bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance of Slanted and Horizontal Wells on an Anisotropic Medium
Authors: Besson J.
Published: December 2007

Although the technology of highly inclined and horizontal wells has recently progressed significantly, a reliable and practical formula to estimate the productivity of the well with respect to any angle of slant and anisotropy of permeability is still missing. This paper provides a method of estimation which fills the gap.

The well pressure decline curves are generated by a semi-analytical in-house simulator. They lead to a geometrical pseudo skin factor which is matched for slanted wells with an analytically-derived equation. For horizontal wells, comparison is made with several existing formulae.

An unrestrictive approach of anisotropy is possible through a spatial transformation from real medium into equivalent isotropic medium : this is achieved by modifying the length, azimuth, inclination and radius of the well. Equations of the pseudo skin factor are modified according to this transformation.

Calculations reveal that a slanted well is less affected by anisotropy than a horizontal well : with a low vertical permeability, it can be more advantageous than a horizontal well of the same length. Graphic charts are displayed to easy the choice between horizontal and highly inclined wells.
Placing Proppant in a Naturally Fractured Reservoir With Unconventional Leakoff: A Field Case
Authors: Cuesta J. F. , Markland J. T.
Published: December 2007

A proppant placement experiment was carried out in February 1989 at the Rosemanowes Research Site in Cornwall, England. The experiment was designed to produce a stimulated region of at least 50 m radial extent when viewed along the RH15 production wellbore. This was believed to be the extent of a high impedance zone around RH15 identified from microseismicity induced during previous circulating, with RH15 as the production well.

The location of the stimulation interval within the wellbore was constrained by wellbore and reservoir considerations. After analysis of the mini-frac, originally intended to optimise the main-frac pumping schedule, a conservative approach was taken to the design of the proppant placement operation. The proppant was placed using a high viscosity non-linear gel.

Consideration of both mini-frac and main-frac operations along with evidence from diagnostic tools suggests that the ‘fracture’ initially grew radially with subsequent substantial confined extension. Fracture growth is inferred to have developed from a single point exit in RH15 at a previously existing flowing joint, and extended into a region of previously observed microseismicity. No wellbore damage was incurred. It is presumed that previous stimulations within the rock mass and thermal contraction resulting from prolonged reservoir circulation were controlling factors in fracture growth.

The experiment successfully demonstrated the concept of proppant placement in a naturally fractured igneous reservoir.
Development of Small Concrete Structures for Safe, Economical Production
Authors: Gudmestad O. T. , Stead B.
Published: December 2007

The interest in concrete structures is presently gaining much attention. This interest is caused by the designers offering optimized structures answering the need to stimulate marginal field developments. Furthermore, the use of high strength concrete, the low installation costs for concrete structures and the need for competition in the platform construction market have enhanced the interest in concrete structures.

Small concrete structures are being studied for several applications both as wellhead platforms and small wellhead/process platforms often combined with storage facilities.

The paper describes recent development towards optimized small concrete structures for safe, economical production. The following items are in particular highlighted: The design process, concrete material aspects and the importance of the fabrication and installation procedures. Furthermore, the safety of the structures in the fabrication and installation phases are discussed in view of the need to secure the investments.

Requirements to secure competitive structures and safe operations are furthermore being reviewed and examples of interesting small concrete solutions are shown.

This paper can be seen as a guidance note related to design of safe economical small concrete structures.
Scaling Relationships in Natural Fractures: Data, Theory, and Application
Authors: Heffer K. J. , Bevan T. G.
Published: December 2007

Length frequency distributions of fractures are shown to have a power-law trend across many orders of magnitude. This allows an estimate to be made of the full number of fractures and faults existing in a reservoir over that which can be measured from core and seismic data. This relationship has been applied to reservoir studies involving the continuity of juxtaposed sands, permeability impairment, and estimating the number of fractures that a horizontal well may intersect.

Many more fractures and faults exist in reservoirs than those that can be observed from seismic and core data, which have significant implications for reservoir characterisation, geomechanical properties and waterflood behaviour.
Gas Condensate Flow Through Chokes
Authors: Osman Mohammed E. , Dokla Mahmoud E.
Published: December 2007

In this study, field data from a gas condensate reservoir located in the Middle East are used to develop some empiricial correlations that describe the behaviour of gas condensate flow through chokes. The data cover wide ranges of flow rates and choke sizes. Four forms of correlation are checked against data. One of the forms is to correlate choke upstream pressure with liquid production rate, gas liquid ratio and choke size. The second form is developed by using gas production rate instead of the liquid rate in the previous form. The other two forms are developed by using the pressure drop across the choke instead of upstream pressure. These correlations are presented in graphical forms. Five error parameters are used to check accuracy of the different forms. Namely: root mean square error, mean absolute error, simple mean error, mean percentage absolute error and mean percentage error. It was found that the correlation is most accurate when using pressure drop data instead of choke upstream pressure in the correlation. The importance of the developed correlations lies in the fact that correlations for gas-condensate systems are not available. Also such correlations will help the production engineer to a great extent in selecting choke sizes to control production of gas-condensate wells and predicting the performance of flowing wells under different conditions.
The Leman F aand G Development: Obtaining Commercial Production Rates From a Tight Gas Reservoir
Authors: Clayton F. M. , Gordon N. C.
Published: December 2007

The Leman F/G development was undertaken to drain the relatively undepleted and poor reservoir quality North Western area of the Leman field and massive hydraulic fracturing is required to achieve commercial production rates.

Two jackets were installed in December 1985 and the first fourteen wells were successfully stimulated and brought on stream on schedule by 1st October 1987. Initial production rates of between 5 and 40 MMscf/d per well were achieved. Further wells were drilled and stimulated in 1988 and 1989. The changes implemented in the design and execution of the treatments during these campaigns are explained and the results compared with the original wells.

The paper outlines the organisation and execution of the programmes of perforation and stimulation followed by clean out with coiled tubing and clean up of these twenty two wells. In total, some 10 million lbs of proppant were placed. The integrated planning required to complete a successful offshore fracturing campaign on a tight schedule is highlighted.

The problems encountered with back production of proppant both during initial production and over the longer term are discussed, as are the measures implemented and under consideration to mitigate future problems.
Results from a Horizontal Well in a Rotliegendes Gas Field
Authors: Hawkings N. , Ramsey C. , Rapach J. , Kristof M.
Published: December 2007

The North Valiant gas field in the Southern North Sea yielded disappointing results during initial development drilling due to the failure of development wells to locate the high permeability dune sands encountered during field appraisal. In order to achieve a better chance of locating these sands in a thin (+/-150′) reservoir it was decided to drill a 2000′ horizontal well. This was the first horizontal well to be drilled in the UK Gas Basin and the first in the UK to use medium radius drilling techniques. The well was successfully drilled, logged, completed and tested and is now on production. The well achieved the best deliverability of any North Valiant well, with a Productivity Index (P.l.) double that of the nearby exploration well. It has doubled the field's available deliverability. The well cost approximately the same as a fracture-stimulated conventional development well.
New Latex, Expanding Thixotropic Cement Systems Improve Job Performance and Reduce Costs
Authors: Jones R. R. , Carpenter R. B.
Published: December 2007

A unique cementing system is presented which provides improved cement bonding and zonal isolation in wells having bottom hole static temperatures (BHST) below 175° F. Selectively formulated with components common to the industry, this system is reliable and versatile.

Latex cement additives are excellent bonding aids, gas migration preventers, matrix intensifiers and fluid loss additives. They improve cement's elasticity and resistance to corrosive fluids. Thixotropic, expanding cements excel in providing annular fill, zonal isolation and lost circulation control. Combining these two technologies into a single, efficient, low cost system has provided technical and economic properties which have had significant impact on cementing operations. This new cementing system is hereafter referred to as LXT for latex, expanding, thixotropic cement.

The properties engineered into the LXT system provide better primary and remedial cementing applications through: (1) reduced invasion of permeable, unconsolidated or "weak" zones by whole cement or cement filtrate, (2) prevention of gas or fluid migration in hydrating cement columns, (3) greater zonal isolation between differentially pressured intervals separated by thin, shale barriers, and (4) rapid compressive strength development and minimal waiting-on-cement (WOC) time. Laboratory studies and case histories are presented to show the merits of this cement system over conventional low water loss (LWL) systems. Numerous applications in East Texas, West Texas (Permian Basin) and on the West Coast have resulted in marked improvements in job quality and success rates over prior cementing practices.
Thermal Alteration of Medium and Heavy Compounds of Crude Oils by Pyrolysis and Combustion
Authors: Pusch G. , Ranjbar-Hamghawandi M.
Published: December 2007

Polymerization induced by radicals may convert normal alkanes into resins or waxy compounds between 300°C and 450°C and resins into asphaltenes at temperatures above 450°C. The nature of this chemical conversion was studied by the use of extracted model compounds and of natural crude oils during isothermal and constantheating rate pyrolysis. A thin bed reactor made from sinter glass which represents the properties of the porous medium was used.

Results of the study show that in the temperature region below 450°C the amount of resins in the crude oils determines the reaction rate of combustion, whereas above 500°C the amount of aspaltenes dominates the reaction rate constant. This tendency was observed with model substances as well as with dead oils, independently of the analytical method applied. Consequently, a large variety of different crude oils from paraffinic light oils to asphaltenic oils is able to produce the required fuel for in situ combustion, provided that the pyrolysis temperature is kept within certain limits. Temperature control in the process is achieved by a variation of the water-oxygen ratio of the injected fluids.
The Thermodynamics of Scale Prediction
Authors: Atkinson G. , Raju K. , Howell R. D.
Published: December 2007

A program has been developed for the prediction of sulfate scale formation in single waters or mixtures. The program considers the effect of pressure, temperature, and brine composition using classical thermodynamics and modem electrolyte theory. The important effect of [MgS04°] ion pairing is considered explicitly. All possible sulfate scales are considered simultaneously. This is a far sounder theoretical approach than the sequential approach used previously.
Performance of Scale Inhibitors in Squeeze Application
Authors: Brod M.
Published: December 2007

This paper reports an investigation into the relative performance of scale inhibitors in squeeze treatment in conditions typical of the U.K. North Sea. The methods used were to run laboratory core tests, model the results using the new computer software "SQUEEZE", and compare the outcome with field experience.

At low water throughput rates, satisfactory modelling could be achieved assuming a simple Freundlich isotherm, although there is evidence that this does not represent a true equilibrium situation. At higher water flows, certain products deviate from the Freundlich isotherm. The deviation takes the form of a reduction in the rate at which inhibitor return concentration goes down with time or cumulative production. The return curve may remain at a level almost until depletion. It was not found possible to model these deviated curves.

For a moderate deviation from the isotherm, the decline is arrested at a low scale inhibitor concentration and effective squeeze life is extended. As water throughput increases further, the plateau occurs at a higher concentration and depletion is brought forward. The critical water production rate for a specific product in the cases studied was about 5000 bbl/D.
The Modelling and Design of Scale Inhibitor Squeeze Treatments in Complex Reservoirs
Authors: Sorbie K. S. , Yuan Ming Dong , Todd A. C. , Wat R. M. S.
Published: December 2007

This paper describes the formulation and application of a simulation tool for modeling scale inhibitor adsorption squeeze treatments in realistic reservoir formations. In this simulator, a three-dimensional (3D), three-phase black oil reservoir model is used to calculate the larger scale reservoir flows such as the local well layer flow rates and watercuts, and the near wellbore area water saturations. However, a very accurate fine grid near well simulation model is embedded into this reservoir scale calculation which models all of the inhibitor transport, including adsorption/desorption behaviour and dispersion, within the maximum penetration distance of the injected inhibitor. Since this penetration distance may only be tens of feet which is generally much smaller than a single grid block in a reservoir model, a rme radial subgrid is used to accurately track the injection and backproduction of the inhibitor. It is demonstrated that this approach provides a vast improvement over any previous methods of modeling this process.

In the paper, the one layer single well radial model is first presented with examples of its application. This is followed by the description of the full reservoir inhibitor squeeze simulator combining the black oil model and the fine grid radial squeeze model. The application of this simulator to some realistic near-well inhibitor squeeze treatments and the key factors governing the process in a heterogeneous formation are then examined. The issues studied include the following; the form and type of inhibitor adsorption isotherm, the equilibrium/non-equilibrium adsorption/desorption processes, the effect of degree and type of reservoir heterogeneity, the concentration of the injected inhibitor slug and the significance of overflush size.
Removal of Hydrocarbons From Oilfield Brines by Flocculation With Carbon Dioxide
Authors: Burke N. E. , Curtice S. , Little C. T. , Seibert A. F.
Published: December 2007

The objective of this research was to develop a model to describe the removal of dispersed petroleum hydrocarbons from oil-field brines using carbon dioxide in a sieve tray extraction column. The model consists of two parts: hydrodynamics of bubble flow and flocculation. The flocculation part of the model will be presented in this work. The system studied in this work was a brine from a California steamflood. The California brine contained a nominal 1000 mg/L of a heavy, asphaltic crude oil (13.2 °API) and had a total salinity of approximately 500 mg/L. The flocculation model was tested with experimental runs at pressures of 83.75 and 97.54 bar and temperarures of 23.9,37.8 and 65.6 °C. Additional flocculation runs were made at pressures of 14.80,42.38, and 69.96 bar at 65.6 °C. It was determined that the flocculation of the dispersed oil droplets was the result of two separate effects: a pH effect due to the acidity of carbon dioxide and a shear effect due to the rising carbon dioxide bubbles. . It was necessary to use an empirical flocculation efficiency in the model in order to effectively predict removal efficiencies for each operating condition.
Modelling of the Collapse of Unconsolidated Rock Formations During Production
Authors: da Fontoura S.A.B. , dos Santos H.M.R.
Published: December 2007

The definition for the maximum allowable drawdown for sand free production in uncased and cased wellbores is discussed herein. An analytical procedure is developed to evaluate the effective stresses around wellbores during production. This methodology takes into account a general stress field as production. This methodology takes into account a general stress field as well as wellbore inclination and azimuth and allows for the mechanical failure of the formation. A number of computational experiments are carried out to demonstrate the effects of the in-situ stress ratios and formation cohesion upon the maximum allowable drawdown for sand free production. production.

Introduction

Large oil and gas reserves stored in rock formations known as unconsolidated or weakly cemented sands are known to exist in several areas. In general, these low-strength rocks do not support the stresses that are generated during the flow of the produced fluid through the formation and eventually faliure will occur causing the breakout of the rock. The positioning of the failed rock mass around the wellbore dictates the conditions for the removal of solids from the formation and its transport by the produced fluid. The transport of solid by the produced fluid is known to be the cause of a number of undesirable problems such as damage to submersible pumps, plugging off the case perforations, and, eventually, total invasion of the production column.

In order to address the questions associated with the production of solids and its impact on the economics of the reservoir expolitation, it is mandatory to have a scheme to predict whether and when a given rock formation subjected to a given production rate will produce solids.

Ideally, for the purpose of selecting a proper completion scheme and of planning the well production strategy, the completion engineer should be planning the well production strategy, the completion engineer should be able to define the maximum allowable drawdown that guarantees sand free production throughout the operational life of the well. This paper production throughout the operational life of the well. This paper discusses some of the necessary steps involved in the determination maximum allowable drawdown for sand free oil production. Initially, a conceptual model for sand production is presented in which both the sufficient and necessary conditions for sand production are highlighted. This conceptual model is used as a background to review critically the existing sand production prediction tools as well as to formulate guidelines for the production prediction tools as well as to formulate guidelines for the development of new analytical prediction methods.
Cation Exchange Capacity Data Derived from Well Logs
Authors: Ramirez Miguel Orlando
Published: December 2007

The Cation Exchange Capacity (CEC) of a formation is an important parameter for the correction of resistivity measurements in the calculation of water and hydrocarbon saturations. Clays in sands provide an electrical conductive path that is related to CEC. This conductivity is parallel and in addition to the conductivity obtained from the pore water. As a result, formations with clay minerals present will be less resistive than if they were the simple systems of quartz and fluids used in most models which are erroneously evaluated since the hydrocarbon saturation decreases. Normally, the only way of determining CEC is in the laboratory, but this way is expensive, and suffers from significant dispersion of results due to differences in laboratory effectiveness in cation replacement, removal of excess cation as well as possible interference. This paper describes the results obtained by calculating CEC from well logs, using the normalized Qv concept of the Juhasz equation. Qv is the cation exchange capacity per unit total pore volume and is calculated from the FDC/CNL and natural gamma ray spectral logging information. A very large and high quality log and laboratory data from low oil gravity shaly sands of the Orinoco Oil Belt was used in order to obtain accurate results. Laboratory measurements of CEC made in cores and sidewall cores, and CEC calculated from a geochemical model, show a remarkably good agreement with the continuous CEC log derived values.
Multiphase Pipeline: A Solution to Cost Savings in Offshore Production
Authors: Guy Jean-Michel , de Merville Eric , Bernicot Michel
Published: December 2007

Offshore production is always considered as a costly and hazardous business.

Multiphase production concepts applied to sealines may lead to considerable reduction in production costs and potential safely hazards due to simultaneous presence of men and production equipment on offshore platforms.

TOTAL experience in multiphase flow transportation systems was once again used for the development of HIDRA field in Tierra del Fuego (Argentina).

This original development scheme comprises two unmanned offshore wellhead platforms linked together by a 3.6 km long 14" sealine. The overall production is then routed without separation to the onshore processing facilities via a 12.8 km long 20" sealine.

This article describes the operating experience of such system on Hidra field and in particular the ways to cope with the hydraulic behaviour of the sealines and its consequences.
Paraffin Precipitation in the Formation in Dom João Field, Brazil
Authors: Romeu Régis Kruel , Khalil Carlos Nagib , Rabinovitz André
Published: December 2007

Despite prolonged water injection and a number of reservoir studies, only 10% of the original oil in place has been recovered during 43 years of production from shallow reservoirs in the Dom João oil field, Recôncavo Basin. The formation temperature being close to the pour point of the crude oil raises the possibility for the ocurrence of paraffin precipitation in the reservoir. A field stimulation test was performed using a nitrogen generation system/emulsion (SGN/EMULSÃO) technique. Two nitrogenated salt solutions, emulsified in a selected organic solvent, were injected into the formation through a single well; their reaction released both nitrogen and heat, in turn yielding a capacity to remove paraffin deposits. A comparison between the production rates and oil compositions before and after stimulation indicates that paraffin deposition was occurring inside the formation. A possible explanation for this phenomenon would be the cooling effect resulting from a post-migration uplifting of the the formation.
Development of a Subsea Module Deployment System for the Disps Project
Authors: Rodda Norman , Paritt Stephen
Published: December 2007

The paper will describe a prototype system developed for deploying equipment packages (modules) without guidelines onto a diverless seabed template in deepwater. The two principal components of the system, namely a negatively buoyant load carrying underwater vehicle (Remote Guidance Vehicle - RGV) and a heave compensated lift wire system (Heave compensation Winch - HCW) have_been designed and manufactured. The RGV was systematically tested in 150 metres of water. This testing demonstrated the suitability of the design and computer simulation for a remotely operated vehicle system to deploy subsea modules in 400 metres water depths and be capable of use in up to 750 metres.
A Systematic Determination of Formation Damage Causes
Authors: Di Giorgi Plínio
Published: December 2007

A new approach is presented for determining the source of formation damage. Based on a train of formation damage evaluation, this comprehensive approach endeavors to (1) improve diagnoses of sources of damage relying on our present knowledge of the topic and (2) identify the critical links within the train and suggest possible advances therein so that damage diagnoses may be made more accurate. The crucial question Is our current inadequate theoretical understanding of the links between physical and chemical phenomena and the nature of each damage mechanism.
Automated Interpretation of Drillstem Tests Pressure Data
Authors: Vidal José Oliveira , de França Correa Antônio Cláudio
Published: December 2007

This paper describes a method for automated interpretation of drillstem tests (DST's) for the cases in which the produced fluids do not fill up the drillstring.

The method is based upon the pressure matching of field data with a theoretical fluid flow model through the use of an unconstrained non-linear regression technique, coupled with numerical inversion of Laplace transforms of the wellbore pressure for both flowing and shut-in periods. The parameter gradients required to implement the fitting process have also been obtained by numerically inverting closed form expressions from Laplace space.

A DST has been treated as a ''slug test" with a step change in the wellbore storage coefficient at shut-in time. With this concept it has been possible to interpret flow and shut-in pressure data simultaneously.

Both simulated and field pressure data have been analyzed in order to illustrate the application of the method using a fluid flow model which considers a homogeneous and infinite reservoir system, inclunding wellbore storage and skin effects.

Application of the method presented in this work to field data may yield estimates of reservoir and wellbore parameters such as the formation permeability, the skin effect and the initial reservoir pressure. Such parameters are important to the determination of wellbore condition and to the forecast of hydrocarbon production.

The methodology described in this paper may be used to extend the automated data fitting algorithm to include more complex fluid flow models, such as fractured or composite systems and other flow geometries.
Interfaces for Remote Operation of Subsea Equipment
Authors: Ribeiro Orlando José S. , Conti Fábio Kerr P. , Flores Mário César X.
Published: December 2007

The availability of a Subsea Production System is closely related to the efficiency of subsea equipment maintenance. Therefore, the use of Remote Operated Vehicles (ROV) is a simple and effective method to perform several tasks which can contribute to increase the system availability.

This paper presents the ROV interfaces designed for the operation of small valves, connection of hot stab tools and override of Wet Christmas Tree valve actuators.

These interfaces will be standardized for the subsea equipment used by PETROBRÁS, after field testing.
Albacora, a Deepwater Giant Field Development
Authors: Pereira de Oliveira Carlos Alberto , Guimarães Dias Marco Antônio
Published: December 2007

Albacora, a giant field located under water depths ranging from 230m to 1,900m, in Campos Basin, offshore Brazil, has an estimated oil-in-place volume of 4.4 billion bbl and extends over an area of 235 km2. The development plan conceived for this field has been divided into three phases, which the first one is a cost-effective pilot production system, which has started field production in October, 1987. This paper describes many alternatives under study by PETROBRAS for installation of the second phase of the field exploitation. Water depths of the wellheads at this phase will reach 1,166m and the start-up is expected to occur in 1994, with a peak production of nearly 200,000 bopd in 1996. The alternatives differ basically in parameters such as the type (semi-submersible, compliant tower, jacket), quantity, size and location of the production units, the type and configuration of the subsea systems, the type of the production and export risers (rigid, semi-rigid or flexible) and also the level of the infra-structure integration. An economical analysis ends the paper and shows that Phase II, besides of performing a pioneer conception at world level, is also a cost-effective production system.
Procelab-Laboratory Methods and Procedures for Oilwell Cementing
Authors: Silva Marins Carlos César , da Rosa Flávio Costa , de Assis Costa Lucelena Ferreira
Published: December 2007

PROCELAB is a manual wrlttten in Portuguese, standardizing laboratory procedures and methods for oilwell cementing, it was cooperatively elaborated by a group of technicians employed by PETROBRÁS and service companies operating in Brazil. its major approach is to assure the reliability of results from tests conducted by laboratories involved with oilwell cement slurries. The manual develops topics which complement the API Spec 10, including from the sampling of cement, water and chemicals to the supply of test results.
Predicting Reservoir Quality in the Cretaceous Maceió Member of the Sergipe - Alagoas Basin, Northeast Brazil
Authors: de Abreu Carlos Jorge
Published: December 2007

Porosity and permeability of the sandstones of the Cretaceous Maceió Member of the Muribeca Formation were studied in 51 cores in the northeastern half of the Sergipe-Alagoas basin of Brazil's passive continental margin. Here the Maceió Member is a feldspathic sandstone that thickens offshore to more than 5.000m. The Maceió includes seven facies ranging from alluvial to submarine fans and includes lacustrine and evaporite environments.

One hundred and thirteen thin sections from plugs were used to systematically quantify 12 pore types and stepwise regression helped to identify the best predictors of plug permeability - intergranular clean pores, intergranular pores with residual solids, and intergranular open pores with carbonate cement. Over 90 clay mineral analyses were made and contributed to the understanding of diagenetic history of the sandstones.

The most important conclusions include the following: Everywhere in the Maceió porosity and permeability are best at the top and highest values occur where it is shallow and near the outcrop. Intergranular secondary porosity is predominant at the top throughout the Maceió and is the best predictor of permeability. Most of the intergranular porosity, especially where the Maceó is shallow, was formed by invasion of meteoric waters. However, minor porosities possibly formed by organic acids in the deeply buried Maceió.

Results of this investigation have been guiding the exploratory geologists encharged for new locations of wells in the Maceió Member.
Effects of the Detrital Composition and Early Carbonate Cementation on Porosity Loss in Sandstones: An Integrated Petrographic and Experimental Approach
Authors: Souza Rogério Schiffer , Elias Vera Lúcia
Published: December 2007

In general, sands at the time of deposition present initial porosity around 40-55%. This primary porosity is reduced by mechanical compaction and/or cementation with increasing burial.

The intensity of the mechanical compaction is a function of detrital mineralogy and grain shape (BENSON, 1981) 1

This paper deals with the relationship among detrital composition, carbonate cement and porosity loss by mechanical compaction.

Statistical analysis from petrophysical data, systematic petrography and experimental analysis were done with sandstones, with variable amounts of ductile grains and carbonate cement.

This study showed that porosity and permeability reduction were more effective in sandstones which present greater amounts of ductile grains. However, petrographic evidences demostrated that early diagenetic process, such as carbonate cementation, can support the mechanically unstable lithoclasts against increasing overburden, preserving the potential porosity and permeability.
Offshore Service Submarine for 1500 m Water Depth
Authors: Freitas Ayres
Published: December 2007

The offshore activities in deeper waters have initiated the development of offshore submarines for subsea work. Several concepts have been produced.

A new concept for a work submarine for operations in water depths up to 1500 m has been developed. This is a short range vessel operating from a base close to the field.

The submarine is powered by a closed cycle diesel engine and propelled by pressure compensated hydraulic thrusters. The life support system has a regenerative CO2 absorption plant.

The submarine can rest on the wellhead protection structure and perform tasks ranging from inspection to module change out and intervention operations. The advantage of the submarine over surface vessels is that it can work close to the subsea site in a calm environment and without the encumbrance of long guide wires and umbilicals.
Reducing Numerical Diffusion in the Modelling of Sharp Saturation Fronts: A Conservation - Law Approach
Authors: Shaw David C. , Dozzo Joseph A.
Published: December 2007

Reservoir studies are often directed at specifically evaluating, amongst other things: The Sweep of Injected Water in a Waterflood, Tracing Injected Gas Through a Field, The Efficiency of a Polymer or Miscible Component Flood. Each of these problems can be completely obscured by the presence of numerical diffusion, which dominates and masks out true, physical saturation changes.

No finite-difference method yet developed which relies on a fixed grid can claim to accurately model any sharp saturation front without degrading it eventually into a smooth, uniform distribution. It is pointless to try and remedy this by increasing the truncation accuracy of the scheme, since it is the physical dynamics of the approximation which are important.

The basic difficulties in capturing and tracing any sharp saturation front with time are best understood by considering the fundamental property laws which are necessary for a physical solution. These are: Conservation Properties, Boundedness Properties, Transport Properties and Shock Capture.

We describe a method based on the finite-element scheme which allows these laws to be closely approximated. In addition, its formulation is such that it can be incorporated easily into existing IMPES black-oil and compositional simulators. The method is validated by comparison with one- and two-dimensional laboratory experiments and by numerical experiments designed to trap shock waves.
Computers And Graphic Display Systems A New Technique For The Petroleum Scientist
Authors: Lowe Howard R. , Ross J. Alan
Published: December 2007

Recent developments in the computer field will soon make it possible for a geologist or engineer to have on-line capability for many complex geological and engineering problems. New computer peripheral equipment includes many different types of graphic display systems. Technical personnel will have unprecedented conversational capability to work with visual graphics data. They can refer to data, change data, initiate new ideas, compare data all within the framework of a defined problem. problem. Now one can perform complex activities such as preparation of contour maps, decline curves, three dimensional representations, stereoscopic or mathematical models in seconds instead of weeks or months. The conversational mode of operation of such units allows the operator complete control of the desired display. Objects can be moved about, using a light pen to detect a particular line segment or symbol. The keyboard allows one to change parameters or add new information. The time parameters or add new information. The time required to solve a problem is cut dramatically. The ability of the technician to change points on a three dimensional basis will be points on a three dimensional basis will be of great value in the fields of exploration, exploitation, and reservoir engineering. Visual display can be obtained along any desired axis or on any scale or projection. Utilization of sophisticated data information systems in conjunction with graphic display systems will undoubtedly revolutionize techniques now In use in the petroleum industry. The speed and versatility which these systems will make possible will create a far greater impact on the industry than anything ever experienced in the past.

Introduction

The application of high speed computers to exploration and exploitation problems is a relatively new technique. Less than five years ago the geologist and engineer found it necessary to spend hours, days, or weeks accumulating and preparing data to eventually make a study. Petroleum technology has advanced by leaps and bounds since the late 1940's: with these advances came a staggering amount of data and information. The advances in technology were actually restricted because of the impossibility of handling vast quantities of scientific data and information.

The increase in exploration and drilling costs has made it necessary to look for techniques outside the petroleum industry to solve these many problems, and thereby cut costs. Decision making, both on the technical as well as management level, requires a much faster means of handling, correlating and interpreting scientific data. No industry collects more varied and voluminous information and data than the petroleum industry.

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Best available copy - damaged original.
A Case Study of the Full-Field Simulation of a Reservoir Containing Bottomwater
Authors: King G. R. , Snyder D. E. , Obut T. S. , Perkins R. L.
Published: December 2007

A recent simulation study was conducted on a reservoir which was completely underlain by bottom-water. Thirteen wells, eleven production wells and two injection wells, were considered in the study. Due to the high vertical permeability (approximately one Darcy) and lack of correlatable shales, the production wells were expected7 to exhibit critical coning rates of approximately 150 BFPD (calculated). To economically justify the project, production rates of 3000 – 5000 BFPD per well were required. Consequently, early water production problems were expected from the reservoir. This paper discusses the methods used in the reservoir simulation study to assess the impact of water production on the project. The simulation study discussed in this paper was comprised of both single-well and full-field simulation models. The objectives of the single-well modeling were to gain insight into the individual well behavior and to calibrate the full-field models by use of well pseudofunctions.

For vertical producers in the full-field models, two approaches were used: the traditional pseudo-function approach and the hybrid-grid approach. In the pseudofunction approach, both vertical equilibrium (VE) well pseudo-functions and dynamic well pseudo-functions were considered. Due to CPU time constraints, the hybrid-grid approach was principally used to validate the pseudo-functions and to "fine tune" key prediction cases.

To alleviate coning problems, horizontal production wells were also considered in the full-field model. For these wells, only dynamic well pseudo-functions were considered. These pseudo-functions were generated using finely gridded single-well models and used in the full-field model to describe well behavior.

Since this paper addresses several current topics in reservoir simulation, such as the use of hybrid grids and the modeling of horizontal wells (along with the scaling of these technologies from the single-well, conceptual scale to the full-field scale), we believe that the material presented in this paper will provide a framework for future simulation studies of bottom-water reservoirs.
Rigorous Black Oil Pseudo Functions
Authors: Stone H. L.
Published: December 2007

A new method of calculating black oil pseudo functions from a fine grid simulation of a reservoir is given. These functions when used in a coarse grid simulation of the same reservoir will reproduce the accuracy of the original fine grid simulation. This accuracy results for any production rate even when used to coalesce non-communicating layers from the fine grid model into a single coarse grid layer. All previously published methods are accurate only for low viscous-gravity ratios, which correspond to a combination of a low production rate and good vertical communication between layers in the reservoir.
Compositional Reservoir Simulation in Parallel Supercomputing Environments
Authors: Briens F. J. L. , Wu C. H. , Gazdag J. , Wang H. H.
Published: December 2007

This paper presents the important considerations, programming and computational techniques for the development of a fully parallel and vectorized compositional reservoir simulator. A modified Young formulation is used for the flash calculations and a novel algorithm called Sequential Staging of Tasks (SST) that can take full advantage of parallel vector processing to speed up the solution of a large linear system is introduced. Compared to domain decomposition, SST has a number of noteworthy advantages illustrated with the results of computer experiments conducted on a parallel supercomputer with 6 vector processors. Memory-efficient techniques for out-of-core simulations are also discussed. The simulator developed with the techniques presented in this paper can handle compositional reservoir simulations as large as 200,000 grid blocks and components with reasonable turn-around times and can provide a 100 times speed-up over conventional serial computers.
Modeling the Performance of Horizontal Injection Wells in Carbon Dioxide Miscible Displacement Processes
Authors: Ammer J. R. , Enick R. M. , Klara S. M.
Published: December 2007

A black-oil, pseudo-miscible simulator, a compositional simulator, and a compositional/ incomplete mixing simulator were used to model first-contact miscible!, carbon dioxide, enhanced-oil recovery experiments. The experiments were conducted by the University of Wyoming in a three-dimensional, high-pressure, physical model to investigate the effect of injection well geometry on oil recovery. These laboratory scale experiments showed that oil recovery could be significantly increased using a horizontal injection well instead of a vertical injection well. The objectives of this study were to evaluate the capability of each simulator to accurately model these displacements and to use the most appropriate simulator to investigate the mechanisms that led to improved oil recovery.

Both the black-oil, pseudo-miscible simulator and the compositional simulator were unable to provide a match of the experimental results. The pseudo-miscible simulator overpredicted the recovery rate and the ultimate recovery of oil because it could not accurately account for the large volume change when mixing carbon dioxide and heptane (laboratory oil). Only limited success in providing better matches was attained when the effects of viscous fingering were incorporated by lowering the value of the mixing parameter. The overproduction of oil resulting from the poor phase behavior description was too large to be compensated for by altering the mixing parameter. The compositional simulator provided a more realistic description of the phase behavior and, therefore, yielded good matches of oil production before breakthrough. However, the recovery of oil after breakthrough was overpredicted. It was not possible to improve these simulation results by accounting for viscous-fingering effects since the compositional simulator assumes complete mixing in all grid blocks.

A compositional/incomplete mixing simulator that empirically accounted for the macroscopic effects of viscous fingering by assuming incomplete mixing within grid blocks was then employed. An additional parameter was required to define the rate of mass transfer of oil from the ‘bypassed’ phase of a gridblock into the oil phase where mixing with the carbon dioxide was allowed to occur. A high value of the parameter (100 or more) corresponded to no viscous fingering as commonly assumed in conventional simulators, while a low value corresponded to the maximum degree of fingering effects. Good matches between simulation and experimental results for both the vertical and horizontal injection schemes were obtained using this model with parameter values of 0.1 and 2.5, respectively. These results indicated that viscous fingering probably occurred in all experiments, with the effect being much less pronounced when the horizontal injector was used.
Stability-Based Switching Criterion for Adaptive-Implicit Compositional Reservoir Simulation
Authors: Grabenstetter J. , Li Y.-K. , Collins D. A. , Nghiem L. X.
Published: December 2007

A stability criterion for determining the degree of implicitness in adaptive-implicit compositional reservoir simulation is derived and discussed. The criterion is based on the Courant-Friedrichs-Lewy (CFL) condition for the stability of explicit discretizations of hyperbolic systems of partial differential equations. The criterion can be computed using quantities either directly available from the Jacobian-building sections of the compositional simulator, or obtainable through minor modifications to the simulator. The criterion can be used for switching both from explicit to implicit and from implicit to explicit discretizations of a block. Several strategies for applying the criterion to determine an appropriate degree of implicitness in practical reservoir simulations are proposed and tested.
Heterogeneous Reservoir Models: Local Refinement and Effective Parameters
Authors: Espedal M. S. , Langlo P. , Saevareid O. , Gislefoss E. , Hansen R.
Published: December 2007

Heterogeneous porous media are generally characterized by many scales of variations. A methodology is required for transporting information from one scale to another. Also, grid refinement techniques require that we are able to assign effective permeabilities on grid-blocks of different sizes. Recently, methods for calculating effective permeabilities on blocks of arbitrary size have been developed for models in groundwater-flow. We have extended these methods to a two-phase model, where a new dispersion coefficient is derived.

Based on operator-splitting techniques and adaptive grid-refinement, we have developed a discretization strategy able to resolve local phenomena in space and time. The solution procedure includes the concept of domain decomposition where the global solution is constructed from local computations on sub-domains. This approach allows the resolution and even the entire solution strategy to depend on local properties of the model. The algorithm is well suited for parallel computer architectures as well as integration into existing large scale simulators.

In the present paper these techniques are tested for heterogeneous, two-dimensional two-phase models. Numerical experiments based on fine-scale discretization are compared with the results from the calculation based on averaged equations.