bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonisothermal Gravitational Equilibrium Model
Authors: Pádua K. G. O.
Published: December 2007

This work presents a new computational model for the nonisothermal gravitational compositional equilibrium. The works of Bedrikovetsky [Mathemathical Theory of Oil and Gas Recovery, Kluwer Academic Publishers, London, (1993)] (gravity and temperature) and of Whitson and Belery ("Compositional Gradients in Petroleum Reservoirs," paper SPE 28000, presented at the 1994 University of Tulsa Centennal Petroleum Engineering Symposium, Tulsa, 29–31 August) (algorithm) are the basis of the mathematical formulation. Published data and previous simplified models validate the computational procedure. A large deep-water field in Campos Basin, Brazil, exemplifies the practical application of the model. The field has an unusual temperature gradient opposite to the Earth's thermal gradient. The results indicate the increase of oil segregation with temperature decrease. The application to field data suggests the reservoir could be partially connected. Fluid composition and property variation are extrapolated to different depths with its respective temperatures. The work is an example of the application of thermodynamic data to the evaluation of reservoir connectivity and fluid properties distribution.
Capillary-Pressure Curves for Low-Permeability Chalk Obtained by Nuclear Magnetic Resonance Imaging of Core-Saturation Profiles
Authors: Norgaard J. V. , Olsen Dan , Reffstrup Jan , Springer Niels
Published: December 2007

A new technique for obtaining water-oil capillary pressure curves, based on nuclear magnetic resonance (NMR) imaging of the saturation distribution in flooded cores is presented.

In this technique, a steady-state fluid saturation profile is developed by flooding the core at a constant flow rate. At the steady-state situation where the saturation distribution no longer changes, the local pressure difference between the wetting and nonwetting phases represents the capillary pressure.

The saturation profile is measured using an NMR technique and for a drainage case, the pressure in the nonwetting phase is calculated numerically. This paper presents the NMR technique and the procedure for calculating the pressure distribution in the sample.

Inhomogeneous samples produce irregular saturation profiles, which may be interpreted in terms of variation in permeability, porosity, and capillary pressure.

Capillary pressure curves for North Sea chalk obtained by the new technique show good agreement with capillary pressure curves obtained by traditional techniques.
Reservoir Polymer Gel Treatments To Improve Miscible CO2 Flood
Authors: Hild G. P. , Wackowski R. K.
Published: December 2007

This paper describes the application of large volume (10,000 bbl) chromic-acetate acrylamide polymer gel treatments to improve sweep in the miscible CO2 flood at Rangely Weber Sand Unit located in northwestern Colorado. Conformance improvement has become the key operating strategy due to the maturing flood's associated natural increase in operating expense and declining oil production. Recent efforts using large volume polymer gel treatments on injection wells have been successful. The key to success has been the pairing of accurate problem characterization with a technology that can effectively impact the deep reservoir problem. The gel system has been effective because it has proven to be resistant to the low pH environment associated with CO2 flooding and has been pumped in significant quantities to improve sweep. Previous application of relatively small volume, near-wellbore treatments were not effective at preventing flow in the high permeability matrix and fracture pathways believed to be responsible for poor sweep. Results from 44 injection well treatments performed through mid-1997 are discussed. Candidate selection, treatment logistics, individual treatment examples, and full project economics are provided. Field modeling and forecasting is discussed to show the significant impact of continued treatments on field performance.
Producing Mississippi's Deep, High-Pressure Sour Gas
Authors: Hamby T.W. , Broussard L.P.
Published: December 2007

Introduction

Shell Oil Co. has three deep, sour gas fields located about 20 miles southeast of Jackson, Miss. The wells in these fields are completed in the Smackover formation of (Jurassic age) between 19,700 and 22,250 ft; bottom-hole pressures range from 17,500 psi at the Southwest Piney Woods field. Bottom-hole temperatures range from 365 to 385F. The well fluids consists of 27 - to 16 percent H2S, 3-to 9-percent CO2, 45- to 65-percent methane, and no condensate. This gas is saturated with water at bottom-hole conditions, and each well appears to produce small amounts of salt based on the chloride content of the produced water. Water production is about 8 to 10 bbl per million cubic feet of gas. Sour gas (hydrogen sulfide) in very low aqueous concentrations can cause failure of some metals, but it can be safely contained with conventional oilfield tubulars such as C-75 and J-55 grades at moderate pressures. Likewise, high pressure (greater than pressures. Likewise, high pressure (greater than 10,000 psi) sweet gas has been safely handled with conventional P-grade tubulars. But combination of sour gas at very high pressures and temperatures cannot be safely contained with conventional tubulars; if CO2 and salt water are present the problem becomes acute. At the time of discovery of Thomasville field in 1969, sustained production of high-content H2S sour gas under conditions of very high pressure and temperature had not been proven or attempted beyond a short field test by Phillips Petroleum Co. in their Josephine "A" well in 1965. The 13,830-psi bottom-hole pressure encountered in this well was considerably below the 17,300 psi found at Thomasville. Testing of the Thomasville well revealed many technical problems that confirmed the need for high-strength tubulars resistant to stress corrosion cracking, high-pressure wellheads, environment-resistant seals, corrosion protection, and the prevention of sulfur plugging. plugging. Because of the toxicity of the produced gas, and the possibility of failure caused by stress corrosion cracking possibility of failure caused by stress corrosion cracking and weight-loss corrosion of metals, safety is the primary concern in the development of these deep, sour gas reserves. Detailed contingency plans are prepared for the entire complex and great care is taken the design, materials selection, and quality-control procedures. In preparing or executing a work plan, careful attention is preparing or executing a work plan, careful attention is given to all aspects of the operation and possible consequences are discussed in detail with all concerned, including service companies.

Well Completion Practices

20,000-psi Systems

A temporary completion was made in the Thomasville discovery well during March 1969 to permit production testing. The well tested at rates up to 10 MMcf/D of sour gas before completion-equipment failures resulted in temporary abandonment of the well.

JPT

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Characterization of Oil-Water Flow Patterns in Vertical and Deviated Wells
Authors: Flores Jose G. , Chen X. Tom , Sarica Cem , Brill James P.
Published: December 2007

An oil-water flow pattern classification and characterization for wellbores is proposed based on the integrated analysis of experimental data, including frictional pressure drop, holdup, and spatial phase distribution, acquired in a transparent test section (2-in. i.d., 51-ft long) using a refined mineral oil and water (ρo / ρw = 0.85,μ o /μw 20.0, and σo-w = 33.5dyn/cm at 90°F). The tests covered inclination angles of 90°, 75°, 60°, and 45° from horizontal.

The oil-water flow patterns have been classified into two major categories given by the status of the continuous phase, including water-dominated flow patterns and oil-dominated flow patterns. It was found that most water-dominated flow patterns show signifi- cant slippage but relatively low frictional pressure gradients. In contrast, all the oil-dominated flow patterns exhibit negligible slippage but significantly larger frictional pressure gradients. Six flow patterns have been characterized in upward vertical flow; three were water dominated and three were oil dominated. In upward inclined flow there were four water-dominated flow patterns, two oil-dominated flow patterns and a transitional flow pattern. Flow-pattern maps for each of the tested inclination angles are presented. A mechanistic model to predict flow-pattern transitions in vertical wells is proposed. The transitions to the very-fine- dispersed flow patterns were evaluated by combining the concepts of turbulent kinetic energy with the surface free energy of the droplets, while the transitions to the churn flow pattern and the phase inversion were predicted based on the concept of agglomeration. The model compares favorably with the measured data.
Polymer Gel Dehydration During Extrusion Through Fractures
Authors: Seright R. S.
Published: December 2007

Some of the most successful water shutoff treatments in fractured reservoirs used relatively large volumes of Cr(III)-acetate-HPAM gel that extruded through fractures during the gel placement process. The gel can dehydrate during extrusion, and consequently, propagate at an unexpectedly low rate if the fracture conductivity or width is sufficiently small. This paper characterizes the dehydration phenomenon and its relation to gel extrusion. The findings are relevant to gel placement during field applications.
Impact of Perforations on Hydraulic Fracture Tortuosity
Authors: van Ketterij R. B. , de Pater C. J.
Published: December 2007

We performed scaled model tests to study the relation between completion and treatment parameters and the near wellbore geometry for highly deviated, cased perforated wellbores. We have instrumented our casings to observe the moment fluid flow around the casing causes a signi®cant increase in the amount of pressure acting on the wall of the borehole. When fluid flow around the casing occurs extensively before fracture initiation, this leads effectively to an open hole situation at the moment of initiation. Otherwise the perforations will be the only possible initiation sites. In our experiments with a perforation phasing of 90° the perforations on top of the borehole acted in most cases as initiation sites. We performed stress calculations with a simple analytical model to understand the influence of the perforation angle on initiation pressure and fracture propagation.
Physical Properties of Carbonated Oils
Authors: Welker J.R.
Published: December 2007

The growing interest in the use of CO2 in crude oil recovery increases the need for data on the effect of CO2 on hydrocarbon physical properties. Data are presented on the solubility of CO2 in various dead oils, the swelling changes in CO2 -oil solutions and the effect of CO2 on dead oil viscosity. This later property shows the most pronounced effect, with viscosity reductions up to 98 per cent of the uncarbonated viscosities. An empirical method of estimating the viscosity of carbonated oils is presented. The apparatus and procedures used are described in sufficient detail to allow others to make similar studies.

Introduction

The effect of dissolved carbon dioxide on the swelling and viscosity reduction of specific hydrocarbon oils has been observed and recorded by a number of investigators. The object of this paper is to offer a means of predicting these effects for crude oils free from natural gas, using the dead state viscosity and gravity of the crude oils. The CO. solubility and swelling of numerous crude oils were determined in a visual cell at various pressure levels. The viscosity of the oils carbonated to various pressure levels was then determined by measuring the pressure drop across a capillary tube. From these data, the physical properties were correlated empirically. The resulting correlations allow the prediction of CO solubility, swelling and viscosity reduction if the dead state gravity and viscosity of the oils are known.
Adaptive Compensation of the Mud Pump Noise in a Measurement-While-Drilling System
Authors: Brandon T. L. , Mintchev M. P. , Tabler Herb
Published: December 2007

Mud pulse telemetry is one of the promising methods for transmission of valuable downhole information in measurement-while-drilling (MWD) processes. Quality, speed, and reliability of mud pulse telemetry are, however, drastically jeopardized by various powerful noise contributors. Among these the mud pump noise could be the most damaging artifact for the mud pulse information signal. The real-time monitoring requirement and the variable dynamic frequency characteristics of the mud pulse signals make the utilization of traditional noise filtering techniques very difficult if not impossible. In this study, two new methods for real-time adaptive compensation in the specific noise environment of MWD are suggested. The methods are designed and tested assuming the worst case scenario of about 50% of the information signal present in the reference channel. Successful real-time compensation in such harsh noise environments is reported.
Water Injection in Water-Wet Fractured Porous Media: Experiments and a New Model with Modified Buckley–Leverett Theory
Authors: Terez Ivan E. , Firoozabadi Abbas
Published: December 2007

This study examines water injection in water-wet fractured porous media and its modeling using the Buckley–Leverett theory. New experimental data on water injection in Berea and Austin chalk matrix block(s) are presented. Water injection in Austin chalk with a permeability of 0.01–0.04 md and porosity of 5% results in about 20% recovery from the rock matrix.

In the second part of the paper, we use the Buckley–Leverett displacement in a dual-porosity model to simulate the literature data as well as experimental data from this work. A new model is devised for the simulation of water injection in fractured porous media. A major element of the new model is the multiplication of the transfer flux by the fracture saturation with a power of 1/2. This simple model can account for both cocurrent and countercurrent imbibition and computationally it is very efficient. The results of the proposed model and the fine-grid simulation are in good agreement with the experimental data.
Conditioning Geostatistical Models to Two-Phase Production Data
Authors: Wu Zhan , Reynolds A. C. , Oliver D. S.
Published: December 2007

A discrete adjoint method for generating sensitivity coefficients related to two-phase flow production data is derived. The procedure is applied to calculate the sensitivity of wellbore pressure and water-oil ratio to reservoir simulator gridblock permeabilities and porosities. Using these sensitivity coefficients, an efficient form of the Gauss-Newton algorithm is applied to generate maximum a posteriori estimates and realizations of the rock property fields conditioned to a prior geostatistical model and pressure and/or water-oil ratio data obtained under two-phase (oil and water) flow conditions.
Designing Under- and Near-Balanced Coiled-Tubing Drilling by Use of Computer Simulations
Authors: Gu Hongren , Walton I. C. , Stein D. A.
Published: December 2007

This paper describes the use of two computer simulation utilities to design underbalanced or near-balanced coiled tubing drilling: one is a steady-state design module and the other is a transient wellbore simulator developed for coiled-tubing operations. The steady-state design module provides various design parameters for a drilling operation, and the transient wellbore simulator predicts the outcome from a particular design for the entire operation. Simulation results show the desired under or near balance can only be achieved by certain combinations of liquid and gas rates when using foam as the drilling fluid or using gas injection through gas-lift mandrel or parasite string. The effects of cuttings loading, depth of injection point and reservoir inflow on the downhole pressure or underbalance are presented and discussed. A procedure for designing under- or near-balanced drilling is described and demonstrated with an example using the computer utilities. A field example is used to show the accuracy of the simulator by comparing the measured and simulated downhole pressures.
An Overview of Air/Gas/Foam Drilling in Brazil
Authors: Negrão A. F. , Lage A. C. V. M. , Cunha J. C.
Published: December 2007

Air, gas, and foam drilling has been used in specific areas in Brazil as an alternative to the traditional drilling process. This work focuses on the benefits and operational improvements obtained with those two-phase flow drilling operations. The comparison between the performance of conventional and two-phase flow drilling has been showing that this technique, when appropriately used, presents some advantages: (1) minimum or no damage to sensitive pay zones, (2) immediate and continuous evaluation of cuttings for hydrocarbon shows, (3) avoidance of lost circulation, and (4) higher penetration rates in hard formations. This work shows recent on-shore two-phase flow drilling field cases in Brazil using both, jointed pipe and coiled tubing techniques. The results obtained in those wells are analyzed and also the surface equipment design, the appropriate technique for connections, as well as the comparison between field data and predictions from simulators are discussed. Future plans for two-phase flow drilling operations in Brazil are also commented. Additionally, potential areas and concrete actions for improving operational feasibility of this technology are identified. The target is a safer and more economical air, gas, or foam drilling operation.
Optimum Conditions for Wormhole Formation in Carbonate Porous Media: Influence of Transport and Reaction
Authors: Fredd C. N. , Fogler H. S.
Published: December 2007

The effects of transport and reaction on the phenomenon of worm-hole formation were investigated for a wide range of fluid systems including strong acids, weak acids, and chelating agents. These fluid systems are influenced by a variety of transport and reaction processes such as the transport of reactants to the surface, the reversible surface reactions, and the transport of products away from the surface. When these transport and reaction processes are taken into account, a common dependence of the dissolution phenomenon on the Damköhler number is observed. There exists an optimum Damkohler number at which a minimum number of pore volumes are required for channel breakthrough. This optimum Damkohler number occurs at approximately 0.29 for all the fluid/ mineral systems investigated in this study. In addition, an optimum kinetic parameter exists at which wormhole formation is most efficient. This optimum kinetic parameter occurs at a value of about 130. Together, the Damkohler number and the kinetic parameter provide a complete description of the dissolution phenomenon.
Effect of Perforation Density on Single-Phase Liquid Flow Behavior in Horizontal Wells
Authors: Yuan H. J. , Sarica Cem , Brill J. P.
Published: December 2007

A general horizontal well friction factor expression was developed using the principles of conservation of mass and momentum. Horizontal well friction factor correlations were developed based on theoretical analysis and a large amount of experimental data. It was observed that the friction factor for a perforated pipe with fluid injection can be either smaller or greater than that for a smooth pipe, depending on influx to main flow rate ratios. The proposed friction factor correlation can be used in any horizontal well model that considers pressure variation along the wellbore.
From Seismic to Reservoir Properties With Geostatistical Inversion
Authors: Lamy Philippe , Swaby P. A. , Rowbotham P. S. , Dubrule Olivier , Haas A.
Published: December 2007

The methodology presented in this paper incorporates seismic data, geological knowledge and well logs to produce models of reservoir parameters and uncertainties associated with them. A three-dimensional (3D) seismic dataset is inverted within a geological and stratigraphic model using the geostatistical inversion technique. Several reservoir-scale acoustic impedance blocks are obtained and quantification of uncertainty is determined by computing statistics on these 3D blocks. Combining these statistics with the kriging of the reservoir parameter well logs allows the transformation of impedances into reservoir parameters. This combination is similar to performing a collocated cokriging of the acoustic impedances.
How Much Core-Sample Variance Should a Well-Log Model Reproduce?
Authors: Jennings J. W.
Published: December 2007

A new log-calibration technique presented in this paper determines how much core-sample variance should be reproduced by a calibrated log. The linear calibration parameters are then calculated from this variance and the log and core-sample means. The method relies on the idea that the correlation structure of core data and a calibrated log should be the same for distances longer than the log resolution, after the variance reduction due to log averaging is accounted for. The procedure is illustrated by using synthetic data, followed by example applications that use real data.
Translating Outcrop Data to Flow Models, With Applications to the Ferron Sandstone
Authors: White C. D. , Barton M. D.
Published: December 2007

Quantitative models are needed to predict interactions between rock properties and drive mechanisms in geologically complex reservoirs. Analog studies using outcrop data provide insights for modeling, understanding, and predicting the behavior of oil and gas reservoirs. Stratigraphic cornerpoint grids preserve the geometries and facies distributions of outcrop data sets. Flow simulations of two outcrop exposures of sandstone-rich fluvial-deltaic tongues within the Cretaceous Age Ferron sandstone (Utah) revealed differences in fractional flow, recovery efficiency, and deliverability that can be related to stratigraphic setting. Compared with homogeneous models, models based on the landward-stepping tongue exposed at the Picture Flats locality had more tortuous flow paths and lower gas recovery efficiency. In the seaward-stepping tongue exposed at the Interstate 70 location, the displacement was layer like. Gas deliverability at the Interstate 70 locality varied with the well location; it was highest when the well penetrated high-permeability shallow-marine sediments and lowest when flow was restricted by a shale-lined valley-fill succession.
Microseismic Monitoring of the B-Sand Hydraulic-Fracture Experiment at the DOE/GRI Multisite Project
Authors: Warpinski N. R. , Wright T. B. , Uhl J. E. , Engler B. P. , Drozda P. M. , Peterson R. E. , Branagan P. T.
Published: December 2007

Six hydraulic-fracture injections into a fluvial sandstone at a depth of 4,500 ft were monitored with multilevel, triaxial, seismic receivers in two wells, resulting in maps of the growth and final geometry of each fracture based upon microseismic activity. These diagnostic images show that the hydraulic fractures are highly contained for smaller-volume KCl-water injections, but height growth is significant for the larger-volume, higher-rate, higher-viscosity treatments. Fracture lengths for most injections are similar regardless of volume and fluid type.
Effect of Wettability on Adverse-Mobility Immiscible Floods
Authors: Vives M. T. , Chang Y.-C. , Mohanty K. K.
Published: December 2007

Many immiscible displacements in reservoirs occur at adverse mobility. The effect of wettability on these displacements is not well understood and often ignored in reservoir simulation. Recent macroscopic theories of viscous fingering treat adverse immiscible flows similar to miscible flows, the mixing in the fingered region being controlled by a Todd-Longstaff-type functional form. The wettability of the medium is taken into account only through the use of appropriate relative permeabilities. The goal of this paper is to understand the macroscopic bypassing in adverse mobility immiscible floods. Immiscible displacements are conducted in a quarter five-spot model in both drainage and imbibition modes at similar effective mobility ratios and viscous-to-gravity numbers. The level of bypassing and gravity override is visualized and measured. Tertiary water-alternating-gas (WAG) displacements are also conducted at various WAG and viscosity ratios. Fractional flow analysis and numerical simulation are used to understand these displacements.

Experiments show that macroscopic viscous fingering is present in adverse viscosity immiscible displacements where no or a small saturation shock is expected from one-dimensional fractional flow theory. Bypassing attributed to both fingering and gravity override is higher in the drainage mode than in the imbibition mode, with other key parameters being the same. Optimum WAG ratio in water-wet rock is a function of oil/solvent viscosity ratio. The macroscopic flow theory needs to include capillarity and viscous fingering to match these experimental findings.
Use of Pore-Network Models to Simulate Laboratory Corefloods in a Heterogeneous Carbonate Sample
Authors: Xu Baomin , Kamath Jairam , Yortsos Y. C. , Lee S. H.
Published: December 2007

Many carbonate rocks have pore features that are large at the core plug scale. Conventional laboratory assessment of recovery behavior in these carbonates can be unreliable. Pore-network modeling offers an approach to improve our analysis of flow and displacement in such heterogeneous rocks. This paper reports on a systematic approach to link pore model inputs and laboratory data to a calibration methodology, and the subsequent use of a porenetwork model to match laboratory corefloods in a heterogeneous dolomite. It is found that spatial correlation effects, determined from core samples using thin section and computed tomography (CT) data, are important for a satisfactory match.
New Environmentally Safe High-Temperature Water-Based Drilling-Fluid System
Authors: Thaemlitz C. J. , Patel A. D. , Coffin George , Conn Lee
Published: December 2007

A new, environmentally safe water-based polymer system has been developed for drilling applications with temperatures up to 232°C (450°F) and high pressures. The system components are newly developed synthetic polymers that do not contain chromium or other environmentally harmful materials. These new synthetic polymers are designed to perform specific functions at high temperatures and the innovative designs of these thermally stable polymers allow for the use of a minimum number of products in the formulation of high-temperature fluids.

The new system consists of two basic polymeric components for rheology and filtration control at high temperatures. High- temperature fluid formulations are greatly simplified utilizing this new system, with only the two polymeric components being required, along with a pH control additive, weight material, and small amounts of clay for filler cake quality. This simplicity is a significant advantage over "traditional" high-temperature systems, which normally require the use of a large number of additives to control or limit the effects of thermal degradation.

The new system may be formulated with fresh water or sea water, providing flexibility for a variety of drilling environments. Excellent resistance to common contaminants, such as calcium and magnesium hardness and solids accumulation, is another important characteristic of this new system.

This paper will review the previous state of the art with respect to high-temperature, water-based muds and will generically discuss the unique chemistry of the newly developed polymer system components. System formulation and application will be discussed.
State-of-the-Art Cuttings Transport in Horizontal Wellbores
Authors: Pilehvari A. A. , Azar J. J. , Shirazi S. A.
Published: December 2007

In the ever-growing use of, directional and horizontal drilling, hole cleaning is a common and costly problem. It can become particularly critical in the case of extended reach drilling where larger and longer wellbores are drilled. During the past two decades, especially in recent years, many laboratory studies as well as field observations have been directed towards addressing the cuttings transport problem. This has resulted in better understanding of the subject and some remedies to the problems. Several correlation/models have also been developed that give the field engineer a tool to better specify the hydraulic requirements in cleaning the hole. However, because of the complexity of the subject, a comprehensive and proven model, which does not exist at this time, requires much more laboratory research and field studies.
Proactive Approach to Well Construction Safety in Alaska's Kuparuk River Field
Authors: Petrash D. K. , Graff A. O. , Trantham J. A.
Published: December 2007

In 1995, the Kuparuk Drilling Group (KDG) recognized that safety performance had continually improved since well construction commenced in the Kuparuk River Field in 1981. However, it was also recognized that performance improvement appeared to be losing momentum. Upon analysis of the trend, it was noted that most efforts to reduce workplace risk were focused on: engineering controls; administrative controls and operating practices; and personal protective equipment.

In order to return to improving safety performance, attain world class status, and help employees return safely from the workplace to their families, the KDG solicited input from the drilling contractor to develop and implement a proactive behavior-based safety program. Part of the development included a goal-driven incentive, the Safety Performance Goals Program, which deem-phasizes safety statistics and fully complements the overall safety objectives.
Uncertainties in Reservoir Fluid Description for Reservoir Modeling
Authors: Meisingset K. K.
Published: December 2007

The objective of the present paper is to communicate the basic knowledge needed for estimating the uncertainty in reservoir fluid parameters for prospects, discoveries, and producing oil and gas/condensate fields. Uncertainties associated with laboratory analysis, fluid sampling, process description, and variations over the reservoirs are discussed, based on experience from the North Sea.
Calibration Measurements of Dielectric Properties of Porous Media
Authors: Nguyen Buu-Long , Geels A. M. , Bruining Johannes , Slob E. C.
Published: December 2007

We present a specially designed experimental setup for accurate measurements of the frequency-dependent relative complex dielectric permittivity (RCDP) in porous media. The setup operates on the principles of steady-state flooding and time-domain reflectometry (TDR). The steady-state flooding technique allows for a well-controlled uniform saturation distribution in the sample. The TDR technique enables on-line measurement of the dielectric response. We derive the equations for the propagation and reflection of an electromagnetic (EM) signal along a coaxial transmission line consisting of a standard coaxial cable, a transition unit, and the sample holder. The RCDP at different oil saturations are calculated by means of frequency analysis of the scattered signal.

We present the RCDP obtained from experiments in sand samples at different saturations. We compare the obtained results with those calculated with a number of existing mixing models, including the complex refractive index (CRI) model and the classical Rayleigh formula.

The experimental method has proved to be suitable for on-line measurement of dielectric properties of porous media with varying fluid saturation. It turns out that a small saturation difference can be discerned in the measurements. We have found that the RCDP calculated with the CRI model (refractive index exponent α = 0.75) show the best agreement with those obtained from the experiments.
Foam Propagation on Semi-Reservoir Scale
Authors: Vassenden Frode , Holt Torleif , Ghaderi Amir , Solheim Arild
Published: December 2007

Foam propagation in co-injection of gas and surfactant solution has been studied in a 10-m-long flow apparatus, equipped with pressure ports and fluid sampling valves for every 1 m. The data have been compared to the results of a core scale foam flooding experiment with the same porous medium.

The propagation experiments on the 10 m scale revealed that the foam front propagated significantly slower than the injected fluid front. It appeared that foam propagation was not limited by surfactant transport, but was delayed due to the presence of oil in the porous medium. The experiments have been interpreted with the aid of a numerical foam simulator.
Prediction of Waterflood Behavior in a Stratified System
Authors: Warren J.E.
Published: December 2007

A general model which approximates the effect of cross-flow has been developed to give a practical method for predicting the water flood behavior of a stratified reservoir. The model is based on a modification of Dietz's theory and allows for variations in both the permeability and hydrocarbon pore volume.in the particular cases considered, it is assumed that the permeability can be characterized by a log- normal distribution and the hydrocarbon pore volume by a normal distribution. A simple graphical method which enables the practicing engineer to predict the behavior of a stratified system is presented The results obtained by the proposed method are compared with those obtained by the Dykstra-Parsons method As a result of this study the following conclusions have been drawn:

- The effect of cross-flow in a stratified system can be appreciable, particularly at very favorable or very unfavorable mobility ratios;

- Under normal conditions, the effect of variations in the hydrocarbon pore volume can be neglected; and

- The failure to use all of the available permeability data can lead to large errors in the prediction of the behavior of a stratified reservoir.

Introduction

Various methods have been proposed to characterize and to predict the waterflood behavior of a stratified reservoir. Most of the methods assume that the reservoir is composed of discrete homogeneous continuous layers. With this model, the degree of stratification can be measured by several parameters based on core-analysis data. Among these are the Lorenz coefficient and the variation of a log-normal permeability distribution. The behavior of stratified systems is usually predicted by the Stiles, Dykstra-Parsons method or some modification of these. In both of these methods the reservoir is divided into discrete homogeneous layers with no cross-flow between layers. In the Stiles method the mobility ratio is assumed to be equal to unity while in the Dykstra-Parsons method it is allowed to take on any value. Other predictive methods have been proposed; Hiatt's method allows for cross-flow between the beds and a method by Schmalz and Rahme correlates the recovery directly with the Lorenz coefficient. In this new approach, which is essentially a continuous analog of Hiatt's method, the effects of both mobility ratio and cross-flow between the beds have been included. It is assumed that the permeability can be represented by a log-normal distribution and the hydrocarbon pore volume or porosity by a normal distribution. These types of distributions have been observed by several authors, and most field data seem to confirm their observations; e.g., if these distributions are assumed and there is a 1:1 correspondence between porosity and permeability samples, the commonly encountered linear relationship between porosity and the log of permeability is obtained.
The Use of Air-Mist for Well Cleanout and Deepening
Authors: Holder Louis E.
Published: December 2007

A method of cleaning out and deepening using air-mist as the circulating fluid and with specially rigged portable rotary drilling tools has been found to be ideally suited for use in fields having low reservoir pressure. Three typical examples from the West Texas-New Mexico Permian Basin are cited. One is the Permian Sand fields of Ward and Winkler County, Texas, and Lea County, New Mexico. Another is the San Andres dolomite fields of Ector, Andrews, Hockley and Terry Countries, Texas, and the third is the Spraberry area trend of Midland, Upton and Reagan Countries, Texas.

The Use of Air-Mist For Well Cleanout and Deepening

As production rates begin to decline in fields which have been producing for a number of years, engineers and management begin searching for ways to restore the productive capacity, either through workover operations or by means of pressure maintenance or secondary recovery projects. Several factors should be considered in deciding the best method to be employed in work-over and/or reconditioning operations. First, an operation which should give the desired result must be selected, with care being exercised to assure no damage to the reservoir could result from the method to be used. Second, the cost of this operation, considering not only the initial outlay, but also loss of revenue during the workover period and the resulting payout, must justify authorizing the work. The use of air-mist as a circulating medium for cleanout and deepening operations has been found to be most satisfactory, having a number of advantages over the conventional reverse circulation, or cable tools for this type work.

Equipment and Processes Used

The equipment for air-mist clean-out and deepening is specialized. To reduce the moving costs to a minimum, a trailer mounted rig is used. For deeper work a conventional rotary table is required; however, for shallow cleanout and deepening, a Guiberson rotating head permits the use of a working platform. This further reduces the moving time and cost by eliminating the need for a substructure. These two types of rigs are shown in Figs. 1 through 4.

A rotating blowout preventer in addition to a conventional double gate type is required for air-mist circulation as shown in Fig. 5, and a discharge or "blooie" line, preferably of at least 7 in. diameter, fitted with quick break type connections is used to handle the return samples and spent air. If the cleanout or deepening operation is being performed in an area where surface damage would result from an unrestricted blowing of the returned fluid and air, a mist arrester can be attached to the end of the "blooie" line to kill any spray before discharging the returns into a pit. This mist arrester is shown in Fig. 6.Air compressor equipment capable of delivering from 1.5 to 2.5 MMcf/D at pressures ranging from 1,200 to 1,500 psi are required.
Streamline Approach for History Matching Production Data
Authors: Wang Y. , Kovscek A. R.
Published: December 2007

In this study, we propose and develop a streamline approach for inferring field-scale effective permeability distributions based on dynamic production data including producer water-cut curve, well pressures, and rates. The streamline-based inverse approach simplifies the history-matching process significantly. The basic idea is to relate the water-cut curve at a producer to the water breakthrough of individual streamlines. By adjusting the effective permeability along streamlines, the breakthrough time of each streamline that reproduces the reference producer fractional-flow curve is found. Then the permeability modification along each streamline is mapped onto cells of the simulation grid. Modifying effective permeability at the streamline level greatly reduces the size of the inverse problem compared to modifications at the grid block level. The approach outlined here is relatively direct and rapid. Limitations include that the forward flow problem must be solvable with streamlines, streamline locations do not evolve radically during displacement, no new wells are included, and relatively noise-free production data are available. It works well for reservoirs where heterogeneity determines flow patterns. Example cases illustrate computational efficiency, generality, and robustness of the proposed procedure. Advantages and limitations of this work, and the scope of future study, are also discussed.
High Volume Pumping in the Rangely Weber Sand Unit
Authors: Allen D.D.
Published: December 2007

A review of high volume pumping operations in the Rangely Weber Sand Unit is presented in this paper. The pumping problems encountered and methods used to combat them are discussed. High volume pumping is utilized on both oil producing and water source wells. Pumping problems resulted from free gas interference and pounding, plus corrosive and scale forming well fluids. Submersible as well as large capacity rod pumps are operating at depths of 6,500 ft. High volume pumping is economically successful.

Introduction

High volume pumping in the Rangely Weber Sand Unit consists of electrically driven submersible pumps and rod pumping units with a stroke length of 100 in. or greater. High volume pumping is utilized in oil producing wells and water source wells. At the end of 1962 there were 73 long-stroke rod pumping units and nine electrically driven submersible pumps in operation in oil producing wells. The water source wells included 10 electrically driven submersible pumps and one shaft driven submersible pump. The Weber wells flowed on initial completion. As the reservoir pressure declined, conventional 64-in. stroke rod pumping units were installed. The wells were pumped through the tubing and flowed on the casing-tubing annulus. When the wells would no longer flow on the annulus they still contained much more potential than could be produced with the conventional units. At this time installation of the 100- to 120-in. units began. Subsequent water flooding increased well potentials, and the 192-in. rod pumping units and electrically driven submersible pumps were installed.

Field History

The Rangely Weber reservoir was discovered in March, 1933, by the California Oil Co. Development of the field was not started until Oct., 1943, and continued through May, 1949.The reservoir structure is an asymmetrical anticline. The field is approximately 12 miles long and 5 miles wide. The Weber sand contains interbedded shale that increases with depth. The Weber is 1,200 ft thick. Only the upper 700 ft is considered oil productive. There was a small original gas cap. The top of the Weber at the crest is –205 ft subsea. The original gas-oil contract was at –330 ft subsea and the water-oil contact at –1150 ft subsea. Surface elevations range from 5,200 ft to 5,700 ft which result in pumping depths to 6,700 ft. The wells have 7-in. casing set to the top of the Weber or gas-oil contact, and then have an open hole completion to the oil-water contact, or to 700 ft of Weber penetration. Approximately one-half of the wells have been shot. Nearly all the wells have been sand-oil fractured. There is a gas injection program that dates back to Nov., 1950. Gas injection has been dispersed over the field rather than all into the gas cap. The field was unitized on Oct. 1, 1957, with the California Oil Co. its operator. A waterflooding program was initiated in Jan., 1958, utilizing water from the Navajo and Entrada formations.
Asphaltene Deposition During CO2 Flooding
Authors: Srivastava R. K. , Huang S. S. , Dong Mingzhe
Published: December 2007

In this article we present results of dynamic and static precipitation tests to investigate the likelihood of asphaltene deposition problems in southeast Saskatchewan's Weyburn reservoir. Tests were conducted at the reservoir temperature and pressure conditions. The effect on asphaltene flocculation/precipitation of the operating pressure, CO2 concentration, gas contaminants in CO2, and presence of formation brine was investigated for three different oil samples using static pressure/volume/temperature (PVT) tests. The extent of asphaltene deposition was also assessed through coreflood experiments and through an x-ray computer- aided tomograph (CAT)-scanning visualization experiment.

Static tests indicated the most important factor on which the asphaltene precipitation depended was the CO2 concentration. For oils belonging to the same pool, the increase in asphaltene precipitation with solvent concentration was proportional to the initial asphaltene contents of the oil. Coreflood experiments showed a considerable increase in asphaltene deposition in the core matrix following CO2 injection. Pore topography of the core matrix played an important role in the extent of CO2-induced asphaltene deposition. X-ray CAT-scanning tests depicted localized areas of asphaltene deposition along the length ofthe core, with significant deposition suspected to be occurring near the inlet of the core.
Post-Frac Analyses Indicating Multiple Fractures Created in a Volcanic Formation
Authors: Sato Kozo , Wright C. A. , Ichikawa Makoto
Published: December 2007

The technology of hydraulic fracturing is faced with a conceptual transition from a classical single-planar fracture to a tortuous fracture network and simultaneously propagated multiple hydraulic fractures. This new concept is applied to analyses of two propped fracture treatments conducted in a volcanic formation. In both cases, the productivity was doubled, but the treatments themselves were unsuccessful, experiencing extremely high net fracturing pressures and very premature screenouts.

The classical concept of a single-planar fracture could not explain either the fracturing-pressure behavior or the post-frac production rate/pressure. Adopting a multiple-fracture geometry resolves this problem. The fracturing pressures are successfully simulated, and the resultant fracture geometries are consistent with both the premature screenouts and the post-frac production performances. Combined analyses of fracturing pressure and subsequent production performances confirm the creation of multiple fractures in a volcanic formation.
A Semianalytical Approach for Productivity Evaluation of Complex Wells in Multilayered Reservoirs
Authors: Basquet Rémy , Caltagirone J. P. , Alabert F. G. , Batsalle J. C.
Published: December 2007

We present a new approach to solve the problem of complex wells located in layered reservoirs with crossflow. First, the well path is discretized into a carefully chosen series of source points. Second, pressure solution for each source point is obtained in the Laplace domain anywhere in a rectangular reservoir, where crossflow is permitted between layers and with possibly mixed boundary conditions (no-flow or constant pressure). We used the Fourier transforms in the space variables after removing the time variable by the Laplace transformation. The problem is reduced to a matrix product to solve in the transformed domain.

The above method is validated through comparisons with known line source solutions and numerical simulations. It can be used to compute the pressure distribution within a well with complex geometry in a stratified bounded reservoir under the assumption of infinite well conductivity. The well can be located anywhere in the reservoir. Boundaries can be no-flow or constant pressure. Last, variable skins along the well path can be imposed.

An application on a field located in the deep offshore of the Gulf of Guinea demonstrates the great value for well design optimization in the context of complex heterogeneous reservoirs where classical analytical approaches are typically inappropriate.