downhole safety valve with crude to return the wells to production after they were shut-in because of hurricane evacuation. Several unsuccessful attempts to melt the hydrate blockages included pumping methanol through the chemical injection lines below the plugs and lubricating in glycol above the plugs. As a last attempt, before using coiled tubing, injecting hot oil into the tubing-casing annulus was considered. Transient simulations were performed to determine the required injection temperature, rate, and time. Well integrity issues were mainly associated with the compatibility of the hot oil with the elastomers and possible as-phaltene or paraffin precipitation in the annulus. Sensitivity studies show that with a 1-bbl/min injection rate and 150°F injection temperature, the pressure-temperature condition inside the tubing located 3,000 ft below the sea level will come out of the hydrate formation region within 4 hours. However, as the section goes deeper, the warm up time increases and at some point the conditions will not warrant being out of the hydrate region even after several days of injection time. Hydrate plugs in two dry tree wells melted after 6 and 60 hours of injection time, respectively. A revised restart procedure has been implemented to eliminate the hydrate problem in future startups.
Casing and Tubing Design Considerations for Deep Sour-Gas Wells
Authors: Stair M. A. , Mclnturff T. L.
Published: December 2007

Tubular metallurgy is usually considered to be the dominant design requirement associated with deep sour-gas wells and as such has received extensive treatment in the industry's literature. Other requirements vital to the assurance of a successful well design, however, have not been treated adequately in the literature. This paper addresses some of the nonmetallurgical requirements incorporated in our drilling operations in the deep, sour, geopressured areas south of Jackson, MS, and in the Tuscaloosa trend in Louisiana. The following topics are included: (1) the need and use of the maximum distortion strain energy—von Mises—technique for designing production tubulars; (2) a testing technique used to evaluate connections for use with these tubulars; (3) unusual design and operational features of these wells; and (4) the inspection and handling requirements to ensure the integrity of the wellbore tubular.
Determination of Gas-Condensate Relative Permeability on Whole Cores Under Reservoir Conditions
Authors: Gravier J. F. , Lemouzy P. , Barroux C. , Abed A. F.
Published: December 2007

Rock samples from a Middle East carbonate retrograde condensate gas field were studied to determine their relative permeability to gas and condensate curves. We have emphasized the determination of condensate minimum flowing saturation—or critical condensate saturation—and the reduction of permeability to gas in the presence of immobile condensate saturation.

A ternary pseudoreservoir fluid of methane/pentane/nonane made it possible to work in simulated reservoir conditions with a greater flexibility for experimental procedures. The initial water saturation equaling that in the reservoir was restored. The results of the gas-condensate system indicate that the critical condensate saturations are high (the average value is 36% PV) and that the reduction of permeability to gas is higher than for a standard gas/oil system. Also presented are the details of the experimental procedures, the fluid characteristics, the results, and a discussion.
Streamtube Relative-Permeability Functions for Flashing Steam/Water Flow in Fractures
Authors: Gudmundsson J. S. , Menzies A. J. , Horne R. N.
Published: December 2007

The flow of steam/water mixtures into geothermal wells is analyzed by use of a two-phase model for flashing flow. The model includes the effect of heat transfer from the formation rock to the two-phase mixture. In the reservoir/well system, the two-phase flashing flow is assumed to occur in fractures. The model can be used to forecast the mass flow and enthalpy characteristics of two-phase geothermal wells. Relative permeability functions are derived for flashing steam/water flow in the feed-zone fractures of geothermal wells.
Alcohol Extraction Technique for In-Situ Determination of Resident Water Saturation and Resident Brine Salinity
Authors: Mut A. D. , Deans H. A.
Published: December 2007

Water saturation and formation water salinity traditionally have been difficult to determine in reservoirs that are at irreducible water saturation conditions. An approach to the problem has been developed in the form of a single-well, in-situ extraction technique that can determine both quantities simultaneously. A mathematical model describing the technique was written and subsequently used to predict the behavior of a series of laboratory experiments. The experiments were performed on Berea sandstone cores at a variety of water saturations and brine salinities. The predicted and observed production profiles are in excellent agreement.
Experimental Investigation of the Effects of Temperature, Pressure, and Crude Oil Composition on Interfacial Properties
Authors: Hjelmeland O. S. , Larrondo L. E.
Published: December 2007

The wettability of the fluid/rock system affects the distribution of fluids within a porous medium; this distribution in turn strongly affects displacement behavior and oil recovery efficiency. This paper is an investigation of the influence of temperature, pressure, and oil composition on the wettability of a specific carbonate reservoir. Contact-angle measurements were used to quantify wettabilities on calcium-carbonate crystals. The experimental conditions included varying temperature and pressure for both dead crude oil and oil recombined to the original bubblepoint. In addition to quantification of wetting properties, interfacial tension (IFT) between oil and water was measured, and formation of rigid films was observed.

A complete reversal from a predominantly oil-wet system at lower temperatures to a predominantly water-wet system at higher temperatures was found. Pressure alone had little effect on the wettability of the system. IFT between crude oil and brine showed an increase with increase in temperature under anaerobic conditions, whereas at aerobic conditions, IFT decreased with increase in temperature. The tendency to form rigid films at the crude-oil/brine interface was found to be temperature-dependent. The formation of rigid films was stronger at lower temperatures.
Automatic History Matching of Laboratory Corefloods To Obtain Relative-Permeability Curves
Authors: Macmillan D. J.
Published: December 2007

A standard automatic history-matching technique is applied to a Buckley-Leverett solution of laboratory corefloods to obtain oil/water relative-permeability curves. Several laboratory coreflooding examples are included to illustrate the usefulness of this method.
Bumper-Pile Design for Mating Platform and Subsea Drilling Template
Authors: Nelson W. E. , Murphy Benton S. , Stahl Bernhard
Published: December 2007

This paper describes the procedures used to design bumper piles for the docking installation of a large North Sea platform jacket over a subsea drilling template. Model tests are described and their response data presented and interpreted for design use. Procedures are presented for evaluating ultimate load- and energy-absorbing capacities of the docking piles together with the jacket-bottom horizontal framing. Conclusions are drawn and observations offered concerning analytical methods for determining docking pile design loads and the feasibility of mating large platform assemblies offshore.
Displacement of a Viscous Oil by the Combined Injection of Hot Water and Chemical Additive
Authors: Karakas M. , Saneie S. , Yortsos Y.
Published: December 2007

A model of an adiabatic hot waterflood assisted by the simultaneous injection of a chemical additive is presented. The process considered is one-dimensional (1D), two-phase flow, with negligible effects of dispersion, heat conduction, and lateral heat losses. The model allows for the chemical to be soluble in the aqueous phase and to be adsorbed on the solid surface. The effects of temperature on the viscosity ratio and the adsorption thermodynamics and of chemical concentration on the fractional flow curves are considered.

The theory of generalized simple waves (coherence) is used to develop solutions for the temperature, concentration, oil-saturation profiles, and oil-recovery curves. The results show that, in the adiabatic case, the combined injection of chemical and hot water enhances the oil recovery considerably. The sensitivity of the recovery performance to the process parameters is discussed. It is shown that, for Langmuir adsorption equilibrium, the chemical resides in the heated region of the reservoir if its injection concentration is below a critical value and in the unheated region if its concentration exceeds this critical value. Typical results for a chemical pulse injection in a tertiary recovery process indicate that the recovery performance is maximized when the chemical resides entirely in the heated region of the reservoir.
A Laboratory Investigation of Sweep During Oxygen and Air Fireflooding
Authors: Garon A. M. , Kumar M. , Lau K. K. , Sherman M. D.
Published: December 2007

An experimental investigation of volumetric sweep during fireflooding was conducted in threedimensional (3D) scaled models. The effect of oxygen vs. air injection, water/oxygen ratios, injection rates, and crude-oil parameters on sweep efficiency and performance of the fireflood were evaluated. Results indicate that the sweep of a fireflood was similar for both oxygen and air combustion; water injection resulted in a small decrease in the sweep of the fireflood; wet combustion required less oxygen or air and increased the oil recovery and recovery rate; fireflooding a medium-gravity crude-oil reservoir resulted in a larger sweep than a heavy-oil reservoir; and (within the limited range of this study) higher injection rates improved the sweep efficiency.
Estimation of In-Situ Stresses From Ultrasonic Measurements
Authors: Mao N. H. , Sweeney J. J.
Published: December 2007

The results of an effort to develop a technique for estimating in-situ stresses by measurement of stress-induced velocity anisotropy around a borehole are presented. Relevant parameters required to make the estimate were identified and measured in the laboratory on a 35.6-cm [14.0-in.] cube of Nugget sandstone with a 10.2-cm [4.0-in.]-diameter hole under biaxial loading. Two pairs each of radially and tangentially polarized transducers were placed inside the hole with displacement directions either parallel or perpendicular to the principal stress directions. With this configuration, relative travel times were measured by both a pulsed phase-locked loop (P2L2) technique and a cross correlation of digitized waveforms. The biaxial velocity data were used to back-calculate the applied stress. The standard deviation of the differences between the calculated and applied stresses is 0.62 MPa [90 psi] for a stress level up to 8.63 MPa [1,252 psi].
Magnus Subsea Wells: Design, Installation, and Early Operational Experience
Authors: Dawson A. P. , Murray M. V.
Published: December 2007

This paper describes the subsea aspects of the Magnus field development. The design and installation of the well completions and control systems are described. Problems encountered during this phase and during the early production life of the system are discussed. Some of the longer-term operational aspects are also discussed, and recommendations are made to improve subsequent subsea developments.
The Geologic Aspects of Reservoir Characterization for Numerical Simulation: Mesaverde Meanderbelt Sandstone, Northwestern Colorado
Authors: Jones J. R. , Scott A. J. , Lake L. W.
Published: December 2007

Major shortcomings in the geologic descriptions used in numerical simulations are addressed by a reservoir characterization of Mesaverde sandstone outcrops in northwestern Colorado. A geologic model for Mesaverde point-bar deposits using core plug data relates permeability trends to stratification type. This reservoir characterization helps develop a general reservoir descriptor that analyzes actual field permeability data that are related to an observable feature (stratification type).
Rock-Property Changes During Reservoir Compaction
Authors: Morlta Nobuo , Gray K. E. , Srouji Farlz A. A. , Jogl P. N.
Published: December 2007

Deformations, absolute permeability, electrical resistivity, PV change, and compressional- and shear-wave velocities were measured for Berea sandstone under various loading paths at temperatures from 70 to 380°F. The experimental behavior was subdivided into five categories. The experimental results were analyzed for each category, and the analysis was used to construct semianalytical rock-propery equations. These equations accurately simulate complex rock properties under various loading paths, which, unlike conventional rock-property equations, are expressed in terms of strain components. This formalism is practical because strains are more directly related to rock properties than are stress components. This paper presents unique rock-property data, including axial and radial measurements with various loading paths and temperatures; semianalytical equations that accurately simulate rock properties under various loading paths up to rock failure; and realistic predictions of rock-property changes during reservoir compaction.
Triple-Fluid Evaluations Using Density, Neutron, and Electromagnetic Propagation Logs
Authors: Peeters M.
Published: December 2007

Determining the remaining oil, gas, and water saturations simultaneously, independent of water salinity, is often necessary for EOR. The triple-fluid method determines these saturations quantitatively using the apparent porosities of the electromagnetic propagation tool (EPT), density, and neutron logs.

Field examples are compared with service-company products to demonstrate that neutron-log shale corrections are mandatory. Dielectric logging tools with larger investigation depth are required to make the method generally applicable.
A New Technique for Visualizing the Distribution of Oil, Water, and Quartz Grains in a Transparent, Three-Dimensional, Porous Medium
Authors: Chen Jing-Den , Wada N.
Published: December 2007

A new technique for visualizing the distribution and structure of oil, water, and quartz particles in a transparent, three-dimensional (3D), porous medium is presented. A laser light sheet illuminates a slice of a rectangular cell containing a mixture of oil, water, and quartz particles. All three phases have the same refractive index. The quartz particles do not fluoresce. From the different fluorescence colors of water and oil, the cross-sectional distribution of the three phases can be visualized. Photographs of different cross sections are presented that show both the solid grain structure and trapped oil blobs. This technique can be used to study two-phase flow in porous media.
Transient Dynamic Analysis of the Drillstring Under Jarring Operations by the FEM
Authors: Kalsi M. S. , Wang J. K. , Chandra U.
Published: December 2007

A drilling or a fishing jar is used in the bottomhole assembly (BHA) of a drillstring to free the string should it become stuck during the drilling operation. Because many expensive sensors are now incorporated in downhole tools, it is necessary to predict the damaging effect of jarring on these downhole sensors accurately. In addition, BHA's are becoming increasingly complex and are difficult to analyze by closed-form methods. For such reasons, the finite-element method (FEM) was used in this study to predict the dynamic response of a drillstring to jarring.
Effect of Mud Composition on Wear and Friction of Casing and Tool Joints
Authors: Bol G. M.
Published: December 2007

Friction and wear between casing and tool joint have been measured on full-scale equipment. The results show that the most important mud property, with respect to lubricity and protection against wear, is its ability to form a film that separates the two steel surfaces. Results from small-scale tests are shown to be nonrepresentative.
Geologic Parameters of Reservoir Sandstones as Applied to Enhanced Oil Recovery
Authors: Gaida K. H. , Kessel D. G. , Volz H. , Zimmerle W.
Published: December 2007

This paper discusses the importance of geological parameters of reservoir sandstones and their fieldwide distribution for proper planning and operation of EOR projects. Such parameters are gross and net pay thickness, permeability, porosity, grain size distribution, composition of detrital minerals, amount and type of mineral cements, and amount and type of clay minerals.

Fieldwide distribution of these parameters is shown for the case history of the Hankensbüttel-Süd oil field in the Federal Republic of Germany. Overlaying the distribution maps made it possible to distinguish areas with excellent to good potential for chemical flooding from areas of fair to poor potential. On the basis of these results, a surfactant/polymer flood pilot has been initiated in this field.
Some Factors That Affect the Sour-Service Performance of Carbon-Steel Oil-Country Tubulars
Authors: Ciaraldi Stephen W.
Published: December 2007

Carbon-steel oil-country tubular goods, such as API 5AC Grade L-80, combine high strengths for deep-well applications with restricted hardness for resistance to sulfide stress-cracking in sour wells. Despite these general characteristics, field experience with such tubulars has not been completely trouble-free. Problems have been encountered with hardness control and testing. Metallurgical factors involved with heat treatment and upsetting have affected tubular performance. Problems associated with threaded connections and tool damage have occurred. Special considerations are required for electrical-resistance-welded (ERW) tubulars, field welding, and completion operations.
Assessment of Sulfide Corrosion Risks in Offshore Systems by Biological Monitoring
Authors: Maxwell Stephen
Published: December 2007

Probably the most common problem encountered with sulfate-reducing bacteria (SRB) in offshore systems is sulfide corrosion. Although SRB-mediated corrosion is related to the production of sulfides at a metal surface, monitoring of SRB has been almost solely by counting of bacteria in and a chemical analysis of the bulk phase. Furthermore, bacterial counts give little information on the in-situ activity of SRB—i.e., the sulfate- reduction/sulfide-production rate. A novel technique that uses [35S] sulfate has been developed, however, that allows for the determination of SRB activity at metal surfaces.

The results of field trials in two situations where the activity of SRB is thought to carry a potential risk of sulfide corrosion are presented: first on external surfaces, the horizontal members of the Thistle platform, and second on internal structures, the metal surfaces submerged in the entrained seawater in the drill leg of the Brent Bravo platform. The results clearly show that current monitoring methods may give misleading results and that by using radiorespirpmetric methods, a better understanding of the processes taking place within these systems can be obtained. Thus remedial measures can be carried out when necessary with greater assurance than previously.
Geological Aspects of the Codell Sandstone, Weld and Larimer Counties, CO
Authors: Hively Roger E.
Published: December 2007

Since 1981, nearly 1,000 wells have been drilled in the Denver basin of northeastern Colorado with the Codell sandstone as their primary target. The majority of this exploration has been in the axial portion of the basin, in Townships 4 to 7 North, Ranges 64 to 68 West, in Weld and Larimer counties. Drilling depths of Codell wells range from 6,800 to 7,400 ft [2073 to 2256 m].

Recently discovered oil and gas production in the Codell sandstone encompasses several hundred square miles. Thickness and lithology of the formation are remarkably similar across this widespread area. Geologic limits of this reservoir are less distinct than in most sandstone exploration targets; therefore, geologic parameters must be considered over a large area.
A Dynamic Computer Model of a Kicking Well
Authors: Nickens H. V.
Published: December 2007

The dynamic effects of variable pump flow rate, formation-influx distribution, blowout preventer (BOP) and choke closure, choke adjustments, and well stabilization are accounted for in the analysis of a kicking well by solution of the appropriate mass- and momentum-balance equations. In the gas/liquid regions, the system is modeled as separated flow. The mass-balance equations are solved for the gas and liquid separately, but the momentum equation is solved for the mixture.

The model predicts the detailed flow and pressure response of the well at all times and wellbore locations during the kick. The model is currently capable of simulating a single kick in a vertical hole (surface or subsea) with water-based mud and the bit on bottom. The drillers' method (DM), wait/weight (WW), or dynamic kill-control procedures for either a "perfect controller" [constant bottomhole pressure (BHP)] or for any of several choke-control procedures may be simulated.
Formation of Water-Soluble Silicate Gels by the Hydrolysis of a Diester of Dicarboxylic Acid Solubilized as Microemulsions
Authors: Vinot B. , Schechter R. S. , Lake Larry W.
Published: December 2007

Relatively inexpensive sodium silicate gels are attractive candidates for large-scale well conformance treatments. For a successful treatment, gelation must be delayed to permit proper placement of the silicate solution within the reservoir, to minimize rock/fluid interactions during placement, and to ensure long-term gel stability. We investigated each of these process phases, focusing on stable high-pH (≈11) sodium silicate solutions ranging up to 10 wt% SiO2 concentration. The addition of an acid or alcohol will cause these high-pH sodium silicate solutions to gel. To regulate the gelling time, an organic material that reacts with water to produce an alcohol and/or acid is often mixed with the silicate solution. An organic rather than inorganic compound is selected because the slow organic reaction rates yield a controlled gelation. The choice of the organic compound normally is quite limited because it must possess sufficient water solubility to be present in the quantities needed to cause gelling. This study shows that diesters, which hydrolize to produce both acid and alcohol, can be solubilized into silicate solutions as a microemulsion (not a macroemulsion), thus eliminating this limitation. All the rules developed with regard to selection of surfactants for EOR also apply to sodium silicate solutions. Field processes should use caustic preflushes to propagate silicate solutions deep into the formation.

Long-term stability studies showed that, upon standing for several weeks, silicate gels tend to contract, expelling water. This process, called syneresis, clearly will affect the long-term effectiveness of a silicate treatment. We investigated syneresis over a wide range of silicate concentrations and temperatures. Gels formed from the high silicate concentrations exhibited the greatest degree of syneresis; up to an 80% decrease in volume. Increasing the temperature increased the syneresis. Some degree of syneresis may be desirable because all treated zones will retain residual permeability.
Performance of Perforated Completions in the Presence of Anisotropy, Laminations, or Natural Fractures
Authors: Tariq S. M. , Ichara M. J. , Ayestaran L.
Published: December 2007

Finite-element method (FEM) was used to evaluate the steady-state flow response of the near-wellbore region in the presence of anisotropy, shale laminations, and natural fractures. The relative importance of various geometric perforation parameters under such conditions was also examined. The study indicated that completion efficiency is strongly influenced by common heterogeneities. The variation in productivity is substantial and emphasizes the importance of including a good description of the formation heterogeneities in the design and evaluation of a perforating program. The best description is derived by use of data from all available sources (cores, well tests, and logs).

The principal findings of this study were (1) that high shot densities are needed in anisotropic and laminated formations, (2) that the performance of perforated completions varies with the type, orientation, and density of the natural fractures, (3) that different geometric parameters assume different significances for different types of fracture networks, and (4) that a sound fracture detection and evaluation program is essential for the proper design and evaluation of the perforated completion in such an environment. The results presented can be used to design and to evaluate perforated completions in naturally fractured environments.
Generation of Earthquake Response Spectra for Production Equipment
Authors: Fisher F. A.
Published: December 2007

The importance of seismic design requirements for the facilities and equipment on the deck of an offshore platform is increasing. This paper presents an efficient procedure for the generation of earthquake response spectra for light equipment in a massive structure. It is assumed that the equipment may be modeled as a single-degree-of-freedom linear oscillator attached at a single point to a multi-degree-of-freedom linear system. Modal properties of the combined equipment/structure system may be determined from the known properties of the separate systems. The peak equipment response to a given ground-motion time history is determined from a frequency domain analysis of the combined system and the ground-motion response spectra. This procedure takes into account equipment/structure interaction, correlation between modes, and response transience, some or all of which are typically ignored in current practice. Because most of the theoretical development for this procedure has been done in the nuclear industry, the primary focus of this paper is on the application of the procedure to offshore platforms. Several numerical examples are included to demonstrate the excellent agreement between this procedure and time-history results.
Design Features of Improved Electric-Submersible-Pump Cable To Withstand Installation and Service Conditions
Authors: Neuroth D. H.
Published: December 2007

Field studies, with oil industry assistance, identified major failure mechanisms that currently limit the service life of conventional electric-submersible-pump (ESP) cable. A new cable, designed to address each of these failure modes, was developed and tested. Special load-bearing members placed within the cable improve crush resistance from 500 lbf/cable in. [876 N/cable cm] with conventional cable to 3,000 lbf/cable in. [5254 N/cable cm], while enhancing decompression strength. The manner in which the new design increases edge protection, eases installation handling, enhances abrasion resistance, and provides greater chemical protection is also discussed. The mechanisms by which design features achieve these improvements are supported by laboratory results and field experience.
Injection Rates - The Effect of Mobility Ratio, Area Swept, and Pattern
Authors: Deppe John C.
Published: December 2007

A method is presented for calculating approximate injection rates in secondary recovery operations. The method can he applied to cases of unequal fluid mobilities, irregular well patterns and boundary patterns.

The steady-state pressure distributions for the four flood patterns reported by Muskat and for five additional patterns reveal that most of the difference in pressure between the injection and producing wells occurs in regions around the wells which can adequately he described as regions of radial flow. This leads to a method of calculating injectivity by approximating the flood pattern with radial flow elements (or a combination of radial- and linear-flow elements for some patterns such as the direct line drive). Irregular and boundary patterns can also be approximated by radial and linear elements.

Each of these elements can be described by radial- and linear-flow equations and the results combined as series flow resistances to give an approximate equation for the initial injection rate. The mobility ratio does not affect the initial rate; therefore, if the well pattern is one of those regular patterns for which theoretical rate equations have been derived for unity mobility ratio, the approximate initial rate equation can be improved by adjusting it to match the theoretical equation. The available theoretical rate equations are listed, including five new cases.

As the flood progresses, the injectivity changes because in general the flood front will divide the pattern into areas of different fluid mobilities. Simple shapes can be assumed for the flood front so that both areas can be divided into radial- and linear-flow elements. Radial- and linear-flow equations are applied to these elements to account for the change in flow resistance behind the front.

To calculate injection rates after breakthrough, it is necessary to know the sweep efficiency at breakthrough. Areal sweep data are available in the literature for a number of patterns, and sufficiently accurate breakthrough sweep efficiency can be estimated from these data if it is not otherwise available.
The Development of Stability Theory for Miscible Liquid-Liquid Displacement
Authors: Perrine Richard L.
Published: December 2007

A stability theory is developed for miscible liquid-liquid displacement within a porous medium. In the usual case considered, a high-density high-viscosity "oil" is displaced downdip by a low-density low-viscosity "solvent". Perturbation methods are used to find the conditions under which the spreading mechanism changes from the stable dispersion process to unstable viscous fingering. We find that instability is conditional, that there is a dependence on the shape of a disturbance leading to a "diameter" effect and that very difficult experimental scaling problems may result. A useful consequence is the definition of a minimum "slug size" for stable miscible displacement. This should make possible optimum use of the solvent process for oil recovery. The results may apply to many situations in which one fluid displaces another of somewhat different fluid properties within a porous medium.

Introduction

The process of miscible liquid-liquid displacement looked very favorable when it first received serious consideration as a means to increase petroleum recovery. Some early laboratory results were interpreted to mean that only a small "slug" of solvent was needed, perhaps 2 to 3 per cent of a hydrocarbon pore volume. This "slug" could recover the oil in an entire reservoir provided the fluids remained miscible. Only a slow growth of the "mixing zone", or gradual transition from oil to solvent, should occur. This would follow naturally from mixing by a dispersion mechanism such as that described by Scheidegger. And, indeed, laboratory cores have shown this kind of behavior provided solvent viscosity was at least as great as that of the oil. The same kind of behavior has also been observed with solvent viscosity lower than that of the oil after the distance traversed became large. Not all laboratory results have been this favorable, however. Mixing zone growth may become proportional to the distance traveled rather than the square root of this quantity. Such behavior accompanies high rates in short systems of large diameter, provided the viscosity ratio is adverse. If this more rapid spreading were to persist in a reservoir, the solvent requirement for miscible "slug" displacement could exceed 30 per cent of a pore volume. There is considerable economic importance in the difference between 3 and 30 per cent solvent.
Effects of Noncondensible Gases on Fluid Recovery in Fractured Geothermal Reservoirs
Authors: Bodvarsson Gudmundur S. , Gaulke Scott
Published: December 2007

Numerical simulations are performed to investigate the effects of noncondensible gases (CO2) on fluid recovery and matrix depletion in fractured geothermal reservoirs. The model is of a well producing at a constant bottomhole pressure (BHP) from a two-phase fractured reservoir. The recoverable fluid reserves are shown to depend strongly on the amount of CO2 present in the reservoir system. The results obtained revealed a complex fracture/matrix interaction caused by the thermodynamics of H2O/CO2 mixtures. Although the matrix initially contributes fluids (liquid and gas) to the fractures, the flow directions later reverse and the fractures backflow fluids into the matrix. The amount of backflow depends primarily on the flowing gas saturation in the fractures; the lower the flowing gas saturation in the fractures, the more backflow. An analytic expression has been derived that allows for the determination of mass backflow on the basis of wellhead measurements of noncondensible gases and flowing enthalpy.
Obtaining Low Bottomhole Pressures in Deep Wells With Hydraulic Jet Pumps
Authors: Christ F. C. , Petrie H. L.
Published: December 2007

Maximizing production in a well requires reducing the bottomhole pressure (BHP) to the lowest practical minimum by artificial lift. This task is particularly difficult in deep wells because of the need to transmit power a long distance to the bottom of the well and because of the high temperatures encountered at depth. Reciprocating hydraulic pumps have historically been used for this purpose in deep wells, especially those deeper than 10,000 ft [3048 m]. For more than a decade, the hydraulic jet pump has successfully produced deep wells. In a number of cases, jet pumps have produced deep wells to less than 10% submergence. This paper identifies the hydraulic jet pump as a reasonable method to produce deep wells to low BHP's with predictable performance. A number of examples and well tests illustrate the performance of jet-pump production systems.
Saturation Distributions During Displacements Generated by the Simultaneous Injection of Oil and Water
Authors: O’Steen B. L. , Holm L. W.
Published: December 2007

Linear oil/water displacement behavior in a water-wet Berea sandstone is examined experimentally with a scanning microwave absorption system. It is observed that simultaneous injection of oil and water into a core initially at residual oil saturation (ROS) produces a region of anomalously high oil saturation and fractional flow, or an oil hump, at the leading edge of the displacement. This region grows in both saturation and breadth as the flood progresses. Studies at different injection rates and WOR’s indicate that the saturation, fractional flow, and propagation behavior of the oil hump are strongly influenced by rate and ratio. The displacements from ROS confirm the secondary imbibition and drainage results for fractional flow obtained by a sequence of small displacements. A strong hysteresis effect is indicated by these results. The displacements from ROS also reveal the existence of a complex network of inner scanning loops in the steady-state fractional flow behavior. These studies indicate that for sufficiently high injection rate, all displacements above a minimum injected WOR will eventually produce a displacement front approaching that of an oilflood. The frontal saturation and fractional flow for the oilflood case are found to be significantly greater than that predicted by the graphic tangent-point construction of Buckley-Leverett (B-L) theory. This result, along with the observed rate dependence of the hump, suggests that traditional B-L theory, even with fractional flow hysteresis included, might not adequately describe oil/water displacement. It is suggested that transient flow response near a wave front is responsible for the observed displacement behavior.
Nonequilibrium Gas Displacement Calculations
Authors: Attra H.D.
Published: December 2007

The effects of phase behavior on reservoir economics is a function of both fluid composition and flow properties of the reservoir rock. In some operations such as gas injection into volatile crude-oil reservoirs, the stock-tank recovery derived from vaporization of the reservoir oil by the displacing gas can approach the recovery derived from the displacement mechanism. In other cases of gas-cycling reservoirs, the dry injected gas can effectively vaporize a retrograde liquid phase, allowing a substantial reduction in cycling pressure with no appreciable loss in recoverable liquids. Because of these effects, it is essential that phase behavior be considered in developing the economics of any secondary recovery program in which gas is the injected fluid.

The inclusion of phase behavior in conventional calculation procedures has been retarded because of the complexity of the calculation and the large volume of laboratory data required. However, by applying high-speed computers and new laboratory techniques, the phase-behavior displacement calculation has been developed to economically include this basic fundamental of gas displacement.

The calculation is performed by reducing the reservoir to a series of one-dimensional segments. Phase changes, saturation distributions and changing fluid properties are evaluated for each segment as a function of time. The relative volumes of equilibrium liquid and gas displaced from each segment are determined by a trial-and-error procedure to meet the requirements of phase equilibrium and two-phase flow. The produced fluids are flashed through conditions of surface separation approximating those in the field to obtain actual values for stock-tank liquid recovery and producing gas oil ratios.

Based on the results of successful field studies, the technique appears to have application to reservoirs producing under a nonmiscible gas-displacement mechanism and should substantially increase the reliability of this type of analysis when phase behavior is an important factor.
The Unsteady-State Nature of Sorption and Diffusion Phenomena in the Micropore Structure of Coal: Part 1—Theory and Mathematical Formulation
Authors: Kolesar J. E. , Ertekln Turgay , Obut S. T.
Published: December 2007

A single-phase, ID mathematical formulation is developed in radial/cylindrical coordinates to examine unsteady-state micropore sorption in a composite micropore/fracture, coalbed-methane transport problem. In the formulation, the micropore transport equation accounts for unsteady-state sorption and diffusion in the primary porosity. Gas entering the fracture network is considered a source term in the fracture-transport equation. The micropore and fracture systems are coupled by equating the gas pressure at the surface of the micropore elements to the pressure in the fracture network.
An Experimental Study of Gas Solubility in Oil-Based Drilling Fluids
Authors: O'Bryan Patrick L. , Bourgoyne Adam T. , Monger Teresa G. , Kopcso Debra P.
Published: December 2007

Experimental data are provided for the solubility of C1, C2, CO2, and a natural gas mixture in base oils and emulsifiers used to prepare oil-based drilling fluids over a range of temperatures. In addition, an empirical correlation for predicting gas solubility in oil-based drilling fluids at low to moderate pressures is presented and a field application is outlined.
A Weight- and Space-Saving Seawater-lnjection System Design
Authors: Gran H. G. , Matthews R. R. , Johnson D. , Sollesnes G.
Published: December 2007

This paper describes an integrated and compact seawater-injection system built around backwashable cartridge filters and catalytic deoxygenation. Suspended solids are removed by a high-efficiency cartridge filter in which the cartridges are regenerated by a proprietary acid rinse. Dissolved oxygen is removed in a single stage to a level of 20 ppb by use of dissolved hydrogen over a palladium catalyst. A combined-cycle power plant makes the unit self-contained. A unit for treating 150, 000 B/D [23 850 m3/d] of seawater is estimated to weigh 260 metric tons [260 Mg] (operating), or about 35% of a comparable "conventional" system using media filters and vacuum deaeration. Space requirements are reduced proportionally.
Transient Response of Nonhomogeneous Aquifers
Authors: Mueller T.D.
Published: December 2007

Many investigators have used the response of the "dimensionless aquifer" to a unit pressure drop or a unit fluid-withdrawal volume to calculate the performance of an aquifer in supplying water influx to an oil reservoir. In the past, these response functions have been calculated with the aid of the Laplace transform. With the advent of ultra high-speed digital computers, it becomes practical to solve for the response functions with finite-difference techniques. The computer method also permits extension of the dimensionless-aquifer concept to include the nonhomogeneous aquifer wherein the permeability and other properties vary as a function of the space co-ordinates. This paper gives results of calculating the response functions for a series of nonhomogeneous aquifers. Response functions are presented for both linear and radial aquifers whose thickness, permeability-viscosity ratio and porosity-compressibility vary. These functions are new and should prove useful to the petroleum engineer in analyzing the behavior of nonhomogeneous aquifers. Results are presented in the form of charts that can be easily used by the field engineer.

Introduction

Aquifers which surround many oil and gas reservoirs have the ability to supply water influx to such reservoirs as oil and gas are withdrawn. This water influx, called natural water drive, provides one of the most effective driving mechanisms for the production of oil and gas. In producing a reservoir, therefore, it behooves one to make the maximum use of natural water drive. To achieve the maximum use, the reservoir engineer must be able to predict the performance of an aquifer under a variety of production schemes that may be proposed for the reservoir. Unfortunately, the physical properties which dictate aquifer behavior often are known only within limits. Seldom do wells penetrate the porous strata of the aquifer.
Density Modeling for Brines as a Function of Composition, Temperature, and Pressure
Authors: Kemp Nantelle P. , Thomas David C. , Atkinson Gordon , Atkinson Betty L.
Published: December 2007

Electrolyte solutions containing high concentrations of salts, such as NaCl, KCl, CaCl2, CaBr2, and ZnBr2, have several important applications in the oil field. The so-called "heavy brines" are used as solids-free completion fluids. Brines are also a major constituent of many drilling-fluid systems, including both water- and oil-based muds. This paper describes the density behavior of brine solutions containing single salts and salt mixtures under various temperature and pressure conditions. Examples are given for using the derived density model to calculate both downhole differential pressures for brine completion fluids and the solids content in brine muds.
Study of Gas Reservoirs Subject to Water Drive on Electronic Differential Analyzer
Authors: Yoo H.D. , Katz D.L. , Tek M.R.
Published: December 2007

The behavior of gas-storage reservoirs subject to water drive is investigated through analog simulation on an electronic differential analyzer. The simulation technique developed on an LM–10 computer permits the prediction of reservoir volume or pressure resulting from the movement of water in the surrounding aquifer.

The method developed on the analog computer consists off-setting up an appropriate transfer-function circuit and feeding the arbitrary time-varying boundary conditions as an input signal. The input may be specified as gas reservoir pressure, pore volume or the water flux.

Several cases studied include an isolated gas reservoir on a limited aquifer, interference among three reservoirs adjacent to a common aquifer and the growth of gas-storage volume on an aquifer.

It is concluded that the method developed on an electronic differential analyzer provides an excellent technique to simulate and investigate the behavior of gas reservoirs subject to water drive. The agreement between the reservoir performance as predicted from the simulation technique and as measured from actual field data is found to be better than the range usually encountered in predicting water-drive behavior.

Introduction

It is generally known that some gas-storage reservoirs are located on top of blanket sands of large extent, saturated with brine called aquifers.

Because the volume of the body of water associated with aquifers is usually very large and water is compressible, the cyclic pressure variations encountered in normal storage service inevitably cause unsteady, compressible flow conditions in the adjacent aquifers.

The solution to radial diffusivity equation for a limited aquifer for constant terminal conditions has been known since the early 1930's. The solution for the constant terminal conditions for an infinite aquifer was published in 1949.