bluuebunny/crossref_metadata_2025 huggingface dataset:
Well Test Analysis of Horizontal wells in Gas-Condensate Reservoirs
Authors: Hashemi Abdolnabi , Nicolas Laurent M. , Gringarten Alain C.
Published: December 2007

Gas condensate reservoirs usually exhibit complex flow behaviors due to the build-up of condensate banks around the wells when the bottomhole pressure drops below the dew point. The formation of this liquid saturation can lead to a severe loss of well productivity and therefore lower gas recovery. Several studies have examined various ways to minimize the pressure drop in order to reduce liquid drop-out and related problems. One solution implemented over the past decade is the use of horizontal wells.

There is a lack of published knowledge on the flow behavior of horizontal wells in gas condensate reservoirs. The limited studies in this area1-3 focused on well performance rather than on well test behavior. There has been no evidence of condensate drop out effects in published horizontal well tests data.

This paper presents preliminary results from a study aimed at establishing an understanding of the near-wellbore well test behavior in horizontal wells in gas condensate reservoirs, with a focus on the existence of different mobility zones due to condensate dropout.

We used a 3D fully compositional model to develop derivative shapes to be expected from horizontal well test data in gas condensate reservoirs below the dew point under various conditions. We then analyzed actual well test data that exhibit such derivative characteristics. Finally, we used a compositional model to verify the results obtained from conventional well test analysis.

It was found that condensate deposit near the wellbore yields a well test composite behavior, similar to what is found in vertical wells, but superimposed on a horizontal well behavior, which makes it much more complex.
Elimination of Biogenic Hydrogen Sulfide in Underground Gas Storage. A Case Study
Authors: Raczkowski Józef , Turkiewicz Anna , Kapusta Piotr
Published: December 2007

The paper reports microbiological study of Sulfate Reducing Bacteria activity in underground gas storage and preventive action against H2S formation. Complex research was performed on natural gas reservoir in Swarzow, where one of a few gas storages in Poland had been arranged. The presence of hydrogen sulfide in the 10-th cycle of UGS exploitation gave impact to search a new effective methods which might limit the microbial processes of sulfate reduction in the reservoir. Having the long-term experience, in 1995-96 operation of biocide treatment in SWARZOW UGS was completed with success. Selective biocides (quaternary ammonium compounds) were applied into the reservoir for the first time in Poland, in accordance with patented technology worked out in Oil and Gas Institute, Department of Microbiology. In 1997-98 the biocide injections to exploitation wells were repeated. These operations conduced to the total elimination of Sulfate Reducing Bacteria from the formation waters and caused partial reduction of H2S content in natural gas recovered from the reservoir. In 2003 the new technology based on synergetic action of biocide, represented by triazine derivatives, and H2S Scavenger (Sulfa Clear) was implemented for the first time in underground environment. Practical application of this technology on 2 objects of UGS was finished with a great success. Content of hydrogen sulfide in the recovered gas and formation waters now accords with European Standards. The paper also discusses microbiological studies of processes observed in the natural gas reservoir in Wierzchowice, which is the largest store in Poland. Its final capacity will be ca. 4,3 billion cubic meters of natural gas. The research was conducted between the 1st and the 8th cycle of UGS exploitation. Present investigations were performed in the monitoring system and included microbiological and chemical analysis of formation waters and drilling fluids. Active strains of H2S producing bacteria (Desulfovibrio sp. and Desulfotomaculum sp.) isolated from the reservoir, have been used for testing biocides selected to protect exploitation wells of WIERZCHOWICE UGS.
Streamline-Based Production Data Integration in Naturally Fractured Reservoirs
Authors: Al-Harbi Mishal , Cheng Hao , He Zhong , Datta-Gupta Akhil
Published: December 2007

Streamline-based models have shown great potential in reconciling high resolution geologic models to production data. In this paper we extend the streamline-based production data integration technique to naturally fractured reservoirs. Describing fluid transport in fractured reservoirs poses additional challenge arising from the matrix-fracture interactions. We use a dual-porosity streamline model for fracture flow simulation by treating the fracture and matrix as separate continua that are connected through a transfer function. Next, we analytically compute the sensitivities that define the relationship between the reservoir properties and the production response in fractured reservoirs. The sensitivities are an integral part of our approach and can be evaluated very efficiently as 1-D integrals along streamlines. Finally, the production data integration is carried out via a generalized travel time inversion which has been shown to be robust because of its quasi-linear properties and utilizes established techniques from geophysical inverse theory.

We also apply the streamline-derived sensitivities in conjunction with a dual porosity finite difference simulator to combine the efficiency of the streamline approach with the versatility of the finite difference approach. This significantly broadens the applicability of the streamline-based approach in terms of incorporating compressibility effects and complex physics. We demonstrate the power and utility of our approach using 2-D and 3-D synthetic examples designed after actual field conditions. The reference fracture patterns are generated using a discrete fracture network (DFN) model that allows us to include statistical properties of fracture swarms, fracture densities and network geometries. The DFN is then converted to a continuum model with equivalent grid block permeabilities. Starting with prior models with varying degrees of fracture information, we match the water-cut history from the reference model. Both dual porosity streamline and finite difference simulators are used to model fluid flow in the fractured media. Our results indicate the effectiveness of our approach and the role of prior information and production data in reproducing fracture connectivities and preferential flow paths.
Is Side-Cutting Really Necessary for Steerable Bits?
Authors: Gaynor Tom , Chen David C-K
Published: December 2007

PDC bits with aggressive gauge designs are often considered to have a higher side-cutting capability and thus are frequently used in directional drilling systems to increase the build rate. However, aggressive bits are prone to bit whirl and hole spiraling, resulting in bit and BHA/MWD failures and poor hole quality. Long-gauge bits are known to reduce bit vibration and produce high quality wellbores. The question is then "can long-gauge bits — which by their nature do not side-cut — be used to drill directional wells?" To solve this puzzle, Halliburton Sperry-Sun has been studying the use of long-gauge bits with steerable motors and rotary steerable systems. The results show that BHA steerability is mostly determined by the dog-leg capability of the BHA and the ease of setting the tool face. The side-cutting capability of the bit can be decoupled from BHA steerability. Therefore, side cutting capability is not necessary for steerable bits when run with an appropriate BHA.
Analytical Method of Evaluating Productivity Index for Constant Production Rate or Constant Wellbore Pressure
Authors: Ibragimov A. , Khalmanova D. , Valko P. P. , Walton J.
Published: December 2007

The existing methods for evaluating the well productivity index are based on solution of transient problems. One approach is to consider the single well problem in infinite domain and subsequently apply the method of images. This puts restrictions on the geometry of the well and of the drainage volume. Another approach is to solve the transient problem in the bounded domain for late times. While in this case restrictions on the well geometry are less severe, the shape of the drainage volume is still limited to the simplest ones. In addition, for the constant rate case highly accurate wellbore pressures, for the constant pressure case highly accurate wellbore rates are required and that puts an extreme computational burden on the semi-analytical or numerical methods involved. Even with the most powerful methods and hardware available, the calculation of the productivity index of directionally drilled and partially penetrating wells, especially in more complex drainage volumes is a formidable task.

An additional problem is that in general, the productivity index for a well produced under constant pressure condition is different, although very close, from the productivity index of a well produced with constant rate.

In this work we present a new technique to evaluate single well productivity indices both for constant pressure and for constant rate conditions. The approach is based on the solution of two steady state boundary value problems with constant pressure prescribed on the wellbore. The two productivity indices, (for constant rate and constant wellbore pressure, respectively) are then computed as integral characteristics of the solutions of the corresponding time dependent boundary value problem. The two productivity indices are computed independently.

The method can be applied to any geometry of the reservoir (both 2-D and 3-D, regular or irregular), and any direction and length of penetration of the well. Designer wells (with a freely prescribed path) can be also considered.
Generating Multiple History-Matched Reservoir Model Realizations Using Wavelets
Authors: Sahni Isha , Horne Roland N.
Published: December 2007

This paper focuses on an automated way to generate multiple history-matched reservoir models with the inclusion of both geological uncertainty and varying levels of trust in the production data, using wavelet methods. As opposed to previously developed automated history-matching algorithms, this methodology not only ensures geological consistency in the final models, but also includes uncertainty in the production data.

A data distribution, say a permeability field, can be (reversibly) transformed into wavelet space where it fully described by a set of wavelet coefficients. It was found that different subsets of the collection of wavelet coefficients can be constrained separately to: (a) the production history, and (b) the geological constraints. This means the history match need only be performed once, after which multiple realizations can be generated by adjusting just the second subset of coefficients.

The ability to include both geological and production data uncertainty into reservoir model automatically is of great consequence to reservoir modeling and hence to reservoir management, risk analysis and making key economic decisions. The more complete and realistic reservoir model will lead to better reservoir production and development decisions.
Identification of Payzones from Log Measurements in Casing in Difficult Drilling Environment
Authors: Endisha Abdurrazag , El Mahdy Reda , Guru Udit Kumar
Published: December 2007

Open hole log evaluation has been traditionally used for formation evaluation purposes and is commonly used for reservoir characterization. Adverse hole conditions precluded use of these services. Under these circumstances, it becomes necessary to acquire the necessary log data after the well is cased for reservoir evaluation.

Cased hole logs provide answers with acceptable uncertainty in characterized formations. However, in cased wells, which are not well characterized, the results tend to have a higher uncertainty.

In one of the wells in Egypt the operator could not acquire the data in the open hole section because of adverse hole conditions. High quality cased hole data was acquired in the interesting section even in difficult borehole condition (heavy wash outs etc). The measurements are compared with the available open hole data and the responses explained. All the data which could have been acquired in the open hole was acquired in the cased hole with the available cased hole sensors. . Based on the data from the cased hole the bore hole condition at the time of casing the well was predicted. .

We also demonstrate that gaseous hydrocarbon can be identified from the cased hole epithermal neutron measurements which compared well with the resistivity and the density neutron separation. Reliable matrix density values have been estimated from the cased hole spectroscopy providing a reliable porosity values from the cased hole density

Reservoir parameters have been estimated in the cased hole section. It was possible to devise cost effective planning for completing the well based on these parameters.

The ability to provide cased hole measurements helped the operator in avoiding a costly side track. .
Use of Production Data Inversion to Evaluate Performance of Naturally Fractured Reservoirs
Authors: Marhaendrajana T. , Blasingame T.A. , Rushing J.A.
Published: December 2007

Many oil and gas production come from naturally fractured reservoirs. The reservoir properties and production performance of this reservoir show a unique behavior, which are different from the homogeneous reservoir. Hence, evaluation and forecasting production of these reservoirs require special models and approaches.

This paper attempts to utilize production data inversion method to obtain parameters such as permeability, skin factor, initial fluid-in-place and production potential in a naturally fractured reservoir. The model can then be used to forecast production from this type of reservoir.

The method uses type curve approach that incorporate concepts of both transient and boundary dominated flow models. Application of this method to oil field data is presented as well as comparison with results obtained from other methods (such as well test analysis and volumetric calculation).

The results of this research provide engineers a tool to evaluate and monitor production/reservoir performance of naturally fractured reservoirs regularly by analyzing production data (which are always recorded) without additional testing.

Introduction

Modeling of single phase flow in fractured reservoir involve the description of the shapes, orientation and sizes orf fractures network, and the mechanism for the transfer of fluid from the matrix to the fracture network. The process of transfer of fluid between matrix blocks and fissures (or fractures) is the points at which various model differ. Some investigators have considered a pseudosteady-state relation for the interporosity flow term. This approach was first suggested by Barenblatt et al1 and was taken up by Warren and Root2 in their pioneering study of the pressure response of naturally fractured reservoirs. Others3,4,5 considered the effect of transient interporosity flow. The transient model is physically much more appealing since it allows for all regimes of internal block flow, i.e. transient, late transient and pseudosteady-state. This was first proposed by Kazemi,3 where the matrix blocks were composed of slabs.
Combinable Through-Tubing Cased Hole Formation Resistivity Tool
Authors: Herold B. H. , Benimeli D. , Levesque C. , Dubourg I. , Cadenhead J.
Published: December 2007

The Cased Hole Formation Resistivity Tool (CHFR*) that measures formation resistivity through casing has detected and evaluated bypassed hydrocarbon, tracked reservoir fluid movements, performed contingency logging, and has complemented the operating envelope of nuclear saturation monitoring tools. It has to be run stand-alone and due to its 3 3/8–in. outside diameter, the completion had to be pulled before logging.

This paper will present some of the field test results of the third-generation cased hole formation resistivity tool. It has a 2 1/8-in. outside diameter and is specifically designed for conveyance through tubing. The tool is also fully combinable with production logging tools and nuclear saturation-monitoring tools. It can be run conventionally on wireline, or deployed on coiled tubing or by tractor in difficult borehole conditions.

Field tests have verified the performance of the slimhole tool. Some of the field test data collected from different locations around the world are presented in this paper. They include log examples acquired in different well completions using various toolstring configurations. The small-diameter version adds new benefits to the industry: increased versatility, improved performance, conveyance under dynamic well conditions, and cost reduction.
A Novel Approach for Globalizing Corporate Sanctioned Standards
Authors: Ross D , Godfrey R
Published: December 2007

The development, implementation and administration of corporate sanctioned standards throughout a multinational service company pose many challenges. Difficulties arise when corporate standards intended for global use do not account for the many influencing factors (such as differences in local governing regulations, geographical locations, climatic conditions and contractual obligations) which will affect the validity and ultimate acceptance of a corporate sanctioned standard. To complicate matters further, in many cases the multinational personnel responsible for complying with the standards may or may not have the language skills required to read or comprehend a given standard unless it is translated into their indigenous language(s). Provided all these challenges can be overcome, the timely and effective distribution of documents to all corners of the globe presents another major challenge in addition to large costs incurred. Due to the dynamic nature of the industry and the desire to continuously improve, standards require periodic revisions, so a means to track and effectively distribute updates around the world is needed. This process requires personnel resources and discipline, and if not done properly, it can lead to a state of confusion among the intended users.

The following paper describes a novel approach for globalizing corporate sanctioned standards in a multinational service company, including standards for: field operations, quality, health and safety, environmental, maintenance, engineering, laboratory, and training. This novel approach, which employs a customized database application, is presented. Most unique to the application is its user interface which allows users to view the standards specifically applicable to their particular business unit, geographic region, and country, and in their native language. The approval process required to ensure all standards are reviewed and authorized at the appropriate level of the organization is addressed. In addition the methodology used for translating documents written in English into four additional languages will be covered. Furthermore, functional aspects of the database which allow multi-language viewing, user feedback, "best practices" photo gallery and additional features will be presented.
Unique Multistage Process Allows Pinpoint Treatment of Hard-to-Reach Pay
Authors: Rodgerson James L. , Lopez Henry (Enrique) , Snider Phil
Published: December 2007

Perforating multiple pay intervals to achieve optimum treatment coverage has long been a topic of considerable debate. Perforation selection can play a crucial role in well performance. The consequences of inadequate perforation coverage can compromise fracture optimization, limit production, result in missed pay and limit reservoir access. Multi-zone fracture treatments have been performed in the past using a variety of methods ranging from limited entry to mechanical isolation with bridge plug and packer. These and other techniques have been routinely applied to stimulate discrete intervals within a formation in an attempt to maximize the production of discrete pay zones or stringers. One method consists of perforating and isolating each zone then performing the stimulation treatment. Wireline is used to isolate the previous zone and perforate the next stage. The treatment of multiple intervals in this manner can be a costly and time-consuming process.

A new multi-stage treatment process optimizes perforation and treatment design. This technique, known as "External casing perforating," allows the operator to perforate and isolate individual zones in as little as 30 minutes between treatment stages. As many as 17 discrete intervals have been treated within a 24-hour period. Moreover, this approach minimizes total treatment volume by using the flush from the previous stage as the pad on the next stage, thus placing less fluid on the formation. The time to first sales has been reduced from days to a matter of hours by eliminating bridgeplug isolation and costly post-job clean up. Production from multiple horizons may be brought on-line quickly in one rig-less operation without damaging and time-consuming shut-ins.

This paper will describe the perforating and stimulation technique and will quantify cost savings to the operator associated with the reduced volumes and timesaving. Additional benefits such as reductions in friction pressure and polymer damage and means for fracture optimization also will be discussed.
Determining In-Situ Stress Profiles From Logs
Authors: Mohaghegh S. D. , Popa A. , Gaskari R. , Wolhart S. , Siegfreid R. , Ameri S.
Published: December 2007

This paper presents a new and novel technique for determining the in-situ stress profile of hydrocarbon reservoirs from geophysical well logs using a combination of fuzzy logic and neural networks. It is well established, that in-situ stress cannot be generated from well logs alone. This is because two sets of formations may have very similar geologic signatures but possess different in-situ stress profiles because of varying degrees of tectonic activities in each region. By using two new parameters as surrogates for tectonic activities, fuzzy logic to interpret the logs and rank parameter influence, and neural networks as a mapping tool, it has become possible to accurately generate in-situ stress profiles from logs. This paper demonstrates the improved performance of this new approach over conventional approaches used in the industry.
Approximate Analytical Solutions for the Pressure Response at a Water Injection Well
Authors: Peres A. M. M. , Boughrara A. A. , Chen S. , Machado A. A. V. , Reynolds A. C.
Published: December 2007

The first and fifth authors have previously used the Thompson-Reynolds steady-state theory to derive solutions for the pressure response at a water injection well. In the vertical well case, their solutions assumed a complete-penetration well; in the horizontal well case, they assumed that the well is equidistant from the top and bottom of the formation. Here, we construct approximate analytical pressure solutions for the restricted-entry vertical well case and for a horizontal well for the case where the well's axis is not equidistant from the top and bottom boundaries. The solutions are based on adding to the single-phase solution, a multiphase term which represents the existence of the two-phase zone and the movement of the water front. We present models for the movement of water based on a combination of Buckley-Leverett equations that allow us to accurately compute the multiphase flow component of the analytical solution. By comparison with a finite-difference simulator using grid refinement and a hybrid grid, it is shown that our multiphase flow solutions are accurate.

The analytical solutions provide insight into the behavior of injectivity tests at horizontal an vertical wells. For example, for a restricted-entry case, it is shown that the pressure derivative may be negative throughout an injection test even when the duration of the test exceeds ten or more days. We also show that for a well near a fault, the ratio of slopes reflected by derivative data will not in general be equal to two but is given by a formula that involves the mobility ratio. In the restricted-entry vertical well case, we provide the equations for three flow regimes.
Fuzzy Analysis for Progressing Cavity Pump
Authors: Correa Jose F. , Carvalho Paulo C. G. , Filardi Vitor L. , Schnitman Leizer , Lepkison Herman A.
Published: December 2007

The Progressing Cavity Pump artificial lift method for oil well production is well known in the oil industry, despite that a poor literature about PCP analysis is available. PCP automation based on ladder programming deploys information such as instantaneous rod torque, production line pressure, and rods rotation to name a few. The use of this information to analyze the well performance, identify imperfections and problems depends on a deep knowledge about the system well-PCP, but the procedures to do so are yet to be developed. To optimize the production and increase the mean time between failures in this type of well is necessary not only to improve the algorithm coded on the ladder programming loaded in the PCP automation PLC but also to develop a knowledge base where the skills and knowledge of the local PCP specialists could be easily coded. To analyze data deployed by the PLC and to improve the firmware customization, an intelligent system is being developed. This intelligent system is based on artificial intelligence concepts such fuzzy functions, coded in a way to easy acquire the PCP specialist knowledge on how to understand what is going on in the well and what to do to bring it back to a proper behavior. The present paper presents an intelligent system for automation of PCP wells capable of acquire and spread the knowledge of the referring specialist in diagnosis and solutions of problems during the well operation. Fuzzy agents are proposed in order to do an intelligent analysis of a set of PCP variables such as friction, motor, pump position, production and volumetric efficiency, … The paper also describes the tools and interfaces designed to acquire the PCP specialist knowledge, the system implementation, and an acquired knowledge base example.
Fluid Front History Matching Using 4D Seismic and Streamline Simulation
Authors: Kretz V. , Vallès B. , Sonneland L.
Published: December 2007

History matching of flow models is typically performed by using production data to calibrate the models. This implies that deficiencies in the models cannot be revealed until the consequences are observed in the well network. The outcome can be highly undesirable, like early water-breakthrough in a production well. A new method is proposed that enables calibration of the flow-model early in the production cycle before the deficiencies can be observed in the wells, so that pro-active action can be taken.

The basic idea behind this new method is to modify a given set of flow properties (e.g. porosity, permeability, cell volume…) along the streamlines so that the computed fluid fronts coincide with the observed fluid fronts derived from 4D seismic. The latter can be extracted from time-lapse seismic cubes with amplitude-based seismic attributes or 4D classification results.

The matching of fluid fronts with this method needs very few iterative steps, contrary to traditional history-matching techniques. This feature allows to reduce significantly the number of flow simulations run during the process. The use of streamline simulators is of key importance in this step. First, the inverse problem is reduced to several easy-to-solve one-dimensional problems. Secondly, the result of the matching is an average calibration of the flow properties along the streamlines from the injector wells to the fluid fronts. Hence, more frequent time-lapse seismic measurements give improved resolution to the calibration of the flow properties.

The method proposed speeds up significantly the calibration of reservoir models to observed fluid fronts and facilitates a more active use of 4D seismic in reservoir management.

The method is then demonstrated on different case studies.
Using Horizontal Wells to Sequester CO2 and Enhance Coalbed Methane Recovery: A Simulation Study of Operating Procedures
Authors: Sams W. Neal , Bromhal Grant S. , Jikich Sinisha A. , Ertekin Turgay , Smith Duane H.
Published: December 2007

Because of increased concern about anthropogenic carbon dioxide emissions, a pilot project is being implemented in northwest West Virginia to study the technical feasibility of carbon dioxide sequestration in unmineable coal seams. The project consists of four 3000 ft horizontal wellbores forming the exterior of a square with four horizontal wellbores at its center. Methane production occurs from all wellbores until the reservoir is sufficiently depleted, then the central wellbores are converted to carbon dioxide injectors while production continues from the exterior wellbores. In our simulations for this project, injection and production continue until the mole fraction of carbon dioxide in the produced gas reaches 0.1.

The design factors studied were the lengths and orientations of the central wells, while the operational factors studied were the pressures in the injection wells. We examined the cases where the injectors are oriented perpendicular to the exterior wellbores and where they are oriented toward the corners. The performance of a pilot project is also compared with that of a pattern in a fully-developed field.

For a pilot project, operating parameters that give the longest project life also yield the greatest methane production. On the other hand, for a developed field the main factor controlling methane production is sweep. Although the longest injectors have poor sweep efficiency, short injectors represent little improvement over the performance of intermediate length injectors, but they significantly lower production rates. Injection pressure has only a weak effect on total methane production in a developed field. Higher injection pressures result in slightly more methane left in place in unswept areas of the reservoir, but also result in a higher production rate. The sequestration performance for either case is controlled by a combination of sweep efficiency and average pressure in the swept area. The interaction of sweep and reservoir pressure on performance results in a maximum in performance for intermediate length injectors. For low anisotropy the diagonal injectors yield better sequestration performance, but for high anisotropy the perpendicular injectors with unequal lengths perform better. In all cases a long diffusion time constant places an upper limit on injection rates that also yield good performance.
Improved Reservoir Management Through Optimal Control and Continuous Model Updating
Authors: Brouwer D. R. , Nœvdal G. , Jansen J. D. , Vefring E. H. , Kruijsdijk C. P. J. W. van
Published: December 2007

There is a potential for large improvements in reservoir management by using optimization and model updating techniques in a closed-loop fashion. Here we demonstrate how the combination of the ensemble Kalman filter technique for continuous model updating with an automated adjoint-based water flood optimization algorithm leads to significant improvements in net present value (NPV) of the water flooding process.

Using the ensemble Kalman filter, both static parameters (permeabilities) and dynamic variables (pressures and saturations) are updated in the reservoir model as new production measurements become available. Other properties are assumed known in advance. At the start of the production process, in the absence of information on the permeability distribution, an optimal control strategy based on a homogeneous reservoir is used. Subsequently production data are at regular intervals assimilated with the ensemble Kalman filter, resulting in an updated estimate of the reservoir pressures, saturations and permeability field. Based on these updated parameters an optimal water flooding strategy is determined for the remainder of the production process. This process of model updating and optimization is continued over the life of the reservoir.

The methodology is applied to two synthetic examples, enabling comparison with traditional production strategies. Significant improvement in NPV, acceleration of oil production, cumulative oil recovery, and reduction of water production were realized. Results were close to those obtained with water flood optimization based on an a-priori known reservoir description. For one example the improvement in cumulative oil recovery is about 44 %, which is quite close to the improvement obtained for an a-priori known reservoir description.
The Heat Transfer Characteristics of Vacuum Insulated Tubing
Authors: Azzola J. H. , Pattillo P. D. , Richey J. F. , Segreto S. J.
Published: December 2007

Thermal effects in vacuum insulated tubing (VIT) have been studied in previously reported experiments2. VIT is usually characterized by a single thermal conductivity ( k -value) based on a one-dimensional radial heat transfer analogy. Despite its simplicity, however, this physical model masks the underlying complexity of the two-dimensional axisymmetric heat transfer field.

Recent theoretical insights have demonstrated that VIT behaves as a fin around the weld and coupling regions, where up to 90% of the overall heat loss can occur. As a result, VIT does not have a single k -value; instead it has a potentially wide range of k -values, depending on boundary conditions. Recent numerical and experimental investigations of vertically aligned VIT demonstrate the highly sensitive nature of thermal performance with respect to these boundary conditions1. With this insight, previous test data2 is reinterpreted in a more revealing light. It can be demonstrated that the 10-fold spread of k -values from these tests is attributable to explainable boundary phenomena.

Another issue which requires clarification is the k -value definition. A standard definition is presented here which 1) is physically related to the effective thermal conductivity of the vacuum and 2) is relatively stable for different VIT configurations.

Transient behavior, including startup, cool down during shut in, ground soak, and convection cell development will be explained, as well as the implications for long-term thermal stability.

The discussion concludes with calculations of k -value for VIT under significantly varied boundary conditions: different annular fluids, different soils, with and without interior or exterior coupling insulators, and using high-temperature steam injection.
Risk, Uncertainty and Optimization for Offshore Gas Asset Planning in Litoral Tabasco
Authors: Solis Romeo , Rojas Santiago , Ramírez Guillermo Bernal , Saputelli Luigi , Narayanan Keshav
Published: December 2007

Litoral Tabasco Integral Asset Management is planning to develop a series of recently discovered offshore gas fields by extensively planning, designing and deploying a world-class reservoir drainage architecture that efficiently produces gas reserves and optimally uses existing offshore surface facilities. The objective of this development is to recover 373 bcf of dry gas from five recently discovered fields (Hap, Akpul, Uchak, Isiw and Chukua) in the most cost-efficient manner and contribute to Mexico's goals of increasing its gas supply.

We develop a case study planning process by using a strategy for balancing reservoir uncertainties (rock properties), optimum field development scenario (rate schedule and start time) and associated risks in the capital expenditures (price inflation and discount factor).

The methodology has proven to optimize capital investment, by selecting an optimum scenario, namely one that best balances risk and uncertainty, and maximize asset profitability. Faster decision making process is enabled by a series of key digital oilfield components, such as an integrated framework for multi-disciplinary and multi-scenario modeling and optimization, and the potential for continuous real-time adaptation of the development plan to prevailing reservoir and market conditions.
Modeling Polymer Displacement in Hydraulic Fractures at the Pore-Scale
Authors: Balhoff Matthew , Thompson Karsten E.
Published: December 2007

Proppant-packed fractures provide a relatively low-resistance pathway for the recovery of reservoir fluids. However, residual polymer left over from the proppant transport can greatly reduce the fracture conductivity and, therefore, productivity. Poor fracture cleanup is often observed and it is important to understand the fundamental reasons behind the phenomenon. It is believed that non-Newtonian fluid rheology, viscous fingering, and leak off may all contribute to the problem. The vast majority of fracture cleanup modeling has been limited to continuum-scale modeling. However, important aspects of the cleanup problem may be affected by pore-scale events. For this reason, it is desired to model flow at the pore-scale to obtain a better understanding of the qualitative fingering patterns and quantitative flowrates in a fracture during the cleanup process, as a function of basic parameters such as proppant size, fluid rheology, and imposed pressure gradients. These pore-scale results may help explain the fundamental reasons for the observed poor polymer cleanup and give insight on how to improve cleanup in the future.

In this work, computer-generated, random sphere-packs are used to approximate a small portion of the propped fracture. The sphere-packs are transformed into physically representative networks of pores and connecting throats. The network models are used to model flow through the proppant pack at the pore-scale. Modeling the dynamic cleanup process consists simulating a low-viscosity, Newtonian fluid (e.g. water) displacing a high-viscosity, non-Newtonian polymer from the pack. A novel approach is used to couple the network to a continuum model for flow in the reservoir, and realistic boundary conditions are used that allow the displacing fluid to flow in from the side of the fracture. Current modeling is used to better understand displacement behavior under different conditions. Future results will be upscaled and integrated with large-scale reservoir models.
Role of Surveillance in Improving Subsea Productivity
Authors: Amin Amin , Smedstad Eric , Riding Mark
Published: December 2007

A number of industry sources have identified the need to improve overall productivity of subsea wells through the application of monitoring and control systems in the wellbore and on the seabed. To achieve this goal, two elements must be mastered: information and measurements of key attributes of the well/reservoir productivity, and a means to change and command the process, preferably through remote-controlled devices rather than traditional well intervention.

With the advent of intelligent wells, the second element has been addressed through a variety of process control devices used at different points in the wellbore and on the seabed. However, the growth of this process was limited by the absence of effective information gathering and data transmission systems in subsea wells, which remained underdeveloped compared to other subsea hardware. This resulted in systematic information bottlenecking caused by poor connectivity between the wellbore and the rest of the subsea infrastructure.

The paper introduces a complementary surveillance system that works with existing subsea devices and highlights its role in gathering and transmitting well and subsea data reliably and in sufficient time needed to maintain optimal production. In particular, the system targets high data traffic areas in order to de-bottleneck the subsea transmission systems and provides wellbore monitoring and inflow quantification. A continuous data highway is now available to both wellbore and subsea-based measurements, leading to improved monitoring and control of the entire subsea system.

The applications and benefits of the system are demonstrated through a case study. The study discusses the role of the surveillance system in bringing the productivity index of subsea wells to be in par with the platform wells. It also demonstrates the need to rethink the flow assurance process as increasing number of distributed seabed measurements become available to the subsea industry and tie-back distances increase to make the best use of expensive host facilities.
Can You Have Probable Without Proved Reserves?
Authors: Etherington John R. , Hunt Elizabeth J.
Published: December 2007

One of the unresolved issues in reserves evaluations is the continuing practice of assessing probable reserves for projects where no proved reserves have been claimed.

The practice typically arises in the early delineation stage. The initial assessment of best estimate recoverable quantities (proved plus probable ("2P")) meets internal criteria sufficiently to justify development. While the project is potentially commercial, it may not meet all the criteria for disclosure of proved reserves under regulatory guidelines. In this paper, it is assumed that governing agency is the U.S. Securities and Exchange Commission (SEC).

The issue is an interesting exercise in logic. Is probable a discrete entity or is it merely the incremental volume beyond proved in a 2P estimate? If no part of the accumulation meets the proved reserves criteria, then can the total 2P estimate be classified as probable reserves?

The resolution may lie in more careful application of the full resource classification published by the Society of Petroleum Engineers (SPE) in 2000. The SPE recognized that ambiguity may exist between their definitions of uproven reserves and contingent resources. While reserves are accumulations that are recoverable under current conditions, this same distribution of volumes would be classified as contingent resources if technical and/or commercial risks prevent development commitment. The separation of risk and uncertainty in the assessment process is critical.

One solution is to initially classify volumes associated with all new discoveries as contingent resources with its internal certainty categories (low/best/high estimates) until such time as the SEC proved reserves criteria are satisfied. As contingencies are removed, volumes would then be transferred to reserves subdivided into parallel certainty categories of proved (1P), proved plus probable (2P) and proved plus probable plus possible (3P).

It may or may not be that simple; this paper critically examines associated issues with examples.
A Methodology to Discover Contaminated Data in Spatial Databases
Authors: Wei Mingzhen , Sung Andrew H. , Cather Martha
Published: December 2007

In this information age, the problem of data quality deserves more attention than it is getting. Contaminated or corrupted data are data that were misunderstood or misrecorded in data sets. The success of the petroleum industry relies upon a combination of multi-dimensional reliable information and proper cross-disciplinary techniques. Contaminated data can mislead the strategic-level decision making and cause operational failures.

This paper presents a methodology to identify contaminated data in large spatial data sets in the data quality control cycle. Graphical and quantitative spatial outlier detection methods are discussed. All these methods are different for identifying spatially abnormal data, both in mechanisms and results. This paper discusses these methods and compares their advantages and disadvantages. The effectiveness of these methods is evaluated by using a real spatial database, the Produced Water Chemistry Database (PWCD) in New Mexico.
Mechanisms and Main Parameters Affecting Nitrogen Distribution in the Gas Cap of the Supergiant Akal Reservoir in the Cantarell Complex
Authors: Rodríguez Fernando , Sánchez José L. , Galindo-Nava Agustín
Published: December 2007

An analysis of the mechanisms and main parameters that determine the distribution of nitrogen in the gas cap of Akal, a super giant naturally fractured reservoir in the Cantarell Complex, during nitrogen injection for pressure maintenance, is presented in this paper.

The analysis follows from a dual porosity compositional numerical simulation study aiming at history matching the behavior of the Akal field, observed before and after nitrogen injection started, particularly the matching of nitrogen concentrations measured in wells invaded by the advance of the gas-oil contact and in other gassed out wells located at the top of the reservoir.

Molecular diffusion and natural convection were considered in matching the observed gas-cap nitrogen distribution of the Akal reservoir, besides other conventional transport mechanisms. It was found that gravity drainage, effective molecular diffusion and the partition of total porosity between matrix and fractures are the main parameters controlling flow dynamics and affecting the distribution of nitrogen in the gas cap. It was also found that these parameters have an impact on the diffusion of nitrogen into the oil column. Analysis of results also shows that gas-cap gas and nitrogen gravity differences play an important role in the distribution of nitrogen in the gas cap and that natural convection, under current conditions, is not relevant. Another finding is that the main transfer mechanism for nitrogen into the gas-cap matrix blocks is the substitution of the gravity-drained oil and that exchange by molecular diffusion is very slow.

In matching the distribution of nitrogen in the gas cap, distinction between small-scale secondary porosity, which dominates fluids flow locally, and large-scale secondary porosity, which dominates fluids flow at the scale of the reservoir, was required. The way this requirement was handled in the dual-porosity model is described.
A New Method for the Determination of Gas Condensate Well Production Performance
Authors: Xiao J. J. , Al-Muraikhi Ahmad J.
Published: December 2007

The determination of gas condensate well production performance when a well's flowing bottomhole pressure is below the original gas dew point requires condensate banking to be taken into account. This can be accomplished with reservoir simulation models with fine grids near the well. The calculation can be significantly speeded up with relatively coarse grid models by applying the two-phase pseudopressure technique.

The two-phase pseudopressure technique, however, cannot be applied independently for well performance evaluation since it requires the well production gas-oil ratio as an input. Simplified methods have been published recently to calculate gas condensate well production deliverability without the use of reservoir simulators. This paper presents a new calculation method. The new method models condensate banking by considering the combinational effects of condensate dropout (PVT effect) and condensate accumulation (relative permeability behavior). This new approach gives a better understanding of the mechanisms involved.

The proposed method is verified with simulation data presented in the literature. The new method gives results that are in good agreement with published data for vertical, fractured and also horizontal wells. High gas velocity impact near the wellbore (non-Darcy flow and high capillary number effect) can be incorporated into the method. As with other simplified methods, the new technique allows quick well performance evaluation as well as full field modeling involving multiple wells and surface facilities without reservoir simulations.