bluuebunny/crossref_metadata_2025 huggingface dataset:
Delta Flow: An Accurate, Reliable System for Detecting Kicks and Loss of Circulation During Drilling
Authors: Speers J. M. , Gehrig G. F.
Published: December 2007

A system to monitor drilling-fluid flow rate has been developed that detects kicks and lost returns in floating, fixed-platform, and land-based drilling operations. The system uses flowmeters that monitor the flow rates of drilling fluids entering the borehole through the standpipe and leaving the well through the return flowline. These readings are processed in a computer-based, data-acquisition system to form a filtered delta-flow signal that identifies the occurrence of downhole fluid gains or losses. The system is designed to trip an alarm when a gain or loss exceeds 25 gal/min [1.6 dm3/s], even in a floating drilling environment. This sensitivity will generally keep gains or losses to less than 5 bbl [0.8 m3].
A Study of Mineral/Alkali Reactions—Part 2
Authors: Mohnot S. M. , Bae J. H.
Published: December 2007

In a study of alkalinity loss by interactions of alkali with minerals and reservoir sands, static tests were conducted with high concentrations of NaOH and a variety of minerals, mineral mixes, and reservoir sands at high temperature. Reactions lasted up to 2 months in some cases. Solutions were analyzed for pH and titratable alkali, silicon, and other elements. The reacted alkaline solution from a reservoir-sand/alkali reaction was used for interfacial tension (IFT) and contact-angle measurements and for sandpack oil-recovery tests.

Alkalinity loss was greatest for kaolinite and gypsum; moderately high for montmorillonite, illite, dolomite, and zeolite; moderately low for feldspar, chlorite, and fine quartz; lowest for quartz sand; and insignificant for calcite. Alkalinity loss was dominated by chemical reactions for kaolinite, by dissolution/precipitation equilibria for gypsum and dolomite, by ion-exchange and silica dissolution for montmorillonite, and by ion exchange and chemical reaction for illite. The alkalinity loss by multimineral mixtures and reservoir sands agreed reasonably well with the sum of contributions by individual minerals. The contribution by highly reactive minerals was disproportionate to their weight fraction and was found empirically. The contributions by other minerals (not very reactive or ion-exchange-dominated) were approximated proportionately to their weight fractions. For reservoir sands, identifying exposed minerals and estimating their exposed surface areas by scanning-electron (SEM) and thin-section microscopy with several samples were important.

In an attempt to determine the influence of dissolved species from reaction, reacted alkali after sand/alkali contact was tested for contact angle, IFT, and oil recovery for a U.S. gulf coast reservoir system. More oil-wet (quartz) conditions were found with reacted alkali than with fresh alkali with one oil sample, and highly oil-wet conditions were found with both fresh and reacted alkali for another oil sample. Minimum IFT values were slightly lower, and no detrimental effects of dissolved species on oil recovery were observed.
A Study of the Reduction of Brine Permeability in Berea Sandstone With the Aluminum Citrate Process
Authors: Parmeswar Ravi , Willhite G. Paul
Published: December 2007

A systematic study of permeability modification of Berea sandstone by the injection of alternate slugs of polymer and aluminum citrate is described. The research included brine permeabilities from 10 to 300 md. Results of treatments with Pusher 700™ showed that permeability reduction was limited to the front end of the core (0 to 4 in. [0 to 10 cm]). The effective mobility of the treated region was so low that in-depth treatment of the remainder of the core was prevented. The amount and distribution of permeability reduction is related to both polymer and aluminum retention. The retention of aluminum was found to be a nonequilibrium process, varying with flow rate and thus residence time in the core. Aluminum was retained in large quantities in Berea core in the absence of polymer. Changing the treatment sequence to aluminum citrate/brine/polymer/brine yielded in-depth treatment of cores 12 to 48 in. [30 to 121 cm] in length. Both magnitude and persistence of permeability reduction were comparable to or better than those obtained with the combination process. Permeability increased with distance from the core inlet in most runs. This is believed to be caused by nonuniform distribution of retained aluminum.
An Experimental Study of Waterflooding From a Two-Dimensional Layered Sand Model
Authors: Ahmed Gulfaraz , Castanier Louis M. , Brigham William E.
Published: December 2007

The effect of flow rate on oil recovery by waterflooding is studied with a two-dimensional (2D), layered sand model that allows visual observation. The model consists of three communicating layers of equal thickness of water-wet sand with the permeability ratio of 2 :4 : 1 from top to bottom. Three white mineral oils of viscosity 15, 30, and 150 cp [15, 30, and 150 mPa · s] have been used for immiscible liquid/liquid displacement under constant pressure drops covering a range of flow rates.

The changes in flow regimes in the various layers are observed with respect to the variations in pressure drop across the model. The effects of capillary imbibition, gravity segregation, and viscous pressure gradient are observed and an attempt is made to calculate the instantaneous crossflow. Crossflow of oil from the tight layers to the most-permeable layer increases the intermediate oil recovery for a given volume of water injected. Oil recovery increases somewhat with a decrease in flow rate and considerably with a decrease in oil viscosity. Slow flow rates produce higher recovery but may not be feasible in the field for economic reasons.

For M > 1, viscous crossflow contributes very slightly to oil recovery until the time of breakthrough of water from the most-permeable layer. After that, the viscous crossflow increases and creates a secondary oil stream close to the interfaces of the most-permeable layer. The additional oil is produced until the least-permeable layer also breaks through. A sequence of slow flow rate followed by a fast flow rate is shown to improve oil recovery for a given volume of water injected, and this occurs within a reasonable experimental time frame. The slow flow rate is set from a criterion of stable displacement in the most-permeable layer based on stability analysis, and the fast flow rate is based on the maximum pressure the model can take.

The effect of variation in interfacial tension (IFT) on the displacement behavior was also studied. IFT is reduced from 35 to 4 and 0.5 dynes/cm [35 to 4 and 0.5 mN/m], respectively, by addition of two surfactants to the injected flood water. These IFT ranges are not sufficiently low to increase oil recovery from interfacial effects. The two surfactants influenced the recovery behavior differently.
Reducing Gravel Pack and Formation Dissolution During Steam Injection
Authors: Watkins D. R. , Kalfayan L. J. , Watanabe D. J. , Holm J. A.
Published: December 2007

Gravel-packing sand and formation minerals dissolve in the hot alkaline water injected with steam. This dissolution is believed to cause gravel-pack failure and other production problems. This paper describes the use of ammonium salts in reducing dissolution by reducing the pH of generator effluents from values of 11 and greater to between 9 and 10. These salts, such as ammonium chloride and ammonium nitrate, do not significantly change feedwater pH. Both laboratory and field test results are presented.

This paper also presents a brief summary of other methods proposed to prevent gravel and formation dissolution. In addition, the need for more information about the role of silica dissolution in causing production problems is discussed briefly.
Effect of Oil Production Rate on Performance of Wells Producing from More Than One Horizon
Authors: Tempelaar-Lietz W.
Published: December 2007

The performance of a two-horizon depletion-type reservoir produced through combination wells is analyzed. By introducing some simplifying approximations it has been possible to obtain formulas which are easy to handle. Only ordinary differential equations are used, and the development of the analysis can he followed without difficulty by the non-specialist. A rigorous analysis has been made of this problem. It has been found that the approximations introduced in the simplified analysis are fully justified and that errors seldom will be more than 2 per cent.

The report shows the effect of the rate of withdrawal upon the relative depletion of the two horizons. Numerical examples are given.

Introduction

In its simplest form an oil reservoir consists of a Continuous, homogeneous body of porous and permeable rock, enclosed at the top and the bottom by impermeable material. The flow of fluid through such a reservoir has been the subject of numerous papers, and the mathematical analysis of well performance, pressure build-up, etc., has reached a high degree of refinement. One of the basic assumptions introduced into these analyses is the homogeneity of the reservoir. In non-homogeneous reservoirs, these computations still can be carried out satisfactorily, provided small irregularities in the physical properties of the rock are distributed in a random fashion.

The flow equations are derived as solutions of the continuity equation, and their solutions are dependent upon the assumption of many constant factors in the reservoir: permeability to oil, compressibility of the reservoir fluid, viscosity saturation, etc. When these are assumed to be constant, the continuity equation can be solved rigorously. When these assumptions do not hold and corrections are introduced, it becomes very difficult and often impossible to solve analytically.
Diverless Installation of the Skuld Modular Subsea Station
Authors: Freudenreich M.
Published: December 2007

In 1984 and 1985, the Skuld experimental station was remotely operated and intensively tested in North Sea conditions for 1 year. This full-scale station, simulating production from a two-well cluster, was installed diverless in June 1984 outside Bergen, Norway, at 90-m [295-ft] water depth. Installation took less than 6 hours per module because we used guidelines and a dedicated landing tool, and the 1-year intensive test confirmed the reliability of the subsea equipment. This experiment demonstrates the validity of the development scheme using the Skuld modular concept.
Magnus Field: Surfactant Stimulation of Water-Injection Wells
Authors: Dymond P. F. , Spurr P. R.
Published: December 2007

Water-injection wells in BP's Magnus field are located updip of the oil/water contact (OWC) because of poor aquifer injectivities. A pilot project was undertaken to increase water-injection rates by improving near-wellbore relative permeabilities to water by use of a surfactant to reduce residual oil saturations. This paper discusses the laboratory reservoir-condition coreflood tests, the field monitoring during surfactant treatment, and an interpretation of the success of the project.
A Study of Bulk Cement Handling and Testing Procedures
Authors: Gerke Richard R. , Simon John M. , Logan Jerry L. , Sablns Fred L.
Published: December 2007

The variation between thickening-time test results from tests on pilot blends and cement-blend sample tests has been a subject of frequent investigation. Disagreement between these test results is often blamed on improper additive proportioning, inadequate blending, or incorrect sampling techniques.

A comprehensive study of blending, sampling, and testing variables was conducted. This paper describes the results of this research testing with a full-scale laboratory bulk plant. It also includes the results of a south Texas field study in which thickening time test results from more than 300 cement-blend samples were examined. Results of these studies suggest that significant statistical variations may be involved in blending, sampling, and testing procedures under deep-well conditions. The variabilities are used as guidelines for determining thickening-time acceptance windows. Variabilities or uncertainties can be minimized by optimization and standardization of these procedures.
Primary Cementing Improvement by Casing Vibration During Cement Curing Time
Authors: Cooke C. E. , Gonzalez O. J. , Broussard D. J.
Published: December 2007

Vibration of casing to improve primary cementing was investigated in the laboratory and in a 200-ft [60-m] deep test well. The effect of vibration is to decrease or to eliminate gel strength of the cement slurry as it is curing. The slurry then flows downward to compensate for shrinkage and re-establishes the hydrostatic head of the cement. This method can prevent pore-fluid entry into the annulus before the cement cures and can increase the radial stress at the interface between the formation and the cured cement.
Effects of Texture on Rheology of Foam Fracturing Fluids
Authors: Harris P. C.
Published: December 2007

A new laboratory technique was developed to measure changes in foam texture (bubble-size distribution) vs. foam viscosity in a recirculating pipeline viscometer. Fluid variables studied included foam quality, surfactant type and concentration, gelling-agent concentration, shear history, system pressure, and liquid-phase chemical type.

The viscous properties of foam fluids are determined primarily by quality (internal-phase volume) and liquid-phase properties. The viscosity of an equilibrated foam is influenced by texture to a lesser extent.

Foams are shear-history-dependent fluids. The bubble size and degree of dispersion will adjust to an equilibrium state that depends on time at a given shear rate. Finer-texture foams are produced by higher shear rates, higher surfactant concentrations, and higher pressures. Viscosity measurements at low pressure may not adequately simulate field use at high pressure.

The liquid-phase chemical type influences texture. The structure of methanol and hydrocarbon foams may result in sensitivity to degradation at high shear rates.
Estimation of Productivity of Lobo 6 Sand, Lower Wilcox, Texas, by Identifying Diagenetic Clays With Well Log Data
Authors: Berilgen B. A. , Sinha A. K. , Fertl W. H.
Published: December 2007

The laminated, structural, and grain-coating primary clays in the Lower Wilcox Sand, Lobo 6, tend to be potassium-bearing illite and some smectite, whereas diagenetic clays, the cause of pore-throat plugging, are largely potassium-deficient kaolinite and chlorite. These diagenetic clays largely control reservoir permeability, depending on the degree of pore-throat plugging. This paper presents different methods for qualitative and quantitative evaluation of these diagenetic clays, which are related to productivity of the Lobo 6 sand.

Qualitative evaluation consists of crossplot techniques using natural spectral gamma ray and other log data plus selected computed reservoir parameters. For quantitative evaluation, a sophisticated clay-analysis program that uses log-derived cation exchange capacity (CEC) and hydrogen index (HI) values is used. The average volume of different clay types in the zones of interest is calculated, presented, and correlated with production and core data. This approach was used on eight wells on which production data are available to evaluate the presence of diagenetic clays and to estimate productivity of the Lobo 6 sand. The reliability of the log-derived method applied is verified by the excellent correlation with actual production data.
Surfactant Selection With the Three-Parameter Diagram
Authors: Puerto Maura C. , Reed Ronald L.
Published: December 2007

A procedure to select surfactants for microemulsion flooding is developed that requires only nominal phase-behavior information, acquired in experiments with pure oils and NaCl brines, provided that the field brine composition, crude oil molar volume, and crude oil hydrogen/carbon ratio are known. It is shown that, for alkylaryl sulfonates, microemulsion phase behavior correlates with ion size and charge rather than with ionic strength alone.
Dynamic Stability of Drillstrings Under Fluctuating Weight on Bit
Authors: Dunayevsky V. A. , Abbassian Fereidoun , Judzis Arnis
Published: December 2007

This paper describes the theory and the underlying formulation behind the development of a drillstring-dynamics simulator that predicts rapidly growing lateral vibrations triggered by axially induced bit excitations. The analyses center on calculations of stable rotary speed ranges for a given set of drillstring parameters and are presented in vibration "severity" vs. rotary speed plots. The critical rotary speeds, which correspond to the rapidly growing lateral vibrations, are pinpointed by spikes on the severity plots. Some applications of the drillstring-dynamics simulator are presented, and limitations and further model development are discussed.
Simultaneous Determination of Capillary Pressure and Relative Permeability by Automatic History Matching
Authors: Jennings J. W. , McGregor D. S. , Morse R. A.
Published: December 2007

This paper presents a new method for the simultaneous determination of capillary pressure and relative permeability that is a modification of the porous-plate capillary pressure experiment. The modifications involve the use of thin core samples and thin plastic filtration membranes, resulting in a significantly faster experiment. Relative permeabilities are determined from the experimental data by the use of an automatic history-matching simulator. The new method is found to be particularly well suited for the measurement of small oil relative permeabilities in gas/oil systems.
Evaluation of Low-Resistivity Cased-Off Reserves With the Shale-Compensated Chlorine Log
Authors: Tanner H. L.
Published: December 2007

Twenty years of experience accrued from analyzing more than 500 wells has substantiated the overall usefulness of the chlorine logging system. This logging system, developed more than 25 years ago, has proved to be an effective log to run when low-resistivity sands of the U.S. gulf coast area are identified and evaluated.
A Borehole Correction Model for Capture Gamma Ray Spectroscopy Logging Tools
Authors: Grau James A. , Roscoe Bradley A. , Tabanou Jacques R.
Published: December 2007

A borehole correction model, based onmore than 1,000 laboratory measurements, has been developed for logging tools that measure gamma ray energy spectra induced by the capture of thermal-energy neutrons. The measurements were made with a field-worthy tool incorporating a pulsed source of 14-MeV neutrons and a NaI(TI) gamma ray detector. In addition to the obvious geometric dependencies on borehole and casing sizes, the sensitivity of the measurement to elements within the borehole was found to depend just as strongly on the porosity and salinity of the borehole and formation fluids. The model decouples the geometric effects from most of the nuclear physics effects by explicitly including the time decay of the neutron flux in each homogeneous region.
Proof of the Two-Phase Steady-State Theory for Flow Through Porous Media
Authors: Chopra Anil K. , Carter Robert D.
Published: December 2007

A two-phase steady-state theory presented by O'Dell and Miller1 and modified later by Fussell2 predicts the performance of single-well gas condensate systems when there is liquid condensate dropout. The proof of this theory is developed with material-balance equations and phase equilibrium concepts. In this proof, dispersion, capillary, and gravity effects are neglected. We also show that this theory can be applied to any two-phase hydrocarbon system (e.g., black oil, volatile oil, or gas condensate) when steady-state conditions exist in the vicinity of a single producing well. Results obtained with this theory are compared with the simulation results obtained with a compositional model. A new procedure to compute the in-place composition profiles for systems under steady-state conditions greatly reduces the computation effort because only the phase equilibrium data for the original reservoir fluid are required. Composition profiles calculated with the proposed procedure are identical to the steady-state composition profiles generated with the compositional model. This theory's usefulness for unsteady flow is also illustrated.
The Effects of Mud-Filtrate Invasion on the Interpretation of Induction Logs
Authors: Semmelbeck Mark E. , Holditch S. A.
Published: December 2007

A rigorous model of mud-filtrate invasion has been developed with a numerical fluid-flow simulator. This model is used to investigate the effects of certain fluid-flow properties on the invasion process. The model also has the capability to calculate the resistivities that would be measured by deep and medium induction logs. The resistivity measured by the two logs is shown to vary with time, and the difference between the resistivities measured by the two logs is indicative of the amount of invasion that has occurred. This study indicates that multiple logging runs over an interval could be used to evaluate the fluid-flow characteristics of a formation.
Toughness Study of Drillpipes by Use of Instrumented Impact Tests
Authors: Tumuluru Muralidhar
Published: December 2007

The toughness behavior of API Grades E and G pipe was studied by use of the instrumented impact test on Charpy V-notch specimens. This study was done at various locations in the pipes, including the upset, nonupset, and transition from upset to nonupset regions. The use of instrumented impact testing made it possible to distinguish the stage of crack initiation from that of propagation during the impact tests. The study revealed that the Grade E pipe possessed poor toughness as evidenced by the low energy values required to propagate the crack. The toughness behavior varied from upset to nonupset regions in the Grade E pipe. The Grade G pipe, on the other hand, exhibited superior toughness uniformly throughout its length as revealed by the high energy values required for crack propagation. Scanning electron microscope (SEM) and metallographic techniques were used to explain the fracture behavior of both types of pipe. The toughness of Grade E pipe, and therefore its tolerance to the presence of defects, can be improved by adopting a quench-and-temper heat treatment.
Recent Developments in the Design of Grouted Connections
Authors: Tebbett I. E.
Published: December 2007

A recently completed major research project on the structural behavior of grouted pile/sleeve connections covered static strength, the effect of cyclic movement during grout setting, long-term fatigue, calibration of measured strengths for different quality-control samples, and the investigation of connections removed after 13 years of service in the North Sea. Preliminary data from this project resulted in the issue of revised guidance notes by the U.K. Dept. of Energy and have been recognized in recent amendments to API RP 2A. This paper discusses unpublished test results, the provisions of the latest design codes in relation to the available data, and the implications for design. Results and discussions apply to all types of grouted connections and many types of structures, including pile/sleeve connections for fixed jackets and tension leg platforms and grouted connections used for repair of tubular structures.
Designing a Sucker-Rod Pumping System for Maximum Efficiency
Authors: Gault Robert H.
Published: December 2007

Consideration of the energy requirements in the design of a sucker-rod pumping system is very important. Examples are given that detail how the use of the largest possible pump with the lightest, strongest rod string and special-geometry units can provide a substantial energy reduction.
Some Invariant Solutions to Two-Phase Fluid Displacement Problems Including Capillary Effect
Authors: Chen Z. X.
Published: December 2007

Analytical investigation of the two-phase displacement problem that considers capillary force is one of the most important and difficult problems in the theory of fluid flow through porous media. This paper presents some invariant solutions on the subject, including a self-similar solution for the axisymmetric case, a self-similar solution in a linear, isoclinal reservoir that considers the effects of gravity and capillary forces simultaneously, and a progressive wave solution corresponding to a stabilized zone of saturation distribution. The relations and differences among (1) a model that completely includes capillary effect, (2) a model that considers capillary action partially and implicitly (the Buckley-Leverett model), and (3) a model that completely ignores capillary effect are indicated and discussed.
Stability Theory and Its Use to Optimize Solvent Recovery of Oil
Authors: Perrine Richard L.
Published: December 2007

This paper shows how stability theory can be used to optimize solvent recovery of oil. Application of the theory leads to definition of the limiting conditions required for stable displacement to occur. One of these conditions is that the size of a solvent "slug" must at least equal a prescribed minimum. The criteria to be satisfied are miscibility and stability. Stability implies that no viscous fingering will occur and that mixing will be caused only by a dispersion process. Miscibility implies that complete recovery will be obtained from the swept regions. Thus, for any specified set of reservoir conditions, an optimum use of solvent is defined.

Introduction

The early outlook for solvent flooding as a means to increase oil recovery was very favorable. Some laboratory results indicated that a "slug" containing perhaps 2 to 3 per cent of a hydrocarbon pore volume could be successful. However, other data suggested as much as 30 per cent would be required. The difference is of considerable economic importance. A theoretical explanation for these divergent results has been advanced by the author. Stability theory defines conditions for two distinct flow regimes. In stable displacement, solvent and oil become mixed by a dispersion process, and the solvent requirement is small. On the other hand, unstable displacement can degenerate into viscous fingering. The practical result is a considerable increase in the extent of mixing and, thus, in the solvent required.

The present paper shows how to use stability theory to optimize solvent recovery of oil. Oil is usually considered to be displaced by a small amount, or a slug, of solvent. Gas in turn follows solvent. Any fingering will permit contact of nearly solvent-free gas and oil, leading to immiscibility and reduced recovery. Thus, our optimum is defined by two restrictions - stable flow and miscibility.
A Study of Multiphase Flow Behavior in Vertical Wells
Authors: Hasan A. Rashid , Kabir C. Shah
Published: December 2007

This paper presents a physical model for predicting flow pattern, void fraction, and pressure drop during multiphase flow in vertical wells. The hydrodynamic conditions giving rise to various flow patterns are first analyzed. The method for predicting void fraction and pressure drop is then developed. In the development of the equations for pressure gradient, the contribution of the static head, frictional loss, and kinetic energy loss are examined. Laboratory data from various sources show excellent agreement with the model.
Analysis of Gas-Cap or Dissolved-Gas Drive Reservoirs
Authors: Stone H.L. , Garder A.O.
Published: December 2007

A numerical method of solving the partial differential equations which describe the one-dimensional displacement of oil by gas has been presented. Possible extension of the method to treat multidimensional flow is discussed, and the limitations of this extension are indicated. Using this method, it is possible to allow for the existence of a gas cap, the presence of any number of gas-injection or oil-production wells and the evolution of dissolved gas from the oil. It is also possible to allow for variation in the cross-sectional area, elevation, porosity and permeability of the reservoir. The influence of relative permeability and the force of gravity in the direction of flow upon the displacement is considered.

The influence of capillary pressure upon the flow and the effect of gravity in the direction perpendicular to flow are neglected. The physical properties of the fluids are considered to be functions of pressure only, and equilibrium between contiguous phases is assumed.

The numerical calculations can be readily carried out by the use of a digital computer. Several example analyses have been performed using the IBM 704 computer, and about one-third of an hour of computing time was required per case. Reservoir behavior predicted by use of this numerical method was compared to data obtained by other methods for three cases - complete pressure maintenance, dissolved. gas drive and gas-cap drive. The independent solutions to these problems were obtained by analytical solution, laboratory experiment and field data, respectively. Agreement of the numerical solution with data from these sources was good; this agreement establishes the convergence and accuracy of the numerical method.

Introduction

Most petroleum reservoirs can be produced by any one of several alternative programs. When a reservoir is produced by primary methods, production economics can be influenced by controlling the number and location of wells and the flow rate of each well.
The Calculated Performance of Solution-Gas-Drive Reservoirs
Authors: Levine J.S. , Prats M.
Published: December 2007

Several methods are available for calculating the performance of solution-gas-drive reservoirs from the PVT properties of the oil and from the relative permeability and other properties of the formation. These methods require a number of simplifying assumptions. The present method of computation has made use of a high-speed computer to solve simultaneously the nonlinear partial differential equations that describe two-phase flow by solution-gas drive in order to calculate the performance of a reservoir. Some of the results obtained by the nonlinear partial differential equation solution are compared with those obtained with an approximate method, which has been called the semi-steady-state solution. The pressure and saturation profiles from the wellbore to outer boundary calculated by the two methods are compared for one constant-terminal-rate case and two constant-terminal-pressure cases. The agreement in these profiles, as well as in the values of average reservoir pressure and cumulative recovery, leads to the conclusion that, for most engineering calculations, the semi-steady-state method will give a reasonable approximation to the numerical solution of the differential equations describing solution-gas drive.

An unfavorable (as regards ultimate oil production) set of relative permeability curve was used in the calculations in the belief that the effect of the parameters which were studied would be emphasized to a greater degree. Furthermore, the reservoir was assumed to be completely homogeneous, and these results should not be considered applicable to any other type of reservoir. Gravity effects are not considered.

The absolute permeability was varied from 25 to 0.5 md. At an economic limit of 2 B/D, the recovery for a 25-md reservoir is about 1.8 times as great as that for a 0.5-md reservoir. The effect of permeability on the producing gas-oil ratio is minor. Once PVT properties of the oil and the relative permeability properties of the reservoir are fixed, the producing gas-oil ratio is found to be a function of the fraction of oil recovered.
Velocity-Log Interpretation: The Effect of Rock Bulk Compressibility
Authors: Geertsma J.
Published: December 2007

Tbe relationsbip between porosity and the speed of propagation of acoustic waves in fluid-saturated porous rocks as measured by the Sonic log and by ultrasonic techniques is analyzed. Biot's continuum theory is used to explain the difference in acoustic wave propagation between a dry and a liquid-saturated porous material. The porosity is a variable in this theory. However, the acoustic wave propagation in the dry rock depends too on porosity, and this dependence is not predicted by the theory. Frequently in dry sandstones, a nearly linear relationsbip between reciprocal acoustic wave velocity and porosity is observed in the low-porosity range. The physics behind this behavior is outlined. An empirical relationship of the form, 1/V ~ A + B ø, applies accordingly for many porous dry rocks, provided the porosity is the only variable. The presence of a liquid in the pores changes the value of B, and this change is found to be in agreement with the Biot theory.

The time-average relation introduced some years ago results in an equation of the same type 1/V = ø/Vf + (1 - ø)/Vr - but is not based on a sound physical picture. Still, this relation sometimes predicts approximately correct A and B values.

Carbonate rocks with their complicated pore structures sometimes show a different relationship between wave velocity and porosity, unfavorable for log interpretation. Examples are presented. The simultaneous presence of calcite, dolomite and anhydrite, with their different grain densities and matrix compressibilities, complicates acoustic-log interpretation in carbonate rocks still further.

Other complicating effects of acoustic-log interpretation are discussed. They are related to the influence of shale streaks and natural fractures on the average wave velocity observed by the logging tool and to the effect of adsorption phenomena on wave propagation in unstressed rocks particularly in sandstones.
Mechanism of Alcohol Displacement of Oil from Porous Media
Authors: Taber J.J. , Kamath I.S.K. , Reed Ronald L.
Published: December 2007

Alcohol floods of consolidated sandstone cores have shown the process to be strongly dependent on the phase behavior of the particular alcohol-oil-water system used. This means that in many cases the mechanism does not conform to the idea of a piston-like displacement. Instead, it is found that by changing the alcohol it is possible to change the relative velocities of the oil and water and, in fact, the entire mechanism of the process. The effects of rate, viscosity, initial saturation, distance travelled and hysteresis of relative permeability on the alcohol flooding mechanism are discussed.

Introduction

Reasons for interest in the use of alcohol to miscibly displace oil and water from a porous medium appear in the existing literature. The mechanism of the displacement has been considered and the apparent implications formulated into a theory which presumably would enable one to predict the essential features of the process. Unfortunately, most of the reported experiments have been performed with unconsolidated or artificially consolidated sands. With these systems some of the noteworthy facets of the process are obscured and resulting data appear uncertain.

It is the purpose of this paper to show how the use of consolidated sandstones has led to revision of the mechanism and, hence, the theory of alcohol flooding. The practical result is increased pessimism toward the possibilities of commercial application of the simplest form of the alcohol-slug process. However elucidation of the mechanism has made it possible to define the essential characteristics of a system of slugs which will behave in a nearly piston-like fashion and, thus, yield the best possible result.

Equilibrium Phase Behavior

Fig. 1 is a diagram of the ternary system isopropyl alcohol (IPA)-Soltrol-calcium chloride brine. Brine was used to prevent plugging of the core and calcium chloride was used because sodium chloride brine exhibits a solid phase with Soltrol and IPA. If alcohol is added in increments to the immiscible mixture of water and oil represented by Point A, the path followed by the successively equilibrated samples will be on the Line ABC and pass from the immiscible region to the miscible region by crossing the binodal curve at B. Consider the intersection D of this path with the tie Line EF. The quantity of oleic phase is proportional to the Segment ED and the quantity of the aqueous phase is proportional to DF. Compositions of the two phases are specified by Points E and F. It is clear that in the case shown the oleic phase is diminishing and entirely disappears when miscibility is achieved.
Predicting Multiphase Flow Behavior in a Deviated Well
Authors: Hasan A. Rashid , Kabir C. Shah
Published: December 2007

In deviated wells of an offshore producing environment, flow of two-or three-phase mixtures is invariably encountered. While many investigators have studied vertical multiphase flow behavior, few studies, often entirely empirical, deal with deviated well systems. The main objective of this work is to present a model that predicts both flow regime and pressure gradient in a deviated wellbore. In the modeling of flow-pattern transition and void fraction, an approach similar to that for vertical flow is taken; i.e., four principal flow regimes are recognized: bubbly, slug, churn, and annular.

The transition from bubbly to slug flow is found to be at a local void fraction of 0.25. This transition criterion in terms of gas and liquid superficial velocities is found to be significantly affected by the well deviation, particularly in highly deviated wells. The transitions from slug to chum flow and chum to annular flow occur at high fluid velocities and are unaffected by well deviation.

The velocity-profile-distribution parameter for bubbly, slug, and churn flows is found to be unaffected by the well deviation angle. Similarly, the terminal rise velocity for small bubbles also appears to be insignificantly affected by the well deviation. In contrast, the "Taylor" bubble-rise velocity changes dramatically as deviation angle is increased. Thus, the characters of slug and chum flows in a deviated well differ from those in a vertical well.

Data on gas void fraction were obtained both from a 5-in. [127-mm] circular pipe and from annular flow channels for deviation angles up to 32° from the vertical. The validity of the proposed model is demonstrated with these data and with laboratory data from other sources. Several field examples are presented to show the application of the model.
An Imbibition Model - Its Application to Flow Behavior and the Prediction of Oil Recovery
Authors: Naar J. , Henderson J.H.
Published: December 2007

Introduction

The displacement of a wetting fluid from a porous medium by a non-wetting fluid (drainage) is now reasonably well understood. A complete explanation has yet to be found for the analogous case of a wetting fluid being spontaneously imbibed and the non-wetting phase displaced (imbibition). During the displacement of oil or gas by water in a water-wet sand, the porous medium ordinarily imbibes water. The amount of oil recovered, the cost of recovery and the production history seem then to be controlled mainly by pore geometry. The influence of pore geometry is reflected in drainage and imbibition capillary-pressure curves and relative permeability curves. Relative permeability curves for a particular consolidated sand show that at any given saturation the permeability to oil during imbibition is smaller than during drainage. Low imbibition permeabilities suggest that the non-wetting phase, oil or gas, is gradually trapped by the advancing water.

This paper describes a mathematical image (model) of consolidated porous rock based on the concept of the trapping of the non-wetting phase during the imbibition process. The following items have been derived from the model.A direct relation between the relative permeability characteristics during imbibition and those observed during drainage.A theoretical limit for the fractional amount of oil or gas recoverable by imbibition.An expression for the resistivity index which can be used in connection with the formula for wetting-phase relative permeability to check the consistency of the model.The limits of flow performance for a given rock dictated by complete wetting by either oil or water.The factors controlling oil recovery by imbibition in the presence of free gas.

The complexity of a porous medium is such that drastic simplifications must be introduced to obtain a model amenable to mathematical treatment. Many parameters have been introduced by others in "progressing" from the parallel-capillary model to the randomly interconnected capillary models independently proposed by Wyllie and Gardner and Marshall. To these a further complication must be added since an imbibition model must trap part of the non-wetting phase during imbibition of the wetting phase. Like so many of the previously introduced complications, this fluid-block was introduced to make the model performance fit the observed imbibition flow behavior.
Microbial Flora in a Number of Oilfield Water-Injection Systems
Authors: Carlson V. , Bennett E.O. , Rowe J.A.
Published: December 2007

This report concerns the microbial flora found throughout the surface facilities of six water-injection systems in Texas and Oklahoma. Each system is described in detail and water quality data are presented when available.

Pseudomonads and sulfate-reducers (Desulfovibrio) were the predominate organisms found in the systems. The genera Sphaerotilus, Bacillus, Achromobacter, Micrococcus, Clostridium, Flavobacterium, and Sarcina were also isolated in significant numbers. Molds, iron bacteria, sulfur bacteria and soil bacteria were found less frequently in the systems.

It is concluded that a complex microbiological flora exists in oilfield water-injection systems. A tendency for waters to deteriorate in passage through solid bed filters is also noted.

Introduction

The injection of water into a subsurface formation is often accompanied by numerous problems, the origin and nature of which are only partially understood. During the past few years, investigators have indicated that bacteria are involved in some of these problems even though very little specific information is available concerning this matter.

It is surprising that investigators working on microbiological problems in water injection have never made a complete study of the flora of these systems. The logical course to pursue is that of identifying the microbial flora and then examining each organism individually and in combination with others to determine if they produce a particular problem.

The objective of the present investigation is to identify the microbial flora in water-injection systems. In addition, the quality of the water in most of the systems was determined and some observations made on the extent to which passage through surface-handling facilities affects water quality. The information derived from this study can serve as a foundation for additional basic investigations.
Rheological Properties of Pseudoplastic Fluids in Porous Media
Authors: Gogarty W.B.
Published: December 2007

With flow of non-Newtonian fluids in porous media, effective viscosities are needed for use in the Darcy equation. These viscosities depend on the rock parameters and flowing conditions. In this investigation, rheological and flow results were correlated to develop an expression for calculating effective viscosities. Surfactant-stabilized dispersions of water in hydrocarbon were used with consolidated sandstone cores of different permeabilities. The average shear rate in a core was related to the permeability and porosity of the core and the frontal velocity through the core.

By using the correlation obtained for determining effective viscosity, experimental and theoretical values were compared for each fluid system by determining average and maximum errors. For the fluid system showing the largest average error, the correlation fit 38 experimental points with an average and maximum percentage error of 4.3 and 14.8, respectively. For the fluid system showing the least error, average and maximum percentage errors of 1.8 and 4.3, respectively, were calculated using 29 experimental points.

Introduction

Use of non-Newtonian fluids in the petroleum industry is not new. Fluids of this type have been used for many years as fracturing agents and drilling muds. Recently, attention has focused on the use of high molecular weight polymer solutions for secondary recovery. Results have been reported on studies relating to the flow behavior of polymer solutions in porous media. Each study gives the viscosity in the Darcy equation as a function of the rheological properties of the fluid, the characteristics of the porous medium and the pressure gradient. The functional forms of the reported expressions differ somewhat in each study.
Fundamentals of Oilwell Jet Pumping
Authors: Grupping A. W. , Coppes J. L. R. , Groot J. G.
Published: December 2007

This paper explains the theory behind the operation of jet pumps, including the effect of density differences between power fluid and produced fluids. By differentiating between the pump intake pressure and the throat-entrance pressure, we provide insight into the factors that affect jet pump performance. A stepwise procedure is given for sizing and selecting a jet pump.
Effect of Vertical Fractures on Reservoir Behavior-Incompressible Fluid Case
Authors: Prats M.
Published: December 2007

The effect of a sand-filled vertical fracture of limited radial extent and finite capacity (fracture capacity is the product of the permeability and width of the fracture) on the flow behavior of a cylindrical reservoir producing an incompressible fluid through a centrally located well has been investigated mathematically. The shape of the lines of equal pressure near the fracture is essentially independent of the size of the reservoir, provided that the field radius is of the order of the fracture length or larger. For reasonable values of production rates and of fluid, reservoir and fracture properties, the total pressure drop between the end of the fracture and the well is generally negligible compared with the pressure drop in the reservoir. With regard to production response, the effect of vertical fractures can be represented by the production response of an equivalent or effective well radius. For a high-capacity fracture, the effective well radius is a quarter of the total fracture length, decreasing with the fracture capacity. When invasion effects are simulated by decreasing the width of the damaged zone with distance from the well, the effect of formation damage around a fracture on the production response is not so serious as indicated by the literature. This suggests that frac fluids with a conventional filter-loss response are better than high-spurt-loss frac fluids, provided the effective permeability of the damaged zone is the same.

Introduction

This paper considers the effect of the fracture capacity, as well as the formation damage which can result from fracture treatments, on the productive capacity of vertically fractured wells. Other publications, notably those of van Poollen, consider these same effects. In addition to providing more general results for vertical fractures than are available from the literature, the present paper gives the equivalent well radius of fractures having different lengths and Capacities and, also, includes pressure distributions in and around the fractures. The effect of a damaged zone around a fracture on the production response was not found to be so great as that reported by van Poollen. This difference probably stems from the fact that we consider a damaged zone which is widest (but is still small) near the well and thins out toward the extremities of the fracture, whereas van Poollen considers a damaged zone having a uniform width for the entire fracture length. Simple, but adequate, equations which describe the effect of these variables on production response are presented (in Appendixes A and B). Thus, results can easily be extended to values of the variables not specifically considered here.