bluuebunny/crossref_metadata_2025_split huggingface dataset:
Error Analysis and Design Considerations for Backpressure Testing of Gas Wells
Authors: Hinchman S. B. , Poettmann F. H. 
Published: December 2007

Abstract
The theoretical validity of backpressure tests has been analyzed for wells in radial flow and for wells intersected by vertical fractures. It is demonstrated that stabilized flow-after-flow and isochronal tests are valid tests. Unstabilized flow-after-flow and modified isochronal tests result in error in predicted deliverability caused by continued influence of prior flow and shut-in periods (superposition error). It is shown how the superposition error can be minimized by proper selection and design of the backpressure test.
Isochronal and modified isochronal tests are unsteady-state methods and provide the transient deliverability of a well. An extended flow period is generally used to determine the stabilized deliverability. In many reservoirs extended flow periods are unreasonably expensive and impractical. Analytical solutions for predicting stabilized deliverability are required. The calculations used in the prediction of stabilized gas deliverability are based on a radial flow geometry. When these calculations are applied to other flow geometries, errorneous conclusions result. In this study a fully-implicit, two-dimensional gas simulator was used to demonstrate the extension of radial flow theory to vertically fractured wells. The effect of fracture length and conductivity was investigated. It was observed that the performance coefficient (Ct) was inversly related to pressure. A proof is presented for the Darcy flow condition. An understanding of how Ct changes with time will allow a more precise estimate of stabilized deliverability.
Advanced Decline Curve Analysis Using Normalized-Time and Type Curves for Vertically Fractured Wells
Authors: Fraim M. L. , Lee W. J. , Gatens J. M. 
Published: December 2007

Abstract
The purpose of this paper is to present a new constant pressure type curve to analyze long-term production from a well with a finite-conductivity vertical fracture. In addition, the paper presents a method to account for real gas properties and non-Darcy flow existing in the fracture. Solutions are presented for production with both'constant bottomhole pressure and constant surface pressure.
At the present, for rapid long-term production predictions for stimulated wells in bounded reservoirs, the Fetkovich1 constant pressure type curve for radial flow can be used. This type curve models production from high conductivity fractures with a maximum fracture half-length one tenth the outer radius of the drainage area. For early transient production, the Guppy2 constant pressure type curves for hydraulically-fractured wells are available. Guppy presents type curves for selected conductivities and non-Darcy flow coefficients. The type curves terminate at the end of bilinear flow, which is about two log cycles before pseudo-radial flow begins.
Constant pressure type curves are particularly useful in modeling long-term production from stimulated low-permeability formations with long fractures, and there is a need for modeling both transient and non-transient flow. To meet this objective, this paper presents overlays for the Fetkovich type curve for dimensionless fracture conductivities, Cr, from 0.2 to 100, (Cr=kfbfπkxf) and drainage area to fracture half-length ratio, xe/xf, from 1 to 64. We use a normalized time function to correct for real gas properties and for non-Darcy flow in the fracture, tubing, and surface facilities.
Permeability Variation in a Sandstone Barrier Island-Tidal Channel-Tidal Delta Complex, Ferron Sandstone (Lower Cretaceous), Central Utah
Authors: Stalkup F. I. , Ebanks W. J. 
Published: December 2007

ABSTRACT
This paper describes a study to determine how permeability varies spatially in outcrops of an ancient barrier island-tidal channel-tidal delta complex. This type of information is useful for developing models of between-well reservoir permeability heterogeneity for application where data are not available.
Fifteen outcrop exposures representing different vertical sections of the complex were examined to determine the lithofacies present and their distribution. Horizontal cores approximately six in. long and one in. in diameter were taken at selected locations for permeability measurements.
These observations and measurements give the following picture of permeability structure in the sediments of this particular complex. Permeability heterogeneity occurs on several size scales. On the largest scale, crossbedded, burrowed, rippled, and shaly lithofacies are distinguished for characterizing gross permeability layering. These permeability units are continuous over distances of at least 500 to 1000 ft in the seaward direction and probably are continuous over much greater distances in the along-shore direction. Some lithofacies did not define independent permeability units, however, and had to be combined with vertically adjacent facies to form a unit. On an intermediate scale, permeability sublayers on the order of 2 to 4 ft thick occur within some of the units. The lateral extent of these sublayers was not determined. On a small scale within the sublayers, permeability variation appears to be random for samples that are separated by at least 6 in., the minimum sample separation investigated. Estimates are given in the paper for the magnitude of permeability contrast between permeability units, the lateral variation of mean permeability within a unit, and the permeability contrast between sublayers within a unit.
Permeability of the rocks in outcrops was compared to that of similar rocks in the same stratigraphic unit in a nearby well. Permeability contrasts among lithofacies are greater in the subsurface than in the outcrops because of surface weathering, but the vertical arrangement of statistically different permeabilities is similar in the two situations.
Multiphase, Multicomponent Compressibility in Petroleum Reservoir Engineering
Authors: Macias L. C. , Ramey H. J. 
Published: December 2007

ABSTRACT
Coefficients of compressibilities below the bubble point were computed with a thermodynamic model for single and multicomponent systems. Results showed coefficients of compressibility below the bubble point larger than the gas coefficient of compressibility at the same conditions. Two-phase compressibilities computed in the conventional way are underestimated and may lead to errors in reserve estimation and well test analysis.
A New Method of Gas-Bearing Zone Identification by Well Logging
Authors: Tan T. 
Published: December 2007

ABSTRACT
Conventional methods for gas bearing zone identification are based on the comparison of the neutron log porosity to the density log porosity. In low porosity, varying matrix formations the gas detection is often difficult.
The method proposed in this paper is a new method which identifies gas bearing zones by using a Difference Ratio of Equivalent Elastic Modulus of formation rock (EDR). The ratio is calculated by the combination of sonic log, density log and neutron log. The formula used to calculate the ratio is as follows: EDR= (Ecw−Ec)/Ec
in which, Ec is the equivalent elastic modulus of the formation of interest in dyne/cm2, Ecw is the equivalent elastic modulus of the same formation of interest 100% water saturated in dyne/cm2.
When Ecw is greater than Ec, EDR is greater than zero and this indicates gas bearing zone. On the contrary, when Ecw is smaller than Ec, EDR is smaller than zero and this indicates a non-gas bearing zone.
The method has been used to interpret some sand and carbonate gas reservoirs of China. The results presented in this paper show that higher resolving power of gas bearing zones, better interpretation accuracy, and "quick look" estimates can be readily achieved.
Stability of Waterflood Diverting Agents at Elevated Temperatures in Reservoir Brines
Authors: Nagra S. S. , Batycky J. P. , Nieman R. E. , Bodeux J. B. 
Published: December 2007

ABSTRACT
Water channelling is a significant problem in oil producing reservoirs. One way to improve sweep is "by diverting water to unswept zones through the placement of polymeric gels as diverting agents. The key to successful application of these materials is the amount of time over which the gels will he effective at reservoir conditions. Gel stabilities of a range of polymer compounds were tested in reservoir brines with salinities up to 10% TDS and at temperatures up to 90°C. One characterization of gel stability was the amount of time (half-life) required for a gel to shrink to half its initial volume. Results at 90°C with Polyacrylamide, cellulosic and xanthan gels showed short half-lives ranging from less than a day (complete syneresis) up to 45 days depending on concentration and polymer type. Intermediate stabilities were observed with scleroglucan while the most stable gels with half-lives of more than a year were observed at 90°C with lignosulphonate and phenoformaldehyde materials. Based on this screening procedure, phenoformaldehyde gels were tested for permeability reduction in both homogeneous and fractured cores after which the products were field tested. Preliminary results from a number of field tests provide optimism to continue a cautious program to develop placement and evaluation techniques.
Restructuring – Survival or Suicide
Authors: Hassell Richard Lee 
Published: December 2007

Abstract
Looking back on the last four plus years, our industry has had the unique opportunity to navigate uncharted waters in our attempts to cope with the slide in oil/gas prices. Most of our forecasts, planning sessions, meetings, and seminars during this time have continually underestimated the extent, duration and depth of the problems we face today. Throughout these years, countless individuals have sold their plans or forecasts by predicting – "When things turnaround …." For those of us believing in a turnaround I suggest that this is like waiting for the flight which has been cancelled.
Some firms have done reasonably well during this time – namely the major international energy companies, a few domestic producers, and a very small percentage of the oilfield service, supply and manufacturing industry. The vast bulk of our industry, however, is still "twisting in the wind" as they attempt to cope with restructuring. Continual application of short-term remedies where more extensive measures are required still is the norm. Many are destined to commit slow suicide, a few will survive.
Although the term "restructuring" may be relatively new, our industry has been going through it for many years, even prior to 1982. Restructuring may be defined as:
General Formulation of Drillstring Under Large Deformation and Its Use in BHA Analysis
Authors: Ho H.-S. 
Published: December 2007

ABSTRACT
The paper presents the basic formulations adopted in a 3-D BHA program called DIDRILSM*, for drillstring deformation under general static downhole loadings. These formulations account for large deformation effects, and have been simplified for fast solution using the finite difference method, while retaining second order terms. An explicit formula for the bit side force is presented. In addition to previously demonstrated effects of WOB, TOB, and borehole curvatures on the bit side force, this paper demonstrates some non-linear effects on the bit side force, which increase with large deformations, mainly due to increased borehole curvatures. For 2-D borehole with less than 5°/100′ curvature, the nonlinear effects on the bit side forces are in general small. The nonlinear effects are seen to be insensitive to WOB, TOB, and hole clearance for the examples considered. Effects due to these latter variables on the local force/moment distributions may be more pronounced.
Combined Effects of Shut-in and Production: Solution with a New Inner Boundary Condition
Authors: Correa A. C. , Ramey H. J. 
Published: December 2007

ABSTRACT
A new approach was used to solve the the problem of pressure buildup following constant bottom hole pressure production. Previous methods of solution involve finite difference solution or numerical evaluation of the superposition integral. An analytical solution correct for both the flowing and shut-in periods was obtained by solving the diffusivity equation with a single inner boundary condition which included the mixed conditions for flow and buildup. Both a skin effect and wellbore storage were included even though the production period was at constant wellbore pressure. Solution was obtained by Laplace transformation.
The procedure presented in this paper may be used to solve other interesting problems. One example presented is the joint solution of constant rate production and shut-in with wellbore storage and skin effect. The procedure used does not involve superposition.
A Comparison of the Use of Pseudotime and Normalized Time for Gas Well Buildup Analysis in Various Geometries
Authors: Spivey J. P. , Lee W. J. 
Published: December 2007

ABSTRACT
The real gas flow equation is effectively linearized for drawdown when expressed in terms of pseudopressure and time. Two time functions have been proposed to linearize the flow equation for buildup: pseudotime and normalized time.
This paper compares the use of pseudotime and normalized time for a variety of different analysis techniques. The study focuses on buildup following constant rate drawdown for systems in which the reservoir is still infinite acting. For radial flow, analysis methods considered include log-log type curve matching and Horner analysis. Analysis methods for wells with infinite conductivity vertical fractures include linear flow analysis, log-log type curve matching, and Horner analysis.
Except for wellbore storage, no major difference in accuracy is found between pseudotime and normalized time.
Also compared are two different methods for treating producing time effects when using pseudo-time or normalized time. A new method of calculating the equivalent drawdown time function is presented which is independent of initial pressure.
Underground Storage in Cerville-Velaine, France: A Case History in Conversion and Inert Gas Injection as Cushion Substitute
Authors: Laille J. P. , Coulomb C. , Tek M. R. 
Published: December 2007

ABSTRACT
Whether on an aquifer or depleted field storage, the cushion gas represents a substantial, if not major, component of Investment required to develop the storage project. The economic advantage of an inert cushion which can be produced at a lower cost than pipeline quality storage gas has been recognized for sometime.
This paper presents a complete case study of a gas conversion and inert gas injection in Cerville-Velaine, an aquifer storage operated by Gaz de France. First, for 1986-87 a programmed change from low BTU to high BTU gas will be described. Then, in second stage, part of the cushion will be replaced by an inert substitute.
The engineering plans for the two equations involved numerical simulation by several different models. The degree of complexity of the simulators ranged from those corresponding to simplified, equal mobility displacements to 3-D with compressibility, miscibllity and diffusional transport through porous environment. The conditions related to mixing were characterized by using data from field tests involving hydrogen as a tracer.
Mechanism-Based Simulation of Oil Recovery Processes
Authors: Heiba A. A. , Jerauld G. R. , Davis H. T. , Scriven L. E. 
Published: December 2007

ABSTRACT
Accurately modeling recovery processes mathematically and simulating their performance numerically requires (1) a consistent theory of capillary pressures, relative permeabilities, and dispersivities that characterize the flow and distribution of fluid phases, and (2) a flexible discretization of the governing equations that resolves the moving steep fronts that often develop. Recent advances in both are combined and applied to two-phase and three-phase displacements as in cores and reservoir streamtubes. Cases exemplifying one-dimensional displacement in various water-drives and gas-drives are examined. Such simulations can be used to design and interpret laboratory measurement of flow properties and tests of process performance.
Capillary Pressure Discontinuities and End Effects in Homogeneous Composite Cores: Effect of Flow Rate and Wettability
Authors: Hinkley R. E. , Davis L. A. 
Published: December 2007

ABSTRACT
The optimum construction methodology of composite cores for multiphase flow tests is an important practical petrophysical concern. The critical feature of construction is the minimization of saturation disturbances which occur due to capillary pressure discontinuities at individual core segment interfaces. The effect of matrix discontinuities on two-phase flow in homogeneous composite cores was studied as a function of flow rate and wettability. Five composite cores, representing a range of wettabilities, were prepared. The composite cores were constructed by splicing multiple core segments with bridging materials of differing wettabilities. Saturation profile data were measured with a microwave saturation scanner during imbibition and drainage floods.
The interface between core segments had a strong effect on the saturation distributions when capillary contact was not maintained between contiguous segments. Under drainage conditions at low flow rates, each core segment behaved as though it were an independent core experiencing a strong exit end effect. In steady-state fractional flow experiments this occurred only at fractional flows close to unity. The most effective bridging materials for water-wet Berea were thin paper sheets. No bridging material was found to be completely adequate in an oil-wet environment. In the absence of good capillary contact, increasing the flow rate is a practical remedy for the saturation disturbances.
3-D Seismic Lithologic Modeling To Delineate Rapidly Changing Reservoir Facies: Case History From Alberta, Canada
Authors: Gelfand V. A. , Taylor G. , Tessman J. , Larner K. L. 
Published: December 2007

Abstract
Although river-channel reservoirs are attractive because of their potential high porosity and permeability, their development is difficult because of rapid variations in the distribution of sands and shales. The Taber-Turin area of Alberta, Canada is a known oil province characterized by such reservoirs. To delineate potential reservoirs in detail, a 4-km2 3-D seismic survey was conducted, resulting in a square grid with traces 20-m apart. The Seismic Lithologic Modeling (SLIM™) process, an automated procedure that refines initial geologic models, was then applied to provide a thin-layer interpretation of the processed data. Although the initial model for the seismic lithological modeling was based on information from only one borehole (primarily for calibration purposes), the derived velocity model revealed, in detail, the thin Glauconitic reservoirs (0-30 m thick) that are the targets of the delineation effort. All six boreholes previously drilled in the area, four of them producers and two dry, are consistent with the SLIM interpretation. With the help of the SLIM results, five additional boreholes were proposed. All of them have been completed, and all are oil producers.
Laboratory Testing of High-Pressure, High-Speed PDC Bits
Authors: Maurer W. C. , McDonald W. J. , Cohen J. H. , Neudecker J. W. , Carroll D. W. 
Published: December 2007

ABSTRACT
A high-speed drilling system has been developed which drills medium strength rocks at rates up to 1000 ft/hr (328 m/hr). This system uses special motors to operate high-pressure PDC bits at pressures up to 10,000 psi (69 MPa) and at speeds of 800 to 1000 RPM. High drilling rates were achieved due to the high rotary speeds and the use of PDC cutters to remove the rock ledges left on the hole bottom by the high-pressure jets.
Roller-Bit Penetration Rate Response as a Function of Rock Properties and Well Depth
Authors: Walker B. H. , Black A. D. , Klauber W. P. , Little T. , Khodaverdian M. 
Published: December 2007

ABSTRACT
A rate of penetration (ROP) prediction equation for an insert roller cone bit is determined from laboratory drilling tests as. a function of bit weight, well depth and laboratory measured rock properties. A complete description of each of the seven rock types used in the study is presented. A comparison of ROP at different flow rates for each rock shows minimal hydraulic cleaning problems at the base hydraulic energy levels chosen. The predictive equation will be valuable in predicting drilling rate and understanding how the rock properties affect it.
Reservoir Simulation Based on the Finite Analytic Method
Authors: Iqbal G. M. , Civan F. 
Published: December 2007

ABSTRACT
Traditionally reservoir simulation has been accomplished by solution of reservoir flow models using variations of the methods of finite differences and less frequently by finite elements. The accuracy of these methods depends heavily on the size of grid blocks and time steps employed for the numerical solution. Consequently, computational time and memory requirements may be overwhelming in many cases.
In the present study, a recently proposed method called the finite analytic method is shown to alleviate the difficulties associated with the conventional methods. The finite analytic method is operationally and principally different than the conventional finite difference and finite element methods in that a general analytical solution of the simulation model is used over mesh elements to obtain a numerical scheme. Therefore, for comparable accuracy, finite analytic method can lead to higher order approximations than those achieved by the finite difference and finite element techniques. Finite analytic schemes are derived from the reservoir flow models and therefore they are naturally problem dependent. This is the reason for the efficiency of the finite analytic method. By this method problems such as numerical diffusion, numerical instability, slow convergence, as well as requirements of large number of time steps and grid blocks are significantly reduced.
In this study, the methodology of formulating and calculating with this method is illustrated by means of a typical two-phase immiscible flow problem described by the Buckley-Leverett equation. The results are compared with the analytic solution of Buckley-Leverett problem and solutions obtained by finite difference and finite element methods. The present study demonstrates that the finite analytic method is capable of producing accurate flow behavior in porous media even when relatively large time steps and grid blocks are used.
Prediction of Static Elastic/Mechanical Properties of Consolidated and Unconsolidated Sands from Acoustic Measurements: Correlations
Authors: Montmayeur H. , Graves R. M. 
Published: December 2007

ABSTRACT
Basic measurements required for a proper static-dynamic rock properties determination were presented in a previous paper by the same authors1. Biot's theory and Walsh's microcrack analysis are combined to study static-dynamic property relations. In the absence of microcracks, Biot's relations are used to compute static "uncracked" rock properties using density, porosity, and the travel times of longitudinal and shear wave velocities. When microcracks are present, relations derived from Walsh's microcrack analysis along with Biot's relations are used to obtain the static properties from dynamic measurements.