bluuebunny/crossref_metadata_2025 huggingface dataset:
Water-Soluble Hydrophobically Associating Polymers for Improved Oil Recovery: A Literature Review
Authors: Taylor K. C. , Nasr-EI-Din H. A.
Published: December 2007

Water-soluble hydrophobically associating polymers are reviewed with particular emphasis on their application in improved oil recovery (IOR). These polymers are very similar to conventional water-soluble polymers used in IOR, except that they have a small number of hydrophobic groups incorporated into the polymer backbone. At levels of incorporation of less than 1 mol%, these hydrophobic groups can significantly change polymer performance. These polymers have potential for use in mobility control, drilling fluids and profile modification. This review includes synthesis, characterization, stability, rheology and flow in porous media of associating polymers. Patents relating to the use of associating polymers in IOR are also examined.
Logically Rectangular Mixed Methods for Darcy Flow on General Geometry
Authors: Arbogast Todd , Keenan Philip T. , Wheeler Mary F.
Published: December 2007

We consider an expanded mixed finite element formulation (cell centered finite differences) for Darcy flow with a tensor absolute permeability. The reservoir can be geometrically general with internal features, but. the computational domain is rectangular. The method is defined on a curvilinear grid that need not, be orthogonal, obtained by mapping the rectangular, computational grid. The original flow problem becomes a similar problem with a modified permeability on the computational grid. Quadrature rules turn the mixed method into a cell-centered finite difference method with a. 9 point stencil in 2-D and 19 in 3-D.

As shown by theory and experiment, if the modified permeability on the computational domain is smooth, then the convergence rate is optimal and both pressure and velocity are superconvergent at certain points. If not, Lagrange multiplier pressures can be introduced on boundaries of elements so that optimal convergence is retained. This modification presents only small changes in the solution process; in fact, the same parallel domain decomposition algorithms can be applied with little or no change to the code if the modified permeability is smooth over the subdomains.

This Lagrange multiplier procedure can be. used to extend the difference scheme to multi-block domains, and to give, a coupling with unstructured grids. In all cases, the mixed formulation is locally conservative. Computational results illustrate the advantage and convergence of this method.
Well Casing Corrosion and Cathodic Protection
Authors: Curry Elmer L.
Published: December 2007

One of the problems concerning the prevention of corrosion of oil and gas prevention of corrosion of oil and gas well casings is that of determining the current requirements for cathodic protection. protection. This paper discusses the causes of corrosion on well casings, suggests well completion practices that would minimize corrosion problems, and explains and discusses two methods of determining current requirements for cathodic protection. Graphs and drawings are included to describe and substantiate both methods.

The casing potential profile tool is the most used tool to locate and evaluate external casing corrosion. It can also be used to determine the current requirements for cathodic protection.

The E-Log-I survey (sometimes referred to as the log-current-potential method) cannot locate or evaluate external casing corrosion, but is a relatively inexpensive method of determining current requirements for cathodic protection. It's accuracy has been verified in tests with the casing profile tool and it's dependability has been substantiated through proven results with the successful application of cathodic protection.

A. CAUSES OF EXTERNAL CASING CORROSION ON OIL AND GAS WELLS

There are five (5) major items which are normally thought to be the cause of well casing corrosion. These are:

Dis-similar metals Dis-similar soil Differential aeration Bacteria "Stray current" interference

Dis-similar metals cause a form of corrosion brought about by the use of different metals electrically coupled together (such as steel pipe and brass gate valves); the use of metals unintentionally caused to be dissimilar by the manufacturing process in either the steel or the pipe; the use of "old" and "new" pipe in the same casing which can include pipe in the same casing which can include oxide scales, etc., and marks and scratches on the pipe left by tools.
Simulation of Independent Reservoirs Coupled by Global Production and Injection Constraints
Authors: Haugen E. D. , Holmes J. A. , Selvig Arild
Published: December 2007

An oil or gas field may comprise a number of isolated reservoir units, each of which may have been studied separately with their own simulation models. If these reservoirs are to be linked to common surface facilities, they are effectively coupled by global production (and perhaps injection) constraints. Their production and injection streams must be combined to obey these constraints. Two approaches are commonly applied to this problem: either amalgamating the simulation models into a single model of the whole field, or using production planning methods on pre-constructed production profiles of the individual reservoirs. The former requires a great deal of effort from the engineers, and may result in a large unwieldy model, while the latter may not be accurate because of rate-dependency effects which are ignored.

This paper introduces a third approach to the problem, which we call Reservoir Coupling. The individual simulation models are still run as separate processes, with minimal change to their data. But they are coupled to a master process which handles the global production and injection constraints and determines the flow rate targets to be applied to the individual reservoirs at each time step. Inter-process communication is handled by the PVM message passing system. This can spawn processes over a network of heterogeneous Unix computers, enabling the individual simulation models to be run in parallel on separate workstations.

The paper describes the Reservoir Coupling algorithm that has been implemented in a commercial black oil simulator, and discusses the advantages and disadvantages of the technique in comparison with the other two approaches. A simulation study is described which illustrates the application of Reservoir Coupling to three isolated reservoirs subject to global production and injection constraints.
Parallel Reservoir Automatic History Matching Using a Network of Workstations and PVM
Authors: Ouenes Ahmed , Weiss William , Sultan A. J. , Anwar Jabed
Published: December 2007

This paper describes a new computing environment for reservoir automatic history matching. A parallel simulated annealing algorithm is used to estimate geologic and reservoir engineering parameters by automatically matching production history of an actual oil reservoir. A complex computer set-up using two networks of workstations simultaneously, located at the New Mexico Petroleum Recovery Research Center (PRRC) and the Los Alamos National Laboratory (LANL), is used to test the concept of distributed optimization. A heterogeneous cluster of two workstations (HP and SUN) is used at the PRRC and a homogeneous cluster of six IBM RISC 6000 workstations is used at LANL. At each site (PRRC and LANL), a Parallel Virtual Machine is created by using the message passing software, PVM. Communication between the two parallel virtual machines located at the PRRC and LANL is achieved with a simple e-mail protocol. In this new environment, the total time required to complete a 22 well oil reservoir study lead to the following observation: two-thirds of the time was devoted to geologic, core, and well log analyses, and one-third of the time to history matching.
Ninth SPE Comparative Solution Project: A Reexamination of Black-Oil Simulation
Authors: Killough J. E.
Published: December 2007

The Ninth SPE Comparative Solution Project presented in the following paper provides a reexamination of black-oil simulation based on a model of moderate size (9,000 cells) and with a high degree of heterogeneity provided by a geostatistically-based permeability field. Nine participants provided data for the comparison which is based on a dipping reservoir with twenty-five somewhat randomly placed producers and a single water injector.

Results showed that significant agreement could be achieved for this problem on the basis of total production rates, saturations, and reservoir pressures. On the other hand, rates for some individual wells did show variations of as much as 30% due to differing treatments of well flowing bottomhole pressures. All participants were able to simulate the study in fewer than sixty time-steps with an average of 4-5 Newton iterations per step. In addition, the results showed that this moderate-sized problem could be simulated in only a few minutes in a workstation environment for the two plus years of data.
Petroleum Reservoir Simulation in a Virtual Environment
Authors: Jacobsen J. S. , Bethel E. W. , Datta-Gupta Akhil , Holland P. J.
Published: December 2007

In this paper, we describe an approach to combining a reservoir simulation with 3-D visualization and virtual reality technology. Our prototype VR/visualization system minimizes human-machine interface barriers and provides enhanced control over the simulation, thereby maximizing scientific judgment and use of intuition. We illustrate the practical advantage of using the VR/visualization prototype system in reservoir engineering by visualizing the results of a waterflood in an oil field with a three-dimensional, spatially correlated heterogeneous permeability field.
A Multiple Right Hand Side Iterative Solver for History Matching
Authors: Killough J. E. , Sharma Yogeshwar , Dupuy Alain , Bissell Robert , Wallis John
Published: December 2007

History matching of oil and gas reservoirs can be accelerated by directly calculating the gradients of observed quantities (e.g., well pressure) with respect to the adjustable reservoir parameters(e. g., permeability). This leads to a set of linear equations which add a significant overhead to the full simulation run without gradients. Direct Gauss elimination solvers can be used to address this problem by performing the factorization of the matrix only once and then reusing the factored matrix for the solution of the multiple right hand sides. This is a limited technique, however. Experience has shown that problems with greater than few thousand cells may not be practical for direct solvers because of computation time and memory limitations.

This paper discusses the implementation of a multiple right hand side iterative linear equation solver (MRHS) for a system of adjoint equations to significantly enhance the performance of a gradient simulator. This was accomplished by saving the inverse of the preconditioning matrix M from the first gradient solution and utilizing it in subsequent solutions. Reduced System/ILU(0) was chosen for the gradient solution since this preconditioner is one of the more robust. In this way, the significant computation time required to calculate the preconditioner is only needed for the first gradient solution, while all subsequent gradient calculations take only a fraction of the CPU time of the first solution.

Numerical experiments were conducted on models of up to 10000 cells and the new MRHS iterative solver was compared with standard red-black line successive overrelaxation (RBLSOR) and Direct(D4) solvers. For the problems which could be compared, overall speedups with the new MRHS solver varied from a factor of 3–6 over other solvers while gain in storage was about factor of 6 over the direct solver.
Calculation of Well Productivity in a Reservoir Simulator (I)
Authors: Chen G. , Tehrani D. H. , Peden J. M.
Published: December 2007

One of the objectives of reservoir performance prediction is to determine the number of wells needed for future development of a field. It is known that most of the wells are deviated, especially in offshore environment. It is also known that conventional simulators cannot simulate the performance of slanted wells with acceptable accuracy in many cases. Many simulators cannot calculate the flowing bottom hole pressure of the wells accurately, even for vertical and horizontal wells in which well block aspect ratios are far from unity or where the well completion interval is short or the well is close to the reservoir boundaries. This paper presents formulations with which the flowing bottom hole pressure of wells (hence their productivity) can be accurately calculated for all wells. These will include vertical, horizontal and slanted wells and generally any well whose trajectory is not parallel with the simulation grid.

A methodology is presented by which a conventional finite difference simulator can be used together with an analytical model that we have developed to calculate accurate well pressure and productivity for many types of wells. At this stage the solutions we offer cover a single well in an infinite slab reservoir or in a fixed boundary rectangular box shaped reservoir with a single phase fluid and only for homogeneous or anisotropic uniform permeability reservoirs. Research is in progress for other situations.

Sensitivity studies on variables such as reservoir rock and fluid properties, simulation gridding, reservoir geometry and well geometry have been conducted.

The validity of the new methodology is demonstrated by comparing the results of our analytical method with numerical solutions for cases in which there is no doubt on validity of the numerical results.

Comparison is made between our analytical method and those available in the literature. The results demonstrate the superiority of the method.

Furthermore, we have developed a new computer program which has coupled our analytical program with a numerical simulator in one package by which the necessary skin factor can be calculated in one run. It is demonstrated that the use of this program eliminates the need for a refined grid and it is less time consuming and much more economical than local grid refinement, where local grid refinement is used only to improve the numerical accuracy and not for inclusion of more detailed geological and petrophysical data.
New Well Models for Partially Penetrating Wells in Heterogeneous Reservoirs Using Non-Uniform Grids
Authors: Lin C. Y.
Published: December 2007

This paper presents new models for partially penetrating wells with any number of perforated intervals in either layered, isotropic, anisotropic, or 3D, heterogeneous reservoirs. These models are applicable to both vertical and horizontal wells and are capable of accurately simulating non-uniform flux distributions along perforated intervals. For a partially penetrating well, the models generate a constant well index for each perforated layer based on the quasi-steady state conditions established early in unsteady state flows.

In general, the predicted flux distributions along the well in a coarse-grid simulation using the new models agree almost identically (within 1% error) with fine-grid solutions. It is shown that well indices depend only on the permeability distribution in the vicinity of the well, reservoir thickness, wellbore radius, and locations of perforated intervals. Finally, for a heterogeneous reservoir, the calculated well indices and the rate distribution along the well can be greatly influenced by the subgrid permeability distribution near the wellbore.
limitations in the Use of Pseudofunctions for Up-scaling Reservoir Simulation Models
Authors: Taggaif I. J. , Soedarmo E. , Paterson L.
Published: December 2007

Pseudofunctions methods have been used to up-scale relative permeability data from the sub-grid scale typical of core data up to grid block sizes used in conventional reservoir simulation. In spite of the widespread use of pseudofunctions, such approaches can be inappropriate due to the use of implicit assumptions regarding the constancy of saturation velocities (as used in the Welge construction).

This work presents an alternative methodology of generating two-phase pseudo relative permeability and capillary pressure functions, using numerical simulation, when non-constant characteristic saturation curves exert a strong impact on the displacement process. The proposed length-dependent pseudofunction technique generates pseudofunctions from 2-dimensional cross-sectional black-oil simulations and later used in a 1-Dimensional reservoir model. The coarse model's simulation predictions are compared to those of the conventional Kyte and Berry method. In addition to this, a case example is given to validate the application of length-dependent pseudos in a 3-dimensional simulation. In this example, sets of length-dependent pseudofunctions were generated and used in a 2-dimensional areal study. Simulation results showed that: a) Curved saturation characteristic velocities occurred in most up-scaled representations and b) The introduction of length-dependent pseudofunctions could result in improved predictions using coarse simulation models.
Dynamical Upscaling Techniques Applied to Compositional Flows
Authors: Thibeau Sylvain , Barker J. W. , Souillard Philippe
Published: December 2007

Lean gas injection in reservoirs is more and more frequently encountered. This production strategy induces strong compositional gradients in the field. Accurate compositional simulations with a coarse grid have been obtained through the use of an upscaling technique based on three main features: the computation of pseudo rel perms upscaling molar, instead of volumetric, fluxes;the reproduction of the fine grid flow through ‘Dual Scale Simulations’ (DSS) which are an alternative to classical Representative Elements of Volume (REV) simulations;the correction, within each phase, of the flux of each component, with the ‘alpha-factor’ pseudo-functions.
Well Productivity for Arbitrarily Inclined Well
Authors: Mochizuki S.
Published: December 2007

This work extends Peaceman's equation to a well areally and vertically inclined at arbitrary angles with respect to grid lines in anisotropic reservoirs. The method is based on the transformation of the anisotropic flow equation to a homogeneous equation, and interpolating the effective well block radius, wellbore radius, and equivalent well length as a function of angles.
3-D Discrete Fracture Flow Simulations Using Monterey Formation Fracture Data
Authors: Schaefer R. A. , Gale J. E. , Herbert Alan
Published: December 2007

A 3-D discrete fracture flow simulator was employed to evaluate the impact of the variability in fracture orientation, fracture interconnectivity, and fracture aperture on rock mass permeability. The fracture data were collected for two distinct fracture scales from outcrops of the Monterey Formation located along the central coast of California using areal and scanline mapping techniques. Differences in structural position were accounted for and statistical methods were used to correct for biases, in trace length, spacing and orientation data, that are associated with scanline mapping. The statistics of trace length, density, and orientation obtained from the field data along with assumed aperture distributions were used in 3-D simulations of rock mass cubes with side lengths of 8 to 18 meters for the small-scale fracture data and 100 to 150 meters for the large-scale fracture data. At the modeled scales the fracture geometry was well connected and imparted a strong anisotropy to flow in the horizontal sections and less so in the vertical sections when the same aperture was assigned to each fracture. Varying fracture aperture logarithmically within fractures of the same set had a strong impact on the magnitude of directional permeabilities but only a slight affect on the direction of the principal permeabilities. This study shows that fracture network simulators can be used to integrate fracture geometry and hydraulic data to provide flow and transport input parameters for large scale 3-D reservoir simulators.
Scaling-up in the Vicinity of Wells in Heterogeneous Field
Authors: Ding Yu
Published: December 2007

It is well known that the equivalent gridblock permeability obtained by the scaling-up procedure from fine gridblocks depends on the boundary conditions. In the literature, most boundary conditions considered represent a "linear" flow pattern, while in reservoir simulation, "radial" flow plays an important role and is related directly to well production forecasts.

In this paper, we will show the need for a specific treatment of the scaling-up procedure in the vicinity of wells due to the "radial" flow pattern with a high pressure gradient. On reservoir field scale, two types of flow should be considered: (1) the "linear" flow pattern, which usually represents a low pressure gradient region; and (2) the "radial" flow pattern, which usually represents a high pressure gradient region. The determination of the equivalent absolute permeabilities by "radial" flow patterns is discussed in this paper. The scaled-up parameters consist of transmissibility and numerical productivity index (PI).
A Massively Parallel Reservoir Simulator
Authors: Kaarstad Terje , Frøyen Johnny , Bjørstad Petter , Espedal Magne
Published: December 2007

A two-phase sequential IMPLICIT three dimensional reservoir simulator has been developed for massively parallel computer systems. The parallel algorithm is based on recently developed domain decomposition methods. The simulator has been tested using a 16384 processor MasPar MP-2.

The simulator building blocks are robust Krylov space iterations using Additive Schwarz as the preconditioner. This approach naturally supports a distributed data structure with overlapping subdomains. In the simulator each subdomain is treated as a small reservoir in its own right, and each subdomain communicates with the neighbouring subdomains through boundary conditions. Previous work has shown that the use of minimal overlap is sufficient and computationally nearly optimal for these problems.

To solve the pressure equation we use a two level Additive Schwarz preconditioner. The coarse grid problem is solved by a multigrid solver and each subdomain problem can be solved with a range of simple iterative or direct methods depending on time, space or robustness considerations. The saturation equation is solved by splitting the equation into one hyperbolic saturation equation and one elliptic saturation equation, The hyperbolic saturation equation is solved by the Modified Method of Characteristics. The solution of the (nonsymmet-ric) elliptic saturation equation is again obtained using an Additive Schwarz preconditioner.
An Asynchronous Parallel Linear Equation Solution Technique
Authors: Kohar Gil , Killough J. E.
Published: December 2007

Key to the development of an efficient parallel reservoir simulator is the implementation of an efficient parallel linear equation solver. Although recent advances in distributed memory parallel computers have seen a significant improvement in communications overhead among the processors, increases in processor performance have kept the ratio of communications to node performance about the same. Previous published parallel linear equation solvers have emphasized the importance of reduced communications and increased granularity for the solver partitioning among the processors. This study investigates the implementation of asynchronous message-passing schemes to further reduce communications overhead for the parallel solver. The basic idea is for each processor to proceed with the linear solution without interruption from waiting to receive messages. If data is available in the buffer from other processors, however, it is utilized.

This study implements an asynchronous parallel preconditioner for ORTHOMIN(k). The preconditioner has two parts: Z-line relaxation and a block incomplete LU factorization (ILU(O)). Also included in the solution is the use of a reduced three-dimensional subproblem which is solved on one of the processors. Because of the asynchronous implementation of the solver, each of the nodes may perform a different number of iterations and converge to different tolerances; however, the overall tolerance for convergence is checked periodically to determine when the linear solution can be halted. This technique has been implemented on the IBM SP2, Intel IPSC/860 and Intel Paragon with problem sizes varying from 4096 to 184,320 grid blocks. For the largest problem significant performance improvements were observed.

For the range of problems investigated the linear solution technique showed excellent robustness and efficiencies. Number of iterations increased only slightly with increasing number of nodes. Moreover, speedups of up to 26 and 37 were observed for 32 and 64 nodes, respectively, for the largest problem investigated.
Application of Adaptive Mesh-Refinement With a New Higher-Order Method in Simulation of a North Sea Micellar/Polymer Flood
Authors: Khan S. A. , Trangenstein J. A. , Horning R. D. , Holing Kent , Schilling B. E. R.
Published: December 2007

This paper demonstrates the application of a higher-order Godunov method and adaptive mesh-refinement to a three-phase, seven-component, micellar/polymer (MP) model and use in the simulation of an MP flood designed for North Sea conditions. Conventional one-point upstream weighting with globally fine mesh is too expensive for obtaining a reasonable level of accuracy for field-scale simulations. The use of higher-order Godunov method with adaptive mesh-refinement not only results in significant reduction in computational times but also reveals more numerical details of the displacement process due to higher-order accuracy. Comparisons are also made between the first- and second-order Godunov methods under field-scale design conditions with and without adaptive mesh-refinement.
Symmetric Flux Continuous Positive Definite Approximation of the Elliptic Full Tensor Pressure Equation in Local Conservation Form
Authors: Edwards Michael G.
Published: December 2007

A classical finite volume scheme well known in computational aerodynamics [1] for solving the Transonic full potential equation is imported into reservoir simulation and applied to the full tensor pressure equation. Cell vertex discretisation is shown to be a natural framework for approximation. With permeability placed at the cell centres and potential at the vertices (cell corner points), of the grid the scheme is flux continuous and locally conservative. Analysis is presented which proves that the resulting discrete matrix is symmetric positive definite provided the full permeability tensor is symmetric elliptic. The discrete matrix is also diagonally dominant subject to a sufficient ellipticity condition. For a diagonal anisotropic tensor the discrete matrix is always symmetric positive definite and the scheme is upto 4th order accurate. A cell centred version of the scheme is indicated.
Different Pressure Grids for Reservoir Simulation in Heterogeneous Reservoirs
Authors: Guérillot D. R. , Verdiere Sophie
Published: December 2007

Petroleum reservoirs are made of highly heterogeneous rocks. These reservoirs could be described by geostatistical models composed of millions of cells. Currently, fluid flow simulations performed within these media need upscaling (or averaging) techniques. Hence, their results are given by averaging on cells which are much larger than the geological model cells.

To overcome this problem, the Dual Mesh Method is proposed here, whose purpose is to solve the pressure equation on a low resolution grid, and then to interpolate pressure over the fine mesh by taking into account small scale heterogeneities of the medium. The aim of this paper is this interpolation step; its implementation is presented and illustrated in a five-spot pattern for three different rock characteristics.
Gas Well De-Watering System and Hydraulic Gas Pump, New Designs and a Discussion on Their Economics
Authors: Amani Mahmood
Published: December 2007

The concepts for two new artificial lift systems were first presented in SPE paper 25422. In the present paper improved designs are presented. The application and the economics of the Hydraulic Gas Pump are compared to the gas lift method that was used in East Quito Fusselman Reservoir, Ward County, Texas. The author concludes that the Hydraulic Gas Pump can be a more economic artificial lift method than gas lift for East Quito Fusselman Reservoir.
Experimental and Analytical Study of Sinusoidal Buckling in Vertical Wells
Authors: Salies J. B. , Cunha J. C. S. , Azar J. J. , Soren J. R.
Published: December 2007

This paper presents results from experimental data for sinusoidal buckling of tubulars in vertical wells and discusses some analytical solutions presented in the literature. An experimental apparatus 55 feet long was used in the tests. Several tests have been conducted and the results are presented and analyzed. The following aspects of sinusoidal buckling were observed during the tests: critical sinusoidal buckling force, contact point between pipe and wellbore, further buckling modes, effect of friction in the post buckling behavior.
History Matching Production Data Using Analytical Solutions for Linearly Varying Bottomhole Pressure
Authors: Spivey J. P. , Frantz J. H.
Published: December 2007

Performance of gas wells is often modeled using analytical solutions which are based on the assumption of constant pressure production at the wellbore. A variable pressure history can be modeled by using superposition of these constant pressure solutions. Unfortunately, each pressure change results in a spike in the resulting production rate. In practice, wells are often operated such that pressure declines slowly and smoothly until line pressure is reached. Thus, superposition of constant pressure solutions does not accurately model production in real wells. In this paper we present a procedure for calculating production rate and cumulative production using superposition of solutions for bottomhole pressure which varies linearly with time. These solutions for linearly varying bottomhole pressure may be easily obtained from the constant pressure solution for the same reservoir geometry. Rates calculated using superposition of linear pressure solutions model actual production data more faithfully than do those calculated using superposition of constant pressure solutions.
Characterization of Michigan Antrim Shale Reservoirs Based on Analysis of Field-Level Data
Authors: Zuber M. D. , Voneiff G. W. , Frantz J. H. , Gatens J. M.
Published: December 2007

This paper focuses on the production characteristics of the Antrim Shale in the Michigan Basin. We have used a large database of Antrim project-level data, including production data; information regarding completion, stimulation and operational practices; and the results of production forecasts for 42 producing projects to provide insights into the impact of various completion and operational practices on Antrim well productivity. We used a production indicator to map well performance and identify wells of above or below average well quality. We have found that advances in completion and operational practices have increased well productivity.
Modeling Multilayer Gas Reservoirs Including Sorption Effects
Authors: Gao Chao , Lee W. John , Spivey John P. , Semmelbeck Mark E.
Published: December 2007

Many coalbed methane reservoirs and Devonian shale reservoirs are naturally fractured with part of the gas adsorbed in the low permeability matrix. The adsorption mechanism is controlled by reservoir pressure; during the depletion of the reservoirs, the adsorbed gas in the matrix is released as free gas flowing from the matrix to the fractures and then to the w'ellbore. In addition, these reservoirs are frequent layered. This paper presents an approximate analytical model for modeling commingled (multilayer) gas reservoir with sorption effects. Our work shows that this model can be developed based on an analytical model developed for slightly compressible liquid commingled systems. To take into account the nonlinearity of the total gas reservoir system, each layer has to be treated as a nonlinear system individually and combine all the individual single-layer solutions with the boundary condition at the wellbore. For this reason, we applied pseudopressure and pseudotime concepts in each layer. The pseudotime definitions take into account the nonlinearity coursed by both the pressure-dependent gas properties and the sorption effects in each layer, both of which we assume to be controlled by average pressure within the layer. We used a numerical simulator to verify our model. The results show that our model agrees well with the numerical simulator.
Evaluation of Height Growth Controlled Fractures With Placement of Artificial Barriers
Authors: Greener M. R. , Snead L. L. , Arbaugh R. M. , Sears S. M.
Published: December 2007

The use of artificial barriers placed at the top and bottom of the producing zones before fracture stimulating a formation can control excessive fracture height growth. The reason for such barrier placement is to contain the fracture treatment within the producing zone when the stress barriers above or below the zone cannot contain height growth. Two case studies are included in this paper on wells fractured in the Richfield formation in the Northern Michigan Basin and in the Codell and Sussex formations in the Denver-Julesburg Basin.
Analysis of Production Response to CO2/Sand Fracturing: A Case Study
Authors: Yost A. B. , Mazza R. L. , Remington R. E.
Published: December 2007

The U.S. Department of Energy, Petroleum Consulting Services, Universal Well Services, and Canadian Fracmaster have recently performed eight CO2/sand stimulations on four Devonian Shale gas wells in the Appalachian Basin. Four two-stage CO2/sand stimulations were executed with two operators in the Pike and Martin County, Kentucky area. All stimulätions involved 120 tons of carbon dioxide (CO2) and up to 47,500 pounds of sand. In addition, there are eleven existing control wells stimulated with four two-stage foam fracs and seven two-stage nitrogen fracs. Production results from these fifteen wells are compared. After nine months of production, CO2/sand fractured wells in the Pike County, Kentucky study area are nearly twice as productive as nitrogen gas fraced wells and nearly five times better than the foam fraced wells in the study group. The per well incremental gas production after nine months ranged from 13.5-22.2 MMcf per well for nitrogen gas and foam fraced wells, respectively. Discussion of the CO2/sand treatment parameters, job execution, and a representative pressure/injection response are discussed in detail. As the operators begin to utilize the CO2/ sand frac process on more wells, the new stimulation process will become commercially available on a routine basis.
Model for Locating Fluids' Contracts in Petroleum Reservoirs
Authors: Udegbunam E. O. , Numbere D. T.
Published: December 2007

Direct determination of the gas-water contact (GWC) or the oil-water contact (OWC) in new wells from geophysical logs, core analysis data and/or whole core inspection is often difficult. Rapidly changing reservoir quality in the interval of interest or gradually changing saturation profiles in the vicinity of the contact can make the determination of the GWC or OWC difficult. This paper presents a model for the accurate placement of the GWC or OWC. The input data are water saturations at various well depths as interpreted from induction logs and the average residual oil saturation. When available, permeability and porosity values from core analysis may improve the result.

Using a power-law equation or a Langmuir isotherm-type equation to represent the capillary pressure-saturation relationship, the GWC or OWC is expressed as a function of water saturation and well depth. A nonlinear optimization technique is then used to determine the GWC or OWC.

The applicability of this model is demonstrated with a field example. The calculated OWC values from all variations of the model fall within 4 feet of the actual OWC value. This model can only be applied in an oil or gas well where an equilibrium capillary curve and a hydrocarbon-water contact occur.
Well Site Digitizing Equipment For Mineral Exploration
Authors: Gearhart Marvin , Hallenburg James K. , Foote Robert S.
Published: December 2007

A large gap exists between the type of equipment in general field use for mineral exploration and the latest state of the art type digitizing equipment. Economic considerations and technical capability of the average logging operator are the two main reasons for this gap.

A new generation of digitizing equipment used for digitizing depth and gamma count rate in uranium exploration holes presents the data on printed tape. This is one of the simplest systems available but still requires key punching before the log data is computer compatible. Such systems are used primarily in the development drilling and economic evaluation of ore bodies. Exploratory logging units are seldom equipped with even this simple type of digitizing equipment since the rate of uranium discoveries is quite low and actual usage would be minimal if on all logging units.

Highly sophisticated digitizing systems of a laboratory type are being field tested for exploratory logging units engaged in basic mineral prospecting. Such systems analyze and process well log data on-site and identify basic elements. The evaluation of californium-252 as a neutron source for mineral exploration by neutron activation analysis is assisted by the use of such a computer system.

Introduction

Digitizing of well logs at the well site seems to be lagging behind the previous expectations of people in the industry. There are specific areas where well site digitizing has been widely accepted, such as in uranium logging. Digital techniques and automatic data processing systems offer the only practical solution for handling large volumes of data accumulated. In the evaluation of uranium deposits by the use of well logs, the logs are accumulated rapidly and final results from the processed data must be obtained quickly. Therefore, beginning with simple digital tape printouts and in some cases advancing to punched tapes, printouts and in some cases advancing to punched tapes, uranium logging field units are currently producing most of their data in both analog and digitized form. Field examples are used to demonstrate typical systems in current use. Such systems are relatively inexpensive and require a minimum of skill to operate.

Highly sophisticated well site digitizing systems are being used for research purposes and one such system is described.

INDUSTRY PRACTICES

Evaluation of the economics involved in all phases of the exploration and development of a mineral deposit have always been essential to the planning of a successful venture.
Well Data Files And The Computer Exploration Tools For The 70's
Authors: Stark Philip H. , Forgotson James M.
Published: December 2007

The purpose of this paper is to illustrate how the computer can be used for processing well data files to provide information that is not only useful for exploration, but essential for economically efficient exploration where large amounts of data from previous drilling are available.

The Industry has made a concerted effort to manage the large volumes of data required to obtain maximum efficiency in the exploration for petroleum and the production of known petroleum and the production of known reserves.

With respect to computer handling of data, the past decade was devoted primarily to accumulating information primarily to accumulating information and building large files of well data and production data within the industry, and special geological or other technical data files within certain companies. The petroleum industry is the only segment of the mineral industry that has a comprehensive data base available in computer processable form. During the decade of the 70's we will see the benefits of these costly investments.

Figure 1 shows the areas of well data file coverage within the United States. Boundaries of each of the nine systems conform generally to the major geological provinces. All producing areas in the provinces. All producing areas in the United States except California and Alaska are covered. Similar systems are operated by the provincial governments and a commercial organization in Western Canada. Approximately 2,200,000 wells have been drilled in the search for oil and gas within the United States and Canada, of these about 1,000,000 have records of sufficient quality to include in a computer-based data system. Petroleum Information currently has approximately 700,000 wells in computer processable data files.

Data are obtained from a variety of sources: Directly from the well site, from state sources, and by field men or contact men who obtain data from the operators of the wells.
How to Organise Mud Logging Data For Modelling Rate of Penetration
Authors: Xu Hong , Fear Martyn , Whelehan Oliver , Ford John , Jensen Jerry
Published: December 2007

ROP (Rate of Penetration) modelling can provide a quantitative tool to reduce drilling costs by means of bit selection and determining the optimal combination of mechanical and hydraulic operating parameters. It is recognised that it would be desirable to model ROP using mud logging and electric wireline logging data because such data closely represent the drilling conditions and formation properties respectively. However, this approach has long been diminished by the apparent poor quality of the data available.

This paper examines the nature of logging data and describes the relationships between ROP and its related variables. We propose an approach to improving ROP modelling using field data. As a result, a number of empirical ROP models have been developed using routinely available mud and wireline logging data. The models are shown to be physically valid under a wide range of conditions. An appreciation of the ranges of conditions under which the model will apply is a critical consideration given the varying contribution of factors affecting ROP under different drilling conditions. The validity and robustness of the new approach are demonstrated by applying it to the logging data from three Poly-crystalline diamond compact (PDC) bit runs in the North Sea area. The method holds the potential to be fully automated for routine application.
The Application of A New Polymer Mud to Horizontal Drilling in the Dagang Oilfield
Authors: Yan Jienian , Jiang Guancheng , Zong Ruiguo
Published: December 2007

A new kind of polymer muds, which is generally referred to as the amphionic polymer mud, has been applied to the two horizontal well driling for the first time in the Dagang Oilfield, located in east China. In this mud system, two amphionic polymers are usually used as the main additives, the one with high molecular weight is an inhibitive encapsuler and filtration control agent, and the other one with low molecular weight is a deflocculant. The amphionic polymer, just as its name, is defined as the polymer that both organic cations and anions simultaneously exist in their molecular chains.

The design criteria, formulations and properties of this mud system are discussed. As a case history, the field performance of this new polymer mud in the different sections of the second well (by name Guan H-l, a medium-radius horizontal well) is also given.

It was shown from the laboratory and field tests that the amphionic polymer mud not only has all the advantages of the polymer muds commonly used, but is able to overcome the disadvantages of those muds, indicated by its highly inhibitive character while maintaining excellent mud performances. For this reason, the major drilling problems for horizontal wells in the Dagang Oilfield, such as hole cleaning, wellbore stability, lubricity, lost circulation and formation damage, which were hardly solved by the use of other water-based muds, could be solved successfully by the use of the amphionic polymer mud at much lower cost than the oil-based mud.
New Tool Designs for High Rate Gravel Pack Operations
Authors: Ross Colby M.
Published: December 2007

A universally accepted practice in the oilfield has been fracturing of the wellbore to improve hydrocarbon recovery. Fracturing procedures reduce skin by breaking through or bypassing near wellbore damage that inhibits production. In loosely consolidated formations, a propped fracture can reduce fluid velocity in the near wellbore region, which subsequently reduces fines migration that can plug the wellbore. Fracturing also provides highly conductive paths for gas and oil production.

Gravel packing is another operation that is often needed during a well's productive cycle. When a highly-conductive fracture is created before a gravel packing operation is run, it has been found that well productivity increases. Performing the operations separately, however, diminishes the productivity gains because of formation damage that can occur between completion operations.

A method of gravel packing that includes a tip-screen-out-design fracturing procedure, performed with the gravel pack packer, screen, and blank in the hole, was proposed to allow the procedures to be performed simultaneously. This paper will describe the various types of gravel packing tools that are currently in use, their specific application, and a new series of gravel packing tools that was developed to resolve the difficulties that arose when the operations of fracturing and gravel packing were combined. Also discussed is the need that arose for tools that could sustain high flow rates in small casing diameters.

Test results will be used to provide acceptable flow rates for different bore sizes.
Sound Reservoir and Production Management will Enable Fifty-Eight Percent Oil Recovery in Colombia's Cano Limon Field
Authors: Ellison R. L. , Ahumada R.
Published: December 2007

The Caño Limón Field, discovered in 1983, is the giant oil field that made Colombia self-sufficient in oil. The field contains over a billion barrels of recoverable oil, and as of publication date, has produced over fifty percent of its reserves. The current production rate is 215,000 BOPD. Sound reservoir and production management has resulted in an expected ultimate oil recovery of about 58 percent of the Oil-in-Place. The field has a current watercut of 80%, thus, the operator is managing the high disposal of large volumes of produced fresh water (over a million barrels per day) with minimum impact on the environment. This has been accomplished by treating and disposing the produced water with compliance of strict environmental guidelines.

High recovery factors have been achieved by the implementation of technologies such as those listed below:

Reservoir management techniques used to define new well locations and strategically select completion and recompletion intervals by: a) making extensive use of a 3-D simulation model, and b) implementing a well defined program of reservoir monitoring using production logs, single well pressure tests and multiwell interference tests.

Experience with state of the art electrical submersible pumps (ESPs) and variable speed drives (VSDs) in lifting large fluid volumes, up to 22000 BFPD per well, with associated sand production ranging from 0 to 200 ppm. This has enabled high oil production rates to be maintained, and oil recovery to be maximized in spite of the high watercuts associated with this very active water drive field. ESP completions with Y-tools are strategically placed to provide for the ability to perform reservoir monitoring surveys.

Automated and continuous well production measurement techniques (rates and watercuts) are used to monitor individual well performance, allowing for the implementation of corrective actions in a timely manner.

Treatment and disposal of the large amount of produced water in compliance with strict environmental guidelines.

The field is located on the eastern edge of the Llanos (Plains) of Colombia, in an ecological area that can be described as flood plains. This area is normally flooded during the rainy season from June through October. Measures are taken to restore and maintain the natural environment of the area.