bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Hybrid Numerical-Analytical Model of Finite-Conductivity Vertical Fractures Intercepted by a Horizontal Well
Authors: Al-Kobaisi M. , Ozkan E. , Kazemi H. 
Published: December 2007

Abstract
This paper presents a hybrid, numerical-analytical model for the pressure-transient response of a finite-conductivity fracture intercepted by a horizontal well. The model dynamically couples a numerical fracture model with an analytical reservoir model. This approach allows us to include finer details of the fracture characteristics while keeping the computational work manageable. For example, the fracture may have irregular shape, nonuniform width, and variable conductivity, and the well may not intersect the fracture at its geometric center. This model can be used as a pressure-transient analysis tool to interpret complex pressure-transient characteristics or as a diagnostic tool to investigate the influence of various fracture properties on the production performance of fractured horizontal wells.
We discuss the effect of fracture characteristics on the existence of different flow regimes. We present the distribution of flow rate into the fracture and flow convergence toward the wellbore. The model helps to understand the productivity loss due to flow choking and nonDarcy flow at the intersection of the horizontal well.
Grid System Requirements in Numerical Modeling of Pressure-Transient Tests in Horizontal Wells
Authors: Al-Mohannadi N. , Ozkan E. , Kazemi H. 
Published: December 2007

Abstract
The common approach of using refined grids and small time steps usually does not provide accurate and efficient numerical models to simulate horizontal-well pressure-transient tests. In most cases, this approach requires impracticably long computational times or creates artifacts on pressure and derivative responses that may be confused with the characteristics of certain flow regimes. The results of this study indicate that the conventional well index should be used with log-distributed grid and time steps to obtain closer match to the analytical solution at early times. There is, however, a limit to grid refinement beyond which the results do not improve. This paper introduces the transient well index that allows the use of larger grids while improving the accuracy of simulations especially at early times.
A Network Model for Two-Phase Flow in Microfractured Porous Media
Authors: Wilson-Lopez R. V. , Rodriguez F. 
Published: December 2007

Abstract
A two-dimensional network model is presented in this paper to study the dynamics of two-phase flow in microfractured porous media. The model here presented is an extension of models used in studying fluid flow in intergranular porous media. The system of microfractures is composed of interconnected orthogonal parallel plates of varying apertures and lengths. Density, length and aperture of the microfractures are randomingly distributed according to distributions reported in the literature for this type of systems.
Fluid flow in each microfracture unit is described by the parallel plate flow model. The network of microfractures is initially satured with a wetting phase and injection of a nonwetting phase at constant rate and given output pressure is established. As the drainage process progresses, the fluids interface is tracked in the network: two-phase flow calculations are performed in those microfractures containing the fluids interface. Capillary pressure for individual microfractures is obtained as a function of fracture apperture, according to a published model.
Relative permeability curves for the microfracture network are calculated through flow parameters gathered from a representative subregion of the network. The effects of viscosity ratio and capillary number on the characteristics of these curves are analyzed. The impact of fracture aperture on these properties is also investigated.
The necessity for understanding and characterizing multiphase fluid flow in microfractures is driven from a field application recently documented in the literature, for which differentiation between fluid flow in the small-and large-scale secondary porosity media was required. The study here presented aims at providing some basic understanding of the behavior of multiphase flow in the small-scale secondary porosity-system and its characterization.
Three-Phase Capillary Pressure Correlation For Mixed-Wet Reservoirs
Authors: Helland J. O. , Skjæveland S. M. 
Published: December 2007

Abstract
We present new three-phase capillary pressure correlations that could be employed to model the dynamics of three-phase transition zones in mixed-wet reservoirs. The capillary pressures are expressed as a sum of two terms. One term is a function of a decreasing saturation and the other term a function of an increasing saturation. Thus the correlations depend on the type of displacement process, i.e., the direction of saturation change. The two-saturation dependency, together with the inclusion of adjustable parameters, ensures that the correlations account for different wettability conditions, saturation histories, and different relationships between the three capillary pressures.
The correlations are compatible with a smooth transition between two- and three-phase flow if one of the phases appears or disappears. In particular, if the gas saturation becomes zero, it is shown that the correlations are reduced to a previously published two-phase correlation validated for oil/water systems in mixed-wet rock.
Capillary pressure curves for various conditions, computed using a previously developed bundle-of-triangular-tubes model, are compared with the correlations, and the match is excellent in all cases. Finally, the correlations are validated experimentally by centrifuge measurements performed on water-wet cores.
Finding Natural Fractures and Improving Reservoir Performance in Western Venezuela: An Integrated Approach
Authors: Franco A. , Diaz D. , Erquiaga M. 
Published: December 2007

Abstract
An integrated approach to characterize natural fractures and optimize reservoir performance for Western Venezuela is presented. Due to poor matrix properties, a thorough reservoir characterization is of key importance. Permeabilities are commonly in the range of 0.01 mD, with natural fracture systems difficult to describe and sensitive to completion fluids and cements.
The approach to fractures includes two main topics: fracture characterization and well design. Fracture characterization comprises the description and analysis of the fracture network at several scales from microfractures up to field size, and includes core, well log images, and seismic data. The methodologies used include microfracture upscaling, core description, image log analysis, petrographic thin sections, scanning electron microscope images, azimuthal coherence seismic processing, and Gaussian curvature analysis. The integration of these analyses together with reservoir engineering data allowed the selection of candidate zones with greater density of open fractures through a semi-qualitative approach.
The well design includes consideration of optimum well trajectory to maximize fracture intersection and the estimation of incremental production based on geometric considerations such as fracture orientation, dip and spacing, presence of more than one set of open fractures, apparent stratal dip, as well as reservoir considerations such as Kh/Kv and geomechanics. These parameters were included in a series of spreadsheets which allow fast estimation of incremental production.
Several completion methods were tested in these reservoirs: cased hole with high penetration perforations, hydraulic fracture with pseudo-point perforating, and open-hole completions. The results of the different completion methods are integrated in this study to optimize well design.
As one of the relevant results of this integration effort, it is concluded that high-angle wells with open-hole completions along the perforated liners is the optimal method of production. This integrated approach allows reclassifying originally sub-commercial reservoirs into economic assets.
Numerical Simulation of Systematic Fracturing and Evaluation of Fracturing Treatments In D37 Zone of Shenli Oil Field in China
Authors: Li Yongming , Guo Jianchun , Zhao Jinzhou , Tang Lin , Fu Ying , Zeng Zhongjie 
Published: December 2007

Abstract

Proposal
By present hydraulic fracturing technology has advanced to reservoir systematic fracturing from single well’s stimulation treatment. Reservoir systematic fracturing has become an important economical treatment for low-permeability reservoirs since a great deal of wells have uneconomical productivity without fracturing. Therefore, it is very important to consider the requirements of fracturing treatments when programming the exploitation project for one new oil field or the future adjustable project for the old field.
Reservoir numerical simulation with hydraulic fractures is the basis of the optimum design of systematic fracturing. The numerical simulation software of systematic fracturing is developed, in which nine-spot pattern, five-spot pattern and rectangular well pattern are considered and both favorable and unfavorable azimuth of hydraulic fractures are included.
D37 is a low-permeability zone of Shengli Oil field in Shandong province of China. Five-spot water flooding pattern has been applied in D37 since 1990 while fracturing treatments since 1995. With systematic fracturing software, the production data has been predicting until water cut reaches 95% for systematic fracturing of five-spot water flooding pattern. By balancing the flooding sweeping efficiency and production rate, the optimum fracturing design is determined by giving a reasonable range of fracturing length and fracturing conductivity. The effects of nine-spot well pattern, azimuth of maximum permeability and injecting rate are synthetically studied. Integrating fracture propagation simulation with analysis of pumping pressure and history matching of post-frac productivity, ten fracturing wells in fD37 are evaluated. The reason why the production rates of some wells declined steeply shortly after the initial improvements is given in this paper. Based on the numerical simulation and evaluation of early fracturing treatment, design principles of systematic fracturing and rules of future exploitation in D37 are suggested.
Methodology to Detect Nitrogen Concentration at Surface Facilities and in the Reservoir Gas Cap in the Akal Field during Nitrogen Injection
Authors: Astudillo-Abundes A. , Miguel-Hernandez N. , Urriza-Vergara A. , Jimenez-Bueno O. 
Published: December 2007

Abstract
At present time, a mature oil reservoir generally has a secondary or enhanced oil recovery process in order to increase production or reserves. That process generates important field information as pressure, production, fluid being injected, and fluid being injected that is produced at surface, among others. This information is useful for others reservoirs with similar geologic properties allowing better recovery factors and increasing oil production.
Injection of nitrogen in the gas cap of the Akal field in Mexico is taking place to maintain pressure in the reservoir. Around the world, there is not enough experience in nitrogen injection in reservoirs with industrial volumes. From this, the necessity of nitrogen control methodologies and procedures arise in this area and extend them for use in other fields.
This paper presents a procedure of sampling and analysis of nitrogen concentration in the field including wells, platforms, separation facilities, gas pipes, and delivery points. This is based on more than 20,000 samples of gas chromatography from gas being produced. The samples are recovered in strategic points by a team work in sampling, chromatography, and data analysis. Sampling and chromatography analysis help to identify the increase or decrease of nitrogen concentration. Additionally, production of nitrogen in gas being produced affects negatively the gas quality.
Additionally, simulation of gas flow pipelines including gas production from other fields, and the presence of high values of nitrogen mol concentration in wells helps to determine the nitrogen concentration in the gas delivery point.
Due to Akal field is a naturally fractured oil reservoir with high density of fractures, nitrogen being injected travels rapidly toward the oil gas contact. Then, nitrogen is used as a tracer for dynamic reservoir characterization. Determination of nitrogen mol percent for each well allows us to know qualitatively the development of the gas cap of the reservoir.
Pressure Transient and Decline Curve Behaviors for Partially Penetrating Wells Completed in Naturally Fractured-Vuggy Reservoirs
Authors: Fuentes-Cruz G. , Camacho-Velazquez R. , Vasquez-Cruz M. 
Published: December 2007

Abstract
This work presents results on both pressure and production responses during transient and boundary-dominated flow periods, in naturally fractured reservoirs with vuggy porosity. It is considered that triple-porosity systems may not be treated as dual-porosity reservoirs, mainly because fractures and vugs have different geological origin and therefore their interaction with matrix blocks do not have to be similar. New solutions are presented for the case where there is no primary flow through vugs, an extension of the Warren and Root model, existing an interaction between matrix, vugs, and fracture systems.
The new model assumes a single partially penetrating well producing from an undersaturated system considering several boundary conditions. The inner boundary condition at the wellbore can be considered either a fixed flux or constant pressure boundary. The upper, lower, and outer boundaries can be modeled at constant pressure or prescribed flux. These boundaries can be closed, or the influx can be modeled via a step rate or a ramp rate function. The step rate function could represent a waterflood effect and the ramp rate function a natural waterdrive or gas drive cap effect. The transient pressure response is also analyzed by considering an infinite outer boundary. In transient well tests and decline curve analysis, the effects of triple-porosity for different upper and lower boundaries conditions are analyzed, besides considering closed upper and lower boundaries as it has been done in the literature. It is shown that for triple porosity systems the derivative function may exhibit different behavior to that of double-porosity reservoirs. It is demonstrated that the presence of vugs and caves may have a definitive influence on transient well test and decline curve behaviors. Synthetic and field examples are presented to illustrate the methodology proposed in this work.
Preventing Lost Circulation Using Lightweight Slurries with Reticular Systems: Depleted Reservoirs in Southern Mexico
Authors: Romero S. N. , Monroy R. R. , Johnson C. , Cardenas F. , Abraham G. A. T. 
Published: December 2007

Abstract
In southern Mexico, 65% of the oil and 74% of the gas production comes from Mesozoic formations—naturally fractured carbonates—with a high potential for loss of circulation. Lost circulation during drilling and cementing often leads to formation damage and can severely impact well costs.
This paper describes the implementation of lightweight (9.17 lbm/gal) slurries and a reticular product technology to avoid losses while cementing and to improve zonal isolation and postcement job evaluation. Applying this combination of technologies improved the success ratio of primary isolation of the wells.
Lightweight cementing slurries with reticular systems were used in two wells in Mexico: Copano 32 on the development side and Malva 201 for exploratory cementing. The wells were drilled underbalanced and, in both cases, lost circulation was a problem during drilling. Circulation of the cementing slurry was regained while cementing and returns reached the designed cement top, avoiding the anticipated remedial cementing job. The pressure behavior during cementing clearly showed the plugging effect of the slurries in the formation; periodic low-pressure intervals were encountered before the final constant increase in pressure, which indicated that the designed cement job had been achieved.
In these wells, implementation of lightweight slurries and reticular-product technology prevented cement invasion into the production zone. Savings in rig downtime and improved zonal isolation led to a significant reduction in costs during the construction of the wells.
The cementing solution represented at least a 300% cost savings related to the cementing process and confirmed that lightweight cement slurries with reticular products are a viable solution for the depleted reservoirs in southern Mexico and for similar wells around the world where lost circulation problems of this kind exist.
Integrated Dynamic and Static Characterization for a Mesozoic Naturally Fractured Reservoir Located in a Platform - Basin Area in Southeastern Mexico
Authors: Padilla-S. Roberto , Pacheco-G. Carlos , Reyes-G. Santos 
Published: December 2007

Abstract
Based on experiences of several integrated studies in naturally fractured reservoirs (NFR´s), this paper shows the success obtained from apply synergism in the dynamic and static conjugation in a complex fractured Mesozoic field producing in the south of Mexico, and its impact in the simulation process, providing the highest possibilities to be successful in the evaluation of different production alternatives.
The methodology contemplate results like those permeability distributions of the well test analysis, petrophysical parameters from the well logs interpretation, validated with fracture models supported in microstructures through a rigorous analysis on core samples. The adequate treatment of seismic data to define both structure and attributes is transcendent. The existence of fractures associated to folds and faults are the source of preferential fluid channels, affecting the petrophysical properties and the flow efficiency of wells, and therefore the fluid flow in porous media. The suitable combination with sedimentary, megascopic and microscopic fracturing studies, make easy to define NFR´s with low productivity or highly fractured with infinite transmissibility, showing a homogeneous behavior.
This work, for the field example shows that the most important producing wells are associated to patchs reefs with high permeability, surrounded in a same area with permeabilities least than 0.01 mD. The existence of fractures associated to normal and strike slip faults and the fold phenomena have influence in its generation and distribution, and impose the best conditions of productivity in wells near to faults. Due to the different scales used in this study to define the fracture model, the preferential directions of flow are consistent with those results of well testing and validated with the numerical simulation.
Optimization of Bit Drilling Performance Using a New Small Vibration Logging Tool
Authors: Schen A. E. , Snell A. D. , Stanes B. H. 
Published: December 2007

Abstract
The effects of downhole vibration on drill bit performance have been discussed a great deal in the past several years. Data acquired on near-bit vibration has proved useful for assessing bit selections, design features and running parameters. Typically, engineers have had only limited access to this type of data because measurement-while-drilling (MWD) tools capable of acquiring vibration measurements are generally placed well above the bit in the bottom hole assembly (BHA), where the dynamics can be significantly different than at the bit. Also, these conventional MWD tools are expensive to operate.
The recent development of an easy-to-use, memory-mode, vibration-logging tool has made obtaining relevant "at-bit" data much more feasible. The tool is very small and can be used in collar sizes as short as 8 in. from shoulder-to-shoulder. The tool can be placed directly above the bit without disturbing the BHA. This paper highlights the development of this tool and presents data from recent field tests that show how it has been used to optimize and evaluate drill bit performance in various applications.
Field Planning Using Integrated Surface/Subsurface Modeling
Authors: Ghorayeb K. , Holmes J. , Torrens R. 
Published: December 2007

AbstractIntegrated surface/subsurface modeling has been shown to have a critical impact on field development. Integrated modeling aims to capture the interaction between the surface facilities, the production/injection system, and the reservoir(s).Among other issues, an integrated surface/subsurface model addresses the following: Pressure interaction between a reservoir and a surface facility network model.Pressure interaction between different reservoirs in the case of multiple reservoirs sharing a surface facility.Improved calculation of pressure and temperature gradients in the wellbore.Influence of facility constraints and equipment on a set of reservoirs sharing a surface facility.Mixing of fluids from reservoirs with different fluid descriptions sharing a common production network.Applying global production and injection constraints to the coupled system (including the transfer of reinjection fluids between reservoirs).In this paper, a set of examples is presented illustrating the use of the above surface/subsurface modeling capabilities and their impact on field planning. The study mainly focuses on the following issues: Multiple reservoirs coupling in a compositional mode involving black oil delumping. Reservoir/network coupling takes place at both the well bottomhole and tubinghead.Integrated surface/subsurface system response to various network choke-setting scenarios.Field events scheduling in response to the behavior of the integrated surface/subsurface system.The results presented in this paper complement those presented in a previous study.[1]
Latest Positive Displacement Motor and Drill Bit Developments for Drilling Hard and Abrasive Formations
Authors: Regener Thorsten , Reich Matthias , Duerholt Ralf , Wagner Bernd 
Published: December 2007

Abstract
Many drilling engineers still associate the use of impregnated bits for hard and abrasive formations with the use of hydrodynamic turbines. In fact, turbines were the first high speed direct bit drive systems on the marketplace — providing maximum bit speed, long life on bottom and, due to the lack of elastomers in the power section, could be used in high temperature environments. However, turbines offer low drilling efficiency, especially in combination with low flow rates, and are very expensive to build and maintain. Positive displacement mud motors are more cost effective and show much better efficiencies, even at lower flow rates, but used to survive fewer hours on bottom and tended to fail at higher bottomhole temperatures. Current manufacturing technologies, especially the capability to manufacture pre-contoured stator tubes covered with a thin layer of elastomer, have helped to overcome the above mentioned problems. Today's latest generation high speed mud motors combine the industry's highest bit speeds with unmatched torque — resulting in a power output of up to 1000 HP. These motors can be used in temperatures up to 160°C and have survived numerous runs consisting of hundreds of hours of on-bottom drilling time without failure. The paper describes latest developments in mud motor design and shows case histories of motor runs from different vertical and directional wells of various hole sizes across multiple continents. Premium drilling performance is not only dependent on the availability on latest mud motor technology, but requires a detailed understanding of the entire drilling process as well as the optimization of the drill rig, the drill string, the BHA and the bit. Special attention is therefore given to an ongoing optimization project, which has taken place in close coordination between a service company and an operator in North Germany. Drilling the very hard and abrasive Bunter Sandstone used to be a time consuming and costly enterprise. Within few years the ROP could be doubled and the distance drilled per BHA could be tripled.