bluuebunny/crossref_metadata_2025 huggingface dataset:
Stochastic Analysis of Immiscible Two-Phase Flow in Heterogeneous Media
Authors: Zhang Dongxiao , Tchelepi Hamdi
Published: December 2007

We present a stochastic analysis of immiscible two-phase flow (Buckley–Leverett displacement) in heterogeneous reservoirs. Since the detailed spatial variabilities of reservoir properties such as permeability and porosity cannot be described deterministically, both permeability and porosity, or either, are treated as random space functions. In turn, water saturation and oil production rate are also random variables. The main purpose of this study is to estimate the saturation field (by its expected value) and the associated uncertainty (by its standard deviation) for Buckley-Leverett displacement in such random media. The expected value and standard deviation may be used to construct confidence intervals for the saturation field in a reservoir and to evaluate the risk associated with a project caused by the incomplete knowledge of reservoir properties. Through transforming to coordinates attached to streamlines, the evaluation of saturation statistical moments is simplified to that of travel time and transverse displacement probability density functions. The latter do not vary with the two-phase composition but entirely depend on the total velocity under some conditions. Through some one- and two-dimensional examples, we found that the well-known discontinuities existing in saturation profiles and oil production curves for homogeneous media disappear in the case of heterogeneous media. This is due to heterogeneity fingering, or the so-called "heterogeneity induced dispersion." The effect of heterogeneity on oil production is the earlier water breakthrough and later oil arrival. The oil production is expected to take longer in heterogeneous media than in homogeneous media.
Polymer-Free Fluid for Fracturing Applications
Authors: Samuel M. M. , Card R. J. , Nelson E. B. , Brown J. E. , Vinod P. S. , Temple H. L. , Qu Qi , Fu D. K.
Published: December 2007

Polymer residues that stay in the fracture after fracturing can limit the treatment effectiveness. A new and easy-to-prepare, surfactant-based polymer-free fluid, ClearFRAC™, that consists of a quaternary ammonium salt derived from a long-chain fatty acid is described. In brine, it builds fluid viscosity and viscoelasticity due to the formation of highly entangled worm-like micelles. The micelles have a gross structure similar to a polymer chain. Since the viscosity of the fluid depends on the nature of micelles, the fluid can be broken by changing this micellar structure. The breaking occurs when the fluid is exposed to hydrocarbons or diluted with formation water. Therefore, conventional breakers are not required, and the produced oil or gas can act as breakers for this fluid system.

The structural characteristics of this viscoelastic surfactant-based fluid to its chemical and physical properties are correlated in this article. Structure, rheology, fluid loss, and conductivity of this surfactant fluid together with its case histories are presented.
Evaluating Reservoir Architecture in the Northern Gulf of Mexico With Oil and Gas Chemistry
Authors: Westrich Joseph T. , Fuex Anthony M. , O'Neal Patricia M. , Halpern Henry I.
Published: December 2007

A post-development study was carried out at Bullwinkle Field in the Gulf of Mexico to develop and test geochemical methods for evaluating reservoir architecture, establish confidence in reservoir geochemistry technology, and provide a framework for surveillance work at Bullwinkle. In line with previous work, this study shows how fluid composition data can be used to obtain improved reservoir architecture interpretations. Geochemistry is a low-cost direct approach for determining reservoir architecture. When data are integrated with results from other tools and techniques, the final result is to improve decision making and production efficiency for both development and redevelopment projects.
Use of Perforation-Tunnel Permeability To Assess Cased Hole Gravelpack Performance
Authors: Burton R. C.
Published: December 2007

This paper proposes a method for comparing the effectiveness of cased hole gravelpacks. The method employs effective perforation tunnel permeability as the primary indicator of gravelpack effectiveness.

Completion pressure losses in cased hole gravelpacked wells are subdivided into categories and systematically reviewed to show the relative importance of alternative design features. From this information, perforation tunnel permeability is shown to be the major determinant of completion skin and flow efficiency in cased hole gravelpacked wells. The technique is shown to be useful in both low velocity (darcy) and high velocity (non-darcy) flow regimes.

Field examples are used to show how this technique can be used to diagnose design flaws and improve well performance results. These examples show that effective perforation tunnel permeabilities in cased hole gravelpacked wells are significantly lower than surface measured gravel permeabilities. This has important implications for well design and remedial candidate selection.
A Model To Predict Wireline Formation Tester Sample Contamination
Authors: Akram A. H. , Halford F. R. , Fitzpatrick A. J.
Published: December 2007

Wireline formation testers (WFTs) collect fluid samples for pressure-volume-temperature analysis through a probe set against the borehole wall. Filtrate contamination is reduced prior to sampling by either pumping the mixture of filtrate and reservoir fluid from the formation to the borehole or flowing the mixture into one or more WFT chambers. The cleanup is monitored at the surface. The time to reach the level of acceptable contamination (LAC) depends on the depth of invasion, pumpout rate, and various fluid and rock properties.

Generalized guidelines predict time to first oil based on simple volumetrics but do not predict the rate of cleanup. Excessive cleanup time increases costs and the risk of differential sticking of the tool/cable. In some cases it may not be practical to attempt the operation as the LAC may take too long to achieve.

A numerical simulator was used to investigate the characteristics of the contamination level versus time curve and to define the variables governing cleanup.

The model was validated using data from five wells from two fields with differing rock and fluid properties. One hundred and fifty simulation runs were made with different invasion depths, flow rates, and rock and fluid properties.

An equation was developed for field use that estimates filtrate contamination fw as a function of cleanout time t.

An alternative approach for WFT sampling is also suggested, using not one but two probes. With this method, both cleanup time and the final level of filtrate contamination can be substantially reduced.
Stochastic Formulation for Uncertainty Analysis of Two-Phase Flow in Heterogeneous Reservoirs
Authors: Zhang Dongxiao , Li Liyong , Tchelepi H. A.
Published: December 2007

In this article we use a direct approach to quantify the uncertainty in flow performance predictions due to uncertainty in the reservoir description. We solve moment equations derived from a stochastic mathematical statement of immiscible nonlinear two-phase flow in heterogeneous reservoirs. Our stochastic approach is different from the Monte Carlo approach. In the Monte Carlo approach, the prediction uncertainty is obtained through a statistical postprocessing of flow simulations, one for each of a large number of equiprobable realizations of the reservoir description.

We treat permeability as a random space function. In turn, saturation and flow velocity are random fields. We operate in a Lagrangian framework to deal with the transport problem. That is, we transform to a coordinate system attached to streamlines (time, travel time, and transverse displacements). We retain the normal Eulerian (space and time) framework for the total velocity, which we take to be dominated by the heterogeneity of the reservoir. We derive and solve expressions for the first (mean) and second (variance) moments of the quantities of interest.

We demonstrate the applicability of our approach to complex flow geometry. Closed outer boundaries and converging/diverging flows due to the presence of sources/sinks require special mathematical and numerical treatments. General expressions for the moments of total velocity, travel time, transverse displacement, water saturation, production rate, and cumulative recovery are presented and analyzed. A detailed comparison of the moment solution approach with high-resolution Monte Carlo simulations for a variety of two-dimensional problems is presented. We also discuss the advantages and limits of the applicability of the moment equation approach relative to the Monte Carlo approach.
A Simple Spinning-Drop Interfacial Tensiometer
Authors: Gash Bruce , Parrish D.R.
Published: December 2007

This article describes the design and use of a simple, relatively inexpensive device for measuring interfacial tension by the spinning-drop technique. The benefit of low interfacial tension between crude oil and a displacing phase (such as a micellar fluid) in tertiary oil recovery is well documented in the literature. Cayias et al. at the U. of Texas perfected the spinning-drop technique for measuring interfacial tension and created a great deal of interest in the use of this technique for formulating suitable micellar fluids. They designed, fabricated, and offered spinning-drop interfacial tensiometers for sale. Because of its capability of operating over a wide range of rotational speeds, the instrument is rather expensive. Use of spinning-drop interfacial-tension measurements for screening, designing, and evaluating micellar fluid systems requires several instruments because a single instrument can be used to make only about four measurements per day, depending on equilibration time. Thus, there is a real need for inexpensive spinning-drop instruments that permit interfacial-tension measurements for formulating micellar fluids on a "mass production" basis. We have found that for interfacial-tension measurements in the millidyne/centimeter region the capillary containing the fluids can be rotated conveniently at 3,600 rpm. A simple and comparatively inexpensive fixedspeed spinning-drop tensiometer can be made easily by using an aluminum collar to fasten a capillary tube to the end of the shaft of a hysteresis synchronous motor driven at 3,600 rpm by the line frequency (Fig. 1). Good quality motors of this type are smooth running and well balanced.

P. 30
Detection and Location of Two Parallel Sealing Faults Around a Well
Authors: Djebbar Tiab , Anil Kumar
Published: December 2007

A new technique is presented for detecting the existence of and distance to two parallel sealing boundaries surrounding a producing oil or gas well. A log-log plot of time rate of change of well pressure vs. time provides a unique behavior to detect such a condition and allows the use of type-curve matching techniques to determine the khproduct.

Introduction

The idea of detecting and locating a reservoir boundary from transient pressure-time data first appeared in 1951. In that year Horner1 presented the transient pressure behavior of a constant-rate well located near a linear sealing fault. He also presented a method to calculate the distance to the fault from buidup pressure data. Dolan et al.2 applied the technique to drillstem tests. Davis and Hawkins3 gave an equation to determine the distance to the fault from drawdown pressure data. Gray4 reviewed these methods and discussed their limitations.

Bixel et al.5considered a more general problem: a well located close to a linear discontinuity across which hydraulic diffusivity changes. They showed a procedure to determine the distance to such a discontinuity.

Evrenos and Rejda6 employed superposition techniques to simulate various combinations of linear boundaries of interest in gas storage systems and showed how a match between the actual test data with various hypothesized model conditions can be used to arrive at a probable configuration of boundary conditions.

Overpeck and Holden7 considered the effect of reservoir anisotropy on fault detection and showed that the distance calculated could differ by as much as 20% with those obtained by assuming isotropic medium. They gave a procedure for imaging when the principal permeability axes are at some angle other than 0 or 90° to the fault boundary.

Rodgers and McArthur8 employed a minimum in standard deviation between observed pressures and a least-squares straight-line fit to determine boundary configuration. Prasad9presented a procedure to compute transient pressures for a well between two sealing faults intersecting at any angle.

Jones10 in 1961 drew attention to the possible use of rate change of well pressure with time in detecting reservoir boundaries. Van Poollen11 presented graphs of time rate of change of well pressure during drawdown for various well locations between faults intersecting at 90 and 36°. Although this approach yields interpretable drawdown behavior, it has not been used widely in the petroleum literature.

Witherspoon et al.12 considered the effect of a linear no-flow or flow boundary and presented the dimensionless pressure behavior caused by a constant-rate producing well at an observation well some distance away. They discussed techniques to analyze drawdown test data.
The Contrast in Initial and Present Application of the Term, "Connate Water"
Authors: Case L.C.
Published: December 2007

For several years it has been noted that the use of the adjective "connate" as applied to buried waters has become increasingly confusing. Recently published articles and discussions on core analyses have made no progress toward clarification of the terminology of pore water. Rather, it would appear that the situation has deteriorated to the extent that very few engineers have a clear idea concerning the conditions implied by "connate" in description of the water of oil formations.

The existing varied usage is best illustrated by the opinions received from a number of engineers. These men are all reservoir or petroleum engineers, excepting one who is a mechanical engineering graduate serving as field area engineer. The following definitions of "connate" water were obtained orally, no time being allowed for reference or discussion.Irreducible minimum water, by any method of obtaining restored state.Interstitial water in the formation, with oil, before wells are drilled.Interstitial water in pores of formation. normally immovable.Interstitial water - will not move.Irreducible water of saturation, sometimes producible.Interstitial water in formation, not necessarily with oil.Water in formations which is immobile.Original water in place.Water which fills finer pores, with oil and above oil-water contact.The per cent of water saturation in an oil reservoir which exists before wells are drilled.Water remaining in the rocks after partial displacement by oil or gas.Water existing in formations before wells are drilled. Some is mobile, some is not.

The absence of agreement in the above definitions is remarkable. Let us now examine briefly the original conception of the term "connate water" and the vicissitudes to which it has been subjected in the last two decades of its 50-year history.

The word "connate" is of Latin origin and antedated considerably its application to subsurface waters. The initial use of "connate water," occurring in 1906 and being firmly established in succeeding publications prior to 1930, caused it to appear in dictionaries long before engineers became aware of core analyses and their interpretation. Webster's New International Dictionary still carries the unchanged definition: "Connate water. Geol. Sea water held in the interstices of sedimentary deposits and sealed in by the deposition of overlying beds."
Conditioning Stochastic Reservoir Models to Well-Test Data
Authors: He Nanqun , Oliver Dean S. , Reynolds Albert C.
Published: December 2007

Generating realizations of reservoir permeability and porosity fields that are conditional to static and dynamic data are difficult. The constraints imposed by dynamic data are typically nonlinear and the relationship between the observed data and the petrophysical parameters is given by a flow simulator which is expensive to run. In addition, spatial organization of real rock properties is quite complex. Thus, most attempts at conditioning reservoir properties to dynamic data have either approximated the relationship between data and parameters so that complex geologic models could be used, or have used simplified spatial models with actual production data.

In this paper, we describe a multistep procedure for efficiently generating realizations of reservoir properties that honor dynamic data from complex stochastic models. First, we generate a realization of the rock properties that is conditioned to static data, but not to the pressure data. Second, we generate a realization of the production data (i.e., add random errors to the production data). Third, we find the property field that is as close as possible to the uncalibrated realization and also honors the realization of the production data. The ensemble of realizations generated by this procedure often provides a good empirical approximation to the posteriori probability density function for reservoir models and can be used for Monte Carlo inference.

We apply the above procedure to the problem of conditioning a three-dimensional stochastic model to data from two well tests. The real-field example contains two facies. Permeabilities within each facies were generated using a "cloud transform" that honored the observed scatter in the crossplot of permeability and porosity. We cut a volume, containing both test wells, from the full-field model, then scaled it up to about 9,000 cells before calibrating to pressure data. Although the well-test data were of poor quality, the data provided information to modify the permeabilities within the regions of investigations and on the overall permeability average.
Drag Forces on an Accelerated Cylinder
Authors: Laird A.D.K. , Johnson C.A.
Published: December 2007

Drag coefficients for a cylinder being towed through water at constant velocity and also at constant linear acceleration were measured. Drag coefficients for constant velocity towing showed reasonable agreement with previous results. The drag coefficients found for constant acceleration showed little correlation with either the magnitude of the acceleration or the value of the modulus and tended to be slightly lower than those for constant velocity.

Introduction

For the design of offshore structures, wave forces acting on immersed cylinders are of importance. Several investigations have been made of these forces and of how they can be predicted from wave theories. A paper by Crooke summarizes much of the work already done. More recent research by the Wave Research Laboratory at the University of California, Berkeley, has added much to the body of data collected under ocean wave conditions, but has not found a reliable method of force prediction from basic theories of wave motion. The present investigation is part of a long-range program to collect data with which to test current and future theories and correlations. The immediate objective was to measure drag forces on a circular cylinder subjected to linear accelerations over a range of Reynolds numbers where the drag coefficient was a constant for constant velocities. In particular, the effect of constant acceleration from rest and from uniform motion was to be investigated.
Determination of Oil/Water Saturation Functions of Chalk Core Plugs From Two-Phase Flow Experiments
Authors: Bech Niels , Olsen Dan , Nielsen C. M.
Published: December 2007

A new procedure for obtaining oil/water saturation functions, i.e., capillary pressure and relative permeability, of tight core samples uses the pronounced end effect present in flooding experiments on such material. In core material with high capillary pressure, the end effect may allow determination of the saturation functions for a broad saturation interval. A complex coreflooding scheme provides the fluid distributions and production data from which the saturation functions are computed for both drainage and imbibition by a least-squares technique. A chemical shift NMR technique is used for fluid distribution determination. An undesirable interdependency of the saturation functions is avoided by their calculation from different data sets. Killough's method is employed to account for the scanning effect in hysteresis situations for both capillary pressure and relative permeability. The procedure is demonstrated on chalk samples from the North Sea. The experimental time is intermediate between the centrifuge and porous plate methods.
Thermodynamic Micellization Model for Asphaltene Precipitation From Reservoir Crudes at High Pressures and Temperatures
Authors: Pan Huanquan , Firoozabadi Abbas
Published: December 2007

Asphaltene precipitation from reservoir crudes has been modeled using liquid-liquid equilibrium; the precipitated heavy phase is assumed to be in the liquid state and to consist of only asphaltene and resin. The light liquid phase is assumed to consist of the monomers of all the components and the micelles. A thermody-namic micellization model and the Peng-Robinson equation of state (EOS) description of all monomers fully describe the ther-modynamic equilibrium state. From the direct minimization of the Gibbs free energy of the liquid-liquid system, the composition and the amount of each of the phases are calculated.

The above model is used to calculate precipitation from three different reservoir crudes. Once vapor-liquid equilibrium parameters are obtained, there is no further adjustment of the parameters of the EOS for precipitation calculations. The predictions from the thermodynamic micellization model are in good agreement with the data. The effect of pressure, temperature, and composition on precipitation is properly predicted by the model.
Designing Effective Sandstone Acidizing Treatments Through Geochemical Modeling
Authors: Quinn M. A. , Lake L. W. , Schechter R. S.
Published: December 2007

This work reports on the application of a complex kinetic geochemical model to explore key issues in sandstone acidizing.1 The issues include the importance of the minerals initially present, the consequences of mineral precipitation, and the effect of acid formulation and injection rate. The model's capabilities exceed those of its predecessors that have greatly simplified the reaction chemistry or have ignored kinetics altogether. No assumptions were made as to the nature of precipitation that could ensue; all potential precipitates were considered.

An important advance is the use of a new permeability prediction model taken from the work of Panda and Lake.2 This model relates the permeability of a permeable medium to the porosity, grain size distribution and the amounts and identities of all detrital minerals present. Coupled with the reaction chemistry, this model allows predictions that are relevant for specific treatments. The use of this model also gives quite realistic productivity improvement predictions.

We study three cases of generic mineral assemblages: high quartz, high clay, and high feldspar. Model results indicate that the precipitation of reaction products is both inevitable and substantial. Hence, the optimal matrix stimulation is a compromise between maximizing the dissolution of the damaging minerals and minimizing secondary precipitation. Given such competitive effects, our results indicate that high rate stimulations tend to give the largest productivity improvements even though these usually do not cause the largest removal of damaging minerals.
Injectivity Decline in Water-Injection Wells: An Offshore Gulf of Mexico Case Study
Authors: Sharma Mukul M. , Pang Shutong , Wennberg K. E. , Morgenthaler L. N.
Published: December 2007

A decline in injectivity in water injection wells can have a large impact on the economic feasibility of offshore water disposal operations. A case study is presented for an offshore Gulf of Mexico water injection project. Data are presented for five typical offshore wells for which a rapid decline in injectivity was observed due to water injection. The wells were successfully acidized every few months over a period of 2 years. An analysis of the data indicates that in injection wells that are not fractured, such declines in in-jectivity may be expected even for relatively clean injection water. A comparison of the different completion types indicates that both open hole and perforated completions would have yielded similar results. Cleaner water would have improved the situation but at a substantial cost. Fracturing the injection wells appears to be the only plausible way of substantially increasing the half life of such injectors. In cases where reservoir conditions dictate that the wells not be fractured, the economics of periodic stimulation vs. the cost of installing surface facilities for cleaning up the water should be evaluated using models for injectivity decline. "What if" simulations conducted to study the impact of different process parameters such as injected particle size and concentration, injection rate and reservoir properties were found to be a useful tool in specifying water quality requirements.
Quantitative Formation Permeability Evaluation from Stoneley Waves
Authors: Brie A. , Endo T. , Johnson D. L. , Pampuri F.
Published: December 2007

The borehole Stoneley wave has been shown to be sensitive to fluid mobility, the ratio of permeability, and viscosity. The phenomenon is well described using the Biot theory and the effect of the mudcake was modeled as an elastic membrane. An inversion technique, which uses both slowness and attenuation of the Stoneley wave over a range of frequency to evaluate mobility, was proposed.

This paper describes the implementation of an interpretation methodology based on this technique. The error analysis shows that an accurate determination of the fluid mobility requires that some critical parameters, such as the mud slowness, mud attenuation, and the pore-fluid modulus, be precisely determined. An interpretation procedure is proposed to determine these parameters with good accuracy. The fluid mobility can then be determined without the need for external calibration with another measurement.

The intrinsic permeability of the rock can then be derived, knowing the various fluid components, their relative permeabilities, and their respective viscosity.

When using the proposed methodology within the applicable limits, the Stoneley wave can provide a continuous estimation of the formation permeability along the well. Core measurements are not required for calibration although they can be used for verification. This technique will find applications in reservoir engineering optimization of well production through better placement of the perforated intervals.
Laminar Flow of Non-Newtonian Fluids in Concentric Annuli
Authors: Vaughn Robert D.
Published: December 2007

The limiting cases of non-Newtonian fluids flowing inside a concentric annular duct are developed without using a model of the fluid behavior. The solutions provide limits with which to test the various models of fluid behavior such as the power law and Bingham plastic models. The results of previous theoretical work are discussed in terms of limiting cases. This limiting case study also shows that experimental work on flow of non-Newtonian fluids in annular ducts should be confined to ducts for which the ratio of the radius of the inner wall to that of the outer wall is less than 0.3 and preferably less than 0.2.

Introduction

During the last 10 years the problem of laminar flow of non-Newtonian fluids in concentric annuli has received much attention largely because of its application to the hydrodynamics of the wellbore. Recently solutions utilizing the power law and Bingham plastic models have been published.In this paper the method of limiting cases, which has been successfully applied to laminar-flow heat transfer will be applied to the problem of flow of non-time dependent, non-Newtonian fluids through annuli. This method permits solutions for the limiting cases to be made without using a model of unknown validity. The solutions, therefore, provide limits with which to test the various models which have been or will be proposed. A pertinent conclusion concerning the region of experimental work is also provided.

DEVELOPMENT OF LIMITING CASES

The limiting cases for the axial flow of fluids in concentric annuli may be defined with reference to Fig. L It is possible to define two limiting cases which pertain to the physical dimensions of the annulus. First, the annulus must degenerate to a circular pipe as the radius of the inner wall decreases or, as K = (KR/R) - 0. Second, the annulus must approach the limit of parallel plates of infinite extent as the spacing between the inner and outer tubes becomes small in comparison with the radius R of the annulus, or as K - 1. It is also possible to ascertain three limbing cases which pertain to fluid behavior.

With reference to Fig. 2, as a fluid becomes progressively more pseudoplastic, the shear stress- shear rate relationship progressively approaches the indicated horizontal line more closely. At this limit the shear stress becomes independent of the shear rate. At the other extreme of increasingly dilatant behavior, the vertical asymptote is approached. Intermediate between these two limiting cases lies the case of the Newtonian fluid. Fluids which exhibit a yield shear stress also approach the limbing case of "infinite" pseudoplastic behavior.

SPEJ

P. 274^
Analysis of Fluid Input Wells by Shut-In Pressures
Authors: Groeneman A.R. , Wright F.F.
Published: December 2007

Introduction

The need for a simple and economical way of determining the operating efficiency of input wells has been evident for many years. Considerable time and money is spent each year in the maintenance of injection wells. Often the results obtained by work-over operations and various treatments do not pay back the extra cost. A method is needed to determine which wells can be expected to respond favorably to treatment. The application of build-up analysis to input wells, both water and gas, is helping greatly ill solving the problem.

The purpose of this paper is to show how the conventional build-up equations can be applied to fluid input wells, how the results are used to evaluate the wells' input efficiency, and to give examples of field tests.

Build-Up Equation

The use of pressure build-up curves in evaluating producing wells has been a valuable tool in the oil industry, particularly in the last few years. The mathematical analysis of these pressure vs time curves has been treated by several authors, some of whom are listed in the references.

More recently it has been confirmed that these same equations are applicable to water injection wells and also to gas injection wells, with some restrictions. The equations used for this study are given in Fig. 1.

Application To Input Wells

The application of these build-up analysis equations to input wells can disclose many useful things about the well and the formation. These include the relative amount of damage or improvement existing in the formation immediately at the wellbore. A comparison of these tests before and after workovers will indicate the degree of success accomplished by the well treatment. These analysis also furnish a yardstick to measure the effectiveness of different well completion methods. They provide a guide to use in a selective plugging program as well as determining the extent of formation fractures. When the effective permeability is considered in conjunction with the skin effect, the injection rate, and the injection pressure, a better understanding of the well's performance is usually reached.

One requirement for the use of these equations is that enough of the injected fluid must be in the formation to insure that the measured pressure drop occurs in that phase only. Minor adjustments may be necessary in some gas input wells for the compressibility factor as well as the weight of the gas column.
Ultrasonic Removal of Organic Deposits and Polymer-Induced Formation Damage
Authors: Roberts P. M. , Venkitaraman Adinathan , Sharma M. M.
Published: December 2007

Experiments were conducted to investigate ultrasonic energy for reducing near-wellbore formation damage caused by organic deposits and polymers. It is shown that mechanical agitation provided by the acoustic waves re-suspends the paraffin and restores the effective permeability of the core to its undamaged condition. The depth of treatment is approximately 12 to 15 cm. This suggests that an acoustic source with or without solvents may provide an effective method of removing paraffins from the wellbore and the near-wellbore region. Ultrasonics was not as effective at restoring permeability damage caused by polymers. Our results demonstrate that ultrasonic cleaning may be a viable method for cleaning the near-wellbore region when paraffin precipitation is a problem. The method would be particularly effective at treating long sections of pay where chemical methods may be too expensive.
Synthesizing Dispersant for MTC Design and Its Effect on Slurry Rheology
Authors: Hou Jirui , Liu Zhongchun
Published: December 2007

The dispersant's synthesis and its effect on slurry rheology are the basis of mud to cement (MTC) technique application. In this article are two methods to synthesize the dispersant by using fractions of C9, which are byproducts of the Daqing ethene production unit. The dispersant's production cost is reduced. Experimental work verifies that material produced by the new process can be used in a MTC design. The effect of the amounts of the dispersant and mud used on the rheology of MTC slurry are studied and discussed. The results show that the thickening time of a MTC slurry is clearly extended by mixing in the dispersant, thus improving the mobility of the slurry. We find that there is a low mobility or high consistency region when a MTC slurry is initially prepared. The appropriate measures for improving the quality of the MTC slurry are provided in this article. Moreover, the rheology of a MTC slurry is studied. We find that the Herschel-Bulkley model is the most accurate for describing the rheological properties of a MTC slurry. Last, the application of MTC technology in the Changqing field is introduced.
Operational Procedures and Applications of a Wireline Formation Tester To Accurately Characterize the Gas Composition of Stacked Multiple Pools in the North Malay Basin
Authors: Baxter M. F. W. , Abdullah Zulkiflie , Pearson M. R.
Published: December 2007

In this article we review the development of techniques to acquire reliable reservoir gas samples using a wireline formation tester in the Malaysia-Thailand Joint Development Area. This region is characterized by gas accumulations comprised of multiple stacked separate pools where reservoir conditions are often considered hostile for wireline logging operations. In the article we use data from the 16-well exploration and appraisal program, during which 1968 pre-tests and 124 samples were successfully acquired, to compare the quality of gas samples from a wireline formation tester with those obtained from drillstem tests in the same zones.
Estimation of Turbulence Coefficient Based on Field Observations
Authors: Kelkar M. G.
Published: December 2007

Isochronal testing is commonly used to evaluate the performance of gas wells. This paper proposes a new technique to estimate the value of the turbulence coefficient based on isochronal tests. The proposed method is easy to apply and evaluate. Further, the method also provides a value of bg under stabilized conditions which can be used to predict the performance of gas wells under stabilized conditions.

The proposed method is validated using field data under a variety of operating conditions. The values of the turbulence coefficient based on the field data can differ significantly compared to the literature correlations. This further shows the importance of obtaining appropriate reservoir parameters based on the field rather than the laboratory data.
Modeling Relative Permeability Effects in Gas-Condensate Reservoirs With a New Trapping Model
Authors: Pope G. A. , Wu W. , Narayanaswamy G. , Delshad M. , Sharma M. M. , Wang P.
Published: December 2007

Many gas-condensate wells show a significant decrease in productivity once the pressure falls below the dew point pressure. A widely accepted cause of this decrease in productivity index is the decrease in the gas relative permeability due to a buildup of condensate in the near wellbore region. Predictions of well inflow performance require accurate models for the gas relative permeability. Since these relative permeabilities depend on fluid composition and pressure as well as on condensate and water saturations, a model is essential for both interpretation of laboratory data and for predictive field simulations as illustrated in this article.
Integration of Discrete Feature Network Methods With Conventional Simulator Approaches
Authors: Dershowitz Bill , LaPointe Paul , Eiben Thorsten , Wei Lingli
Published: December 2007

The discrete feature network (DFN) approach offers many key advantages over conventional dual porosity (DP) approaches, particularly when issues of connectivity dominate recovery and reservoir stimulation in fractured and heterogeneous reservoirs. DP models have been developed for complex multiphase and thermal effects, and have been implemented for basin scale modeling. However, DP models address only the dual porosity nature of fractured reservoirs, generally simplifying connectivity and scale-dependent heterogeneity issues which are modeled efficiently and more accurately by the DFN approach.

This paper describes the development of techniques to integrate DFN and DP approaches. These techniques allow the analyst to maintain many of the advantages of the DP simulator approach without losing the realism of complex fracture system geometry and connectivity, as captured by DFN models.

The techniques described are currently used within a DOE funded research project for linking a DFN and a DP thermal simulation model for the Yates field, Texas. The paper describes some of the geological and engineering aspects of the Yates field and gives two examples of how DP parameters for the thermal simulation can be derived using DFN modeling techniques.
Relative Permeability at Near-Critical Conditions
Authors: Blom S. M. P. , Hagoort Jacques , Soetekouw D. P. N.
Published: December 2007

We have measured a series of two-phase drainage relative permeability curves at near-critical conditions by means of the displacement method. As a fluid system we have used the model system methanol/n-hexane that exhibits a critical point at ambient conditions. In the measurements we have varied the interfacial tension and the flow rate.

Our results show a clear trend from immiscible relative permeability functions to miscible relative permeability lines with decreasing interfacial tension and increasing superficial velocity. The relative permeability measurements show that the controlling parameter is the ratio of viscous to capillary forces on a pore scale, denoted by the capillary number Nc=k‖∇Φ‖/ϕσ.

To demonstrate the significance of using the proper relative permeability functions, we have calculated the well impairment due to liquid drop-out in a model gas condensate reservoir, for four different rock types showing four different relations between relative permeability and the capillary number. The calculations show that near-miscible relative permeability functions come into play in the vicinity of the well bore. This is contrary to what happens if the relative permeability would be a function of interfacial tension alone. In addition, the results show that well impairment by condensate drop-out may be significantly overestimated if the dependence of relative permeability on the capillary number is ignored.
New Empirical Correlation To Predict Apparent Viscosity of Borate-Crosslinked Guar Gel in Fractures
Authors: Goel Naval , Shah S. N. , Asadi Mahmoud
Published: December 2007

Successful design and completion of hydraulic fracturing treatments depend on accurate estimation of fracturing fluid viscosity. This requires better knowledge of the fluid viscosity under in situ conditions. The viscosity estimation is even more important for borate-crosslinked guar gel because the gel behavior depends on temperature, wellbore shear pre-conditioning, fracture shear rate, and fluid pH. These factors require that the fluid characterization be performed under representative field conditions. Borate-crosslinked gel rheology is currently characterized in the laboratory and there is no theoretical correlation available to describe the gel rheology as a function of its dependent properties. The present study describes a correlation that is developed from data gathered by utilizing a field-scale fracture simulator and is based on the method of reduced variables. The study also extends the method to include the effect of shear history on the rheology of guar crosslinked with borate ions.

The correlation relates the apparent viscosity of the crosslinked guar to the fluid temperature, shear history, and shear rate. It is presented in a simple equation, which can be incorporated into fracturing software. The present study also provides master curves of the reduced apparent viscosity-shear rate for the borate-crosslinked guar at three pH values.
High-Silica Waters in Steamflood Operations
Authors: Bowman R. W. , Gramms L. C. , Craycraft R. R.
Published: December 2007

Most steamflood operations recycling water will experience silica scales at some location in the field operation. It is usually noticed in the steam generators or heat recovery steam generators (HRSG) used for cogeneration. Whether fresh water or recycled water is used, the hot water, high pH portion of the steam will affect the steam injection wellbore. Silica scaling in the formation around production wells, in the screen of the production wells, and in the pump in the production wells are also noticed due to flashing and deposits of silicates.

Some of the silica scales can be controlled, some are beneficial, and some are very costly and difficult or impossible to control. In the formation the silica is in equilibrium with quartz so quartz solubility applies, while the more soluble amorphous silica solubility controls when not in contract with quartz rocks.
Commercial Deployment of Low-Dosage Hydrate Inhibitors in a Southern North Sea 69 km Wet-Gas Subsea Pipeline
Authors: Argo C. B. , Blain R. A. , Osborne C. G. , Priestley I. D.
Published: December 2007

Threshold hydrate inhibitor (THI) has been successfully commercially deployed at a low-dose rate in a wet-gas pipeline connecting the Hyde-West Sole gas fields to the onshore Easington gas terminal. These gas fields are BP Amoco operated assets and are located in the U.K. sector of the southern North Sea, approximately 70 km offshore of the Easington gas terminal. Three gas platforms: Hyde, West Sole Charlie, and West Sole Bravo, are connected to a common 24-in.-diam flowline to shore and typical gas production lies in the range 50-180 mmscf/d (million standard cubic feet per day). The three platforms were sequentially converted from glycol to the new THI reagent. During the changeover period to THI reagent the pipeline operated a mixed system containing both THI reagent and glycol. As of 31 October 1996, the THI reagent has been deployed for 14 weeks. In the last three week period glycol content of the produced water arriving at the onshore terminal has been at a low level, typically, <0.5 wt%.
Determination of the Viscosity-Temperature Relationship for Crude Oils With the Ultra-Viscoson
Authors: Howell James N. , Jessen F.W.
Published: December 2007

Introduction

The determination of cloud points has to date been limited to rather transparent oils, visual observation of the formation of a solid phase being the criterion for the standard ASTM D 97-47 method.

The need for a quick and simple method for determining cloud points under dynamic conditions for opaque crude oils became necessary in a study of fundamental aspects of paraffin deposition from crude oils.

Previous Work

The determination of cloud points in opaque oils by viscosity temperature curves is fairly new, Young described a method employing the capillary tube principle. No information exists relative to the determination of cloud points of crude or refined oils under dynamic conditions.

Shock noticed that deposition of paraffin from crude oils took place at temperatures at or below the temperature at which a sharp inflection point occurred in the viscosity-temperature curve. This observation indicates a possible correlation between this temperature and the cloud point of the crude oil.

Reistle and Vietti have reported that when crude oils containing small amounts of asphaltic materials were heated to temperatures sufficiently high to solubilize these materials and immediately cooled the pour point of the crude oil was lowered as much as 70°F, Sachanen ascribes this effect to the action of colloidal asphaltenes in preventing the formation of the crystalline structure necessary to maintain the oil in a rigid state. At high temperatures, asphaltenes are peptized, and the paraffin crystals formed at these temperatures adsorb the colloidal asphaltenes on their surface thereby hindering further growth of the crystals. Reistle found, however, that such heating and cooling of crude oils had no effect upon the cloud points. This latter work dealt with a crude oil of fixed composition, and the question immediately arises as to the effect of varying the concentration of asphaltic materials on the cloud point.
Method for Delumping the Results of Compositional Reservoir Simulation
Authors: Leibovici C. F. , Barker J. W. , Waché David
Published: December 2007

A new method for delumping the results of a compositional reservoir simulation is presented. The method is based on a previously published algorithm for delumping the results of a single flash calculation. Results are presented for two cases: depletion of a volatile oil reservoir and depletion with lean gas reinjection. The compositions obtained by delumping the results of a 7-component reservoir simulation are compared with those obtained from a 16-component reservoir simulation. If there are no binary interaction coefficients, the agreement is almost exact, and the delumping takes only a fraction of the computation time of the 16-component simulation. When nonzero binary interaction coefficients are introduced, the accuracy of the method is slightly reduced.