bluuebunny/crossref_metadata_2025 huggingface dataset:
Porosity and Permeability of Eastern Devonian Gas Shale
Authors: Soeder Daniel J.
Published: December 2007

High-precision core analysis has been performed on eight Devonian gas shale samples from the Appalachian basin. Seven of the core samples consist of the Upper Devonian Age Huron member of the Ohio shale, six of which came from wells in the Ohio River valley, and the seventh from a well in east-central Kentucky. The eighth core sample consists of Middle Devonian Age Marcellus shale obtained from a well in Morgantown, WV.

The core analysis was originally intended to supply accurate input data for Devonian shale numerical reservoir simulation. Unexpectedly, the work has identified a number of geological factors that influence gas production from organic-rich shales. The presence of petroleum as a mobile liquid phase in the pores of all seven Huron shale samples effectively limits the gas porosity of this formation to less than 0.2%, and gas permeability of the rock matrix is commonly less than 0.1 μd at reservoir stress. The Marcellus shale core, on the other hand, was free of a mobile liquid phase and had a measured gas porosity of approximately 10%, and a surprisingly high permeability of 20 μd. Gas permeability of the Marcellus was highly stress-dependent, however; doubling the net confining stress reduced the permeability by nearly 70%.

The conclusion reached from this study is that the gas productivity potential of Devonian shale in the Appalachian basin is influenced by a wide range of geologic factors. Organic content, thermal maturity, natural fracture spacing, and stratigraphic relationships between gray and black shales all affect gas content and mobility. Understanding these factors can improve the exploration and development of Devonian shale gas.
Probable Pattern of United States Petroleum Supply
Authors: Hill Kenneth E.
Published: December 2007

Introduction

To render an intelligent judgment on the future of the petroleum industry, it is necessary to look ahead for as long a time as feasible, even though forecasting always is fraught with danger. It particularly is useful to study the outlook for the United States petroleum industry, because it is not only the largest producer, but also the consumer of over one-half of all the petroleum produced in the world. Because of this dominant position, the U.S. price structure-particularly for crude continues to be the principal influence on prices for both crude and crude products throughout the world. Therefore, it is quite important to focus attention on the long-range outlook for petroleum demand in the U.S. and on the probable sources of supply.

Demand

It now is becoming apparent that U.S. consumption of petroleum will grow less rapidly in the future than during the first postwar decade when it averaged 5.8 per cent per annum. This appears probable principally because of several factors:the impact of cheaper natural gas on petroleum consumption,a slower rate of industrial expansion anda slower rate of growth in gasoline use as a result of compact cars and congested highways.

The consensus of most observers leans toward a rate of about 4 per cent for the next few years, and then a slow decline.

In this analysis, a simple expedient has been used-the assumption of constant increments in demand each year. Thus, for the next few years, an increment of 400,000 B/D is expected, equal to a growth rate of about 4 per cent each year. During the latter part of this decade, consumption should increase by 450,000 B/D each year. By 1970, the increment likely will be 500,000 B/D. By 1975, domestic demand for petroleum liquids will total approximately 17 million B/D. This represents an increase of about 7 million bbl (or 70 per cent) during the 15-year period, or an average of about 3.6 per cent per annum.

During the same time, natural gas demand (which currently supplies about 27 percent of our energy needs) should continue to grow at a faster rate than petroleum at an estimated rate of about 5 per cent per annum. As has been pointed out many times, this is a mixed blessing because natural gas does reduce the demand for petroleum. Otherwise, crude-oil production would be larger relative to capacity than herein estimated, thus accelerating the time when domestic production would reach a peak and begin to decline.
Pressure Distribution in Three-Dimensional Hydraulic Fractures
Authors: Vandamme L. , Jeffrey R. G. , Curran J. H.
Published: December 2007

Summary. Stress intensity factors, calculated along the edge of an elliptic fracture with a three-dimensional (3D) coupled hydraulic fracturing model, differ significantly from those that arise from a uniform pressure within the fracture. Interactions between the two branches of a T-shaped fracture are shown to affect the geometry of the overall fracture.
Measurement While Drilling - A New Tool (includes associated papers 15328 and 15343 )
Authors: Fontenot John E.
Published: December 2007

Definition

Measurement while drilling (MWD) is the downhole measurement of important parameters and (in most cases) the simultaneous transmission of those measurements to the surface while drilling.

Need for MWD

In the past, hole-making and formation evaluation processes have been accomplished with different technologies, separated in time. Drilling (hole-making)is a complicated technological process with many uncertainties. Ignorance of what is taking place downhole during this process has caused it to be viewed more as an art than as a science. The most important parameters controlling this process are the physical properties of the formation (and the pore fluid)being drilled, which are largely unknown at the time of drilling.

The big mistakes that involve the loss of well control (blowouts) are well known. The many "small" mistakes (kicks, lost circulation, stuck pipe, lost cones, twistoffs, etc.) are not so well known, but cost considerable time and money. The conventional (wireline) formation evaluation process, while very important to the geologist, the petrophysicist, and the reservoir engineer, is also very expensive in terms of rig time and trouble cost.

History

The first U.S. patents and technical papers on MWD appeared in the early 1930's. The first practical approach that resulted in technical success was J.J. Arps' mud pulse system that made its debut in the 1950's. In the late 1960's, Exxon and Texaco experimented with downhole recording while drilling. The lack of high-density electronics packaging, a suitable memory medium, and the ability to ruggedize the systems adequately made them unattractive for extensive use.

As a result of the efforts of SNEA (Elf Aquitaine)and Raymond Engineering, and with the financial assistance of the U.S. DOE, Teleco introduced the first commercial MWD system in 1978. At the current time, many companies are investing in this technology, while eight offer commercial services.

Data Rate Requirements

When designing or selecting an MWD system for use, one must specify the types of downhole information desired and the measurement rates needed. Some information is needed on a "time(ly) basis" and other on a "footage basis." To convert from a time base to a depth base, the drilling rate must be known. A curve of average penetration rate as a function of depth that is typical of the Gulf of Mexico was used to prepare Fig.

It provides a rough guide as to the suitability of various mud-pulse data rates for providing multiple-service MWD.
A Rule-Based System for Well Log Correlation
Authors: Startzman Richard A. , Kuo Tsai-Bao
Published: December 2007

Computer-assisted approaches to well log correlation are of interest to engineers and geologists for two reasons. In large field studies, a computer can be used simply to reduce the time required to correlate zones of interest. It is also possible that computer-assisted correlations may suggest zonal matches of interest and originality that might not have been considered. This paper presents a new approach to the computer-assisted log correlation. Geologic horizons are correlated between wells by use of an artificial intelligence rule-based technique. Using the symbol-manipulation capabilities of a computer language called List Processing (LISP), we developed a prototype rule-based system that (1) has symbolic representation of log data, (2) recognizes log shapes from traces, (3) identifies geologic zones from a sequence of shapes in a log, (4) characterizes the zones, (5) correlates zones from well to well with a set of "if/then" type of rules, and (6) uses a forward-chaining inference scheme to execute the rule base. The purpose of this paper is to describe the use of the LISP language and the methodology involved in the development of this system.
Two-Point Determinations of Permeability and PV vs. Net Confining Stress
Authors: Jones Stanley C.
Published: December 2007

Empirical equations are presented that accurately fit permeability, PV, or porosity data vs. net confining stress. Each of these equations has four adjustable parameters. With little loss of accuracy, however, two of the coefficients can be preset. Consequently, permeability, PV, or porosity measurements need to be made at only two confining stresses—e.g., at 1,500 and 5,000 psi [10.3 and 34'.5 MPa] to define the stress dependence within close tolerances completely.

With the techniques described, economical measurements of these stress-dependent properties can be made on a routine basis. The results can be used to calculate PV compressibility and to estimate productivity declines resulting from permeability reduction as deep, high-pressure reservoirs are drawn down.
Factors Affecting the Equivalency of Different Capillary Pressure Measurement Techniques
Authors: Omoregie Zuwa S.
Published: December 2007

The results of a laboratory investigation of the effects of some factors that affect the equivalency of different drainage capillary pressure measurement techniques are presented. These factors are Bond number, clay alteration by sample drying, wettability, equilibration, sample orientation, and overburden pressure. The results, among other things, suggest an extension of the range oof validity of liquid/liquid centrifuge tests. A method of estimating contact angles of weakly wetting systems with capillary pressure data is presented.
Measurement and Correlation of Diffusion Coefficients for CO2 and Rich-Gas Applications
Authors: Renner T. A.
Published: December 2007

A novel in-situ method for measuring molecular diffusion coefficients of CO2 and other solvent gases in consolidated porous media at high pressure has been developed and is described. This technique is unique because visual observations and measurements of composition are not required. Experimental diffusion coefficients are reported for CO2 in decane up to 850 psia [5.86 MPa], for CO2 in 0.25 N NaCl brine up to 850 psia [5.86 MPa], and for ethane in decane up to 600 psia [4.14 MPa]. All tests were conducted in Berea cores saturated with liquid phase at 100°F [311 K]. Cores were oriented both vertically and horizontally to assess the effects of gravity-induced convection on the observed mass transfer. The experimental diffusion coefficients obtained from this study have also been correlated, together with literature data for methane, ethane, and propane, as a function of liquid viscosity and thermophysical properties of the diffusing gases.
Vapor-Density Measurement for Estimating Minimum Miscibility Pressure
Authors: Harmon Richard A. , Grigg Reid B.
Published: December 2007

A rapid experimental method is described that uses the solvency (density) properties of CO2 and the actual stock-tank oil to determine the minimum miscibility pressure (MMP).

The "vapor-density" method directly measures the density of the injection-gas-rich upper phase in contact with the crude oil as a function of pressure. This measurement correlates very well with the MMP from slim-tube experiments below about 110°F [43°C] and may be extended to higher reservoir temperatures.
Analysis of Mudcake Structures Formed Under Simulated Borehole Conditions
Authors: Hartmann Albert , Özerler Mustafa , Marx Claus , Neumann Hans-Joachlm
Published: December 2007

Tiny pieces of filter cake were shock-frozen and broken while immersed in coolant. The specimens were studied with scanning electron microscopy (SEM) in both freeze-dried and frozen-hydrated stages. These techniques were used to show that the original structure of the filter cake is preserved. The investigation covered filter cakes of four different drilling fluids with respect to fluid loss data and thermal and chemical degradation. Honeycomb structures of bentonite containing drilling fluids were also found in the resultant filter cakes. The investigation showed that gel strength of the drilling fluid exerts a considerable influence on dynamic filter-cake structures.
The Influence of Sample Size and Permeability Distribution on Heterogeneity Measures
Authors: Jensen Jerry L. , Lake Larry W.
Published: December 2007

This study evaluates the influence of sample size on the Dykstra-Parsons and Lorenz measures of heterogeneity. Because either coefficient is <>determined for a reservoir from a finite number of data, only an estimate is made of the true coefficient. We show that, on average, the estimate is less than the true value. We give the relationship between estimate error and number of samples and show how significant errors may arise when too few data are used.

The influence of the permeability distribution on heterogeneity measures is also studied. We show that a variety of distributions exhibiting different reservoir performance can have the same Dykstra-Parsons coefficient.

We propose a heterogeneity measure that includes an indication of the permeability distribution. The new measure requires fewer data than the Dykstra-Parsons estimator. The relationships between the new measure and the Dykstra-Parsons and Lorenz coefficients are given.
Experimental Studies on the Waterflood Residual Gas Saturation and Its Production by Blowdown
Authors: Flshlock T. P. , Smith R. A. , Soper B. M. , Wood R. W.
Published: December 2007

Experiments performed on long sandstone cores determined the waterflood residual gas saturation and the mobilization of this trapped gas by reduction of pressure. The trapped gas apparently did not become mobile immediately as it expanded: the gas saturation had to increase appreciably to a critical value for gas remobilization. This new finding has unfavorable implications for possible processes to increase liquids recovery from gas-condensate reservoirs and for enhanced recovery from gas reservoirs invaded by water.
New Concepts for Helical Buckling
Authors: Mitchell R. F.
Published: December 2007

An approximate analytic solution for the helical buckling of tubing with weight has been determined. This solution has good accuracy except near the neutral point. The solution used by Lubinski to solve the helical-buckling problem is shown to be a special case of this new analytic solution. It is generally accepted that Lubinski's solution is a good approximate solution, but the range of applicability has been unknown because the approximations used in its derivation were not well understood. In this new solution, the approximations are explicit and an accuracy criterion is established. Initial conditions at the packer are investigated and their effects on the solution are described. Finally, the effect of this solution on tapered strings is described, and a new approximate buckled solution for tapered strings is presented. This analysis puts the Lubinski solution in a technical context that allows such further developments as inclined wellbores and friction.
Analyses and Applications of Pressure, Flow Rate, and Temperature Measurements During a Perforating Run
Authors: Tarlq Syed M. , Ayestaran Luis C.
Published: December 2007

Perforating technology has undergone significant advances during the last decade. Tubing-conveyed perforating, under-balanced perforating, high-shot-density guns, better shaped charges, and improved gun systems have contributed to safer operations and improved productivity of the perforated completions. A recent development described in this paper is a perforating tool that makes real-time downhole measurements [including pressure, flow rate, temperature, gamma ray, casing-collar locator (CCL), and cable tension] during a perforating run and can selectively fire a number of guns at different depths or times. In addition to providing better control of the perforating process, the simultaneous downhole measurements can provide in a single trip a production log, conventional well tests before and after perforating, and a fill-up or slug test soon after perforating for underbalanced conditions. Thus, the completion can be evaluated in real time and any needed remedial reperforating can be performed while the gun is still in the hole. Other applications include limited-entry perforating, monitoring of bottomhole pressure (BHP) during minifracture jobs, better depth control with a gamma ray detector, fluid-level monitoring, and underbalance control. The applications of these measurements, with field data obtained with the Measurement While Perforating (MWPSM) tool, are the subject of this paper. Examples show the capabilities and the versatility of the MWP tool.
Transient Analysis of Acoustically Derived Pressure and Rate Data
Authors: Kabir C. S. , Kuchuk F. J. , Hasan A. R.
Published: December 2007

A pressure-buildup test conducted on a sucker-rod pumping well is often distorted by long-duration wellbore storage. In fact, this distortion could be so severe that even a week′s shut-in period may not allow a semilog analysis. A longer shut-in period becomes economically discouraging because of lost production.

Low energy and low transmissivity in the reservoir, coupled with increased fluid compressibility, contribute to this long-duration storage phenomenon. One way of reducing the storage effect clearly lies in the simultaneous analysis of downhole pressure and flow rate, estimated from casinghead pressure and rising annular liquid-level measurement made by acoustic well sounding (AWS). Ascertaining the quality of the indirectly measured pressure and rate data constitutes one of the objectives of this study.

Several methods exist to translate the AWS measurement to downhole pressure and rate data for the subsequent transient analysis. We show that even an empirical hydrodynamic correlation provides satisfactory transient-pressure/flow-rate data for convolution and deconvolution analyses for moderate pumping-liquid columns. When long annular liquid columns are encountered, translating the AWS measurement with a mechanistically based hydrodynamic model appears to be a prudent approach.

Interpretation of several transient tests show that automated convolved-type-curve or history matching of field data is a powerful tool for reservoir-parameter (total mobility, skin, fracture half-length, and storage coefficient) estimation. Use of downhole rate for the convolved type-curve matching reduces the variable storage coefficient by several orders of magnitude, thereby enhancing the quality of the estimates. Deconvolution of downhole pressure and rate data and the pressure-derivative approach significantly aided in well/reservoir flow-model identification.

A simple algorithm for computing the Laplace transform of the wellbore pressure for an infinite-conductivity vertically fractured well in an infinite reservoir is developed in this work for a rapid, iterative-type computation used in automated convolved-type-curve analysis.
Stability of Boreholes Drilled Through Salt Formations Displaying Plastic Behavior
Authors: Infante E. F. , Chenevert M. E.
Published: December 2007

This paper presents a mathematical and laboratory analysis that provides solutions to the problem of plastic flow of salt formations into wellbores. The paper predicts how the salt will flow and what type of mud might be used to control such flow for various well conditions. In the mathematical analysis, it is assumed that the incipience of plasticity in the formation is regulated by the level of octahedral shear stress and that the formation is neither permeable nor porous, but homogeneous and isotropic. The stress distribution in the neighborhood of the borehole is studied, and conditions under which this distribution is elastic, elastoplastic, or plastic are determined. Equations are derived that, in terms of two constants of the formation material, yield, and the limit of elasticity. Factors calculated include the radius of the plastic front and the percent of the borehole-diameter shrinkage as a function of mud weight used. This study was prompted by past failures in drilling through the Louann salt formation at depths of 12,500 to 14,000 ft [3810 to 4270 m], a formation that exhibits rapid plastic flow at low mud weights and at the temperatures and pressures encountered. The techniques presented were applied to subsequent drilling of this salt section, and the zone was penetrated without the problem of plastic flow. Salt-property constants were developed at elevated temperatures and pressures for the Louann salt formation by use of the triaxial test cell. Data are presented for elastic, plastic, and creep deformation of salt for pressures to 13,200 psi [91 MPa] and temperatures to 350°F [177°C]. Nomographs are also presented to facilitate the rapid determination of salt behavior. For a given depth and temperature, it is possible to specify a mud weight so that the salt will behave either elastically, in creep flow, or plastically. If plastic flow is predicted, the amount of borehole-diameter reduction is specified. Although this study focuses on the Louann salt section, we believe that the results apply equally well to any other salt section with physical constants similar to those in the Louann salt.
Depletion Performance of Volumetric High-Pressured Gas Reservoirs
Authors: Begland T. F. , Whitehead W. R.
Published: December 2007

A method to predict the percent recovery of volumetric, high-pressured gas reservoirs from the initial pressure to the abandonment pressure with only initial reservoir data is presented. This method can also be used with early-life production data to predict the initial gas in place. The method is based on an incremental solution to the general material-balance equation. All parameters in the material balance are pressure-dependent and are recalculated for every 100-psi [690-kPa] drop in reservoir pressure. Procedures were developed to calculate these parameters with correlations and data available in the literature. PV compressibilities, formation-water compressibilities, and gas compressibility factors were determined for temperatures and pressures ranging up to 400°F and 20,000 psia [204°C and 137.9 MPa], respectively. The pressure dependency of the PV compressibility and the formation-water compressibility is a unique feature of this model.

The reservoir depletion model presented here was applied to a field example, as were three published techniques for determining reserves in abnormally pressured reservoirs. When predictions of initial gas in place were compared, the reservoir depletion model yielded a more accurate value than the other techniques.
Obtaining Structural and Stratigraphic Dip Information Using Segmentation Trees and Optimization
Authors: Kerzner Mark G.
Published: December 2007

A new method of dipmeter computation is described that is based on formalizing and implementing some of the rules of optical dipmeter correlation. The new techniques used for this are segmentation trees and hierarchical, multilevel optimization. Use of this method results in precise definition of dip information on both structural and stratigraphic levels.
Improved Environmental Corrections for Compensated Neutron Logs
Authors: Galford J. E. , Flaum C. , Gilchrist W. A. , Soran P. D. , Gardner J. S.
Published: December 2007

The basic openhole responses and environmental correction algorithms for compensated neutron logging (CNL™) tools have been updated. The improved processing is based on an extensive set of laboratory formation measurements to which mathematical modeling calculations have been added. In all, the new algorithms include basic responses for the three principal formation matrix types and corrections for seven environmental effects and formation-fluid salinity.

A total of 467 laboratory formation measurements have been augmented with 245 data points generated through mathematical modeling. This data base has been used to define more accurately the effects on the tool response of variations in logging conditions from those considered standard in the laboratory. More accurate corrections for the effects of formation pressure, temperature, mudcake, natural or barite mud, and borehole salinity have been defined. Certain other effects depend on more than one parameter. For example, the effect of formation salinity is somewhat matrix-dependent; therefore, the corrections are handled differently for sandstone, limestone, and dolomite. The effect of tool standoff depends on the borehole size; consequently, the standoff correction is larger for larger boreholes.

The porosity crossplots and environmental correction charts based on the new algorithms represent a significant evolutionary improvement over previous techniques. They should be an important aid to the use and interpretation of neutron logs.
Vertical-Interference Pressure Testing Across a Low-Permeability Zone With Unsteady Crossflow
Authors: Wijesinghe Ananda M. , Kececioglu Ifiyenia
Published: December 2007

Existing analytical models for interpreting vertical-interference pressure tests across the low-permeability zone in a three-layered reservoir usually assume transient radial flow in the high-permeability layers and pseudosteady vertical crossflow in the intervening tight zone. The neglect of vertical flow in the high-permeability layers and of radial flow in the tight layer requires that the permeability contrast between these layers be large. When this assumption is satisfied, however, it is also very likely that the pressure diffusivity in the tight layer is much smaller than that in the high-permeability layers. Thus, to be consistent, the flow across the tight layer must be treated as an unsteady diffusive process driven by the transient pressure changes occurring in the high-permeability layers.

In this paper, we extend the analysis of Ehlig-Economides and Ayoub by replacing their pseudosteady crossflow assumption with unsteady crossflow and interpret the crossflow response in terms of near- and far-boundary flow-response functions for the tight zone. The inclusion of unsteady crossflow requires one additional dimensionless parameter and results in a set of governing equations that are different from but similar to the equations of the dual-porosity, dual-permeability model with unsteady interporosity flow presented by Wijesinghe and Culham for naturally fractured reservoirs. As in the case of dual-porosity, dualpermeability reservoirs, the pressure response with unsteady crossflow is significantly different at early times from that for pseudosteady crossflow under practical conditions.

Exact and asymptotic solutions and type curves for the wellbore pressures at the upper and lower perforations are presented for flow-rate-specified vertical interference tests. The solutions account for different formation properties, wellbore storage, and skin factors of the two high-permeability layers and the formation properties of the tight zone. The impact of unsteady and pseudosteady crossflow model assumptions on the wellbore pressures and on the spatial distributions of fluid pressures and crossflow rates is examined in detail.
Analysis of Pressure Data From a Restricted-Entry Well in a Multilayer Reservoir
Authors: Yeh N. , Reynolds A. C.
Published: December 2007

This work presents new semilog type curves for analyzing data obtained at a restricted-entry well completed in a multilayer reservoir where crossflow occurs between reservoir layers. Use of the new type curves along with standard semilog analysis of pseudoradial-flow pressure data makes possible a complete analysis of pressure data. Specifically, standard semilog analysis of pseudoradial-flow pressure data yields estimates of the total flow capacity and the total skin factor. The new type curves can then be used to estimate the real mechanical skin factor resulting from damage or stimulation, the flow capacity adjacent to the open (perforated) interval, and the effective average vertical permeability.
Prediction of Abrupt Reservoir Compaction and Surface Subsidence Caused By Pore Collapse in Carbonates
Authors: Smits R. M. M. , de Waal J. A. , van Kooten J. F. C.
Published: December 2007

A new procedure has been developed to predict the abrupt in-situ compaction and the associated surface subsidence above high-porosity carbonate fields that show pore collapse. The approach is based on an extensive laboratory compaction study in which the effects of carbonate type, porosity, core preparation, pore saturant, horizontal/vertical stress ratio, and loading rate on pore-collapse behavior were investigated.

For a number of carbonate types, a trendline was established that describes the relationship between the porosity after collapse and the vertical effective stress. This trendline concept, in combination with existing subsidence models, enables reservoir compaction and surface subsidence to be predicted on the basis of wireline porosity logs. Static and dynamic elastic constants were found to be uncorrelated during pore collapse.

The position of the trendline depends strongly on carbonate type, pore saturant, loading rate, and stress ratio. Therefore, procedures are given to derive the correct in-situ trendline from laboratory compaction experiments.
Correlation of Interfacial Tension of Hydrocarbons
Authors: Hough E.W.
Published: December 2007

Correlation of interfacial tension of the methane-n-pentane and methane-n-decane systems was made by Hough and Stegemeier by the use of the Weinaug and Katz equation. The methane-n-heptane and ethylene-n-heptane systems were investigated by the authors. Additional systems taken from the literature were the methane-propane system by Weinaug and Katz, the methane-n-butane system by Pennington and Hough, and the n-butane-carbon dioxide system by Brauer and Hough. These systems were analyzed by the Weinaug-Katz equation and the Sugden equation on the IBM 1620 II computer using a regression analysis program. Parachor and exponent values for each component and system were determined. The experimental work was close to the critical point of the light component in the n-butane-carbon dioxide and ethylene-n-heptane systems, between the critical points of the light and heavy components in the methane-n-pentane, methane-n-heptane and methane-n-decane systems, and close to the critical point of the heavy component in the methane-propane and methane-n-butane systems. An empirical formula was developed to find a value of the constant B in the Sugden equation for binary hydrocarbon systems from the parachor values of the two components. interfacial tension for binary hydrocarbon Systems was found to be a direct function of liquid-vapor phase density difference in the same manner as a single-component system.

Discussion

Interfacial tension may be defined as the measure of the specific free surface energy between two phases having different compositions. The interfacial tension (IFT) for a binary system may be predicted for any temperature and pressure if the mole fractions and molal volumes of the liquid and gaseous phases are known. One method of correlating IFT was proposed by Weinaug and Katz and modified by Hough and Stegemeier. The modified formula is:

(1)

where y = interfacial tension, dynes/cmP1 = parachor of the first componentP2 = parachor of the second componentx1, x2 = mole fractions in the liquid phasey1, y2 = mole fractions in the vapor phaseVL, Vv = molal volumes (cu ft/lb mole)1/62.43 = conversion factor, lb/cu ft to gm/ccK = exponent of the parachor relation and subscriptsL = liquidV = vapor1 = component 12 = component 2. In a binary system, there are two degrees of freedom; that is, the values of x1, x2 y1, y2, VL and Vv are determined at any particular temperature and pressure. Therefore, for each temperature and pressure at which an experimental value of IFT was measured, the values of x1, y1, VL and Vv were found, and the following values were calculated:

(2)

(3)

SPEJ

P. 345ˆ
Hot-Water and Steamflood Laboratory Experiments Under Reservoir Conditions
Authors: Quettier L. , Corre B.
Published: December 2007

Hot waterfloods at four temperatures (between 30 and 240°C [86 and 464°F]) and a steamflood were performed on the same porous medium (compacted silt) under reservoir conditions. Dynamic isothermal displacements were interpreted with a thermal simulator, taking into account capillary end effects. The corresponding oil/water relative permeability curves were obtained by matching observed pressure drop and oil production. Results show that temperature influences the endpoint saturations but not the shape of the curves.

The steamflood experiment was carried out with an adiabatic core holder. The oil recovery was 70% higher than the recovery by the hot waterflood at the same temperature (240°C [464°F]). Oil stripping and production of a large amount of CO2 caused by dissolution of carbonates were pointed out. In the numerical interpretation of this experiment, we used oil/water relative permeabilities to provide the three-phase oil relative permeability. These experiments allow a better understanding of steam displacement mechanisms and supply essential data for numerical interpretation of a steamflood pilot.
Laboratory Evaluation of a Crude-Oil-Sulfonate/Nonionic-Cosurfactant Micellar Fluid
Authors: Kremesec V. J. , Raterman K. T. , Taggart D. L.
Published: December 2007

Phase behavior, interfacial tension (IFT) measurements, fractionation studies, and core tests have been used in the formulation of a crude-oil-sulfonate (CROS)/ethoxylated-alcohol micellar fluid for application in a changing ionic environment that attains a relatively high hardness concentration as a result of ion exchange. By varying the hydrophile/lipophile balance (HLB) of the nonionic cosurfactant, phase behavior can be shifted from lower to upper phase and the optimum can be found. It is shown that the solubilization of oil and brine and the value of the optimum can be controlled further by blending different nonionic surfactants with CROS samples whose properties were altered by controlling variables in the manufacture. Effects of such system variables as surfactant and hardness concentration and the ratio of CROS/nonionics have a significant effect on phase behavior. The IFT vs. solubilization parameter correlation was in reasonable agreement with that of Huh1 and is shown.to hold over a wide range of surfactant and hardness concentrations, but the intercept is different for each CROS/nonionic pair. IFT’s and phase behavior from core-test effluents are shown to agree with the phase-behavior studies. Fractionation phase-behavior studies indicate that chromatographic separation will affect the process significantly only if oil is inefficiently displaced; this is supported by core tests. Excellent oil recovery was attained in Berea over a wide range of concentrations and HLB’s, and with small slugs. Oil recovery in field core tests was poor because of stringent capillary desaturation requirements.
Microemulsion to Liquid-Crystal Transition in Two Anionic Surfactant Systems
Authors: Hackett J. L. , Miller C. A.
Published: December 2007

The phase behavior of two anionic surfactant systems, one containing a commercial alpha olefin sulfonate (AOS) and the other containing pure sodium dodecyl sulfate (SDS), was determined in the region where a transition from microemulsion to liquid-crystalline phases occurred with decreasing alcohol content and temperature. A general and rather complex pattern of phase behavior was seen that included a four-phase coexistence region of brine, microemulsion, lamellar liquid crystal, and oil, and two three-phase regions containing both microemulsion and liquid crystal. In much of the four-phase region, complete separation of the phases did not occur even after equilibration for 1 year or more at constant temperature. Instead, oil and brine were observed to coexist with stable birefringent dispersions that (for some compositions at least) apparently contained three phases: microemulsion, liquid crystal, and oil. Solubilization of brine was uniformly low in the phases making up the dispersions. The dispersions in the SDS system exhibited non-Newtonian behavior with apparent viscosities in the range of 50 to 100 mPa·s [50 to 100 cp] at a shear rate of 10 seconds−1. Microemulsion viscosities in the same system were about an order of magnitude lower. No plugging or other adverse behavior was seen when such dispersions flowed at a velocity of 10−5 m/s [3 ft/D] through a model porous medium having pore sizes comparable with those in reservoirs. In preliminary experiments, selected dispersions appeared to be capable of displacing oil from the same model porous medium.
Methods for Predicting Wax Precipitation and Deposition
Authors: Weingarten J. S. , Euchner J. A.
Published: December 2007

Removal of wax from wells and flowlines can account for significant additional operating costs. To evaluate these potential costs, the operating conditions that allow waxes to precipitate in the wellbore must be identified, and deposition rates must be estimated to determine the costs associated with removal of wax deposits. Presented in this paper are laboratory and analytic methods that can be used to estimate both The critical operating conditions and the deposition rates. The laboratory tests and analysis presented may be used to characterize any type of oil.
An Improved Method for Calculating Bottomhole Pressures in Flowing Gas Wells With Liquid Present
Authors: Peffer J. W. , Miller M. A. , Hill A. D.
Published: December 2007

A method is presented for calculating bottomhole pressures (BHP's) from wellhead measurements in flowing gas wells with liquid present in the well stream. This method, a modification of existing methods, is based on including the contribution of entrained liquid to gravitational gradients. The study also includes evaluation of effective roughness factors evident from actual flowing pressure data.

The proposed method was tested vs. both a two-phase flow model developed by Govier and Fogarasi1 and currently applied methods based on dry-gas wells. The method was also tested with Govier and Fogarasi's data from 94 flowing wells and with data from 50 wells from the public files of the Texas Railroad Commission. The new method compared favorably with the two-phase flow model and was superior to currently applied methods.
Analysis and Evaluation of Alternative Concepts in Modeling Tarmats To Conform to Laboratory Investigations and Field Conditions
Authors: Tripathy B.
Published: December 2007

Black-oil reservoir simulators are universally formulated to handle a maximum of three different fluid phases—i.e., oil, water, and gas. The phase identity of tar, occurring in concentrations called "tarmats" within or marginal to petroleum reservoirs, varies widely from highly viscous hydrocarbon fluid to near-solid material. In black-oil modeling of tarmat reservoirs, therefore, considerable challenge is posed in characterizing tar as a drastic departure from the three fluid phases. No published literature provides concentrated details on tarmat modeling with an emphasis on comparative analysis and adaptability of different state-of-the-art modeling techniques. This paper compares the two approaches adopted most often to characterize tar in a model— i.e., as a highly viscous hydrocarbon fluid and as a relatively impermeable rock matrix. Other less commonly used methods that also may be reasonable are not discussed.
Low-Resistivity Hydrocarbon-Bearing Sand Reservoirs
Authors: Zemanek Joe
Published: December 2007

It has been found that significant amounts of water-free hydrocarbons can be produced from sandstone reservoirs that have water saturations greater than 50%. From comprehensive core and log analyses, the sands were found to have high surface areas that immobilize large amounts of water. The actual water saturations can be high, but water-free hydrocarbons will be produced.
Oil Production Using Pumped Multiphase Systems
Authors: Leggate J. S. , Iball W. N. , McJarrow S.
Published: December 2007

This paper reviews the production system options available for the development of remote oil fields by unmanned facilities at the remote site. Various types of artificial-lift techniques, surface multiphase fluid pumping, and flowline systems are compared and the attributes of each system illustrated, including an evaluation of the useful operational envelope of each system and its economics.
Improved Disposal-Water Treatment at Bahrain Oil Fields
Authors: Murti D. G. K. , Al-Maskati A. H. , Sood L. K.
Published: December 2007

Bahrain's Awali oil field is one of the oldest in the Arabian Gulf region. The recent sharp increase in produced water cut at Awali has resulted in higher oil carry-over in the produced water, which is currently disposed of in an aquifer about 700 ft [210 m] deep. The steps taken by Bahrain Natl. Oil Co. (Banoco) and the problems encountered in improving the quality of effluent are described in this paper.
Deltas
Authors: Richardson J.G. , Sangree J.B. , Sneider R.M.
Published: December 2007

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

A major part of the oil produced from sandstone reservoirs has been fromancient delta systems. Because of their importance and their variedcharacteristics, deltas are the subject of a three-article series. This initialarticle discusses the general building processes of deltas. Future articleswill focus on characteristics of sand-rich, high-energy deltas and mud-rich, low-energy deltas. Deltas form near the mouths of rivers that dischargesediments into oceans or other bodies of water. Two main stratigraphic eventsoccur in the building processes of all deltas:sediments are carried anddeposited in channels andthe sediments arc then reworked by waves andtides.

All materials reaching the delta mouth generally will be reworked it thesediment volume is low relative to the energy levels of the waves and tides. Inhigh-energy environments the clays and silts are eroded. leaving sand-richdeposits. Conversely, mud-rich deposits are left if the sediment flow rates arehigher than ocean flow rates. High-energy sand deltas have few activedistributry channels: these channels are meandering or braided. Shorelines arecontinuous sands. A good modern example is the sand delta now forming at themouth of the Nile River (Fig. 1). Mud-rich delta have many straight to sinuouschannels that form frequent branches. Shorelines are discontinuous stretches ofsands and muds. The best modern example is the Mississippi River delta (Fig.2). Sand bodies deposited, formed, and left in different parts of a delta havedifferent characteristics. For example, sand bodies deposited upstream in adistributary channel are not reworked by ocean currents, and have the coarsestmaterial at the base and finer sand, silt, and clays toward the top. At thechannel mouth and near shore, sand reworked and moved by tides forms bars thatgenerally run parallel to the shoreline. The bars have the coarsest material attheir tops. Farther offshore, sands are spread and deposited in thin sheets bycurrents that fan out from a channel mouth. These thin sheets of sand areusually interspersed with thin layers of shale that settle in the water anddrape over the sands during periods of lower river flow rates. Fig. 3 showsseveral such near-shore areas.

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Mud-Rich Deltas
Authors: Richardson J.G. , Sangree J.B. , Sneider R.M.
Published: December 2007

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

Mud-rich deltas form when the sediments brought in by the rivers aredeposited faster than they can be reworked by basin currents. Compared withsand-rich deltas, which are at the other end of the spectrum of delta types, mud deltas contain more silt and shales in the river-mouth bars and delta-frontsheet sands and have poorer continuity among the various sand bodies. Muddeltas characteristically have many straight distributary channels that branchfrequently. Sands deposited and preserved in the channels have the samedistributions as the sand-rich deltas discussed in Ref. 3. The coarsest, cleanest sand is left at the base. Finer sand, silt, and clay are left at thetop. The channel sands also become progressively thinner and of poorer qualitytoward the channel mouth in mud deltas, as in sand-rich deltas. Mud deltas canbuild very rapidly. For example, the modem Mississippi delta complex, formedduring the past 5,000 years, now encompasses hundreds of square miles, as shownin Fig. 1. This rapid building process often leaves large areas of mud-richdeposits, which prevent communication among the various bodies of channelsands, bars, and sheet sands. The distributary channel that cuts into previousdeposits of bar sands as the delta builds seaward usually has clay/silt bedslining the channel boundary, as shown in Fig. 2. These act as barriers to fluidflow. Along the shore and offshore, the sheet sands and river-mouth barsdeposited during a given sequence are often isolated by large areas containingbeds of silt and clay. The prodelta sheet sands are typically interbedded withsilts and clays (see Fig. 3). These sand beds may be less than 1 in. [2.5 cm]thick, may appear as water-saturated sands on resistivity logs, and yet may beprolific oil producers. Fig. 4 illustrates the conceptual geologic model of amud-rich delta. High-quality sands are distributed in the channels and inriver-mouth bars similar to those found in sand-rich deltas. The principaldifferences between the mud-rich and sand-rich delta models are the lowerquality of the bars and sheet sands, the poorer lateral continuity, and thelarge areas along the shoreline and offshore that are covered by beds of siltand clay. Oil recoveries and sweep efficiencies in mud-rich deltas are expectedto be less than those in sand deltas. Problems in locating wells and developingprojects are more critical than in sand-rich deltas because of the poorercommunication among sand members. Location of pilot-test areas for evaluationof additional recovery processes requires special studies by all disciplinesinvolved in describing the reservoir and designing the recovery process.

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Improved Thermoplastic Materials for Offshore Flexible Pipes
Authors: Dawans F. , Jarrin J. , Hardy J.
Published: December 2007

Long-term aging tests representative of field operating conditions have been conducted on various thermoplastic materials proposed for the inner tube of flexible pipes for offshore drilling and production applications. In particular, experimental data are provided about the changes of the mechanical properties of selected thermoplastic materials owing to optimized formulation when the pipes are exposed over time to crude oil in the presence of gas and water.
Development of a Twin-Screw Pump for Multiphase Duties
Authors: Dolan P. J. , Goodridge R. A. , Leggate J. S.
Published: December 2007

This paper discusses the reasons for developing a pump capable of pumping gas/liquid mixtures. Preliminary trials that led to the design, construction, and testing of a full-specification pump are described.