bluuebunny/crossref_metadata_2025 huggingface dataset:
Cased Hole Formation Resistivity Applications in Alaska
Authors: Hupp Douglas , Kidd Gordon , Harris Jeff , Frankforter Matt
Published: December 2007

This paper describes the theory of cased hole formation resistivity measurements and presents examples demonstrating the diversity of their use. Resistivity behind casing has many applications, from evaluating formations in new wells to monitoring water influx and bypassed hydrocarbons in producing wells. These robust deep-resistivity measurements can be combined with data from traditional cased hole and openhole evaluation tools to provide a comprehensive formation evaluation from behind casing.

Example A highlights the use of these measurements in the successful completion of a new Cook Inlet offshore well. Traditional openhole logs were not obtained because of hole conditions and the borehole environment, which also limited traditional cased hole evaluation techniques such as sigma and carbon-oxygen logging. The new resistivity measurements were instrumental to the successful completion of this well as an oil producer with low water cut.

Examples B and C, from wells in a mature field, demonstrate the use of the measurements to identify water influx and encroachment, which is vital for reservoir monitoring. Both wells produced water from high-permeability thief zones, which prompted profile modification to limit water production and enhance off-take from zones with lower permeability. The new cased hole resistivity measurements provided valuable data, not available from traditional production logs, to assess sweep efficiency, which will be used to guide recompletion or sidetrack decisions.
PEBI Grid Selection for Numerical Simulation of Transient Tests
Authors: Escobar Freddy H. , Tiab Djebbar
Published: December 2007

Accuracy and efficiency of reservoir simulators in complex systems depend highly upon a proper grid selection. Grids based on a cartesian coordinate system have been widely used, but have some disadventages: (a) Flexibility in description of faults, pinchouts, hydraulic fractures, horizontal wells and general discontinuities presented in reservoirs, (b) inflexibility in representing well locations; and (c) suffer of grid orientation effects1,6.

Local grid refinement2, nine-point3,4, and thirteen point5 schemes were introduced to enhance the performance of cartesian grids. Research has covered other techniques to reduce grid orientation effects, starting from the development of a uniform hexagonal grid block pattern until the application until the application of Voronoi or PEBI grids. However, the experience on PEBI grids is very limited since their application and development are still in their childhood, as far as the oil industry is concerned. PEBI grids have been applied to the oil industry for about a decade. Besides, last applications are being introduced during the last three years. On the other hand, generation and construction of PEBI grids are not as easy as cartesian grids. The construction of a PEBI grid for a reservoir is feasible only if it is done by a numerical grid generation procedure. A PEBI (PErpendicular BIsection) grid or Voronoi6,7 grid is defined as the region of the space that is closer to its gridpoint than to any other gridpoints. The PEBI is locally orthogonal. It means the block boundaries are normal to lines joining the nodes on the two sides of each boundary. This allows a reasonable accurate computation of interblock transmissibility for heterogeneous but isotropic permeability distribution.

Currently, five types of PEBI grids–namely: hexagonal, elliptical, rectangular, circular and varieable – are being applied, but there is no evidence of their limitations and/or applicability to simulate well transient behavior. Therefore, the point of this paper is to establish and recommend their use for simulation of transient pressure behavior horizontal wells, vertical wells and vertical hydraulic fractured wells. The effectiveness of the PEBI grids was tested by matching numerical to analytical results.

It was found and shown though simualtion experiments that any PEBI grid describes very well the transient behavior of a horizontal well, however, it is not the same for vertical wells. For instance, it is shown that only the elliptical PEBI grid describes transient behavior of hydraulically fractured vertical wells. Circular PEBI grids are good to simulate vertical unfractured wells. Additionally, it is also demonstrated through different simulated experiments the power of PEBI grids to handle non-orthogonal systems8.
A Multi-Level Iterative Method For Solving Finite Element Equations
Authors: Bank Randolph E. , Sherman Andrew H.
Published: December 2007

Subroutine PLTMG is a Fortran program for solving self-adjoint elliptic boundary value problems in general regions of R2. It is based on a piecewise linear-triangle finite element method, an adaptive grid refinement procedure, and a multi-level method to solve the resulting sets of linear equations. In this work we describe the method, and present some numerical results and comparisons.

Introduction

Consider the model elliptic boundary value problem problem(1.1)

where the coefficient a(x,y) (b(x,y)) is positive (nonnegative) in omega. In this work we discuss the performance of a program which solves (1.1) using a performance of a program which solves (1.1) using a Rayleigh-Ritz-Galerkin method based on piecewise-linear triangular finite elements, a multi-level piecewise-linear triangular finite elements, a multi-level iterative scheme for solving the resulting matrix equations, and an adaptive grid refinement procedure. A more detailed discussion of the program appears in [14].

For expositional convenience, we assume g1 + g2 = 0, and that omega is a polygon, although our FORTRAN subroutine PLTMG is designed for the more general equation (1.1).

In the Rayleigh-Ritz-Galerkin procedure, we seek an approximate solution to the weak form of

(1.1)

(1.2)

where

and (,) denotes the usual L2(omega) inner product. We use (omega) (omega) to denote the subspace of the usual Sobolev space (omega) whose elements satisfy essential boundary conditions. Associated with the bilinear form a(,) is the energy norm= a(u,u).

Let denote a triangulation of omega, and let(omega) denote the N-dimensional space of C piecewise-linear polynomials associated with. The piecewise-linear polynomials associated with. The finite element approximation of u in (1.2) is the function epsilon which satisfies

(1.3)

Once a basis for has been selected (the nodal basis is usually chosen), (1.3) can be reformulated as a system of linear equations

(1.4)

where Aij = a(phi j, phi i), and Fi = (f, phi i). Usually N is large and the stiffness matrix A is sparse.

Our multi-level solution procedure involves a sequence of nested triangulations, with nested in, and the corresponding Nj-dimensional subspaces,, of C0 piecewise-linear polynomials. (By nested, we mean that each triangle polynomials. (By nested, we mean that each triangle of intersects the interior of exactly one triangle of. Corresponding to each subspace N is the problem Pj, the analog of (1.3): Find uj epsilon Mj satisfying

(1.5) a(uj,v)=(f,v) for all v epsilon j.
Solving Approximations To The Convection Diffusion Equation
Authors: Eisenstat S.C. , Elman H. , Schultz M.H. , Sherman A.H
Published: December 2007

Several numerical algorithm for solving a discretized version of the convection-diffusion equation are examined. The algorithms considered areiterative methods derived from the conjugate gradient method, with preconditioning by point - SSOR and incomplete LU factorization. The results ofnumerical experiments with the algorithms, for various values of the coefficient of the convection term and various mesh sizes, are reported.

We consider algorithms for solving a finite difference discretization of the convection-diffusion equation(P)â?'(uxx+u yy)+Bux=f

on the unit square with homogeneous Dirichlet boundary conditions. For the discretization of (P), we use the modified upwind scheme described by Axelsson and Gustafsson [1].[2/(1+(1/2)Bh)+2+Bh] u(i,j)â?'[1/(1+(1/2)Bh)]u(i+1,j)â?'u(i,j+1)â?'[1/(1+(1/2)Bh)â?'Bh] u(iâ?'1,j)â?'u(i,jâ?'1)=f(i,j).

which provides order of accuracy 0(h**2), where h is the mesh size. If the coefficient B of the convection term is nonzero, then the above system of linear equations is nonsymmetric.

The conjugate gradient algorithm for solving systems of linear equationsAx=b

requires that the matrix A be symmetric and positive definite. This paper reports the results of some numerical experiments run on a collection of algorithms modeled after the conjugate gradient algorithm for which it issufficient that the symmetric part M of A,M=(1/2) (A+AT),

be positive definite,

Three classes of algorithms are considered:a collection of algorithms modeled after the conjugate residual algorithm(described below);the generalized conjugate gradient algorithm developed by Concus and Golub[3] and Widlund [9] andthe conjugate gradient algorithm applied to the normal equationsATAx=ATb.

The conjugate residual algorithm for the symmetric problem consists of the following iteration:Choose x(0).Compute r(0)=bâ?'Ax(0)Set p(0)=r(0).

For i=0,1,2, . . ., computea(i)=(r(i),Ar(i)/(Ap(i),ap(i)),x(i+1)=x(i)+a(i)p(i),r(i+1)=r(i)â?'a(i)Ap(i),b(i)=(r(i+1),Ar(i+1))/(r(i),Ar(i))p(i+1)=r(i+1)+b(i)p(i)

Ignoring roundoff error, this algorithm produces the solution to the system of equations in at most N iterations, where N is the size of the system (see Chandra, [2]). Each direction vector p(i) is ATA-orthogonal to the previous directions computed. The choice of a(i) minimizes the L 2-norm of the residual r(i+1) considered as a function of a(i). x(i+1) is also the point in the affine spacex(0)+

which minimizes the L2-norm of the residual.
Novel High Membrane Efficiency Water-Based Drilling Fluids for Alleviating Problems in Troublesome Shale Formations
Authors: Tan Chee P. , Amanullah Mohammed , Mody Fersheed K. , Tare Uday A.
Published: December 2007

A major collaborative effort was undertaken to develop novel environmentally acceptable water-based drilling fluids with high membrane efficiency to help meet the future requirements of the petroleum industry. This paper describes the development of the drilling fluids and practical guidelines for maintaining shale stability with the drilling fluids. Specialised test equipment, including a membrane efficiency screening equipment, and test procedures were developed for simulation of key drilling fluid-shale interaction mechanisms. More than 300 membrane efficiency screening tests were performed on Pierre II shale samples to screen a wide range of novel compounds for their membrane generation capacity in the shale. Typical examples of the tests conducted with three novel compounds that generated moderately and highly efficient membranes are presented and discussed. The results demonstrate that some of the compounds are capable of generating membrane efficiencies of between 55% and 85%. The new generation of water-based drilling fluids developed performs essentially like oil-based muds in terms of shale stabilisation. Practical mud design guidelines developed can be used to optimise the drilling fluid design, in terms of mud weight, salt type and salt concentration, to manage time-dependent well-bore instability in troublesome shale formations efficiently.
Phenomenological Inventory Analysis of Underground Gas Storage in Salt Caverns
Authors: Steinberger Anita , Civan Faruk , Hughes Richard G.
Published: December 2007

This paper presents a model for effective management of natural gas storage in salt caverns. An interactive and dynamic phenomenological inventory model is developed that considers the effects of hydrocarbon thermodynamics, phase behavior, and heat and mass exchanges along cavern walls during gas loading, storage and unloading. The model predicts cavern behavior and accounts for gas ballooning, losses due to porous characteristics and leaky salt formation fractures, variation of temperature and pressure, vapor and liquid composition changes and cavern volume change due to salt creep. The model consists of a set of coupled nonlinear algebraic and differential equations, for which the solution as a function of time is obtained by numerical means. The capabilities of the proposed model are demonstrated by analyses of several field scenarios. The dynamic response of the cavern-well assemblage to injection and production cycles is simulated.
Making a Case for Rethinking Lost Circulation Treatments in Induced Fractures
Authors: Ivan Catalin D. , Bruton James R. , Thiercelin Marc , Bedel Jean-Philippe
Published: December 2007

The challenges of preventing and controlling fluid losses when drilling formations prone to induced fractures have been well documented. The narrow operating window between pore pressure and fracture gradient often results in massive fluid losses when drilling, running casing, and cementing.

Many products and techniques have been used in attempts to restore circulation while drilling induced fractures. These include fibrous, flaky and granular materials, as well as techniques such as gunk and reverse gunk squeezes, high fluid-loss squeezes and cement squeezes. Even though these techniques sometimes restore partial or full circulation, more often than not they are temporary solutions as losses often reoccurre as drilling proceeds. It was thought that the particulate materials and the high compressive strength lost-circulation pills first were failing to reach the tip of the induced fracture and nevertheless were acting as a proppant, thus not allowing the fractures to heal. The low fracture reopening pressures then allow for continued losses.

More recently, a new generation of chemically activated cross-linked pills has been developed and applied to challenging induced fractures environment to cure and limit losses.

This paper substantiates the observed effectiveness of soft visco-elasto-plastic lost circulation pills in solving lost circulation problems in induced fractures as well as the application of the cross-linked polymer pills. The work presented in this paper first consisted of determining the mechanical properties of these pills under downhole conditions by using a vane rheometer. The theory of hydraulic fracture mechanics was then applied to model the behavior of these visco-elasto-plastic soft pills and demonstrate the superiority of these pills in solving lost circulation problems. Results show that once the soft cross-linked polymer pills have been squeezed into the induced fracture, the fracture gradient has been increased. This behavior, enhanced by the gel elasticity, helps the fractures to heal and the losses to be stopped. In addition to healing fractures, the soft cross-linked polymer pills also provide a mechanism for bridging micro-fractures and thus preventing losses into the formation.
Application of Quantitative Risk Analysis to Pore Pressure and Fracture Gradient Prediction
Authors: Liang Q. J.
Published: December 2007

The present deterministic pore pressure and fracture gradient prediction techniques simplify the input variables from a statistical range of data to a deterministic value, thereby producing over-simplified deterministic pore pressure and fracture gradient results. As a consequence, we lose the ability to quantitatively analyze risks, and we cannot quantify the uncertainties of our pore pressure and fracture gradient prediction.

This paper describes a methodology for quantitative risk analysis (QRA) of pore pressure and fracture gradient prediction and shows that applications of QRA in this area will improve the techniques of pore pressure and fracture gradient calculations. In addition, QRA will open a full range of new applications in risk prediction, risks evaluation, risk management, decision making, real-time kick and loss-return risk monitoring, risk control, and casing design.
Assessing the Value of 3D Seismic Data in Reducing Uncertainty in Reservoir Production Forecasts
Authors: Varela Omar J. , Torres-Verdín Carlos , Lake Larry W.
Published: December 2007

Using three-dimensional (3D) seismic data has become a common way to identify the size and shape of putative flow barriers in hydrocarbon reservoirs. It is less clear to what extent determining the spatial distribution of engineering properties (e.g., porosity, permeability, pressures, and fluid saturations) can improve predictions (i.e., improve accuracy and reduce uncertainty) of hydrocarbon recovery, given the multiple non-linear and often noisy transformations required to make a prediction. Determining the worth of seismic data in predicting dynamic fluid production is one of the goals of the study presented in this paper.

We have approached the problem of assessing uncertainty in production forecasts by constructing a synthetic reservoir model that exhibits much of the geometrical and petrophysical complexity encountered in clastic hydrocarbon reservoirs. This benchmark model was constructed using space-dependent, statistical relationships between petrophysical variables and seismic parameters. We numerically simulated a waterflood in the mo del to reproduce time -varying reservoir conditions. Subsequently, a rock physics/fluid substitution model that accounts for compaction and pressure was used to calculate elastic parameters. Pre-stack and post-stack 3D seismic data (i.e., time -domain amplitude variation of elastic responses) were simulated using local one-dimensional approximations. The seismic data were also contaminated with noise to replicate actual data acquisition and processing errors. We then attempted to estimate the original dis tribution of petrophysical properties and to forecast oil production based on limited and inaccurate spatial knowledge of the reservoir acquired from wells and 3D seismic data.

We compared the multiple realizations of the various predictions against predictions with a reference model. Adding seismic data to the static description affected performance variables in different ways. For example, the seismic data did not uniformly improve the variability of the predictions of water breakthrough time; other quantities, such as cumulative recovery at a later time, did exhibit an uncertainty reduction as did a global measure of recovery. We evaluate how different degrees of spatial correlation strength between seismic and petrophysical parameters may ultimately affect the associated uncertainty in production forecasts.

Most of the predictions exhibited a bias in that there is a significant deviation between the medians of the realizations and that the value from the reference case. This bias is evidently caused by noise in the various transforms (some of which we introduced deliberately) coupled with nonlinearity. The key nonlinearities seem to be in the numerical simulation itself, specifically in the transform from porosity to permeability, in the relative permeability relationships and in conservation equations themselves.
Real-Time 4D Reservoir Characterization Using Passive Seismic Data
Authors: Maxwell S. C. , Urbancic T. I.
Published: December 2007

This paper details the application of passive seismic monitoring to image reservoir fracturing and deformation from the stage of an initial well completion to final field production. Instrumented oilfields with either permanently seismic arrays or temporarily deployed on wireline, offers the possibility of imaging production activities in a real-time sense that compliments other seismic reflection and enpineering measurements. During the well completion stage of development, real time microseismic imaging of well stimulation offers the ability to ensure the execution of the intended fracture design. Fracture images can also be used to optimize the fracture design and the net present value well production, understand fracture complexity and the associated well drainage pattern to target future well placement. During production, time-lapse microseismic imaging can be used to image deformation associated with fracture sealing and reservoir compartmentalization, localization of deformation associated with compaction, fracture reactivation or pressure or stress changes, monitor deformations in the overburden in fields with casing deformation problems, and image fronts associated with secondary recovery. In this paper, case studies are used to illustrate various potential applications along with discussion of the potential limitations. The reservoir conditions necessary for the successful application are presented along with a potential method to quanitify the technical feasibility at a particular site.
Correlating Particle Size Distribution in a Crushed Zone to Perforating Permeability Damage and Modeling Using Fragmentation Fractal Theory
Authors: Karacan C. Ozgen , Halleck Phillip M.
Published: December 2007

Conventional oilfield shaped charges form a jet consisting of hypervelocity metallic particles, whose pressure pulse can exceed 4 × 106 psi. When the metallic jet hits the rock target, the resulting shock forms a path of mechanically deformed rock as a tunnel. The shock wave also alters the rock mass around the tunnel by fragmenting rock and mineral grains. This is phenomena is an important issue in shaped-charge perforating due to its potential effect on decreasing the permeability of the rock surrounding the tunnel and decreasing the efficiency of costly perforating job. Although operating parameters can be set to remove fragmented sand grains (underbalanced perforating), it is practically difficult to remove all of them to regain the decreased permeability.

Determination of permeability and the thickness of crushed zone around perforation tunnel are important for productivity calculations and especially for near-wellbore modeling. Although productivity of a well after perforating is a good indication of the permeability damage due to perforating, it does not give the permeability distribution at the vicinity of the tunnel. Even in the laboratory shots performed under insitu pressure conditions, it is a difficult task to map the permeability distribution around the tunnel.

This paper proposes an easier way to estimate the permeability distribution in the crushed zone by modeling the distribution of grain fragments using fragmentation fractal theory. The resulting Eq. describes the permeability by a fractal model. It calculates pore size distribution from particle size data by setting up a hierarchical scaling concept for fragmentation to calculate the porosity of incompletely fragmented fractal porous medium. Estimated permeabilities were compared against the permeability distribution measured by using pressure transient analysis and computerized tomography (CT) scanning during injection test. It was seen that the values are close to each other.
New Reservoir Dynamic Connectivity Measurement for Efficient Well Placement Strategy Analysis Under Depletion
Authors: Ballin P. R. , Solano R. , Hird K. B. , Volz R. F.
Published: December 2007

A dynamic measurement of reservoir connectivity based on a parameter called resistivity index (RI) is evaluated. The RI parameter takes into account the pressure effects from wells but does not solve pressure equations. This technique is compared with other static connectivity measurements and with streamlines (another dynamic-connectivity technique) for gas reservoirs producing by depletion. Reference flow simulations were used to validate these comparisons.

Two real field models were used in this study. In both cases, the RI analysis reproduced the reference flow simulation results significantly better than the other techniques while requiring orders of magnitude less time than the finite difference flow simulator. The results of an uncertainty study based on the RI supported the approval of the infill-drilling program for the first field model. This technique has been implemented as a special option for a commercial geostatistical software application.
A Combined Geostatistical and Streamline-Based History Matching Procedure
Authors: Le Ravalec-Dupin Mickaële , Fenwick Darryl H.
Published: December 2007

One of the most challenging subjects in reservoir engineering concerns the conditioning of large reservoir models to the available data: dynamic data in the form of production history and a priori (static) geological or geostatistical knowledge. Streamline simulation has been proposed as an ideal tool for rapid conditioning of large, fine-grid geologic models. We develop a novel procedure that combines a streamline-based history matching method and a geostatistical parameterization technique to estimate the distributions of permeability and porosity in heterogeneous petroleum reservoirs.

An efficient two-step procedure was introduced recently for history matching. It consists first in matching the streamline effective permeabilities to production data, then mapping the resulting perturbations to the grid block permeabilities. This procedure requires relatively simple postprocessing of a single, standard streamline simulation and results in an extremely rapid history match to the production data. However, the mapping step often induces an undesired departure from the a priori geostatistical variability model. To circumvent this drawback, we modify the second step. The "optimal" streamline effective permeabilities obtained at the end of the first step are integrated into a new objective function which is minimized using the gradual deformation method. This parameterization technique allows for matching the "optimal" streamline effective permeabilities by changing the grid block permeabilities while at the same time preserving the a priori spatial variability model.
Modeling the Effect of External Gas Flux on Reservoir Fluid Distribution
Authors: Montel F. , Bickert J. , Caillet G. , Le Goff C.
Published: December 2007

In some circumstances, particularly in recent mature and permeable petroleum systems, hydrocarbon accumulations are subjected to gas fluxes, which lead to non-conventional fluid distribution.

After their migration into the trap, various forces shape the fluids. Among them, gravity has the most striking effect and has been widely studied. But in many cases, there is evidence for the contribution of other forces like thermal gradients and external mass flux at a geological time-scale. Taking all these phenomena into account to obtain a consistent picture of fluid distribution is an important challenge for the petroleum industry.

There are already a number of tools available for calculating the compositional gradient within a reservoir, including the contribution of gravity and thermal gradient. In many field cases, the actual profile differs from the one calculated. The discrepancies are imputed to other external forces: the mass fluxes at the reservoir boundaries. In this paper, we present the modeling of diffusion fluxes across the reservoir.

Drawing on field examples, the paper provides a methodology for dealing with dynamic reservoir fluid systems and offers petroleum engineers guidelines to avoid many pitfalls during the field evaluation procedure. The model matches the observed compositional gradient and corresponding PVT properties. It allows reliable connectivity assessment in cases where gravitational modeling fails.

The main contributions are a methodology for integrating the geological constraints in the evaluation of fluid distribution in a reservoir and the description of the model, which includes the impact of gravity, thermal gradient and external component fluxes.
Environmental Regulatory Framework in the North Sea: an Update of the Existing and Foreseeable Constraints
Authors: GARLAND Emmanuel
Published: December 2007

Major measures have been taken during the past thee years by the Convention for the protection of the marine environment of the North-East Atlantic (known as OSPAR), a legally binding Convention which came into force in 1998 and plays a key role regarding environmental regulations in the North Sea.

OSPAR adopted in 1999 a "Strategy on Environmental Goals and Management Mechanisms for Offshore Activities", a decision and two recommendations pertaining to the use and discharge of offshore chemicals (in 2000), a decision on organic-phase drilling fluids (also in 2000), a recommendation for the management of produced water (in 2001), in addition to its decision on disposal of disused installations (already adopted in 1998, to be revised in 2003).

Additional measures concerning the measurement of the oily compounds in produced water and the reduction of discharge of aromatic hydrocarbons are currently being discussed amongst OSPAR contracting parties, as well as contaminated drill cuttings piles, and implementation of environmental management systems.

In their Declaration made in Bergen in March 2002, the Ministers of the Environment of the countries bordering the North Sea recalled their desire to have as much of the OSPAR work programme completed by mid 2003, and to see OSPAR addressing new issues such as impact of seismic activities, disused pipelines and cables, use of renewable energy, etc.

The European Community appears to play a key role in addressing and implementing most of the other international legal instruments which affect the North Sea offshore industry.
Feature-Based Geostatistics: An Application to a Submarine Channel Reservoir
Authors: Arpat Burc , Caers Jef , Strebelle Sebastien
Published: December 2007

Characterization of developing submarine channel reservoirs requires geostatistical methods that are capable of reproducing channel facies morphologies. Such deep marine settings are generally characterized utilizing seismic data while in the development phase. Typically, the seismic is analyzed by means of clustering methods to partially interpret facies. Then, facies models are generated using geostatistical simulation methods. Yet, due to the incompatibility between the pixel-based nature of many geostatistical methods and the pattern-catching ability of seismic, making the resulting reservoir models satisfy seismic, geological interpretation and actual well-log / core data is an outstanding challenge. Object-based techniques are not viable for this problem because they are difficult to constrain to well-log data or partially interpreted geobodies. This paper attempts to solve the above problem by proposing a novel geostatistical approach making use of so-called "features". Instead of using single pixels, feature-based geostatistics attempts to work directly on templates of pixels, which represent geologically realistic object pieces, thereby decreasing the dimensionality of the pattern matching problem and promoting geology reproduction. In this sense, feature-based geostatistics is a middle-ground approach between pixel-based and object-based methods. The paper includes a submarine channel case study where the seismic is available and analyzed using a clustering method. A feature-based simulation technique is applied to this data. The method manages to reproduce the facies morphologies desired and conditions to data easily at considerable less CPU demand than either pixel-based or object-based methods.
Representation of Reservoirs Generated by Object-Based Stochastic Simulation in Numeric Flow Modeling
Authors: Pumputis A. , Schiozer D. J.
Published: December 2007

The interest for the reservoir characterization through the use of object-based stochastic simulation has increased recently in the petroleum industry, mainly because it is a promising technique for the evaluation of new fields. The objective of this work was to study the representation of object-based stochastic reservoirs in numerical flow simulation and the influence of such a process in the petroleum production forecast. Using data of object-based stochastic simulations of a real petroleum field containing sand rich turbidities reservoirs poorly connected, it was studied the interaction of four different reservoir characterization tools: (1) object-based stochastic simulation, (2) calculation methods of petrophysical properties, (3) upscaling and (4) numeric flow simulations.

Aiming the representation of the real model with the smallest acceptable computational effort, it is shown how the choice of the calculation method of petrophysical data and the upscaling process affect the flow simulation results. It was possible to test the importance of each part of the process, especially the influence of the model heterogeneity and of use of different grids in the flow simulations. Concerning volumes in situ and oil and gas production the effect of the object-based stochastic simulation and of different methods of properties calculation were more important in the final results. Water production was most influenced by the upscaling process.

It is shown the importance of each part of field production prediction process from the reservoir characterization through the flow simulation. The influence of heterogeneity and details about the upscaling process are discussed.
Development of Novel Membrane Efficient Water-Based Drilling Fluids Through Fundamental Understanding of Osmotic Membrane Generation in Shales
Authors: Mody Fersheed K. , Tare Uday A. , Tan Chee P. , Drummond Calum J. , Wu Bailin
Published: December 2007

Wellbore instability in shales is a major problem costing the petroleum industry US$900 million annually, according to conservative estimates. Water-based drilling fluids are being increasingly used to drill through troublesome shale formations. Major drivers for using water-based drilling fluids over oil-based drilling fluids are their cost-effectiveness and greater environmental acceptability. Despite these incentives to use water-based drilling fluids, improper application of such fluids while drilling sensitive shale formations can lead to costly wellbore instability problems. For correct application of water-based drilling fluids, an in-depth understanding of their physico-chemical interaction with the shale formations being drilled is important.

Shale stabilization with water-based drilling fluids can be achieved through a combination of osmotic outflow of pore fluid (chemical potential mechanism) and minimization of mud pressure penetration. Mud pressure penetration can either be prevented by generating an isolation membrane on the borehole wall or be reduced by minimizing hydraulic diffusivity. To help ensure adequate outflow and/or minimize hydraulic diffusivity with water-based drilling fluids, an efficient semi-permeable membrane should be generated within the shale. Several membrane generation mechanisms with varying degrees of effectiveness, depending on shale properties, are described in this paper. Mechanisms described involve chemical reactions between the drilling fluid and shale pore fluid, generation of electrical charges on exposed shale surface to selectively restrict ion movement and modification of clay structure by chemical and mechanical means.

Laboratory experiments on shale samples under realistic downhole conditions exposed to a range of water-based drilling fluids are presented to emphasize the time-dependent nature of membrane generation. The experiments showed that maintenance of shale stability with a new generation of water-based drilling fluids can be achieved through significant increase in membrane efficiencies (greater than 80%) within relatively short exposure times.

A fundamental understanding of the osmotic membrane generation in shales and the application of experimental data have resulted in the development of a new generation of water-based drilling fluids designed to successfully achieve drilling objectives through shale stabilization. Guidelines presented here for drilling of shales should help to significantly reduce shale stability-related non-productive time during drilling.
Effect of Scale Up and Aggregation on the Use of Well Tests to Identify Geological Properties
Authors: Raghavan Rajagopal , Dixon Thomas N. , Thomas Olubusola O.
Published: December 2007

This paper discusses specific issues encountered when pressure tests are analyzed in reservoirs with complex geological properties. These issues relate to questions concerning the methodology of scale up, the degree of aggregation, and the reliability of conventional methods of analysis.
Timing and Distance of Well Interference in Anisotropic Reservoirs
Authors: Chen Her-Yuan , Teufel Lawrance W.
Published: December 2007

This work provides a technique for determining the time and the point at which pressure disturbances originating from two adjacent wells begin to interfere significantly. Reservoir continuity and flow anisotropy due to natural fractures are common issues in tight-gas reservoir. Lacking and accuracy of pressure data makes the interpretation highly uncertain. The developed technique will provide a method to assist the interpretation of well-interference issue and the optimization of well spacing/pattern in tight-gas reservoirs. The technique is based on analytical model and is easy to apply.
The Study of Performance Prediction of Treatment Wells in Low Permeability and Abnormal High Pressure Gas Reservoirs
Authors: Tingxue Jiang , Wu Qi , Wang Xugang , Zhang Fuxiang , Ding Yunhong , Zou Honglan , Fan Yonghong
Published: December 2007

The result worked out in laboratory under the condition of in-situ stress indicates that a strong stress sensitivity is usually a main character of low permeability and abnormal high pressure gas reservoirs, i.e., the permeability decreases with the increase of effective stress (the result of decrease of pore pressure), which will cause a reduction of gas wells’ rate in some degree. Therefore, a finite element model is established to simulate above problem. Compared with other models, the model put forward in the paper can take into account the following factors:1)The sensitivity of permeability to effective in-situ stress;2)Non-darcy flow within an artificial fracture;3)Skin factor and erosion depth;4)The fracture conductivity is a function of time, fracture length and effective in-situ stress as well;5)three dimension flow in gas reservoirs, and the state parameters of rock and gas such as density and porosity are functions of pore pressure. After that, a computer program has been worked out by virtue of VISUAL BASIC, and a case study conducted in a gas well of AK1 which is located in TARIM basin, Xinjiang, China.with the simulation result shows a high precision compared with the field data. What's more, the simulation results indicate that: 1)a reduction of a gas well's production rate may decrease up to 10 to 40 percent of its original rate;2)the impact of skin factor is bigger than that of erosion depth;3)a reduction of a gas well's rate may decrease up to 10 to 50 percent of its original value as a result of conductivity damage which is a function of time, fracture length and in-situ stress as well. It should also be noted that the model put forward in the paper can be used to conduct performance prediction of such treatment wells as hydraulic fracturing wells, matrix acidizing wells and acid fracturing wells, so that it has a great significance in improving above wells’ optimal design level and decision making level as well as the production level of overall gas reservoirs, and if it is popularized to field applications, a great benefit may be expected.
Gas Diffusion – Its Impact on a Horizontal HPHT Well
Authors: Bradley Nigel D. , Low Eric , Aas Bjarne , Rommetveit Rolv , Larsen Hans F.
Published: December 2007

If a HPHT well with oil based mud is left undisturbed for a period, eg. when tripping or logging, methane will diffuse from the formation through the mud invaded zone and mud filter cake into the well bore. This can amount to substantial quantities and will occur despite an overbalance of mud hydrostatic pressure existing. Consequences can be potential well control problems when circulation is resumed or pipe is tripped back into the well or degradation of mud properties including loss of weighting material or ‘baryte sag’.
Field Testing of a New Nuclear Magnetic Resonance Logging-While-Drilling Tool
Authors: Morley Jan , Heidler Ralf , Horkowitz Jack , Luong Bruno , Woodburn Charles , Poitzsch Martin , Borbas Tim , Wendt Brett
Published: December 2007

Downhole nuclear magnetic resonance (NMR) measurements are evolving into a powerful formation evaluation tool, providing unique and critical information including formation porosity, pore-size distributions, bound-fluid volume (BFV), free-fluid volume (FFV), permeability, and fluid properties. Obtaining this information while drilling can have a significant impact on drilling and completion decisions. In addition, low rates of penetration common in many drilling environments can be advantageous in improving the NMR measurement statistics.

This paper describes results gained during field tests of a new NMR logging-while-drilling (LWD) tool that has been designed to run in any standard measurement-while-drilling (MWD) bottomhole assembly. The new tool presents no special operational complications in terms of mechanical specifications or wellsite hardware and software, and it has been tested successfully in both real-time and recorded modes in a wide range of formations and drilling conditions. A key consideration in the design of this tool has been to deliver an NMR measurement of wireline quality with a minimum of interference to the drilling process. To this end, the tool is usable in various modes of operation (stabilized, unstabilized, while drilling, while reaming, etc.).

The detrimental effects of tool motion on the NMR measurement are minimized through the hardware design. Motion-effects modeling and log examples address these issues. Having the capability of acquiring data in the conventional T2 mode, this tool offers a familiar interpretation strategy for those users accustomed to evaluating wireline NMR data along with a significant advantage in statistical precision over a T1 acquisition mode.
An Integrated Caliper from Neutron, Density, and Ultrasonic Azimuthal LWD Data
Authors: Ortenzi L. , Evans M. , Maeso C. J.
Published: December 2007

Accurate logging-while-drilling (LWD) borehole caliper data are important for drilling, logging and well completion. A single, accurate LWD caliper can greatly minimize risk and improve quality by bringing critical new information to these applications.

Presently, an LWD azimuthal density porosity tool can provide three different hole-size measurements. In addition to an ultrasonic caliper, a neutron-derived and a density-derived caliper have been recently introduced. Each method has different advantages and limitations that are related to the physics of the measurement and environmental conditions. This paper provides an overview of the ultrasonic caliper, the new neutron- and density-derived calipers and also describes the applicability range of each measurement. A method is also proposed to integrate the different techniques in order to form a single, robust and accurate LWD caliper. Examples of the individual and integrated calipers from an azimuthal density porosity tool are presented.
Estimating Non-Darcy Flow Coefficient from Buildup Test Data With Wellbore Storage
Authors: Spivey J. P. , Brown K. G. , Sawyer W. K. , Frantz J. H.
Published: December 2007

An algorithm has been developed for computing the pressure response for a well with constant wellbore storage and non-Darcy skin factor across the completion. The algorithm has been used to generate type curves for drawdown and buildup tests. The buildup pressure derivative response for a well with non-Darcy flow across the completion exhibits a much steeper slope during the transition out of wellbore storage than that of a well with constant skin.

No reservoir model with constant wellbore storage and skin can reproduce this steep derivative. Thus, if it is present in a buildup test, the well is experiencing either decreasing wellbore storage or decreasing skin factor, or both.

With the new type curves, under favorable conditions, both Darcy and non-Darcy skin components may be estimated from a single buildup test following constant rate production. The new algorithm may also be used to model a test sequence comprising multiple flow and buildup periods.
Reverse Like-Kind Exchanges for Oil and Gas Transactions Enter a New Era: New IRS Procedures Add Needed Flexibility
Authors: Brown C. D. , Brown A. J. , Phillips R. C.
Published: December 2007

Oil and gas transactions frequently result in sizable capital gains taxes that have a negative impact upon profitability. The Internal Revenue Code, Section 1031, has long provided a method to defer the tax by using a deferred like -kind exchange process, whereby a property must be sold before the "target" can be bought.

Last year, the IRS endorsed and published the reverse like-kind exchange procedures, which allow companies to purchase properties before selling others. This paper explains both procedures and provides examples for utilizing one or both to provide companies with the maximum rate of return from their acquisitions and divestitures. Key elements of the like-kind exchange procedures are identified to assist operators and help them avoid costly oversights that can cause a like -kind exchange to be ruled ineligible.
Would You Know a Good Decision if You Saw One?
Authors: Bratvold R. B. , Begg S. H. , Campbell J. M.
Published: December 2007

Ever since the early publication by Grayson,1 we have seen an increasing interest in decision-analysis in the oil and gas industry. There have been numerous studies and publications discussing methods and models for rational decision-making. Given the inherent limitations of intuition and heuristics, one might expect decision-makers to be delighted with the more consistent approach provided by rational decision-making techniques. Modern decision models can help process large amounts of information without losing valuable pieces. They never suffer from distraction, fatigue, boredom or random error. They are consistent, week after week.

Yet, in spite of these obvious advantages, people treat these with a nearly instinctive distaste. They are particularly resistant to the idea that simple models can validly make such subjective evaluations. For some, that resistance may stem simply from unfamiliarity with the statistics and probability involved. Many more, however, subscribe to the widespread assumption that human judgment is more discerning than a model. They are reluctant to believe that simple mathematical calculations can match the complexity of the human mind. "Take away an ordinary person's illusions," says Dr. Relling in Henrik Ibsen's Villanden, "and you take away happiness at the same time."

A particularly interesting aspect of human judgment and decision-making are the traps we unknowingly step into. Many decision-makers believe that intuition, repeated experience and their general intelligence will see them through. Unfortunately, as will be discussed in the paper, intuition and repetition are unreliable teachers at best.
Fluvial Channel Parameter Estimation Constrained to Static, Production, and 4D Seismic Data
Authors: Phan Vinh , Horne Roland N.
Published: December 2007

This paper proposes a subcell technique for modeling geometry and spatial distribution of channels in a fluvial reservoir by history matching of production and 4-D seismic data while constraining to well log and 3-D seismic information. The method developed here is capable of processing any number of geological objects with arbitrary geometric shapes and results in a fast and feasible inversion. The application of the proposed technique is presented in this work through several two- and three-dimensional examples in a two-phase water-oil case. The results of this work also show that the ntegration of production and 4-D seismic data can give us a better understanding of the reservoir geology and geophysics.