bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Simulation Comparison of Five-Spot vs. Line Drive in Micellar/Polymer Flooding
Authors: Kazemi H. , MacMillan D. J.
Published: December 2007

The work presented in this paper was undertaken to study the effect of pattern configuration on oil recovery by the Maraflood™ oil-recovery process. The patterns studied are the five-spot and the 4× 1 line drive. These patterns are obtained by placing infill wells in an existing 10-acre (40 469-m2) waterflooded five-spot pattern to obtain the 2.5-acre (10 117-m2) patterns. The number of infill wells is the same for both the new five-spot and new line-drive configurations and is about three times the number of existing wells. Both patterns have been used successfully in field applications by Marathon before this study. For instance, a line-drive pattern was used in Project 119-R and a five-spot pattern was used in Project 219-R.

This work shows that the line drive produces more tertiary oil than the five-spot under otherwise identical reservoir conditions. Breakthrough times and oil rates for line-drive production wells are nearly the same. Meanwhile, five-spot production wells have vastly differing oil breakthrough times and oil rates. Both of the latter effects result from a nonuniform distribution of waterflood residual oil saturation in the field.

Our study also shows that if producing wells in each line-drive row are connected by a perfect vertical fracture and if the same is true of the injection wells, the line-drive efficiency will improve very little.
An Improved Blotter Model for Analog Studies
Authors: Fothergill C.A.
Published: December 2007

An improved blotter model is described which makes use of a plastic sheet as base for the blotter field and pins to represent the input wells. The model is simple to construct and adapt and is particularly useful for demonstration purposes. Operational details are given.

Introduction

The blotter model was first applied to the investigation of oilfield problems by Wyckoff, Botset and Muskat, primarily in order to demonstrate the flood patterns which could be expected from various arrangements of input and output wells in waterflooding projects. In recent years the model has been largely superseded for analog studies by the potentiometric and electric analog models which are more refined and versatile, since they can simulate the form, and, in certain cases, permeability variations which it is not possible to do with the blotter model. However, the latter is still used for analog studies where the reservoir can be represented as being uniform in thickness and permeability, and where a visual record of the flood advance is required. Ramey and Nabor, for example, have applied the model to the investigation of areal sweeps in oil recovery by in-situ combustion.

Because of its limitations, the blotter model can be used in general for only very simple arrangements of input and output wells, but within these limitations it has a definite advantage over all other types, in that it provides a picture of the advancing flood using the simplest and most easily constructed apparatus, by contrast with the gelatin model, for example, which requires more elaborate equipment. Moreover, the experiments can be quickly repeated and modified if necessary, whereas considerable time is required to prepare a gel field, compared with that required for the preparation of sheets of conducting blotting paper.

For these reasons the blotter model can be very useful for demonstration and teaching purposes, enabling the student to experiment for himself with different arrangements of input and output wells.
Evidence of Chromatographic Effect During Flow of Gases Through Oilfield Cores
Authors: Roper W.A. , Doscher Todd , Kobayashi Riki
Published: December 2007

Introduction

The chromatographic effect refers to the separation of constituents in a moving fluid phase which occurs when the phase is passed over a stationary phase, either solid or liquid, or large areal extent. In performing chemical analyses, the large surface contact area is provided in the case of gas-solid chromatography bypassing the gas over a porous solid and for gas-liquid chromatography bypassing the gas over a porous solid which has been coated with a nonvolatile liquid. The porous medium is usually placed in a cylindrical tube, although it may be a relatively flat sheet as in paper chromatography.

According to one theory, the separation results from the difference in time spent by various components in the stationary phase. A gaseous component which is completely insoluble in the stationary phase, or is not adsorbed on the solid, proceeds unimpeded through the column.

The versatility and power of the various types of chromatography for the analysis of complex mixtures are evident from their widespread use in performing chemical analyses and from the large number of symposia, books, and papers devoted to the subject in recent years. Associated developments are the application of chromatography to the determination of heats of solution, heats of adsorption, solubilities or K-values, etc.

Gas-liquid chromatography analyses may be characterized by the manner in which the samples are introduced and displaced from the column. The three techniques used are known as(1) frontal analysis, (2) displacement analysis, and (3) elution analysis. The frontal analysis is performed by displacing an inert gas from the column by a continuous stream of the sample.

As indicated in Fig. 1(A), all but the first fraction leaving the column represent mixtures rather than pure components. The displacement analysis is conducted by filling the column with a sample, then displacing it with a more strongly adsorbed or absorbed vapor. The resulting chromatogram is illustrated by Fig. 1(B). Finally, in the elution analysis a small sample of the mixture to be analyzed is introduced as a "plug" into a flowing stream of carrier gas to give an elution-type chromatogram, Fig. 1(C). The three techniques may be used to provide models to which flow patterns in other physical situations may be compared.
An In-Situ Combustion Process Simulator With a Moving-Front Representation
Authors: Hwang M. K. , Jines W. R. , Odeh A. S.
Published: December 2007

This paper describes THERMS, a new three-phase, black-oil simulator for in-situ combustion processes. The model also can simulate steam and hot-water injection operations. To simulate field-scale in-situ combustion projects, THERMS uses experimental data obtained from laboratory combustion-tube runs. Detailed kinetics and thermodynamic relations are not used. The model treats the burning zone as a moving front. The front is viewed not only as a moving heat source, but also as a displacement pump enhancing oil flow. This approach results in a new algorithm. The model has been designed with strongly field-oriented features. Its utility is illustrated by a history-matching study of the South Belridge, CA, dry-combustion pilot test.
Neutron-Induced Gamma Ray Spectroscopy for Reservoir Analysis
Authors: Westaway Peter , Hertzog Russel , Plasek Ronald E.
Published: December 2007

The weighted least-squares (WLS) approach to spectral analysis has enabled more information to be extracted from the downhole recorded induced gamma ray spectra than was previously possible. GST™ (gamma ray spectroscopy tool), with its optimized inelastic and capture spectral modes, permits analysis of most and often all significant elements present in the formation and provides the possibility of evaluating hydrocarbons, salinity, lithology, porosity, and shaliness.

Data have been obtained in a wide range of conditions in open and cased holes with the GST tool both in its present and experimental versions. This paper presents field examples to demonstrate the versatility and potential of the technique, not only as an effective oil-finder independent of water salinity conditions but as a valuable input to a more complete interpretation of well logs.
Case Study of a Multiple Sand Waterflood, Hewitt Unit, OK
Authors: Ruble David B.
Published: December 2007

Synthetic two-component mixtures (uraninite and iron sulfide) as well as native uranium ores obtained from Texas and Wyoming have been examined. Physical/chemical ore properties are correlated with observed laboratory leach response. Data show a large inherent selectivity of oxidant for uranium in the early stages of a leach period. Uranium head grade was found to increase in a nearly linear fashion with hydrogen peroxide concentration in the leach solution. As uranium in the ore is depleted, uranium response decreases and the oxidant serves mainly to leach iron sulfide gangue material.

Introduction

Uranium historically has been mined by two methods, open pit (strip) or underground shaft mining. These two methods require high-grade uranium deposits to justify the large investment of personnel and material required to process the uranium into saleable form. New reserves of high-grade uranium ore are not being discovered in large quantities, indicating the need to locate new types of uranium deposits to fill future demands of the nuclear power industry. New sources of uranium exist in the form of low-grade ore deposits approximately 60 to 600 m below ground level. Recovery of some of these low-grade deposits became economically feasible when the price of uranium increased in the early 1970's. It is too costly, however, to mine these uranium deposits by conventional techniques (i.e., open pit or underground shaft), so a new mining method was developed. This new method is known as in-situ leaching or solution mining and involves selective leaching of the uranium from the ore deposit by use of a special solution injected into the ore body. Ore body composition and leach solution chemistry have a large effect on uranium recovery and are investigated in this study.

Chemistry

Uranium present in an ore body is generally in the reduced tetravalent (U+4) state and first must be oxidized to the more soluble hexavalent (U+6) state before it can be leached. Various oxidants are available, with hydrogen peroxide and molecular oxygen being the most widely used in commercial practice. Aside from uranium, an ore body contains other oxidant-consuming species such as pyritic iron sulfides and carbonaceous material (Table 1). Uranium leach chemistry can be described best by the following equations, with hydrogen peroxide (H2O2) as oxidant.

(1)

(2)

(3)

(4)

(5)

Eqs. 1 and 2 describe uranium oxidation and solubilization, respectively. Oxidant is added to a leach solution composed of either sodium or ammonium carbonate, and is injected into the ore body. Dissolved uranium is transported through the ore body to the recovery wells in the form of a uranyl carbonate complex. Eqs. 1 through 5 show that more oxidant can be consumed by oxidation of the iron sulfide and carbonaceous gangue materials than by uranium itself.

JPT

P. 937^
Acoustic Emissions as a Tool for Hydraulic Fracture Location: Experience at the Fenton Hill Hot Dry Rock Site
Authors: Albright James N. , Pearson Christopher F.
Published: December 2007

Microearthquakes with magnitudes between −6 and −2 have been observed in three successive massive injections of water at the hot dry rock geothermal energy development project's demonstration site at Fenton Hill, NM. The injections were part of a program to increase the heat transfer area of hydraulic fractures and to decrease the flow-through impedance between wells in the energy extraction system under construction. The microearthquakes were used in mapping the location of the extended hydraulic fractures.

The large shear- to compressional-wave-amplitude ratio observed in the signals suggests that the microearthquakes result from shear failure, probably on preexisting planes of weakness that intersect or make up the main hydraulic system. Failure resulting from increased pore pressure is a likely cause for the microearthquakes. Knowledge of the failure criterion for the reservoir rocks permits calculation of the pore pressure increases necessary for failure. At Fenton Hill, it appears that pressures 2 Pa (0.00029 psi) above hydrostatic are necessary. For this hypothesis of microearthquake occurrence to hold, the effective reservoir permeability must be four orders of magnitude above that for the bulk rock, as would be the case if there were permeable joints or fractures in the reservoir before hydraulic stimulation.
Non-Plugging Emulsions Useful as Completion and Well-Servicing Fluids
Authors: Priest G.G. , Allen T.O.
Published: December 2007

The development and use of nonplugging emulsions has provided a solution to certain problems associated with completing and reworking wells which have plagued the industry for years.

In the present work emulsions free of insoluble solids have been developed for use in wells with temperatures up to 250°F and with pressures requiring densities up to 12.5 lb/gal. They possess the required properties of a satisfactory fluid for completing and reworking wells; they are non-plugging, they exhibit a low fluid loss, and they have a controllable density.

Non-plugging emulsions have been used in approximately 200 completion and well-servicing operations. They were positioned to cover the interval to be perforated or to protect existing perforations during workover operations. Comparative data from several wells show that the productivity indices of wells perforated in the emulsions were substantially higher than the productivity indices of offset wells perforated in mud or water. Fewer difficulties in servicing wells and in getting wells back on production were experienced when emulsions were used as protective fluids to prevent water or mud from contacting exposed formations. In one field, the use of emulsions as perforating fluids has reduced the incidence of expensive sand control measures.

Precautions should be taken to avoid contamination of drilling muds and cements by the emulsions. Contamination can be avoided in most operations by following careful placement procedures.

Introduction

Research conducted during the past few years has demonstrated that perforations are often plugged by debris from the perforator, pulverized sand from the formation, and mud solids when drilling mud is in the casing at the time the perforations are made. This plugging of perforations causes numerous problems in the completing, producing, and repairing of wells. For example, low well productivity, sand production, premature gas or water production, and failure of squeeze-cementing jobs are but a few problems recognized as being aggravated by plugged perforations.
G-2 and G-3 Reservoirs, Delta South Field, Nigeria: Part 2 - Simulation of Water Injection
Authors: Thakur G.C. , Stanat P.L. , Aruna M. , Poston S.
Published: December 2007

To date, laboratory experiments to evaluate a fieldprospect for CO2 flooding have concentrated on determining minimum miscibility pressure. Other experiments include core floods and single- and multiple-contact phase behavior studies. This paper discusses relationshipsbetween the various experiments in the light of current understanding of the mechanisms operating in the CO2-flooding process. Objectives and limitations ofeach experiment are discussed. Limitations on the use of the resulting data to estimate recovery from field CO2 floods also are reviewed. A new experimental procedure is described that permits rapid determination of phasebehavior and fluid properties of CO2 /crude-oil mixtures at reservoir conditions. The experimental procedure, which involves continuous contacting of the reservoirfluid with CO2, can be used efficiently to obtainphase-behavior and fluid-property data that would require difficult and time-consuming experiments if obtained bypreviously available techniques.

Introduction

Although CO2 flooding has been investigated since theearly 1950's, consensus has not developed as to thelaboratory experiments required for the evaluation of a CO2-flooding prospect. Laboratory experimentsperformed most often, however, fall into three generalareas:slim-tube displacements,core displacements, andhigh-pressure volumetric (PVT)and vapor/liquid equilibrium (VLE) experiments.

Thethree types of experiments yield different information about a potential CO2 flood. This paper reviews brieflythe uses and limitations of the information obtained inthe various laboratory experiments.

Design of any large-scale CO2 flood inevitably involves the use of numerical reservoir simulators. Those applicable to CO2 flooding also fall into three general groups:miscible simulators,compositional simulators, andhybrid miscible/compositional simulators.

The type of data required to support a simulation effort depends (in part, at least) on the choice of the simulator. Miscible simulators based on the work of Todd and Longst afftreat CO2 as completely miscible with theoil, and require little more than the permeability, relative-permeability, capillary-pressure, viscosity, anddensity data common to black-oil simulators. Routine reservoir-fluid volumetric and fluid-property measurements, in addition to standard core characterizations (permeability, relative permeability, and capillary pressure), are adequateto support such simulations.

JPT

P. 888^
The Fry In Situ Combustion Test-Reservoir Characteristics
Authors: Hewitt C.H. , Morgan J.T.
Published: December 2007

The Fry cocurrent in situ combustion project was carried out in a 3.3-acre portion of a lenticular body of Robinson sandstone of Lower Pennsylvanian age. This particular sand body is about 12,000 ft long and 3,500 ft wide; it varies in thickness from 0 to 55 ft, trends northeast-south west, and occurs at depths between 880 and 936 ft. The reservoir is made up of three distinct types of sandstone, each having characteristic reservoir properties. (See Table 1.)Textural gradients, sedimentary structures, erosional basal contact, absence of marine fossils, and geometry of the sand body all indicate that the sandstone is of fluvial origin and part of an extensive complex of river-deposited sediments. Geographically oriented cores reveal that the direction of depositing currents was to the southwest, parallel with the sand-body trend. Directions of maximum permeability also parallel the northeast-southwest trend. The layered nature of the sandstone reservoir and its directional properties have controlled the areal distribution of produced gas, the ignition behavior, and the vertical profile and horizontal extent of the combustion zone.

Introduction

This paper is the first of a series of three papers that describe Marathon Oil Co.'s Fry in situ combustion test. This first paper contains the results of a detailed study of the geology and reservoir characteristics of the Robinson sandstone reservoir in which the Fry test was conducted. The second and third parts of this series report on the field operations and performance. The geologic work related to cores cut through the combustion zone, and to the effect of reservoir properties on the combustion process is included in the third paper.

GEOLOGIC STUDY OF THE FRY RESERVOIR

The close spacing of continuous cores in the Fry combustion site provided an unusual opportunity to study the details of distribution of lithology and reservoir properties within a petroleum reservoir. The objectives of the study were:1. To determine the distribution of rock types within the Robinson sandstone in the Fry area;2. To determine the relationship of porosity and permeability to rock properties and establish the distribution and homogeneity of reservoir properties;3. To determine the origin of the Robinson reservoirs so that attempts could be made to predict the size, shape, distribution, extent and continuity of Robinson reservoirs; and4. To determine what effects, if any, the reservoir rocks might have on the combustion process, so that the process might be better evaluated.

AVAILABLE MATERIALS

Continuous cores were cut from 14 wells in the vicinity of the Fry site. Ten of the cores are from within the 3.3-acre pattern; six of the 10 were cut prior to combustion, and four were cut through the combustion zone.

JPT

P. 337ˆ
The Fry In Situ Combustion Test-Field Operations
Authors: Clark G.A. , Jones R.G. , Kinney W.L. , Schilson R.E. , Surkalo H. , Wilson R.S.
Published: December 2007

This paper describes the field operations at the Fry in situ combustion project in Crawford County, Ill. Field operations may be divided into three phases preliminary engineering studies of 1960 and 1961, ignition, and, finally, operation of the test. The Fry combustion project was a pilot test of cocurrent in situ combustion on a 3.3-acre inverted five-spot. In the summer of 1960, air injection tests were conducted using old wells in the area and a new air injection well drilled especially for the test. In the summer of 1961, four new oil wells were drilled on a 3.3 acre pattern for the pilot test. All old wells in the near vicinity of the pilot test were abandoned to preclude any possibility of gas escaping to adjacent formations. A compressor plant was also installed at the test site in 1961. Air injection tests and other engineering studies were made. At the conclusion of these tests, ignition was accomplished with a 40 kw electrical igniter. Operation of the Fry combustion test was little different from the usual oilfield operation with the exception of the high rate of air injection. No difficulty was found with the openhole completion. There were no unusual corrosion or emulsion problems until bottom-hole temperatures exceeded 150F. Four cores were drilled into the burned-out portion of the reservoir with no mechanical difficulties.

Introduction

A cocurrent or conventional in situ combustion test was conducted on the Fry unit of the Marathon Oil Co., in Crawford County, Ill. Besides testing combustion in the Fry type of reservoir, the test was intended to evaluate various operating procedures. This paper presents a discussion of the Fry combustion test field operations. The geology of the reservoir and the test performance are discussed in other papers.

HISTORY OF THE FRY UNIT

The Fry unit consists of 11 leases totaling 337 acres in an area in which oil was originally discovered in 1906. Production from this reservoir, as from all Robinson sand reservoirs in the area, was very high during the first few years. As the dissolved-gas energy was dissipated, early attempts to retard the decline consisted of vacuum, air, and gas repressuring, and recently, most of the area has been subjected to water flooding. Following early air repressuring, the Fry waterflood unit was formed and water flooding initiated in July, 1952. In the area in which the Fry combustion test was conducted, a peripheral water flood of a 160-acre area was developed as shown in Fig. 1. Between 1956 and 1960, it became apparent that the water flood was unsuccessful. In looking for a suitable site for an in situ combustion test, the Marathon Oil Co. selected the Fry unit as possessing those features most desirable for such a research project. Field operations associated with the Fry combustion test began in the spring of 1960.

JPT

P. 343ˆ
Evaluation of Porosity Derivation from Neutron Logs
Authors: Widmyer R.H. , Wood G.M.
Published: December 2007

In order to evaluate the quantitative determination of porosity by various neutron logging systems, four test wells were constructed to simulate some of the possible variables found in field logging conditions. All of the test holes contain sections of limestone with one section of sandstone included in one well. Each well has a representative section of high, medium, and low porosity. Three borehole sizes are represented by three of the test wells, all containing fresh water. One test well contains saturated brine. Statistical and time constant checks are made for each system evaluated. Runs and repeat runs are made with the son de centered and eccentric. Factors evaluated are the effect of borehole size, sonde position, salinity, chemical composition of rock, and statistical variation. A semi-quantitative method of evaluation of these effects is used giving the average maximum per cent error possible for each. Drift and calibration procedures are also discussed. The effect of the various factors appears to be largely a function of the phenomena detected as well as the means of detection. Graphic illustrations of some of these effects are presented. It is concluded, that for accurate log interpretation, the hole size and sonde position should be known.

Introduction

The use of neutron logs for the derivation of porosity has become an accepted practice in many areas. In recent years, many different neutron logging systems have been offered to the industry. The neutron sources presently available are of the radium-beryllium or polonium-beryllium type. Detector types used are ionization chambers, Geiger-Mueller-type counters, proportional counters, or scintillation detectors used to detect or measure gamma rays, thermal neutrons, epithermal neutrons, fast neutrons or combinations of these. It is well-known that all systems do not respond alike in all environments. As a result, testing facilities and an evaluation method were developed for use in evaluating the porosity discriminating ability of neutron logging systems using conditions simulating those normally encountered in the field. With such an evaluation, the suitability of a logging system can be determined for selected field conditions.
A New System of Tools for Better Control and Interpretation Of Drill-Stem Tests
Authors: McAlister J.A. , Nutter B.P. , Lebourg M.
Published: December 2007

The Multi-Flow Evaluator (MFE) is a new system of tools providing an original approach in drill-stem testing. It improves control during the testing operation and gives a more accurate evaluation of the fluid recovered while providing additional pressure information for reservoir analysis. The tools are operated entirely by up and down motion of the drill stem. This up and down operation provides a positive means of control and offers easily observed surface indications of tool operating position. An unlimited number of shut-in and flow periods may be taken with this tool while in the hole. The key to the success of the MFE system of tools is the safety seal packer. Until this development, operation of the tools by up and down motion only had proven unreliable. The success ratio of the MFE now exceeds the ratio achieved by conventional tools. The equipment includes a 2,750-cc chamber in which a representative sample of the flowing formation fluid is trapped at the end of the last flow period and brought to the surface under pressure. The sample can be evaluated at the wellsite or transferred under pressure for laboratory analysis. The sampling feature of the tool allows a sample to be obtained from a reservoir which has suffered minimum influence from production. A representative sample can be obtained for laboratory or empirical analysis by employing a testing technique to minimize drawdown during flow periods. Interpretation methods to take advantage of this additional information are presented and supported by actual field examples.

Introduction

The Multi-Flow Evaluator (MFE) represents the most recent technical advance in formation testing. Drill-stem testing techniques prior to the MFE have been limited in three areas(1) operation, (2) recovery analysis, and (3) reservoir analysis. The tools in the MFE system allow maximum control during testing and provide test information superior to that obtainable with conventional tools. The system of tools and the operation procedures are described to illustrate the mechanical advantages over present tools.

JPT

P. 207ˆ
Sand Stresses Around a Wellbore
Authors: Risnes Rasmus , Bratli Rolf K. , Horsrud Per
Published: December 2007

We have studied theoretically the stresses in a poorly consolidated sand around a cylindrical well, assuming axial symmetry. Applying theories of elasticity and plasticity on this three-dimensional (3D) model, analytical solutions for all three stress components have been worked out.

The existence of a plastic zone around an uncased wellbore is confirmed, and the size of the zone is determined. When allowing an incompressible fluid to flow radially into the wellbore, a stability criterion describing the failure of the sand is found to exist. This criterion relates fluid flow forces to rock strength properties.

Consideration also has been given to the stress distribution around a cased hole. It is shown that a decrease in the size of the plastic zone relative to an uncased hole occurs.
Reliable Interpretation of Waterflood Production Data
Authors: Jordan J.K.
Published: December 2007

The most reliable method of interpreting the performance of secondary recovery water floods is through the use of the complete reservoir analysis. Although complete field data are not always readily available, the operator can usually make a quantitative interpretation of waterflood performance from information generally available on these projects. Water injection and oil and water production data, the time and location of water appearance, and the production behavior of individual wells can be utilized to obtain a positive measure of the sweep efficiency and oil recovery at any stage of depletion. The various methods of interpreting waterflood data have been examined to determine the degree to which these methods significantly describe waterflood performance.

Introduction

Expansion of secondary recovery waterflood operations in recent years has emphasized the need for thorough methods of evaluating the production behavior and performance of such projects. Through the use of sound engineering techniques, it is possible to determine the susceptibility of the reservoir formation to water flooding, to evaluate the efficiency of the project with respect to movement of flood water through the reservoir, and to predict the future oil recovery from the flood area. A continuing appraisal of the current and predicted behavior of the reservoir and of wells under flood can enable the operator to follow closely the progress of the flood throughout its operating life. In this manner, positive control of the water flood can be maintained and necessary steps can be taken to assure the success of the project.

Proper interpretation of behavior of secondary water floods depends upon a thorough understanding of the fundamental principles underlying the mechanism of the displacement of oil by water. Through controlled laboratory experiments and observation of the performance of many water-drive fields, produced both by primary and by secondary methods, knowledge has been obtained delineating the recovery process and the several factors that influence displacement of oil by water. In light of these studies, the engineer is able to apply this knowledge to interpretation of field waterflood performance and to obtain practical solutions of field operating problems.
Pore Volume Compressibilities of Sandstone Reservoir Rocks
Authors: Fatt I.
Published: December 2007

Pore volume compressibilities measured in tile laboratory on core samples are reported for typical reservoir sandstones at reservoir pressures. These compressibilities are different for each reservoir sample and cannot be correlated to porosity. The compressibilities are also functions of pressure.

Introduction

In recent years several authors have pointed out the importance of including pore volume compressibility of the reservoir rock in certain reservoir engineering calculations. Hall showed that in calculating the hydrocarbon volume of an undersaturated reservoir from the production per unit change in reservoir pressure, the neglect of rock compressibility could, in the extreme case of low porosity rock, lead to results in error by a factor of two. Hawkins and Hobson and Mrosovsky showed that both rock and interstitial water compressibilities must be included to achieve satisfactory accuracy in this calculation.

Although rock compressibility is an important reservoir property in these calculations, very few data are available. Hall made compressibility measurements on a few samples in a small pressure range. No other direct pore volume compressibility measurements have been reported. Geertsma discussed the elasticity of reservoir rock but did not present any new data. In this paper, rock compressibilities suitable for reservoir calculations are reported for a variety of sandstones typical of U.S. reservoirs. The measurements were made through a range of pressures which is also typical of reservoirs.

Experimental Procedure

Plugs 1 in. in diameter and 2- to 3-in. long were diamond drilled, 14 from cores from seven oil-bearing or potentially oil-bearing sandstone, one from a quarried sandstone, and another from a shallow, oil-free, pure orthoquartzite. The plugs were extracted in toluene, vacuum dried and then weighed. The plugs were then saturated with kerosene and reweighed. This gave pore volume. They were then again extracted in toluene, vacuum dried and jacketed in 0.004-in. thick copper foil. A short length of ¼-in high pressure tubing led from the jacket. The jacketed sample was then saturated with kerosene and placed in the hydraulic pressure cell as shown in Fig. 1. Movement of the mercury slug showed the change in pore volume of the sample under a given pressure change. Temperature was about 72° F for all measurements.
Comparison of Solutions to a Three-Dimensional Black-Oil Reservoir Simulation Problem (includes associated paper 9741 )
Authors: Odeh Aziz S.
Published: December 2007

A comparison of solutions to a three-dimensionalblack-oil reservoir simulation problem is presented.The test of the problem and a brief description of theseven simulators used in the study are given.

Introduction

Seven companies participated in a reservoirsimulation project to compare the results obtained bydifferent black-oil simulators. The companies werechosen to give a good cross section of the solutionmethods used in the industry. The participants wereAmoco Production Co., Computer Modelling Groupof Calgary (CMG), Exxon Production Research Co., Intercomp Resource Development and EngineeringInc., Mobil Research and Development Corp., ShellDevelopment Co., and Scientific Software Corp.(SSC). The paper presents the text of the problem, acomparison of results in graphical form, and a briefdescription of each model. The descriptions weresupplied by the participants.

A variety of computers was used. Amoco usedIBM 3033, IBM 370/168, and Amdahl V/6. CMGused Honeywell 6000 DPS, and Exxon used Amdahl470/V5 and IBM 370/168. Intercomp used Cray-1and Harris/7. Mobil and SSC used CDC Cyber 175, and Shell used Univac 1110/2C Level 36. Thenumber of time steps and the central processor timesvaried considerably. Those interested in the actualvalues should contact the individual companies.

Except for Shell, all the participants usedsingle-point upstream mobility weighting. Shell used twopoints upstream. Constraints and data are given inthe text.

Statement of the Problem

Areal and cross-section views of the reservoir aregiven in Figs. 1 and 2. The grid system is given in Fig.1. Stratification and reservoir properties are given inFig. 2. The reservoir is initially undersaturated. A gasinjection well is located at Grid Point (1, 1), and aproducing well is located at Grid Point (10, 10).Pertinent data and constraints are given in Table 1.PVT properties and relative permeabilities are given in Tables 2 and 3. The participants were asked tomake the runs and report the results described below.

Runs To Be Made

Case 1

Let the bubble-point (saturation) pressure beconstant with a value equal to the original value.

Case 2

Let the saturation pressure vary with gassaturation - i.e., this is a variable saturation-pressurecase. The PVT lines at pressures above the calculatedsaturation pressures are parallel to the original line.

Results To Be Reported

The following results are to be reported.1. Plots of:a. Oil rate vs. time.b. GOR vs. time.2. Report annually and at abandonment:a. The pressures of the cell where the injectorand producer are located.*b. Gas saturation at Grid Points (1, 1, 1), (1, 1,2), (1, 1, 3),(10, 1, 1), (10, 1, 2), (10, 1, 3), (10,10, 1), (10, 10, 2), and (10, 10, 3).3. Report at the end of 8 years:a. Tables of gas saturation.b. Tables of cell pressures. *c. Tables of saturation pressures for the variablesaturations-pressure case. *

JPT

P. 13^
Stability of Piston-Like Displacements of Water by Steam and Nitrogen in Porous Media
Authors: Krueger David A.
Published: December 2007

Downhole steam generation leads to consideration of reservoir fluid displacement by a mixture of steam and nitrogen. The linear stability analysis of the steam condensation front has been generalized to include a non-condensing gas. Roughly speaking, the addition of nitrogen increases the likelihood of having fingers, but, compared with the no-nitrogen case, the fingers will grow more slowly.
Bottom Furrows and Estimated Currents in the Mississippi Delta Region
Authors: Adams Charles E. , Prior David B. , Coleman James M.
Published: December 2007

A simple model of a neutrally buoyant, steady-state benthic boundary layer is used to examine the relationships between the dimensions of secondary roll vortices in the boundary layer and the spacing of a system of bottom furrows located offshore of the Mississippi Delta. The mean free-stream flow velocity predicted by the model, which creates the desired ratio between those two parameters, is an estimate of the free-stream current speed necessary for furrow erosion. In the absence of direct current measurements, such estimates are of value not only for offshore design but also for planning subsequent current measurement programs.
Numerical Simulation of Miscible and Immiscible Fluid Flows in Porous Media
Authors: Casulli V. , Greenspan D.
Published: December 2007

Fast, economical, and accurate finite-difference numerical methods are developed for approximating continuum models of both miscible and immiscible fluid flows in porous media. The methods apply to very general systems of equations and boundary configurations. Computer examples are described and discussed.
Simultaneous Drilling: A Radical New Method for Drilling Development Wells
Authors: Theriot Walter A.
Published: December 2007

Introduction

Recent reports from the Soviet Union indicate that a fair degree of success is being attained with simultaneous drilling in certain fields. Although there is not a great deal of information available about the process, it is possible to determine the basic principles and some of the mechanical details involved. While any radical change in drilling methods is viewed with skepticism, only a critical evaluation can determine if it is justified or if some part of it may be made to serve our purposes.

Simultaneous drilling is a method of drilling two directional wells alternately from a single rig and using a single drilling crew. While originally used with turbodrills, it lends itself to adaption so that it may be used with rotary drilling equipment. It is not intended for wildcat drilling, but will find its widest application in development drilling, particularly from offshore platforms.

In simultaneous drilling, the two wells are drilled from the same rig, alternating the drilling from one well to the other each time a "round trip" is made. Actually, no round trips are made with this method of drilling the drill stem coming out of one hole being run down the other hole without the necessity of stacking the pipe.

Rig Design

In order to accomplish this with maximum speed and still retain simplicity in the drilling rig, the following rig is proposed. The floor of the simultaneous drilling rig is somewhat larger than that of the conventional rotary rig in order to accommodate a second rotary table and provide working space around each rotary (see Figs. 1 and 2). A single crown and traveling block assembly is used, which is shifted on a geared track by a series reversible motor between predetermined positions over each rotary as required. Two different mud systems are used with a single set of mud pumps and a manifolding system to give individual control of mud conditions in each well. Fingerboards and other auxiliary equipment are provided so that either rotary may be used for conventional drilling should the need arise. Two sets of terminal equipment are required, and certain other adaptations must be made.
Dispersive Mixing Effects on the Sloss Field Micellar System
Authors: Gupta Surendra P.
Published: December 2007

This paper presents results of laboratory experiments and computer simulation studies of the micellar/polymer fluids injected in the Sloss field, NE. The paper shows that the dispersion coefficient for the partitioned sulfonate in the oil phase can be an order of magnitude larger than the dispersion coefficient in the water phase. The results show that the two principal components of the micellar fluid (sulfonate and polymer) propagate at different rates because of partitioning and dispersive mixing effects. Sulfonate is produced much earlier than polymer and is concentrated in the produced oil. Sulfonate partitions into the oil phase as a consequence of ion exchange, and the polymer remains in the water phase. The oil phase that contains the partitioned sulfonate—i.e., upper-phase microemulsion—has high mobility. The increased dispersion coefficient for a component in the nonwetting phase, in this case the partitioned sulfonate into the oil phase, is supported by an independent study. These mechanisms contribute to early sulfonate breakthrough and a larger sulfonate requirement per barrel of oil displaced than anticipated for a nondispersive displacement. The results of this paper can be beneficial for design of other micellar fluids and performance predictions and interpretation of micellar floods in other fields.
An Improved Technique for Estimating Permeability, Fracture Length, and Fracture Conductivity From Pressure-Buildup Tests in Low-Permeability Gas Wells
Authors: Holditch S.A. , Lee W.J. , Gist S.R.
Published: December 2007

Introduction

Long hydraulic fractures are usually required to optimize recovery from low-permeability gas reservoirs. Since these fractures can be quite expensive to create and since there is still a great deal of "art" associated with fracture design and creation, it is frequently helpful to use pressure-transient tests to determine created fracture properties. In this way, optimal fracture treatments can be developed for a given area. Fast et al. 1 and Kozik and Holditch presented examples showing the potential benefits of such an approach. In addition, Veatch demonstrated the effectiveness of combining the efforts of operations and research personnel to characterize and then to improve stimulation treatments in specific areas.

The specific task of the engineer is to estimate propped fracture length and effective fracture conductivity for treatments in a given geological formation, If the reasons for success or failure of previous fracture treatments can be determined, the engineer can then do a better job in the future when designing fracture treatments for the same area.

There are currently four basic techniques used to analyze postfracture pressure-transient tests:semilog (pseudoradial flow) analysis,square-root-of-time (linear flow) analysis,type-curve analysis. andreservoir simulator history matching.

The strengths and weaknesses of each technique were discussed by Lee and Holditch. No existing technique is without problems or possible ambiguity in some applications; thus, there is a need for still other techniques that may succeed in some situations for which existing techniques are inadequate.

The purpose of this paper is to introduce such a new technique for analyzing postfracture pressure-buildup tests. This technique can be particularly helpful when analyzing data from wells in which a finite-conductivity fracture has been created.

Proposed Technique

The pressure-buildup test analysis technique proposed in this paper requires that the analyst prepare a semilogarithmic graph and a square-root-of-time graph of the test data. The technique also requires use of two correction curves developed from the analytical solutions for finite-conductivity fractures presented by Cinco-Ley et al. The analyst chooses a single straight line on each of the graphs prepared for the test data and solves for fracture length, formation permeability, and fracture conductivity with an iterative procedure.

Semilogarithmic Graph

As a first step in understanding the basis for the proposed method, consider Fig. 1.

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Influence of Fracture Heterogeneity and Wing Length on the Response of Vertically Fractured Wells
Authors: Bennett C. O , Rosato N. D. , Reynolds A. C. , Raghavan R.
Published: December 2007

A finite-conductivity vertical fracture intersecting a well produced at a constant rate or at a constant pressure is considered. The pressure (or rate) response is obtained from a numerical model. Two aspects of this problem are considered: (1) variable fracture conductivity and (2) unequal fracture wing lengths.

The first part of this paper examines the influence of fracture conductivity on the well response. In practice, the fracture conductivity is a decreasing function of distance from the wellbore. If the fracture conductivity decreases monotonically with distance from the wellbore, then at late times the variable fracture conductivity solutions behave like a constant-conductivity fracture, with conductivity equal to the arithmetic average of the conductivity. At early times the response is identical to that of a constant-conductivity fracture, corresponding to the highest conductivity of the fracture. For the variable fracture conductivity case, the bilinear flow period characterized by a one-quarter slope line may be obscured. Thus, analysis of short-time data can be difficult. We also consider situations where the fracture conductivity does not decrease monotonically with distance. The response for these cases is discussed in detail.

The second part of the paper examines the effect of unequal wing lengths on the pressure response. We delineate conditions under which the effect of wing length on the response will become dominant. We discuss the influence of wing length on both early- and long-time data.
Multiple Fracturing of Boreholes By Using Tailored-Pulse Loading
Authors: Swift R. P. , Kusubov A. S.
Published: December 2007

A laboratory experiment was developed to study the effects of pressurizing boreholes of rock samples with tailored pulses at intermediate loading rates. The experiment focused on ascertaining the loading conditions needed to initiate multiple-fracture growth from a borehole. Experiments were performed under controlled loading conditions with borehole pressures ranging from 10 to 100 MPa, loading rates from 1 to 100 MPa/ms, and pulse durations on the order of from 1 to 50 ms. The initial conditions of samples were varied to include dry, quasidry, and fully saturated states along with pressure confinement of the samples up to 50 MPa.

Observations on samples of a medium-porosity sandstone showed that the degree of multiple fracturing is quite sensitive to the condition of the borehole as well as to the loading rate and appears strongly influenced by transient pore-pressure effects. The loading rate for the onset of multiple fracturing decreased with an increase in sample water content. The influence of water was much more marked at loading rates below 30 MPa/ms than at higher rates. For loading rates above the onset, the number of fractures initiated increased with an increase in loading rate, with about 10 to 12 at a loading rate of 100 MPa/ms. The fracture threshold-breakdown pressure increased proportionately with loading rate, a dependence that is attributed to transient water-intrusion effects around the borehole. The effect of sample confinement caused the threshold-breakdown pressure to increase and noticeably lowered the loading rate for multiple-fracture onset. Only two fractures (e.g., a typical hydrofracture) occurred when water was prevented from invading the borehole region. The tailored-pulse loading tests demonstrated their viability to determine the susceptibility of various rock types to multiple fracturing at intermediate loading rates.