bluuebunny/crossref_metadata_2025 huggingface dataset:
Constant-Pressure Interference Testing: Detecting Double-Porosity Properties
Authors: Grasman T. J. , Grader A. S.
Published: December 2007

This study presents an analytical method to determine double-porosity reservoir properties with interference pressure data in an infinite reservoir producing at constant pressure. Wellbore-storage and skin effects at production and observation wells are neglected. The effects of rD, λ, and ω on interference pressure responses are examined. For dimensionless interwell distances ≥ 100, the pressure responses are practically collapsed. As a result, a general type curve, which can be used for any value of rD, is presented that yields unique values of λ and ω for a given pressure response and rD. In addition to the log-log type curve, a semilog type curve that is more useful for pD values >0.1 is presented. Semilog derivatives of the interference pressure responses are considered. The pressure derivatives enhance small variations that occur in the pressure response during the flow period affected by the double-porosity nature of the reservoir.

It is observed that for a simple correlation with λ and rD, the derivative curves for rD values > 100 can be collapsed. Hence, a semilog derivative type curve is developed. This type curve has two maxima. Early- and late-time behaviors are influenced by λ. The time separation between the first and second maxima is a function of ω.
Clay Stabilization in Low-Permeability Formations
Authors: Himes R. E. , Vinson E. F. , Simon D. E.
Published: December 2007

The most popular clay stabilizers used recently in well-treating solutions are classified as cationic organic polymers (COP's). Recent studies have shown these stabilizers to be ineffective in microdarcy to low-millidarcy sandstones. Recent research led to the development of a stabilizer applicable to formations with permeabilities of 0.010 md and higher that also provides enhanced load-water recovery and more efficient placement from gelled-water solutions.
Analysis of Fluid-Loss Data
Authors: Clark Peter E. , Barkat Omar
Published: December 2007

Over the last few years, fluid-loss testing has evolved from static to dynamic testing. Data analysis, however, has not progressed as rapidly as the experimental techniques used to gather the data. In this paper, various techniques of analyzing dynamic fluid-loss data are discussed and a simple, yet effective, method of describing dynamic fluid-loss curves is presented.

The analysis of dynamic fluid-loss data is usually based on the traditional square-root-of-time treatment. This type of analysis works well for static fluid-loss test data because the dynamic processes are less complex than those in dynamic situations. During a dynamic fluid-loss test, a number of different events influence the fluid loss and the shape of the fluid-loss curve. Not only filter-cake compression, but also dynamic cake deposition and cake erosion must be taken into account. In most cases, Darcy flow does not occur over the whole time span of the test.

Several complex methods of treating the data from dynamic fluid-loss tests have been suggested, but most rely on modifications of the static fluid-loss-data analysis technique. These techniques are based on the data as a function of the square root of time. With dynamic fluid-loss test data, the square-root-of-time relationship does not adequately describe the fluid-loss data. A straightforward technique to analyze dynamic fluid-loss data is discussed in this paper.
In-Situ Wettability Determination in Gas Reservoirs
Authors: Desbrandes Robert , Bassiouni Zakl
Published: December 2007

Gas reservoirs are generally assumed to be water-wet. This is probably true in most shallow reservoirs where gas has migrated, partially replacing water in a porous and permeable trap. Gases normally do not contain impurities that are likely to alter the affinity of the grain surface for water. In deep reservoirs, oil may have been trapped first and then transformed into gas because of pressure and temperature changes. In this case, residues of bitumen and occasionally sulfur may coat the grains with a non-water-wet film. Water ganglia, then, are free in the pores, and water can flow even at a relatively low saturation.

Laboratory work has been done to define and measure the pressure profile in oil- and water-wet sandpacks at the oil/air or water/air contact. Pressure profile measurements are used to determine the free-oil or free-water level, the liquid capillary rise or fall, and fluid densities. Laboratory results show that even with the high porosity and permeability of the sandpacks, the pressure pattern at the gas/water contact is typical of rock wettability, which can be quantified. At the gas/oil contact (GOC), all sands exhibit an oil-wet behavior regardless of the wettability and residual water saturation. A field example of a pressure profile run in a gas/water transition zone is presented and interpreted in terms of wettability.
WAG May Improve Gas-Condensate Recovery
Authors: Cullick A. S. , Lu H. S. , Jones L. G. , Cohen M. F. , Watson J. P.
Published: December 2007

This paper shows that the water-alternating-gas (WAG) process may improve sweep efficiency and gas-condensate recovery compared with continuous cycling in highly stratified reservoirs. The study used extensive numerical simulation to investigate the sensitivity of the process to several variables, including reservoir layering, permeability, relative permeability, capillary pressure, and trapped gas. The process mechanics were confirmed by laboratory displacements in layered core.
Theory of Three-Component, Three-Phase Displacement in Porous Media
Authors: Falls A. H. , Schulte W. M.
Published: December 2007

A theory of multicomponent, multiphase displacement in porous media is further developed for three-component, three-phase systems. In regions of a tie-triangle in which one or two of the phases is (are) immobile, the description of solutions to the differential equations that govern flow is shown to be independent of the way relative permeabilities depend on saturations. When three phases flow simultaneously, key features of the mathematical solution space can be described analytically for an exponent-type relative permeability model.
Effect of Bacterial Polysaccharide Production on Formation Damage
Authors: Lappan R. E , Fogler H. S.
Published: December 2007

In-situ growth of cellular material is known to cause formation damage. Bacterial reproduction and polysaccharide production are the key factors that segregate bacterial formation damage from fines and particulate damage. Carefully controlled experiments conducted on both high- and low-permeability ceramic cores showed that bacteria can plug the pore space and damage the cores. However, further experimentation demonstrated that polysaccharide production is largely responsible for this damage. This conclusion is based on a comparison of two experimental systems: core plugging from bacterial replication and polymeric production and plugging of the porous medium caused solely by cell division with no polysaccharide production. In light of these results, the interpretation of reservoir plugging resulting from the presence of bacteria requires further scrutiny.
Simulation of Sandstone Acidizing of a Damaged Perforation
Authors: Lea C-M. , Hill A. D. , Sepehrnoori Kamy
Published: December 2007

A mathematical model was developed to study the effect of acidizing on the productivity of a single perforation penetrating a sandstone reservoir as a function of the distribution of damage around the perforation. Assuming the perforation to be ellipsoidal, we derived a 2D model that describes the single-phase flow of an acid through a perforated sandstone that contains two pseudochemical minerals dissolving at different rates. This paper presents cases that show the effectiveness of acidizing in removing both drilling-fluid damage and perforation damage. The most effective stimulation occurs when the perforation damage is removed by the acid.
Interpretation of Swelling/Extraction Tests
Authors: Hand John L. , Pinczewski W. Val
Published: December 2007

This paper describes an experimental and theoretical investigation of the relationship between the phase behavior observed in swelling/extraction tests and either slim-tube-determined minimum miscibility pressure (MMP) or critical gas enrichment. The results indicate that no simple relationship exists between the phase behavior observed in the tests and either MMP or critical gas enrichment. It is concluded that the primary value of swelling/extraction tests is that they provide phase-behavior data that can be used to calibrate equation-of-state (EOS) models, which, when used with 1D compositional simulators to model slim-tube displacements, provide realistic estimates for MMP and critical gas enrichment.
Modifying In-Situ Combustion Performance by the Use of Water-Soluble Additives
Authors: Shallcross D. C. , de los Rlos C. F. , Castanier L. M. , Brigham W. E.
Published: December 2007

Experiments were performed to study the effects of various additives on the oxidation kinetics of Californian and Venezuelan oils. Aqueous solutions of 10 metallic salts were mixed with sand and Huntington Beach, CA, oil. The mixtures were subjected to a constant flow of air and a linear heating schedule while the effluent gases were analyzed for composition. The variation in the oxygen consumption was analyzed with a model of three competing oxidation reactions. Values for the important kinetic parameters for the three reactions were obtained for each additive. Iron and tin salts were found to enhance fuel formation, while copper, nickel, and cadmium salts had no significant effects. Other experiments with a heavy Venezuelan oil showed that, contrary to earlier suggestions, the use of a ketal did not decrease fuel formation.
New Well-Testing Pressure Functions With Applications
Authors: Onur Mustafa , Peres Alvaro M. M. , Reynolds Albert C.
Published: December 2007

New pressure and pressure-derivative functions for analyzing well-test data are presented. The new pressure function represents the integral of pressure with respect to time divided by time. Thus, this new pressure function represents a moving or cumulative average of the pressure over time. It is shown that the logarithmic derivative of this pressure function is equal to a moving or cumulative average of the standard logarithmic pressure derivative. It also is shown that this new derivative function is useful for analyzing well-test pressure data in cases where the pointwise pressure-derivative data are difficult to interpret because of noise.
Wellbore Stress Distribution Produced by Moisture Adsorption
Authors: Yew Ching H. , Chenevert Martin E. , Wang Chein L. , Osisanya Samuel O.
Published: December 2007

For this study, we evaluated the stress distribution produced by moisture adsorption around a wellbore by applying the mechanics of deformable solids. This paper shows that the moisture-adsorption process is governed by a diffusion equation and that the equations governing the moisture-induced stresses around the hole are similar to those equations used in thermoelasticity. A computational method is developed for calculating the stress distribution around the borehole, and the experimental procedure for obtaining the material constants needed in the computation is presented. This paper also studies the effect of borehole pressure on the stress distribution around the hole. Results show that the magnitude and distribution of stresses around the borehole are very sensitive to the adsorption characteristics and the moisture-induced modulus change of the material.
A Comparison Between Capillary Pressure Data and Saturation Exponent Obtained at Ambient Conditions and at Reservoir Conditions
Authors: Søndenå Erik , Brattell Fred , Kolltveit Krlstofer , Normann Hans P.
Published: December 2007

The porous plate method was used to determine capillary pressure curves and saturation exponents at ambient conditions and at full reservoir conditions (reservoir pressure, temperature, and fluid) on sandstone core plugs from a North Sea reservoir. The main objective of this study is to determine whether any difference exists between the capillary pressure curves and the saturation exponents obtained at ambient conditions and those obtained at reservoir conditions for a North Sea reservoir. Results show that the capillary pressure and electrical resistivity measurements performed at ambient conditions with nonreservoir fluid displacing water can give results different from measurements performed at conditions prevailing in the reservoir.
A New Biopolymer for High-Temperature Profile Control: Part 1—Laboratory Testing
Authors: Strom E. Thomas , Paul James M. , Phelps Craig H. , Sampath Krishnaswamy
Published: December 2007

An extracellular polysaccharide produced by Alcaligenes bacteria has been crosslinked to form firm gels that are stable for long periods at elevated temperatures. The biopolymer can be gelled with multivalent ions such as Cr+3; it can also be gelled at the 2, 000-to-4, 000-ppm level without Cr+3 in high-salinity [∼20% total dissolved solids (TDS)] brines. Gel samples have been stable for 2 years at 74 and 93°C. Gels could be formed over a wide pH range, but best long-term stability was achieved in the pH range of 7 to 8. A flow test of Alcaligenes biopolymer gel in Berea sandstone at 74 °C showed that the gel gave a brine permeability reduction factor of 320.
Improved Scleroglucan for Polymer Flooding Under Harsh Reservoir Conditions
Authors: Rivenq R. C. , Donche Alain , Nolk Christine
Published: December 2007

Polymer flooding is commonly used to improve water sweep efficiency in oil reservoirs. Successful application of this method, however, has been restricted to low-temperature reservoirs because suitable polymers are not available for harsh conditions. Scleroglucan, a polymer produced by fermentation that shows promising properties, forms solutions that are very viscous and highly resistant to shear. Viscosity is insensitive to both salts and pH and only slightly affected by temperature. To facilitate industrial development of scleroglucan polymer, improvements in the filterability of the solutions and better knowledge of their behavior in pOrous media are necessary. A high-quality scleroglucan was obtained by eliminating the impurities responsible for polymer aggregation. This allowed evaluation of the intrinsic properties of the polymer molecules. Complete elimination of impurities from the polymer solution led to a scleroglucan without any aggregation tendency and with a good filterability, particularly at high temperatures. The performance of this improved scleroglucan in porous media was evaluated by coreflood experiments in Berea cores at temperatures ranging from 30 to 90°C. Results showed low permeability reduction and a mobility reduction close to relative viscosity. Injection of successive slugs into a Berea core under anaerobie conditions indicated low polymer retention at high temperatures (30 p.g/g at 90°C).
Features of Three-Component, Three-Phase Displacement in Porous Media
Authors: Falls A. H. , Schulte W. M.
Published: December 2007

A theory of 1D dispersion-free displacement in porous media is used toreveal features of floods in which three phases flow simultaneously. Theanalysis shows how the sequence of compositions realized in given classes ofproblems can be recognized from a single diagram. It also explains whythree-phase routes of physical interest shock into and out of tie-triangles, why composition routes measured during relative permeability experiments oftenare identical through the three-phase region, and how an equilibrium tertiarydisplacement can evoke either an oil bank that runs ahead of the phasecontaining the active agent or one that breaks through with it.
Measurements of Supersaturation and Critical Gas Saturation
Authors: Flroozabadi Abbas , Ottesen Baard , Mikkelsen Morten
Published: December 2007

Supersaturation and critical gas saturation were measured for two core samples with different pore structures. In these measurements, a pump with a constant rate of expansion was used to avoid steep pressure changes. Binary mixtures of C1/n-C10 at two saturation pressures were used as the fluid system. The surface tension of the binary mixtures varied from 2 to 13 dyne/cm. The data show that pore structure could significantly affect the degree of supersaturation. The supersaturation in a porous medium with small pores may be less than in a porous medium with large pores. The critical gas saturation data of this work are lower than literature values. Measurements on a chalk sample reveal critical gas saturations of about 0.5%.
Static Proppant-Settling Characteristics of Non-Newtonian Fracturing Fluids in a Large-Scale Test Model
Authors: McMechan D. E. , Shah S. N.
Published: December 2007

Large-scale testing of the settling behavior of proppants in fracturing fluids was conducted with a slot configuration to model realistically the conditions observed in a hydraulic fracture. The test apparatus consists of a ½ × 8-in. [1.3 ×20.3-cm] rectangular slot 14 ½ ft [4.4 m] high, faced with Plexiglas™ and equipped with pressure taps at 1-ft [0.3-m] intervals. This configuration allows both qualitative visual observations and quantitative density measurements for calculation of proppant concentrations and settling velocities. We examined uncrosslinked hydroxypropyl guar (HPG) and hydroxyethylcellulose (HEC) fluids, as well as crosslinked guar, HPG, and carboxymethyl HPG (CMHPG) systems. Sand loadings of 2 to 15 lbm/gal [240 to 1797 kg/m3] (8 to 40 vol% of solids) were tested. Experimental results were compared with the predictions of existing particle-settling models for a 40-lbm/l, 000-gal [4.8-kg/m3] HPG fluid system.
Numerical Simulation of Gravel Packing
Authors: Winterfeld P. H. , Schroeder D. E.
Published: December 2007

To obtain maximum productivity from unconsolidated formations where sand control is required, it is important to understand the mechanics of gravel packing. This paper describes a finite-element, numerical simulator that can predict gravel placement in the perforations and annulus of a wellbore. The equations for the simulator include mass and momentum conservation. Wellbore geometry, physical properties, and fluid and gravel-pack properties are simulator input. Experiments in a 100-ft full-scale wellbore model for three gravel-packing configurations have been successfully simulated. These configurations are a circulating pack with a washpipe, a squeeze pack, and a circulating/squeeze pack with a washpipe and a lower telltale screen. The low cost, speed, and extrapolation capabilities of the numerical simulator will greatly enhance our ability to predict gravel placement in a wellbore.
Barium and Calcium Sulfate Precipitation and Migration Inside Sandpacks
Authors: Allaga D. A. , Wu Gang , Sharma Mukul M. , Lake Larry W.
Published: December 2007

This paper is an experimental and theoretical study of permeability reduction of sandpacks caused by solids generation and migration. Two solids, calcium and barium sulfate crystals, were injected into and generated within the sandpacks by chemical reaction. We found that we could simulate the effluent concentrations, including the produced solids, with a fractional flow model for solids migration.
A New Method for Predicting Friction Pressures and Rheology of Proppant-Laden Fracturing Fluids
Authors: Keck Richard G. , Nehmer Warren L. , Strumolo Gary S.
Published: December 2007

The prediction of friction pressures for proppant-laden fracturing fluids requires estimations of both the base-gel friction factor and the effect of proppant on fluid rheology. This paper introduces two new expressions, each theoretically based with constants determined from data, that address these two issues for hydroxypropyl guar (HPG)-based fracturing fluids in laminar and turbulent flow.

The paper first introduces a new expression for the turbulent friction factor of HPG base gels. This implicit expression for the friction factor is more theoretically correct and requires one less empirical constant than explicit forms currently used. The effect of proppant on the effective viscosity of non-Newtonian fluids is then discussed and a new expression, which includes shear rate, temperature, gel concentration, and proppant volume fraction as parameters, is derived. Developed from laboratory data and existing slurry rheology theories, this expression is shown to provide excellent predictions of laboratory and field data for both tubing and annulus injection.
Implementation of the Ekofisk Field Waterflood
Authors: Hallenbeck L. D. , Sylte J. E. , Ebbs D. J. , Thomas L. K.
Published: December 2007

This paper describes the design, implementation, and initial results of the full-field water-injection program in the Ekofisk field of the North Sea. Two pilot waterfloods, injection-well-pattern design, vertical confinement considerations, optimization of production-well sidetracks, core fracture analysis and orientation, regional permeability variations, reservoir geology and faulting, and overall anisotropy are discussed. Results of a comprehensive waterflood surveillance program are presented as well as 3D-model predictions for ultimate recoveries.
Field Study of Offshore Cement-Spacer Mixing
Authors: Benge Glen
Published: December 2007

Rheological data from cementing-spacer fluids are usually based on laboratory-prepared samples of the spacer and used to determine the flow rate required to provide the flow regime necessary for maximum efficiency of the spacer and to estimate the annular friction pressures associated with the spacer. Actual rheological properties are rarely measured on location, and the problems experienced with settling, foaming, and mixing are difficult to simulate in the laboratory. This paper reviews the field data from three commercial spacers mixed at offshore locations and compares them with laboratory data for base spacer materials and weighted spacer mixes. The flow rates required to obtain turbulent and plug flow for each spacer are compared, and settling, foaming, and mixing problems are discussed. Because of solids settling in either the slugging pits or surface samples, the spacer formula is sometimes modified on location to improve solids suspension. The rheological effects of increasing concentrations of base spacer material, bentonite, and polyanionic cellulose (PAC) are discussed with a comparison of the rheological data from these spacers.
Effects of Strain Rate and Confining Pressure on the Deformation and Failure of Shale
Authors: Cook J. M. , Sheppard M. C. , Houwen O. H.
Published: December 2007

Previous work on shale mechanical properties has focused on the slow deformation rates appropriate to wellbore deformation. Deformation of shale under a drill bit occurs at a very high rate, and the failure properties of the rock under these conditions are crucial in determining bit performance and in extracting lithology and pore-pressure information from drilling parameters. Triaxial tests were performed on two nonswelling shales under a wide range of strain rates and confining and pore pressures. At low strain rates, when fluid is relatively free to move within the shale, shale deformation and failure are governed by effective stress or pressure (i.e., total confining pressure minus pore pressure), as is the case for ordinary rock. If the pore pressure in the shale is high, increasing the strain rate beyond about 0.1 %/sec causes large increases in the strength and ductility of the shale. Total pressure begins to influence the strength. At high strain rates, the influence of effective pressure decreases, except when it is very low (i.e., when pore pressure is very high); ductility then rises rapidly. This behavior is opposite that expected in ordinary rocks. This paper briefly discusses the reasons for these phenomena and their impact on wellbore and drilling problems.
Slim-Hole Drilling in Harsh Environments
Authors: Fultz J. D. , Plttard F. J. , Sawyer F. D. , Farmer W. R.
Published: December 2007

Wells with small liners occasionally require unique methods of drilling, completion, and reworking, especially deep-hole wells and wells with severe doglegs. Innovative drilling procedures were used successfully on two wells with those downhole conditions. On the first well, cement was drilled in a 3½-in. liner with a small mud motor and heavyweight mud. On the second well, a large mud motor was used as a downhole power swivel to drill in a 3½-in. liner. Both jobs were completed at depths of 13, 000 to 20, 000 ft with mud weights > 18 lbm/gal and bottomhole temperatures (BHT's) >300°F.
Understanding Kick Tolerance and Its Significance in Drilling Planning and Execution
Authors: Redmann K. P.
Published: December 2007

Kick tolerance is a drilling parameter that has prompted both confusion and misunderstanding in the drilling industry, yet its importance to drilling engineers may be increasing exponentially. The increasing number of worldwide drilling catastrophes may spur government agencies to tighten controls on casing-setting-depth criteria, requiring pipe to be set once minimal kick tolerance values are reached. A thorough understanding of kick tolerance is necessary in both drilling operations and casing program design. Confusion involving kick tolerance may be attributed to the concept of zero gain, which is commonly referred to in many accepted definitions of kick tolerance. This paper presents an innovative approach to determining true kick tolerance that not only incorporates the conditions of an influx within the wellbore but also considers the possible reductions in kick tolerance caused by the circulation of that influx from the wellbore. New techniques are available for hand-held calculators, which are now more accurate in determining influx pressure and volume anywhere within the wellbore. A typical well example with illustrations describes kick tolerance and empha sizes the influence of other drilling parameters. Integration of kick-tolerance considerations into the well planning process also is dem onstrated.
Light-Oil Steamdrive Pilot Test at NPR-1, Elk Hills, California
Authors: Gangle F. J. , Weyland H. V. , Lassiter J. P. , Veith E. J. , Garner T. A.
Published: December 2007

A steamdrive pilot was run on a light-oil reservoir at the Naval PetroleumReserve No. 1 (NPR–1) in the Elk Hills oil field, Kern County, CA. From areservoir perspective, the steamdrive process behaved much as expected. Thefirst event to occur was the appearance of freshened water productionaccompanied by CO2 gas 3 months from startup of steam injection. The secondevent, an increase in crude gravity, appeared 3 months later, or 6 months intothe project. Finally, the third event was the arrival of the heat front at theproducing wells 13 months after startup. From a production perspective, CO2 in the freshened produced water caused wellbore scale damage and loss of well productivity. The steamdrive, however, mobilized residual oil, which mostly wascaptured outside the pilot pattern area. Acid stimulations to restore well productivity were done by injecting inhibitor in the steam feedwater and by designing acid cleanup treatments on the basis of results from laboratory tests.
CO2 Foam With Surfactants Used Below Their Critical Micelle Concentrations
Authors: Kuhlman M. I. , Falls A. H. , Hara S. K. , Monger-McClure T. G. , Borchardt J. K.
Published: December 2007

Using surfactants below their critical micelle concentrations, CCMC, to reduce gas mobility throughout a reservoir can be advantageous. When used in reservoir brines below their CMCMC inexpensive anionic surfactants propagate through rock with little delay owing to adsorption. Yet gas mobility is reduced below that of a watertlood in either surfactant-water-altemating-gas (SWAG) or coinjection experiments. Moreover, oil recovery is higher than in processes without surfactant. In contrast, at concentrations above the CCMC, surfactant adsorption is much higher and the injected surfactant concentration can be greatly delayed. In addition, CO2 mobility can be reduced so far below that of a watertlood that injectivity suffers. Moreover, oil recovery can be reduced because oil is emulsified and its mobility is lowered. This type of foam should be considered only for near-wellbore fluid diversions.
Change in Apparent Viscosity off CO2 Foam With Rock Permeability
Authors: Lee H. O. , Heller J. P. , Hoefer A. M. W.
Published: December 2007

This paper summarizes new and previous high-pressure experiments measuring the mobility of CO2 foam in porous rock, including both sandstones and carbonates, with permeabilities ranging from < 1 md to hundreds of millidarcies. Foam mobility is defined here as the ratio of the combined flow rate per unit superficial area to the pressure drop required for simultaneous flow of dense CO2 and brine/surfactant through the sample and can be expressed in units of millidarcies per centipoise. The measured results, which can also be expressed in terms of the apparent viscosity of the CO2 foam, give a quantitative basis for the belief that this displacing fluid should be particularly effective in heterogeneous formations. From a macroscopic viewpoint, the CO2 foam acts like a single fluid with a viscosity equal to the ratio of the rock's brine permeability to the measured mobility. According to our results, the apparent viscosity depends on rock permeability in a nonlinear fashion, increasing from a minimum of about 2 cp for the tightest rocks to an apparent maximum of about 1, 000 cp for Berea. Individual mobility measurements were made at steady-state conditions; this is justified by consideration of oilfield operational constraints. Results of auxiliary experiments are given and the methods described. These include measurements of essential surfactant characteristics, such as durability against coalescence of the dense CO2 bubbles in brine/surfactant solution. Results given also show the influence of other factors, such as surfactant concentration and type, flowing fraction of the dense gas, and overall rate, on foam mobility.
Microvisual and Coreflood Studies of Foam Interactions With a Light Crude Oil
Authors: Schramm Laurier L. , Turta Alexandru T. , Novosad Jerry J.
Published: December 2007

Foam stability in the presence of crude oil is important to foamflood performance. Microvisual observations were made to assess the degree of foam-lamella/oil interactions occurring between a light crude oil and foams being considered for foam flooding applications in Alta., Canada. Foam behaviors ranged from quite stable, with almost no foam/oil interactions, to quite unstable, where oil was extensively emulsified and imbibed into the foam. These behaviors matched phenomenological model predictions and also were consistent with coreflood mobility reduction factors and incremental oil recoveries obtained in foam flow experiments in Berea sandstone cores at ambient temperature, low pressure, and residual oil saturation (ROS).
Design, Operation, and Evaluation of a Surfactant/Polymer Field Pilot Test
Authors: Holley S. M. , Cayias J. L.
Published: December 2007

Oryx Energy Co. evaluated the design and operation of a low-tension surfactant/polymer pilot in the McCleskey sandstone of the Ranger field in Eastland County, TX. The test was performed in a watered-out area developed on 40-acre spacing that was chosen because good reservoir permeability, the availability of fresh water, and high residual oil saturations (ROS's) made it suitable for a surfactant/polymer process. Major disadvantages of the area were a potential lack of pattern confinement and a salinity contrast caused by the injection of fresh water. The purpose of the test was to determine the applicability of the technology and its implementation. The pilot was successful on the basis of both monitored results and produced oil but did not achieve its design objectives because of reservoir heterogeneity and reduced sweep efficiency. The successful propagation of chemical fronts and oil recovery within the pilot area demonstrated that in this and similar reservoirs, surfactant flooding can recover tertiary oil in significant quantities on large areal spacing. This paper discusses the design, operation, and evaluation of the field project and includes considerations for the successful implementation of the technology.
Formation Damage From Polymer Solutions: Factors Governing Injectivity
Authors: Fletcher A. J. P. , Lamb S. P. , Clifford P. J.
Published: December 2007

This paper addresses polymer-solution injectivity and what physico-chemical environments result in formation damage. The roles of Fe(III) and filtration are shown to be particularly important. The effects in the field are predicted, with special reference to wellbores likely to suffer from thermal fracturing. It is shown that fractured wellbores are unlikely to suffer from injectivity problems.
Physical Model Steamflood Studies Using Horizontal Wells
Authors: Ahner P. F. , Sufi A. H.
Published: December 2007

A small, scaled physical vacuum model was built to study a steamflood process that uses a horizontal well to form a communication between vertical injector/producer well pairs in a heavy-oil reservoir. Linedrive steamflood operation was simulated over 1.37- and 2.75-acre patterns at 427- and 650-bbl/D injection rates. These studies yielded 60% to 80% recoveries at steam/oil ratios between 4 and 6.
Improvement of Gravity Drainage by Steam Injection Into a Fractured Reservoir: An Analytical Evaluation
Authors: van Wunnik John N. M. , Wit Krijn
Published: December 2007

Analytical techniques were used to study improvement of gas/oil gravity drainage by steam injection in a densely fractured dome-shaped low-permeability reservoir containing viscous oil. Aspects of the process studied include mixing of the steam and hydrocarbon gas, the temperature distribution in the caprock and reservoir, and oil production by thermal expansion and gravity drainage. The models developed are applied to the Qarn Alam reservoir of Oman, which may be a candidate reservoir. The steam-injection process appears very attractive for this reservoir; an oil/steam ratio of 0.5 m3/Mg may be achieved.
A New Recovery Technique for Heavy-Oil Reservoirs With Bottomwater
Authors: Islam M. R. , Chakma Amit
Published: December 2007

This paper proposes a new recovery mechanism for heavy-oil reservoirs containing bottomwater zones. Many heavy-oil reservoirs are considered unproductive because of the presence of a bottomwater zone. No known mechanism now exists for producing oil from these reservoirs. Recently, horizontal wells have been proposed as a unique solution for producing reservoirs that are thin, fractured, or contain a bottomwater zone. For heavy-oil reservoirs, however, horizontal wells alone may not be sufficient. The electro magnetic heating process has proved to be effective in in-situ heating of oil-bearing formations. Such heating, which is limited to small radii, in combination with a horizontal well offers an attractive process for recovering billions of barrels of oil unrecoverable by other means. The process of electromagnetic heating proposed here is coupled with gas or water injection to create a favorable pressure gradient in the presence of a bottomwater zone. Scaled model experiments were performed to study the feasibility of the process of inert-gas injection along with electromagnetic heating. The variables studied were oil/water-zone thickness ratio, oil viscosity, horizontal-well placement, inert-gas injection rate, and production-well temperature. A recovery as high as 77 % oil in place (OIP) was obtained even in the presence of a bottomwater zone as thick as the oil zone. This technique offers heavy-oil production at a cost lower than that of any other thermal recovery scheme.
Development of a Method for Partially Uninvaded Coring in High-Permeability Sandstone
Authors: Rathmell J. J. , Tibbitts G. A. , Gremley R. B. , Warner H. R. , White E. K.
Published: December 2007

A newly designed polycrystalline-diamond-compact (PDC) core bit and water-based muds with bridging solids are shown to provide 4-in. diameter cores with a 2.5-in. uninvaded center. High-permeability sandstones were cored at rates exceeding 90 ft/hr in laboratory and field tests. The mechanisms controlling filtrate invasion are quantified.
Foamed Cement for Squeeze Cementing Low-Pressure, Highly Permeable Reservoirs: Design and Evaluation
Authors: Chmilowski Walter , Kondratoff L. B.
Published: December 2007

Four different cement squeezing techniques have been used on wells producing from the Keg River formation in the Rainbow Lake area of Alberta, Canada. This paper evaluates 151 cement squeeze treatments performed at 96 wellsites and compares the use of foam cement vs. conventional squeeze treatments and techniques. Discussion includes key aspects, such as candidate selection, slurry design, treatment design, economic evaluation, and operational considerations.
Electrical Stability, Emulsion Stability, and Wettability of Invert Oil-Based Muds
Authors: Growcock F. B. , Ellis C. F. , Schmidt D. D.
Published: December 2007

Until now, drilling-fluid specialists measured trends in the electrical stability (ES) test to decide the appropriate emulsifier treatment for invert-emulsion oil-based muds without knowing what the ES test was measuring. This paper describes what happens in a mud during an ES test, how mud composition affects trends in the ES measurements, and how observed trends can be used to deduce mud-emulsion stability and oil wettability. During an ES test, electrical breakdown is induced in the mud between the electrodes. This process was observed, with an optical microscope, to involve formation of a conductive bridge composed of aqueous fluid and particulate matter. Experiments showed that water forms the conductive pathway in the bridge, whereas the solids appear to be involved only as carriers of the water. Eo, the voltage at which the conductive bridge is formed and the current rises abruptly, was found to be a function of the viscosity and the types and concentrations of solids, aqueous fluid, and emulsifiers (surfactants). These trends are consistent with a theoretical expression for breakdown of paniculate-contaminated dielectric fluids, which suggests that the Eo of a mud is an absolute measure of its emulsion stability but only a relative measure of its oil-wetting tendency. Trends in Eo are also consistent in most cases with other field indicators of emulsion stability, such as high-temperature, high-pressure (HTHP) fluid loss. Anomalies in E0 trends are explained in terms of a physicochemical model for electrical breakdown.
Use of New Ranging Tool To Position a Vertical Well Adjacent to a Horizontal Well
Authors: Tarr B. A. , Kuckes A. F. , Ac M. V.
Published: December 2007

As part of a heavy-oil pilot project, three vertical wells had to be drilled in close proximity to the horizontal section of a horizontal well. Because the separation distances specified were smaller than the position uncertainty associated with conventional directional surveying, a special electromagnetic ranging technique had to be developed. The technique proved reliable and was used to complete the project successfully.
Interrelationship Between Critical Cement Properties and Volume Changes During Cement Setting
Authors: Sabins F. L. , Sutton D. L.
Published: December 2007

This paper surveys cementing terminology for clarifying cement setting and its capability to control interzonal fluid flow. It also demonstrates the results of several test procedures designed to measure two or more cement properties simultaneously under conditions that simulate job applications. These procedures test the validity of theories and procedures for controlling annular gas flow, cement bonding, interzonal channeling, and intrazone isolation. From these results, guidelines may be developed for using laboratory data to determine times for temperature logs, perforating, and stimulation treatments. Existing laboratory equipment was modified and new equipment was designed to measure the interrelationships between static-gel-strength development, volume reductions, hydration temperatures, permeability changes, net plastic-state shrinkage, and compressive strength.

Test results indicated that (1) hydration volume reduction (HVR) during the transition period is relatively small and shows a general correlation to unit volume cement content; (2) temperature increases from hydration show a rough correlation to static-gel-strength development; (3) permeability during static-gel-strength development decreases rapidly and shows a definite correlation to fluid-loss test values; (4) plastic-state shrinkage is only a very small part of the total HVR; (5) a general correlation exists between compressive strength, HVR, and heat of hydration; (6) the HVR for an expansive cement was greater than that of a nonexpansive cement, but its plastic-state shrinkage was less.
A Novel Method of Developing In-Depth Permeability Modification Using Surfactant/Alcohol Blends
Authors: Llave Feliciano M. , Burchfield Thomas E. , Dobson Randy E.
Published: December 2007

This paper describes the development of a novel method of in-depth permeability modification in porous media using specific surfactant/alcohol blends. The unique features of this method come from (1) the development of permeability modification primarily resulting from component separation of injected blends, (2) in-depth penetration of formations without premature injectivity loss, (3) the capability to propagate the permeability barrier farther through the porous media, and (4) ease of cleanup of the porous media. Laboratory studies showed that injecting these blends into porous media can reduce permeability significantly. The degree of permeability barrier penetration was controlled experimentally, and this barrier was propagated in-depth by subsequent injection of alcohol slugs. The permeability modification potential of these blends was comparable with that of conventional gelled-polymer treatments.
An Experimental and Modeling Study of Miscibility Relationship and Displacement Behavior for a Rich-Gas/Crude-Oil System
Authors: Mansoori John , Haag Gary L. , Bergman Dave F.
Published: December 2007

This paper presents an experimental study that uses many slim-tube displacements to characterize the effect of hydrocarbon solvent composition on miscibility development. It was found that the minimum enrichment requirement can be estimated reliably with a previously proposed pseudocritical temperature, Tpc, concept. Tuning equation-of-state (EOS) parameters to match these results required incorporating rate and recoveries from selected slim-tube displacement tests in addition to conventional PVT data.
Testing Injection Wells With Rate and Pressure Data
Authors: Ramakrishnan T. S. , Kuchuk F. J.
Published: December 2007

Injection tests can give such information as the effective mobilities of fluids, wellbore damage, and saturation change during displacement, which often require use of rate and pressure data. Although exact solutions for injection and falloff pressure response of a well in an infinite reservoir may be obtained for a constant injection rate, they are not readily extended for the general case of varying flow rates and bounded reservoirs. We present a perturbation theory for multiphase testing that leads to a weakly nonlinear convolution and give a technique to calculate pressure response rapidly for arbitrary flow rates for this form of convolution. The technique is specifically suited for solving inverse problems with nonlinear estimation. We present modifications to the solutions for positive and negative skin factors and demonstrate that the effect of wellbore storage is not easily accounted for in an injection test, unlike single-phase well testing. We give a procedure to correct the system response to storage and propose a variable-rate injection test to improve system parameter estimation. The main idea of the test is to excite the reservoir sequentially and continuously to keep it under strong transient conditions. We present interpretation results for such a sequential testing.
A Method To Derive Dips From Bedding Boundaries in Borehole Images
Authors: Antoine Jean-Noël , Delhomme Jean-Pierre
Published: December 2007

This paper describes a computerized technique to derive reliable and accurate dips from high-resolution electrical images automatically, taking full advantage of their lateral continuity and azimuthal coverage. The quality of these dips can be checked by visual inspection. Results derived from three different geologic contexts illustrate the technique.
Improved Reservoir Characterization From Waterflood Tracer Movement, Northwest Fault Block, Prudhoe Bay, Alaska
Authors: Nitzberg K. E. , Broman W. H.
Published: December 2007

Simulation models of the Prudhoe Bay Northwest Fault Block (NWFB) waterflood project, with core-plug-derived permeabilities, predicted that injected water would slump because of gravity segregation. Detailed analysis of surveillance logs and production data for one pattern identified tritium tracer breakthrough in surrounding producers without significant slumping. To duplicate the nearly horizontal movement of injected water, a kV/kH ratio that is an Order of magnitude lower than previously modeled is required. This improved reservoir characterization led to revision of the reservoir management strategy for the NWFB.
Well-Test Analysis in Solution-Gas-Drive Systems for Fractured Reservoirs
Authors: Camacho-V. Rodolfo G. , Raghavan Rajagopal
Published: December 2007

This study examines issues pertaining to two-phase (oil and gas) transient flow in fractured reservoirs. Dual-porosity and dual-permeability models are examined. Pressure, saturation, and flowing GOR behaviors are noted, and the influence of communication on these behaviors is documented. Methods to compute saturation as a function of pressure for the fracture and matrix systems are presented.
Gas-Cap Effects in Pressure-Transient Response of Naturally Fractured Reservoirs
Authors: Al-Bemani Ali Soud , Ershaghi Iraj
Published: December 2007

This paper presents a theoretical framework of gas-cap effects in naturally fractured reservoirs. General pressure solutions are derived for both pseudosteady-state and unsteady-state matrix-fracture interporosity flow.

Deviation from the fracture or fracture-matrix response occurs as the gas-cap effect is felt. Anomalous slope changes during the transition period depend entirely on the contrast between the fracture anisotropy parameter,λ1, and matrix-fracture interporosity parameter, λ, and between the total gas-cap storage capacitance (1 − ω1) and oil-zone matrix storage (1 − ω).

A composite double-porosity response is observed for ω1 ≤ ω1c and 1.0 ≤ λ1/λ ≤ 1000. A triple-porosity response is observed for ω1 ≥ ω1c and 140 < ωλ1/λ < 1.0E05.
Case Study of the Effectiveness of Nitrogen Foam and Water-Zone Diverting Agents in Multistage Matrix Acid Treatments
Authors: Kennedy D. K. , Kitziger F. W. , Hall B. E.
Published: December 2007

Several oil wells producing water have been stimulated successfully with multistages of mud acid, nitrogen foam, and water-zone diverting agents. This procedure has improved well performance significantly while having little or no effect on post-treatment water production. The diverters’ effectiveness was analyzed with radioactive tracers, gamma spectroscopy logs, and surface pressure equipment. Results indicate that water-zone diverters and nitrogen foam are effective diverters when used in matrix acid stimulations. Case histories and associated data are included in this paper.