bluuebunny/crossref_metadata_2025 huggingface dataset:
Effective Proppant Flowback Control Following Hydraulic Fracturing Treatments in Shallow Reservoirs
Authors: Stephenson Chris J. , Crabb Terry M. , Orrego Guillermo Villa , Khachatrian Mikael B.
Published: December 2007

Proppant flowback within shallow wells, as with all wells, can be a significant problem in the oil and gas industry. Under the typical low-stress and low-temperature conditions found in shallow formations, many of the current products and processes to control proppant flowback often fail or have only limited success. As such, improved or alternative technology and procedures are constantly being sought. One such technology is the development of a deformable proppant for use under low closure stress conditions. Laboratory testing of this ‘low-stress’ (LS) deformable proppant, blended with typical fracturing sand, has shown 20 fold increases in flowrate and 10 fold increases in pressure-drop are attainable without proppant pack failure, while still maintaining or in some cases increasing fracture conductivity.

Furthermore, this ‘low-stress’ (LS) deformable proppant has been successfully applied in shallow reservoirs with typical closure stresses +/-500 psi and bottom-hole temperatures of +/-100°F. Several case histories, along with the development of equipment and monitoring procedures required to facilitate field application will be discussed.
Field Verification: Invert Mud Performance from Water-Based Mud in Gulf of Mexico Shelf
Authors: Klein Aaron L. , Aldea Catalin , Bruton James R. , Dobbs Williams R.
Published: December 2007

A uniquely designed water-based mud (WBM) was used in two shelf areas of the Gulf of Mexico to drill highly reactive gumbo sections. The drilling performance and inhibition in these shale intervals resembled that of synthetic-based muds (SBM) previously used in offset wells. Owing to new environmental regulations, obtaining the drilling performance characteristics of a synthetic-based fluid and the stability of a water-based fluid is a high priority for Gulf of Mexico operators.

A special characteristic of this fluid is its ability to deliver SBM-like shale inhibition without using any salts, through an ideal combination of a polyamine shale inhibitor, a polymeric encapsulator and an anti-accretion additive.

This paper presents field data comparing the drilling performance and the inhibition in gumbo shale sections between the new WBM and previously used SBM. With instantaneous rates of penetration up to 85% higher than synthetic-based fluids used in similar well sections, the average time required to drill identical intervals was reduced dramatically. No accretion or bit balling was noted on bottomhole assemblies during bit runs, and the cuttings drilled were well encapsulated and protected from hydration. Economic savings were realized by reducing the drilling time and by not requiring the essential waste management equipment and engineering associated with SBM cuttings discharge. Furthermore, the new high-performance WBM was easily prepared at the wellsite using seawater, which also translated into cost savings by reducing the volumes handled by the workboats.

These field applications demonstrate that this uniquely designed water-based fluid can effectively replace invert-emulsion fluids in many highly reactive shale sections without sacrificing drilling performance or increasing environmental risk.
Towards Truly Permanent Intelligent Completions: Lifelong System Survivability Through a Structured Reliability Assurance Process
Authors: Veneruso A. F. , Kohli H. , Webster M. J.
Published: December 2007

This paper describes a structured reliability assurance process to quantify and optimize the reliability of electric permanent monitoring and control systems for application in intelligent completions. Although reliability is essential to unlock the potential of the intelligent well, there are challenges in terms of the long lifetimes involved, high risks and high costs associated with failure, and the difficulty of diagnosing problems, retrieving failed parts, and learning lessons from equipment within the reservoir.

A structured reliability process is described that is based on innovative techniques to address these inherent challenges and help overcome barriers many perceive as impediments to the acceptance and growth of this important technology. These techniques have been developed and proven in quite different areas of technology such as aerospace, defense, biology, and health science as well as the risk assurance industry.
A New Optimization Methodology for Portfolio Management
Authors: April J. , Glover F. , Kelly J. , Laguna M.
Published: December 2007

A new portfolio optimization software system simultaneously addresses financial return goals, catastrophic loss avoidance, and performance probability. The innovations embedded in the system enable users to confidently design effective plans for achieving financial goals, employing accurate analysis based on real data. Traditional analysis and prediction methods are based on mean variance analysis – an approach known to be faulty. The new software system takes a much more sophisticated and strategic direction. State-of-the-art technology integrates simulation and metaheuristic optimization techniques and a new surface methodology based on linear programming into a global system that guides a series of evaluations to reveal truly optimal investment scenarios.

Portfolio analysis tools are designed to aid senior management in the development and analysis of project portfolio strategies, by giving them the capability to assess the impact on the corporation of various investment decisions. To date most of the commercial portfolio optimization packages have been relatively inflexible and are often not able to answer the key questions asked by senior management. In this paper we will present new techniques that increase the flexibility of optimization tools and deepen the types of portfolio analysis that can be carried out. We also include some examples applied to P&E portfolios.
Gas Storage and Flow in Coalbed Reservoirs: Implementation of a Bidisperse Pore Model for Gas Diffusion in Coal Matrix
Authors: Shi Ji-Quan , Durucan Sevket
Published: December 2007

Unipore diffusion models are widely used for modelling gas transport in coal matrix in conventional dual-porosity coalbed reservoir simulators. The unipore models implemented in conventional coalbed reservoir simulators assume that free gas phase is negligible and gas exists only in adsorbed state in coal matrix. In low-rank coals, however, a substantial amount of free gas may exist in the macropores of coal matrix.

There is strong laboratory evidence that many coals exhibit bi- or multi-modal pore structure. This paper describes the implementation of a bidisperse pore-diffusion model in a coalbed reservoir simulator. In the bidisperse model, gas adsorption is assumed to take place only in the micropores, with the macropores providing storage for free gas, as well as tortuous paths for gas transport between the micropores and cleats. Gas production performance from a sub-bituminous Powder River Basin coalbed reservoir has been studied using the in-house Imperial College coalbed reservoir simulator. The implementation of the triple-porosity formulation in the simulator overcame the reported inconsistency between field gas production rates and predicted rates obtained using conventional dual-porosity simulators. With the introduction of an appropriate storage volume of free gas in the macropores, the predicted increase in gas production rates are consistent with the published field data.
Role of Convective Mixing in the Long-Term Storage of Carbon Dioxide in Deep Saline Formations
Authors: Ennis-King Jonathan , Paterson Lincoln
Published: December 2007

Storage of carbon dioxide in deep formations is being actively considered for the reduction of greenhouse gas emissions. Relevant experience in the petroleum industry comes from natural gas storage and enhanced recovery using carbon dioxide, but this experience is over a time scale less than the hundreds or thousands of years required for carbon dioxide storage. On these long time scales different mechanisms need to be considered.

In the long-term the dominant mechanism for dissolution of carbon dioxide in formation water is convective mixing rather than pure diffusion. This arises because the density of formation water increases upon dissolution of carbon dioxide, creating a density instability. Linear stability analysis has been used to estimate the time required for this instability to occur in anisotropic systems. For sufficiently thick formations with moderate vertical permeability, this time is years to decades. Further approximate analysis shows that the time needed for the injected gas to dissolve completely is typically much longer, of the order of hundreds to thousands of years, depending on the vertical permeability. This theoretical analysis is found to be in broad agreement with the results of fine scale reservoir simulations. Laboratory experiments on an analogous system demonstrate the same phenomena.
Completion of Aconcagua Field With a Dual Derrick Drilling Unit
Authors: Geyelin Jean-Louis , Clergier Alberic , Bouget Ronan , Manchon Xavier
Published: December 2007

Dual derrick drilling units were claimed to reduce drilling time by +/- 25%, taking advantage of their enhanced handling capacity. These statements were issued bearing in mind drilling activities.

The Aconcagua Field - operated by Total E&P USA, Inc. - is located on Mississippi Canyon 305 and was completed by means of a dual derrick drilling unit (DDDU).

This paper describes the lessons learned to complete deep water, multi-zone, sand controlled, intelligent wells by using a DDDU in ultra deepwater.

Careful planning and rigorous organization were essential to take full advantage of the dual derrick capabilities, and run simultaneous completion phases. Permanent procedures and operational improvement during the four month campaign allowed to develop a learning curve. Substantial cost and time savings were achieved while delivering wells with excellent production performance.
A New Type of Hydraulic Hammer Compatible with Conventional Drilling Fluids
Authors: Plácido João Carlos R. , Lage Antonio Carlos V. M. , Carvalho Daltro J. L. , Hardie Ronnie , Wajid Rasheed
Published: December 2007

This paper describes the tests and concept behind a new hydraulic hammer. The objectives of these tests were to evaluate penetration rate performance of this hammer when used in conventional drilling conditions.

To date the usage of hydraulic hammers has been hindered due to limited compatibility with drilling fluids solids content. Therefore, this hammer was conceived to operate with all kinds of drilling fluid, including Lost Circulation Materials. Additionally, this hammer would be used with conventional tri-cone bits. This is significant because inter-bedded formations can be drilled without repeated changes to the bottom-hole assembly and drilling can continue in the event of hammer failure.

The technology consists of a rotating valve system that alternately directs fluid to a piston that drives down a steel mass to strike the rear of the bit and then to a port that bypasses the piston. This action allows the mass to return to its original position ready for the next downward stroke. The valve operates at a known frequency that is directly proportional to flow rate.

Due to these unique characteristics, the Hard Rock Drilling JIP decided to test the hammer, the results of which are discussed here.
Mobile Offshore Jackup Units: A New Innovation for the Next Frontier in the Gulf of Mexico - Deep Drilling for Natural Gas on the Shelf
Authors: Robertson John E.
Published: December 2007

With the resurgence of deep gas drilling in the Gulf of Mexico specifically on the shelf, the focus has shifted to the need for a new design in offshore drilling units. This paper will discuss the reasons for pursuing exploration in such an environment, why it is more cost effective to build new rigs instead of modifying existing units, and the design and equipment used to enhance its performance.
Novel Wireline Coring System
Authors: Fleckenstein W. W. , Eustes A. W.
Published: December 2007

The value of core samples to enhance reservoir evaluation and completion strategies has long been recognized. A large percentage of the cost of coring is the rigtime associated with the tripping of the corebarrels. As rig rates increase, particularly in deepwater areas, the cost of coring becomes prohibitive due to excessive trip costs. A solution to this problem is to trip the core from the well at wireline log recovery speeds, yet still recover the length and diameter of core associated with conventional coring operations.

Since the 1960's, international teams which include the United States, Europe, Japan, and Russia, have developed a wireline coring system for recovering 4 to 5-1/4" (101 to 133 mm) diameter, ice and rock cores to 12,000 feet (3,660 m) in Antarctica and Greenland. This paper describes this wireline coring technology. This includes the self-contained fluid circulation, cuttings recovery, instrumentation, core barrel, core catcher, and core bit systems. The operational history for the recovery of both ice and rock cores on multiple wellbores, including the Greenland Ice Sheet Project, is presented and possible oilfield applications, emerging from a recent optimization study, including replicate coring, are discussed.
Application of Stream Conversion Methods to Generate Compositional Streams From the Results of a Multi-Million Cell Black Oil Simulation Study of the Shaybah Field
Authors: Al-Awami Bassam , Hemanthkumar K. , Al-Awami Fatema , MohammedAli Mansour
Published: December 2007

Detailed compositional simulation of a giant reservoir with many components is not practical. However, detailed multi-million cell black oil simulation of giant reservoirs is now quite feasible. In this work we apply an efficient method to generate the compositional rates from a black oil simulation of the giant Shaybah field.

In situations where the reservoir recovery mechanism is not dominated by compositional effects, an Equation of State (EOS) based stream conversion method can be used. This stream conversion method relies on the fact that when laboratory PVT data measured on available well stream compositions are used to generate the black oil PVT tables, some of the compositional information is lost. The stream conversion model retains this valuable compositional information and applies it to each producing well completion in the black oil simulation at every time step.

As proof of concept, the stream conversion method was applied to a black oil simulation and to a limited (eight-component) compositional simulation to generate a 17-component compositional stream and the results were compared to the respective full EOS compositional simulation for a relatively small sector (250,000 cells) of the giant Shaybah field. The compositional stream rates are in excellent agreement with the stream converted black oil results. As would be expected, the computational costs of using the EOS based compositional simulator (with 17 components) is in excess of 40 times the black oil simulation time for the small sector model. In general, the stream conversion method can be used to generate the dynamically varying compositional streams from any black oil simulation for use in the design and operation of surface facilities and in calculating the amounts of a certain cut (e.g. NGL) from the production streams.
WAG Optimization for Gas Floods above the MME
Authors: Johns Russell T. , Bermudez Leonardo , Parakh Harshad
Published: December 2007

Water-alternating-gas floods (WAG) are commonly used to improve sweep efficiency in heterogeneous reservoirs. There has been little reported in the literature, however, on the effectiveness of WAG processes where the gas is enriched above the minimum miscibility enrichment composition (MME). This paper examines how to optimize WAG processes for enriched gas floods above the MME, particularly as a primary recovery method. Compositional simulations of x-z cross-sections are used to quantify the effects of WAG parameters, numerical dispersion, level of enrichment, and heterogeneity on local displacement efficiency and sweep efficiency.

The main conclusions of this research show that the richer the gas above the MME, the fewer the number of WAG cycles required for maximum oil recovery at a given WAG ratio. Another significant observation is that over-enrichment above the MME improves recovery the most when the largest permeability layers are at the bottom of the reservoir. Continuous slug injection performs better than WAG when the largest permeability layers are at the bottom of the aquifer, richer gases are used, and the vertical to horizontal permeability ratio is small.
Reservoir Monitoring and Continuous Model Updating Using Ensemble Kalman Filter
Authors: Nævdal Geir , Johnsen Liv Merethe , Aanonsen Sigurd Ivar , Vefring Erlend H.
Published: December 2007

The use of ensemble Kalman filter techniques for continuous updating of reservoir model is demonstrated. The ensemble Kalman filter technique is introduced, and thereafter applied on two 2-D reservoir models. One is a synthetic model with two producers and one injector. The other model is a simplified 2-D field model, which is generated by using a horizontal layer from a North Sea field model.

By assimilating measured production data, the reservoir model is continuously updated. The updated models give improved forecasts. Both dynamic variables, as pressure and saturations, and static variables as the permeability are updated in the reservoir model.
Formation Damage Assessment and Remedial Economics from Integration of NMR and Resistivity Log data
Authors: Altunbay M. , Sy R. , Martain R.
Published: December 2007

The main objective of this study is to devise a methodology, utilizing a wealth of information gained from NMR (Nuclear Magnetic Resonance) and resistivity logs, and to assess and to quantify formation damage due to filtrate invasion in the flushed zone. Quantification of the damage, in terms of damage-ratio within vertical resolution of the logging tools, provides the input for the calculation of economic implications of the problem. This, in turn, helps us decide either the need or the scope of the remedial action.

The quantification of the damage relies on the determination of the amount of shift in the relative permeability curves for the flushed zone against the undamaged zone. Depth of investigation for the NMR logs is limited to the flushed zone while the resistivity logs provide a deeper insight into the formation. The DWT (Dual Wait Time) mode of an NMR logging pass yields the movable and immovable parts of the porosity in addition to the type of the fluids contained within. Derivation of an absolute permeability profile from the Bound Water Model in conjunction with synthetic capillary pressure-based RBVI (bulk volume irreducible as capillary pressure approaches to infinity) or Purcell's technique along with water saturation profile from DWT NMR data yield the foundation for computing the relative permeability characteristics of the formation by using empirical equations. A water saturation profile for the uninvaded zone is computed from resistivity logs using the proper petrophysical model while corresponding relative permeability characteristics are obtained via the same set of equations. The superimposed relative permeability curves from NMR and resistivity-based data indicate the presence and/or amount of the shift of the curves between the flushed-zone versus the uninvaded zone. The amount of increase in effective permeability to water and drop in effective permeability to hydrocarbons are computed from the superimposed relative permeability curves. The radius of the damaged zone is determined from the 2D inversion of resistivity data and inserted into the DR (damage-ratio) equation together with the effective permeability of the undamaged and damaged zones. Skin factors can also be computed as a function of the available data. The annual revenue loss per well, formation damage dollars lost (FD$L)3, due to filtrate invasion-based damage can then be assessed by multiplying the damage-ratio with the current price of the hydrocarbon and the rate of production. To further evaluate the economics, the damage-ratio and FD$L can be plotted for various damaged radii to determine the threshold radius for economically justifying the cost of remedial action.
Calibration of Log Permeability Models Using Fluid Flow Measurements
Authors: Poe B. D. , Butsch R. J.
Published: December 2007

This paper presents the results of a research effort to develop, test, and apply a numerical minimization procedure for determining the coefficients and exponents of some of the more popular formation permeability estimation models that are used with open hole well log analyses. The calibration of the log permeability models is performed using reference values of formation effective or absolute permeability (or conductivity) derived from fluid flow measurements. Sources of the reference formation permeability values that have been used in this study include reservoir pressure-transient test analyses, commingled multilayer reservoir production performance analyses using production log information, core analyses, and formation tester results.

In this paper, an efficient numerical minimization algorithm has been implemented to determine the best estimates of the coefficients and exponents of the Coates1 and Timur2 log permeability models that agree with fluid flow measured values of formation permeability (or conductivity). These models were chosen due to their popularity, but the basic minimization procedure presented in this paper is applicable to other log permeability prediction models as well.

Special consideration is given to the implementation of the Coates1 model in the minimization process by the introduction of the Heaviside unit step function into the published model for use in the minimization process to relate the bulk volume water irreducible and the total porosity (or irreducible water saturation and effective porosity).
The Use of An Integrated Approach in Estimation of Water Saturation and Free Water Level in Tight Gas Reservoirs: Case Studies
Authors: Ding Sheng , Pham Tai , Yang AnPing
Published: December 2007

To reduce the uncertainty in the estimation of hydrocarbon in place and fluid contact in tight gas reservoirs, it is essential to integrate core data and log analysis. A newly developed saturation-height function approach has been successfully applied to calibrate log analysis to better define petrophysical properties such as formation water saturation and free water level in tight gas reservoirs. The application of this approach has played a critical role in exploration and development decision-making processes for tight gas reservoirs.

Unlike most of the models published in the literature, this approach accommodates different forms of J-Sw regressions, which is applicable to different pore geometries and very powerful in tight gas reservoirs. Also, water saturation is calculated continuously from log porosity and free water level without formation resistivity and Archie exponents. In addition, this approach estimates free water level by iterating on water saturations until matching those derived from log data.

In a case of a tight gas "wild-cat" well where the porosity from most of the well logs is much larger than that from core analysis, this new approach reconciled the difference and predicted the rock quality up-dip. The results are confirmed by the pressure transient analysis from the production test. Based on the integrated analysis, the decision to abandon the current well and the up-dip drilling location saved the company millions of dollars.

In the second case, the reservoir simulation failed to get a history match for a tight gas field. The parameters of this new approach were calibrated to several key wells with core data.

The results of the calibration were then used to populate water saturation throughout the field. Eventually, the history match was achieved and an infill drilling opportunity was identified for this field.

In summary, this paper proposes an integrated EXCEL-based saturation-height approach. Case studies in tight gas reservoirs using the new approach demonstrated that failures were avoided, and opportunities were realized.
Assessment of Remediation Treatments in Underground Gas Storage Wells
Authors: Brown Kenneth G. , Frantz Joseph H. , Sawyer Walter K. , Heckman Glenn C.
Published: December 2007

The underground gas storage (UGS) industry uses more than 400 reservoirs and 15,000 wells to store and withdraw natural gas and is thus a significant contributor to gas supply in the United States.1 Previous work indicates that many gas storage wells show a loss of deliverability each year due to numerous damage mechanisms and it is estimated that tens of millions of dollars are spent each year to recover or replace this lost deliverability.2

Prior Gas Technology Institute (GTI) studies3,4 have been aimed at qualitatively reviewing completion and deliverability enhancement techniques used in the storage industry, identifying specific damage mechanisms present in storage reservoirs, and establishing procedures for damage mechanism identification. This paper presents key results of a major new study sponsored by the Gas Technology Institute (GTI) that focused on a comprehensive, quantitative assessment of the effectiveness and longevity of the various stimulation treatments employed in the UGS industry.

Specifically, this paper summarizes the major results of the most comprehensive quantitative study conducted to date of stimulation treatments employed in the UGS industry. The study involved seven operators and 23 reservoirs (14 carbonate and 5 sandstone). Data were collected, entered into the database, and reviewed for 381 stimulations in 365 wells. Deliverability data were entered for 159 stimulations in 155 wells (67 in carbonate reservoirs and 88 in sandstone reservoirs) with sufficient data for inclusion in the study.

The most popular stimulation treatments currently employed in the UGS industry are identified, the effectiveness and longevity of various treatment types are quantified and compared, and a new quantitative indicator designed to capture the results of effectiveness and longevity calculations in a single benchmark indicator is presented. In addition, the frequency and duration of cleanup effects for various treatment types and the post-stimulation decline rates typically observed for various treatments are also quantified and compared.

The implications of conclusions reached in the study, as they relate to future UGS R&D efforts, are also discussed, and specific areas of additional study are recommended.
Evaluation of a Hybrid Water-Frac Stimulation Technology in the Bossier Tight Gas Sand Play
Authors: Rushing J. A. , Sullivan R. B.
Published: December 2007

This paper presents results from an evaluation of water-frac stimulation treatments in the Bossier tight gas sand play in the East Texas Basin. The primary objective of our study was to compare the stimulation effectiveness of conventional water-fracs with a hybrid water-frac technology. The hybrid water-fracs combine the advantages and benefits of both conventional gel and water-frac treatments. Stimulation effectiveness, measured in terms of fracture half-length and conductivity, was evaluated using short-term pressure buildup testing integrated with decline type curve analysis of long-term gas production data. The results of our study indicate that we can achieve longer effective fracture half-lengths and higher effective fracture conductivities more consistently using the hybrid water-frac technique.
Production and Injection Profiling: A Novel Application of Permanent Downhole Pressure Gauges
Authors: Ouyang Liang-Biao , Sawiris Ramzy
Published: December 2007

Production and injection profiling through permanent downhole pressure gauge, a novel and unique application, has been proposed in the present paper. Theoretical development of the new technique is first provided. Example studies are then given to illustrate the application of the technique. Application scenarios, practical issues as well as key impacting parameters have also been addressed. Finally, a field case study implementing the new technique for a long horizontal well has been performed to demonstrate how the production profiles calculated from PDG data compare to the results from a recent PLT survey which turns out to be expensive yet unsatisfactory.

The technique could be applied to real-time production and injection profiling for different well configurations (vertical, horizontal, deviated and multilateral) and bring tremendous financial benefits through replacing conventional production logging surveys that could be cost-extensive for horizontal or multilateral wells offshore.
A Comprehensive Model of Horizontal Well Completion Performance
Authors: Furui K. , Zhu D. , Hill A. D.
Published: December 2007

Horizontal wells or laterals are completed as openhole, slotted liner, cased and perforated, or gravel pack completions. We have developed a comprehensive skin factor model to predict the performance of any of these completion types, and calibrated this model with extensive finite element simulations of flow for a horizontal well completion. This model can be used to predict the performance of virtually any horizontal well completion.

The new completion skin factor model accounts for the effects of formation damage, convergent flow to perforations and slots, and flow through slots, with interaction among these effects. To account for formation damage, we extended our previous rigorous model of a damaged horizontal well to include the presence of perforations within, or extending through, the damage zone. The formation damage model is also integrated with the models of slotted liner performance to model these completions. The model of slotted or perforated liner performance is based on the relationship between pressure drop and flow rate for turbulent flow in these geometries. The slotted liner model accounts for partial plugging of the slots by grains of formation minerals or precipitates (scale). Turbulence effects are a major part of the apparent skin factor for these completion types.

The model shows the recommended conditions to obtain high productivity (low skin factor) completions in horizontal wells. In particular, the interactions among damage effects and skin effects due to perforations or slots are shown to greatly affect horizontal well completion performance. The models developed can be applied to design optimal completions for horizontal wells or laterals.
Geostatistical History Matching Using a Regional Probability Perturbation Method
Authors: Hoffman B. Todd , Caers Jef
Published: December 2007

Petroleum reservoirs are large, geologically complex and usually contain multiple wells. Building numerical models for reservoirs is not a simple task, and it is further complicated when production data is incorporated into the reservoir models. Integrating production data into the model requires an iterative process of changing the model and observing how those changes effect the flow of fluids in the model. This process should be as efficient as possible because each iteration requires a time-consuming flow simulation, and it should honor all available data so that the predictive models are as accurate as possible.

This paper lays out a general procedure for modifying geostatistical realizations in a geologically consistent manner that efficiently matches production data. To achieve this goal various regions in the reservoir are perturbed by different amounts, yet no geological artifacts are created at the borders of these regions. The methodology relies on a region-wise perturbation of the probability model used to generate the geostatistical realization. Perturbing probabilities rather than actual petrophysical properties guarantees that border artifacts are avoided. A new, simple yet efficient optimization method is developed that can jointly optimize the magnitude of the perturbations and is able to handle a large number of regions. We demonstrate with realistic synthetic examples that the method allows perturbing under various geological scenarios, and a 3D realistic synthetic case of a North Sea fluvial channel type reservoir demonstrates how the method would work in practice.
Time-Dependent Matrix-Fracture Shape Factors for Partially and Completely Immersed Fractures
Authors: Rangel-German Edgar R. , Kovscek Anthony R.
Published: December 2007

Modeling multiphase flow in fractured porous media relies on the accurate description of matrix to fracture transfer of water. The rate of mass transfer between the rock matrix and fractures is significant, and calculation of this rate, within dual-continuum models, depends on matrix-fracture transfer functions incorporating the shape factor. Typically, matrix-to-fracture transfer functions are obtained by assuming all fractures to be instantaneously immersed in water (instantly-filled), with a uniform fracture pressure distribution under pseudo-steady state conditions. The result is constant, timeindependent, shape factors. Clearly, this is not necessarily true. Partially immersed fractures and other unsteady-state conditions do not lead to constant shape factors. The current formulations for modeling flow in fractured porous media need to be reconsidered.

A new time-dependent matrix-fracture transfer shape factor formulation and transfer functions for both filling- and instantly-filled fracture transfer are derived based on dimensional analysis of experimental data. The general shape factor is expressed as the area of the matrix block contacted by the wetting phase divided by the product of the bulk volume of the rock matrix times the distance between the saturation at the fracture and the matrix average saturation. These parameters are readily obtained. The dimensional analysis of full-physics data avoids simplifications that may lead to expressions that do not represent accurately matrix-fracture transfer. The new shape factor carries information of the transient behavior of the water saturation, Sw, and so it leads to more accurate description of the matrix-fracture transfer. Good agreement was found between experimental data, an analytical model, and a proposed modified dual-porosity formulation with the new time-dependent shape factor and transfer function.
Integration of Seismic Anisotropy and Reservoir Performance Data for Characterization of Naturally Fractured Reservoirs Using Discrete Feature Network Models
Authors: Will Robert , Archer Rosalind , Dershowitz Bill
Published: December 2007

This paper proposes a method for quantitative integration of seismic (elastic) anisotropy attributes with reservoir performance data as an aid in characterization of systems of natural fractures in hydrocarbon reservoirs. This method is demonstrated through application to history matching of reservoir performance using synthetic test cases.

Discrete Feature Network (DFN) modeling (Dershowitz et al.1) is a powerful tool for developing field-wide stochastic realizations of fracture networks in petroleum reservoirs. Such models are typically well conditioned in the vicinity of the wellbore through incorporation of core data, borehole imagery, and pressure transient data. Model uncertainty generally increases with distance from the borehole. Threedimensional seismic data provides uncalibrated information throughout the inter-well space. Some elementary seismic attributes such as horizon curvature and impedance anomalies have been used to guide estimates of fracture trend and intensity (P32) (Dershowitz and Herda2) in DFN modeling through geostatistical calibration with borehole and other data. However, these attributes often provide only weak statistical correlation with fracture system characteristics.

The presence of a system of natural fractures in a reservoir induces elastic anisotropy that can be observed in seismic data. Elastic attributes such as azimuthally dependent normal moveout velocity (ANMO), reflection amplitude versus azimuth (AVAZ), and shear wave bi-refringence can be inverted from 3D seismic data. Anisotropic elastic theory provides physical relationships among these attributes and fracture system properties such as trend and intensity. Effective elastic media models allow forward modeling of elastic properties for fractured media.

A technique has been developed in which both reservoir performance data and seismic anisotropic attributes are used in an objective function for gradient-based optimization of selected fracture system parameters. The proposed integration method involves parallel workflows for effective elastic and effective permeability media modeling from an initial DFN estimate of the fracture system. The objective function is minimized through systematic updates of selected fracture population parameters. Synthetic data cases show that 3D seismic attributes contribute significantly to reduction of ambiguity in estimates of fracture system characteristics in the inter-well rock mass. The method will benefit enhanced oil recovery (EOR) program planning and management, optimization of horizontal well trajectory and completion design, and borehole stability studies.
Case Study: Merging Modern Reservoir Characterization with Traditional Reservoir Engineering
Authors: Rothkopf Brian , Fredrickson Steve , Hermann Jeff
Published: December 2007

Modern reservoir characterization-simulation studies integrate geology, seismic, petrophysics and engineering to build three-dimensional (3D) static geologic and dynamic fluid flow models. These models have repeatedly proven their worth through reduced risk and improved reservoir management decisions. Prior to the advent of modern computers and software, traditional reservoir engineering techniques served the industry well through analytic and graphical analysis techniques. It would seem that the modern characterization tools would make these traditional reservoir engineering techniques obsolete; however, this paper shows that integrating these traditional techniques can improve the quality of modern 3D models.

This paper describes a field example where traditional reservoir engineering techniques from 40 years of waterflooding history were integrated into the modern reservoir characterization-simulation workflow.
Underbalanced Perforating of Long Reach Horizontal Wells Using Coiled Tubing: Three North Sea Case Histories
Authors: Bayfield Ian , Murphy Stuart , Taylor Don
Published: December 2007

It is acknowledged that in many reservoirs, perforating in under-balanced conditions can bring significant and obvious production benefits. Under-balanced perforating in vertical or "near" vertical wells may be performed with wire-line, whilst perforating in highly deviated or horizontal wells through the completion tubing normally requires intervention with either a wire-line tractor, hydraulic work-over unit unit, or Coiled Tubing. Consideration of all parameters surrounding the choice of what method should be used to transport the guns into long reach horizontal wells will quite often direct the operator to choose Coiled Tubing as the optimum conveyance tool.

Achieving true under-balanced perforation of a long reservoir section(s) utilising coiled tubing in an offshore environment presents a collection of technical, logistical and financial challenges.

Three North Sea case histories of such operations are illustrated. These examples demonstrate how gun lengths of over 2,800 ft and 24,500 lb in weight can be deployed to a measured depth of 17,800 ft through a challenging well profile. Particular attention is paid to equipment challenges and selection, the use of friction reducers and techniques employed to maximise the operating window, hence achieving the operator's desired results and realise the benefits associated with under-balanced perforating.
Simulating Carbon Dioxide Sequestration/ECBM Production in Coal Seams: Effects of Permeability Anisotropies and Other Coal Properties
Authors: Smith Duane H. , Sams W. Neal , Bromhal Grant , Jikich Sinisha , Ertekin Turgay
Published: December 2007

Coalbed methane now accounts for a significant fraction of domestic natural gas production. Injection of carbon dioxide into coal seams is a promising technology for reducing anthropogenic greenhouse gas emissions and increasing ultimate production of coalbed methane. Reservoir simulations are an inexpensive method for designing field projects and predicting optimal tradeoffs between maximum sequestration and maximum methane production. Optimum project design and operation are expected to depend on the anisotropy of the permeability along the face-cleat and butt-cleat directions, the spacing between cleats, and the sorption isotherms for methane and carbon dioxide.

In this work PSU-COALCOMP, a dual-porosity coalbed methane simulator, is used to model primary and secondary production of methane from coal, for a variety of coal properties and operational parameters. It is assumed that the face and butt cleats are perpendicular to each other, with horizontal wells parallel to one type of cleat and perpendicular to the other. The well pattern consists of four horizontal production wells that form a rectangle, with four shorter horizontal wells centered within the rectangle. In the limiting case of no permeability anisotropy, the central wells form a "plus" sign within the square of production wells. All wells are operated as producers of methane and water until a specified reservoir pressure is reached, after which the central wells are operated as injectors for CO2. Production of methane continues until the CO2 concentration in the produced gas is too high.

The simulation results predict the optimum lengths of the injection wells along the face- and butt-cleat directions, and how these optimum lengths depend on the permeabilities in the two directions. If the cleat spacing is sufficiently small and diffusion of the gas through the pores to the cleats is sufficiently rapid, instantaneous sorption may be assumed. Otherwise, the field performance depends on the characteristic time for transport to the cleats. The pressures at which the injection wells are operated also affect the amounts of CO2 sequestered, through the pressure and volume constants of the sorption isotherms.
Coalbed Methane Reservoir Simulation: An Evolving Science
Authors: Hower T. L.
Published: December 2007

It wasn't always this complicated! In 1990, Seidle and Arri1 demonstrated how to easily adapt a conventional black oil simulation model for use in coalbed methane simulation. These days, when setting up a coalbed methane simulation model, one needs to worry about a single or multi-component gas description; depletion or enhanced coal bed methane recovery; single, dual or triple porosity; vertical, horizontal, or multi-lateral wells; coals only or a mix of coals and sands; and coalbed methane or coal mine methane? Correctly determining what to model is almost as daunting a task as the simulation work itself. All of these variations add complexity to the task and, in some cases, require specialized simulation models to adequately characterize the problem.

This paper discusses how the exploitation and development of coalbed resources throughout the world is changing, and with it how our approach to reservoir simulation of the process is changing as well. The paper will provide a valuable resource to engineers and geoscientists faced with developing predictive tools to assist them in evaluating the optimum strategy to exploit these valuable resources.
Africa Is Poised to Become the Next Energy Superpower
Authors: Oyewole Peter O. , Economides Micheal J.
Published: December 2007

In early 2002 Washington DC policy-makers suggested, that within a generation, Africa might supplant the Middle East as the United States most critically strategic energy supplier. This is a significant departure from the situation, which permeated the previous three decades when the Middle East was perceived as the singularly most important source of world energy. Such potential of Africa, if realized, would have a decided influence on future energy economics and geopolitics.

Grandiose statements notwithstanding, is Africa (and in this context this implies the Sub-Saharan regions) at the brink of becoming an energy superpower? Does Africa have the potential reserves, production capability and capacity for such a role? This is not just an issue of geology but also one that touches on the rest of the development of the continent, its economic and political future.

This paper presents an in-depth investigation of the true energy potential of Africa. One obvious focus is the potential of deep- and ultra-deep-water production, spanning almost the entire Western Coast of Africa. Areas of interest involve the deep waters off the Gulf of Guinea and the continental shelves and include the inland basins of Benin, Nigeria, Cameroon, Sao Tome and Principe, Equatorial Guinea, Gabon, Congo and Angola.

We are proposing here a number of mechanisms of potential production and couplets of exploitation, i.e., optimum and likely ways to link producers with consumers, taking into account distances and hydrocarbon volumes and incorporating regional integration and co-operation.

Finally, we are offering conclusions and recommendations that will enhance sustainable energy development in Africa, and continuous availability of uninterrupted global supply of oil and gas, which indeed will usher the era of Africa as an energy superpower.
Building a Dynamic Interactive Information Website with Limited Artificial Intelligence: A Case History
Authors: Shaw Andrew , McCracken Daryl
Published: December 2007

The systematic design process used and design logic behind building an interactive information management site is described. The site was planned for use by internal employees, as an information resource, and as an external technical and information resource for approved users. A third consideration was an efficient web-enabled business to business quotation mechanism for wireline services.

The initial design objectives centered on the need for a web based information management tool with an easy to use navigation and a strong visual component that facilitated information based productivity utilizing a web enabled database.

A number of design considerations will be discussed:

type and range of data components, and challenges of handling multimedia assets in the database (html, images, text, PDF) information content customizable to individual user capability

The complexity of the data types, the desire to provide easy navigation, and a way to match services and equipment to match reservoir problems and needs involved building limited artificial intelligence into the user interface. The logic and criteria considered during this phase of development is presented.

Several business considerations influenced the design and each will be presented.

A database interface that did not require high technical competence in a database language to input and manage data. reducing dependence on printed material providing customized reports and technical catalogues site and database maintenance criteria measurement of the success of the site in terms of return on investment and strategic value

The information site was field tested and launched during 2002. Conclusions relating to the design of the site and the methodology used will be presented in the context of current user and growth history statistics.