bluuebunny/crossref_metadata_2025 huggingface dataset:
A Reservoir Simulator Based on the Method of Characteristics
Authors: Hales H. B.
Published: December 2007

A two-dimensional, two-phase, incompressible reservoir simulator has been developed with a solution method based on characteristic theory. The model has been benchmarked against traditional finite difference simulators with four simple problems. The results suggest that new the method is greatly superior to finite difference methods. At equal accuracies the characteristic model is estimated to be much faster than finite difference models, often by several orders of magnitude.
Determination of Hydraulic Fracture Azimuth by Geophysical, Geological, and Oriented-Core Methods at the Multiwell Experiment Site, Rifle, CO
Authors: Teufel L. W. , Hart C. M. , Sattler A. R. , Clark J. A.
Published: December 2007

A comprehensive program for prediction of hydraulic fracture azimuth is being conducted in the tight, lenticular, gas sandstone reservoirs of the Mesaverde Group in the Department of Energy's Multi-Well Experiment near Rifle, Colorado. Methods used in the program can be divided into two groups: 1) indirect, predictive techniques which determine either the principal paleo-stresses or in situ stresses prior to fracturing and 2) direct observation from either geophysical detection and mapping of hydraulic fracture propagation or wellbore impression-packers of open-hole hydraulic fractures. Predictive methods which determine the paleo-stress directions include geologic observations of the orientation of normal faults and fractures at the surface and in oriented core and twinned calcite strain analysis of oriented core. These methods show a consistent direction of N 75°W ± 10° for the maximum horizontal paleo-stress. Predictive methods which determine the in situ stress directions include 1) oriented core analysis using anelastic strain recovery measurements and differential strain curve analysis, 2) oriented caliper and televiewer logs to infer stress directions from wellbore breakouts, and 3) computer modeling of the horizontal stress directions due to gravitational loading of topographic relief. The results of these methods are fairly consistent, and are in general agreement with the paleo-stress results, but also suggest a possible 20° clockwise rotation with depth of the maximum horizontal in situ stress from N 89°W ± 10° in the upper fluvial zone starting at 1330 m to N68°W ± 9° in the marine zone ending at 2450 m. The clockwise rotation of the horizontal stresses with depth may be due to large, local topographic relief superimposed on the regional stress field of the basin. Confirmation of the predicted fracture azimuth in the paludal zone at 2100 m was made using a borehole seismic detection method during hydraulic fracturing, which incorporated an observation well that was within 80 m of the stimulation well. The fracture height and azimuth was mapped for 3 different fracture tests and showed a mean azimuth of N 67°W ± 8°. In addition, an open-hole hydraulic fracture test in which impression packers were used, showed a fracture azimuth at the wellbore ranging from N50°W to N 70°W in the marine zone at 2306 m.
The Evaluation of Uncertainty in Surfactant EOR Performance Prediction
Authors: Brown C. E. , Smith P. J.
Published: December 2007

This paper describes a method for evaluating the uncertainty in Surfactant Enhanced Oil Recovery performance prediction given the intrinsic variability in the physical properties which govern the displacement process. This work forms a stage in the detailed assessment of the economic viability and associated risk of an EOR project. The method uses Monte Carlo simulation techniques to calculate the probability distributions of key output variables: (i) breakthrough times (ii) displacement efficiency (iii) oil cut. The uncertainty associated with the performance prediction is derived from probability distributions to define the variations in: (a) adsorption (b) residual oil saturation to water and surfactant and (c) the shape of the surfactant relative permeability curves. The probability distributions are generated from laboratory core data, and the partial dependency between parameters specified from knowledge of the chemical displacement process. Each replicate evaluation requires the determination of the output variables (i) - (iii) using fractional flow theory, given a correlated random sample of the parameters (a) - (c). The results illustrate the importance of allowing for uncertainty in predicting EOR performance. The extension of this stochastic modelling technique to describe the effects of reservoir heterogeneity is discussed.
Using Ultraviolet Radiation for Controlling Sulfate-Reducing Bacteria in Injection Water
Authors: Clark J. B. , Luppens J. C. , Tucker P. T.
Published: December 2007

Laboratory and field experiments have shown that ultraviolet light may be as effective a treatment for microbial control in injection waters as many biocides. In many cases, the use of ultraviolet light is less expensive. The ultraviolet unit must be properly designed and constructed, and the effectiveness of the unit must be determined by a bioassay rather than by Ohysical measurements. Experimental results are presented and recommendations for design and use of ultraviolet units are given.
Drilling Forecast Model
Authors: Hunt S. G.
Published: December 2007

An economic modeling technique is employed to determine the profitability of various market segments for drilling contractors. Based upon the historic supply of and demand for oil and gas well drilling services, the model provides data for use in strategic and capital planning.
Fishing
Authors: Walker G.
Published: December 2007

Any object dropped or stuck in a well that interferes with it's normal operations is called a fish and must be removed from the well. The operation of removing these objects is called a fishing job. When we are involved in a fishing job, we simply say – "We are fishing".

Why or when these terms were first used, no one seems to know, but there are some similarities. We use a long line (the work string). The fish cannot be seen, but we do have to catch it (engage it) before the fish can be pulled out. I cannot think of any better terms, so let's go fishing.

Fishing jobs are put into two classifications, open hole and cased hole. When there is no casing in the area of the fish, it is called open hole fishing. When the fish is inside casing, it is called cased hole fishing. There are numerous kinds of fishing jobs. Wash over job, overshot run, spear run, stripping job, jar run, --that's just a few.

There are many things that can become a fish -- stuck drill pipe, broken drill pipe, drill collars, bit, bit cones, hand tools dropped in the well, sanded up or mud stuck tubing, packers become stuck, and much more. Wire line broken or stuck in open hole or cased hole can create a bad fishing job. There are many other things that can develop into a fish and many other causes that create a fishing job that haven't been mentioned here.

Since there is so many different kinds of fish and fishing jobs, there are many different tools and methods to do the job. Some of the tools are very simple and some are very complex.

There are no two fishing jobs alike, yet there are lots of fishing jobs similar. An experienced fishing tool man will draw from the experience he has gained on each job.

It is very important on a fishing job for all parties involved to cooperate with each other. It is important for the fishing tool people to obtain all the information concerning the well. That way they can can select the right tools and methods to clean the well out as quickly as possible.
Optimizing Hydraulic Fracture Designs in Formations With Poor Containment
Authors: Ahmed U. , Thompson T. W. , Kelkar S. M. , Strawn J. A. , Veghte R. , Hathaway S.
Published: December 2007

Hydraulic fracturing is a commonly used technique to improve hydrocarbon recovery from low permeability reservoirs. Practical fracturing treatments are designed to maximize the high conductivity propped fracture area in pay while minimizing the formation damage resulting from various fracturing materials within economic constraints. The effectiveness of hydraulic fractures can be greatly improved by controlling the geometry of the created fracture to maximize the fraction of the fracture area in the pay zone.

In situations where vertical fractures tend to migrate due to insufficient fracture containment, the effectiveness of a treatment may be increased by using a number of techniques. These include the proper selection of the perforation placements, controlling pumping rates and the use of various fluid types and other additives. Some of these techniques are currently under investigation in a Gas Research Institute funded project in western tight sands formations.

This paper reviews general considerations regarding hydraulic fracture designs, and presents the development of a perforation placement technique and a field application to verify the technique.
A New Fully Implicit Compositional Simulator
Authors: Chien M. C. H. , Lee S. T. , Chen W. H.
Published: December 2007

A new fully implicit formulation for compositional simulators is presented. Rather than solving for pressure, saturations and phase compositions, the new formulation solves for pressure, overall concentrations and K-values. This change of primary unknowns to be solved improves numerical stability by yielding a more diagonally dominant Jacobian. The use of K-values as primary unknowns also allows the composition constraints to be solved separately from the other equations. The solution of the constraint equations is very efficient because they can be reformulated as monotonic functions*. The primary unknowns are further classified into reduced-unknowns and pivotal-unknowns. The latters are eliminated from the mass conservation equations using the fugacity equalities and constraints. The pivotal-unknowns are selected according to the sensitivity of the equations to the unknowns. This selection conforms to the partial pivoting strategy of Gaussian elimination and enhances numerical stability. Finally, a partial solution method is introduced to eliminate unnecessary calculations of those equations which have met the convergence criteria.

For a simple system, it is shown that the new formulation results in a more diagonally dominant Jacobian matrix. Numerical experiments involving one dimensional multicontact-miscibile (MCM) and immiscible problems, a two dimensional MCM problem and a three dimensional MCM problem are conducted to illustrate the capability and efficiency of the new formulation. Results indicate that the number of iterations per time step required by the new formulation is only about 40% – 60% of an existing fully implicit scheme. It is almost as low as that required by an IMPES scheme.
Air Drilling Operations Improved by Percussion Bit/Hammer Tool Tandem
Authors: Whiteley M. C. , England W. P.
Published: December 2007

Tenneco and other operators air drill whenever possible to improve rate of penetration. This is done with pneumatic hammer tools and various bit types used with standard rotary air rigs. The recent application of a "flatbottom" percussion bit combined with a custom designed hammer tool originally developed for mining operations has significantly improved air drilling operations in the Arkoma Basin. The improvements include a large increase in ROP, improved hole geomotry, reduced drillstring stresses and a substantial reduction in cost/ft. This paper provides:

Discussion of the engineering design and operation of the flatbottom bit/hammer tool tandem Applications and limitations of the tools Guidelines for optimization of performance Documentation of field performance on Tenneco wells in the Arkoma Basin to demonstrate the improvements in air drilling operations provided by the flatbottom bit/hammer tool tandem.
Evaluation of Collapse Strength of Cemented Pipe-in-Pipe Casing Strings
Authors: Marx C. , El-Sayed A. A. H.
Published: December 2007

The first test series has proved the high collapse strength of a combination of 5" casing cemented into 7" casing and the importance of high strength cement /5/. The extent of the tests included twelve pipes of 13-3/8" – 9-5/8" (P 110 -N 80) casing combination, as well as two pieces of 5-5/8" thin wall (0.08 in wall thickness) −7" (P 110) and eight pieces of 7" – 5" (P 110 – C 95) casing combination. The cements used were of API Class G type, blast furnace slug cement, and API Class G type with silica flour. The paper describes the results obtained, discusses possible field applications, and presents equations for calculating the collapse strength of cemented pipe-in-pipe casing strings.
Lost Circulation Treatments for Naturally Fractured, Vugular, or Cavernous Formations
Authors: Canson B. E.
Published: December 2007

This paper presents methodologies to resolve severe lost circulation problems involving naturally fractured, cavernous or vugular formation intervals in which a pressure environment below .432 psi/ft exists. Lost circulation events in these rock conditions are compared to lost circulation events that are caused by induced fracturing or by drilling through permeable zones having intergranular porosity with excessive mud density.

Treatment philosophy and guidelines, methods of problem analysis, treatment materials and special techniques for their emplacement are discussed and evaluated. Procedures for several types of lost circulation treatments are included. Planning considerations are reviewed and the need to evaluate alternatives to drilling with conventional fluid circulating systems when operating in areas where the geological conditions exist to produce these rock anomalies is also discussed.
Low-Heat Input Welding Process for Corrosion-Resistant Cladding of Wellhead Components
Authors: Kovach P. J. , Williams T. D.
Published: December 2007

Welding has historically been used to clad or overlay low alloy steels with corrosion resistant alloys (CRA's), with successful applications in the chemical processing, nuclear power, and oilfield industries. One of the main concerns about weld cladding, however, has been that weld penetration required to assure good bonding results in significant dilution of the CRA and thereby changes its composition.

This paper presents the results of developments to minimize dilution of the CRA composition while maintaining high integrity bonds. Research has yielded in a low heat input welding process which achieves good bonding with minimum dilution. The products of this new welding technology are compared to the properties of cladding as applied by the Hot Isostatic Pressing (HIP) process.

The results show that both the low heat welding process and the HIP process deposit cladding of the specified chemistry and have bond strengths comparable to the low alloy steel base material mechanical properties. However, it is evident that HIP clad deposits are prone to carbide precipitation at the interface resulting in reduced ductility and sensitivity to cracking at the interface when deformed.
Comparison of Laboratory and Field Data for a PDC Bit
Authors: Clark D. A. , Walker B. H.
Published: December 2007

This paper compares penetration rate data for a polycrystalline diamond compact (PDC) bit generated at Drilling Research Laboratory (DRL) with data from an actual well. The bit was lab tested in new condition before being run in the field and in worn condition afterwards. The paper shows the usefulness of doing lab testing along with the field testing of PDC bits.

A Christensen 8 3/4 inch R40LF bit was tested at DRL in Mancos shale and oil base mud. Bit weight and rotary speed were varied from 4,000 to 16,000 lbs and from 90 to 140 rpm, respectively. It then was run in Sussex well #217, Johnson County, Wyoming, drilling over 4,100 feet in oil base mud. During the bit run, penetration rate data at bit weights of 8,000 to 20,000 lbs and rotary speeds of 75 and 105 rpm were taken at 1,000 feet intervals. Finally, it was retested at DRL in Mancos shale and oil base mud. In the second lab test, bit weight and rotary speed were again varied.

Differences between the hardness of the lab shale samples and the shales drilled in the field make direct comparison of the data difficult. However, similarities in the response of the PDC bit to changes in bit weight and rotary speed in the lab and the field are shown. The relative effect of bit wear and shale hardness on the penetration rate of the R40LF are discussed. Data from other R40LF bit runs in the same field are also presented.
Economical Drilling With Rock Bits Equipped With Extended Nozzles; Field Experiences in the North Sea
Authors: Peschel E. , Abdullah H. F. , Walters G.
Published: December 2007

Extended nozzles are features added to soft formation three cone drill bits for improved bottom hole cleaning. Field results from the North Sea indicate increased ROP up to 50%, an average of 16%. Cost calculations prove that more expensive extended nozzle bits are reducing cost/ft by increasing the ROP by more than 4%.
Matrix Body PDC Bits Prove Most Cost Effective in the Powder River Basin
Authors: Gill C. W. , Martin J. L. , Mounder T. E.
Published: December 2007

In the past four years, Polycrystalline Diamond Compact (PDC) bits have gained recognition as a viable tool in the drilling industry, with many spot applications in soft to medium-hard formations. Prior to December 1983, PDC bits had been only marginally successful in the Powder River Basin of Wyoming. With the higher cost of PDC bits and the low rig cost, substantially longer runs were necessary for PDC bits to be economical. This was not being accomplished primarily due to the inability of Steel body bits to maintain gauge when drilling through the harder sandstone sections. Since many of these sandstone sections occur between the depths of 4,000 and 6,500 feet and surface casing is set between 1,000 and 2,500 feet, this left only 1,500 to 2,500 feet of shale to be drilled. Most PDC bits runs were less than 3,000 feet before the bit was worn out. Although some of these bits could be rebuilt, the cost and delays outweighed the advantages. With design changes made to Matrix body PDC bits, it became possible to drill the shales faster and maintain gauge while drilling the sandstones. This has led to more footage per bit and very cost effective savings when drilling with Matrix body PDC bits. The advantages of the Matrix body PDC bit are such that one major manufacturer of both styles stopped running Steel body PDC bits in this area and two other manufacturers have introduced their Matrix body PDC bits to this area.
Effects of Selected Mud Properties on Rate of Penetration in Full-Scale Shale Drilling Simulations
Authors: Cheatham C. A. , Nahm J. J. , Heitkamp N. D.
Published: December 2007

Full-scale drilling simulations were conducted to determine effects of mud weight and static fluid loss on rate of penetration in medium-hard shale with water-base and oil-base muds. Two new 6 1/8 inch(156 mm) bits were tested: a natural diamond and a roller-cone insert type. Test data were analyzed using regression techniques. Results are presented in the form of four equations which predict rate of penetration – one for each combination of mud and bit type. Mud properties affected rate of penetration for the roller bit much more than for the diamond bit. Rate of penetration was usually greater for the roller bit except when high mud weight or overbalance conditions occurred.
Performance Drilling Optimization
Authors: Karlsson H. , Brassfield T. , Krueger V.
Published: December 2007

The use of a newly-designed bottomhole assembly in the Kuparuk River Field on Alaska's North Slope has proven to be a cost-effective improvement over traditional rotary drilling methods.

The bottomhole assembly consists of a polycrystalline diamond compact bit, a positive-displacement downhole motor with specially-designed tilted drive sub (called a navigation sub), and a measurement while drilling system. The use of these tools in combination allows the driller to constantly monitor the well path and either drill straight ahead or make necessary course corrections, while drilling continues uninterrupted.

The savings from such a system have proven to be substantial, with significant reductions in drilling time, increases in rate of penetration, and average savings to the operating company of over $50,000 per well.
Reduction of Nonmagnetic Drill Collar Length Through Magnetic Azimuth Correction Technique
Authors: Russell A. W. , Roesler R. F.
Published: December 2007

Traditional compass-type surveying instruments with their ability to sense only the direction of the local magnetic field vector must be used in conjunction with appropriate lengths of nonmagnetic drill collar to ensure that the local magnetic field vector is uncorrupted by drillstring magnetization. It is now possible to compensate for the effects of drill-string magnetization and, hence, utilize much shorter nonmagnetic drill collars by using solid-state surveying instruments which use gravity and magnetic transducers. Measurements in different bottom hole assemblies show that the required nonmagnetic collar lengths can be reduced in most situations using this compensation technique. This ability to run with shorter collars has significant impact on the use of MWD tools because it allows greater flexibility in the configuration of the bottom hole assembly as well as allowing the directional sensor and other MWD sensors to be positioned closer to the bit.
Directional Drilling Using the Catenary Method
Authors: McClendon R. T. , Anders E. O.
Published: December 2007

The catenary curve method of drilling a directional well is a radical departure from conventional drilling methods. Examples demonstrate the process used to select a catenary curve and its application to a typical directional drilling program. Comparative studies provide supporting evidence of the catenary curve method's advantages over conventional directional methods.
High-Current, Deepwater Drilling Experiences
Authors: Shanks F. E.
Published: December 2007

HIGH CURRENT and DEEPWATER are two topics which each require very special considerations and equipment to allow trouble free drilling throughout the waters of the world. There has been a substantial increase in the interest and activity of drilling in deepwater, high current, and deepwater high current locations. This paper will focus on the planning and equipment required for drilling in those areas where deepwater and high currents exist. The combination of the two requirements requires each have its own stand-alone considerations as well as a special merging of the separate considerations.
Use of Drillstring Models and Data Bases for the Scientific Control of Vertical and Directional Hole Paths
Authors: Amara M. H.
Published: December 2007

From the early fifties, several authors and companies have made significant efforts in the field of bottom hole assemblies modelization.

This work has resulted in considerable improvements in drilling practices such as the use of pendulum and packed-hole assemblies.

Nonetheless, heuristics and empirism remain the rule as far as directional drilling is concerned.

Part one of this paper establishes the necessary link between theory and practice, missing so far, by the use of computer models and data bases together with realtime follow-up of vertical and deviated drilling operations.

The scientific criteria used to optimize the design of rotary drill strings are presented. Their theoretical and practical bases are underlined.

Concepts of BHA's relative rigidity, BHA efficiency related to ROP and hole curvature are developed and quantified.

Part two underlines the practical usefulness of such concepts for the control of vertical and deviated hole paths and ROP optimization. It is illustrated by four examples:

6″ hole drilling in Montmirail field onshore cluster 12 1/4″ phase in ISIS field offshore TUNISA. 17 1/2″ lock-up phase in ABK field offshore drilling. 12 1/4″ motor kick offs offshore INDONESIA.
Detailed Validation of a Liquid and Heat Flow Code Against Field Performance
Authors: Tsang C. F. , Doughty C.
Published: December 2007

The numerical code PT, which calculates liquid and heat flow in a saturated porous or fractured porous medium, has been validated against a series of field experiments involving the injection and subsequent production of hot water into a confined aquifer. The layered structure of the aquifer and strong buoyancy effects, indicating highly coupled liquid and heat flows, provide a stringent test of the code's ability to model the real world.
Multidimensional Flux-Corrected Transport for Reservoir Simulation
Authors: Christie M. A. , Bond D. J.
Published: December 2007

Flux Corrected Transport (FCT) is a method which was developed to reduce numerical diffusion in simulation of compressible flow. This paper describes how to implement FCT in an IMPES simulator. We first review the properties required of a difference scheme for accurate resolution of shocks. We then describe implementation of FCT in an IMPES simulator, and finally show examples for both miscible and immiscible flow.
Front Tracking in Two Dimensions Without a Grid
Authors: Karp A. H. , Greenstadt J.
Published: December 2007

We present a method for handling non-linear partial differential equations having solutions that develop steep fronts. Traditional methods for solving such problems (the finite difference and finite element methods) implicitly assume a simple form for the solution over a limited domain. Instead of using a simple basis set and many small spatial elements, we use a complex basis set and no spatial discretization. The method produces accurate results because we are able to include in the basis set a non-rational function that can represent a step.

We have chosen to use the Buckley-Leverett equations to model the quarter 5-spot problem of oil reservoir modeling in two dimensions. The problem is a coupled system of partial differential equations – the flow equation which is nearly hyperbolic, and the pressure equation which is elliptic. In this paper we discuss the solution of the flow equation; the solution of the elliptic equation is discussed elsewhere.

The test problem is two dimensional and restricted to the unit square. Extensions to three dimensions and more general geometries will be discussed.
An Effective Method To Reduce Grid Orientation Effects in Steamflood Simulations
Authors: Caracotsios M. , Bertiger W. I. , Woo P. T.
Published: December 2007

The velocity interpolation technique of Bertiger and Padmanabhan (1983), was formulated for block lefted cartesian grids and implemented in a fully implicit steamflood simulator. A detailed numerical study shows that the technique essentially eliminates grid orientation effects in uniform grids and greatly reduces them in non-uniform symmetric ones. Furthermore, it was found that for asymmetric diagonal orientations the results agree with those of symmetric ones. However, for parallel asymmetric configurations, grid orientation effects reappear.
Finite Element Methods for Enhanced Oil Recovery Simulation
Authors: Cohen M. F.
Published: December 2007

A general, finite element procedure for reservoir simulation is presented. This effort is directed toward improving the numerical behavior of standard upstream, or upwind, finite difference techniques, without significantly increasing the computational costs. Two methods from previous authors' work are modified and developed: 1) upwind finite elements and 2) the Petrov-Galerkin method. These techniques are applied in a one- and two-dimensional, surfactant/ polymer simulator. The paper sets forth the mathematical formulation and several details concerning the implementation. The results indicate that the Petrov-Galerkin method does significantly reduce numerical-diffusion errors, while it retains the stability of the first-order, upwind methods. It is also relatively simple to implement. Both the upwind, and Petrov-Galerkin, finite element methods demonstrate little sensitivity to grid orientation.
Higher-Order Godunov Methods for Reducing Numerical Dispersion in Reservoir Simulation
Authors: Bell J. B. , Shubin G. R.
Published: December 2007

Standard finite difference methods used in reservoir simulation employ large amounts of numerical dispersion. This inherent numerical dispersion causes sharp fronts to be smeared over many grid blocks, and can cause their shapes to be wildly distorted. In this paper we discuss a new method that substantially reduces the effects of numerical dispersion. The new method significantly improves the resolution of fronts, and is specifically constructed to be essentially free of grid orientation effects.
Infinite Element Modeling of Heat Losses During Thermal Recovery Processes
Authors: Lewis R. W. , Morgan K. , Roberts P. M.
Published: December 2007

This paper reports on preliminary investigations into the application of recently developed ‘infinite elements’ for modelling heat losses from a reservoir during thermal recovery techniques. The infinite elements were chosen for their ease of incorporation into an efficient alternating-direction finite element simulator. The numerical examples presented are based on modelling the simplest non-isothermal displacement process, i.e. hot-waterflooding, but the techniques demonstrated may be extended to the simulation of more sophisticated processes such as (cyclical) steam-flooding and in-situ combustion.
Simulating Steam Additive EOR Processes
Authors: Buchanan W. L.
Published: December 2007

The simulation of EOR processes characterized by the injection of gases, solvents and/or chemicals with steam into a petroleum reservoir requires a fully implicit, thermal, compositional formulation. The simulator must be able to handle robustly and efficiently all the different types of PVT-composition behavior found in these processes. For reliable predictions, it also must accurately account for the complex physical effects that these additives have on oil, gas and aqueous phase properties such as density and mobility. Finally, the formulation must be able to accommodate future developments in steam additives EOR processes with a minimum of change to the simulator.

This paper describes such a multi-phase multi-component thermal model. The use of global mole fractions as primary variables permits all phase equilibrium calculations to be carried out in an interchangeable flash module which is designed specifically for the type of additive being injected. Two examples of these flash modules are presented. The phase equilibrium constraints are coupled to the flow equations using a novel method which optimizes robustness and efficiency. Phase properties are calculated in another interchangeable module which is tailored to reproduce the desired effects of the additive.

Results show that the simulator can handle a wide range of steam injection processes efficiently. Several examples are used to compare this model with another model that employs a more conventional formulation.
Reduction of Grid Effects Due to Local Sub-Gridding in Simulations Using a Composite Grid
Authors: Quandalle P. , Besset P.
Published: December 2007

Our previous paper [1] described and analyzed the performance and some of the advantages obtained when a reservoir simulator is upgraded with: the possibility of flow between any given grid blocks, especially from one to several blocks;a multiple time step calculation.

These improvements were appreciated by modelling engineers. The upgraded simulator was used for the simulation of actual reservoirs with complex geometry (such as faulted reservoirs), and for its possibility of having a composite discretization grid (i.e. a grid with several nested levels of local sub-gridding). This practical need justified further extensive study of the flow behaviour near a sub-gridding boundary in a composite grid.

Composite grids possess some features which do not exist in regular classical grids. In a regular grid system, when two blocks are neighbours in a certain direction, their grid centers are always drawn up in that direction. In a composite grid, this is not always the case for neighbouring blocks belonging to different levels of local sub-gridding. As a consequence, in a composite grid, approximation of material exchange between two blocks by the classical two point finite difference scheme may be less accurate than in a regular grid. Tests have shown that a significant grid effect may be induced by computing flows between neighbouring blocks belonging to different sub-gridding levels with this scheme. To eliminate these effects, a more sophisticated numerical scheme, involving more than two points, must be used for flow computation.

This paper reports an analysis of this phenomenon. It also gives a description of some schemes especially designed for this purpose. These schemes may be viewed as being the classical two point scheme with one of the two points being a grid point but not a grid block center. Reservoir data are then approximated at this new grid point by interpolating data values at the grid block centers. More or less sophisticated interpolations are considered. It also describes some numerical examples performed to compare these schemes when they are used for the simulation of multiphase flows with a composite grid. One of the schemes is selected for its accuracy, its reliability, and its simplicity. On numerical examples, it is shown to nearly reproduce, with a composite grid, results obtained with a fine regular grid having a much larger number of blocks. Moreover, this scheme is implemented on a black oil simulator using a Sequential Solution Method and designed for the simulation of three dimensional three phase flows in large reservoirs with composite grids and several thousands of blocks.
Averaging Laws for Flow Through Grid Blocks Containing Heterogeneities
Authors: Shaw D. C. , Dawe R. A.
Published: December 2007

Many natural rock systems contain small patches of different permeability which affect the flow of fluids through them. As these heterogeneities become smaller and more numerous, they become harder to model numerically. We consider two dimensional flows through such systems, where each patch is many radii away from another. For finite numbers of heterogeneities, they can be replaced by single dipoles to leading order, and this approximation predicts a number of features of the flow. In some circumstances, the entire system can be described by assigning an average permeability tensor to it. Several infinite systems including vertical and horizontal bands are also considered, leading to quite simple expressions for the flow rate and average permeability. The theory is extended to the case where there is a small change in capillary pressure within each heterogeneity as well as a nearly-unit mobility ratio at the displacement front. First-order corrections for these effects are found and applied to the model.
Sparse Gaussian Elimination for Complex Reservoir Models.
Authors: Sherman A. H.
Published: December 2007

The simulation industry is rapidly moving towards the frequent use of complex reservoir models including such features as faults, implicit well terms, and thermal or compositional effects. All of these things can pose great difficulties for the standard direct elimination methods typically found in reservoir simulators. This paper takes a new look at sparse Gaussian elimination methods in the context of the current technology and trends in simulation and computing. A novel implementation is described, and numerical results are presented that indicate that this implementation can be a more effective tool for simulation than previous versions of sparse elimination.
Constrained Residual Acceleration of Conjugate Residual Methods
Authors: Wallis J. R. , Kendall R. P. , Little T. E.
Published: December 2007

This paper describes a new iterative technique for the solution of linear systems of equations arising in petroleum reservoir simulation. The procedure exploits a powerful, vectorizable preconditioner to accelerate generalized conjugate residual methods. Speed and robustness of the new method compare favorably with previously published schemes. These attributes will be demonstrated in actual applications.
Release and Deposition of Clays in Sandstones
Authors: Sharma M. M. , Yortsos Y. C. , Handy L. L.
Published: December 2007

An attempt is made to prescribe conditions under which deposition or release of physically adhering clay particles occurs on pore walls in sandstones. Quantitative models for the physicochemical interactions between clay particles and pore walls are used to estimate rates of deposition and release in a single pore. It is found that the rates change rapidly from zero to a finite value governed only by the local Peclet number. This makes it possible to delineate regions in the ψ1 – ψ2 phase plane where deposition or release dominates. The onset of clay release or deposition is determined by these surface chemical parameters. However in the deposition or release dominated regimes, the actual rates are shown to be only functions of fluid pore velocity.

Since the surface electrostatic potentials ψ1 and ψ2 are crucial in determining the onset of deposition or release, they were experimentally measured. Ottawa sand, kaolin, and fired and unfired Berea sandstone samples were studied. The sandstone samples were disaggregated and separated into the oxide fraction and the clay fraction. Surface charges were measured on each as a function of pH and ionic strength. These experimental results in conjunction with the regions of deposition and release in the ψ1 – ψ2 phase plane were used to construct stability diagrams. The stability diagrams delineate regions in the pH – ionic strength phase plane where clays will be released from pore walls. These regions are referred to as regions of instability for the sandstone. The results obtained for Berea sandstone agree well with those reported earlier. Similar stability diagrams can be constructed when other species such as polyvalent cations or anions are present in the system. Some experimental results are provided here towards this end.
Bulk Gel Strength Tester
Authors: Meister J.
Published: December 2007

A simple screen extrusion rheometer (Gel Strength Tester) was designed to quantitatively compare strong bulk gels of the compositions used for conformance improvement in near-wellbore treatments. In addition, this tester should be able to measure other strong gels, such as thick drilling muds.

To demonstrate this device, the strength of aluminum crosslinked polyacrylate-acrylamide copolymer type gels was measured as a function of the effects of gel age, sheared polymer, salinity, polymer concentration, intrinsic viscosity and percent anionic character. All gel systems investigated had a characteristic yield pressure, below which the gel could not be extruded, and also an apparent viscosity which was dependent on shear rate.

It may be possible to correlate bulk gel strength with permeability reduction in cores.
Graphical Prediction Of Waterfloods
Authors: Higgins R.V. , Boley D.W. , Leighton A.J.
Published: December 2007

A method using relative permeability curves is presented to determine in about 30 minutes by the use of a desk calculator and graphs the recovery vs. cumulative water-injected of linear and 5-spot waterfloods. The determinations for the linear model are nearly identical to, and for the 5-spot within an average of 2 percent of, those calculated by the electronic computer used in the Higgins and Leighton technique. The 5-spot results by the graphical method are also within an average of 5 percent of those for presently available experimental 5-spot waterfloods. The graphical method does not give, however, the time or rate of oil recovery. The procedure uses the fractional flow, or fw, curve from the relative permeability curves and uses Welge tangents to the fw curve. Cumulative water injection is calculated from the slopes of the tangents, and recovery is calculated using extension of tangents to fw=1 From these data, recovery vs. pore volumes injected for a linear waterflood are plotted.
Qualitative and Quantitative Analysis by High-Performance Liquid Chromatography of Synthetic Alkylaryl Sulfonates: Surfactants for Potential Application in Enhanced Oil Recovery
Authors: Pols P. D. , Agterof W. G. M.
Published: December 2007

In chemical enhanced oil recovery methods such as surfactant flooding and steam-foam soaks or drives, surfactants are used to achieve low interfacial tensions or to make a viscous foam respectively. These products consist of a mixture of homologuous series of surfactant components, while each homologue contains isomers. A careful design of the surfactant system is required to tailor its composition to the characteristics of the reservoir in which it is to be applied. From this work a laboratory prototype surfactant mixture is produced which is the basis for a blend to be manufactured on a large scale. A quality control procedure is imperative in this stage. A direct approach is a comparison from a detailed analysis of the laboratory prototype and the product manufactured on a large scale. It has been shown before that high performance liquid chromatography (HPLC) is a very useful technique for this purpose.

We report on the separation by reversed-phase ion-pair HPLC of synthetic alkylaryl sulphonates into their individual components, which has been significantly improved by the modification of previously published experimental conditions. Good baseline separation of homologues can be reached and isomers can be easily recognised in the chromatograms. Specific UV detector response factors are reported, which enable reliable quantitative composition analysis of sharp cuts and blends.
The Effect of Inaccessible Pore Volume on Polymer Coreflood Experiments
Authors: Lötsch T. , Müller T. , Pusch G.
Published: December 2007

Laboratory flooding experiments with polymer solutions in sandstone cores are usually performed for studying the mechanisms of polymer flooding processes, and for measuring the properties which describe the process. A determination of the slug profile of the polymer solution allows the measurement of retention characteristics while taking into account the portion of the pore volume not in contact with the polymer solution.

By means of a simple tracer test with the use of inorganic salts, the inaccessible pore volume for a xanthan-type and a scleroglucan-type polymer in highly saline brine was measured. The amount of inaccessible pore volume had to be considered in the determination of retention isotherms for these polymers in core flooding experiments. An analytical simulation model according to immiscible displacement theory was applied for simulating linear displacement experiments effectively by considering inaccessible pore volume and retention characteristics.
Gas Hydrates at Two Sites of an Active Continental Margin
Authors: Kvenvolden K. A.
Published: December 2007

Sediment containing gas hydrates from two distant Deep Sea Drilling Project sites (565 and 568), located about 670 km apart or the landward flank of the Middle America Trench, was studied to determine the geochemical conditions that characterize the occurrence of gas hydrates. Site 565 was located in the Pacific Ocean offshore the Nicoya Peninsula of Costa Rica in 3,111 m of water. The depth of the hole at this site was 328 m, and gas hydrates were recovered from 285 and 319 m. Site 568 was located about 670 km to the northwest offshore Guatemala in 2,031 m of water. At this site the hole penetrated to 418 m, and gas hydrates were encountered at 404 m.

Both sites are characterized by rates of sedimentation exceeding about 30 m/m.y. and organic carbon contents exceeding about 0.5%. The magnitudes and trends of gas compositions, residual gas concentrations and chlorinity variations are generally similar at both sites. The major organic geochemical differences at these sites appears to be in the carbon isotopic composition of methane [δ13 C(CH4)] and pore water ΣCO2[δ13C(ΣCO2)] at depth. The carbon isotopic compositions are significantly heavier at Site 568 than at Site 565. For example, δ13C(CH4) values at sites 565 and 568 are about −64 and −40 per mil, respectively; δ13C(ΣCO2) values are about +17 and +35 per mil. The isotopic compositions and trends at Site 565 are typical of biogenic methane generation. At Site 568, the isotopic compositions are very heavy, reflecting an unusual source of ΣCO2. In spite of its heavy carbon isotopic composition, this methane is believed to have a biogenic source.
Injection-Production Strategies for Reservoirs Having a Bottomwater Zone
Authors: Singh B. , Malcolm J. D. , Heidrick T. R.
Published: December 2007

The major oil sands deposits of Alberta are estimated to contain 197 billion cubic meters (1.23 × 1012 bbls) of heavy oil. In situ, thermal recovery techniques must be used to recover the vast majority of this resource. These techniques are complicated by the fact that about 25% of the deposits have a high water saturation zone underlying the formation. The extent of this bottom water zone varies from a few meters to tens of meters under a payzone averaging between 10–25 meters depending on the particular reservoir.

In designing a suitable thermal recovery method for these deposits, the presence of bottomwater is likely to have two important but competing effects. First, it may serve the purpose of providing initial injectivity in the highly viscous oil sand deposits. The second effect, however, is that this zone may act as a heat sink and significantly reduce the efficiency of heating oil sand above. The magnitude of these effects will depend on a variety of factors, notably oil viscosity, vertical permeability, injection rates, and oil saturation in the water sand, if any. Thus it is evident that for most reservoirs, the injection-production strategy must be "tailor-made" to optimize recovery.

This paper presents the results of numerical simulation studies undertaken to evaluate the effectiveness of steam and steam-additive processes to recover heavy oil from deposits with bottom water zone. It is concluded that additives such as carbon dioxide and permeability blocking agents do not improve recovery in many cases. However, it is shown that suitable injection-production strategies can be developed to improve oil recovery by using steam-additive processes.
Pressure Behavior of Layered Reservoirs with Crossflow
Authors: Bourdet D.
Published: December 2007

Experience with a large number of well tests has shown that the analysis of some field tests using currently available interpretation models is not satisfactory. Marked departure from homogeneous behavior is evident and none of the available heterogeneous models, such as the double porosity models, yields a convincing interpretation. This is particularly apparent when the pressure derivative behavior is examined.

In this paper, a new analytical solution is presented that describes the pressure response of a well intercepting a layered reservoir with crossflow. The model is designed to describe a system of alternating beds of relatively high permeability contrast. The interpreation models currently in use (homogeneous reservoir, two layers without crossflow, double porosity reservoir) are shown to be limiting forms of the new solution which is therefore a more general description of transient pressure responses.

The layered reservoir behavior is discussed in terms of the pressure and the derivative of pressure. The limits of applicability of the homogeneous and the double porosity solutions for analysis of tests in layered formations are clearly defined.

The new model is used to analyze an actual field case and a good match is obtained when no other solution is found to be applicable. In addition to the usual well and reservoir parameters (total permeability thickness product, skin and wellbore storage constant), analysis yields quantitative information on the storativity and permeability of the contrasting layers.