bluuebunny/crossref_metadata_2025 huggingface dataset:
Field Experiences with a Combined Acid Stimulation and Scale Inhibition Treatment
Authors: Smith P. S. , Cowie L. G. , Bourne H. M. , Grainger M. , Heath S. M.
Published: December 2007

Calcium carbonate scale impacts oil production in a large number of fields worldwide. This scale is generally managed by acid washing to remove the scale and/or by performing scale inhibition treatments. The methodology adopted is usually cost driven with high cost operations generally selecting scale prevention rather than removal.

Recently reported work 1 showed the potential to integrate scale removal and scale inhibition treatments into a single package, offering clear economic and technical advantages. The combined treatment inherently reduces well intervention costs and well downtime, and protects the value added by the scale removal treatment - by assuring that all of the zones that are stimulated are also inhibited.

Combining acid stimulation chemicals and scale inhibitors is by no means a simple process. Compatibility between the acid, the acid additives and the scale inhibitor presents a significant issue in both live and spent acids. This paper will examine these technical challenges and describes the desired properties of such combined systems. Case histories of recent field trials of combined scale removal and inhibition treatments will be presented, including details of job design, job execution and post-job evaluation. Data demonstrating the scale inhibitor return profile in these treatments will be shown, and lessons learnt from the initial trials will be discussed. Comparative performance data for previous acid treatments will also be presented.
Economy and Technology Balance in Well Life Cycle Management
Authors: Matanovic D. , Gaurina-Medjimurec N. , Rajkovic D. , Kristafor Z.
Published: December 2007

Crucial in well life cycle management is an analysis of technology and economy balance from the beginning (well project) to the end (well abandonment and environment sanitary improvement).

On the basis of over one thousand drilled oil, gas and geothermal wells (since 1950.), on-shore and off shore, over fifty thousand completions and workovers and about five hundred abandoned wells, an overall analysis will be done to state problems and solutions considering the technology to economy balance.

In the paper we will try to point out phases in well life cycle that are of the greatest influence on economy.

Finally, the optimal way of well or entire field abandonment and produced waste management will be discussed from technological and economical standpoint.
Numerical Modeling of Salt Precipitation During Produced Water Reinjection
Authors: Rocha A. A. , Frydman M. , da Fontoura S. A. B. , Rosário F. F. , Bezerra M. C. M.
Published: December 2007

This paper presents a coupled chemical-hydro-mechanical model for the evaluation of the fluid behavior around an injector well taking into account insoluble salt precipitation (barium and strontium sulfate). A salt precipitation model is developed and coupled with the ion transport equation describing the ion movements and reactions through porous media. The finite element method has been used to obtain the solution for the coupling amongst the ion transport, the fluid flow and the mechanical response of the rock. A computer program has been developed to solve this highly nonlinear problem. Results of an experimental test1 carried out in a sand pack with the analysis of the barium sulfate crystal growth was selected as benchmark to test the computer program developed using the methodology described above, showing an excellent agreement between the numerical and the experimental results.
Evolving State of Ecological Risk Assessment at the Former Guadalupe Oil Field, California
Authors: Lundegard P. D. , Garcia G. F.
Published: December 2007

The former Guadalupe Oil Field, in the central California coastal region, is the location of past and ongoing efforts to assess ecological risk. While there are a number of chemicals of concern, the main focus of the risk assessment is a crude oil thinning agent, known as diluent. Approximately 8 million gallons of diluent were accidentally spilled within the 3000 acre property during its 45 year history of use. The risk assessment must consider the hundreds of plant and animal species, both terrestrial and aquatic, that inhabit the site and its neighboring properties. Among these plants and animals are at least 40 threatened and endangered species.

The first efforts to evaluate ecological risk at the site were initiated during a Natural Resource Damages (NRD) lawsuit. These efforts focused on developing a case for biological injury and establishing a basis for financial damages. Since settlement of the NRD lawsuit in 1998, risk assessment has focused on providing input to decision-makers so that objective remediation goals can be established. This paper reviews the status of the ecological risk assessment, its role in site decision-making, and specific technical challenges that have been encountered.
Laboratory Testing of High-Pressure Coiled-Tubing Drilling System
Authors: Cohen J. H. , Maurer W. C. , Leitko C. C. , Gwilliam W. J.
Published: December 2007

A new high-pressure coiled-tubing (CT) drilling system has been developed with support from the DOE that drills 2 to 3 times faster than conventional CT motors. Downhole motors have been developed that utilize diamond thrust bearings, titanium flexshafts, high-pressure rotor/stator sections and other advanced features that allow these motors to operate at high pressures. Laboratory tests have been conducted using the high-pressure system to cut 1 to 2 inch deep helical slots in wellbore walls to remove formation damage (patent pending) and to drill cement out of drillpipe at rates up to 1,400 ft/hr compared to 60 ft/hr for conventional motors. This jet-drilling system can also be used to remove barite scale from tubing, to clean slotted liners, to ream holes at high rates, and to under-ream when drilling with casing. The high-pressure system will be field tested and commercialized during the next phase of this DOE project.
Optimization of Decision Tree and Simulation Portfolios: A Comparison
Authors: Erdogan M. , Mudford B. , Chenoweth G. , Holeywell R. , Jakubson J.
Published: December 2007

This paper compares the results of carrying out portfolio analysis and optimization of a collection of exploration projects that have been modelled using both decision tree and stochastic simulation approaches. The collection of exploration projects comprises the opportunity set for the portfolio. In the decision tree approach, selecting a few scenarios from the full distribution and assigning probabilities to those scenarios approximates the range of possible project outcomes. In contrast to the decision tree method, stochastic simulation proceeds by assigning probability distributions to key input variables. In a single iteration of the simulation each of these variables is randomly sampled, with allowances for dependencies, in order to calculate cash flow and economic parameters such as net present value. This process is repeated many times for each exploration project to produce a distribution of economic outcomes. Earlier studies have shown the difficulty of adequately characterizing projects with large uncertainty using the decision tree approach. In this paper we take the comparison between decision tree and simulation methodologies to the next stage by looking at the effect on portfolio selection of the differing evaluation methodologies.

The portfolio analysis is carried out using the optimization methodology pioneered by Markowitz to estimate the combination of projects, which produces the maximum NPV for a given level of risk. Comparison of the project selections made for the decision tree and stochastic simulation portfolios shows significant differences between the project selections required to produce an efficient portfolio for the two different evaluation methodologies. This result implies that, even if a decision tree model could be constructed which adequately characterized the uncertainty in a project, the optimization of a collection of projects modelled using decision trees may not yield an efficient portfolio if the full range of uncertainty were to be considered.
Probabilistic Prospect Evaluation With Spreadsheets
Authors: Hooper H. T.
Published: December 2007

This case history describes the creation of a spreadsheet-based, Monte-Carlo economic model for exploration prospects. Looking at "probabilistic economics" instead of "probabilistic reserves" allows decision-makers a better understanding of the potential outcomes associated with a prospect. Although commercial software exists for such analyses, creating this spreadsheet model proved more efficient in this case through the utilization of spreadsheet algorithms already in place. The simulation model is now used routinely in-house for individual prospect analysis and is considered a viable alternative to the commercial packages.

A probabilistic reserve distribution can be generated using uncertainty distributions for volumetric input parameters and then sampling the input distributions through Monte Carlo simulation. After sampling the input distributions and calculating the corresponding reserves many times, a probabilistic distribution of reserves is created. Often in rank exploration prospects, a given reserve size is not a unique solution to the volumetric equation. Different reserve scenarios, e.g. combinations of lateral extent and recovery per acre, may yield the same reserve size but may differ in capital requirements by an order of magnitude or more. In these cases especially, it is appropriate to consider not only the range of reserve outcomes resulting from the full range of possible scenarios, but also the range of corresponding economic outcomes for the many possible scenarios. Meanwhile every single realization within the range of outcomes must be realistic. Furthermore, by calculating economics stochastically, other probabilistic methods such as mean reverting price models may be incorporated.

The spreadsheet economic model was used because it provides a significant advantage where evaluation time is limited. For the evaluation described in this paper, the analysis of exploration prospects was accomplished within a very short time frame. As the prospects were in remote locations outside of the Lower 48 and estimation of capital expenditures and production taxes was complicated, a spreadsheet program provided the desired degree of flexibility. The model was created quickly since spreadsheet algorithms already existed to calculate reserves, capital, production taxes, mean reverting price forecasts, and AFIT economics.

This paper describes how five existing spreadsheet algorithms were integrated to develop a robust Monte Carlo economic model for exploratory prospect evaluations. Emphasis is placed on the advantages of using the spreadsheet platform to establish dependencies between variables and to facilitate customization of the model.
Subsurface Appraisal: The Road From Reservoir Uncertainty to Better Economics
Authors: Demirmen Ferruh
Published: December 2007

Subsurface or field appraisal is an activity aimed at reducing reservoir uncertainty. For optimal results from appraisal, it is necessary to have a clear understanding of appraisal, to distinguish between two types of appraisal, and to use a decision tool that ties reservoir uncertainty to potential economic consequences in the event of development. The tool proposed is "value of information" (VOI), which provides a consistent, auditable criterion for decision-making. In the case of optimization appraisal, VOI enables an analysis of the economic merits of a series of development scenarios with and without appraisal information. The probability distribution of the underlying uncertainty, e.g. reserves, is a key ingredient. A truly cross-disciplinary effort is called for. The ultimate goal in appraisal is to reduce economic risk with regard to field development.
Residual Hydrocarbon Saturations in the Maui Field
Authors: Verbruggen M. H. W. , Adams S. J.
Published: December 2007

Residual gas and oil saturations and relative permeabilities have been quantified in the Maui Field. Additional Special Core Analysis (SCAL) laboratory data was acquired using decane/brine and oil/brine centrifuge experiments. Such measurements are considered most representative of water influx into gas and oil reservoirs respectively. In the case of oil, ageing of the samples to restore wettability is shown to be essential. Relative permeability curves were obtained by history matching the raw experimental production data via numerical simulation. This process corrects for experimental artefacts and limitations, resulting in a significant reduction in residual hydrocarbon saturations compared to typical analytical interpretations. A correlation using a form originally proposed by Land has been used to relate the residual hydrocarbon saturations to the initial water saturations. In-situ field measurements of hydrocarbon saturations using pulsed neutron logs in water-flooded zones are shown to support the SCAL data.

The work described represents the state-of-the-art in quantification of residual hydrocarbons. In particular, the combination of the sampling methodology, the experiment design, the advanced numerical interpretation and the in-situ measurements is material previously unpublished in technical literature. The results are significant in that they show lower residual saturations than commonly expected, while adding to the limited published data on residual hydrocarbons. Use of lower residual hydrocarbon saturations together with the appropriate relative permeabilities in reservoir simulation has resulted in improved reservoir history matches and has had a positive influence on Maui Field reserves. Application of these state-of-the-art techniques to other water-drive fields is likely to have a similar impact.
West Seno Field Development: the First Deepwater Field in Indonesia
Authors: MacArthur J. , Inaray J. , Setiawan Y. , Terry A. , Palar S. , Darmono S.
Published: December 2007

West Seno Field is located in deepwater offshore East Kalimantan, Indonesia. The field was discovered in August 1998 and after appraisal drillings, the field was deemed commercial. Efforts are underway now for a target initial production in fourth-quarter 2002. The Seno anticlinal structure is an elongate, 4-way dipping closure, about 70 square kilometers in area. A total of 205 ft of oil was found by the discovery well, West Seno-2. Subsequent well tests (DST) confirmed the producibility of the hydrocarbon-bearing sand. The field lies in 2400 to 3200 ft of water hence upon production, this will be the first producing deepwater field in Indonesia. Two Tension Leg Platforms (TLP) with one Floating Production Unit (FPU) and supporting pipelines are envisaged to handle oil and gas production with the peak rates estimated to be 60 MBOPD and 150 MMCFD respectively. A blue print to develop this field has been approved by the Indonesia government. The plan of development lists in the expenditures and the infrastructures required to bring in this 280-MMBOE field to production. This paper is the summary of the plan of development.
Advances in Petroleum Reservoir Monitoring Technologies
Authors: Islam M. R.
Published: December 2007

Most oil fields do not produce more than 45% of the oil-in-place, even after enhanced oil recovery schemes have been applied. Most of this unproduced oil is missing because most displacement techniques by-pass significant portion of the original reserve. Finding this missing oil can lead to significant economic windfalls because the infrastructure for additional oil recovery is already in place and the cost of production is likely to be minimal. In this paper, all existing monitoring techniques, including 4D seismic and downhole seismic sensors, are reviewed. This is followed by a comprehensive review of emerging technologies in subsurface monitoring. These techniques include multi-well seismic, electrical resistivity tomography, electromagnetic and ultrasonic imaging, acoustic and fibre-optic imaging, as well as laser/infrared or MRI/NMR visualization near the wellbore region.

A detailed analysis indicates that for an accurate reservoir engineering analysis, geostatistical models should have information of 1m scale. This is the only scale that would satisfy the representative elemental volume (REV) requirement of an enhanced oil recovery (EOR) system. This scale length is orders of magnitude higher than that of core samples and at least an order of magnitude lower than the conventional seismic data. This data gap constitutes the weakest link between geophysical information and reservoir engineering. Any attempt to reconstitute the reservoir without information regarding petrophysical properties and fluid saturations in the 1m level, one risks falling into the trap of multiple solutions – a typical problem of history matching through reservoir simulation. To obtain a resolution of 1m scale, one must investigate the possibility of using 50-2000 Hz seismic frequency range. While this seismic range cannot be used with vertical seismic profiles (VSP) because of the travelling distance constraints, multiwell imaging can be used with multi-component receivers. This system, in combination with borehole seismic sources, can provide one with the desired resolution. The same system can be used in combination with resistivity tomography, a method that has recently given satisfactory results for tracking ground-water contamination. The images can be further refined with acoustic and fibre-optic imaging techniques. These techniques can provide satisfactory details to track viscous fingering, wormholes, and other time-dependent properties of an active reservoir. Finally, infrared/laser or MRI/NMR imaging of a wellbore is still in its nascent state of development, but holds great promises for the future applications of real-time monitoring and eventual dynamic reservoir management.
Enhanced Production in Horizontal Wells by the Cavity Failure Well Completion
Authors: Wang Yarlong , Tremblay Bernard
Published: December 2007

High viscosity and weak cementation existing in heavy oil reservoirs present great challenge to us in rich heavy oil reservoirs in Northwestern Canada for production and well completion. On one hand, we attempt to increase the exposure of the reservoir to the well so that we can maximize the production potential. On the other, we must select an adequate strategy for well completion in order to maintain the integrity of the well during production. A well completion strategy by cavity-failure mechanism has been used for coalbed methane and heavy oil production during SAGD. The success of their previous operations leads us to investigate the feasibility of such a well completion strategy in both cold production and other enhanced production process in poorly consolidated heavy oil reservoirs. A coupled reservoir-geomechanics model is developed. A black-oil model is fully coupled to a Mohr-Coulomb type elastoplastic geomechanics model. An open hole condition with slotted liner is simulated. The wellbore pressure is rapidly reduced to create a massive dilation zone near the well so that the intact porosity can be mobilized. Consequently, an enhanced zone near the slotted liner with a higher permeability can be generated, leading to negative skin factor during the production. The field conditions reported in Cold Lake are used to evaluate our study and simulations.
Successful Mud Acid Stimulations Maintain Productivity in Gravelpacked Wells at Heidrun
Authors: Wennberg K. E. , Vikane O. , Kotlar H. K. , Poitrenaud H.
Published: December 2007

The Heidrun Field is located on the Haltenbanken area in the Norwegian Sea was discovered in 1985, and has been producing since October 1995. The hydrocarbons are present in 3 reservoirs of Jurassic age, the high quality Fangst group, and the more heterogeneous Tilje and Are formations. The initial reservoir pressure is 250 bar and the reservoir temperature is 88 °C. The drainage strategy utilizes injection of produced gas and seawater for pressure support.

The reservoir sands are in general poorly consolidated and contain fairly high quantities of clay with kaolinite content well above 25 % in Fangst and Tilje. Most of the producing wells have sand control devices (gravel pack or screen) installed. The cased-hole gravelpacks in the high-permeable Fangst formation have shown extensive productivity decline after water breakthrough. Initial oil rates in these producers exceed 6000 Sm3/d, but the rates drop rapidly even at very low water cuts. A team of engineers and scientist from the operator and service companies analyzed the problem and started to develop solutions. Migration of kaolinite fines was identified as the major cause for productivity decline. A mud acid/clay acid system to remove damage and maintain productivity was designed. Several successful treatments with this fluid system have now been carried out. Detailed monitoring and analyses of the fluids that are backproduced after the treatments have proven to be crucial in continuous improvement of the stimulation system. An extra oil production of approximately 500 000 Sm3 is ascribed to successful stimulation treatments in the first year following the treatment. It is now recognized that successful acid stimulation will be necessary to maintain production rates from the Heidrun field in years to come.

Details about the acid stimulation design, pumping schedule and ion composition analysis of the spent acid return will be given in the presentation.
Mechanisms of Arch Instability and Sand Production in Two-Phase Saturated Poorly Consolidated Sandstones
Authors: Bianco L. C. B. , Halleck P. M.
Published: December 2007

This paper addresses the problem of instability and sand production in poorly consolidated sandstones subjected to a water influx. New phenomenological evidences were collected in a series of unprecedented experiments, improving the understanding on the sand production mechanisms. Two different groups of experiments studied behavior, morphology, and stability of sand arches in two-phase saturated sand samples. The effects of changes in fluid flow velocity and water saturation were deeply analyzed, and the distributions of porosity and water saturation in the arched region were mapped during the sand production process.

The results showed that single-phase saturated sands did not develop enough cohesive strength to support a stable arch and sand was produced massively, generating a high-porosity and unstable zone. However, a small increase in wetting-phase saturation developed enough cohesive strength to stabilize an arch, reducing sand production. Within a defined range, a progressive increase in wetting phase saturation did not impact arch stability and sand production was sporadic and minimum. As the wetting-phase saturation exceeded critical value instability occurred; the arch was enlarged and massive amounts of liquefied sand were produced. A decrease in the non-wetting phase flow rate did not affect the stability of the arched zone and reduced sand production. Finally, it was observed that dilated, unconfined and agglomerated blocks of sands, with uniform porosity and wetting-phase saturation, filled the space inside the arched region.
Scale Inhibitor Squeeze Treatment Strategy on Heidrun
Authors: Wat Rex , Selle Olav Martin , Børstad Hege , Vikane Olav , Hagen Thomas , Chen Ping , MacLean Alan
Published: December 2007

The Heidrun Field, located on the Haltenbanken area, is one of the major fields which came on stream in the Norwegian Sea since 1995. At peak production the field is capable of producing 38,000 m3 of oil and 6 MSCM gas per day. It also takes in 22,000 m3 of injection water each day. The field is characterised by the large clay content in its three formation sands Fangst, Tilje and Are. Most of the producing wells are installed with gravel pack or screens due to poor sand consolidation. The reservoir has a bottom hole temperature of 85 °C and a relatively low reservoir pressure of 250 bar, hence seawater injection for pressure support is needed. With Ba++ level ranging between 180 to 700ppm in the different formations, the potential for downhole sulphate scale deposition within both the formation and the gravel pack, after seawater breakthrough is extremely high. A scale control strategy based on preventive squeeze treatment is therefore desirable to minimise any formation damage caused by such deposition.

However, two treatments using water based scale inhibitor carried out prior to 2000 had caused significant process problems during back flow. Severe emulsion problems were experienced, resulting in process upset and poor water quality. The low reservoir pressure meant that long clean up periods were needed with much deferred oil production. Such undesirable side effects make the operator less willing to take preventive action. Over the past 6 months, with the availability of an oil based scale inhibitor and a new ‘biodegradable, green’ water based product, we have successfully treated a number of oil producers with a wide range of water cut. In all cases, there was minimum process upsets on flow back and resumption of oil production shortly after. In the case with the ‘green’ product, it is most encouraging since this is the FIRST North Sea application and the chemical offers a high degree of biodegradability. This contributes significantly to the step improvement on the environmental impact when the return of a large peak of unwanted chemical is often associated with a traditional water based squeeze. In this paper we shall describe the processes of selection, evaluation, design, implementation and follow up of these new treatments. Based on these results, we have now established a treatment strategy which can be applied to wells producing from the different formations and with various water cut.
The Precipitation of Salt in Gas Producing Wells
Authors: Kleinitz W. , Koehler M. , Dietzsch G.
Published: December 2007

The entrainment of reservoir water from gas reservoirs and the associated precipitation of dissolved salts in the late production stage can impair the productivity and may even result in the abandonment of wells, even in reservoirs without active edge water drive. The causes of precipitation of dissolved salts from the entrained water, the chemical composition and plugging behaviour of the precipitates, as well as stimulation concepts with field results are discussed.

On the basis of the thermodynamic equilibrium between reservoir water and gas, on the one hand, and between the dissolved salts and the reservoir water, on the other hand, the effect of the reservoir pressure on the aqueous phase is investigated, and the mechanisms of the transport and precipitation of salts are explained.

Special emphasis is placed on early identification of downhole salt precipitation on the basis of the chemical composition and derived ionic parameters of wellhead water samples from different gas wells. The results obtained with water from Rotliegende, Dolomite and Bunter reservoirs are discussed. Experience gained in operations and stimulation with the measures thus derived for controlling the salt problems is described.
Numerical Modeling of Fracture Propagation Induced by Water Injection/Re-Injection
Authors: Longuemare P. , Détienne J-L. , Lemonnier P. , Boutéca M. , Onaisi A.
Published: December 2007

The evolution of water-injector injectivity is a complex phenomenon because of the opposite effects induced by thermal fracturing and formation damage. A numerical model HydFrac, based on a two-phase thermal reservoir simulator including descriptions of fracture mechanics and formation plugging by injected particles, is first presented. Special attention is paid to the analysis of fracture closure rate during injection shut-in and to the description of formation damage. The results show the importance of injection duration on fracture closure rate during shut-in. On the other hand, a case including a first step of clean water injection and a second step of produced water re-injection is presented. The obtained results indicate a stabilization of fracture length at the end of clean water injection followed by a rapid increase during produced water re-injection. The evolution of the effective fracture width is analyzed to indicate the start of fracture filling by particles.
Energy Strategies: An Industry View
Authors: Kircher John E.
Published: December 2007

I feel like the man in the middle here today, sandwiched between Mr. Lovins and Mr. Guthrie on the one side and Miss Skelly and Mr. Lower on the other. You've had two tastes of this energy sandwich thus far, and now its my turn to try to add some flavor, and hopefully a little meat, to the menu. I only hope I don't spoil your appetite for what follows.

I do want to comment the program committee for bringing the participants in this panel together today. The groups and the participants in this panel together today. The groups and the points of view we represent cover the spectrum of significant points of view we represent cover the spectrum of significant opinion that must go into any resolution of the energy problem. Without input from any on e of the five - - environmentalists, government, industry, the public or the media - - any resolution of the energy issue would be incomplete, and thus probably also unsatisfactory.

Our comments, and the discussion that follows, are really a microcosm of the larger debate that has been taking place across the nation for the last few years, a give-and-take about energy that has culminated in the National Energy Plan and the actions that have been taken by Congress regarding it during the past several weeks.

Bear with me for a few minutes while I recap what I perceive our energy situation to be today.
Porosity Correction Method Developed for a High Vertical Relief Field in Eastern Venezuela
Authors: Clark Robert A. , Leza Fernando , Hetzel Allan , Minicucci David , Rigatti Vincent
Published: December 2007

A method has been developed that allows the estimation of porosity as a function of reservoir depth in high vertical relief fields. Porosity is known to decrease as net overburden pressure increases. This porosity reduction in turn leads to large reductions in reservoir permeability, the end result being a significant reduction in productive pore volume, net pay, and well productivity. The Eastern Overthrust Fields in Venezuela's El Furrial Trend produce from thick Miocene to Cretaceous sandstones and have very large hydrocarbon columns (two to three thousand feet is not unusual). Therefore, significant deterioration in pay quality is observed in the downdip areas. Using data from wells drilled in the Repsol/YPF Quiriquire Block, we observed that it was difficult to understand the true nature of the reservoir sands because the data was distorted by reservoir compaction in downdip wells. A method was developed to eliminate the distortion introduced by depth and overburden stress in porosity logs. This technique allows the well data to be interpreted as if all the wells had been drilled at a common datum. Once the undistorted data is interpreted and contoured, the data is re-shifted up or down using a depth grid map. Reservoir property grid maps can be prepared which better represent the sandstone properties at the depth at which they are found today. These maps can then be used in reservoir simulators to match and predict reservoir volumes and performance. The proposed method is most useful in development situations where there is sparse well control. Therefore, our first application has been in the Repsol/YPF operated Tropical Field, a 1998 discovery. Using this method, we prepared a reservoir description that depicts undrilled downdip areas much more accurately than would be possible using conventional methods. The new method resulted in large changes in our estimates of hydrocarbons in place and reserves and significantly impacted future development plans.
Dynamic Processes of Multiphase Flow in Subsea Flowline/Riser Systems During ESD Valve Shut Down
Authors: Chin Y. Doreen , Xu Zeng-Gang
Published: December 2007

Multiphase product transportation from offshore is facing the challenges of deepwater exploration and long-distance tieback. Prior predictions of the multiphase flow behavior, both steady state and transient, are crucial for successful design and operation of offshore facilities. The pressure surge and thermal stresses caused by transient multiphase flow during emergency shut down (ESD) are critical design criteria for pipeline systems.

Numerical methods have been developed to simulate the subsea HIPPS/ESD shut down and the ensuing system transient behaviors. These methods are able to predict pressure and temperature response during and after ESD valve closure. The analytic predictions are used in the design of deepwater pipeline and riser systems.

This paper demonstrates the use of transient multiphase flow analyses in the design of a deepwater subsea pipeline and riser systems. The pressure and temperature responses, and the pressure and temperature profiles from wellheads to the platform are investigated. The system design criteria are validated. The study improves the understanding of transient process in multiphase flow pipelines, and will benefit the deepwater production system design.
Compositional Variability in the Horizontal Section of Re-Entry Well, Orocual Field, Monagas State, Venezuela
Authors: Parra G. , Carvajal G. , Guevara J.
Published: December 2007

The description of the reservoir heterogeneities could be described utilizing diverse tools, one of these, the gas chromatograph in reentry wells and new horizontal wells. One of these wells is located to the northwest of the field, the objective was the base sands of the Las Piedras Formation, with 1425 feet of horizontal section. The analyzed parameters were: the Gas Ratio, relying on these outputs it is possible to estimate the API gravity. The Wetness Ratio (Wh) involves the light and heavy part of the mixture, this parameter by itself, estimates the gravity of the analyzed fluid with certain grade of confiability. The Balance Ratio (Bh) compares the light an the heavy fraction. The Character Ratio compares the components of the heavy fraction.
How To Determine The Best Exploitation Strategy From A Reservoir Simulation Model
Authors: Wences Acosta , Jesus Andrade , Hidalgo Oswaldo
Published: December 2007

A systematic approach showing a step by step procedure has been developed to guide the post calibration work of a reservoir simulation model to determine the best exploitation strategy.

The methodology presented on this paper appraises the best exploitation scheme based on economic analysis of reservoir simulation results.

Evaluation of mobile saturation distribution, cell productivity along with a net present value analysis provided a way to minimize the number of forecasts needed based on best-ranked cases.

The technique is able to estimate the optimum number of additional wells and their grid locations, to better define the most appropiate injection process and to determine the optimum injection rate.

A combination of primary, secondary and enhanced oil recovery exploitation strategies could be analyzed on the same scale to determine which is the most valuable in economical terms. Therefore, the best exploitation strategy can be selected.

The technique is an extension of a previously presented work to determine the optimum number of infill wells.
Chihuido de la Sierra Negra: Petroleum in Nonconventional Reservoirs
Authors: Comeron R. E. , Valenzuela M. E. , Ramírez J. L.
Published: December 2007

Chihuido de la Sierra Negra field is the main Repsol-YPF SA oilfield. It is located in the northeastern margin of Neuquén Basin. Main reservoir units are aeolian sandstones from Lower Troncoso Member (Huitrín Formation, Aptian) and Avilé Member (Agrio Formation, Hauterivian), with more than 1,000 MM stb oil in place. In 1993 oil was discovered in a thick basic intrusive body intruded pulling apart evaporitic rocks from Upper Troncoso Member (Aptian). The starting of the oilfield development was disappointing due to difficulties in locating wells with the 2D seismic that was available at that moment and the low production rates. 3D-survey acquisition, identification of fracture zones and drilling of horizontal wells increased dramatically the production rates. In this moment the field is under development, producing 12,000 bl/d with 11 wells.

This article discusses technical ideas, which have contributed the successful development of a nonconventional reservoir.
Enhanced Iterative Formation Evaluation of El Tordillo Field, San Jorge Basin, Argentina: Using Electrofacies and Production Prediction Index Determination
Authors: Stinco L. , Elphick R. , Moore R.
Published: December 2007

Formation evaluation, electrofacies and production prediction index determination based on inductive and deductive methodologies were completed in El Tordillo Field, North Flank of the San Jorge Basin, Argentina. The applied methodology consists of a number of steps including: data editing and normalization of the log data, modeling of the deep resistivity, electrofacies determination, standard log analysis, computing a production prediction index and summations. The 15 electrofacies determined were associated with the geological facies encountered within the field using cutting and core data. Consequently, porosity/permeability relationships were established between the core data and the productive electrofacies. These relationships permit to compute permeability from the computed effective porosity. A production prediction index was derived from the computed results which correlate well with existing production data. Zones of possible by-passed production were identified and some tested successfully. Finally, summations were used as input for original oil in place estimation, geological modeling and numerical simulation.
Saturation Distribution in a Linear System During Oil Displacement
Authors: Bail P.T. , Marsden S.S.
Published: December 2007

Displacement studies were performed on a Berea sandstone core in which a residual brine saturation was initially present. The oil saturation was determined as a function of time and distance by measuring the electrical resistance of segments of the core. Relative permeability was measured by a modified Penn State method for the same porous medium used in the displacement studies and static capillary pressures were determined for adjacent samples. The shape of the stabilized zone and recovery at water breakthrough were calculated using both measured and computed relative permeability data and these agreed with the experimental. The fraction of brine flowing at a given oil saturation was determined from saturation distribution data at various times and distances during the displacement runs by calculations based on the continuity equation. As the stabilized zone is formed, the shape of the fw vs So curve approaches a straight line for a certain range of saturations.

Introduction

A wide variety of experimental work on fluid displacement in porous media has appeared in the petroleum engineering literature during the last two decades. Along with this has appeared the theoretical treatment which forms the basis of our present concepts in this field. One of the first papers of background interest for this particular study was that of Leverett in which was developed the fractional-flow formula. A short time later Buckley and Leverett presented a form of the continuity equation as well as a method of using it and a simplified version of the fractional-flow formula (gravity and capillary-pressure terms neglected) to calculate the distance which any saturation has traveled in a given time interval. Terwilliger et al observed that after their water gas interfaced advanced a certain distance from the inlet of the system, all gas saturations over a certain interval beginning at the extreme flood front advanced at the same velocity. On the basis of the continuity equation they concluded that the change of fractional flow (gas) with saturation must be constant and this zone wherein all saturations moved at the same rate was named the "stabilized zone." They presented a method of calculating the saturation distribution in the stabilized and non-stabilized zones and obtained reasonable agreement between calculated and experimental values.
Structural Integrity Evaluation of the Heat Exchangers of a Hydrocracking
Authors: Edén Roberto D. , Roman Raúl
Published: December 2007

The objective of this work is to evaluate the structural integrity of the feed-effluent heat exchangers of the Hydrocracking of the Luján de Cuyo Refinery, belonging to Repsol-YPF S.A.

This equipment operates under a hydrogen load at a pressure of 2133 psi and at a temperature that varies between 300°C (572°F) and 400°C (752°F).

An inspection performed during the plant maintenance shutdowns revealed several cracks on the channel of one of the equipment. These cracks had a depth of 2.4 in and a length covering almost all the circumference of the channel. It was concluded after several studies that during the 27 years service period and being exposed to temperatures of above 300°C (572°F), the material suffered an embrittlement process due to a phenomenon known as Temper Embrittlement, and that at room temperature, the material was within the range of brittle fracture.

The commencement of the crack can be associated to the presence of hydrogen, to the effects of local stress concentration and to the plant maintenance shutdowns.

It was estimated that probably the growth of the cracks was produced by the thermal stresses originated during the plant starting and the plant maintenance shutdowns, and that it is facilitated by the embrittlement of the material and by the presence of hydrogen.

A risk evaluation was performed to analyze the feasibility of the continuous operation of the equipment under the described metallurgic conditions.

By accepting a criterion of risk decision, it was concluded that the operation under such conditions was "not desirable" and that situation must be accepted by a high rank executive officer.

A heat exchanger was shut down from service and used to perform several tests to determine its condition and therefore to provide the necessary technical background to the management decision making.

This study was highly significant because the remaining four heat exchangers were in similar metallurgical conditions than the equipment removed from operation and they should continue with their service operation.

Several studies were performed such as Charpy V tests, fracture tests and stress analysis calculations to determine the value of the stress intensity factor (J).

These studies were then used as technical background and support material for decision making in regards to the continuity of the service operation of the equipment for a certain period of time and under certain operational conditions.
Monetizing Gas Reserves: Trinidad and Tobago's Approach
Authors: Marcelle-De Silva J. , Jagai T.
Published: December 2007

The petroleum sector of the Republic of Trinidad and Tobago has made substantial contribution to its economy over the last 90 years. The major contribution during the period 1908 to 1995, came from oil production. Starting in 1996, there were major developments in the gas sector to the extent that revenues from gas production in 2000, exceed that from oil production. This paper reviews the natural gas industry and summarises the factors that contributed to the successful monetization of stranded gas reserves.

The Government of the Republic of Trinidad and Tobago (GORTT) have undertaken many initiatives that have promoted upstream exploration and production activities both onshore and offshore. As a result, a number of investors were encouraged to explore for and develop gas reserves resulting in the proved gas reserves increasing to 22 Tcf in 2000. Policies were also adopted which facilitated the development of a range of petrochemical and other gas based industries. These encouraged investments in the methanol, fertilizer, iron and steel industries. More significantly, Train 1 of a liquefied natural gas plant was commissioned in 1999, and the first shipment was exported in April 1999. This plant is being expanded, with the construction of Trains 2 and 3 presently in progress. Consideration is being given to Trains 4 and 5. The coming onstream of Trains 2 and 3, together with an additional ammonia plant and a methanol plant, will reduce the reserves to production ratio from 37 years at January 2000 to 21 years by December 2003, until more reserves are proved.

Future potential projects aimed at sustaining the development in this sector have also been identified. In this regard, additional deep-water acreage will be placed up for bids, and discussions are ongoing for the establishment of an aluminium smelter plant, additional fertilizer plants, an ethylene project and a gas to liquids project.
A Study on Blowouts in Ultra Deep Waters
Authors: Santos O. L. A.
Published: December 2007

This paper presents the preliminary results of a research project on ultra deepwater blowouts. This research is a part of a comprehensive study currently conducted by Petrobras, the Brazilian oil company, aiming at drilling and producing safely, in terms of well control, in water depths as deep as 10000 feet (approximately 3000 meters). Firstly, the paper presents a mathematical procedure that predicts wellbore pressures and flow properties during a gas blowout using an unsteady state model that considers the multiphase nature of the flow. Coupled to this procedure, there is a gas reservoir model that calculates gas flow rates entering the well during the unloading part of the process and later on during the blowout itself. The mathematical procedure was implemented in a FORTRAN computer program and several simulation runs were performed to analyze the effect of some drilling variables and reservoir properties on blowout flow rates including the effect of the high backpressure generated by the seawater hydrostatic head. Afterwards, the paper shows the modifications implemented in the computer program to make possible simulations of the dynamic kill technique using a relief well drilled by a dynamically positioned vessel. Finally, the results of the simulations are discussed and analyzed and, when pertinent, recommendations for field application are suggested.