bluuebunny/crossref_metadata_2025 huggingface dataset:
Permeability Determination With a Multiprobe Formation Tester
Authors: Goode Peter A. , Thambynayagam R. K. Michael
Published: December 2007

This paper presents analytic models to interpret the pressure transients measured by a multiprobe formation tester. The multiprobe tester discussed consists of three probes. The sink probe generates a pressure pulse by withdrawing fluid from the formation while the resulting pressure response is measured at the sink probe and at each of two observation probes. One observation probe is positioned on the opposite side of the borehole on the same vertical plane as the sink, and the other is displaced vertically on the same azimuthal plane as the sink. The effect of the various reservoir parameters on the pressure response is discussed. Application of the models is demonstrated through an actual field example.
A Grouping Method To Optimize Oil Description for Compositional Simulation of Gas-Injection Processes
Authors: Danesh Ali , Xu Dong-hai , Todd Adrian C.
Published: December 2007

This paper presents a grouping method that optimizes compositional description so that the modeling of the progressive phase behavior of injection gas and reservoir oil systems requires less computation. The method allows the retrieval of the full composition to select new groups for further calculations with very little effort and almost no extra computational time. A new mixing rule, based on the parameters of an equation of state (BOS), also has been developed and incorporated into the grouping method. Multistage experiments simulating the progressive compositional variations of injection gases and reservoir oils were used to evaluate the proposed grouping method.
Successful Inhibition of Deep, Hot, Sour-Gas Wells
Authors: Cameron G. R. , Katz D. C. , Hull J. E. , Barker D. E. , Eiser M. W.
Published: December 2007

The sour-gas wells in the Big Escambia Creek (BEC) field of South Alabama have a production environment that consists of 280°F, 21% H2S, 40% CO2, and up to 190, 000 ppm chlorides in the produced water. The highly corrosive conditions demand the ultimate in a corrosion mitigation program to produce these wells safely and economically. This paper describes the background, technical development, and results of the downhole and gathering-system corrosion inhibition and monitoring programs: continuous downhole inhibition by means of annular injection of a water-dispersible inhibitor in the most aggressive wells; downhole batch treatments with nitrified tubing displacements of an oil-soluble inhibitor in the remaining wells; continuous injection of a water-dispersible inhibitor in the gathering lines to augment the batch treatments and in selected highly corrosive wells; monitoring of inhibitor residuals and plotting of trends to ensure the effectiveness of downhole treatments and to optimize injection rates; and flowline calipers and hydrotests to monitor the gathering-line inhibition programs. The paper also describes the computerized approach used in designing, calculating, and updating both the continuous downhole injection system and the nitrified batch treatments. The success of the inhibition and monitoring program is demonstrated by the tubing life achieved, field data on inhibitor residuals, and flowline and downhole calipers. The technical data presented will aid in the design and implementation of successful inhibition programs for highly corrosive production environments.
Performance of a Heavy-Oil Field Under CO2 Injection, Bati Raman, Turkey
Authors: Issever Kayhan , Pamir A. Necdet , Tirek Ali
Published: December 2007

Batı Raman heavy-oil (12°API [0.986 g/cm3]) field, with 1.85 × 109 STB (294 × 106 stock-tank m3) original oil in place (OOIP) and poor primary recovery (1.5% OOIP), was a good candidate for EOR applications. Detailed studies resulted in application of an immiscible CO2 injection in a 33-well pilot area. An initially planned huff ‘n’ puff became a successful continuous CO2 flood and encouraged us in our decision to widen the project to the central part of the field. Incremental oil production of 5.742 × 106 STB [913 × 103 stock-tank m3] resulted from 28-MMscf [7.9 × 105 std m3] CO2 injection. Oil production increased from 900 STB/D [143.1 stock-tank m3/d] primary production to 10, 500 STB/D [1669 stock-tank m3/d] in the treated area.
Thermally Induced Fracturing off Ula Water Injectors
Authors: Svendsen A. P. , Wright M. S. , Clifford P. J. , Berry P. J.
Published: December 2007

This paper describes the impact that thermally induced fracturing (TIF) has had on the North Sea Ula field injection wells, allowing higher than anticipated water injection rates to be achieved. This work also discusses how thermal stress reduced fracture propagation pressures by 2, 000 psi and how a 3D simulation code developed to model TIF was used. Injection-water-quality specifications and techniques to optimize TIF are presented.
Improving the Reliability of Cement-Setting-Time Tests by Taking Into Account the Influence of Shear
Authors: van Kleef R. P. A. R. , van Vliet J. P. M.
Published: December 2007

During a laboratory API thickening-time test of a cement slurry, temperature and pressure are simulated according to downhole conditions. However, the shear rate applied to a slurry in the API test generally differs considerably from the shear rate in actual field cementations. This leads to inaccurate prediction of slurry setting time. Cement setting times should be determined in a laboratory test under realistic conditions of temperature, pressure, and shear.
Whirl and Chaotic Motion of Stabilized Drill Collars
Authors: Jansen J. D.
Published: December 2007

Stabilized bottomhole assemblies (BHA's) often exhibit complicated lateral vibrations. This paper aims to clarify this behavior with the theory of rotor dynamics. The motion of the collars varies from simple whirling motion, like that of an unbalanced centrifuge, to highly irregular motion caused by nonlinear effects of fluid forces, stabilizer clearance, and borehole-wall contact. In the extreme case, the vibrations can be classified mathematically as chaotic. The results presented in this paper are important in the interpretation of field measurements and indicate the limits of large-scale computer simulations for the prediction of directional tendencies.
Fracturing of High-Temperature, Naturally Fissured, Gas-Condensate Reservoirs
Authors: Cikes Marin , Economides Michael J.
Published: December 2007

Eleven hydraulic fracture treatments were performed in deep (3300 to 3800 m [10, 830 to 12, 470 ft]), extremely high-temperature (180 to 195°C [356 to 383°F]), naturally fissured, gas-condensate reservoirs. Formation permeabilities at the fracturedwell locations range from 0.003 to 0.2 md, while the initial formation pressure gradient is about 0.13 bar/m [0.57 psi/ft]. The producing fluid is high-gravity gas (0.83 to 1.15 to air) and contains up to 22% CO2 and up to 4% H2S. Job sizes have ranged from 300 to 2000 m3 [80, 000 to 528, 400 gal] of fluid and 50 to 600 Mg [110, 130 to 1, 321, 590 lbm] of high-strength proppant. This paper emphasizes the general approach to well completion and stimulation treatment design, treatment execution, and evaluation. Interesting items include the engineering of the fracturing fluids to sustain their viscosity at the extreme temperatures and to reduce leakoff in these highly fissured formations. An outline of the reservoir description is also given.

Post-treatment well production has been excellent in most cases. Well PI's increased from 0.01 to 0.6 m3/d·bar2 [0.0017 to 0.1 scf/D-psi2] to 0.235 to 7.83 m3/d·bar2 [0.04 to 1.3 scf/D-psi2]. Treatment results suggest that leakoff can be controlled with particulate agents, that delayed crosslinking is the only way to execute these treatments, and that hydraulic fracturing can greatly improve the production from naturally fissured formations. Fracture design and the predicted well production are compared with post-treatment performances in selected wells.
Imaging the Effects of Capillary Heterogeneities on Local Saturation Development in Long Corefloods
Authors: Graue Arne
Published: December 2007

Experiments on the effects of capillary heterogeneities and permeability variations on local saturation distributions were conducted using a nuclear saturation imaging technique. Capillary heterogeneities were obtained in alternating sand layers with different permeabilities in the direction of displacement. The paper reports wetting-phase accumulation at the transition zones, step-like saturation profiles, various recovery efficiencies, and different local residual saturations.
Free-Fall-Effect Calculation Ensures Better Cement-Operation Design
Authors: Campos Wellington , Lage A. C. V. M. , Poggio Ademar
Published: December 2007

A cement-operation simulator was developed that takes the free-fall effect into account. This simulator allows prediction of well-fluid behavior and pressure, making proper field-operation design possible. The proposed mathematical model was derived from mass and momentum conservation laws by means of a macroscopic balance that reduces field equations to a ID model. The resulting initial value problem is solved numerically with the Runge-Kutta method. Special care is taken to control the interfaces between two different fluids while the system is in free fall. A microcomputer program has been implemented with a user interface that permits complex well geometries. Other models are compared with the program to demonstrate its software capabilities.
Mothballing and Demothballing of an Onshore Oil Field
Authors: Benbrahim A. A.
Published: December 2007

This paper analyzes recent experience gained after mothballing and demothballing the Bab onshore oil field. It reviews the type and method of protectionlinhibition applied to the wells, flowlines, production and water injection facilities, and other related equipment. The work carried out during shutdown and field recommissioning is discussed along with reservoir engineering aspects, including the monitoring program and performance review. The method used to check the tubing integrity also is addressed. The impact and consequences of mothballing an onshore oil production field are presented, together with the findings and work done to recommission the field. The paper discusses the procedures used to protect the field facilities to minimize equipment deterioration and to optimize the cost of mothballing. The time required to recommission the field also is discussed.
Quantitative Monitoring of Gasflooding in Oil-Bearing Reservoirs by Use of a Pulsed Neutron Tool
Authors: Ruhovets Naum , Wyatt D. F.
Published: December 2007

We developed a new method to monitor gasflooding of oil reservoirs. The method is based on computing two porosities: the base true porosity determined before gasflooding and monitor-apparent neutron porosity determined after gasflooding. The base and monitor porosities provide determination of a hydrogen index of the reservoir fluid after the flooding. The hydrogen index is then used to determine saturation of the flood agent after flooding and, consequently, saturation of water and oil after flooding. An example of quantitative analysis of base and monitor logs illustrates monitoring of CO2 flooding by use of the described method.
Resource Description and Development Potential of the Ugnu Reservoir, North Slope, Alaska
Authors: Hallam R. J. , Plekenbrock E. J. , Abou-Sayed A. S. , Garon A. M , Putnam T. W. , Weggeland M. C. , Webb K. J.
Published: December 2007

The Ugnu deposit, located on the North Slope of Alaska, contains more than 6 billion bbl [954 × 106 m3] of oil in place (OIP) in the Kuparuk area. The oil has been biodegraded. At reservoir temperature, the dead-oil viscosity varies from 100, 000 to 10, 000, 000 cp [100 to 10 000 Pa·s]. The paper provides reservoir and geological descriptions of the resource and discusses the key aspects affecting development. These aspects include high-temperature formation damage, the projected production performance, and the design considerations for injecting steam through a thick permafrost interval.
Large-Diameter Glory-Hole Drilling: Evolution From 12- to 20-ft Diameter
Authors: Shields Roger
Published: December 2007

To drill for oil and gas in shallow, ice-infested waters, a hole needs to be excavated in the seafloor to protect subsea blowout preventers (BOP's) from ice-scour damage. Canadian Marine Drilling pioneered the use of large-diameter glory-hole drilling systems by designing, building, and patenting a 12-ft [3.7-m] -diameter prototype bit system, a 17-ft [5.2-m] -diameter upgrade, a 20-ft [6.1-m] -diameter standard system, and a 20-ft [6.1-m] -diameter enhanced system. The enhanced bit design incorporates high-pressure jetting, boulder storage, pilot-hole centering, and other features that allow a 36-in. [0.91-m] hole to be drilled through the body of the bit. An optional feature is the ability to drill and case the glory hole simultaneously. To date, penetration rates up to 4.5 ft/hr [1.37 m/h] in soils with a shear strength 5,000 lbf/ft2 [239 kPa] have been obtained. Glory-hole drilling times have been reduced from more than 20 days in 1978 to approximately 1% days since 1986.
Stochastic Characterization of Gridblock Permeabilities
Authors: Gómez-Hernández J. Jaime , Journel André G.
Published: December 2007

Permeability is generally measured at the core scale and only at a few sites. By using geostatistical techniques, one can generate alternative high-resolution images of the reservoir at the measurement scale. These images will honor both the data values at the data sites and some prior structural information as modeled, for example, by a covariance function. However, these images must be averaged to the scale of the flow-simulation gridblocks. Two questions arise: (1) how should averaging be carried out? and (2) could the gridblock values be generated directly from the core or log without the intermediary step of small-scale imaging? This paper proposes avenues to answer both questions. First, we propose an averaging technique from point to block permeabilities, accounting for the tensorial character of permeability. Second, we propose a method to infer the covariances and cross-covariances among the different components of the block permeability tensor, and the cross-covariances between these block values and the point measurements. This set of covariances and cross-covariances is then used to generate directly multiple, equally likely spatial realizations of gridblock permeability tensors conditioned to the point measurements. The method is not constrained by small variability of the underlying point permeability distribution, nor does it require a multi-Gaussian-related hypothesis.
A Laboratory Investigation of Permeability in Hemispherical Flow With Application to Formation Testers
Authors: Ramakrishnan T. S. , Dave Yogesh , Cappiello Alphonse
Published: December 2007

We use borehole and laboratory measurements with a probe to obtain local permeability estimates. Under ideal conditions sufficiently far from the probe, the flow induced is hemispherical. We describe an experimental apparatus that can flow fluids through a probe under isotropic confining stresses and present an analysis to deduce the optimal dimensions of a finite cylindrical rock to simulate hemispherical flow like that in a semi-infinite medium. We derive equations for permeability interpretation of laboratory measurements.

We made pressure measurements on a number of synthetic and natural rocks as functions of confining stress, probe size, flow rate, and flow direction. For synthetic rocks, the calculated permeability shows little dependency on these factors. For natural media, however, flow direction appears to have a major effect at high rates that increases with decreasing probe size. On the basis of these data, we propose a fines-migration mechanism. As expected, permeabilities show a hysteretic dependence on confining stress.

Hemispherical flow measurements with homogeneous porous media indicate that fluid injection would yield permeability close to the true value. Furthermore, sequential injection of multiple phases shows that endpoint effective permeabilities may also be obtained.
Comparison of Different Techniques for Obtaining Capillary Pressure Data in the Low-Saturation Region
Authors: Melrose J. C. , Dixon J. R. , Mallinson J. E.
Published: December 2007

Capillary pressure data obtained by different methods in the low-saturation range are compared at the same values of the Leverett J function. The paper shows that in this range, saturations obtained by the mercury-injection method are significantly lower than saturations obtained by other standard methods.
Evaluation of Fractal Models To Describe Reservoir Heterogeneity and Performance
Authors: Pérez G. , Chopra A. K.
Published: December 2007

Our work uses fractals to characterize the spatial correlation structures of porosity and permeability of vertical and horizontal logs in a braided-fluvial sandstone reservoir. The data comprise cores and logs of adjacent vertical wells and logs of horizontal wells. Small-scale realizations of interwell heterogeneity were generated with successive random additions (SRA) technique for new observed fractal models. A deterministic description is also developed. Effects of fractal and deterministic reservoir heterogeneity on reservoir performance were studied for waterflood and water-alternating-gas (WAG) injection processes. The effects of scale up on spatial correlation of porosity was investigated.

The fractal model of fractional Brownian motion (FBM) in the horizontal direction, having same intermittency exponent as for fractional Gaussian noise (FGN) in the vertical direction, is not supported by log observations in horizontal wells. Fractal character of core and log data of vertical wells is similar. The incremental WAG recovery response compared to waterflooding response is more sensitive to reservoir heterogeneity. Scale-up experiments indicate that spatial correlation structure of reservoir properties may be different at different scales.

Results of this paper will be useful for evaluation of infill drilling, and design, selection, and optimization of an EOR process. The proposed techniques also provide a framework to quantify uncertainty in reservoir performance.
Characterization of the Jet Perforation Crushed Zone by SEM and Image Analysis
Authors: Asadi Mahmoud , Preston Floyd W.
Published: December 2007

This paper presents a method to measure porosity and permeability alteration of the crushed zone with scanning electron microscopy (SEM) and image analysis. A new phenomenon, shock metamorphism, was used to evaluate shock-wave penetration. Berea sandstone samples were prepared with a modification of the API recommended practice for test-sample preparation. Samples were perforated with low- and medium-penetration shaped charges. Analysis of the low-charge shot sample indicated an average porosity reduction of 25% and an average permeability reduction of 55% in the crushed zone. The sample shot with the medium-penetration shaped charge showed planar-element shock metamorphism.
Application of a General Material Balance for High-Pressure Gas Reservoirs
Authors: Fetkovich Michael J. , Reese Dave E. , Whitson C. H.
Published: December 2007

This paper presents the derivation of a general gas material balance that has particular application to high-pressure gas reservoirs, [both normal pressured and overpressured (geopressured)]. Its main application is to calculate original gas in place and assist in calculating remaining recoverable reserves from pressure/production data.

The form of the material-balance equation is (p/z)[1−c¯e(p)(pi−p)]=(p/z)i(1−Gp/G),, which includes a pressure-dependent cumulative effective compressibility term c¯e(p) that is defined in terms of the following reservoir parameters: pore compressibility, water compressibility, gas solubility, and total water associated with the gas reservoir volume. "Associated" water includes connate water, water within interbedded shales and nonpay reservoir rock, and any limited aquifer volume. c¯e physically represents the cumulative change in hydrocarbon pore volume (PV) caused by compressibility effects and encroaching water.

High pressure gas reservoirs typically have concave downward p/z vs. Gp plots which may result in serious overestimation of original gas in place and remaining recoverable reserves. The proposed form of the gas material balance equation provides a method to linearize the p/z vs. Gp plot, and thereby predict the true original gas in place. A method is suggested to determine initial gas in place by analyzing the behavior of cumulative effective compressibility backcalculated from pressure/production data. The c¯e(p) function determined by this procedure, or estimated from logs and geological maps when sufficient production data is not available, is then used to forecast pressure/cumulative behavior. Two field examples are provided showing the application of the material balance equation to high pressure gas reservoirs.
Evaluation of Corrosion Inhibitor for Low-pH Ammonium Nitrate-Methanol Completion Fluid
Authors: Krilov Zoran , Soric Tomislav , Tomic Mihovil , Wojtanowicz A. K.
Published: December 2007

A specially formulated completion fluid, low-pH ammonium nitrate-methanol-water mixture (ANM), compatible with argillaceous and calcareous Adriatic Sea sandstone formations, appears to be very corrosive for steel wellbore equipment. More than 12 commercially available, as well as some originally formulated, chemical additives were laboratory tested at room temperature using weight-loss and electrochemical methods to find an effective corrosion inhibitor for ANM.

Two inhibitors, a commercially available, organic, amine base (OA) and an originally formulated, inorganic, ammonium dihydrogen phosphate base (IB), showed effective protection of carbon steel in contact with ANM fluid (corrosion rate was less than 5 mil/yr). Both selected corrosion inhibitors did not exhibit any additional rock permeability impairment during fluid-rock compatibility flow tests if ANM fluid was filtered before injection into the core samples. For inorganic inhibitor IB, additional filtration of inhibited fluid is not required.
Strategies and Structures for Drilling and Service Contracts in the 1990's
Authors: de Wardt J. P. , van Gils J. M. I.
Published: December 2007

Drilling in the nineties initiatives were introduced to the industry in early 1990. Contractual mechanisms for application of these initiatives have been developed. A strategy is developed for integrating services to provide a total service concept either directly through or parallel with a drilling contractor. Development of cooperative customer/supplier relationships are emerging as the way to sustain per-formance improvements.
Rheologically Stable, Nontoxic, High-Temperature, Water-Based Drilling Fluid
Authors: Elward-Berry Julianne , Darby J. B.
Published: December 2007

An exceptionally stable, high-temperature, water-based drilling fluid has been developed based on a fundamental redesign of drilling fluid components and functions, while still using commercially available materials. Rheological stability was characterized by extensive Fann 50C low-shear-rate viscosity vs. temperature studies and supporting viscoelastic rheological data. The fluid has been used in both offshore and land applications, at temperatures as high as 420°F and densities as high as 15.5 lbm/gal.
Quantitative CO2-Flood Monitoring—Denver Unit, Wasson (San Andres) Field
Authors: Kittridge Mark G.
Published: December 2007

This paper presents a technique for monitoring CO2-flood response and performance with wireline-derived petrophysical data. Gas saturation data derived with this method are in agreement with independent estimates available from a CO2 pilot project. Examples show the application of the method in the Denver unit (DU). Results obtained with this technique are useful for quantifying CO2 saturation, monitoring flood progress and vertical sweep, identifying potential out-of-zone injectant losses, and detecting non-responding layers.
Influence of Wellbore Hydraulics on Horizontal Well Pressure Transient Behavior
Authors: Suzuki Koichi
Published: December 2007

In this paper, we discuss the influence of wellbore hydraulics in a horizontal wellbore on horizontal well pressure transient behavior. A finite-conductivity solution is obtained by a semianalytical method that incorporates three-dimensional (3D) flow in a reservoir and fluid flow inside a wellbore ranging from laminar to turbulent-flow regimes. On the basis of the finite-conductivity solution, finite-conductivity pressure transients are presented in terms of type curves, pressure derivatives, production distribution along a wellbore, and a pressure difference between the two ends of a wellbore. Furthermore, we provide a quantified criterion that allows us to approximate finite-conductivity solutions to an infinite-conductivity solution with respect to the following parameters: a formation flow capacity, a wellbore length, a wellbore radius, a relative pipe roughness, and the Reynolds number at the downstream end of a wellbore.
Estimates of Formation Sound Speed From Ultrasonic Reflections
Authors: Davidson J. A. , Morriss S. L. , Podio A. L.
Published: December 2007

This paper presents preliminary results from experimental research concerning the ultrasonic reflectivity of rock samples. The goal is to determine whether meaningful petrophysical properties can be obtained through the analysis of reflected acoustic signals of the type produced with the new generation of ultrasonic borehole televiewers. Present emphasis is on analysis of the full-reflected waveform. Time-domain samples of the transmitted and reflected signals are transformed into the frequency domain by means of digital Fourier methods to determine the complex reflection coefficient of the rock. A simplified viscoelastic wave-propagation model converts the reflection coefficient estimates into wave velocity estimates. Sound speed estimates in reasonable agreement with those determined by use of standard experimental techniques have been obtained for a variety of sandstone samples. Signal-processing techniques for the analysis of waveforms recorded in an attenuating mud-filled borehole have been developed and tested in the laboratory.
Practical Application of Fractal Pressure-Transient Analysis in Naturally Fractured Reservoirs
Authors: Acuna J. A. , Ershaghi Iraj , Yortsos Y. C.
Published: December 2007

Pressure-transient tests in naturally fractured reservoirs often exhibit nonuniform responses. Various models explain such nonuniformity; however, their relevance is often not justified on a geologic basis. Fractal geometry provides a method to account for a great variety of such transients under the assumption that the network of fractures is fractal. This paper presents an application to real well tests in various fractured reservoirs. The physical meaning of the fractal parameters is presented in the context of well testing. Examples showing a behavior similar to the finite-conductivity fracture model or to spherical flow are presented and explained by the alternative of fractal networks. A behavior that can be mistakenly interpreted as a double-porosity case is also analyzed.
Variable S-Matrix Method To Compensate for the Influence of Shaliness on Pulsed-Neutron-Capture Log Response
Authors: Neuman Charles H.
Published: December 2007

An important limitation in applying pulsed-neutron-capture (PNC) logs to measure fluid saturation is the imperfect correction for the influence of rock-matrix shaliness. Most methods for calculating saturations when log data are influenced by shaliness use gamma ray response to divide the Σ measured into clean sand and shale components. The nonlinear relation between shale volume and fractional gamma ray response commonly assumed results in significantly smaller correction for intermediate shaliness than would a linear relationship. This paper presents core data that support the idea that Σma, varies almost linearly with gamma ray response. A simple method to compensate for shaliness is proposed that uses gamma ray response to predict composite Σma rather than dividing the rock matrix into sand and shale components.
Stochastic Reservoir Modeling Using Simulated Annealing and Genetic Algorithms
Authors: Sen Mrinal K. , Datta-Gupta Akhil , Stoffa P. L. , Lake L. W. , Pope G. A.
Published: December 2007

This paper discusses and compares three different algorithms based on combinatorial optimization schemes for generating stochastic permeability fields. The algorithms are not restricted to generating Gaussian random fields and have the potential to accomplish geologic realism by combining data from many different sources. We have introduced a "heat-bath" algorithm for simulated annealing (SA) as an alternative to the commonly used "Metropolis" algorithm and a new stochastic modeling technique based on the "genetic" algorithm. We applied these algorithms to a set of outcrop and tracer flow data and examined the associated uncertainties in predictions.

All three algorithms reproduce the major features of permeability distribution and fluid flow data. For relatively small problems, the Metropolis algorithm is the fastest. For larger problems, the heat-bath algorithm is at least as fast and often faster than the Metropolis algorithm, with significant potential for parallelization. The performance of the genetic algorithm is highly dependent on the choice of population size and probabilities of crossover, update, and mutation.
The Use of Air-Bubble Spoilers To Suppress Vortex-Induced Vibrations of Risers
Authors: Abbassian Fereidoun , Moros Thanos
Published: December 2007

For this paper, we considered the feasibility of a bubble spoiler as a vortex-suppression device. The introduction of bubbles in the flow reduced the dynamic forces on the riser by destroying the vortex-shedding structure. We constructed a semiempirical equation relating the reduction of the vibration amplitude to the amount of air required. Then we considered the effectiveness of bubble spoilers as a suppression device by investigating the dynamic response of a typical jack-up drilling riser for various suppression scenarios. We found that the volume of air required to effectively suppress the vortices was about 2.0 m3/s at 500 kPa.
Transient 2D Flow in Layered Reservoirs With Crossflow
Authors: Liu Ci-qun , Wang Xiao-Dong
Published: December 2007

Analytical solutions of transient 2D flow through double-permeability media are presented. The pressure response of a vertically fractured well intercepting a layered reservoir with crossflow is described through the methods of integral transform and variable separation. The influences that parameters of a double-permeability model such as the permeability ratio, Fk interporosity flow parameter, λ, and storativity ratio, ω, have on the pressure response of a fractured well are calculated and analyzed by numerical inversion. Log-log diagnosis graphs of fractured well pressure are given and analyzed here.
How Fluid Loss Influences Primary Cementing: Literature Review and Methodology
Authors: Daccord Gérard , Baret J. F.
Published: December 2007

Fluid loss during cementing has long been suspected to have detrimental consequences, including reduction of slurry volume; increased slurry density and viscosity; cement-cake deposition, which may cause additional decreases in friction pressure during placement; and near-wellbore reservoir filtrate invasion. This paper briefly reviews and quantifies these consequences. Given well geometry, job design, and cement slurry fluid-loss properties, we show how to predict the critical phenomena that are most likely to impair cementing and the most sensitive well or slurry parameters. By coupling these results and the degree of accuracy with which well parameters are known, one can calculate prediction uncertainty (the error bar) and deduce the key parameters that affect this error bar.
Effects of Crossflow and Layer Permeability Contrast on the Effectiveness of Gel Treatments in Polymer Floods and Waterfloods
Authors: Gao Hong W. , Burchfield Thomas E.
Published: December 2007

Permeability-blocking treatments with gels were simulated for a reservoir composed of two independent, homogeneous layers, each with traverse isotropic permeability. Horizontal permeability contrast between the layers ranged from 0.0033 to 0.5. Vertical/horizontal permeability ratios for both layers were the same and set between 0.001 and 0.1. Gel treatments were pumped into the high-permeability lower layer. Polymer floods/waterfloods entered both layers; allocation of the pumped fluid depended on the mobilities for each layer. Near-wellbore gel treatments increased oil recovery in cases of low vertical/horizontal permeability ratios by improving the injection profile. Under the conditions examined (equal layer thickness and 3-cp oil and 0.8-cp water viscosities), results were most beneficial in reservoirs with a horizontal permeability contrast of ≈ 0.05. Gel treatments placed in the reservoir at the near-wellbore region or deep in the reservoir were ineffective in cases of high crossflow.
Water/Oil Relative Permeability Endpoints of Intermediate-Wet, Low-Permeability Rocks
Authors: Kamath Jairam , deZabala E. F. , Boyer R. E.
Published: December 2007

The relative permeability endpoints of low-permeability, intermediate-wet mudstones increased with flow rate. This was because of both a decrease in capillary end effect and an increase in capillary number. Hence, conventional analysis will incorrectly describe field behavior. We recommend an improved methodology.

We imaged steady-state saturation profiles at the end of different rate floods on one sample. We analyzed these profiles, which were axially nonuniform, to obtain capillary-end-effect-corrected data for each flow rate. The saturation distributions were also radially nonuniform. We characterized core-scale heterogeneity using a miscible flow test and examined the influence of heterogeneity.

We conducted long-term tests on three short samples to study the higher-capillary-number regime. These tests displayed the existence of a critical capillary number, where the water relative permeability endpoint increased dramatically. The corresponding rate was over a magnitude smaller than flow rates traditionally recommended to eliminate capillary end effects.
New Results on Transient Well Tests Analysis Considering Nonlaminar Flow in the Reservoir
Authors: Rodolfo Camacho-V. , Mario Vásquez-C. , José Roldán-C. , Fernando Samaniego-V. , Luis Madas-C.
Published: December 2007

The aim of this work is to examine the wellbore pressure behavior in reservoirs with single-phase non-Darcy flow conditions produced at a constant sandface rate. The transient flow period is analyzed by means of results generated with a finite difference model. Analytical expressions of pressure drop and its semilogarithmic slope are presented for the first time. These equations contain the laminar flow solution as a particular case, and they provide means to evaluate the total skin factor. Another use of the analytical solution to the non-Darcy flow problem is to identify the presence of inertial effects by using a diagnostic plot, which consists of graphing the derivative of the pressure data vs. the inverse of the square root of time on a Cartesian paper. In this way, an analyst easily can predict the magnitude of the skin owing to nonlaminar flow under any condition of mechanical skin and rate. Furthermore, better stimulation jobs can be designed if non-Darcy flow conditions during a transient test are properly identified through the methodology presented in this study.

The use of the methodology obtained in this work is illustrated with synthetic examples for homogeneous and naturally fractured reservoirs. Also, a field example of an undersaturated reservoir and a dry gas case (taken from the literature) shows the application of this technique. For the case of naturally fractured reservoirs, new insights are provided.
Pressure and Volume Evolution During Gas Phase Formation in Solution Gas Drive Process
Authors: Firoozabadi Abbas , Kashchiev Dimo
Published: December 2007

The pressure and volume evolution during gas phase formation in porous media is modelled by an instantaneous nucleation process. This model reveals that supersaturation (i.e., non-equilibrium state) for gas bubble formation is affected by the pressure decline rate. As a result, laboratory recovery measurements are influenced by rate effects, and material balance expressions may not be used to calculate the amount of oil and gas phases.
Coiled Tubing Sidetrack: Slaughter Field Case History
Authors: Hightower C. M. , Blount C. G. , Ward S. L. , Martin R. F. , Cantwell D. L. , Ackers M. J.
Published: December 2007

The paper describes the successful sidetrack of an oil well in the Slaughter Field in West Texas using coiled tubing (CT). Several first-time CT operations performed during this workover include:

Setting a whipstock in casing on CT Cutting a window with CT Using mud pulse measurement-while-drilling (MWD) with CT in a "real" well Use of a fluid-operated orientation tool for in-hole toolface changes Successful use of an "autodriller" to maintain weight on bit while drilling

Directional control of the sidetracked hole proved to be ineffective due to a surface software problem. The resultant wellbore was not horizontal as planned, but instead closely paralleled the original well for much of its length. However, the previously non-productive well flowed 1000 barrels of fluid per day (BFPD) from the sidetrack following the workover.
Reservoir Description by Integrating Well-Test Data and Spatial Statistics
Authors: Sagar R. K. , Kelkar M. G. , Thompson L. G.
Published: December 2007

We present a method to integrate log, core, and well-test pressure data to describe reservoir heterogeneities. The conditional simulation method of simulated annealing is used to incorporate diverse sources of data.

We use analytical solutions for radially heterogeneous reservoirs to define an equivalent radial permeability and a corresponding region of investigation. By numerical experimentation on drawdown well-test simulations in heterogeneous permeability fields, we determine that a weighted-area-based geometric average of the grid-block permeabilities within the region of investigation best defines the equivalent radial permeability. This information, along with the spatial statistics from core/log data, are coded into the overall objective function of the simulated annealing algorithm to yield a consistent reservoir description.
The Use of Broadband Microseisms for Hydraulic-Fracture Mapping
Authors: Sleefe G. E. , Warpinski N. R. , Engler B. P.
Published: December 2007

We conducted a series of hydraulic-fracture experiments to examine improvements in seismic-fracture diagnostic technology that are available with the application of advanced receiver capabilities. We present characteristics of the microseisms, tool response behavior, and the results of the tests.
Laboratory Development and Field Testing of Succinoglycan as a Fluid-Loss-Control Fluid
Authors: Lau Hon Chung
Published: December 2007

Research has shown that the biopolymer succinoglycan possesses a unique combination of desirable properties for fluid-loss control, including ease of mixing; cleanness; shear-thinning rheology; temperature-insensitive viscosity below its transition temperature, Tm; and adjustable Tm over a wide range of temperatures. Because succino-glycan is a viscous fluid, it relies solely on viscosity to reduce fluid loss. It does not form hard-to-remove filter cake that can cause considerable formation damage. On the basis of these findings, we used succinoglycan successfully as a fluid-loss pill before and/or after gravel packing in > 100 offshore wells. Calculations based on laboratory-measured rheology and field experience have shown succino-glycan to be effective in situations where hydroxyethyl cellulose (HEC) is not. Even fluid loss > 40 bbl/hr was reduced to several bbl/ hr after application of a properly designed succinoglycan pill. Most wells experienced no production problem after completion.
Field Test of a Downhole-Activated Centralizer To Reduce Casing Drag
Authors: Kinzel Holger , Calderoni Angelo
Published: December 2007

A good cementation is based on an adequate centralization. Conventional bow-type centralizers create a drag force, which is not acceptable under certain conditions. The downhole-activated centralizer (DACTM ) was developed for use in highly inclined wells and whenever restrictions in the wellbore like close tolerance wellheads have to be passed. It can be released by external hydraulic pressure, by temperature or by a chemical reaction.

The first downhole-activated centralizers with pressure released locking mechanism were field tested in two wells offshore Italy.

These field tests proved the function and the effectiveness of the downhole-activated centralizers under operational conditions.
Comparison and Verification of Electric-Log-Derived Rock Stresses and Rock Stresses Determined From the Mohr Failure Envelope
Authors: Hareland Geir , Harikrishnan Ramesh
Published: December 2007

This paper evaluates the correlation between values of minimum principal in-situ stress derived from sonic logs and those obtained from triaxial core tests and coefficient for earth at rest correlations. The minimum principal in-situ stress is then compared to actual field mini-frac test data, which accurately determine the minimum principal in-situ stress and are used to verify the accuracy of the correlations. The cores and the mini-frac stress test were obtained from two wells, the Gas Research Inst.'s (GRI's) Staged Field Experiment (SFE) #1 well through the Travis Peak Formation in the East Texas Basin, and the U.S. Dept. of Energy's Multiwell Experiment (MWX) wells located west-southwest of the town of Rifle, Colorado, near the Rulison gas field. Results from this study indicate that of the two approaches used in obtaining the minimum principal in-situ stress, the normalized Mohr failure envelope approach is in better agreement with the measured stress values (from mini-frac tests) in sandstone, while the sonic log approach gives closer match in shale.
A Study of Formation Damage of Selective Clay and Other Minerals Caused By Bacterial Plugging
Authors: Hayatdavoudi Asadollah , Ghalambor Ali
Published: December 2007

In this study, we investigate the nature of formation damage caused by growth of bacteria on formation minerals. The bacteria growth results in plugging the pores with consequent reduction in permeability. We performed experiments by injecting live bacteria cells through pipettes packed separately with different clay and nonclay minerals. We tested a total of eight minerals: nonclay (quartz, feldspar, calcite, and olivine) and clay (illite, kaolinite, calcium montmorillonite, and sodium montmorillonite). Bacteria used for the experiment was Bacillus Cereus. A 10% trypticase soy broth (TSB) solution as a brine was passed through packed minerals, and the flow rates were recorded periodically before and after the bacteria injection. The flow pressure, temperature, and the concentration of bacteria cells were held constant during these experiments. The absolute permeability of packed porous media was determined with Darcy's equation. The pore plugging effects were analyzed with the percentage ratio of reduced absolute permeability to the initial absolute permeability vs. the injection PV.

We measured the zeta potential for each mineral under test before and after its interaction with bacteria. This was another way of testing the affinity of bacteria with a negative charge toward any particular mineral and their subsequent accumulation around that mineral in the pore space. For this purpose, we used a particle microelectrophoresis instrument to measure the zeta potential of the bacteria, the minerals under test, as well as the cumulative zeta potential of mineral-bacteria assemblage.

Permeability measurements and zeta potential readings indicate that the type of mineral present has a significant effect on plugging characteristics of the porous media. We determined that olivine as compared with other minerals had the highest tendency to attract bacteria. The reason for this appears to be the abundance of magnesium and iron as nutrient sources for bacteria. These studies also showed that both clays (calcium and sodium montmorillinite) carry a larger net negative charge than other clay minerals after interaction with bacteria. To be certain about the accuracy of the results of mineral-bacterial interaction, we measured the optical density of solutions as well with a third testing before and after injection of bacteria into porous column. Furthermore, we verified the growth and plugging effect of bacteria in the minerals porous column through the use of a scanning electron microscope (SEM). As remedial measures, although not a part of this work, we have recommended a few techniques.
Application of a Microbial Selective-Plugging Process at the North Burbank Unit: Prepilot Tests
Authors: Jenneman G. E. , Moffitt P. D. , Young G. R.
Published: December 2007

Microbial enhanced-oil-recovery (MEOR) nutrients were injected in an injection well at North Burbank unit (NBU) in Oklahoma to plug off high-permeability layers through the growth of indigenous microorganisms and to divert injection fluid to lower-permeability, higher-oil-saturation zones. Several different types of treatments were performed using both sequential and co-injection of nutrients. Pressure falloff/injection tests and vertical injection profiles were conducted before and after nutrient injection. The results of pressure injection tests following co-injection of nutrients and an incubation period indicated a 33% drop in the effective permeability to the injection fluid and a negative skin factor, while injection profile surveys showed a 33% reduction in the zone taking water. Swabbed samples from the injector following shut in revealed abundant bacterial concentrations and products as well as oil and inorganic solids. Although significant in-depth permeability reduction was observed following nutrient co-injection tests, the unstable behavior of the plug suggested that insufficient biomass was being formed to effectively seal off the higher-permeability zones.
Recent Advances in Understanding Perforator Penetration and Flow Performance
Authors: Halleck P. M.
Published: December 2007

Driven by the importance of perforation performance in both natural and stimulated completions, our understanding of the factors that control penetration depth and formation damage has improved significantly over the last 10 years. Improved test procedures and their tabulated results are now available to predict downhole penetration as a function of rock properties and overburden stress. Progress has also been made in understanding the nature of permeability damage around perforations and how to prevent, remove, or bypass it. In particular, the mechanisms behind underbalanced perforating are being clarified, leading to better engineering of perforating procedures and better prediction of their results.