bluuebunny/crossref_metadata_2025 huggingface dataset:
Constant-Pressure Production in Solution-Gas-Drive Reservoirs: Transient Flow
Authors: Camacho-V. Rodolfo G.
Published: December 2007

This paper presents procedures to obtain reservoir parameters from constant-pressure drawdown data in solution-gas-drive reservoirs. A novel procedure to determine the mechanical skin factor is introduced. Examples, including a field case, illustrate the use of this procedure. An estimate of the drainage area can be obtained with the derivative of rate data. A theoretical basis for analyzing data by the pressure-squared, p2, approach is presented; this procedure permits the approximate determination of sandface effective permeabilities in the transient flow period. For damaged wells, it is possible to obtain rough estimates of the size of the skin zone and the ratio of reservoir/skin-zone permeability when early transient data are available. The expression of the appropriate dimensionless rate in terms of physical properties for solution-gas-drive systems is presented. Finally, this paper presents a procedure to obtain an estimate of the change in sandface saturation during the transient flow period.
The Ford Geraldine Unit CO2 Flood: Operating History
Authors: Pittaway Kenneth R. , Runyan Edward E.
Published: December 2007

This paper describes the operating history of the tertiary CO2 flood in the Ramsey (Delaware sand) formation of the Ford Geraldine Unit. Injection and production history, operating techniques and problems, and flood monitoring and planning are discussed.
Organic Deposition From Reservoir Fluids: A Thermodynamic Predictive Technique
Authors: Kawanaka Seldo , Park S. J. , Mansoori G. A.
Published: December 2007

A molecular model is developed to predict onset and amount of organic deposition from reservoir fluids caused by variations in temperature and pressure and introduction of miscible solvents. The model is used successfully to predict the phase behavior and deposition regions of asphaltene in CO2/oil mixtures.
Use of a Monte Carlo Method To Simulate Unstable Miscible and Immiscible Flow Through Porous Media
Authors: Hughes D. S. , Murphy P.
Published: December 2007

A Monte Carlo solution technique has been implemented within the framework of an implicit-pressure, explicit-saturation (IMPES) simulator for two-phase, or two-component, flow. The saturation equation is interpreted as a probability density function and solved statistically. This automatically triggers an unstable solution when the mobility ratio is unfavorable, thereby mimicking the instability produced by heterogeneities in the porous medium. Results are presented for linear and one-quarter five-spot miscible and immiscible problems.
Preconditioning Concepts in Polymer Flooding in High-Salinity Reservoirs: Laboratory Investigations and Case Histories
Authors: Sohn Wolfgang O. , Maitin Balram K. , Volz Hartwlg
Published: December 2007

In polymer-flood field projects with partially hydrolized polyacrylamide (PH PAA) solutions, Deutsche Texaco A.G. (DTA) has applied two methods of preconditioning: a preflush with fresh water and the use of a relatively small slug of a less-salt-sensitive polymer. Results of laboratory work that led to an improved preconditioning concept with polymer are described. Case histories of two projects with two different preconditioning processes are presented and discussed in detail.
Analysis of Uncertainties in Applying the Waxman-Smits Equation to the Determination of Remaining Oil Saturation
Authors: Rackley S. A. , Tannemaat R. J.
Published: December 2007

An analysis of the Waxman-Smits equation is presented that describes how uncertainties in the input log data and evaluation parameters affect computed water saturation, Sw, values, taking into account the interdependence of uncertainties that arises when intermediate parameters in the evaluation (water resistivity and excess clay conductivity) are derived from log data. The analysis is applied to the evaluation of remaining oil saturation from openhole logs taken in a number of reservoirs in the Baram delta, offshore Sarawak, Malaysia. When an original water zone is available for the determination of intermediate parameters in these formations, it is concluded that remaining oil saturation in the 0.10- to 0.30-PV range can be determined with a standard deviation of ≈0.04 PV from openhole logs.

A comparison with core-measured Sor values indicates that laboratory measurements and log-derived results differ significantly in these reservoirs. In one field example, this difference is attributed to reservoir inhomogeneity and the averaging inherent in the logging-tool resolution. In a second example, there is evidence that the discrepancy is a result of continued oil drainage after water breakthrough, which may be attributed to a mixed-wettability condition in the reservoir.
Accurate Prediction of Compressibility Factors by the GERG Virial Equation
Authors: Jaeschke Manfred , Audibert Serge , van Caneghem Patricia , Humphreys A. E. , Janssen-van Rosmalen Renée , Pellei Quinto , Schouten J. A. , Michels J. P. J.
Published: December 2007

The European Gas Research Group (GERG, Groupe Européen de Recherches Gazières) performed an extensive research project involving the measurement of compressibility factors of pure gases and binary mixtures and of natural gases in the temperature range of 265 to 335 K and at pressures up to 12 MPa. These pure gas and binary mixture data, together with high-quality data from the literature, were used to develop the GERG virial equation for the accurate prediction of the compressibility factor of natural gas (multicomponent) mixtures. Pressure, temperature, and a 13-component composition are used as input data. Eighty-four sets of experimental natural gas data made up of more than 4, 000 data points were used to validate the GERG virial equation of state (EOS). The target accuracy of the GERG virial equation is ±0.1 %. A comparison of experimental and predicted compressibility factors shows that this target was achieved. The average root-mean-square (RMS) error for the differences between the experimental and the predicted compressibility factors is 0.06% for pressures up to 12 MPa. Even in the high-pressure range between 8 and 12 MPa, the RMS error is only 0.07%.
Daily Morning Production Report System
Authors: Branch H. O. , Breaux K. A.
Published: December 2007

This paper describes a PC-based database system used by Chevron U.S.A.’s Eastern Region to input, store, gather, and report daily oil and gas production information from remote field locations. The system provides the following functions.

Data input at any location with data-integrity checks. Automated data transfer between locations by modem using in-place company telecommunications facilities. Data aggregation at field, base, and divisional levels. Retransmission of any data changes to appropriate locations. Compiled program written in DBASE III™. "User-friendly" menu interfaces. Fast report generation using arrays.

The system, known as the daily morning production report (DMPR), replaces faxing of paper between locations. The DMPR system is faster than the old reporting method and allows data to be sent to the mainframe computer or outloaded to spreadsheets. The DMPR system reduces the time needed for generating production data reports for operations management.

The data-gathering system is set up so that field locations enter and validate the data and generate reports. The field data are automatically sent to a shore base location and aggregated with data from other fields, analyzed, and reported on. Shore base locations send the aggregated data to the division office, where the data are further aggregated and stored and reports are generated for management. Reports may be produced at any location. Telecommunication is managed by commercially available software and is initiated within the program. The user does not need to leave the program to perform any of these functions.

This paper covers database and program design, program installation, user training, and field experience with the DMPR system.
Subsea Systems of the Argyll Area Fields
Authors: Huber D. S. , Burnett R. C.
Published: December 2007

This paper highlights the major subsea/subsurface systems and equipment installed over the past several years in the Argyll area fields that have resulted in extended field life. Three major innovations emphasize the design philosophy of minimizing cost while maximizing flexibility, reliability, and the use of simple, existing technology. Details include the pioneering installation of gas lift, waterflooding of the Duncan field with its unique manifold system, and remote tie-in of wells 9 miles [14 km] away with a simple hydraulic system.
Seeking Engineers in the Sellers' Market
Authors: Stacy T. Don , McCain William D.
Published: December 2007

A common goal of the recruiting efforts of the various petroleum companies is to supply their needs for engineering manpower. Within this common purpose four recruiting techniques are used. These techniques may be described as the Miles Standish Method, the Combination Mode, the Lothario Approach and the Back Door Path. Each technique is described and evaluation of the effectiveness of each is given. A definite correlation is shown between the recruiting technique employed and the success of the company in attracting young engineers.

The basic principle underlying the success of any recruiting program is the exhibition of a sincere personal interest in each candidate. Observation over a period of years indicates that there are both a wrong and a right recruiting approach.

The paper outlines observations of how certain actions affect the student and his opinion of a company. Salaries, telephone communication, choice of assignment, plant visits, recruiting gimmicks, on-campus interviews, organization charts and other factors, are discussed.

Introduction

In no case is the struggle of supply and demand more severe than when the product is a prospective employee. As long as engineering enrollments are low, and industry demand is high, this struggle remains acute. The major oil companies must compete with graduate school, military service, and other industries in filling their needs for engineering manpower. Every recruiter wonders "what went wrong" when a promising young engineer accepts the offer of another company. We have observed the recruiting merry-go-round for several years and have noted that although the companies visiting our campus use the same general approach, the degrees of their success vary widely.

The general program for recruiting engineers follows a pattern of: on-campus interviews, interview trips by the engineering student and follow-up. The major difference among the would-be employers is each one's specific application of this general program. This paper attempts to classify the recruiting techniques and correlate them with their success in the hiring of engineers.

A direct contrast is drawn between the unsuccessful and the successful methods of handling engineering students.
Threshold Pressure Phenomena in Porous Media
Authors: Thomas L.K. , Katz D.L. , Tek M.R.
Published: December 2007

Threshold displacement pressures are needed to determine how much overpressure can be used in storing natural gas. An experimental technique for determining threshold pressures by displacing water with gas from samples saturated with water is presented. Threshold pressures for eight low permeability samples were measured. Threshold pressure data obtained in this work, plus data on higher permeability samples reported in the literature, are correlated with porosity, permeability, surface tension and formation resistivity factor, Mercury injection pressures also were measured and correlated with air-water threshold pressures. Threshold pressures were found to be independent of time.

An aerial photograph of gas emerging from The top of a core shortly after its threshold pressure has been exceeded shows that the gas bubbles we uniformly distributed across the face of the core. Channeling will occur, however, when an increased gas phase permeability is reached.

A porous medium can be resealed after its threshold pressure has been reached provided it has not been desaturated below a fixed saturation. Its new threshold pressure will be lower than when the sample is 100 percent saturated with water.

Introduction

The degree of overpressure in excess of the discovery pressure that a gas storage reservoir can withstand is determined by the ability of its caprock to contain gas, providing the pressure does not exceed the structural limit of the reservoir. The retention of gas in a reservoir by a caprock saturated with water is a result of the capillary forces acting at the gas water interface. Without the presence of water in a caprock, gas would leak out of the reservoir at a rate determined by the permeability of the caprock to gas.

The ability of a caprock to contain gas is expressed in terms of its threshold displacement pressure, which is defined as the minimum pressure needed to initiate the displacement of a wetting phase by a nonwetting phase from a porous medium 100 percent saturated with the wetting phase.

The gas industry must be able to predict how much "overpressure" a gas reservoir can withstand before leakage occurs by gas displacing water from caprock overlying the reservoir. This is of economic importance since the storage capacity of a gas reservoir is proportional to its pressure.

The discovery pressure for most reservoirs is found between the upper and lower limits shown in Fig. 1. Discovery pressures in excess of their hydraulic pressure gradient are attributed to the compaction of an isolated shale formation by the overburden. The lower limit of 0.433 psi/ft corresponds to the weight of the overburden, the gradient of the rock itself.
Insights on Rheological Testing and Flow Behavior of Delayed-Crosslinked Fracturing Fluids
Authors: Cameron J. R. , Gardner D. C. , Veatch R. W.
Published: December 2007

Our research findings show that the rheology of delayed-crosslinked fracturing fluids depends not only on the shear and thermal histories, but also on flow geometry, stress level, and time. These gels can flow as nonhomogeneous fluids and have an as yet unreported stress-state (phase) transformation property. These phenomena currently are not accounted for in gel testing or data scale-up but can manifest themselves in apparent test-geometry and time dependencies. This research also indicates that delayed-crosslinked fracturing fluids may give better proppant transport than expected.
Treatment of Variations of Composition With Depth in Gas-Condensate Reservoirs
Authors: Wheaton R. J.
Published: December 2007

Considerable variations of hydrocarbon composition with depth have been reported in several North Sea gas-condensate fields. Within the gas phase, the mole fraction of methane present, for example, may change by several percent between the top and bottom of the field. These compositional gradients can cause dewpoint variations of as much as 4 psi/ft [90 kPa/m]. Neglect of these effects in simulation will lead to significant errors in the estimates of hydrocarbons initially in place. These errors can, in turn, cause errors of up to 20% in predicted cumulative oil production in some condensate fields. In this paper, we develop a theoretical treatment of variations of composition with depth in hydrocarbon reservoirs. Results of sample calculations show the type of results predicted by the theory and the extent of the errors that may occur if compositional gradients are neglected.
Experimental and Theoretical Investigation of Methane-Gas-Hydrate Dissociation in Porous Media
Authors: Youslf M. H. , Abass H. H. , Selim M. S. , Sloan E. D.
Published: December 2007

Vast quantities of natural gas deposits exist in the form of solid hydrates. Methane gas hydrate was formed and dissociated for the first time in Berea core samples. A three-phase ID model was developed to simulate the process of gas production from Berea sandstone samples containing methane hydrate by means of a depressurization mechanism. The model closely matched the experimental data of gas and water production, the progress of the dissociation front, and the pressure and saturation profiles.
Characterization of Fluvial Sedimentology for Reservoir Simulation Modeling
Authors: Henriquez Adolfo , Tyler Kelly J. , Hurst Andrew
Published: December 2007

This paper presents a critical study of a 3D stochastic simulation of a fluvial reservoir and of the transfer of the geological model to a reservoir simulation grid. The stochastic model is conditioned by sand-body thickness and position in wellbores. Geological input parameters—sand-body orientation and width/thickness ratios—are often difficult to determine, and are invariably subject to interpretation. Net/gross ratio (NGR) and sand-body thickness are more easily estimated. Sand-body connectedness varies, depending on the modeling procedure; however, a sedimentary process-related model gives intermediate values for connectedness between the values for a regular packing model and the stochastic model. The geological model is transferred to a reservoir simulation grid by use of transmissibility multipliers and an NGR value for each block. The transfer of data smooths out much of the detailed geological information, and the calculated recovery factors are insensitive to the continuity measured in the geological model. Hence, we propose improvements to the interface between geological and reservoir simulation models. Input for our conditional, statistical, sedimentary, process-related model includes regional geological parameters (rates of subsidence and aggradation and grossly contoured paleotopography) and local values (depth, thickness, and direction and width of sand bodies ascertained from well-test and core analyses). Integration of sedimentological understanding of the reservoir's depositional environment is emphasized.
Valid Capillary Pressure Data at Low Wetting-Phase Saturations
Authors: Melrose J. C.
Published: December 2007

Air/brine capillary pressure data obtained by three different techniques are reported as a function of saturation for several Berea core-plug samples. The capillary pressure values ranged from about 0.67 to 9.5 MPa [97 to 1, 380 psi]. The corresponding brine saturations ranged from 10 to 3% PV. The techniques used were high-speed centrifuge, porous plate, and water-vapor desorption (WVD). The results show that a plot of log Pc vs. log Sw is linear in the saturation range studied. These data are believed to be the first valid capillary pressure data reported for Berea samples in the high-pressure, low-saturation region. Also, no comparable data appear to have been published for any sedimentary rock in the permeability range above 1 md.
Pressure-Transient Analysis of a Composite Naturally Fractured Reservoir
Authors: Satman Abdurrahman
Published: December 2007

An analytical model describing the transient pressure behavior of a well completed in a composite naturally fractured reservoir is presented. This model was derived by extending the naturally fractured reservoir model with unrestricted interporosity flow to a composite reservoir. The composite reservoir has a circular inner region with fluid and rock properties different from those of the outer region. It is a concentric composite model with a finite-radius well located in the center.

Two new solutions for analyzing the pressure response at the producing (or injection) well in infinitely large composite and bounded composite naturally fractured reservoirs are given. The results were obtained with the Stehfest algorithm for Laplace-transform inversion. Depending on the reservoir and fluid properties, various semilog straight lines may be observed in a particular pressure/time curve. The pseudo-steady-state approach can be used to determine the swept volume. On the basis of model results for different parameter values, guidelines are provided for conducting and interpreting a pressure test to determine the characteristics of a composite naturally fractured system, provided that wellbore-storage effects do not mask early-time data.
New Solutions for Well-Test-Analysis Problems: Part 2 — Computational Considerations and Applications
Authors: Ozkan Erdal , Raghavan Rajagopal
Published: December 2007

Computational considerations in obtaining well responses and pressure distributions for several problems presented in Part 1 are discussed. In addition, new asymptotic expressions for pressure distributions in closed drainage volumes applicable during the boundary-dominated flow period are derived. Interestingly, these expressions, which are much simpler than those available in the literature, can be used to derive shape factors for a variety of completion conditions (vertical, horizontal, and vertically fractured wells). Application of constant-rate solutions to more complex conditions is also presented.
Rock Failure During Tooth Impact and Dynamic Filtration
Authors: Myers G.M. , Gray K.E.
Published: December 2007

In previous publications, results of single-blow bit tooth impacts on saturated rocks at various stress states were reported. This paper extends these earlier works to include study of bit impact tests on salt water-saturated Berea and Bandera sandstone samples under conditions of elevated confining and pore pressure. During the tests dynamic filtration and deposition of a mud cake were occurring due to the presence of drilling mud in the borehole and a borehole-to-formation pressure differential.

Results indicate that saturation of these sandstones with salt water tends to make them weaker than when saturated with nonreactive fluids. Plastic failure often occurs even when extremely high fluid-loss muds are present in the borehole. The failure mode tends toward plasticity with decreasing fluid loss. Brittle failure of sandstones in mud-filled holes is apparently relatively rare. Depending on the stress level, and the associated failure mode, withdrawal of the bit tooth induces a tensile force that seems rather important relative to the quantity of rock removed by vertical tooth impact.

Introduction

A vast majority of the oil wells drilled today involve the use of colloidal muds having a measurable mud filtrate loss. It is known from field experience that reduction of the water loss of a mud generally results in a reduction of the penetration rate. This paper describes an investigation of crater formation at simulated bottom-hole pressure conditions for drilling fluids having different water losses.

The literature on single bit tooth impact (cratering) at atmospheric conditions is extensive, but only a limited amount of work has been performed at the stress conditions similar to that found in oil wells. Spherical penetrator cratering tests on rocks at hydrostatic pressure were performed by Payne and Chippendale. Chisel impact studies on limestone with independently varying overburden and borehole pressure and atmospheric pore pressure were reported by Garner, et al. Gnirk and Cheatham performed "static" penetrator tests on dry rocks at equal overburden and borehole pressures. Podio and Gray studied the effect of pore fluid viscosity at atmospheric pore and borehole pressures and varying overburden pressures. Their results illustrated the importance of fluid saturation of the rock. Yang and Gray reported single tooth impact tests on saturated rocks at elevated borehole, pore and confining pressures, but with equal pore and borehole pressures. For the work reported in Refs. 4 and 5, filtration across the hole bottom purposely was avoided. Maurer has investigated the effect of independently varying pore and borehole pressures at elevated overburden pressures by using a zero water-loss mud in the borehole. His tests were carried out under conditions that allowed independent control of overburden, pore and borehole pressures, but without control of filtration at the hole bottom.
Case History: PC Analysis of Bit Records Enhances Drilling Operations in Southern Alabama
Authors: Thomas J. M.
Published: December 2007

Kelly No. 1 was drilled on a footage basis in Escambia County, AL. Computer bit-record analysis provided summarized information in a format easily read and understood by field personneL With a PC used to compare surrounding bit records on a cost-per-foot basis, the best bit type, weight on bit (WOB), and bit speed for a given section of hole were identified. From the analysis, field personnel were able to improve bit selection, resulting in three bit runs having the lowest cost per foot in a given section of hole and an overall lower-cost-per-foot drilling operation.
Inhibition of Gas Hydrates in Deepwater Drilling
Authors: Hale Arthur H. , Dewan Ashok K. R.
Published: December 2007

With the movement of offshore rigs into deep water, the problem of gas hydrates has become an important issue in drilling. If a kick is taken, gas hydrates can form in the blowout preventer (BOP) or chokelines while the kick is circulated out. The water-based pill presented here significantly improves gas-hydrate inhibition. This pill, which can be spotted in the BOP and weighted up, is environmentally safe and easily adaptable to offshore operations. Compatible with commonly used drilling fluids, the pill can be mixed directly into the mud system without any adverse effects after the danger of hydrate formation diminishes. This technology is an important safety consideration for deepwater drilling well control and hydrate-free operations above the mudline.
Saturation From Logs Laboratory Measurements of Logging Parameters
Authors: Walther H.C.
Published: December 2007

While logs provide the only in situ measurement of water saturation, the measurement is not direct. Calculated saturation depends upon the value assumed for the saturation exponent n. The literature furnishes evidence that n varies and that it depends upon the type of rock and fluids, wettability, confining pressure, etc. Hence, a laboratory technique was developed for measuring m and n under a confining pressure and at formation temperature. The technique involves mounting a sample in a Hassler-type sleeve, using an oil-brine flow system and making two- and four-electrode measurements. Results of measurements on Frio, Miocene and Berea sandstones and Cretaceous limestones are presented with applications to log analysis.

Introduction

Decisions of whether or not to complete and how to complete, as well as reservoir engineering calculations, all require accurate water saturation data. Narrowing profit margins and development of marginal fields place strong demands on accuracy of data.

Logs provide the only in situ technique for determining water saturation. However, the measurement is not direct since the logs only measure formation resistivities. While equations relating resistivities to saturations were developed more than 20 years ago, these equations are too general for accurate application to all fields or formations. Also, the equations contain constants which are known to vary with rock type, stress, water resistivity, wettability, etc. Until more is known about these basic relationships, the recent advances in log quality and application of computers to log analysis cannot be fully utilized. The basic equations for resistivity log analysis are

(1)

where phi = fractional porosityF = formation factor (the ratio of the resistivity ofa brine-filled core, Ro, to the resistivity ofthe brine, Rw)m = m factor or cementation factora = an empirical constant

(2)

where Ro = resistivity of brine-filled coreRt = resistivity of core at saturation, Swn = saturation exponent.

Constants a, m and n ideally should be determined for every reservoir. Currently, if no laboratory-measured values are available, the values a = 1.0 and m 2 are commonly used for limestone reservoirs, and a 0.62 and m = 2.15 are used for sandstone reservoirs. A value of 2.0 is assumed for n.

Values for n ranging from 1.0 to 4.3 for natural core, and up to 54 for synthetic cores, are reported in the literature (Table 1). Also, several references show that the measuring technique is very important and that many of the problems associated with relative permeability measurements might be expected. Even allowing for measurement problems, there is ample evidence to show that n does vary.

JPT

P. 251ˆ
Needed: Greater Teamwork Between Disciplines
Authors: Halbouty Michel T.
Published: December 2007

Petroleum industry management, as well as individuals, must realize that greater teamwork between disciplines is needed to meet the challenges of the future. In the area of exploration this teamwork is indispensable. Future successful exploration will depend an the coordinated efforts of the geologist, geophysicist and the petroleum engineer. Ways by which this coordination can be achieved are discussed.

Introduction

There is no question that greater teamwork among the disciplines of geology, geophysics and petroleum engineering is needed today more than ever before. There was a time, during the so-called golden years of the industry, when little attention was paid to combining the resources of these three powerful technical segments.

In order to understand what is needed today and what will be required in the future from these three disciplines, it is important to reflect on the status of world petroleum production on Jan. 1, 1901. The world's annual production was about 138 million bbl. Russia was the leading oil-producing nation with 68 million bbl. Of the 58 million bbl produced in the U. S., 92 percent, or 53 million bbl, was from the so-called "oil region" of Ohio, West Virginia, Pennsylvania, Indiana and New York. Four million bbl, or 6 percent, was from California, and the remaining 1 million bbl, or 2 percent, was produced from the Corsicana field in Texas.

The average production for the so-called large producers in the U. S. was 75 B/D. The entire world production was consumed in lubrication and illumination. Civilization was still in the lubrication age. There was not enough petroleum produced to justify its use as a liquid fuel. But Spindletop changed all of this.

On Jan. 10, 1901, in the dawn of a new century, the Spindletop discovery fired the imagination of the entire world. The potential from the discovery well, if estimated on a per-year basis, was more than the combined production of the entire world. Spindletop brought on the liquid fuel age and was the beginning not only of the world's industrial revolution, but also, certainly, of the oil industry.

Prior to the Spindletop discovery and for a decade after, the status of the petroleum geologist was that of a college professor who was retained occasionally by oil companies to do consulting work. On the other hand, the early engineer was merely a roughneck or a roustabout or a driller who had no formal engineering education. But these men who did the work in the field with countless improvisions and inventions brought about the know-how that is recognized throughout the world as distinctly American.
Numerical Methods of Higher-Order Accuracy for Diffusion- Convection Equations
Authors: Price H.S. , Cavendish J.C. , Varga R.S.
Published: December 2007

A numerical formulation of high order accuracy, based on variational methods, is proposed for the solution of multidimensional diffusion-convection-type equations. Accurate solutions are obtained without the difficulties that standard finite difference approximations present. In addition, tests show that accurate solutions of a one-dimensional problem can be obtained in the neighborhood of a sharp front without the need for a large number of calculations for the entire region of interest.

Results using these variational methods are compared with several standard finite difference approximations and with a technique based on the method of characteristics. The variational methods are shown to yield higher accuracies in less computer time.

Finally, it is indicated how one can use these attractive features of the variational methods for solving miscible displacement problems in two dimensions.

Introduction

The problem of finding suitable numerical approximations for equations describing the transport of heat or mass by diffusion and convection simultaneously has been of interest for some time. Equations of this type, which will be called diffusion-convection equations, arise in describing many diverse physical processes. Of particular interest here is the equation describing the process by which one miscible liquid displaces another liquid in a one-dimensional porous medium.
Predicting Gravity-Drainage Performance Using a Three-Dimensional Model
Authors: Hall H.N.
Published: December 2007

Reservoir and producing characteristics can govern the decision to use either a one-, two- or three-dimensional model for making predictions for gravity-drainage reservoirs. Examples of conditions requiring one-, two- and three-dimensional calculations are given. In 1961 the author presented a method for predicting one-dimensional gravity-drainage performance. This work has been extended to obtain a three-dimensional model, which is described and for which a sample problem is presented.

Introduction

Many papers on gravity drainage or gas-cap drive have been presented for conditions where the reservoir is treated as a single areal segment so that, in effect, only one-dimensional flow is considered. Other authors have given evidence showing that the one-dimensional concept would be unsatisfactory to predict reservoir performance for certain types of reservoirs. Experience has indicated that specific reservoir and producing conditions govern whether one-, two- or three-dimensional concepts must be used as a basis for reliable reservoir performance predictions.

Previously the author presented a paper outlining a method for predicting the performance of gravity-drainage reservoirs. That paper treated the reservoir as a single areal segment so that it was applicable for only one-dimensional flow. The work has been extended to obtain a three-dimensional model that can be used to predict performance of gravity-drainage reservoirs. Although capable of being three-dimensional, it can be used equally well for one- and two-dimensional predictions.

This paper discusses those reservoir and producing conditions governing the choice of model, and also describes a three-dimensional model suitable for predicting reservoir performance in the more complex situations.
Effects of Pipe Roughness on Friction Pressures of Fracturing Fluids
Authors: Shah Subhash N.
Published: December 2007

In this study, the effects of pipe roughness on friction pressures of uncrosslinked and crosslinked fracturing gels are reported from flow data gathered in smooth and rough pipes. Pipe-roughness effects are found to be very significant in the estimation of friction pressures of fracturing fluids. These effects are more pronounced with less viscous fluids than with more viscous fluids and at higher rates with both fluids. From the data gathered with fluids tested in this study, correlations to estimate friction pressures of fracturing gels in turbulent flow in rough pipes are also presented. Though not ideal, these correlations allow better estimates of friction pressures in rough tubular conductors than existing methods do.
Performance of Seeligson Zone 20B-07 Enriched-Gas-Drive Project
Authors: Walker J.W. , Turner J.L.
Published: December 2007

In 1957 Humble Oil and Refining Co. initiated a program in the Seeligson (Zone 20B-07) field, Kleberg County, Tex., that involved displacement of oil by enriched gas. Early evaluation showed that nearly 100 percent oil recovery was being obtained in the volume of reservoir swept by enriched gas. Subsequently, it was observed that the enriched gas way breaking through at producing wells earlier than expected, and that volumetric sweep efficiency was lower than anticipated. Simultaneous injection of water and enriched gas was begun in 1963 in an attempt to improve sweep efficiency. In 1965 it was determined that sufficient enriched gas had been injected into the reservoir, and the injection substance was converted to water and dry gas.

The experiment program in Zone 20B-07 is largely complete. Cumulative production froth the reservoir has been 3.7 million bbl of oil, and oil recovery froth the Zone 20B-07 enriched-gas project has been 50 percent of the original ail in place. Production to date has greatly exceeded the native dissolved-gas-drive recovery that was predicted to be 22.3 percent of in-place oil. As another comparison, current recovery also exceeds expected waterflood recoveries in the range of 42 to 48 percent- estimates based on experiences in similar reservoirs in this area.

This paper covers field results, particularly those regarding displacement and sweep efficiency and the effects of changes in injected fluids. Reasons for observed performance are discussed with regard to future application of miscible displacement.

Introduction

The Seeligson Zone 20B-07 enriched-gas-drive project is completed. The theory of miscible displacement, reasons for experimenting in the zone, and early performance data are well documented by earlier reports. This paper presents final results of the project and discusses factors that will assist future evaluations of enriched-gas-drive applications.
Performance Review of Shoats Creek Unit Vaporizing Gas-Drive Project
Authors: Dorsey J.B.
Published: December 2007

Performance of a high-pressure, vaporizing gas-drive project in a volatile oil reservoir is discussed. The project has been in operation for over 8 years. Present recovery from the over-all displaced portion of the reservoir is 40 percent, and an ultimate recovery of 60 percent is indicated. Calculations reflect an over-all displacement volume of 50 percent for the entire reservoir; therefore, ultimate oil recovery will be 30 percent of the entire reservoir oil originally in place. Laboratory vaporization tests conducted prior to project initiation also are presented and discussed, along with an analytical method of determining stock-tank oil production and gas injection requirements related to over-all volumetric displacement efficiency from these data.

Introduction

The Shoats Creek field is located in Beauregard Parish, La., in the extreme western part of the state (Fig. 1 ). Discovered in 1956, the field is productive in three Cockfield sand zones, ranging in depth from 8,000 to 9,000 ft. The upper two zones, 1st and 2nd Cockfield, are condensate-bearing gas reservoirs. The lowest zone, the 5th Cockfield, is a volatile-oil reservoir. Laboratory work conducted on crude oil from the 5th Cockfield zone shortly after field discovery demonstrated that, when contacted with dry gas, significant volumes of the oil could be vaporized at reservoir temperature and at an appropriately high reservoir pressure. Further study led to the conclusion that early initiation of a crude vaporization project in the 5th Cockfield zone would be superior economically to other methods of reservoir depletion. Consequently, the zone was unitized and gas injection operations started late in 1958. This paper discusses laboratory work performed in conjunction with the project, and project performance to the present.
Gas Turbines -Application and Experience
Authors: Porter John A.
Published: December 2007

Gas turbine engines, which convert chemical energy to mechanical energy, have become increasingly popular for industrial uses during the past few years. Oil and gas are used as fuel for the turbine. As the demand for turbine engines grows, new markets for oil and gas products will be created. A description of the basic theory, construction and performance of the gas turbine engine, with emphasis on oil and gas field applications, is presented.

Introduction

In recent years, the gas turbine engine has captured a significant portion of the industrial prime mover market. The "1967 Annual Gas Turbine Catalog" lists a total of over 35 million industrial gas turbine horsepower now in use. The total was only 24 million hp in 1966. The population of industrial gas turbine horsepower increased 50 percent in 1 year - proof of the increasing acceptance of the industrial gas turbine engine.

Gas turbines convert chemical energy to mechanical energy. Natural gas and petroleum products are the source of chemical energy for gas turbines. In a larger sense, the oil and gas industry is interested in every turbine sold. As turbine technology improves, new markets will be created for oil and gas products. More directly, the oil and gas industry itself provides a great part of the existing turbine market.

Basic theory, construction, performance and application of the modern gas turbine is reviewed. Oil and gas field applications are emphasized.
Vertical Fracture Height-Its Effect on Steady-State Production Increase
Authors: Tinsley John M. , Williams J.R. , Tiner Robert L. , Malone W.T.
Published: December 2007

Data taken from a steady-state electrolytic model have been used to developcurves showing production increase as a f unction of fracture height, fracture length, reservoir height, drainage radius, fracture flow capacity, formation permeability and wellbore radius. The work allows a fullerevaluation of the effect of fracturing parameters on productivityincrease.

Introduction

Hydraulic fracturing methods for productionstimulation have become a common procedure in the oiland gas industry. Fracturing treatments areperformed on wells of various potentials to help increasethe production rate. In addition to the desire forincreased production is the need to predict whatincrease might be expected. This knowledge is usefulin economical treatment planning to accomplish thedesired production goals for the well.

Theoretical production increases due to horizontalradial fractures may be calculated using equationsdeveloped from mathematical analyses and electricalmodels. It also is possible to predict theoreticalproduction increases due to vertical fractures usingcurves developed from electrical and mathematicalmodels." However, these studies assumed that thevertical fracture height and the formation height wereequal, which may not be true." In addition, the finalfracture height through which fluid is produced maynot be equal to the created height.

The development of vertical fracture proppanttransport relationships has made unrealistic theassumption that propped fracture height is equal tocreated fracture height. Through the use of publishedproppant transport equations, it is possible tocalculate the height of a bed of propping agent depositedin a fracture of a given height. Assuming that thefluid flowing in the fracture moves through only thepropped portion of that fracture (i.e., that theunpropped part of the fracture heals) it becomesessential to know how production increase varies with theratio of propped fracture height to formation height.

It should be recognized that future investigationmay determine that the fracture does not healcompletely and that a highly permeable channel existsover the deposited bed of proppant. The effect of thischannel was not considered for the present study.

The following analysis of experimental dataallowed development of curves to determinetheoretical production increases considering fracture heightas a variable.

Discussion

In designing a fracturing stimulation treatment anumber of variables must be considered. The size ofthe treatment, type of proppant used, proppantconcentration, treatment fluid properties and wellconditions are all factors affecting the dimensions andpermeability of the fracture.

Production increase due to a vertical fracture isaffected by propped length, height, width andpermeability of the fracture for a given set of formationconditions. Production increase may be defined asthe ratio of production rate after fracturing to theproduction rate before fracturing at the samepressure differential, pe - pw.

JPT

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The Energy Balance Concept of Hydraulic Fracturing
Authors: Perkins T.K. , Krech W.W.
Published: December 2007

This paper explains the concept of a damaged region arising from high stress concentration at the leading edge of a hydraulically created fracture. Approximate stresses near the tip of the crack are calculated, and it is shown that a stable crack shape is possible for which all stresses are finite. A new energy balance is derived incorporating these thoughts, and it is shown that predicted fracturing pressures (using surface energies determined by cleavage) agree with experimental fracturing pressures determined in models. All calculations apply to the case of a nonpenetrating fluid. It is concluded from these studies that in some cases, particularly in small laboratory models, these phenomena significantly affect extension pressures and crack widths.

Introduction

One of the perplexing questions about hydraulic fracturing that has not been satisfactorily answered is, what pressure is necessary to extend a fracture? For many engineering problems involving failure, it is sufficient to calculate those loading conditions which would bring a stress or elastic strain within the material to a level that could not be tolerated. However, this approach is not useful when considering a sharp-edged crack; calculated stresses and elastic strains always reach infinitely large values near the tip of the crack if fluid pressure is applied all the way to the crack extremity. This difficulty has led to the concept of cohesiveness or absorption of surface energy, implying that behavior near the tip of the crack is not purely elastic.

Additional note of the nonideal behavior of rocks will be made in this paper. Then, by simplifying and dealing with an average stress in an inelastic region, the approximate stress distribution around a hydraulic fracture will be calculated and the conditions under which a stable fracture can exist will be shown. A new energy balance equation is then derived incorporating the modified stress picture. Finally, predicted fracture extension pressures are compared with breakdown pressures obtained in laboratory models. This comparison shows that surface energies measured by the cleavage technique are consistent with those values manifested during fracture extension.

PROBLEMS OF INDUCED STRESS

It will be revealing to consider first the calculated stresses around a penny-shaped line crack, assuming that the rock behaves as a linear, elastic material. Fig. 1 shows the stress distribution in the plane of the crack as calculated with Sneddon's equation. If pressure p is applied uniformly within the crack, then infinitely large tensile stresses would be induced in the rock near the crack tip. Such stresses could not be sustained in a real material. Two approaches have been proposed to explain this dilemma.

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