bluuebunny/crossref_metadata_2025 huggingface dataset:
Managed Pressure Drilling for Subsea Applications; Well Control Challenges in Deep Waters
Authors: Fossil Børre , Sangesland Sigbjørn
Published: December 2007

This paper describes a new drilling riser concept and drilling method that will remove some of the well control challenges presently encountered and provide improved well control procedures, when handling deepwater kicks and deep formation gas flow into a well being drilled. The new system will also allow for longer hole sections to be drilled in deepwater, thus reducing the number of casing strings required in the well and reduce the chances of hydrate plugs forming at seabed.

The main element in the system is based on using a smaller size (14"-12.5" ID) high pressure drilling riser with a split BOP between surface and subsea, a subsea mud pump connected to the high pressure drilling riser, taking returns from a lower level in the riser. The mud level in the riser is dropped down to a level considerably below sea level to create a mud/air interface ("mud cap") that can be continuously adjusted up or down by the mud-lift pumping system. As a consequence, the bottom hole hydrostatic pressure will be controlled. One of the main purposes of this system is to mitigate the inherent problems with a conventional 21" marine drilling riser during well control scenarios in deepwater operations. It will adjust the bottom hole pressure accordingly and compensate for frictional pressures due to circulation.
Field-scale Polymer Flooding: Lessons Learnt and Experiences Gained During Past 40 Years
Authors: Du Y. , Guan L.
Published: December 2007

Early in 1964, Pye and Sandiford established the fact that polymer flooding can result in greater oil recovery than the conventional water flooding. Many additional papers sustaining and extending this information have since appeared in the literature. In the past forty years, many field-scale polymer flooding projects have been put into production and lots of information has been available from which to draw conclusions regarding of lessons learnt and experiences gained on field-scale polymer-flooding. The purpose of this paper is to examine the ranges of some important parameters within which successful polymer flooding has been achieved and to present lessons learnt and best practices on polymer flooding, thus direct to design and further achieve a high-performance polymer-flooding project.
Uncertainty Assessment using Experimental Design: Minagish Oolite Reservoir
Authors: Peake W. T. , Abadah M. , Skander L.
Published: December 2007

A peripheral waterflood is planned in the Minagish Oolite Reservoir, Burgan Field. This is a large carbonate reservoir which has been under limited primary production since 1965. There is considerable uncertainty in the waterflood oil forecast because of the minimal amount of data with which to characterize the reservoir. This study identifies key subsurface uncertainties impacting waterflood performance and quantifies uncertainty with P10/P50/P90 oil forecasts.

Experimental design (ED) techniques were used to establish the minimum number of reservoir simulation runs needed to quantify uncertainty. Both traditional and ED techniques were used to preserve history matches for all simulations. Analysis of variance and multiple linear regressions were used to identify the most significant uncertainties and to create a proxy for the simulator. The proxy was used in Monte Carlo simulation to develop P10/P50/P90 oil forecasts.

Uncertainty analyses have not often been conducted on producing reservoirs. In this report a new technique combining ED with history matching has been successfully demonstrated. The technique can be applied to other producing reservoirs. Despite the need to restrict simulator inputs for history matching, it was shown that considerable uncertainty exists in the waterflood oil forecast. The results are valuable for: a) identifying actions to reduce uncertainty and b) input to additional development evaluations.
Characterization of a Vuggy Fractured Media: A Practical Approach
Authors: Pérez-Rosales C. , Luna E.
Published: December 2007

This paper presents the theoretical, experimental, and operational bases of a practical procedure for decomposing total porosity into its basic components, i.e., primary, secondary, fracture, and vug porosities. The procedure makes use of total porosity and formation resistivity factor data obtained through geophysical well logs, and is based on a general formulation which has as particular cases all other formulations commonly used to relate formation resistivity factor and porosity, such as Maxwell, Fricke, Archie and generalized Archie equations. To visualize its potential as a tool for interpreting well logs, an application example is presented.
Dynamic Behavior of Discrete Fracture Network (DFN) Models
Authors: Araujo Hugo , Lacentre Pablo , Zapata Tomás , Del Monte Aldo , Dzelalija Francisco , Gilman James , Meng Hai-Zui , Kazemi Hossein , Ozkan Erdal
Published: December 2007

This work shows that discrete fracture network modeling is very desirable for the characterization of naturally fractured reservoirs but it is only a highly subjective starting point. Thus, calibration against short and long term pressure transient tests is most crucial. This paper shows how the dynamic behavior of a discrete fracture network model of Margarita gas field compared against pressure transient measurements in a sidetrack delineation-well. The performance comparison of a very fine-grid reservoir model, which included the discrete fracture network information, versus a much coarser upscaled grid model is also documented.
In Situ Upgrading Heavy Oil by Aquathermolytic Treatment Under Steam Injection Conditions
Authors: Jiang S. , Liu X. , Liu Y. , Zhong L.
Published: December 2007

Aquathermolytic technology that involves upgrading heavy oil using chemical additives is introduced in this paper. Laboratory experiments were carried out under steam injection conditions to investigate catalysis of some metal species and synergetic effect of catalyst and hydrogen donor on aquathermolysis of Liaohe and Shengli heavy oils. As a result, significant reduction in viscosity and contents of asphaltene and resin was obtained, thus heavy oils were upgraded greatly. Then the mechanism of aquahtermolysis is discussed further. Additionally, the field test in Liaohe Oifield is introduced. The future is suggested in the end.
Reservoirs Simulations of Gel Treatments to Control Water Production, Improve the Sweep Efficiency and the Conformance Factor in Eastern Venezuelan HPHT Fractured Reservoirs
Authors: Herbas Julio , Kumar Sujit , Moreno Raul , Romero Maria F. , Avendaño Horacio
Published: December 2007

A numerical simulation study was undertaken to model the gel treatments in injector and producer wells in Eastern Venezuela Fractured HPHT Reservoirs in exploitation under secondary and tertiary recovery process.

The objective of the simulation study is to develop a numerical simulation model based on field and laboratory data to model the gel treatments to block induced fractures and high permeable channels in water injection and oil producer wells, and to improve the conformance and the recovery factors.

Field data representation of a HPHT Fractured Venezuelan reservoir with preferential water movement and induced fractures was used to build a conformance field prototype model.

The gel used in the simulation study is a polymer system composed by polyacrylamide with phenol and formaldehyde crosslinkers suitable to stand HPHT reservoir conditions. Available laboratory work and field data to characterise the performance of polymer gels in fractured wells were included in the model and were history matched to predict alternate gel treatment scenarios.

The developed simulation model provides a tool to predict the production performance of gel treatment in Eastern Venezuela Fractured HPHT Reservoirs under different treatment scenarios; useful to assist in the determination of: optimum treatment intervals, optimum procedures; and to develop data for economic evaluations, improving the design of gel treatment and reducing associated uncertainties.
Modeling of Gravity-Drainage in Naturally Fractured Reservoirs Using Flow in Angular Capillary Tubes
Authors: Xu Q. , Gupta A.
Published: December 2007

This paper presents an investigation of gravity-driven flow in naturally fractured reservoirs via multiphase flow in angular capillary tubes. The study includes theoretical and numerical analyses, and is supported by laboratory measurements.

Gravity is important in many oil recovery processes, either acting as the driving force in processes using horizontal wells or altering displacement patterns during waterflooding, chemical flooding, CO2 flooding, and other EOR processes.

Gravity drainage driven oil production in naturally fractured and other complex reservoirs falls into two regimes: the bulk flow and the film/corner flow. After the bulk flow at constant production rate and a short period of transition, the corner/film flow dominates the production. The flow in the corners and films in fractures and pore-channels is the focus of this study. Modeling the flow channels as angular capillaries of variable polygon shapes provides a valid physical basis for corner flow.

The fluid distribution above the gas/oil contact is influenced by in-situ capillary force but more by the fluid dynamics. Numerical simulation of the film/corner flow was conducted for various cross sectional shapes using finite element analysis (FEA). Experiments were conducted using space between packing of glass rods as flow channels that capture the essential features of flow channels in rocks and natural fractures. Comparison between the simulation predictions and experimental observations allowed validation of the modeling process.

The results of this study provide basis for more detailed network models, which describe rock-fluid systems at microscopic level with deterministic solutions. The modeling procedure presented in this study and the results are useful for modeling the performance of gravity dominated improved oil recovery processes.
Improving the Recovery Factor of Heavy Crude Reservoirs by Co-injecting CO2 and Other Conventional Gaseous Injecting Materials at Immiscibility Condition with Foam
Authors: Panahi Hamed
Published: December 2007

Gas injection process as both a pressure maintenance method & an IOR method has a long background in the upstream. Adding foam is a proven method for decreasing gas mobility in both homogeneous and heterogeneous reservoirs. Foamed gas, though is a promising agent for achieving mobility control in porous media. Its profound impact on the efficiency of different gas injection applications fascinated the industry on considering using it to supply the future needs of the world to hydrocarbons.

The idea here is to inject CO2 which is immiscible at the start of injection along with a kind of foamer solution. The role of foam is to increase the contact area of the reservoir by reducing the gas mobility leading to higher volumetric sweep efficiency and mitigating the so-called effect of gravity override. The process is completed by injecting gas to the amount that it becomes miscible. (Reservoir pressure goes beyond MMP). No production is expected after the initial injection to the time we are certain that the whole system is in thermodynamic equilibrium. The in depth theoretical description is included.

The simulation of the process is performed using a coded isothermal compositional simulator together with commercial reservoir simulation soft-wares, though simulation models and simulation tools that accurately gauge the effects of foam on gas mobility in porous media are not readily available.

The simulation results are compared with the experimental results. Feasibility study is performed and the setbacks of the process are analyzed. Some remedies are offered to improve the process.
Case Histories - Combining Crossed Dipole Sonic Anisotropy and Oriented Perforating To Optimize Hydraulic Fracturing In the Burgos Basin - Reynosa Mexico
Authors: Patino Antonio Hernandez , Garcia Eduardo Rodriguez , Torne Juan Pablo , Lazo Jorge , Kessler Calvin
Published: December 2007

Proposal

Based on local experience, a well-accepted work flow or set of best practices has been developed for optimizing stimulation treatments in the Burgos Basin. Recently, these best practices have been enhanced by combining stress field orientation and gyroscopically oriented wireline perforating. Orienting perforations in the direction of maximum horizontal stress has greatly reduced near wellbore tortuosity and friction in hydraulic fracturing treatments. The result has been improved proppant placement resulting in higher proppant conductivity and increased production.

The best practices for optimization of the stimulation design and economic modeling include many steps.1,2,3,4,5,6,7,8,9,10 The candidate selection process evaluates the net-to-gross sand thickness ratio, reservoir pressure, and permeability for each zone. The net-to-gross ratio provides information on productive and non-productive fracture height, which is needed for inflow analysis. The reservoir fluid, pressure, and permeability of the formation are vital for determining the fluid leakoff/fracturing fluid rheology requirements and required fracture conductivity. Geological and geophysical data are reviewed to identify potential reservoir boundaries such as faults or pinch-outs that could impede hydraulic fracture propagation. The vertical stress profile between the zone to be treated and the underlying and overlaying formations is used in 3D fracture simulators to evaluate the fracture height (and any possible unwanted out-of-zone fracture height) versus fracture half-length and proppant concentration.

To implement the oriented perforating enhancement to the best practices crossed dipole sonic anisotropy analysis is used to determine the far-field stress orientation and magnitude combined with the six electrode dipmeter for orientation and ovality visualization. Borehole breakout analysis and anelastic strain recovery of whole cores can provide near-field stress orientation data. These factors are then used to determine optimum perforation direction. In this paper, several case histories will be presented comparing the results of stimulation treatments using the normal practices and traditional perforating methods versus stimulation treatments using the same practices but incorporating oriented perforating.
Fracturing Microseismic Response in Turbidite Reservoirs in Tajin Field
Authors: Berumen Sergio , Kaiser Penelope , Gachuz Heron , de Swaan Abraham , Rodriguez Juan M.
Published: December 2007

Selection of optimum well locations in heterogeneous turbidite reservoirs such as those found in Chicontepec basin, depends strongly on the description of heterogeneities--facies distribution and flow quality properties--as well as on the evaluation of the extent and orientation of propped fractures. Fracture growth propagation and orientation play an important role in visualizing and optimizing the drainage pattern of such complex reservoirs.

To better understand the fracturing response of these formations and support the design of development strategies, several measurements of microseismic response under hydraulic fracturing were carried out in wells in the Tajin field. By deploying sensor on-tubing tools of treatment wells, microseismic data were recorded following the injection operation, yielded fracture extent and orientation and stress anisotropy. The computed hypocentre locations are distributed in a non symmetric cloud of seismicity with a global trend extending no farther than 195m away from the wellbore in the N20-30°E direction. Moreover, the acoustic emissions presented a remarkably consistent direction.

Interpretation of location of shear-slip and acoustic emissions events is consistent with results provided by dipolar sonic image logging tools run on the same wells. Better understanding of reservoirs` response to stimulation leads the operator to review its fracturing practices for cost-effective reservoir stimulation. Numerical reservoir simulation grids for reservoirs in the zone were oriented according to the observed fracture trend.
Reservoir Simulation of Non Selective Placement of a Polymer Gel Treatment to Improve Water Injection Profiles and Sweep Efficiency in the Lagomar Field Western Venezuela
Authors: Herbas Julio , Moreno Raul , Marin T. Amaury , Romero Maria F. , Coombe Dennis
Published: December 2007

A reservoir numerical simulation study was done to model a polymer gel treatment pilot test without mechanical isolation, that was performed to improve the injection profiles and the sweep efficiency in a water injector well of an hexagonal pattern in the Lagomar field located in the Maracaibo Lake in western Venezuela.

The gel treatment pilot test was performed in the C-4 reservoir, a layered highly heterogeneous Eocene sandstone. In this reservoir water injection for secondary have been performed for over tree decades. High water cuts have forced management to shut in several producing wells.

A reservoir characterization analysis that included PLT logs, core analyses, and geomechanics, identified the presence of induced fractures as a cause of low sweep efficiency. Based on this reservoir study, a polymer gel treatment was designed for an injection well located in the center of a hexagonal well pattern.

A commercial gel polymer technology (MARCITsm) was selected to modify the injection profile in this pilot test. The results from the test injecting 3700 barrels of gel in the water injector well were very promising, showing an average reduction of 30% in water cut and 26,850 barrels of incremental oil five months after the treatment.

A reservoir simulation study was developed using STARS, a K-value compositional reservoir simulator with gel modelling capabilities. The model reproduces reasonably the performance observed in the field pilot test.

The simulation study is a first approach to developing a predictive tool to assist in the planning and design of future non selective gel treatments in water injector wells, applicable in the Lagomar field and analogous water injection projects.
Seismically Driven Improved Fractured Reservoir Characterization
Authors: Ouenes Ahmed , Zellou Abdel M. , Robinson Gary , Balogh Dave , Araktingi Udo
Published: December 2007

Characterization of naturally fractured reservoir is a recurring challenge for many oil and gas companies that manage and develop fractured reservoirs. Several techniques have been applied in the past to characterize these complex reservoirs; most of them have been proven unreliable. This paper will describe a methodology to improve the characterization of fractured reservoir using seismic attributes derived from pre-stack and post-stack high resolution inversion and spectral imaging.

The methodology presented in this paper uses the simultaneous integration of geophysical, geologic, and engineering data to improve the reservoir description. At the root of this reservoir characterization technique is the increasingly accurate seismic data collected on most of the reservoirs world-wide. Extensive use of this seismic information is made possible through the use of pre-stack high-resolution elastic inversion, post-stack high resolution inversion, and spectral imaging. These processes allow the derivation of seismic attributes that are extremely relevant to fracturing and could also be used as input in the continuous fracture modeling approach. Based on this seismically driven reservoir characterization, the fractured reservoir properties could be accurately estimated in 3D. An application of this technology and workflow is presented on a very complex fractured reservoir.
Forty Years of Improved Oil Recovery: Lessons from Low-Permeability Turbidites of the East Wilmington Field, California
Authors: Jenkins Creties , Al-Sharif Shahin , Harris Randy , Weisgram John , Michel Don
Published: December 2007

The U-P Ford zone in the Long Beach Unit of the East Wilmington Field consists of low-permeability (2-50 millidarcies) turbidites that have been waterflooded since field start-up. Forty years of successes and failures have provided valuable insights into how to best waterflood these reservoirs given their thin-bedded nature, lateral and vertical changes in reservoir quality, formation damage susceptibility, and sand control problems. Multiple techniques and technologies have been applied to describe their reservoir architecture, quantify reservoir performance, and extract the oil. This work has become more challenging as the waterflood has matured and will require the close integration of all disciplines to identify and exploit remaining opportunities.
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

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

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

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

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

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

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

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

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

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

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

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

Integrated 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

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.
4D Seismic and Through Tubing Drilling and Completion Wells Extend Life on the Gullfaks Field
Authors: Todnem Annick Chazy , Arnesen Linn , Gaasø Rune
Published: December 2007

The Gullfaks Main Field is one of the largest oil fields in the Norwegian sector of the North Sea. Production started in 1986 and reached a peak in 1994. Today approximately 90 % of the base reserves have been produced from this mature field. Locating remaining oil reserves is therefore a challenging and important task for the future of Gullfaks. The reservoirs are comprised of middle and early Jurassic sandstones, possessing overall excellent reservoir properties. The structural setting of the field is complex, and represents one of the main factors of uncertainty concerning the drainage of the field. The paper describes how multiple time-lapse seismic (4D) have proven very accurate in identifying undrained oil pockets in the Brent Group. The importance of 4D/4C in the wells drilled is estimated to represent a reserve oil volume of approximately 4 Mill. Sm³ per 2004, (25 Mill. Sbbl). TTD&C (Through Tubing Drilling and Completion), being a more flexible and less expensive technology, has also been crucial in reaching smaller oil pockets on the Gullfaks Main Field. The potential offered by these technologies has been optimized by multidisciplinary teamwork on Gullfaks, thus creating synergy and flexibility. These three key elements have contributed to reverse the oil production decline, establish a new plateau, reduce costs and increase profit.