bluuebunny/crossref_metadata_2025 huggingface dataset:
Geology, Geometry, and Effective Flow
Authors: Pickup G. E. , Ringrose P. S. , Corbett P. W. M. , Jensen J. L. , Sorbie K. S.
Published: December 2007

The effects of small-scale structure are frequently ignored in reservoir simulation, although they may have a significant effect on hydrocarbon recovery. Many sandstones exhibit lamination, and in such rock structures, permeability may vary by an order of magnitude over distances of a centimetre or less. Frequently, the laminae are inclined with respect to the pressure gradient, which gives rise to crossflow within the unit. In this case a tensor may be used to represent the effective permeability of the bed.

In this paper the effect of small-scale geological structure on single phase flow is investigated using a model of a crossbedded unit to determine which factors have the greatest effect on crossflow. In addition, a range of other types of bedding are considered, including models with stochastic variation. We have found that, in general, the geometry of the sedimentary structure has a significant effect on flow. The crossflow is greater (and therefore tensors are more likely to be necessary) when the angle of the laminae is large relative to the pressure gradient (up to 45°), when the permeability contrast between laminae is large, or when the structure is asymmetric.
Production Applications of Reservoir Geochemistry: A Current and Long-Term View
Authors: Larter S. R. , Aplin A. C.
Published: December 2007

We describe two facets of reservoir geochemistry: (1) reservoir fluids (oil, water and gas) are often compositionally heterogeneous and can give insights into reservoir continuity early in field development; (2) interactions between non-hydrocarbons, water and rock minerals, suggesting the key role that non-hydrocarbons play in influencing wettability, plus the viscosity and PVT properties of reservoired petroleum.
Bayesian Sequential Indicator Simulation of Channel Sands From 3-D Seismic Data in The Oseberg Field, Norwegian North Sea
Authors: Doyen P. M. , Psaila D. E. , Strandenes S.
Published: December 2007

Subsurface models of lithology are often poorly constrained due to the lack of dense well control. Although limited in vertical resolution, high quality 3-D seismic data usually provide valuable information regarding the lateral variations of lithology. The Bayesian Sequential Indicator SIMulation (BSISIM) technique is a new stochastic method to generate seismically constrained models of lithology. Unlike cokriging-based simulation methods, BSISIM does not rely on a generalized linear regression model, which is inadequate when combining lithology indicator variables and continuous seismic attributes. Instead, BSISIM uses a Bayesian updating rule to construct a posterior probability distribution of lithoclasses at each location. The posterior distribution combines a local prior distribution obtained by indicator kriging with a function representing the seismic likelihood of the different lithofacies. The local posterior distributions are sampled sequentially at all points in space to generate realizations from the joint posterior distribution. The realizations define alternative, equiprobable lithologic models, representing a compromise between fidelity to the seismic data, as measured by the likelihood functions, and consistency with spatial continuity information, as expressed by the lithology indicator correlation functions. The simulation technique is applied to predict the lateral distribution of channel sands in the Ness Formation of the Oseberg Field. Channel sand maps are simulated using lithologic observations in fourteen wells, and seismic amplitude and channel orientation data extracted from a 3-D survey. Sand probability maps, generated by summarizing a large number of simulations, allow delineation of the probable lateral extent of the channel deposits. Comparison of seismically derived lithologic models to well-derived models demonstrates the improved definition of channel geometry achieved by integrating the geophysical information.
Integrated Reservoir Characterization: Beyond Tomography
Authors: Lines Larry , Tan Henry , Treitel Sven , Beck John , Chambers Rich , Eager John , Savage Charles , Queen John , Rizer William , Buller Paul , Cox Dale , Ballard James , Kokkoros George , Sinton John , Track Antoine , Guerendel Philippe , Harris Jerry , Lazaratos Spyros , Van Schaak Mark
Published: December 2007

In 1992, there was a collaborative effort in reservoir geophysics involving Amoco, Conoco, Schlumberger and Stanford University in an attempt to delineate variations in reservoir properties of the Grayburg unit in a West Texas Co2 pilot at North Cowden field. Our objective was to go beyond traveltime tomography in characterizing reservoir heterogeneity and flow anisotropy. This effort involved a comprehensive set of measurements to do traveltime tomography, reflector imaging, analysis of channel waves, shear wave splitting for borehole stress estimation, seismic anisotropy, combined with 3D surface seismic and sonic log interpretation. Results are to be validated with cores and engineering data by history matching of primary, water and CO2 injection performance. The implementation of these procedures should provide critical information on reservoir heterogeneities and preferential flow directions.
Transient Pressure Behaviour of Selectively Completed Horizontal Wells
Authors: Yildiz Turhan , Özkan Erdol
Published: December 2007

This paper investigates the transient pressure behavior of selectively completed horizontal wells. A new solution in Laplace space is presented and asymptotic approximations are derived. Computational issues are also addressed. Flow characteristics of sectionally completed horizontal wells are discussed and the information that can be obtained from the analysis of pressure and derivative responses during various flow regimes are documented. It is shown that the solutions existing in the literature cannot completely describe the essential features of flow toward a sectionally completed horizontal well.
Static Modeling at Prudhoe Bay - Integrating Reservoir Characterization and Reservoir Performance
Authors: Wilson A. P. , Severson C. D.
Published: December 2007

Static modeling of the Sadierochit reservoir is proving to be an integral tool in depletion planning and reservoir management at Prudhoe Bay. A versatile engineering tool has been developed by integrating geological descriptions of the reservoir and field performance data. This paper details a novel methodology used to build 3-D models of field-wide fluid distributions within a relational software application.

Seismic and geological layering information is manipulated to form a 3-D cell lattice, or static model, of the reservoir. Petrophysical properties are calculated externally from well logs, averaged by zone, and interpolated into each cell within the geological layer. These properties plus volumetrics are stored by cell within the relational database framework of the application. Yearly fluid distributions at the well level are generated from a field- wide surveillance program. These well-level fluids are distributed within the Static Model layers and fluid phase volumes are calculated by cell. Examples of applying these models to reservoir management decisions are discussed. At Prudhoe Bay, static models assist in visualizing reservoir structure, rock properties and fluid distribution, calculating phase volumes, aquifer modeling, and history matching simulators.
Interpretation of Wireline Formation Tester Packer and Probe Pressures
Authors: Kuchuk F. J. , Ramakrishnan T. S. , Dave Yogesh
Published: December 2007

In this paper, we describe the basic features of the packer module and the observation probe tool combination of the multiprobe wireline formation tester. We present a model that captures the essential tool physics. A link between events within the tool and the formation pressures at the observation points is provided. Analytical solutions for both packer module and the observation probe are given.

A new interpretation method is presented for simultaneous interpretation of the packer interval and the observation probe pressure measurements. An optimization scheme that corrects the guessed rates calculated from the tool mechanical characteristics and simultaneously finds the formation parameters, such as reservoir pressure, and vertical and horizontal permeabilities is also presented.
Tandem Density Logging in Rugose, Tectonically Stressed Boreholes, Oman
Authors: Kimminau S. J. , Edwards John
Published: December 2007

Tectonic stress in Oman causes boreholes to breakout along the direction of least horizontal stress. Logging tools which apply a spring loaded pad to the borehole wall (such as density and microresistivity logs) tend to align with the breakout axis. Unfortunately the breakout axis is rugose, which severely affects tool readings, causing considerable uncertainty in porosity and net-to-gross calculations. The conventional technique of ‘short-axis’ logging has been tried, but with limited improvement. Various options were considered, with the most sucessful solution being to run two similar pad contact tools in tandem, but aligned at 90 degrees to each other, thus ensuring that one is in the smoother axis of the borehole. Examples of logs affected by rugosity and recorded with tandem pads are presented and discussed. This technique has contributed to a significant improvement in the evaluation of deep reservoirs in Oman, and should be of benefit in other tectonically stressed areas.
Geostatistical Modeling of Permeability with Annealing Cosimulation (ACS)
Authors: Deutsch C. V. , Cockerham P. W.
Published: December 2007

To provide accurate predictions of flow performance, the numerical model of permeability used by flow simulators must be consistent with all available geological and engineering data. The available data includes core permeability measurements, relevant permeability statistics (particularly, histograms, measures of spatial variability, and correlation with secondary variables such as porosity), and well test-derived permeability measurements. This paper documents an algorithm to generate 3-D permeability models that honor this variety of data. The algorithm, referred to as annealing cosimulation (ACS), generates stochastic permeability models using the numerical optimization algorithm known as simulated annealing. The application of simulated annealing to reservoir modeling is not new. The variety of information considered, however, and the practical example presented in this paper will be of interest to reservoir modelers.
Application of Simulated Annealing and Other Global Optimization Methods to Reservoir Description: Myths and Realities
Authors: Ouenes Ahmed , Bhagavan Srinivasa , Bunge P. H. , Travis B. J.
Published: December 2007

This paper gives a general review of the application of global optimization methods to reservoir description problems. The important parameters that control the performance of these algorithms are described and illustrations of the effect on the convergence are provided. A detailed review of past applications is presented and used to illustrate the fact that current computer technology is sufficient. Several current applications of global optimization, other than stochastic modeling, are used to emphasize the benefits of these methods. With the development of routine codes designed for everyday use, the need for parallel/distributed systems becomes apparent. An inexpensive and affordable parallel/distributed optimization approach that uses workstations, and even PCs, is described and illustrated with geostatistical optimization.
Thermal Well Test Analysis Using an Analytical Multi-Region Composite Reservoir Model
Authors: Acosta L. G. , Ambastha A. K.
Published: December 2007

For thermal recovery processes, the use of well test analysis to determine the swept volume is an important concern. Well tests conducted on wells undergoing a thermal recovery process have been typically idealized using a two- or three- region composite reservoir model. However, simulated thermal falloff tests have shown that mobility and storativity may be continuously changing in the swept region. For these reservoirs, a two- or three- region composite model may not be appropriate, while a multi-region composite model is suitable. A multi-region, composite reservoir analytical model has been developed to study the effects of various trends of mobility and storativity variations, within the swept region, on well tests for reservoirs undergoing a thermal recovery process. Pressure transient responses from this multi-region composite reservoir model show that on a log-log graph, the intermediate-time semi-log pressure derivative data falling on a straight line, whose slope is less than unity, is due to continuously changing mobility or storativity. The preceding behavior has been observed on several simulated thermal well tests. However, no theoretical explanation for this phenomenon has been advanced prior to this study.
Improved Rxo Measurements Through Semi-Active Focusing
Authors: Eisenmann Pierre , Gounot M-T. , Juchereau Bernard , Trouiller J-C. , Whittaker S. J.
Published: December 2007

A quantitative measurement of the flushed zone resistivity, Rxo, is one of the key parameters for complete log interpretation. When available at very high vertical resolution, evaluation of thin beds is rendered more accurate. To this end, a new device has been developed which not only provides good performance in thick mudcake/high resistivity contrast situations but has also proved reliable in the presence of thin mudcakes and/or low resistivity contrasts.

The pad-mounted device uses dual current focusing — vertically unmonitored and azimuthally monitored. This combination provides fine vertical resolution and strong immunity to mudcake or standoff effects. Three measurement buttons, optimally positioned within the main electrode, provide resistivities at three different depths of investigation. The central button reads the flushed zone resistivity, while two others, located towards the pad edges, are predominantly sensitive to mudcake properties.

Finite-element simulations were used for design optimization and for construction of the tool response data base. From this data base, the forward model of the tool was obtained by interpolation. The three parameters - Rxo, mudcake resistivity and mudcake thickness - are estimated in real time by a robust inversion algorithm based on the extended Kaiman filter method.

This new tool provides superior quantitative measurements of Rxo at a vertical resolution of less than one inch. Log examples show significant improvements in vertical resolution and accuracy in the determination of Rxo. Coherent quantitative estimations of mudcake thickness have been obtained allowing identification of permeable zones.
Applications of the Azimuthal Resistivity Imager Tool in Saudi Arabia
Authors: Al-Waheed H. H. , Audah T. M. , Cao Minh C.
Published: December 2007

The Azimuthal Resistivity Imager (ARI*) is a new laterolog-type resistivity tool introduced in Saudi Arabia in 1993. Along with the conventional Deep and Shallow laterolog (LLd and LLs), the tool gives 12 directional high-resolution deep resistivity curves that may be used in the following reservoir description applications.

1. The vertical resolution of the deep azimuthal resistivity is found to be better than one foot as compared with three feet for the conventional deep laterolog. Natural applications are the determination of Rt in thin beds and fractured reservoir characterization.

2. In "low" resistivity, we have observed interesting situations: where we normally expect the Groningen effect, there is none; where we don't, the effect shows up strongly. In each case, the ARI resistivity is found to agree well with a companion induction log.

3. The ARI resistivity image adds a new dimension to log analysis: the geological picture. Besides Rt, the image may be used effectively to estimate formation dips, study lateral heterogeneities, pinpoint fault planes as well as describing the reservoir rock texture.
Blast Furnace Slag Technology: Features, Limitations, and Practical Applications
Authors: Mueller D. T. , Dickerson J. P.
Published: December 2007

The use of blast furnace slag to convert drilling mud into a cementitious material has been the subject of much debate among cementing professionals. The conversion technology, recently introduced to the oil and gas industry, has been used in lieu of Portland cement in primary and remedial applications. The legitimacy of this technology has been challenged, however, by concerns over the mechanical integrity of the set product.

The purpose of this paper is to define the features and limitations of slag-converted drilling muds by investigating the physical and mechanical properties of the material. Alternative water-based designs using slag in lightweight and whipstock plug applications are also presented.

Test results indicate that the technical viability of slag-converted drilling mud designs are heavily influenced by factors such as the original density/dilute density/final density relationship and activator loadings. Proper consideration of these engineering elements is central to producing systems with predictable performance characteristics.

Additionally, the type and concentration of activator is shown to be the predominant factor influencing the brittleness and stress-cracking of slag-converted drilling muds.
The Kinetics of Hydrate Formation
Authors: Yousif M. H.
Published: December 2007

The kinetic and thermodynamic inhibition of gas hydrates occurs by disruption of the hydrogen bonding process that otherwise leads to clustering of water molecules as a solid lattice. Consequently, and in order to design better inhibitors for gas hydrates, it is of utmost importance to understand the mechanisms that lead to the formation of gas hydrates.

The interaction of the hydrate forming molecules with the water molecules at the onset of hydrate formation is re-examined in light of the results of NMR and X-ray diffraction data, and the statistical mechanics models. This re-examination shows that the large cages of structures I and II hydrates are almost always preferentially occupied regardless of the molecular size of the hydrate former. In other words, the large cages 512 62 and 512 64 of the hydrate structures, I and II, dominate the hydrate nucleation process.
Field Application of Static Tubing Pressure Data and On-Site Fracture Modeling
Authors: Cipolla C. L. , Meehan D. N. , Dunleavy J. R. , Stevens P. L.
Published: December 2007

This paper details the application of static tubing pressure measurements and on-site fracture modeling on over 70 wells in the Moxa Arch and Wamsutter areas in the Green River Basin, Wyoming. Specific examples illustrating the field procedures that evolved during a 2-year development program are presented, including on-site analysis of mini-fracture treatments, pad optimization, and treatment evaluation. Field applications include foamed and water based fluids in low and moderate permeability Frontier and Mesaverde gas sands. Bottom-hole pressure (BHP) measurements in all 70-plus treatments were obtained using a static tubing string, eliminating the inaccuracy of surface estimated BHP. Field data illustrate large variations in friction pressures that occur during many treatments which may lead to erroneous interpretations and premature job termination.

The quality of the data coupled with on-site three dimensional (3D) fracture modeling allowed field engineers to evaluate minifrac data and optimize pad volumes within 30 minutes. On-site modeling of the mini-frac data eliminated the need to measure fracture closure time which requires long shut-ins for many tight gas formations. This procedure includes the mini-frac volume in the pad volume, decreasing mini-frac costs and job delays.
Designing Oil and Gas Facilities for Russia
Authors: Kulish K. M.
Published: December 2007

This paper will describe Paragon Engineering Services’ past and current work in designing oil and gas facilities for Western joint ventures located in northwestern Russia in the Timan-Pechora basin. Also, this paper will further describe our current joint venture with a local Russian design institute, a comparison of Russian and Western design philosophies, and our observations and conclusions about work in Russia. The civil and mechanical designs have been influenced by the arctic environment, sourcing of materials and equipment, local environmental regulations, geotechnical considerations, and logistics. The civil design discussion centers on issues dealing with pile supported foundations, roads, and pads, performed in permafrost regions. The project’s civil design had to meet the goals of maintaining the thermal stability of the permafrost, minimizing physical damage to the tundra, and supporting equipment. The mechanical design discussion focuses on freeze protection, module sizing and configuration, and operating and maintenance practices for a development north of the Arctic Circle. Due to the high pour point of the crude oil, the mechanical design had to address the problem of a

flow stoppage at low ambient temperatures, along with the usual freezing problems due to the arctic climate. The basis for selecting the size and configuration of equipment modules was based on sourcing materials and equipment in the U.S., the logistics of transportation, and operations and maintenance. Paragon began performing joint work with a local Russian design institute located in the Komi Republic while working on a recent project. Paragon became familiar with the institute’s capabilities and gained greater understanding of the similarities and the differences between Russian and Western engineering firms. From past and ongoing work, we believe that to have a successful facilities project you must study the local logistics, consider environmental issues, gather geotechnical data, develop a plan of supply for equipment and materials, and involve a local Russian design institute as early as possible.
Control of Hydrate Formation by Surfactants and Polymers
Authors: Kelland M. A. , Svartaas T. M. , Dybvik L. A.
Published: December 2007

This paper describes new classes of chemical inhibitors that delay or interfere with the hydrate formation process that could be used to cost-effectively maintain produced gas/oil/water systems in readily transportable form. Our approach has been to look at the problem of hydrate formation on a molecular scale, and determine classes of so-called "kinetic inhibitors" that can act at much lower concentrations than anti-freezes.

Using experiments conducted in high pressure sapphire cells we have determined various classes of chemicals that affect the hydrate formation process. In particular, one class delays the growth of hydrate crystals for substantial periods but after a certain gas uptake this eventually leads to hydrate plugging. A second class of inhibitor prevents agglomeration of hydrate crystals so that a transportable slurry is maintained. A third class can incorporate both these inhibition properties to a limited extent.
A Simple Model for the Efficiency of Rotary Separators
Authors: Alhanati F. J. S. , Sambangi S. R. , Doty D. R. , Schmidt Z.
Published: December 2007

This paper presents, for the first time, a theoretical model for the bottomhole gas separation efficiency in Electrical Submersible Pump Installations. The model is based only on fundamental physical principles. New experimental data, collected in a field scale apparatus, and covering a wide range of liquid flow rates, GLRs, pressures and rotational speeds, are also presented. Predictions of the model are verified against the experimental data and limited published field data.

It was detected that, when rotary separators are used, two possible operating regions exist on a map of separation efficiency versus liquid flow rate and pressure. In one region the separator is quite effective and in the other the separator is not effective at all. The transition from the high efficiency zone to the low efficiency zone, in terms of liquid flow rate, is sharp. This behavior has never been reported in the literature before.

The model is simple enough that a small subroutine can be easily written, from the equations presented in the paper, to be included in design and troubleshooting programs for ESP installations. Overall agreement of the model’s predictions with the experimental and field data was good in both high and low efficiency zones.
ESP Gas Separator’s Affect on Run Life
Authors: Wilson B. L.
Published: December 2007

This presentation examines the phenomena of ESP run life reduction that can occur when rotary gas separators are employed. This reduction can be severe enough that some producers have stopped using them all together1. This paper presents information for the need for rotary gas separators and some alternate production strategies that could be attempted. The ESP manufactures now offer equipment that can extend the run life of these units in the problem wells. Familiarity with some of the alternate strategies and the improved equipment available will aid the user in selecting the strategy and equipment to optimize the run-life/production in his particular situation.
Increasing the Run Life of ESP’s in High H2S Wells
Authors: Wilson B. L. , Comeau T. P. , Davis P. M.
Published: December 2007

Mobil Oil Canada’s Wimborne Producing Team identified an economic opportunity to increase production and reduce operating expenses in the Wimborne field by converting several gas lift wells to electric submersible pumps (ESP). The economic success of the project demands that a one year ESP run life be achievable in the Wimborne field’s high hydrogen sulfide (H2S) environment. This paper reports on work performed to increase the life of ESP’s in wells with high concentrations of H2S (20% + ). The field experience had shown corrosion could be severe enough to destroy any copper alloys and some stainless steel alloys despite their location in the unit. Research work and failure analysis led to the development of unique ESP equipment designed to maximize run life in the Wimborne field. The work represents a joint effort among a major oil company, a ESP manufacturer and an academic research institution to develop methods to eliminate the sources of failures.
Dynamic Fluid Loss in Hydraulic Fracturing Under Realistic Shear Conditions in High-Permeability Rocks
Authors: Navarrete R. C. , Cawiezel K. E. , Constien V. G.
Published: December 2007

A study is presented of the dynamic fluid loss of hydraulic fracturing fluids under realistic shear conditions. During a hydraulic fracturing treatment, a polymeric solution is pumped under pressure down the well to create and propagate a fracture. Part of the fluid leaks into the rock formation, leaving a skin layer of polymer, or a polymer filter cake at the rock surface or in the pore space. The fluid-loss behavior depends on the extent to which the polymer invades the porous rock and the thickness of the polymer filter cake, which is limited by the shear stress that the flowing fracturing fluid exerts on it. In this paper the effect is studied of shear rate on the dynamic fluid-loss behavior of linear gels and crosslinked borate guars using cores of permeabilities ranging from 0.5 to 70 md, pressure drops of 1000 psi and temperatures between 75°F and 150°F. The effect of shear on the formation of external filter,cake and on the effectiveness of particulate fluid-loss additives was also studied. A shear rate history representative of that experienced by a rock segment in the fracture was used. In this history the shear rate drops from a very high rate of 380 s-1 down to 40 s-1 due to the widening of the fracture width as time advances.

Constant shear rate results show that high shear rates eliminate external filter cakes. In the absence of external cakes, the formation of internal filter cakes controls the fluid loss, especially in high-permeability cores. The effectiveness of particulate fluid-loss additives increases with the permeability of the rock and decreases with the shear rate and viscosity of the fluid. Shear history tests with high permeability cores show that the highest leakoff

rates and volumes occur during the first 10 min of leakoff, i.e., when the rock surface is exposed to high shear rates. Once the shear rate drops below a critical shear value, polymer filter-cake deposition begins and the leakoff rate slows down. To have a major effect of reducing fluid loss in this environment, the emphasis has to be placed on plugging the porethroats at the surface of the rock.
The Effect of Pressure on Two-Phase Zero-Net Liquid Flow in Inclined Pipes
Authors: Amaravadi Sridhar , Minami Kazuioshi , Shoham Ovadia
Published: December 2007

ABSTRACT1

The effect of pressure on two-phase zero net liquid flow in upward inclined pipes has been studied experimentally and theoretically. Experimental data were acquired for four upward inclination angles, namely, 1°, 2°, 5°, and 9°, and for three system pressures of 14.7 psia, 44.7 psia and 64.7 psia. A sequence of flow configurations was observed with increasing gas flow rate, as follows: Slug flow for low superficial gas velocities, protoslug for medium velocities, and pulsating small amplitude waves or roll waves at high velocities. At a particular velocity of gas, termed the blowout velocity, all the liquid was blown out of the pipe. An analysis of equilibrium stratified flow at the limit of very low and zero liquid flow rates has been carried out. It was found that under these conditions, the flow is always unstable, resulting in intermittent or pulsating stratified flow. A model has been developed for the prediction of the blowout velocity, as well as average liquid holdup and pressure gradient under zero net liquid flow conditions. A very good agreement was observed between the prediction of the proposed model and the experimental data
TACITE: A Transient Tool for Multiphase Pipeline and Well Simulation
Authors: Pauchon C. L. , Dhulesia Hasmuekh , Cirlot Georges Binh , Fabre Jean
Published: December 2007

The paper presents the principal characteristics of the TACITE code which has been developed to simulate transient and steady state multiphase flows, for the design and control of oil and gas production networks.

The hydraulic model is presented briefly and the resulting flow regime prediction is compared with experimental data. The performance of the code is illustrated with respect to steady state and transient experimental and field data.
Optimum Injection Rate from Radial Acidizing Experiments
Authors: Mostofizadeh Behdokht , Economides M. J.
Published: December 2007

The optimum injection rate for the matrix acidizing treatments of carbonate reservoirs has been the subject of debate and several recent experimental studies. Because acid attacks the rock in different modes depending on the injection rate (i.e., compact dissolution, dominant wormhole, leakoff-dominated wormholing and uniform dissolution), it is essential to identify the rate at which the transition between dominant wormholes and leakoff-dominated wormholing occurs. This is the optimum injection rate at which the greatest penetration is accomplished with the least volume of acid injected. Linear or radial laboratory experiments can be done from which field conditions can be extrapolated through dimensional analysis. This is the subject of this paper. Optimum HCl injection rates for a low- and a moderate-permeability limestone using radial cores have been determined. The effects of temperature and acid concentration have also been studied. Analysis of the results shows that the optimum injection rate depends greatly on the rock and reservoir conditions and can be determined from experiments.
Microseismic Monitoring of Hydraulic Fractures in Prudhoe Bay
Authors: Brady J. L. , Withers R. J. , Fairbanks T. D. , Dressen Don
Published: December 2007

Production stimulation is commonly performed on reservoirs by hydraulically fracturing the formation. Fracture geometry is controlled by the regional stress field, strength and contrast in local rock stress and fracture fluid properties. Computer models predict the length and height of the fracture as a function of injection volume, pressure and rate, and, fluid and rock properties. Until recently, these computations were unable to be verified except for the fracture half length with pressure transient analysis and through log interpretation in close proximity to the well. Direct confirmation of fracture geometry has been shown possible with availability of downhole geophysical monitoring of the seismicity associated with the fracture production. This paper presents results of a test to directly measure the height, length, and azimuth of a fracture generated in the Prudhoe Bay Field, Alaska.

Two triaxial geophone tools were deployed during August 1993 to monitor for microseismicity associated with a hydraulic fracture. One tool was deployed in an offsite monitoring well, and the second tool was deployed in the rathole of the fractured well. The objectives of the test were (1) to determine if seismicity existed and if it could be detected from within the fractured well and from the distant offsite monitoring well, (2) to evaluate techniques used to locate the fracture, and (3) provide guidance for the development of seismic recording systems used in fracture monitoring.
Current Drilling Practices, Gomez Field, Pecos County, Texas
Authors: Reddig L.W.
Published: December 2007

Many changes in drilling technique have been made during the development of the Gomez Field in Pecos County, Texas. These changes have reduced the time required to drill and complete a deep Ellenburger gas well to less than 50% of that required in the early development stage of this field. Detailed well planning, thorough supervision, and continual effort to improve each phase of the operations involved have been instrumental in creating these changes. Improved drilling fluids and bit designs have contributed significantly to the reduction in time and money necessary for such drilling.

Introduction

Since completion of the discovery well in the Gomez Field in October, 1963, a total of 50 wells have been completed and 14 wells were being drilled as of February 1, 1970. Not only is Gomez the world's deepest commercial production, it is by far the largest concentration of wells producing from below 20,000 feet. Although development is not yet complete, average well costs in excess of 1.5 million dollars represent an enormous investment by the operators in this field. Possibly of more interest to operating personnel are the improvements in techniques, tools, and materials that have evolved from this program. Substantial improvements in drilling techniques have been made during the development of this field. An average well is now drilled to total depth in 150 days, or less, as compared to 350 to 400 days required in the beginning of this development program. Well (costs have decreased in program. Well (costs have decreased in relation to the number of days required to drill.

CURRENT PRACTICES

Gulf is a major operator in the Gomez Field, and the following discussion pertains to Gulf's experience and present operating procedures which are present operating procedures which are not significantly different from those employed by other operators in the field.
Use of Partial Perforations in Oseberg Horizontal Wells
Authors: Søgnesand Sigmund , Skotner Peder , Hauge Jan
Published: December 2007

This paper describes the planning, implementation, and results of partial perforations in Oseberg horizontal wells completed with cemented liners. Partial perforations are used primarily to achieve sufficient areal sweep, drain multi-formation systems, delay gas and water breakthrough, and to control the watercut. The perforation strategies are determined utilizing simulation models. The well trajectory and the permeability variation are obtained from measurement-while-drilling logs. The effects of the horizontal well trajectory modelling, permeability, structural dip, interlayer permeability, and factional pressure drop on the inflow profiles are discussed in the paper.

Detailed well and reservoir modelling are necessary to arrive at a successful partial perforation strategy in horizontal wells. Incorrect parameters such as the permeability profile may result in selected perforation intervals that yield non-uniform inflow, lack of multi-formation drainage, and in some cases lift problems. This paper demonstrates the importance of knowing the permeability profile along the horizontal well section prior to determining the perforation intervals.

The influence of the factional pressure drop in the producing well section on the uniformity of the horizontal well inflow profile is important in highly-permeable formations. Matching of the actual inflow observed utilizing production logging allows for estimating the horizontal and vertical permeability profiles, and the permeability profiles determined from M WD logs and geological permeability maps appear to be confirmed. However, unique estimates of the permeabilities cannot be obtained.

Production logging in the Oseberg horizontal wells shows that the inflow profile can be controlled by use of selective perforations. The field data also indicate that the partial perforation strategies have provided acceptable results. The Oseberg field examples yield new and useful information regarding perforating horizontal wells completed with cemented liners.
Coalbed Methane - A Decade of Success
Authors: Schraufnagel R. A. , Hill D. G. , McBane R. A.
Published: December 2007

Between 1983 and 1993, the coalbed methane (CBM) industry changed from a high cost operation to a competitive main line gas resource. In 1983, there were approximately 165 coalbed methane wells in the United States with an estimated total annual production of 6 BCF. Between 1983 and 1993, industry drilled an estimated 6600 CBM wells that account for nearly 5% of domestic annual natural gas production. The rapid growth in production from this resource required technology advances in reservoir characterization, stimulation and production. These technology advances have reduced the cost of production from this resource, allowing production to expand from the sweet spots of two basins to multiple basins.
MOTHER: A Model for Interpreting Thermometries
Authors: Maubeuge Frederic , Didek Michel , Beardsell M. B. , Arquis Eric , Bertrand O. , Caltagirone J. P.
Published: December 2007

Despite many attempts to develop quantitative interpretation methods, the interpretation of temperature profiles has remained mostly qualitative. Most temperature models have concentrated on the wellbore thermal exchanges due to conduction and convection and have assumed that the produced fluid enters the wellbore at the geothermal temperature. Some authors have recognized the importance of the heating or cooling of the produced fluid before it enters the wellbore and have developed models incorporating the Joule-Thomson coefficient to take this into account. Flow in a porous media however does not satisfy the precise definition of a Joule-Thomson isenthalpic process, due to heat transfer between formation and fluid and since the Joule-Thomson process is by definition steady state both in terms of pressure and temperature.

This paper describes an energy equation that takes into account the temperature effects due to the decompression of the fluid and the frictional heating that occurs in the formation, and how this equation is coupled with the pressure equations in a finite element numerical well model.

The application to temperature log interpretation is demonstrated on real data sets. The ultimate goal would be to use the thermometry model for multilayer interpretations that differs from conventionnal methods in that both rate temperature can be matched.
A Foam Pilot in a North Sea Oil Reservoir: Preparation for a Production Well Treatment
Authors: Aarra M. G. , Skauge Arne
Published: December 2007

Displacement tests in sandstone cores have been applied to quantify the gas blocking ability of water continuous foams. The core flood experiments at reservoir condition have shown that such foams can create high pressure gradient also in the presence of North Sea crude oil. The pressure development during the flow in porous media was related to the variation of the foam quality (gas-water ratio). Several foam forming aqueous surfactants have been compared in static and dynamic foam tests. The placement of foam for blocking of a gas cone is discussed and different injection procedures are evaluated.
Performance of Immiscible Water-Alternating-Gas (IWAG) Injection at Kuparuk River Unit, North Slope, Alaska
Authors: Ma T. D. , Youngren G. K.
Published: December 2007

Immiscible water-alternating-gas injection (IWAG) has proven to be effective in managing produced gas at Kuparuk River Unit. The process is expected to improve oil recovery due to more efficient waterflooding in the presence of trapped gas. Laboratory data showed that trapped gas reduced water mobility by forcing water to displace oil from smaller pores. This mechanism resulted in lower residual oil saturation. Fully compositional simulation showed that IWAG may get an incremental oil of 1-3% of the original oil-in-place. Several years of operations have also revealed other significant tangible and intangible benefits for IWAG. These benefits are higher production rates, reduced water handling costs, and better reservoir management. Field experience shows that a tapered WAG helps keep produced gas oil ratio manageable. There are ongoing efforts to optimize WAG parameters (WAG ratio and gas slug size) and reduce costs. A potential injection scheme that does both is simultaneous water and gas injection.
A Statistical Approach to Material Balance Methods
Authors: Fair W. B.
Published: December 2007

Material balance methods have been used in petroleum engineering for many years to evaluate the performance of oil and gas reservoirs. It has been previously shown that in many cases the standard material balance equation results in a linear form that is particularly convenient for graphical analysis. In many cases of interest, however, the linear terms exceed those which can be subjected to graphical methods.

This paper documents a modification of the classical material balance method which preserves linearity in most reservoir types and is convenient for the application of statistical regression techniques. It is shown that by applying these standard statistical methods, many pitfalls in applying material balance analysis methods can easily be avoided and more insight into reservoir performance can often be gained.
A Full-Field Forecasting Tool for the Combined Water/Miscible Gas Flood at Prudhoe Bay
Authors: Wingard J. S. , Redman R. S.
Published: December 2007

This paper describes COBRA a PC/wo rkst at ion based full-field forecasting tool for the Prudhoe Bay Water/Miscib!e Gas Injection Project. The paper discusses the models of field performance and operation that comprise COBRA. These models are: a solvent allocation model, a throughput based waterflood performance model that is coupled with an EOR performance model, a surface infrastructure model, and a pattern reconfiguration model.

COBRA was used to evaluate Stage 1 of the waterflood/EOR infill expansion project in Prudhoe’s Northwest Fault Block (NWFB). COBRA was used to evaluate the various development options proposed in the NWFB infill project. COBRA determined the amount and timing of incremental reserves associated with different development alternatives in the active flood area.

Compared to isolated evaluations, COBRA was able to incorporate the full field effects of solvent reallocation, pattern reconfiguration, and the effects of surface fluid handling constraints on the future production.
Optimizing Gas Storage Reservoir Performance
Authors: McVay D. A. , Spivey J. P.
Published: December 2007

As gas storage becomes increasingly important in managing the nation’s gas supplies, there is a need to develop more gas storage reservoirs and to manage them more efficiently. Using computer reservoir simulation to predict gas storage reservoir performance, we present specific procedures for optimization of gas storage reservoir performance for two different problems. The first is maximizing working gas volume and peak rales for a particular configuration of reservoir, well and surface facilities. We present a simple procedure to determine the maximum performance with a minimal number of simulation runs. The second problem is minimizing the cost to satisfy a specific production and injection schedule, which is derived from the working gas volume and peak rate requirements. We demonstrate a procedure to determine the optimum combination of cushion gas volume, compression horsepower and number and locations of wells. The use of these procedures is illustrated through application to gas reservoir data.
Some Theoretical Aspects of Gravity Drainage in Naturally Fractured Reservoirs
Authors: Luan Zhi-An
Published: December 2007

The mathematical model of gravity-drainage in naturally fractured reservoirs and singular perturbation analyses are presented which explore the effect of capillary, gravity, and wettability on oil saturation distribution and oil recovery in reimbibition. This study shows that wettability, capillary end effect and fracture transmissibility appear to be most important factors in oil recovery. Numerical results are also presented which summarize and compare the effective saturation in nonequilibrium state with the actual saturation in equilibrium state. Based on this work, we believe reimbibition or capillary continuity in a stack of matrix blocks can not provide higher oil recovery than in continuity core.
Auger Tension Leg Platform: Conquering the Deepwater Gulf of Mexico
Authors: Bourgeois T. M.
Published: December 2007

Conquering the ultra-deepwater Gulf of Mexico (GOM) is among the greatest challenges facing the oil and gas industry today. Explorationists have found significant quantities of hydrocarbons in the ultra-deep GOM. Since Shell Offshore Inc. (Shell) has over one-third of the deepwater GOM acreage under lease today, development of this vast new oil and gas reserve represents a major opportunity.

Shell's "Auger" field, located in Garden Banks 426, was discovered in 1987 in 2,860 feet of water. This discovery kicked off a project of mammoth proportions for Shell and the industry. Shell designed and built a Tension Leg Platform (TLP) and related drilling and producing facilities for the major discovery at Prospect Auger. A TLP is a floating structure which is tethered to the seafloor, This $1.2 billion development is located in a world record shattering water depth of 2,860 feet. Integrating the complexities of this floating structure with the challenges of the subsurface makes Auger the most complex project ever undertaken by Shell's Production Department.

The Auger Project, which was conceived in 1989, is now installed within three months of the original target and $100 million under the original estimate. This is a significant success for Shell and the industry in the deepwater GOM as it opens the ultra-deepwater GOM frontier as an energy source to fuel America for decades to come.