bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Way to Diagnose Injectivity Decline During Fractured Water Injection By Modifying Conventional Hall Analysis
Authors: Ojukwu K. I. , van den Hoek P. J.
Published: December 2007

For many years, unfiltered produced water has been used in the flooding of heavy oil reservoir in Southern Oman for pressure maintenance. Initially it was thought that the water injection was under matrix conditions. However, it is well accepted in the industry that water injection and particularly produced water injection almost, always takes place under fracturing condition. Significant decline in injectivity was repeatedly seen due to downhole blockages. Routine clean-ups and acidizations were carried out without success. Early 2003, a dedicated study was conducted to identify the root cause of this problem and recommend a remedial action. The purpose was to determine if the decline is due to poor water quality, reservoir compartmentalization, matrix/fracture or wellbore plugging.

An unconventional approach was used to conduct a comprehensive study using historical data by modifying the Hall-Analysis technique. It was concluded that poor water quality was the problem. The interpretation of the Modified Hall Plot together with Bottomhole Pressure (BHP) vs. Rate plot also provided evidence of wellbore and/or fracture plugging. Both qualitative and quantitative analyses characterized the initial matrix injection period and fracturing injection regime that followed. Fracture plugging, routine well stimulations and fracture propagation trends were interpreted from the plots. A 3D in-house simulation package for waterflood under fracturing conditions was used, independently, to simulate injection conditions and confirm the results. Simulated injection pressure was much lower than actual field data confirming severe plugging. Further analysis showed that the plugging was due to unconventional particulates different from solids and oil contaminants in water. Recommendation was made to identify the contaminant and maintain a maximum suspended solid concentration of 100ppm to contain fracture propagation. A recent filter trial confirmed the presence of FeS contaminant.

Successful remedial action was taken followed by recommissioning and water treatment facility design to realize estimated 150m3/d/well and improving ultimate recovery. Recently, another field study has successfully completed adopting same technique. By modifying Hall Analysis technique, it is possible to use field data for diagnosing matrix/fracturing regimes, assessing degree of damage and determining the location of the damage.
Cyclic Water Injection Simulations for Evaluations of its Potential in Lagocinco Field
Authors: Stirpe M. T. , Guzman J. , Manrique E. , Alvarado V.
Published: December 2007

Cyclic Water Injection (CWI) has been proposed as a technique to improve water sweep in stratified and fractured reservoirs. This recovery process takes advantage of the pressure transient response in regions of different permeability, leading to forced imbibition of the lesser permeable layers, in the case of stratified reservoirs. A process such as this is expected to yield an additional recovery between 2 and 7% over continuous waterflooding and a significant reduction in watercut, reason why it has been proposed as a zero cost EOR process, wherever facilities for water injection are already available. Several mechanisms have been attributed the additional oil production, among which are listed pressure differences between layers with limited communication and hysterisis of the capillary pressure and relative permeability curves. Here we have taken a full-field model of an extensively investigated reservoir of Western Venezuela, the VLE-305, located in the Lagocinco field to analyze some of the critical variables of the process and determine the potential for cyclic water flooding. The reservoir has been proposed as a candidate for immiscible WAG injection and a successful pilot test has been carried out. This deep, stratified sandstone reservoir meets the characteristics sought in cyclic water injection projects. In recent work, it was shown that some potential exists for water cyclic injection in the WAG pilot area. Production history of the field has been used to help with the analysis of critical variables of this process, including injector-to-producer well distance and reservoir pressure relative to the bubble point pressure, among others. Additionally, a recently developed analytical model of the process was also tested to determine its potential as a fast evaluation tool for CWI. Results show that permeability trends, reservoir pressure, well distance and water saturation at the startup of the process have high impact on the potential additional recovery, leading to recommendations for the application schedule of the process.
Improve Injection Profile by Combining Plugging Agent Treatment and Acid Stimulation
Authors: Zhao Puchun , Zhao Huating , Bai Baojun , Yang Xinming
Published: December 2007

Plugging agent treatment and acid stimulation has completely different mechanisms for improving injection profiles. In this paper, a hybrid procedure is introduced to reduce the damage of plugging agent to low and medium permeability zones and the penetration radius of acid into high permeability zones. The procedure is: first inject plugging agent to block high permeability zones, and then inject acid to remove plugging agent damage from the low and medium permeability zones and stimulate them. For performing this procedure successfully, three kinds of plugging agents were screened out for using in different reservoirs:

Strong strength plugging agent for the wells with fractures or high permeability streaks;

Weak gel for those with thick layer in which serious heterogeneity exists;

Temporary plugging agent for those in which the absorption ability of high permeability zones needs maintaining.

Several acid systems were evaluated to be compatible with the three kinds of plugging agents.

The objectives of this paper are: (1) To show the screen results about the compatible plugging agent and acid; (2) To show how to optimize the operation process; (3) To tell some experiences learnt from the oilfield applications of this technique.

From Jan. 2001 to Dec. 2002, 46 operations using this procedure were carried out in Weicheng and Mazhai Oilfields of SINOPEC. Results show that the average benefit/cost ratio is over 3.5. Experience learnt from these applications was summarized in the paper.
Foam Displacements With Multiple Steady States
Authors: Rossen W. R. , Bruining J.
Published: December 2007

A number of experimental and theoretical studies suggest that the fractional-flow function for foam can be either multivalued in water saturation or else comprise distinct fractional-flow curves for two or more foam regimes, with jumps between them where each regime reaches its limiting condition. We construct fractional-flow solutions for these cases. When such a foam is employed in a surfactant-alternating-gas (SAG) process, the usual "tangency" condition is modified and the foam can be considerably weaker than the foam formed at what appears to be the point of tangency of the multi-valued fractional-flow function. If the capillary-pressure function differs between foam regimes, that difference can substantially change the nature of the displacement. This alters the effective fractional-flow function and hence the global solution of the equations. It is therefore important to determine how capillary pressure varies in foam displacements, by direct measurement in situ if possible. Special care is needed in numerical simulation of processes using fixed grids if capillary pressure depends directly on foam regime. Using grid blocks that are too large can weaken the effect of capillary pressure enforcing the correct shock on the small scale. Using an upscaled fractional-flow function appears to eliminate this problem, however.
A Simple Approximate Method to Predict Inflow Performance of Selectively Perforated Vertical Wells
Authors: Guerra E. , Yildiz T.
Published: December 2007

This paper presents an approximate model to forecast the productivity of selective perforated wells. The model includes algebraic equations and it could be easily computed using a programmable calculator or spreadsheet program. The model has been compared against the rigorous 3D semi-analytical model and software existing in the literature. The approximate model compares well against the 3D model and the software. The model is useful for designing perforation parameters.
Application of DLVO Theory to Characterize Spreading in Crude oil-Brine-Rock Systems
Authors: Busireddy Chandrasekhar , Rao Dandina N.
Published: December 2007

The presence of thin aqueous films and their stability has a profound effect on reservoir rock-fluids interactions involving spreading and adhesion. The stability of thin wetting aqueous films on rock surfaces is governed by several variables including pH, brine and crude oil compositions, and capillary pressure. These variables govern the wetting states in the solidliquid-liquid systems. The wetting states influence the residual oil saturation and the oil-water relative permeabilities and consequently the oil recovery.

The objective of this study is to deduce a functional dependence of thin film stability on the above parameters by considering intermolecular and surface interactions in crude oil-brine-rock systems. The surface forces are manifested as disjoining pressure in thin films. The disjoining pressure isotherms for the selected solid-liquid-liquid system have been computed in terms of the bulk properties of the media. The equilibrium contact angles have also been computed from the integration of the Young-Laplace equation, which relates contact angle to the capillary pressure and disjoining pressure isotherms of the system. The contact angle data obtained from sessile drop experiments have been compared with the calculated results as well as with other published results. Adhesion maps, which relate the film stability to brine pH and molarity, have been developed.

The rock-fluids system considered for study consisted of smooth Glass, Quartz and Yates reservoir fluids. The DLVO theory has been used to model the intermolecular forces. The structural forces are incorporated to overcome the limitations of the DLVO theory. A charge regulation model was used to analyze the crude oil-brine and Glass-brine interfaces. The effects of multivalent ions have been incorporated by an equivalent molarity concept. The overall computational model being developed in this study is aimed at providing a-priori prediction capability of rock-fluids interactions in petroleum reservoirs for inclusion in reservoir simulators.
Adomian Solution of Forchheimer Model to Describe Porous Media Flow
Authors: Belhaj Hadi , Biazar Jafar , Butt Stephen , Islam Rafiq
Published: December 2007

Currently, fluid flow in porous media is mostly calculated by utilizing the well known diffusivity equation based on Darcy’s law. This diffusivity equation is the core fluid flow equation in all modern reservoir simulators used to predict flow behaviors. Inaccurate predictions of reservoir simulators have been reported nevertheless, history matching has been achieved. This dilemma led to questioning the adequacy of the basic governing equation of fluid flow behavior in porous media.

This paper suggesting a new governing equation that includes Darcy’s viscous term, Forchheimer’s inertial term and Brinkman’s viscous term all in one model called the Modified Brinkman Model "MBM". MBM proven to accurately describe fluid flow in porous media in both Darcian and non-Darcian domains and can be used in both oil and gas reservoirs for both matrix and fracture systems. A genuine mathematical solution "Adomian decomposition technique" has been successfully employed to solve the partial differential model with great deal of accuracy and ease. The proposed MBM is expected to have wide applications in oil, gas and underground water reservoirs.
Laboratory Investigation of Stress-Sensitivity of Non-Darcy Gas Flow Parameters
Authors: Zeng Zhengwen , Grigg Reid B. , Gupta D. B.
Published: December 2007

Non-Darcy flow parameters were investigated in 159 series of high pressure/high temperature/high velocity gas flooding experiments on five different rock samples under field reservoir conditions. The results of these experiments reconfirm and extend to new conditions that permeability increase, while non-Darcy flow coefficient decreases with effective stresses; both are independent of shear stresses. General formulas have been developed to quantify the stress-sensitivity in terms of nominal non-Darcy parameters. General equations have been proposed to predict the change of permeability and non-Darcy flow coefficient with given effective stresses and nominal non-Darcy flow parameters.
Modelling Asphaltene Precipitation and Deposition in a Compositional Reservoir Simulator
Authors: Kohse Bruce F. , Nghiem Long X.
Published: December 2007

This paper describes asphaltene precipitation and deposition models implemented in a compositional reservoir simulator. The asphaltene precipitate is modelled as two solids: Solid 1 is thermodynamically reversible and is in equilibrium with the asphaltene component in the oil phase. Solid 2 is created from Solid 1 via a chemical reaction. Solid 2 can be used to represent the flocculation of smaller precipitated asphaltene particles into larger aggregates. This aggregation can be made fully reversible, fully irreversible or partially irreversible. Solid 1 flows as suspended particles in the oil phase, while Solid 2 may flow with the oil or deposit in the rock matrix.

The deposition model incorporates surface deposition, pore-throat plugging and re-entrainment of deposited solid into the flowing liquid phase. Porosity and permeability impairment due to asphaltene deposition are also modelled. Model results are compared to laboratory core floods illustrating core damage due to asphaltene deposition. The model is also applied to studies of primary depletion, and core flood simulations of miscible gas injection for light oils.
Multiphase Equilibrium Calculation Using Reduced Variables
Authors: Nichita Dan Vladimir , Broseta Daniel , de Hemptinne Jean-Charles
Published: December 2007

A new method for multiphase equilibrium calculations with cubic equations of state (EOS) has been developed. The minimum of the Gibbs free energy and of the tangent plane distance function should be found in a space with a significantly reduced number of dimensions. The number of independent variables for phase equilibrium calculations does not depend on the number of components in the mixture and non-zero binary interaction coefficients (BIC) are taken into account by our approach.

Phase splitting calculations consists in successive substitution (SSI), followed by Minimum Variable Newton-Raphson (MVNR) iterations. The tangent plane distance criterion is used for testing the thermodynamic stability. The nonlinear system of equations for phase stability is solved by a globally-convergent Newton method.

The calculation of multiphase equilibrium is organized in a stepwise manner, combining phase stability analysis by minimization of the tangent plane distance (TPD) function with phase splitting calculations. The phase distribution for three-phase calculation is found by the constrained minimization of a convex smooth function.

The robustness of the proposed method is tested for several systems of interest in reservoir and production engineering. The reduction in computer time as compared to conventional methods is all the more important as the number of the components is greater. The most important savings in computer time are expected for mixtures with many components and relatively few BIC’s.

The proposed method using reduced variables represents a new, efficient, and reliable tool for the many practical situations when multiphase equilibria calculations are needed. To the best of our knowledge, it is the first implementation of the reduced variables to multiphase equilibrium calculation.
Three-phase Compositional Streamline Simulation and Its Application to WAG
Authors: Yan Wei , Michelsen Michael L. , Stenby Erling H. , Berenblyum Roman A. , Shapiro Alexander A.
Published: December 2007

This paper presents the development of a three-dimensional (3D), three-phase compositional reservoir simulator based on the streamline method and its application to the simulation of water-alternating-gas (WAG) processes. The three-phase compositional streamline simulator has been developed by integrating a one-dimensional (1D) three-phase compositional solver into the 3DSL streamline simulator.

2D and 3D simulations of WAG processes have been performed using the developed simulator. Comparison with the commercial finite difference simulator Eclipse 300 (E300) has also been made. The results from the two simulators are generally in good agreement while the streamline simulator is much faster than E300 and the speed-up factor increases with the simulation size.

This study further extends the application area of the streamline method and shows that the streamline technique can be used successfully for displacement processes with complex physics like that encountered in a WAG process.
Analytical Model for 1-D Gas Flooding: Splitting between Hydrodynamics and Thermodynamics
Authors: P. Pires, A. , G. Bedrikovetsky, P. , A. Shapiro, A.
Published: December 2007

The compositional model for two-phase multicomponent flow is discussed with applications to gas based IOR processes. Analytical models for 1-D displacement of oil by gas have been developed during last 15 years. It was observed from semi-analytical and numerical experiments that several thermodynamic features of the process (compositional path on phase diagram, MMP, etc.) are independent of transport properties. In this paper two flow potentials are introduced; being used as new independent variables they split the compositional (n-1)*(n-1) model for n-component flow into a thermodynamics auxiliary (n-2)*(n-2) system and one transport equation. Explicit projection and lifting procedures are derived. The new technique developed permits splitting for both self-similar continuous injection problems and non-self-similar slug injection problems. The "concentration" part of compositional model solution, including MMP, is independent of transport properties.
Modeling Fluid Flow Through Single Fractures Using Experimental, Stochastic and Simulation Approaches
Authors: Dicman Alfred , Putra Erwinsyah , Schechter David Stuart
Published: December 2007

A fracture is usually assumed as a set of smooth parallel plates separated by a constant width. However, the flow characteristics of an actual fracture surface would be quite different, affected by tortuosity and the impact of surface roughness. Though several researchers have discussed the effect of friction on flow, their efforts lack corroboration from experimental data and have not converged to form a unified methodology for studying flow on a rough fracture surface.

In this study, we have shown an integrated methodology, involving experiments, stochastics and numerical simulations that incorporate the fracture roughness and the friction factor, to describe flow on a rough fracture surface. Laboratory experiments were performed to support the study and the flow contributions from the matrix and the fracture were matched through modified cubic law. Observations suggest that the fracture apertures need to be distributed to accurately model the experimental results.

The methodology successfully modeled fractured core experiments, which were earlier not possible through parallel plate approach. A gravity drainage experiment using an X-ray CT scan of a fractured core has also validated the methodology.
Streamline Simulation of Water Injection in Naturally Fractured Reservoirs
Authors: Al-Huthali Ahmed H. , Datta-Gupta Akhil
Published: December 2007

Until recently1,2 streamline simulators were limited to single-porosity systems and not suitable for modeling fluid flow and transport in naturally fractured reservoirs. Describing fluid transport in naturally fractured reservoirs entails additional challenge because of the complicated physics arising from matrix-fracture interactions. In this paper the streamline-based simulation is generalized to describe fluid transport in naturally fractured reservoirs through a dual-media approach. The fractures and matrix are treated as separate continua that are connected through a transfer function, as in conventional finite difference simulators for modeling fractured systems. The transfer functions that describe fluid exchange between the fracture and matrix system can be implemented easily within the framework of the current single-porosity streamline models. In particular, the streamline time of flight concept is utilized to develop a general dual porosity dual permeability system of equations for water injection in naturally fractured reservoirs. We solve the saturations equations using an operator splitting approach that involves ‘convection’ along streamline followed ‘matrix-fracture’ exchange calculations on the grid. Our formulation reduces to the commonly used dual porosity model when the flow in the matrix is considered negligible.2

We have accounted for the matrix-fracture interactions using two different transfer functions: the conventional transfer function (CTF) and an empirical transfer function (ETF). The ETF allows for analytical solution of the saturation equation for dual porosity systems and is used to validate the numerical implementation. We also compare our results with a commercial finite-difference simulator for waterflooding in five spot and nine-spot patterns. For both dual porosity and dual permeability formulation, the streamline approach shows close agreement in terms of recovery histories and saturation profiles with a marked reduction in numerical dispersion and grid orientation effects. An examination of the scaling behavior of the computation time indicates that the streamline approach is likely to result in significant savings for large-scale field applications.
Integrating Dynamic Data in Reservoir Models Using a Parallel Computational Approach
Authors: Srinivasan Sanjay , Bryant Steven
Published: December 2007

Conditioning reservoir models to dynamic data is challenging due to the non-linear relationship between the measured flow response data and the model parameters (porosity, permeability etc.). The focus of this paper is to present a methodology for efficiently integrating dynamic production data into reservoir models. In contrast to other methods for production data integration, the proposed methodology attempts to quantify the information in production data pertaining to reservoir heterogeneity in a probabilistic manner. The conditional probability representing the uncertainty in permeability at a location is iteratively updated to account for the additional information contained in the dynamic response data. A localized perturbation procedure is also presented to account for multiple flow regions within the reservoir. The proposed methodology is demonstrated on a realistic case example. The methodology for implementing the proposed algorithm on parallel cpu’s is presented. The computational synergies realized through domain decomposition flow simulation are likely to result in significant cpu savings.
Numerical Simulation of Water Injection in Disconnected and Connected Fractured Media Using Jacobian-free Fully Implicit Control Volume Method
Authors: Monteagudo J. E. P. , Firoozabadi A.
Published: December 2007

In this work we present an algorithm for water injection in 2D and 3D connected and discrete fractured media using a fully implicit approach for the control-volume method. The crossflow equilibrium concept (that is, the discrete fracture approach) is used to reduce the fracture dimension by one. A congruent mathematical formulation is provided for the discrete fracture approach, establishing a relationship between the matrix and fracture main variables following the physics of two-phase flow at the matrix-fracture interface. The system of partial differential equations is discretized within the discrete-fracture framework using the control-volume method in a fully-implicit formulation. The resulting system of non-linear equations is solved with a Jacobian-free Newton-Krylov solver. In this solver, there is no need to assemble the Jacobian matrix of the non-linear system of equations, which reduces memory and computational effort requirement. We present numerical results for several examples with various degrees of non-linearity in capillary pressure and relative permeability using both 2D and 3D discrete-and connected-fractured media. The Jacobian-free Newton-Krylov method demonstrates to be very efficient for all the numerical examples. The performance of the fully-implicit model is compared with the IMPES formulation to determine the range of applicability of the proposed method.
Evaluation of Matrix-Fracture Imbibition Transfer Functions for Different Types of Oil, Rock and Aqueous Phase
Authors: Babadagli T. , Zeidani K.
Published: December 2007

Several different versions of the transfer functions evolved from classical Mattax and Kyte’s dimensionless group and Aranofsky et al.’s abstract relationship were tested. Another transfer function derived analytically based on power law relationship between recoverable oil and time was also included in the testing process. The exponents in all these transfer functions reflect the strength and type of the transfer. The recovery curves obtained from the spontaneous imbibition of different aqueous phases (brine and surfactant) into cylindrical rock samples saturated with different types of oil were used to fit the transfer functions. The exponents yielding the best fit to experimental data were obtained and correlated to the effective parameters such as the viscosity of oil, matrix permeability, IFT, matrix size, and wettability using multivariable regression analysis.

The correlations developed were analyzed for the rock and oil types, and IFT. It was observed that the exponential relationships were more suitable for synthetic and processed oil samples whereas the power law transfer functions were more applicable for crude oil cases.

It is hoped that the analysis provided in this paper would facilitate the selection of proper transfer function type for performance estimation of naturally fractured reservoirs.
Recent Successes: MEOR Using Synergistic H2S Prevention and Increased Oil Recovery Systems
Authors: Hitzman Donald O. , Dennis Michael , Hitzman Daniel C.
Published: December 2007

Contemporary investigations of Microbial Enhanced Oil Recovery (MEOR) technologies began in earnest in the 1980’s. Since then, numerous programs have examined the reliability of the concepts, processes, and technical efficacy of recovery biosystems. Despite reported successes, MEOR technologies have not been widely accepted by the oil and gas industry as a means to recover residual oil. The Bio-Competitive Exclusion (BCX) biological process has successfully demonstrated significant oil recovery results in mature waterfloods from the deliberate alteration of indigenous reservoir microflora to an anaerobic denitrifying bacteria (DNB) population through the use of nitrate-based formulae as alternate electron acceptors and microbial nutrient. These environmentally safe inorganic salts complement the naturally occurring volatile fatty acids (VFA) in the reservoir and produced waters, selectively stimulating and increasing the targeted DNB. This designed and controlled manipulation of an indigenous DNB population initiates and increases the production of multiple gas, solvent, and surfactant bio-products which have known and demonstrable oil recovery properties. The BCX technology offers a feasible, practical, and very cost effective, tertiary oil recovery system that concurrently controls reservoir and surface system souring. Field data from California, Oklahoma, China, and Canada are presented.
Dewatering in Hunton Reservoir—Drill Vertical or Horizontal Well?
Authors: Zubarev D. , Patwardhan S. , Kelkar M. , Keefer B.
Published: December 2007

The paper describes an economic analysis carried out for the wells drilled in Hunton Formation in Carney Field in Lincoln County, Oklahoma. The Carney Field produces oil and gas from the Hunton Formation. The field was developed starting in 1995. The Hunton formation covers 2.7 million acres in Oklahoma and in surrounding states of Texas, New Mexico and Arkansas and is one of the most prolific oil producing reservoirs in Oklahoma. Marjo operating Co. is one of the many operators involved in producing from this reservoir. The early development of the Carney field was mostly accomplished through vertical wells. However, in the last two years, the new wells drilled are mostly horizontal wells. It is believed that horizontal wells have better probability of success and better productivity. Horizontal wells also have added advantage of bigger spacing as compared to vertical wells. In this paper, we investigate the efficacy of horizontal wells as against the vertical wells. Our evaluation is based on wells operated by Marjo Operating Company as well as some other operators.

We observe that vertical wells are as economically efficient, or perhaps better, than horizontal wells. We did not find any correlation between horizontal well length and the productivity of the well. Further, for reservoir regions, where the initial oil saturation is higher, vertical wells performed significantly better than horizontal wells.
Chemical Treatments to Enhance Productivity of Horizontal and Multilateral Wells: Lab Studies and Case Histories
Authors: Al-Otaibi M. B. , Nasr-El-Din H. A. , Siddiqui M. A.
Published: December 2007

Many soft sandstone formations are completed with horizontal wellbore. The drilling fluid, water based mud, filter cake is left in place until the completion operations are finished. At that time, a cleanup fluid is pumped to remove the filter cake deposition from the wellbore face. These cleanup fluids can be acid, specific enzymes, oxidizers or acidic water. Reservoir heterogeneity complicates the cleaning process. There is a need for a slow, efficient method to remove filter cake, without affecting the integrity of the formation.

In this paper, a comparison of various cleaning methods was conducted in the lab (using ceramic disks, core plugs) and in the field. Chemical analysis for core effluent and well flowback samples after various treatments was conducted. These tests included: Anthrone method for carbohydrates, and full analysis of the produced solids using acid solubility, XRD, and SEM.
Revitalization of Pilar Field (Sergipe-Alagoas Basin, Brazil) using deviated wells along fault planes – a successful experience.
Authors: Borba C. , Takeguma M. S. , Filho E. J. Souza , Schneider K. N.
Published: December 2007

Pilar oil and gas field, located onshore northeastern region of Brazil, had the production peak by 1985, when produced 1300 m3/d of oil, decreasing since then until reaching 350 m3/d in 1997. Forecasts at that time indicated a very low oil production of about 200 m3/d by year in 2002.

A study was launched in 1997, strongly focused on the characterization of sealing fault planes that control the oil and gas accumulations, which resulted in the projects of deviated wells, following the fault planes. This approach has made possible to drill one single well crossing multiple sets of reservoirs, increasing the possibility of finding virgin reservoirs along trends of producing reservoirs.

As a result, the oil rate has been rising since 1998, reverting the declining tendency of the period between 1985 and 1997. In 2003 the oil rate reached 1100 m3/d. In the period of revitalization, the OOIP has increased 50%.
Modeling CO2 Storage in Aquifers with a Fully-Coupled Geochemical EOS Compositional Simulator
Authors: Nghiem Long , Sammon Peter , Grabenstetter Jim , Ohkuma Hiroshi
Published: December 2007

This paper describes a fully coupled geochemical compositional Equation-of-State (EOS) compositional simulator for the simulation of CO2 storage in saline aquifers. The simulator (GEM-GHG) models the following phenomena: (1) convective and dispersive flow in porous media; (2) phase equilibrium between the oil, gas and aqueous phase; (3) chemical equilibrium for reactions between the aqueous components and (4) mineral dissolution and precipitation kinetics. For numerical robustness and stability, all equations are solved simultaneously. The simulator is applied to the simulation of typical field-scale CO2 sequestration processes, showing the migration of CO2(g) and CO2(aq), the dissociation of CO2(aq) into HCO− and its subsequent conversion into carbonate minerals. Convection of high-density plumes of CO2-rich brine in conjunction with CO2 mineralization around the plumes is illustrated.
Effect of CO2 Impurities on Gas-Injection EOR Processes
Authors: Zhang P. Y. , Huang S. , Sayegh S. , Zhou X. L.
Published: December 2007

Carbon dioxide flooding is a promising enhanced oil recovery method both on technical and, if operating costs are properly controlled, economic grounds. Injecting this greenhouse gas also has environmental merits. Flue gas from power plants is a ready source of CO2; however extracting CO2 for enhanced oil recovery from such a source will increase project costs. Furthermore, to reduce both the net CO2 utilization and the cost of purchasing gas, it is usually necessary to recycle the produced CO2 with as little purification as possible. Therefore, understanding the roles of impurities in fluid phase behaviour and miscibility characteristics is necessary for designing a cost-effective CO2 enhanced oil recovery process.

Laboratory studies of the effect of CO2 impurities on phase equilibrium and minimum miscibility pressure (MMP) were conducted on two Saskatchewan light oils covering a range of densities from 29.5°API to 38°API. The results indicate that the MMP for these light oils could increase unfavourably as the N2 and/or CH4 concentration increased in the CO2 stream. The MMP changes as the type and concentration of impurities in the injected CO2 stream change. However, coreflood tests showed that the near-miscible CO2 displacement might employ the same mechanisms as miscible CO2 flooding to mobilize and displace oil; thus, good oil recovery can be achieved in the vicinity of the MMP. While laboratory measurements are essential in the evaluation of a gas injection process, an equation of state (EOS) simulation was demonstrated to be a useful tool in analyzing the phase behaviour of various injection gases, reservoir fluids, and the gas-oil interactions.
Evolution of Completion Practices in the Wild River Tight Gas Field
Authors: Colwell D. A. F. , O'Brien C. G. J. , Gates T. D.
Published: December 2007

This paper presents the evolution of completion practices and fracture stimulation that has taken place in the Wild River area of Canada over the past 2 years. Since being acquired in March of 2001, 67 wells have been drilled and completed in the field, which is characterized by multiple stacked, tight gas reservoirs. During that time, seven distinct completion phases can be identified, each targeting either a reduction in the total capital expenditure or enhancing production performance by fracture stimulation optimization. On the capital front, a progression of completion tools occurred including standard bridge plugs, proprietary permanent packer frac systems, and composite bridge plugs. Focus areas for production performance improvement included fluid systems, proppant selection, perforating strategy, energizing fluids, and third party quality control. As a result of this evolution, the average completion cost per zone has been reduced by approximately 40% and the average initial production rate has been increased by approximately 150%.
Improved Petrophysical Methods and Techniques for Shaly Sands Evaluation
Authors: Al-Ruwaili Saleh B. , Al-Waheed Hilal H.
Published: December 2007

Clean sands have null or minimal shale and clay, and can adequately be evaluated using petrophysical techniques like neutron-density cross-plot and Archie's equation. Routine core analysis can be enough for validating log-analysis results in clean sands. On the other hand, shaly sands have considerable shale and clay; consequently the above petrophysical evaluation techniques are not adequate. Porosity logs, e.g. neutron, density and sonic, and saturation logs, i.e. deep-resistivity, are affected by the shale and clay present in shaly sands. Additionally, shale and clay affect the electrical properties, the capillary pressure and the transmissibility in shaly sands. The effects of shale and clay, on logs and log-analysis, need to be modeled and incorporated in the petrophysical evaluation in order to obtain a more accurate assessment of shaly sands.

Soft and hard data was acquired in some shaly sands, in Saudi Arabia, to evaluate their storage and flow capacity. Density, neutron, sonic, resistivity and gamma-ray logs were routinely acquired in wells drilled in these formations. Logs like Elemental-Capture-Spectroscopy (ECS) and Nuclear-Magnetic-Resonance (NMR) were acquired in key wells. In some key wells, the core was cut and core analysis was conducted to obtain formation porosity, electrical properties and clay attributes, e.g. clay-type and clay-abundance. The above data was exploited in improving shaly sands petrophysical evaluation, which is discussed and demonstrated in this paper.
Definitive Method of Flow Analysis of Surface Pipeline Networks
Authors: Kappos Leonidas , Economides Michael J.
Published: December 2007

The producing wells and the surface pipeline network comprise a dynamic system. Flow rate changes in the individual wells affect the flow in the pipeline network and the fluid distribution among the gathering stations and, vice versa. Many times, the surface network is constructed responding to the necessity of merely connecting the wells to the separators or gathering stations without accounting for the impact that dramatically increased or decreased well flow rates may have. Nevertheless, in the life span of a reservoir, the hydrocarbon production may be substantially altered owing to several processes that may take place, such as fracturing, or gas/water injection. Thus, it is imperative that the surface pipeline network be effectively designed to ensure an unobstructed production regardless of the well flow rates. It is readily acknowledged that a computational tool is needed to perform a hydraulic analysis of the pipeline network for any set of flowing conditions.

An iterative algorithm is developed for the quantitative analysis of any surface pipeline network configuration. Pipe gas flow under isothermal conditions is studied. The algorithm uses the minimal information that is commonly available for a surface pipeline network, namely the well mass flow rates, the temperature and molecular weight for the well pipes, the chokes pressures, the gathering stations pressures and the geometric characteristics of the pipes, and does not require the knowledge of the location of the split nodes. It calculates the mass flow rate, temperature and molecular weight in each pipe of the network as well as the nodal pressures. It also derives the flow direction in each pipe identifying the location of the split nodes. The algorithm incorporates an approximation scheme used for large and complex network configurations. The scheme is validated through mass balance and pressure drop tests. The algorithm is a generic tool of network analysis as it can be modified to account for liquid or two-phase flow in the pipes. Application of the iterative algorithm indicates a notable accuracy (the absolute error in calculating mass flow rates and nodal pressures is less than 1%).
Exploring Reservoir Engineering Aspects of Completion in Gas-Condensate Reservoirs: West African Examples
Authors: Kabir C. S. , Chang M-M. , Taghizadeh O.
Published: December 2007

This paper explores multiple completion options in gas-condensate reservoirs with compositional simulations. Besides intelligent well completion (IWC), other options included commingling two reservoirs of contrasting conductivity (permeability-thickness product), and selectively perforating zones or reservoirs to offset the permeability contrast. At the outset, a value of information exercise suggested probing downhole sensing and completion issues in a stacked-reservoir situation. The ultimate objective of this study was to ascertain economic completion strategy so that depletion of reservoirs occurs evenly at the project's termination.

Single-well compositional simulations formed the backbone for our evaluation of three completion options. Each reservoir was characterized by history-matching drillstem tests. Experimental design reduced the large number of simulation runs to a manageable few for probabilistic forecasting. Comparison of three options suggested that all of them nearly produced the desired results of maximum liquid recovery, despite a ten-fold difference in permeability between the two horizons. As expected, direct commingling of reservoirs produced somewhat unfavorable results, which was mitigated by the other two completion options.

Results further showed that condensate banking was a nonissue in this high-kh system of reservoirs as far as the gas deliverability is concerned. In other words, although 40% to 60% degradation in the gas productivity index (PI) occurred, gas deliverability remained intact. In contrast, both the liquid PI and rate declined with time owing to the phase-behavior issue. Finally, we learned that the net income generated by the IWC is no better than the selective-perforation completion (SPC).
Field and Laboratory Analyses of Effluent Water
Authors: Qabazard Hassan , Salman Mohammad , Moshfegian Mahmood
Published: December 2007

In order to establish water qualities for re-injection purposes, four crude oil gathering centers (GC) in of Kuwait were investigated. Extensive field and laboratory measurements were made for several sampling points. Two modes of operations, namely "normal operation" and "recycled operation" were studied. During the normal operation of a GC, the effluent water represents a mixture of wet tank water and desalter water. In recycled operation, the effluent water was pumped back into the wet tank and the water disposed from the wet tank. No conclusive observation was made on the quality of effluent water but water quality was much lower at the wet tank sampling point for recycled mode. The lowest water quality was at the discharge of the desalters sampling points. The corrosion rate in general was lower at the sampling points for recycled mode as compared to corresponding points in normal operation. However, total iron and soluble iron were much higher at different sampling points of recycled mode of operation. Detail field and laboratory measurement results for each sampling points is reported. The results of this study may be used for core flooding evaluation and also for compatibility analysis of water injection.
Klinkenberg-Corrected Permeability Measurements in Tight Gas Sands: Steady-State Versus Unsteady-State Techniques
Authors: Rushing J. A. , Newsham K. E. , Lasswell P. M. , Cox J. C. , Blasingame T. A.
Published: December 2007

This paper presents results from a laboratory study comparing Klinkenberg-corrected permeability measurements in tight gas sands using both a conventional steady-state technique and two commercially-available unsteady-state permeameters. We also investigated the effects of various rate and pressure testing conditions on steady-state flow measurements. Our study shows the unsteady-state technique consistently overestimates the steady-state permeabilities, even when the steady-state measurements are corrected for gas slippage and inertial effects. The differences are most significant for permeabilities less than about 0.01 md. We validated the steady-state Klinkenberg-corrected permeabilities with liquid permeabilities measured using both brine and kerosene. Although gas slippage effects are more pronounced with helium than with nitrogen, we also confirmed the steady-state results using two different gases. Moreover, we show results are similar for both constant backpressure and constant mass flow rate test conditions. Finally, our study illustrates the importance of using a finite backpressure to reduce non-Darcy flow effects, particularly for ultra low-permeability samples.
Modeling Proppant Settling in Water-Fracs
Authors: Gadde Phani B. , Liu Yajun , Norman Jay , Bonnecaze Roger , Sharma Mukul M.
Published: December 2007

Water-fracs, consisting of proppant pumped with un-gelled fluid are the type of stimulation used in many low-permeability reservoirs throughout the United States. The use of low viscosity, Newtonian, fluids allows the creation of long narrow fractures in the reservoir without the excessive height growth often seen with cross-linked fluids. Proppant transport is a central issue in all these treatments because of the low viscosity of the fracturing fluid.

New models for proppant transport and settling in hydraulic fractures were developed and implemented in a 3-d hydraulic fracturing code. It is shown that a simple Stokes settling model is grossly inadequate. The proppant settling models developed in this paper account for the effects of fracture walls, changes in settling velocities and rheology caused by changes in proppant concentration, turbulence effects due to high fluid velocities and inertial effects associated with large relative velocities between the proppant and the fluid. Narrower fractures, higher proppant concentration and smaller proppant size reduce settling whereas turbulence leads to an increase in settling. Results are presented to show how the settling velocities are impacted by fluid velocity, proppant size, fluid rheology and fracture width. In most instances settling velocities differ significantly from the Stokes settling velocity. The new proppant settling model was incorporated into a 3-D hydraulic fracture simulator (UTFRAC-3D). Simulation results show that when settling is accounted for, significantly shorter propped lengths are obtained. The narrow fractures associated with water-fracs alter settling and thereby alter the proppant placement significantly. Although increasing fluid viscosity can reduce settling rates, increased height growth reduces the distance to which proppant can be placed. This clearly suggests a need to optimize fluid rheology. The improved fracture simulator can be used to better design fracture treatments (fluid rheology, injection rates, proppant concentration and size) for better proppant placement under a given set of in-situ stress conditions.
Multi-Sensor through-Casing Density and Saturation Measurement Concepts with a Pulsed Neutron Source: A Modeling Assessment
Authors: Badruzzaman A. , Badruzzaman T. , Zalan T. A. , Mai K.
Published: December 2007

The paper discusses an assessment, using Monte Carlo modeling techniques, of the advantages we could derive and challenges we would face in utilizing multiple sensors with a pulsed neutron (PN) source for cased-hole logging to obtain petrophysical parameters. Current PN devices are primarily based on two detectors, with source-detector spacing often similar among the various vendors. We consider four sensors to investigate three measurement types, 1) a pseudo-density through casing concept that shows the potential to distinguish between gas and tight zones, 2) computing oil saturation from Carbon/Oxygen logs with oil present in the borehole, and 3) estimation of Sigma and hence water and steam saturation from PNC logs. We illustrate the advantages of using modeling to study measurement concepts independent of specific tools. We identify areas of further research in basic measurement concepts using pulsed sources and in related radiation transport theory.