bluuebunny/crossref_metadata_2025 huggingface dataset:
Heterogeneity Modeling Used for Production Simulation of a Fluvial Reservoir
Authors: Tyler Kelly J. , Svanes Tarald , Henriquez Adolfo
Published: December 2007

The application of a stochastic model used for the description of channel sand and overbank flood plain shales of the complicated and heterogeneous Statfjord formation of a field under evaluation for development in the North Sea is presented. The channel sands contain other internal sand facies that have permeabilities different from those of the channels. These internal facies are also modeled. Permeability variations are modeled for each facies type with a Gaussian random field. At the facies and permeability stages of modeling, the stochastic model honors well data, seismic interpretations, and sedimentological knowledge gained by geologists from neighboring fields, outcrop analog studies, and general sedimentological principles. Permeability data, modeled in a fine grid, is upscaled to a coarser corner-point geometry grid used in numerical reservoir simulation. Production profiles resulting from geologic realizations carried forward to the reservoir simulator are compared with profiles obtained from a base-case model with smoothed permeability. The uncertainty originating from the unknown facies architecture and permeability distribution between wells is evident from production-profile analysis.
Analysis of Transient-Pressure Response of Horizontal Wells in Bounded Reservoirs
Authors: Du Kui-Fu , Stewart George
Published: December 2007

The main purpose of this paper is to present analysis methods for transient-pressure response of horizontal wells in bounded reservoirs. Several lateral-boundary models are examined, and detailed explanations of possible derivative responses are given. New, generalized diagnostic rules and well-test analysis procedures are provided. Practical issues are discussed at length.
Shallow Horizontal Drilling in Unconsolidated Sands Offshore California
Authors: Payne J. D. , Huston C. W. , Bunyak M. J.
Published: December 2007

Four shallow horizontal wells were drilled from Platform C in Dos Cuadras field offshore California to recover reserves inaccessible with conventional drilling techniques. The wells had true vertical depths (TVD's) ranging from 746 to 989 ft with total horizontal displacements from 1, 613 to 3, 788 ft. The wells had horizontal displacement TVD ratios up to 3.95. The targets were unconsolidated, high-permeability sands. This paper details well planning, drilling, and completion.
Formation Damage and Filter Cake Buildup in Laboratory Core Tests: Modeling and Model-Assisted Analysis
Authors: Liu Xinghui , Civan Faruk
Published: December 2007

A mathematical model for the analysis of formation damage in laboratory core tests is presented. The model considers filter cake buildup on sand face, invasion of external particles, release of formation fines, migration and retention of external particles and formation fines, interphase transfer of particles, and alteration of porosity and permeability. The effects of wettabilities of fine particles and pore surfaces, relative permeabilities and capillary pressure on formation damage in two-phase flow conditions are also included. Simulation results from the model are in good agreement with experimental results from core tests. This model can be used for the analysis of formation damage due to particulate processes in laboratory core tests.
Helical Buckling and Lock-Up Conditions for Coiled Tubing in Curved Wells
Authors: He Xiaojun , Kyllingstad Age
Published: December 2007

An improved formula for critical buckling loads has been derived. This formula, which takes the well curvature into account, has been verified in small scale laboratory tests. The theory has been applied to survey data from a real horizontal well and it predicts that the well curvature substantially affects the critical force for helical buckling, and thereby also the maximum run-in length of coiled tubing. Criteria for operational limits, such as lock-up and tubing failure, are also discussed in the paper.
Effects of pH and Shear on the Gelation of a Xanthan-Cr(III) System
Authors: Dolan D. M. , Thiele J. L. , Willhite G. P.
Published: December 2007

A study was undertaken to determine the effects of pH and shear rate on the gelation of a xanthan-Cr(III) solution of the type that has been used successfully for permeability modification of oil fields. The rate of gelation and gel strength were determined using small-amplitude oscillatory methods under zero shear and superimposed steady-shear rates approximating those anticipated during placement in the porous matrix. At zero-net shear, the rate of gelation was first order in the inverse of the hydrogen-ion concentration up to pH 6.5. At pH 6.5 and above, precipitation of chromium slowed the gelation. The effect of shear was quite pronounced. No permanent gel structure was observed while the gel was under shear, regardless of pH or shear rate. Gelation was observed after shear was removed. However, the rate of gelation was 1.5 to 2 orders of magnitude slower than observed for zero-net shear runs. The rate of gelation decreased with increasing duration of shear. This effect was more pronounced at higher pH, indicating the ratio of applied-shear duration to solution-gel time may be the factor controlling gelation. Gels were not observed when the gel system was subjected to continuous shear for times longer than the zero-shear gelation time.
Relationship of Core-Scale Heterogeneity With Non-Darcy Flow Coefficients
Authors: Al-Rumhy M. H. , Kalam M. Z.
Published: December 2007

An experimental research program to investigate the effects of liquid saturations upon non-Darcy flow coefficients is presented. The presence of a wetting phase fluid plays an important role in high velocity flow of a gas well, producing condensate or water, and in propped fractures containing liquid saturations.

This study initially examines the errors commonly encountered but ignored in evaluating the permeabilities and the coefficient of inertial resistance during the flow of gases through porous media. Experimental techniques, such as constant overburden pressure, changing overburden pressure, forward flow, and backpressure flow, are applied to optimize and obtain accurate evaluations of Klinkenberg parameters and inertial resistance coefficients for a selection of Omani reservoir cores. Gas-slippage factor significantly influences the derived viscous and inertial coefficients from highvelocity gas flow data. An increasing wetting phase saturation increases the non-Darcy coefficient up to thirty-fold.

Analysis of the experimental data revealed that unique relationships exist between the non-Darcy flow coefficients and the equivalent liquid permeability, porosity, and liquid saturation. Heterogeneity of the core as mapped by pore-scale measurements provide an insight into the mechanism for such a large increase in the non-Darcy coefficients.
Drilling Extended-Reach/High-Angle Wells Through Overpressured Shale Formation
Authors: Guild G. J. , Jeffrey J. T. , Carter J. A.
Published: December 2007

This paper discusses Amoco U.K. Exploration Co.'s unsuccessful attempt to drill an extended-reach well in Arbroath field (U.K. Block 22/17) and how problems encountered were resolved on subsequent high-angle and extended-reach drilling operations in the field. The resolution of these problems over the course of drilling four high-angle wells and one extended-reach well involved (1) de-termining mud weight by use of rock mechanics principles, (2) evaluating hole conditions with a wellsite torque-and-drag program, (3) optimizing BHA performance, and (4) developing techniques for effective high-angle hole cleaning. By use of the methods outlined in this paper, improved drilling performance and significant cost savings are demonstrated.
A New Methodology for Minimizing Investment in the Development of Offshore Fields
Authors: Garcia-Diaz Juan C. , Startzman Richard , Hogg Gary L.
Published: December 2007

The development of an offshore field is often a long, complex, and extremely expensive undertaking. The enormous amount of capital required for making investments of this type motivates one to try to "optimize" the development of a field. This paper provides an efficient computational method to minimize the initial investment in the development of a field. The problem of minimizing the investment in an offshore field is defined here as the problem of locating a number of offshore facilities and wells and allocating these wells to the facilities at minimum cost. Side constraints include restrictions on the total number of facilities of every type and design and various technology constraints. This problem is modeled as a 0/1 integer program. The solution method is based on an implicit enumeration scheme using efficient mathematical tools, such as Lagrangean relaxation and heuristics, to calculate "good" bounds and, consequently, to reduce the computation time. The solution method was implemented and tested on some typical field-development cases. Execution times were remarkably small for the size and complexity of the examples. Computational results indicate that the new methodology outperforms existing methods both in execution time and in memory required.
Drilling Fluid Conversion: Selection and Use of Portland or Blast-Furnace-Slag Cement
Authors: Schlemmer R. P. , Branam N. E. , Edwards T. M. , Valenziano R. C.
Published: December 2007

Conversion of drilling mud to oilwell cement has advanced from an unpredictable laboratory curiosity to a practical reality. Recent field introduction of polymer dispersants, organic accelerators, and an alternative cementitious material have provided two refined and prac-tical conversion methods. Each method claims universal applicability plus performance superior to that of conventionally mixed and pumped Portland cement. Both blast-furnace-slag (BFS) and Portland cement are used for drilling-mud conversion. Portland and BFS mud conversions can use the same recently developed polymer dispersants, filtration-control materials, defoamers, and other additives that are typically used to treat high-temperature, highly-salt-contaminated drilling muds. Experience in the field and laboratory has demonstrated that conversion with BFS or Portland cement is essentially one technology from a pilot-test and application standpoint. While use of these two materials reflects essentially one technology, distinct performance and cost differences exist. These differences define the specific economic application advantages and must be considered when a decision to use BFS or Portland cement is made. Rational selection of mud-to-cement conversion depends on a detailed economic comparison of basic materials, logistics, and equipment availability.
Effects of High-Speed Pipe Rotation on Pressures in Narrow Annuli
Authors: McCann R. C. , Quigley M. S. , Zamora M. , Slater K. S.
Published: December 2007

Variations in annular geometry, eccentricity, and pipe rotational speed strongly affect pressure loss of a fluid flowing in the narrow annulus of a slimhole well. Due to these factors, accurately calculating and controlling pressures in slimhole wellbores are difficult. Accurate pressure calculations are crucial for safely controlling formation pressures and protecting wellbore integrity. Attempts to model non-Newtonian fluid flow in narrow annuli with high-speed pipe rotation have been hampered by the lack of quality data. The results of numerous annular flow experiments presented herein partially correct this deficit. These results supplement annular pressure data from a 2500-ft slimhole test well and standpipe pressure data from a slimhole exploration well.

Sensitive pressure measurements were used to characterize fluid flow in concentric narrow annuli created by a 1.25-in. diameter (Dp) steel shaft inside clear acrylic tubes with 1.375-in. to 1.75-in. inside diameter (Dh). Similar tests were conducted in a fully eccentric annulus formed by the steel shaft inside an acrylic tube with Dh = 1.50 in. Maximum shaft rotational speed was 900 rpm and maximum fluid flow rate was 12 gpm. Test fluids included water, glycerin solutions, viscosified clear brines, and several slimhole drilling muds.

Models selected from the public domain were used with varying success to calculate results from the hydraulics tests. Simple models typically used by the drilling industry calculated annular pressure loss for non-rotating cases with reasonable accuracy. However, the simple models seldom calculated absolute effects of pipe rotation even though calculated trends correctly match those in measured data. For turbulent flow, annular pressure loss increased with increasing pipe rotation. For laminar flow, annular pressure loss decreased with increasing pipe rotation. In all cases, annular pressure loss increased with increasing mud rheology and decreased with increasing eccentricity.
Pressure Transient Behavior In Reservoirs With An Internal Circular Discontinuity
Authors: Rosa Adalberto J. , Horne Roland N.
Published: December 2007

This paper presents the pressure transient response for reservoirs with an internal circular subregion. The solution is a generalization of that previously presented in the literature, which assumed that the subregion was either an impermeable barrier or a constant pressure circle. Two cases were considered, with the well located either inside or outside the circular discontinuity. When the well is located inside the circular subregion, the solution developed in the study is also a generalization of the well-known pressure response for a composite two-region system.

The solution was obtained by using the concept of Green's function and by applying the Laplace transformation technique. The Laplace space response, although very complex, was inverted to real space with the Stehfest1 algorithm.

When the well is located inside the circular subregion, the wellbore pressure response shows a behavior typical of radial composite systems, except for the effect of the well eccentricity, which acts as a skin factor. For the case where the active well is external to the subregion, three flow regimes are observed. The initial infinite-acting behavior and the late-time pseudoradial flow produce semilog straight lines which are parallel and reflect the transmissivity of the external region. The long-time effect of the discontinuity can be regarded as an apparent skin effect.

The dependence of the solution on the diffusivity ratio, the mobility ratio, the geometric configuration and the size of the system was also investigated in the study.

The solution can be used to simulate the pressure behavior for reservoirs which contain circular or approximately circular discontinuities, such as those caused by variations in rock and/or fluid properties due to the presence of shale lenses or fluid injection, for instance. The pressure solution can also be used to interpret single-well or interference tests in systems with these configurations.
Pressure Behavior in Finite Channel-Levee Complexes
Authors: Bourgeois M. J. , Daviau F. H. , de la Combe Jean-Luc Boutaud
Published: December 2007

In a channelized environment, the overbank facies (levees, crevasse-splays) have poorer reservoir qualities than the channel itself. In this type of environment, the geometry of this two-feature complex, together with its permeability contrast, influences the pressure transient response. The pressure behavior of this kind of reservoir has been computed for well-test analysis purposes.

Our geometric model comprises a main channel bounded laterally with finite or infinite width levees. It is conceptualized as a composite linear strip reservoir with different mobilities and diffusivities. The length of the whole system also can be either finite or infinite. The solution uses a time-space Laplace transform and a spatial Fourier transform already used by Ambastha,1 Butler,2 and Kuchuk.3 Moreover, our model adds lateral limits by no-flux boundary conditions and longitudinal limits by superposition of image wells or by using a finite Fourier transform.

This paper exhibits specific features of the type curves generated for the model. The influence of the levees and of the permeability ratio between channel and levees on the derivative signature is discussed. Hints are given for diagnostic purposes and parameter estimation. Fieldcase buildup analyses show the applicability of the approach.
Distinct Element Simulation of Faulted Reservoir Behavior
Authors: Makurat A. H. , Gutierrez Marte , Knapstad Børge , Johnsen J. H. , Koestler A. G.
Published: December 2007

With a distinct element code, we analyzed a compartmentalized North Sea oil reservoir's mechanical behavior during fluid pressure drawdown. Special emphasis was given to the affect of compartment pressure reduction on the activation of existing faults, the change of the fault-sealing properties as a result of fracturing of the intact rock mass, and the determination of the existing faults' behavior during fluid pressure drawdown with respect to shear displacement and changes in the fault/fracture conductivities. The simulations showed that several segments of the existing faults in the vicinity of the drawdown region could be activated. Some faults with shear stresses below peak showed large shear displacements and were therefore considered to be activated. Shear fracturing of the intact rock was found to be possible in several zones around the drawdown region.
An Improved Method for Acidizing Oil Wells in Sandstone Formations
Authors: Gidley J. L. , Brezovec E. J. , King G. E.
Published: December 2007

A previous analysis of field experience1 indicates that in the acidization of oil wells, unlike that of gas wells, response peaks at relatively low acid volumes per foot of formation treated, and declines beyond the optimum treating volume. One method of removing this treatment-volume barrier is to displace oil from the zone to be acidized and to replace it with gas. In this manner, the interaction between the spent acid products and formation fluids is similar to that found in a gas zone. This paper describes the results of acidizing oil wells where the resident oil in the near-wellbore region has been replaced with a gas. Early results with this treatment indicate an improved acid response, less stimulation of water, and reduced emulsion separation problems at the surface.
The Effects of Unbroken Fracture Fluid on Gaswell Performance
Authors: Voneiff G. W. , Robinson B. M. , Holditch S. A.
Published: December 2007

Research sponsored by the Gas Research Inst. (GRI) indicates unbroken fracture fluids can lower gas reserves by 30%, reduce initial gas rates by 80%, and delay fracture-fluid cleanup by weeks or months. The unbroken fracture fluids flatten the production profile. In extreme cases, gas production slowly increases for weeks or months despite constant flowing pressures. The fracture fluids must break to a viscosity of 50 cp or less to ensure that gas reserves are maximized.
The Application of Advanced PDC Concepts Proves Effective in South Texas
Authors: Dahlem J. S. , Baxter R. L. , Dunn K. E. , Arfele R. W. , Hicks M. G.
Published: December 2007

Over the years, a variety of problems with polycrystalline diamond compact (PDC) bit design and application has been documented, with "bit whirl" being identified as the cause of many inherent problems. The goal of most PDC manufacturers, and the subject of this paper, is development of a better-performing, "whirl-resistant" PDC bit design. Similarly, the goal for most operators is the lower cost resulting from effective application of such bits.

Toward those ends, a cooperative development effort between operators and a manufacturer was undertaken to apply advanced concepts effectively to the design, manufacture, and application of a new series of PDC bits in south Texas. Adoption of design concepts, such as force-balanced cutting structures, asymmetric blade layouts, spiral blade designs, and tracking cutter arrangements, proved effective in countering the destructive effects of bit whirl, and allowed PDC bits to be used in harder formations. Summaries of both operational and economic performance confirm the success of the undertaking.
Narrow Annulus Cementing in the Deep Anadarko Basin
Authors: Waters G. A. , Wray B. L.
Published: December 2007

With the widespread use of tubingless completions and narrow annulus liners now employed in the Anadarko Basin the applicability of conventional cementing placement techniques and cement systems has been brought into question. The narrower annuli necessitate the use of a more dispersed cement to impart acceptable friction pressure. Excessive friction pressure may lead to formation breakdown, lost circulation and potential well control problems. If lower friction pressures can be achieved higher pump rates should be attainable which may improve fluid placement efficiency.

The dispersed slurry must still maintain acceptable fluid loss control and solids suspension properties. These parameters are critical in narrow annulus cementing since high fluid loss and/or sedimentation is much more likely to cause annular bridging than in a conventional annulus.

As in most cases, it is desirable to use a slurry with a rapid and predictable transition from a fluid to set state. This will reduce the likelihood of reservoir fluids flowing into the wellbore and compromising the integrity of the cement as compressive strength develops.

It must be recognized that mud removal is critical in a narrow an-nulus because a small volume of contaminated fluid can occupy a large interval in the annulus. Fortunately, because of the narrow an-nulus, it may be possible to utilize turbulent flow profiles to remove drilling mud during the cementing process.

To address these issues a study was initiated to develop a methodology for cementing in this environment. The first step was to determine spacer and cement properties required to optimize mud removal and cement placement via computer modeling. Laboratory testing was then performed to develop spacer and cement systems to meet the required parameters. Third, the new fluids and placement techniques were employed in the field using placement pressures as an initial indicator of success or failure. Finally, a measure of zonal isolation was estimated through wireline bond logs to quantify the degree of success.
Asymmetrically Propped Hydraulic Fractures
Authors: Jeffrey R. G.
Published: December 2007

Mapping during and after mining of four hydraulic fractures placed in the German Creek coal seam of the Bowen Basin in Queensland, Australia, revealed that in all four cases the fractures were propped asymmetrically. Three treatments resulted in vertical fractures and one resulted in a T-shaped but mostly horizontal fracture. In all cases, the proppant extended to a greater distance in the down-dip than in the up-dip direction. The transport of proppant in the down-dip direction by gravity currents is consistent with the field and laboratory data and is able to explain the asymmetry.
Performance Evaluation of Trilateral Wells: Field Examples
Authors: Vo D. T. , Madden M. V.
Published: December 2007

Recent advances in horizontal drilling and completion technology have led to the successful completion of multilateral horizontal wells (wells with two or more laterals penetrating separate zones that produce through a single wellbore to the surface). Evaluating performance of these commingled horizontal wells poses unique problems that have led to development of a practical procedure for that puφose. This paper demonstrates a practical procedure used in evaluating the performance of three lateral (trilateral) horizontal wells. The procedure, coupling the analysis of pressure-buildup and rate/time data, involves use of a consistent mathematical model to generate pressure and rate responses for pressure-test interpretation and performance prediction. The procedure is demonstrated for several new trilateral wells drilled in the Dos Cuadras field, offshore California. Results from field tests indicate that the procedure is efficient in evaluating the performance of these wells. Reservoir and well parameters are obtained and the contribution of all laterals is confirmed from pressure-test interpretation. The computed model parameters are then used in a rate history match and accurate long-term performance predictions are made. Deconvolution is shown to improve the history-match process. In addition, the performance evaluation of these trilateral wells is compared with previously drilled single-lateral horizontal wells in the same field. The comparison confirms that the new trilateral horizontal well technology is economically viable, allowing reserves to be developed for approximately two-thirds the cost of three single-lateral horizontal wells.
Nash Reservoir Management Study With Stochastic Images—A Case Study
Authors: Fanchi J. R. , Meng Hai-Zui , Stoltz R. P. , Owen M. W.
Published: December 2007

An application of geostatistical modeling in the context of a full-field reservoir model study of the Northeast Nash waterflood is described. Geostatistics provides value in preparing and quickly modifying a self-consistent model of reservoir geology. It does not, however, provide a complete description of all the geologic features that impact fluid flow. A rationale for selecting a stochastic description instead of a deterministic description is presented.
Improved Borehole Imaging by Ultrasonics
Authors: Hayman A. J. , Parent Philippe , Cheung Philip , Verges Patrick
Published: December 2007

A new ultrasonic tool for borehole and casing imaging has been developed based on recent cementation-imaging technology. A rotating ultrasonic transducer scans the borehole at a high sampling rate to provide detailed images of echo amplitude and radius.

A 250- or 500-kHz focused transducer gives high resolution, penetration in heavy mud, and low sensitivity to tool eccentering. The echoes are analyzed by a downhole digital signal processor to optimize the accuracy and reliability of the radius measurement. The measurements are corrected for eccentering, and the image color scales are dynamically adjusted for optimum sensitivity in real time by the surface computer.

Comparisons with electrical imaging tools show that the ultrasonic amplitude measurement tends to respond to lithology indirectly by changes in borehole radius or rugosity. Ultrasonic imaging is unique in making quantitative high-resolution measurements of borehole geometry that are useful for borehole-stability analysis. Examples of automatic hole-shape analysis are shown. The tool can also evaluate internal casing corrosion and detect holes.
Rheology of Crosslinked Foams
Authors: Harris P. C. , Heath S. J.
Published: December 2007

The rheology of foam fracturing fluids has been previously described as a yield-pseudoplastic fluid for a broad range of qualities, linear gel concentrations, and temperatures. With the increased use of foams for fracturing with higher proppant concentrations, crosslinking agents are often added. Because the viscous character of the external phase of the foam strongly influences the viscous properties of the foam, the viscosity of the foam will increase if the external phase is crosslinked.

Rheological properties of 25%- to 75%-quality N2 foams containing borate-crosslinked guar were measured on the recirculating flow-loop viscometer at temperatures from 75 to 300°F. When polymer was crosslinked in the foam, viscosity increased by factors of 3 to 10 or more over foams that contained only linear gel.

The fluid viscosity developed in a foam is a product of gas quality, external phase fluid viscosity, and crosslinking of the polymer in the external phase. The extent to which each of these factors is important depends upon both the quality and the concentration of the crosslinked polymer. Viscosity resulting from borate crosslinking is a stronger factor than either quality or linear polymer concentration. Borate crosslinking influence is greatest at low quality and at high polymer concentration.
Dynamic Fluid Loss in Hydraulic Fracturing Under Realistic Shear Conditions in High-Permeability Rocks
Authors: Navarrete R. C. , Cawiezel K. E. , Constien V. G.
Published: December 2007

A study of the dynamic fluid loss of hydraulic fracturing fluids under realistic shear conditions is presented. During a hydraulic fracturing treatment, a polymeric solution is pumped under pressure down the well to create and propagate a fracture. Part of the fluid leaks into the rock formation, leaving a skin layer of polymer, or polymer filter cake, at the rock surface or in the pore space. The fluid-loss behavior depends on the extent to which the polymer invades the porous rock and the thickness of the polymer filter cake, which is limited by the shear stress that the flowing fracturing fluid exerts on it. The effect of shear rate on the dynamic fluid-loss behavior of linear gels and crosslinked borate guars was studied using cores of permeabilities ranging from 0.5 to 70 md, pressure drops of 1,000 psi, and temperatures between 75 and 150°F. The effect of shear on the formation of external filter cake and on the effectiveness of particulate fluid-loss additives was also studied. A shear rate history representative of that experienced by a rock segment in the fracture was used. In this history, the shear rate drops from a very high rate of 380 sec−1 down to 40 sec−1 because of the widening of the fracture width as time advances.

Constant shear rate results show that high shear rates eliminate external filter cakes. In the absence of external cakes, the formation of internal filter cakes controls fluid loss, especially in high-permeability cores. The effectiveness of particulate fluid-loss additives increases with the permeability of the rock and decreases with shear rate and viscosity of the fluid. Shear history results show that the highest leakoff rates and volumes occur during the first 10 minutes of leakoff, i.e., when the rock surface is exposed to high shear rates. Once the shear rate drops below a critical shear value, polymer filter-cake deposition begins and the rate of leakoff slows down. The effect on fluid loss is that a majority of the fluid is lost at high shear rates during a fracturing treatment (i.e., when no polymer filter cake is formed), especially at the beginning of the treatment. To have a major effect on reducing fluid loss, the emphasis has to be placed on plugging the pore throats at the surface of the rock.
Water-Salinity Variations in the Ivishak and Sag River Reservoirs at Prudhoe Bay
Authors: McCoy D. D. , Warner H. R. , Fisher T. E.
Published: December 2007

More than 2,000 chloride-concentration measurements made on extracted water from oil-base-mud cores show areal and vertical varia-tions in the salinity of Ivishak and Sag River reservoir brines. These data compare favorably with compositional analyses of produced and extracted water, spontaneous-potential (SP) analyses, and resistivity-log calculations. In calculating water saturations with the Archie equation, it was critical that variations in resident water resistivity be recognized. This paper describes the variations observed and the work done to validate the extent and magnitude of the salinity variations.
Validation of As-Received Oil-Based-Core Water Saturations From Prudhoe Bay
Authors: Richardson J. G. , Holstein E. D. , Rathmell J. J. , Warner H. R.
Published: December 2007

Determining connate-water saturations is a key factor in calculating original hydrocarbon pore volume (HCPV) for the Ivishak reservoir, the largest productive horizon in the Prudhoe Bay field. As-received water saturation, Sw, measurements on oil-based-mud cores (OBC's) from 27 wells were used as the core standard for Sw determination. Measured values ranged from < 1 to >56% PV, which raised questions as to the validity of these values as being representative of in-situ conditions. Studies of the effects of the cutting, surfacing, and handling of these cores were conducted. Some cores were recovered with centers uninvaded by mud filtrate. Sw values in these sections were the same as those in mud-filtrate-invaded sections of other portions of the same core. Pressure and conventional cores had similar Sw values in adjacent intervals and to nearby oil-based-mud-cored wells. Rigsite Sw were measured and found to be the same as those determined routinely by Core Laboratories in Anchorage. These data offered convincing proof that, above the oil/water transition zone, water was not flushed from the core during the coring process, expelled or evaporated during surfacing, or evaporated while in transit to Anchorage for routine measurements.

A large, alternative, centrifuge capillary pressure database was developed to provide an independent check of the OBC results. De-velopment of this database required selection of samples statistically representative of rock types in the reservoir and use of laboratory techniques that produced reliable results. Comparing Swpc with Swobc values required the consideration of the burial and hydrocarbon accumulation histories and the variations in hydrocarbon properties within the reservoir.
Measurement and Prediction of Hydrate-Phase Equilibria for Reservoir Fluids
Authors: Tohidi Bahman , Danesh Ali , Todd A. C. , Burgass R. W.
Published: December 2007

Problems associated with gas hydrates in the production and transportation of unprocessed wellstreams can be avoided by either preventing hydrate formation or allowing the formation of hydrates, but preventing their aggregation, and transporting them as slurry.

The first approach, which is the current practice in the industry, can be made more cost effective by determining the hydrate-phase boundary more reliably. For the second approach, it is necessary to determine the amount of hydrates to be transported as slurry.

This paper reviews the effect of electrolyte solutions and heavy hydrate formers (such as benzene, cyclohexane, and methylcyclopentane) on the hydrate-free zone and discusses new methods and equipment for measuring the amount and composition of different phases in hydrate-forming conditions. An in-house numerical model has been successfully employed for prediction of the hydrate-free zone and the compositional data.
Deasphalted Oil: A Natural Asphaltene Solvent
Authors: Jamaluddin A. K. M. , Nazarko T. W. , Sills Suzanne , Fuhr B. J.
Published: December 2007

Asphaltene deposition in the near-wellbore region can block pore throats, change wettability characteristics and relative-permeability relationships, and therefore, reduce oil production. Conventional aromatic solvents (e.g., toluene and xylene) alone or in combination with various dispersants are used to remove asphaltene damage from the near-wellbore region. However, these aromatic solvents are expensive and are not environmentally friendly. The objective of this work was to systematically evaluate the asphaltene-solvating power of various nonconventional solvents, including deasphalted oil, using a light-scattering technique.

Experimental results suggest that deasphalted oil is a strong asphaltene solvent presumably because of its native resin and aromatic contents. Addition of asphaltene dispersants also increases the solubilizing power of the deasphalted oil. Furthermore, various refinery and heavy oil upgrader streams show strong ability to solubilize asphaltenes.
Residual Oil Reservoir Recovery With Seismic Vibrations
Authors: Nikolaevskiy V. N. , Lopukhov G. P. , Liao Yizhu , Economides M. J.
Published: December 2007

Evidence suggests that certain vibrations, generated either by natural seismic events or by artificial explosions, have altered the production behavior of oil wells at distances as much as 200 km from the epicenter. These changes have affected the produced water/oil ratio: the water production rate increased from a formation that was at approximately the interstitial water saturation, while the oil rate increased in watered-out reservoirs that were near the residual oil saturation.

Theoretical and field investigations of the phenomena suggest that vibrations may influence substantially the water or oil relative permeability that appears to be partially reconstituted at saturations that ordinarily would prohibit the flow of a particular phase. The key role is played by ultrasound oscillations, generated by seismic waves within the stratum, and it has been confirmed by in-situ measurements during the vibrostimulation of reservoirs.

This paper provides an interpretation of the process and describes wave requirements, wave generation, and propagation in oil-bearing porous media supported by laboratory experiments and field cases of vibrostimulation of oil production from water-flooded reservoirs.
Determination of Perforation Schemes To Control Production and Injection Profiles Along Horizontal Wells
Authors: Asheim Harald , Oudeman Piet
Published: December 2007

The flowing pressure drop along the wellbore gives rise to increasing drawdown in the direction of flow. Particularly for long horizontal wells, this may lead to strongly nonuniform inflow. Lithology variation has similar effects.

For production wells, nonuniform inflow may aggravate cresting and cause premature breakthrough of gas or water. For water flooding, sweep efficiency often depends on uniform injection over long horizontal distances. Thus, control of the injection profile may be imperative to efficient recovery.

The paper describes a scheme for control of production and injection profiles by means of perforation-density variation. The method developed enables determination of such perforation schemes on the basis of classical inflow efficiency concepts and models.
Designing and Qualifying Drill Strings for Extended Reach Drilling
Authors: Hill T.H. , Guild G.J. , Summers M.A.
Published: December 2007

Extended reach (ER) drill string design involves selecting from a variety of available drill string components, those best suited to drill an ER well. In a typical ER well, torsion loads will be higher and tension loads will be lower than for a vertical well of the same measured depth. These differences in applied loads and the need to apply bit weight with normal weight drill pipe pose design and operating questions that are answered in this paper. ER drill strings are often very complex. Also, most available components are in used condition, and thus have been exposed to unknown histories of wear and fatigue. A system for qualifying the drill string is required to ensure that the components we use conform to our design requirements. This paper covers some of the issues the authors have faced in designing and qualifying drill strings for extended reach wells, and how these issues were successfully resolved.

ER Drill String Design Model

Figure 1 shows a general model for drill string design in an extended reach well. We first estimate the loads that the drill string will experience (step 1), then select components that can safely carry these loads (step 2). Since the two steps are interdependent, this is an iterative process, and the arrow is drawn both ways. In addition, the final selection of drill string configuration is also heavily influenced by many issues other than applied loads. These "side issues" shown on Figure 1 are also interdependent, often conflicting one with another, and rarely cut-and-dried. For example, hole cleaning needs and pump pressure limitations may favor 6-5/8 inch drill pipe over 5-inch, but ECD, rig setback space and availability issues may be forcing us toward the smaller pipe. The final design is invariably a compromise between all these issues, and thus will rarely be "optimum", if indeed such a thing exists. Rather, we aim for a "successful" design, one that gets us safely to TD within budget and without either experiencing a drill string failure or wearing out our casing.

Typical Drill String Loads and Load Limits

Imagine that we plan to drill a series of 20,000 ft MD wells with 5-inch drill pipe. We'll drill the first one vertically to TD. The others will be kicked off at 1000 feet and build angle at 2 degrees/100 feet until they reach some desired tangent angle between 0 and 90 degrees, then continue straight until they reach 20,000 ft MD. Figure 2 shows the expected surface hanging load and torsion to rotate the drill string off bottom in these hypothetical wells as tangent angle increases to 90 degrees. Although rotating off bottom is only one of many possible operations, it's readily apparent from Figure 2 that torsion will often be a major concern in ER drilling.
Effects of Well Deviation on Helical Buckling
Authors: Mitchell R. F.
Published: December 2007

Current helical buckling models are valid for vertical wells, but the validity of these solutions for deviated wells was not known. This paper describes the numerical solution of the non- linear buckling equations for arbitrary well deviation. Stability criteria are developed for lateral and helical buckling, and simple correlations are developed for buckling length change, maximum bending stress, and contact force.
Understanding the Performance of a Low-Permeability Gas Reservoir: Hyde Field, Southern North Sea
Authors: Baron R. P. , Pearce A. J.
Published: December 2007

Hyde is a small, low-permeability gas field in the U.K. southern North Sea, which has been developed using horizontal wells. Shortly after production startup in Sept. 1993, the field performance began to give cause for concern. Both wells were producing formation water, and the gas deliverabilities were lower than predicted. This paper describes how field data were collected, analyzed, and used in a full-field simulation model to diagnose the cause of the poor performance and to plan the future development of the field.
A Review of Completions and Gravel-Pack Techniques of the Xijiang Development
Authors: Rodgers J. T. , Bennett J. S. , Grigsby Tommy , Zhang Y. K. , Yang Y. J.
Published: December 2007

The first gravel-packed completions have been run in the Pearl River mouth basin of the South China Sea in the Xijiang fields. The reservoirs in these fields are characterized by unconsolidated, friable, high-permeability sandstones, and, as such, presented many challenges. This paper addresses the development of these fields and how reservoir characteristics and parameters and unexpected deviations were experienced by the operator, as well as the impact these deviations had on completion designs.

Important considerations included the need for sand control, zonal isolation, high-rate production, and reduced completion durations. Finally, the practical application and evaluation of pregravelpack stimulation techniques, gravel-pack carrier consideration, fluid-loss controls, and general completion procedures are presented, along with the innovative completion designs developed to manage these needs.
Zonal Isolation and Evaluation for Cemented Horizontal Liners
Authors: Gai Huawen , Summers T. D. , Cocking D. A. , Greaves Chris
Published: December 2007

This paper discusses the novel application of technology in the cementing and bond evaluation from the world-record breaking ERD (Extended Reach Drilling) wells in Wytch Farm, where horizontal liners of the order of 800m to 1300m at TvD of ca 1600m have been successfully cemented and perforated.

Detailed analysis of the conditions by a multi-disciplinary team provided some practical procedures which enabled us to achieve our objectives of zonal isolation and cement bond evaluation successfully. Important aspects of zonal isolation, such as the use of spiral-blade centraisers, rotating the liner, and trials of the ECPs (External Casing Packer) are discussed in detail. Cement bond evaluation is also detailed, involving CT (Coiled Tubing) deployment and various bond logging tools, including ultrasonic tools. The CBL was found to be surprisingly reliable if used correctly.
An Experimental Evaluation of the Formation-Damage Potential of Cement Filtrates and Leachates
Authors: Hill P. I. , Hughes C. R. , Isaac K. P.
Published: December 2007

Chemical reactions between reservoir minerals and cement filtrates and leachates have been investigated experimentally under simulated reservoir temperature and pressure. Results indicate that individual filtrate/mineral and leachate/mineral reactions are markedly different, with cement leachate appearing much more aggressive than cement filtrate. In all experiments, dissolution and precipitation reactions were rapid, on a scale of days, with the formation of a range of low-density, high-volume calcium/aluminium/silicate/hydrate minerals. A very large increase in solid volume was observed in a number of filtrate and leachate reactions with single mineral separates. Clearly, porosity occlusion associated with these reactions could lead to impaired permeability. In contrast, however, an observed decrease in cohesiveness in quartz sandstone used in coreflood experiments implies that permeability enhancement is possible through primary mineral dissolution. The significance of these results, with regard to cement/fluid reactivity under real reservoir conditions, needs to be investigated further.
Water Shutoff in the North Sea: Testing a New Polymer Gel System in the Heather Field, UKCS Block 2/5
Authors: Whitney D. D. , Montgomery D. W. , Hutchins R. D.
Published: December 2007

A new polymer gel system developed for high-temperature applications was successfully employed on Well H-43 of the Heather Field to isolate a high-rate water production zone. The high-temperature, organic polymer gel system has demonstrated long-term stability when mixed with seawater at temperatures as high as 350°F. Gel times can be delayed, allowing a large volume of polymer gelant to be placed. For Well H-43, 1,095 bbl of gelant were pumped through 1½-in. coiled tubing into a 15-ft layer of the Brent Group. The treatment increased oil production by 300 B/D and decreased water production by 2,290 B/D. A production log run 8 months later confirmed effective isolation, allowing the lower Brent to produce.
A Quantitative Investigation of the Fracture Pump-In/Flowback Test
Authors: Plahn S. V. , Nolte K. G. , Thompson L. G. , Miska S.
Published: December 2007

Fracture-closure pressure is an important parameter for fracture treatment design and evaluation. The pump-in/flowback (PIFB) test is frequently used to estimate its magnitude. The test is attractive because bottomhole pressures (BHP's) during flowback develop a distinct and repeatable signature. This is in contrast to the pump-in/ shut-in test, where strong indications of fracture closure are rarely seen. Various techniques are used to extract closure pressure from the flowback-pressure response. Unfortunately, these techniques give different estimates for closure pressure, and their theoretical bases are not well established. We present results that place the PIFB test on a firmer foundation. A numerical model is used to simulate the PIFB test and glean physical mechanisms contributing to the response. On the basis of our simulation results, we propose interpretation techniques that give better estimates of closure pressure than existing techniques.
A New Approach to the Analysis of Drillstring Fatigue Behavior
Authors: Baryshnikov Anatoly , Calderoni Angelo , Ligrone Angelo , Ferrara Paola
Published: December 2007

This paper presents a method for determining the fatigue behavior of drillstring (DS) components under given environmental conditions. Over the past few years, field data for DS failures have been gathered from certain wells drilled in Italy and West and North Africa. Fatigue phenomena were identified as the main cause of most of such failures. Among the several factors that can affect DS-element fatigue resistance are tensile load, makeup torque, material properties, corrosive environment, abrasive wear, and so on. However, simply on the basis of the existing guidelines, it is difficult to define the real cause of a failure under given operating conditions. A comparative study of full-scale fatigue-test results and field data suggests a new approach for the analysis of some of the drilling technology factors that can affect the DS fatigue behavior.