bluuebunny/crossref_metadata_2025 huggingface dataset:
Bonded Half-Planes Containing Two Arbitrarily Oriented Cracks: A Study of Containment of Hydraulically Induced Fractures
Authors: Lu Chien-Ke , Yew Ching H.
Published: December 2007

In the first part of this paper, the title subject is studied by introducing two modified singular integrals. The problem is reduced to a set of singular integral equations; and it is solved numerically by employing the Lobatto-Chebyshev method. The stress intensity factor at the fracture tips of a hydraulically induced fracture in a layered medium is calculated in the second part of the paper. The effect of the fluid pressure and the in-situ stress gradient as well as the effect of the relative layer material properties on the magnitude of the stress intensity factors are studied numerically. It has been shown that the relative magnitude of the stress intensity factor at the fracture tips can be used to indicate the direction of fracture movement.
Steam Zone Growth in Cylindrical Channels
Authors: Closmann Philip J.
Published: December 2007

The rapid breakthrough of steam that sometimes occurs in steam injection projects has been treated as a case of steam flow through a channel of high permeability. With the assumption of a cylindrical cross-section and steam zone growth limited by heat losses normal to the channel wall and sensible heat requirements within the zone, it is possible to estimate the channel size from the time of steam breakthrough at a producer.
Fully Coupled Multiblock Wells in Oil Simulation
Authors: Behie A. , Collins D. , Forsyth P. A. , Sammon P. H.
Published: December 2007

A fully coupled treatment of oil wells that are completed in more than one zone results in a bordered matrix. This paper develops solution algorithms that incorporate existing direct and iterative (incomplete LU) solutions in a straightforward manner. Timings in scalar and vector modes on the Cray-1 for a typical reservoir simulation problem are presented.
Thermal Response of Polycrystalline Diamond Compact Cutters Under Simulated Downhole Conditions
Authors: Glowka D. A. , Stone C. M.
Published: December 2007

An analytical method is developed to predict temperatures in polycrystalline diamond compact (PDC) drag cutters under steady-state and transient downhole conditions. The method is used to determine mean wearflat temperatures for cutters under conditions used in previous experiments to measure cutter wear. A correlation between wearflat temperatures and cutter wear rates is demonstrated, and it is shown that, for the particular rock type tested, cutter wear rates increase significantly above 350°C [662°F]. The concept of a critical weight on bit, above which wear-flat temperatures exceed this value, is introduced. The effects of several parameters on the critical WOB are examined. These include cutter thermal conductivity, diamond layer thickness, rock properties, convective cooling, bit balling, and transient events such as bit bounce. Preliminary results of thermal stress modeling show that plastic yielding of the cutter structure can occur under certain downhole conditions.
Flow Visualization for CO2/Crude-Oil Displacements
Authors: Campbell Bruce T. , Orr Franklin M.
Published: December 2007

Results of visual observations of high-pressure CO2 floods are reported. The displacements were performed in two-dimensional (2D) pore networks etched in glass plates. Results of secondary and tertiary first-contact miscible displacements and secondary and tertiary multiple-contact miscible displacements are compared.

Three displacements with no water present were performed in each of three pore networks: (1) displacement of a refined oil by the same oil dyed a different color; (2) displacement of a refined oil by CO2 (first-contact miscible); and (3) displacement of a crude oil at a pressure above the minimum miscibility pressure. In addition, three tertiary displacements were performed in the same pore networks: (4) displacement of the refined oil by water, followed by displacement by the same refined oil dyed to distinguish it from the original oil; (5) tertiary displacement of the refined oil by CO2; and (6) tertiary displacement of crude oil by CO2. In addition, recovery of oil from dead-end pores, with and without water barriers shielding the oil, was investigated.

Visual observations of pore-level displacement events indicate that CO2 displaced oil much more efficiently in both first-contact and multiple-contact miscible displacements when water was absent. In tertiary displacements of a refined oil, CO2 effectively displaced the oil it contacted, but high water saturations restricted access of CO2 to the oil. The low viscosity of CO2 aggravated effects of high water saturations because the CO2 did not displace water efficiently. CO2 did, however, contact trapped oil by diffusing through water to reach, to swell, and to reconnect isolated droplets. Finally, CO2 displaced crude oil more efficiently than it did the refined oil in tertiary displacements. Differences in wetting behavior between the refined and crude oils appear to account for the different flow behavior.
CO2 Minimum Miscibility Pressure: A Correlation for Impure CO2 Streams and Live Oil Systems
Authors: Alston R. B. , Kokolis G. P. , James C. F.
Published: December 2007

This paper presents an empirically derived correlation for estimating the minimum pressure required for multicontact miscible (MCM) displacement of live oil systems by pure or impure CO2 streams. Minimum miseibility pressure (MMP) has been correlated with temperature, oil C5+ molecular weight, volatile oil fraction, intermediate oil fraction, and composition of the CO2 stream.

The effects of temperature and oil C5+ molecular weight on pure CO2 MMP have been well documented. However, CO2 sources are rarely pure, and solution gas usually is present in reservoir oils. The correlation presented in this paper accounts for the additional effects on MMP caused by the presence of volatile components (methane, C1; and N2) and intermediate components (ethane, C2; propane, C3; butane, C4; hydrogen sulfide, H2S; and CO2) in the reservoir oil. This correlation also is capable of estimating MMP for a contaminated or enriched CO2 stream on the basis of the pure CO2 MMP.
Multicomponent CO2/Water/Hydrocarbon Phase Behavior Modeling: A Comparative Study
Authors: Kuan D. Y. , Kilpatrick P. K. , Sahimi M. , Scriven L. E. , Davis H. T.
Published: December 2007

Phase behavior predictions of the Peng-Robinson (PR) equation and the Kleintjens-Koningsveld (KK) equation, a lattice-gas model, are compared for pure CO2, water, methane, n-butane, n-octane, n-decane, and several binary and ternary mixtures of these components. The KK equation is more accurate than the PR equation for predicting the saturated liquid densities of pure fluids. The two equations are comparable in predictions of binary pressure/composition phase diagrams and ternary-composition phase diagrams. Thus for these properties, the PR equation is preferred because it is a simpler equation, has fewer adjustable parameters, and has parameters available for more systems than the KK equation.
Eight-Well Interference Test in the Anschutz Ranch East Field
Authors: Pollock C. B. , Curtis Bennett
Published: December 2007

In many new fields, it is necessary to plan for secondary recovery methods before the field is fully developed or extensive reservoir data have been obtained. Shortly after discovery of the Anschutz Ranch East field, the working-interest owners recognized that planning for an improved recovery program should begin as soon as possible. Knowledge regarding the degree of communication in the reservoir, the magnitude of any directional permeability trend, and the interwell reservoir properties would be needed to select a suitable reservoir management method. A large-scale interference test was chosen as a way to provide part of this information during the early stages of development.

This paper describes how the test was planned and executed and includes some of the problems that were encountered during the test performance and interpretation. The results obtained from the test confirmed the geological interpretation of a directional formation flow capacity and indicated that the Nugget formation is at least partially anisotropic.
Estimation of Formation Pressures From Electrical Surveys-Offshore Louisiana
Authors: Foster J.B.
Published: December 2007

Discussion

Background Theory

Origin of Abnormal PressuresThe origin of abnormal pressures has been discussed by numerous researchers and several theories, well summarized by Watts in 1948, have been advanced to explain such pressures. The generally accepted theory explaining the occurrence of abnormally high pressures in the offshore area is paraphrased below. Consider a layer of sediments deposited at the bottom of the sea in a fluid environment. As more and more sediments are added above this layer, the grains of the sediments will pack closer together and accept the added weight of the overburden. Some of the water within the pore spaces will be squeezed out by the compaction. Since the water is continuous with (or in communication with) the water in the sediments and sea above, the pressure with-in the water is hydrostatic. As long as this process continues through geologic time so that water in the pore spaces is free to move out with the addition of overburden weight, the pressure of the fluid in the pores will remain hydrostatic or normal. As reported by Cannon and Craze in 1938, the normal pressure gradient in the Gulf Coast region approximates 0.465 psi/ ft, or the weight of a column of water with 80,000 ppm salt.

JPT

P. 165ˆ
Low-Temperature-Oxidation Kinetic Parameters for In-Situ Combustion: Numerical Simulation
Authors: Adegbesan K. O. , Donnelly J. K. , Moore R. G. , Bennien D. W.
Published: December 2007

The principal objective of this study was to provide low-temperature-oxidation (LTO) reaction models that are suitable for use in numerical simulators of in-situ combustion for bitumen and heavy-oil reservoirs. A systematic study investigated the LTO reactions of the liquid-phase components of bitumen and heavy oils. Athabasca bitumen, free of water and minerals, was oxidized by use of a laboratory-stirred semiflow batch reactor. Kinetic studies were carried out in the 333 to 423 K [140 to 300°F] temperature range and at an oxygen partial pressure of 50 to 2233 kPa [7.3 to 324 psi]. The total pressures applied in the reactor ranged from 2190 to 4415 kPa [318 to 640 psi]. Experimental data were collected in the kinetic subregime. Reactor product gas was analyzed with a gas Chromatograph, and the liquid-phase oxidation product was separated into six main components (lumped or pseudocomponents): saturates, aromatics, Resins 1, Resins 2, asphaltenes, and coke (SARA).

Kinetic models are established for the liquid-phase LTO reactions. The models involve further lumping of the pseudocomponents. Saturates and aromatics are lumped to form the maltenes, Resins 1 and 2 to form the resins, and asphaltenes and coke to form asphaltenes/coke components.

On the basis of experimental kinetic data, two main types of reaction models are proposed: (1) a non-steady-state kinetic model representing the overall rate of oxygen consumption and (2) four non-steady-state multiresponse kinetic models representing the oxidation reactions of the liquid-phase components. Proposed models were found statistically adequate and suitable for use in numerical simulators.
Petroleum's Place in the Future Energy Requirements of the United States
Authors: Phelps Thomas W.
Published: December 2007

Introduction

Although we expect the total energy requirements to rise from an equivalent of 20.0 million BOPD in 1957 to 28.5 million BOPD in 1968, we predict oil's actual contribution to decline from 44 per cent in 1957 to 43 per cent by 1968. Obviously, this is an important assumption to which everyone will not agree. This prediction is shown in Fig. 1, which also shows actual United States consumption in 1957, 1948 and 1928. The year 1957 was selected as a benchmark because the recession in 1958 will distort comparisons based on that year. Viewing oil and gas as a whole, we expect our industry's share of the energy market to increase at least up to 1968. To see why, let's turn to natural gas, the tail that is increasingly wagging the petroleum dog. In Fig. 1 the figure beside the natural gas segment and the oil segment of each bar represents the consumption for that year. For natural gas this is shown in millions of barrels a day oil equivalent, computed on the basis that 5,500 cu ft of gas equals 1 bbl of oil.

Analysis of Energy Sources Competitive to Petroleum

Now let's look at the contribution of coal, hydroelectric power, and, in 1968, atomic energy. As can be seen it is estimated that coal's share of the total market will decline to 24 per cent by 1968 from 27 per cent in 1957 and 67 per cent in 1928, but we believe the decline in tonnage of coal consumed each year is ending. We estimate consumption of coal in 1968 at the equivalent of 6.9 million BOPD compared with 5.5 million BOPD in 1957 and 7.1 million BOPD in 1928. The last small strip in Fig. 1 at the top of the 1928, 1948 and 1957 bars represents hydroelectric power. This hydro segment at the top of the 1968 bar is capped by a thin strip representing our estimate of U. S. consumption of nuclear energy in that year. Awed as we are by the longer-range potentialities of atomic power, we estimate its contribution to our 1968 total energy picture to be 10 million kw, the equivalent of a mere 300,000 BOPD.
Displacement of Viscous Oil From Consolidated Cores by Caustic at Temperatures Above 257°F
Authors: Medizade Mason M. , Handy Lyman L.
Published: December 2007

Laboratory data were obtained to investigate the use of alkaline material with or without a small amount of surfactant as an additive to steam to enhance oil recovery from that portion of a reservoir subjected to a hot waterflood in a conventional steamflood. A series of hot alkaline floods (some containing surfactant) was performed on fired cores previously subjected to a hot waterflood in an isothermal flooding apparatus with temperatures as high as 356°F [180°C]. Floods with no previous waterflood were also tested. In addition to temperature, salt content of the injected solution, tertiary flood rate, pH of the injected solution, oil saturation, and surfactant concentration were investigated with respect to their effects on recovery mechanism and efficiency, alkaline consumption, and surfactant loss.

Results show that tertiary recovery increases with increasing temperature, increasing flood rate, increasing salt concentration in the injected caustic, and the addition of surfactant. The ultimate recoveries for the floods with no previous waterflood are comparable to those for the tertiary floods. Alkaline consumption in the presence of oil is less than that reported in the absence of oil, but still increases with increasing temperature and with decreasing flood rate. Results also show that oil is recovered with the chemical additive and that no significant oil bank is formed ahead of the chemical.
Litho-Density Tool Calibration
Authors: Ellis D. , Flaum C. , Marienbach E. , Roulet C. , Seeman B.
Published: December 2007

A second-generation density logging tool has been developed that uses a gamma-ray source and two Nal scintillator detectors for borehole measurement of electron density, pe, and a quantity Fpe that is related to the lithology of the formation. An active stabilization system controls the gains of the two detectors, which permits selective gamma-ray detection. Spectral analysis is performed in the near detector (two energy windows) and in the detector farther away from the source (three energy windows). This paper describes the results of laboratory measurements undertaken to define the basic tool response. The tool is shown to provide reliable measurements of formation density and lithology under a variety of environmental conditions.
Thermal Effects of Reinjection in Geothermal Reservoirs With Major Vertical Fractures
Authors: Pruess K. , Bodvarsson G.S.
Published: December 2007

Introduction

Reinjection of spent geothermal brines is the most attractive method for their disposal. Field experience and theoretical work have shown that properly designed injection systems can avoid premature thermal interference at production wells and may serve additional purposes, such as maintenance of reservoir pressures and enhancement of ultimate energy recovery. There has been some controversy in the literature regarding benefits and drawbacks of reinjection. At the present time it seems clear that the issues are largely site-specific, and that reservoir response to reinjection is strongly dependent on formation properties and the thermodynamic state of the reservoir fluids. Whether or not reinjection at a given site is deemed desirable from the standpoint of reservoir management, it appears that for environmental reasons most future geothermal projects will require full reinjection as a method of waste disposal. There is a need for methods of designing and testing reinjection systems to avoid premature breakthrough of colder fluids at the production wells. production wells. An advisory panel convened by the U.S. DOE identified the development of techniques for monitoring, prediction, and control of the migration of injected prediction, and control of the migration of injected waters as an urgent priority. Depending on the geological characteristics of a geothermal reservoir, this can be a rather difficult task. For reservoirs approaching the idealization of a porous medium of uniform thickness, porosity, and permeability, analytical solutions are available for estimating the migration of thermal (cold) fronts away from injection wells. However, most high-temperature geothermal reservoirs are situated in fractured volcanic rocks. There is plenty of field evidence showing that in fractured reservoirs injected water can migrate rather rapidly to production wells. The possibility of rapid thermal breakthrough along preferential pathways is of obvious concern to field developers.

In the next section we review some field evidence for fast paths, and discuss possibilities and limitations for determining the thermal characteristics of fast paths by nonthermal means. We present idealized models of fast paths, and examine their applicability to field situations. paths, and examine their applicability to field situations. It is emphasized that tracer tests and pressure transient tests can provide only incomplete and ambiguous information on the thermal characteristics of fast paths. More reliable predictions of thermal interference are possible from nonisothermal injection tests. Numerical simulations incorporating approximate analytical solutions then are used to examine thermal breakthrough and recovery in vertical fractures.

JPT

p. 1567
Effect of Temperature on Oil/Water Relative Permeabilities of Unconsolidated and Consolidated Sands
Authors: Miller Mark A. , Ramey H. J.
Published: December 2007

Over the past 20 years, a number of studies have reported temperature effects on two-phase relative permeabilities in porous media. Some of the reported results, however, have been contradictory. Also, observed effects have not been explained in terms of fundamental properties known to govern two-phase flow. The purpose of this study was to attempt to isolate the fundamental properties affecting two-phase relative permeabilities at elevated temperatures.

Laboratory dynamic-displacement relative permeability measurements were made on unconsolidated and consolidated sand cores with water and a refined white mineral oil. Experiments were run on 2-in. [5.1-cm] -diameter, 20-in. [52.-cm] -long cores from room temperature to 300°F [149°C].

Unlike previous researchers, we observed essentially no changes with temperature in either residual saturations or relative permeability relationships. We concluded that previous results may have been affected by viscous instabilities, capillary end effects, and/or difficulties in maintaining material balances.
Prediction of Approximate Time of Interference Between Adjacent Wells
Authors: Stevens William F. , Thodos George
Published: December 2007

The point-source function introduced by Horner as a solution to the general unsteady-state equation for the flow of fluids through porous media has been utilized to calculate pressure profiles for adjacent wells as a function of time. By trial and error, the time at which the pressure waves meet to cause interference can then be calculated. For this calculation, the time of interference is arbitrarily defined as that time when both pressure waves exhibit a pressure decrease of 25 psi at the same point within the formation. To illustrate the method, an example involving two adjacent wells producing at different rates has been worked out and is presented in detail.

Introduction

The initiation of production of a new well is usually accompanied by pressure drawdown measurements in order to establish the extent and characteristics of the formation. The interpretation of such pressure drawdown data is based on mathematical developments involving a single well in an infinite reservoir. If more than one well is present in a reservoir, the possibility of interaction between wells exists. Therefore, care must be taken in interpreting the pressure drawdown data. It becomes important to be able to determine when this interaction, or interference, becomes significant. This paper presents a method for the prediction of the approximate time of interference between two such adjacent wells. The basic differential equation describing the pressure distribution existing during unsteady-state flow of a slightly compressible fluid has been solved by Horner, for a constant production rate from a circular homogeneous reservoir of infinite extent. The solution utilizes the point-source function to define the pressure at various points within the formation as a function of time.
Cation Exchange in Porous Media With Broad-Equivalent-Weight Sulfonate Micellar Fluids
Authors: Chan A. F. , Kremesec V. J.
Published: December 2007

This paper describes experimental and theoretical studies of cation exchange in porous media with micellar fluids formulated using a broad-equivalent-weight (BEW) sulfonate. The sulfonates can be described as composed of two pseudocomponents—a quasi-monosulfonate (the oil-moving component) and a quasi-disulfonate (the sul-fonate-solubilizing component). With this description and a mass-action model for cation exchange between the micelles, clays, and solution, a match between computer model predictions and results of laboratory single-phase flow tests in Berea sandstone was carried out. The assumptions required are reviewed and independent experimental results presented. With these assumptions and parameter values determined from the Berea history match, satisfactory predictions of divalent cation concentrations in field core experiments have been made. The good predictive capability of this model allows initial screening and development of micellar formulations for specific reservoir applications to be conducted at appropriate hardness levels.
Design and Construction of a High-Volume Flow Gas Metering Facility
Authors: Messmer J.H. , Jones E.H.
Published: December 2007

Introduction

The need for a high volumetric rate natural gas proving facility has become more evident recently. The value of natural gas transferred has risen dramatically, and the inadequacies of the standard means of measurement have become more apparent.

Natural gas use, material, and energy balances also require more precise calibration of flowmeters. A meter proving loop facility was therefore built, and a critical flow nozzle proving capability was installed to prove meters to 40 MMSCF/D (1.1327 × 10(6) m3/D).

A description of the system and some results obtained with orifice meters and other commercial meters are shown.

SYSTEM LOCATION AND CONSTRUCTION

A proving facility must necessarily have an adequate volumetric through-put and adequate pressure to operate the critical flow nozzles.

The site chosen was the Sand Hills Plant, South and West of Odessa, Texas, operated by Warren Petroleum Company (a wholly owned subsidiary of Gulf Oil Corp.). The line chosen for flow-verification was a residue gas product line delivering a nominal 40 MMSCF/D (1.1327 × 10(6) m3/D). A criterion that had to be satisfied was that the test system will not interrupt the normal delivery of product when in use.

A simple schematic is shown in Figure 1. Though the system is folded for construction ease it is noted that it is basically a parallel loop to an existing flow system in which valves are used to transfer the added flow piping to a series connection. Additionally, since Valve 1 can be used for piping to a series connection. Additionally, since Valve 1 can be used for flow control, flow may be partially diverted to divide the flow between the two parallel loops without limiting the flow when operating the loop with critical flow nozzles for meter proving.

CRITICAL FLOW NOZZLES

Six critical flow nozzles conforming to ISO specifications (Ref. 1) for shape were purchased from Flow Measurement Systems, Longmont, CO, and calibrated for discharge coefficient by Colorado Engineering Experiment Station, Inc., Nunn, CO over the pressure and Reynold's number (Re) range of interest: 400–1000 psig (2.76–6.89 MPa) and 4 to 15 × 10(6) Re.

Some properties of the nozzles are shown in Table 1.

Table 1

Nozzle Specifications

MeanCD = A+BRe(-1/2)Re × 10–6

No. Throat D, in (mm) A B1 .4383 (11.133) .989205 -3.215 6.585

2 .6495 (16.497) .991425 -4.7 10.24

3 .851 (21.615) .994279 -3.44 13.61

4 1.0621 (26.977) .994142 1.94 17.20

5 1.180 (29.972) .993791 -7.67 19.38

6 1.4390 (36.550) .991394 6.6 22.65

CD = Discharge Coefficient Re = Reynolds No All calibrations certified traceable to NBS.
Slim Hole Drilling Decreases Carter's Development Costs
Authors: Flatt H.J.
Published: December 2007

Rising development costs are recognized as one of the major problems facing the oil industry today. To combat this situation, several new concepts designed to improve drilling techniques have been advanced within recent years. Among the ideas proving most effective is slim hole drilling.

Carter's slim hole experience has been in both exploration and pool development wells. In addition, slim hole practices have been successfully applied to water injection wells. In comparison with standard operations, both penetration rate and bit life decreased using slim hole methods. No difficulty was encountered in coring, logging and testing in reduced diameter holes. Actual slim hole costs indicated a significant economic advantage over conventional practices. Savings in dry hole costs ranged up to 25 per cent, primarily from reductions in footage and day work rates. Additional savings accrued in producing wells from economy in tubular goods. Slim hole methods may not always be applicable, as consideration should be given to specific drilling problems and objectives. In many cases, however, slim hole drilling provides significant economic advantages over conventional practices.

Introduction

Increasing development costs are widely recognized as one of the major problems facing the oil industry today. Inflationary effects are firmly evident in all of the principal components of drilling costs, including labor, transportation, steel products and chemicals. Furthermore, deeper drilling is necessitated to offset depletion of shallow reserves. During recent years the concept of slim hole drilling has been experimentally applied within industry to evaluate its significance as a cost reduction measure. In most cases, slim hole results are reported to be proving effective. The purpose of this discussion is to review experience of The Carter Oil Co. in drilling 108 slim holes which have resulted in estimated savings of $162,000 below the cost which would have been incurred with conventional sized holes.
Progress Report of LPG Injection in the Meadow Creek Unit, Lakota B Reservoir
Authors: Harbert L.L. , Reed P.W. , Bray R.K. , Dew J.N.
Published: December 2007

Results of a field test of oil displacement by liquid propane and butane are presented. Since March, 1956, an LPG miscible flood project has been in operation in the Lakota B reservoir, a small reservoir of nine wells located in the Sussex area, Johnson County, Wyo. The Lakota in this reservoir consists of two zones separated by a shale break of 10 to 12 ft. Injection has been into the upper zone only. The average producing depth is 7,350 ft and as of July, 1958, the average bottom-hole pressure at datum (–2,120 ft) was 589 psig. Data on GOR, injected volumes and individual well performance are discussed. During the 28-month period the flood was in operation, 275,000 bbl of propane and butane were injected into two wells, and 72,000 bbl of oil were recovered over normal decline. The reservoir was shut-in July, 1958, to build up pressure to obtain miscibility between LPG and gas.

Introduction

LPG injection has been carried out in the Meadow Creek Unit, Lakota B upper zone since March, 1956. From March 29, 1956, to July 15, 1958, 275,000 bbl of LPG were injected into the reservoir to recover approximately 72,000 bbl of secondary oil. The purpose was to initiate a field test of miscible displacement, a process which promises to increase oil recovery beyond that obtainable by conventional methods of water flooding and gas injection. The basic process involves the injection of LPG followed by the injection of a gas. A preferred method of operation maintains the pressure in the reservoir above that required for miscibility between the LPG and gas. Operations at a lower pressure, where the oil and LPG are still miscible but the LPG and gas are not, are also possible; however, recoveries comparable to the completely miscible operation require the injection of larger quantities of LPG and gas. In either case, essentially 100 per cent of the oil in place can be recovered in that portion of the reservoir swept by the LPG, although the high pressure operation more efficiently utilizes the relatively expensive LPG.
A Mathematical Model for the Solvent Leaching of Tar Sand
Authors: Oguztoreli M. , Ali S. M. Farouq
Published: December 2007

Solvent flooding is the basis for a wide range of EOR methods and has been shown to be a possible method of creating initial steam injectivity in tar sands. This paper presents a unique model of the dissolution of a semisolid bitumen, resulting from the injection of a solvent. The solution of the mathematical equations describing this phenomenon is discussed. Results, including a series of two-dimensional (2D) problems, are presented. Numerical aspects are addressed.

The mathematical treatment is based on a pore model that contains bitumen particles dissolving in an interstitial solution. Macroscopic transport mechanisms, based on the microscopic phenomenon, trace the course of diffusing species in a dynamically interactive solid/liquid network. The bitumen particles are given a spherical symmetry such that a radial dissolution integro-differential equation accounts for the volume changes from solvent transfer into an initially immobile bitumen.

An overall numerical approach to the nonlinear system of equations determines the state vector of pressure, saturation, and concentration of the leaching solution. We show that three dimensionless groups control the bitumen-leaching process. The Damköhler and solvent capacity numbers govern the dissolution process, while the Peclet number governs miscible displacement.
A New Pseudosteady-State Model for Dual-Porosity/Dual-Permeability Aquifers and Two Interconnected Single-Porosity Aquifers
Authors: Leung Woon F.
Published: December 2007

A new pseudosteady-state (PSS) aquifer model for simulation of the interaction of reservoirs with finite-extent aquifers in dual-porosity/dual-permeability formations has been developed. The fast convolution method,1 which does not require lengthy data manipulation as with the superposition method, is used to implement the analytical solution of the model for time-dependent reservoir/aquifer boundary pressure. The model does not require a table lookup of the rate or pressure function; thus it is computationally efficient and lends itself readily to hand calculations or numerical reservoir simulations. A numerical example on water influx from a naturally fractured aquifer is used to show the utility of the model. The example shows the correct behavior of fractured aquifers quantitatively. The model is also applicable to a system of two interconnected single-porosity aquifers. An example demonstrates that the complex behavior associated with an interconnected aquifer system can be studied with the current model.
Quantitative Evaluation of the Density Log in the Rocky Mountain Area
Authors: Edwards J.M.
Published: December 2007

The neutron log has been accepted as a standard means of porosity determination for a number of years. The presence of clay or silt in sandstone or carbonate reservoirs has an adverse effect on the quantitative use of the present neutron log. A system responsive to the physical properties of the formation and not to its chemical properties overcomes this limitation. A properly collimated logging tool will accurately measure bulk density of a formation. The intensity of gamma rays (from the source) that have undergone Compton scattering in the formation can be recorded and related to the density of the particular medium.

Grain densities of major minerals are known. Fluid density can be considered unity unless gas is the saturating medium. Bulk density from the density log completes the solution of the equation and provides the formation porosity. Success has been obtained with the density log in the Paradox, San Juan and Green River basins of the Rocky Mountain area.

Introduction

Porosity determination in Cretaceous and Paleozic sand sections of the Rocky Mountain area, as well as Paleozoic carbonate sections of the Paradox basin, has with conventional logging methods been difficult. The radioactive density log has been utilized in a number of wells in the Paradox, San Juan and Green River basins and has given extremely accurate results in a large majority of cases.

Since experience is always necessary in order to properly evaluate any new logging device, an attempt has been made to run the radioactive density log through sections representative of typical conditions throughout the area with as many varying conditions of lithology, borehole conditions and drilling methods as possible. This paper dwells predominantly on results obtained in the Paradox zone of Pennsylvanian age in southwestern Utah, the Mesa Verde formation of the San Juan basin and the Frontier sands and Dakota sandstones of the Green River basin of southwestern Wyoming.
EOR With Penn State Surfactants
Authors: Art T. G. , LaBelle G. , Klaus E. E. , Duda J. L. , Nagarajan R. , Biterge M. B. , Ertekin T.
Published: December 2007

Petroleum sulfonate surfactants were synthesized from C19, C22, and C26 feedstocks and evaluated in core tests for their ability to enhance oil recovery. All three feedstocks are composed predominantly of saturated paraffinic and naphthenic hydrocarbons. The C19 feedstock includes about 12% aromatics. The hydrocarbons were vapor-phase oxidized at low temperatures to provide cyclic ethers, which subsequently were sulfonated to form a product mixture of mono-, di-, and trisulfonates.

Corefloods were conducted with both sulfonates developed at Pennsylvania State U. and commercial sulfonates in Berea sandstone cores. Production performances have been related to recovery and interfacial activity of the sulfonates. The core tests show that the optimum use of Penn State sulfonates for oil recovery is in the form of dilute slugs. High oil recovery efficiencies are realized when the Penn State sulfonates are used without cosurfactants to form dilute chemical slugs. Specifically, the enhanced oil recoveries obtained with C22 sulfonates are significantly larger than those obtained with the C19 and C26 sulfonates. This is consistent with the oil/water interfacial tension (IFT) and phase behavior of the three types of sulfonates. Furthermore, EOR results and core-effluent analysis studies indicate that sodium carbonate (Na2CO3) in low concentrations is an effective sacrificial agent for Penn State sulfonates.
Paraffin Control in the Northern Michigan Niagaran Reef Trend
Authors: Newberry M. E. , Addison G. E. , Barker K. M.
Published: December 2007

Wax deposition on downhole equipment and in chokes, flowlines, separators, dehydration and storage equipment is a costly problem in the northern Michigan area called the Niagaran Reef trend. A number of mechanical removal techniques have been used to treat for paraffin. Among these are paraffin cutters, plunger lift, rod scrapers, hot oil or water, plastic coatings, and flowline pigging. Improvements in chemical formulation, testing, and applications have resulted in a number of economically successful chemical programs for paraffin control. Examples of field problems and solutions are presented.
A New Look at Gravel-Pack Carrier Fluid
Authors: Scheuerman R. F.
Published: December 2007

For gravel-pack carrier fluids, less viscosity is needed downhole than for suspending and pumping high gravel loadings on the surface. To achieve this dual viscosity, breakers are added to degrade the viscosifying polymers. Unfortunately, viscosity breakback criteria are not well-defined. In addition to the type and concentration of breaker and temperature, the apparent viscosity breakback time of a polymer solution also depends on the shear rate at which the viscosity is measured. As a result, industry breakback data generally disagree because of the variety of instruments and shear rates used to measure viscosity.

This paper discusses new viscosity breakback criteria for polymer-viscosified gravel-packing carrier fluids that are based on gravel settling. Because settled, noncompacted gravel remains fluid, the time required for gravel compaction to begin is a useful criterion for maximum slurry placement time. Similarly, the time for the entire settled gravel column to become compacted is useful as a minimum shut-in time to ensure a stable pack. These criteria correlate well with fluid performance and apply to slurries with different initial viscosities (including crosslinked gels), brine densities, and gravel sizes. These times also can be correlated with low-shear-rate (0.03 second−1) Brookfield carrier-fluid viscosities when it is more convenient to take viscosity rather than gravel-settling data. Data useful for formulating gravel-pack carrier fluids are also presented.

Although this paper does not define optimum downhole carrier-fluid properties, the new criteria reflect downhole conditions better than most previous criteria. They should give better correlation with model studies and field experience and, in turn, should lead to a better understanding of the requirements for optimum downhole performance.
Economic Evaluations
Authors: Watkins P.B.
Published: December 2007

Formulas are developed and presented graphically which permit the rapid evaluation of projects, with the minimum of data and calculation. Methods for more detailed appraisals are discussed with particular reference to the Canadian income taxes, but U.S. taxes are also treated. "Rate of return", or "profitability index", is related to payout times and "profit ratio" for 100 per cent working interest cases.

Introduction

Many arguments can be put forth both for and against the inclusion of a tax factor in economic analyses. No attempt is made in this paper to resolve this particular controversy, other than to suggest that the payment of income taxes is inevitable, sooner or later, and in one form or another, for any company that is to survive beyond an initial expansion stage.

In the first part of this paper, the formulas and arguments are developed both for those who (for policy or other reasons) ignore income taxes, as well as for those who face the prospect of reaching a taxable position in the near future. For the latter cases, it is assumed that the project under consideration is subject to various income tax rates from zero upwards. This, of course, can lead to a conservative estimate, and further, it allows a consistent series of analyses to be made in line with any given tax policy which will be directly comparable as to profitability.
N2 and CO2 in the Oil Field: Stimulation and Completion Applications
Authors: Ward Victor L.
Published: December 2007

The use of both N2 and CO2 in oilfield stimulation treatments dates back more than 20 years.1 Early use was limited, but the past few years have brought about an increase in the use of both, as well as new, unconventional applications of these products.
Simulation of Compositional Processes: The Use of Pseudocomponents in Equation-of-State Calculations
Authors: Schlijper A. G.
Published: December 2007

A new method is presented for performing equation-of-state (EOS) calculations with pseudocomponents that are obtained by lumping pure components of a multicomponent reservoir fluid description. The method recognizes that a pseudocomponent represents a mixture of components and thus has the thermodynamic behavior of a mixture, rather than that of a single component. The standard expression for the chemical potential is replaced by an adapted pseudopotential. The method also yields convenient procedures for obtaining phase densities and viscosities.

The accuracy of the method is demonstrated by comparing phase splits, lumped mole fractions in liquid and vapor phases, and phase densities and phase viscosities obtained from a lumped fluid description with the same data as those obtained from a fully compositional description of hydrocarbon systems. Generally, deviations are not more than a few percent. The method enables the use of a reduced compositional fluid representation in numerical simulation studies without any essential loss in modeling accuracy.
An Experimental Study of the In-Situ Gelation of Chromium(+ 3)/Polyacrylamide Polymer in Porous Media
Authors: Huang Chyi-Gang , Green Don W. , Willhite G. Paul
Published: December 2007

Gelled polymers are being used increasingly as reservoir flow control agents to improve the water-to-oil ratio (WOR) in waterflooding. To date, little has been published in the literature on the in-situ gelation of polymers in porous media. This work was undertaken to study the process of in-situ gelation of a gel system consisting of a polyacrylamide polymer, sodium dichromate, and thiourea. The experiments consisted of continuous injection of gel solutions into 1-ft [0.3-m] unconsolidated sandpacks. Pressure distributions along the flow direction were used to interpret the nature of gelation in the porous media. We found that gelation occurred much earlier than anticipated from beaker tests where gel solutions were under conditions of no shear-e.g., a gel solution with a nominal 10-day gel time in a beaker gelled in 85 hours in a porous-medium run. Shear was considered one of the major factors affecting the in-situ gelation rate, and we determined that gelation times decreased with increasing in-situ shear rates. Under the same in-situ shear rate, the in-situ gelation times were approximately equal in sandpacks prepared from different grain sizes. The order in which in-situ gelation occurred along the flow direction indicated that the shear history affected gelation time. Effluents from displacements with gel solutions were analyzed to evaluate die change in the properties of a gel solution as it moved through the porous media. The chemical analysis indicated that the retention of polymer was marked after the in-situ gelation developed.
Rock Dissolution and Consumption Phenomena in an Alkaline Recovery System
Authors: Krumrine Paul H. , Falcone James S.
Published: December 2007

Consumption of alkali in the reservoir (loss of pH value) is a major concern to engineers designing alkaline slugs for EOR. Although several attempts have been made to model and to quantify these effects, the complexity of silicate chemistry has been a major stumbling block in adequately and realistically describing the mechanisms.

The data and mechanisms presented in this paper indicate that recently proposed consumption models should be modified to incorporate lower limits on SiO2 solubility at high pH values. A simple pseudo-first-order kinetics model is presented that provides an easy method to estimate the decrease in pH value and buildup of silica vs. time for any reasonable reservoir conditions where alkaline chemicals are used. When these limits are properly applied, the past long-term trends in laboratory data can be better explained. The implications of these changes in the dissolution rate model for improved slug design are discussed.
The Role of Thermal Analysis Techniques in the ln-Situ Combustion Process
Authors: Jha Kamal N. , Verkoczy Bela
Published: December 2007

Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) studies were conducted on two Lloydminster region, Canada, heavy-oil cores, extracted oil, and mineral matter. Fig. 1 is a general schematic of the thermal process, such as evaporation, distillation, thermolysis, low-temperature oxidation (LTO), thermal cracking, combustion, coking, polymerization, and thermal alteration of mineral matter.

Four core samples and their extracted oils were examined for propensity of coke formation under helium atmosphere. A two- or three-fold increase in the fuel content was observed in the cores compared with the extracted oil. This indicates a selective and significant contribution of the minerals to the coke-forming mechanism. The data from DSC and TGA experiments were used to calculate enthalpy values and ignition temperatures. These data suggest that heat generated by LTO reactions is significant during in-situ combustion.

With the exception of Sand D, the thermal alteration of the mineral matter at 600 and 900°C [1,112 and 1,652°F] was significant. In Sands A and B, the percentage of fine particles, <2 μm, doubled at 600 and 900°C [1,112 and 1,652 °F] compared with that at 100°C [212 °F], Although kaolinite constituted between 15 and 75% of the fine particles in all cases, it was not detected in appreciable concentrations when the sand was heated at 600 or 900°C [1,112 or 1,652°F]. These results indicate that potential problems during oil production could arise from the migration of fine particles. The mineral-analysis data obtained from these core samples suggest that swelling of clays during wet combustion may not be sufficient to have a deleterious effect on air/water injectivity or oil production. The results from TGA/DSC experiments are complementary to those from combustion-tube tests and provide the kinetic, thermal, and mineralogical data required for numerical simulation, planning, and design of an in-situ combustion project.
Evaluation of the Wilmington Field Micellar/Polymer Project
Authors: Fanchi J. R. , Carroll H. B.
Published: December 2007

The Long Beach micellar/polymer pilot in the Wilmington field has been evaluated. Actual recovery efficiency is about two-thirds of coreflood and simulation model estimates. This relatively high recovery efficiency represents a technically successful flood. Oil recovery was less than optimal, however, because of problems associated with production from an unconsolidated formation and the presence of Desulfσvibrio bacteria.