bluuebunny/crossref_metadata_2025 huggingface dataset:
Laboratory Characterization of Anisotropic Rocks
Authors: Auzerais F. M. , Ellis D. V. , Luthi S. M. , Dussan V E. B. , Pinoteau B. J.
Published: December 2007

A number of layered rock samples with large permeability contrasts has been collected mostly from the western United States. The collection provides samples from a variety of depositional geological environments with bedding thicknesses ranging from millimeters to decimeters. The objective of this study was to investigate the origin of the large permeability anisotropy.

To characterize these rocks, conventional laboratory methods have been used such as macroscopic petrographic description, mineralogical analysis using Fourier transform infrared spectroscopy, as well as permeability, porosity, conductivity and acoustic velocity measurements on Hassler cores orthogonal and parallel to the bedding surfaces. Additionally, novel techniques consisting of permeability scans on the rock surfaces with an experimental minipermeameter setup, petrographic image analysis from thin sections, and density profiles obtained from a computerized tomographic (CT) scanner were used. These provided detailed maps of vertical density, porosity and permeability changes within these rocks. Results of CT scanning at two different energies allowed us to simultaneously determine densities and estimate photoelectric factors.

All of these rocks are layered and exhibit large porosity changes over very short vertical distances of sometimes as little as one millimeter. Some sandstone samples as well as an interlayered sand/shale sample were found to exhibit permeability anisotropies of more than one-hundred and vertical porosity variations of up to a factor of three. Conductivity anisotropies of these samples, however, were generally less than 1.6, and acoustic anisotropies less than 1.2.

The sedimentological origin of these anisotropic rocks is attributed to an interaction of two or more depositional processes during lateral acceration or vertical aggradation, producing vertical variations in mineralogy, grain size and other petrographic characteristics.
Calcite Cementation: Description and Production Consequences
Authors: Omre H. , Sølna K. , Tjelmeland H. , Claesson L. , Holter C.
Published: December 2007

Stochastic modeling in reservoir description should be classified with respect to the type of variables involved in the study: continuous, mosaic or event spatial variables. The calcite cemented units in a sand stone reservoir is considered as a mosaic variable, and the stochastic model is based on Markov random field theory. The model and parameter values, constrained by the well observations, provide the base for generating several realizations of the reservoir description. These realizations are homogenized and the production potential is evaluated by a preliminary numerical production simulation. The set of production profiles corresponding to the reservoir realizations will reflect the uncertainty due to lack of exact geological knowledge about the reservoir. The importance of establishing an automatic line of production for uncertainty evaluation is emphasized.
Acidization of Analcime-Cemented Sandstone, Gulf of Mexico
Authors: Underdown D. R. , Hickey J. J. , Kalra S. K.
Published: December 2007

In a number of offshore Louisiana oil wells a white powdery, finely granular siliceous material was swabbed from wells and found on screens after acidizing with mud acid. The white material was analyzed as silica gel or aluminosilicate gels. Analysis of the formation sands which produced the white material after acidization shows the sands to be extensively cemented with analcime.

Analcime is a hydrated sodium aluminosilicate related to zeolites. Analcime is a low density (2.3 gm/cc) mineral which is highly soluble in HF and will form hydrated gels with concentrated HC1. Analcime is associated with volcanic ashes, altered volcanic sandstones and salt domes. There are many salt dome related oil fields in the central Gulf where volcanic ash beds are locally common. Therefore, the occurrence of analcime cemented sandstones may be more widespread in the Gulf than previously suspected.

A significant production decline was noted in a number of wells in the South Pass Blk. 61 field, a complex salt dome related structure, after acidization with HF or concentrated HC1. In many cases, production decline is attributed to damage by mineral precipitation or gel formation from acid spent on analcime-cemented sands.

This paper describes the petrographic and fluid/rock studies done to optimize pre and/or post gravel pack acid stimulation system for analcime- cemented sandstones from South Pass Blk. 61. SEM photos show the effect of various acid systems on analcime and an effective acid system for these types of formations is discussed.
A Comprehensive Mechanistic Model for Two-Phase Flow in Pipelines
Authors: Xiao J. J. , Shonham O. , Brill J. P.
Published: December 2007

A comprehensive mechanistic model has been developed for gas-liquid two-phase flow in horizontal and near horizontal pipelines. The model is able first to detect the existing flow pattern, and then to predict the flow characteristics, primarily liquid holdup and pressure drop, for the stratified, intermittent, annular, or dispersed bubble flow patterns.

A pipeline data bank has been established. The data bank includes large diameter field data culled from the A. G. A. database, and laboratory data published in the literature. Data include both black oil and compositional fluid systems.

The comprehensive mechanistic model has been evaluated against the data bank and also compared with the performance of some of the most commonly used correlations for two-phase flow in pipelines. The evaluation, based on the comparison between the predicted and the measured pressure drops, demonstrated that the overall performance of the proposed model is better than that of any of the correlations, with the least absolute average percent error and the least standard deviation.
The Measurement of Crude Oil/Natural Gas/Water Flow Rates by Using Microwave Technique
Authors: Lin Feng , Chen Xuejun , Zhou Fangde
Published: December 2007

The individual flowrates of crude oil, natural gas and water three-phase mixture are measured separately by using a single phase flowmeter. The microwave technique is used to measure the water to oil and gas ratio. It can measure 0-100% water concentration in water/oil two-phase and oil/gas/water three-phase mixtures. This instrument is not temperature or salinity sensitive - a shortcoming of the capacitance and conductivity probes. The capacitance cross-correlation method is used to measure the overall flowrate of a three-phase fluid. A new cross-correlator is developed, cheaper than others. Its calculating time is much shorter than before. A bypass is used to separate the liquid from the three-phase mixture, and to measure the oil fraction in the remaining oil/water mixture. The natural gas fraction in three-phase fluid is measured from the main flow. The experiments have been done in the laboratory and field. The flowrate range measured is more extended than that of single phase flowmeters, such as a turbo-meter or orifice plate. The flowrate measuring error is less than 5%.

This kind of three-phase flowmeter is suitableto many kinds of oil wells to measure the flowrates of crude oil, natural gas and water, including flows with high water to oil ratios or high gas and oil ratios. The flowmeter is compact and non-invasive. It keeps high accuracy during measuring, despite the presence of paraffins, tar and sand. Its low cost makes it possible to install a flowmeter in each oil-well .
Fracture Height Growth and Production From Multiple Reservoirs
Authors: Saulsberry J. L. , Schraufnagel R. A. , Jones A. H.
Published: December 2007

The objective of two separate fracture treatment experiments performed in the Oak Grove Field, Alabama, was to estimate fracture geometry and effectiveness. In the first treatment an innovative design to connect a number of thin seams with one stimulation was tested. In the second treatment the goal was to determine the height growth and fracture length that might be achieved in a typical conventional water/sand stimulation design. Fracture diagnostics and modeling were used to estimate fracture geometry. Post-fracture production analysis indicates that the treatment using a crosslinked gel created a more effective propped fracture than the treatment using fresh water.
Gas-Lift Troubleshooting Engineering: An Improved Approach
Authors: Ortiz J. L.
Published: December 2007

The present paper describes the basis and applications of some gas lift troubleshooting techniques being used in the production operations of Lake Maracaibo field, Venezuela.

By integrating simple physical models and analytical procedures, engineers are able to diagnose a broad range of gas lift wells.

The presented techniques have been applied successfully on a large amount of gas lift wells, making them an alternative to some methodologies that appear in the literature.

Representative field cases have been included to illustrate the explanations.
The Role of Asphaltene in Wettability Reversal
Authors: Kim S. T. , Boudh-Hir M- E. , Mansoori G. A.
Published: December 2007

Wettability is an important factor in a number of petroleum production processes. Asphaltene deposition can have a strong role in wettability reversal. Among many factors, the high molecular weight, polar fraction of crude oils, including the asphaltenes, are considered to be the primary wettability altering agents.

Understanding the role of asphaltene in wettability of reservoir fluids on solid surfaces and its reversal will help us plan for more efficient oil recovery processes. It will also establish the role of asphaltene deposition in the production operation of asphaltic crudes including heavy petroleum crudes. In this paper the groundwork for the study of the complex role of asphaltene and its deposition in altering the wettability of reservoir fluids on solid surfaces is presented. A number of experimental observations in support of the strong role of asphaltene in altering the interfacial tensions and wettability is reported. A new molecular theory for prediction of wettability and its reversal is also introduced.
A Method for Computing the Vertical Coverage for an In-Situ Combustion Process
Authors: Mikkelsen P. L. , Ramey H. J.
Published: December 2007

The Dykstra-Parsons approach for computing the vertical coverage of a waterflood has been modified in order to estimate the vertical coverage for an in situ combustion process. The modified approach for combustion ignores the effect of gravity forces in determining burn thickness. It simply assumes that the burn moves to the top of the pay zone. Burn thickness is then shown to be dependent upon the reservoir permeability variation, the mobility ratio of the injected gas (containing oxidant) to the combustion gas, initial reservoir temperature and the combustion temperature.

The model was successfully applied to field core data from the Fosterton Northwest combustion project, using spreadsheet software on a personal computer. An average 31 percent burn thickness determined from the model, compared favourably with a field-observed value of 34 percent which was determined by post-burn coring. The model performance was improved by using multiple pseudo-permeability variations for the core data, instead of a single variation value, as is often used when applying the Dykstra-Parsons model.
Characterization of Residual Hydrocarbons in Produced Water Discharged From Gas Production Platforms
Authors: Callaghan D , Baumgartner W.
Published: December 2007

An investigation is described to select the best practical technique for reducing the residual hydrocarbon in produced water discharged from gas production platforms to less than 40 mg/l. The aliphatic and aromatic components of the dissolved and dispersed hydrocarbon have been separately measured on a number of platforms, together with the droplet size distribution for the dispersed phase.

In addition to previously recognized problems caused by high pressure drops together with corrosion inhibitor, disposal of condensed vapours from glycol regeneration has been identified as a major contributor.

Significant reduction in the level of total residual hydrocarbon can be achieved in future by process modifications instead of ‘end of pipe’ solutions.
Lacq Gas Field (France): Monitoring of Induced Subsidence and Seismicity Consequences on Gas Production and Field Operation
Authors: Maury V. , Grasso J. R. , Wittlinger G.
Published: December 2007

Between 1957 when the Lacq gas field was first put into production and 1967, a 3 cm subsidence occurred. This period corresponded to a 30 MPa depletion. From 1967 until 1989, further depletion of 25 MPa induced an additionnal subsidence of 2.5 cm which this time coincided with more than 1000 microearthquakes and earthquakes, 44 with magnitudes greater than 3 and 4 with magnitudes greater than 4.

This paper gives a brief review of earlier case histories. It then goes on to describe a local seismic monitoring network which was installed on the Lacq field. The method used for processing and interpretating the seismological data takes into account the lithologies and the mechanical properties of the rocks and the source parameters. From the information obtained, the global mechanism of the gas field deformation appears to be the lowering of a rigid block located at the top of the structure by a succession of reverse movements along preexisting fractures and faults.

The paper goes on to demonstrate the practical consequences with regard to safety and gas production, and the contribution to our knowledge of reservoir behaviour over the course of time. Close monitoring of subsidence and seismic events is a new and useful aid to understanding the reservoir response to fluid withdrawal.
Thixotropic Cementing With Coiled Tubing at Prudhoe Bay
Authors: Welch J. L. , Mason C. M. , Pavlich J. P.
Published: December 2007

This paper presents a new coiled tubing unit (CTU) thixotropic squeeze cementing technique developed by BP Exploration (Alaska) Inc. for use in remedial cementing operations on water injection wells and other wells with low fracture gradients. Results of application of this technique are also presented.

Preliminary attempts at squeeze cementing seawater injection wells with conventional CTU cement slurries have required multiple attempts and very large volumes of cement. In some cases these conventional CTU squeezes have been relatively unsuccessful.

This thixotropic squeeze cementing technique has been utilized to successfully squeeze seawater injection wells. This is believed to be the first time a cement system designed with thixotropic properties has been successfully used as part of a coiled tubing workover technique.
Quantitive Risk Assessment of Subsurface Well Collisions
Authors: Thorogood J. L. , Tourney F. G. , Woo G.
Published: December 2007

Subsurface separation criteria have been evolved empirically over the years. They are still largely based on un-tested assumptions about safety factors, comfort values and survey tool accuracy. A mathematical analysis of the probability of collision is presented. This calculation is linked by means of a decision tree to an assessment of the consequences of a well intersection. The mathematics can be simplified for the case where the two wells are parallel, enabling key features of the problem to be illustrated. A flow chart of the directional drilling tolerance setting procedure is used to show how the methods described can be used in day-to-day well planning operations. The risk based approach simplifies management of the operations and enhances safety and efficency because appropriate margins can be applied in each individual case.
The Flow of Real Gases in Porous Media
Authors: Clegg M.W.
Published: December 2007

American Institute of Mining, Metallurgical and Petroleum Engineers Inc.

The pressure dependence of the viscosity and deviation factor of real gases means that the flow equations for gases in porous media are highly non-linear. The linearisation of these equations leads to diffusion-type equations similar to those governing the flow of slightly compressible liquids in porous media. Such approximations are only porous media. Such approximations are only valid for small changes in pressure; for large pressure changes the non-linear terms must be retained.

The use of a "pseudo-pressure" variable for transforming the gas flow equation has recently been studied by a number of authors, and numerical solutions of the equations obtained. In this paper the radial flow of gas to a well is considered, and it is shown that a simple approximation technique leads to analytical solutions involving only elementary functions. These solutions agree well with the numerical results and provide a sound theoretical basis for empirical equations derived by other authors.

The possibility of extending these methods to two-phase flow systems is briefly reviewed.

Introduction

During the past twenty years an increasing amount of effort has been devoted to the study of gas flow in porous media. In spite of this activity the development of solutions for the equations governing the flow of real gases in porous media has not progressed as far as one would have hoped. progressed as far as one would have hoped. The reason for this is not difficult to discover. The equations are highly non-linear and present great problems when analytical solutions are sought. An excellent survey of the literature on the flow of gases through porous media is given in Al-Hussainy et al. porous media is given in Al-Hussainy et al. The basic equation for the flow of real gases in porous media, taking account of the variation of viscosity and deviation factor with pressure, may be written as

..........................................(1)
Relative Permeability and Low Tension Fluid Flow in Gas Condensate Systems
Authors: Haniff M. S. , Ali J. K.
Published: December 2007

This paper summarises the results of an experimental study on fluid flow and residual saturations in a methane-propane gas condensate fluid system. Significant reduction in residual saturation and much improved flow rates are observed below a critical value of IFT (0.05mNm−1). At IFT values greater than 0.05mNm−1 phase distribution in the porous media is maintained through a balance in capillary and gravitational forces. The symmetry is, however, destroyed below 0.05mNm−1 when capillary forces become negligible and a first order transition in phase distribution takes place. Now, gravitational forces become important and the Bond Number more appropriate in interpreting the data. The micromodel work of Williams and Dawe, and Danesh et al established that under these conditions the liquid exists as a thin film along the grains while the gas occupies the centre of the pores, that is, a complete wetting situation. The absence of hysteresis effects in relative permeability curves confirm these observations. Under low IFT conditions, the liquid phase flows more easily, probably by a mechanism similar to that of gravity flow in hydrology studies, that is, as ‘free surface’. Here, the liquid surface is considered as a ‘stream line’ and flows when it intersects a ‘surface of seepage’. This could account for the phase separation caused by gravity often referred to as ‘gravity segregation’ and which generally occurs at conditions close to the dew line pressure.
Critical and Trapped Hydrocarbon Saturations in a Condensate Reservoir
Authors: Eldon M. , Puckett D.
Published: December 2007

The Strathspey field in block 3/4a in the UK sector of the North Sea is comprised of two reservoirs. The lower is called The Statfjord reservoir and contains gas condensate, undertain by an oil rim. In order to predict the likely production from this reservoir a compositional reservoir simulation was performed. To perform this simulation, trapped and critical oil and gas saturations for both the gas condensate and oil rim regions had to be defined.

The relatively small amount of published data, and lack of critical saturation data from the Statfjord SCAL data, resulted in the decision to design a series of floods to determine these parameters using reservoir core and fluids at reservoir conditions The flood sequences were also designed to mimic the depletion processes that were expected to occur in the field.

The apparatus and experimental procedures used, together with the results obtained, are reported in this paper. Furthermore these results are compared with the published data and the effect on the final simulation results is also reported
Active Witnessing in Cement Bond Logging
Authors: Rouillac D.
Published: December 2007

This paper describes a witnessing procedure based on a review of experience acquired during cement bond logging operations by ARTEP (French Petroleum Research Association) members.

The aim is to provide an answer, on the wellsite, to the following two questions:

– are the anomalies observed on cement logs genuine and significant? – if so, what are the chances of success of any remedial action?

The described operational procedures and standard presentation have now been successfully implemented in hundreds of cases where the oil Company witness has been helped in the interpretation of a CBL/VDL or a CET to determine the potential risk of a leaking barrier. The paper also highlights the cash savings linked to sound log quality control, when one pays exclusively for qualified and reliable data. Some case histories of insufficiently studied cement bond logs are presented.
Effect of Steerable BHA on Drag and Torque In Wells
Authors: Aarrestad T. V.
Published: December 2007

Steerable bottom hole assemblies are often used when drilling deviated wells. Planning of such deviated wells often include studies of torque and drag calculations for the planned well-path and BHA's in order to have a fairly good idea of friction and torque to be encountered when drilling.

The paper discusses some effects of using steerable bottom hole assemblies or other means of directional control. It is shown in the paper that in extreme situations, extensive use of directional control methods, may result in problems with high drag and torque in the wells. In some cases TD may not be reached due to large doglegs in building parts of the well.
The "Guided Owners’ Process": A New Approach to Equity Determinations
Authors: Hope M.
Published: December 2007

The Guided Owners’ Process is designed to facilitate negotiated agreement of field unitisation between the Owners. This is achieved by replacing the usual separate Owner and Expert processes by a single negotiation between the Owners with the Expert present throughout.

The Expert works in parallel with the Owners and helps to ensure that a reasonable timetable for the technical discussions is adhered to. If agreement on key issues has not been reached by certain pre-defined deadlines ("Key Steps") each Group submits its case to the Expert for resolution. The determination then moves forward to the next Key Step : there can be no turning back and no external expert referrals.

The Guided Owners' Process is a flexible concept and can be adapted to accommodate any field's equity procedures. Two major North Sea fields have recently negotiated agreements utilising this concept.
SPT: Tool for Improved Placement of Chemicals in a Live Well
Authors: Leerloyer K. , Hughes R. H. , Misselbrook J. G.
Published: December 2007

A straddle-packer selective placement tool has been developed that is run on coiled tubing, can pass through production tubing and can be repeatedly set in casing. The tool was built to improve the placement of chemicals in long and inhomogeneous intervals. Its capabilities and possible applications are described, together with an outline of some of the jobs done so far.
Cementing Through Coiled Tubing and Its Influence on Slurry Properties
Authors: Vidick B. , Nash F. D. , Hartley I.
Published: December 2007

The use of coiled tubing for cement squeezing operations presents significant economic benefits for offshore workover operations. This paper demonstrates that batch mixing small volumes of slurry may, if care is not taken, lead to dramatic variations in slurry properties, especially the thickening time. A field mixing methodology based on the concept of mixing energy has been developed. Also, evidence gathered during this work indicated an even more dramatic effect on thickening time while pumping the cement through coiled tubing.
Multiple-Fracture Horizontal Wells: Performance and Numerical Simulation
Authors: Conlin J. M. , Hale J. L. , Sabathier J. C. , Faure F. , Mas D.
Published: December 2007

Six Multiple Fracture Horizontal (MFH) Wells have been drilled in the Dan Field, located in the Danish North Sea. The field is a low permeability chalk reservoir producing under a combination of solution gas and gas cap drives.

Single well numerical models were built to determine the primary factors controlling the performance of these complex wells. In the two wells which have been successfully history matched, dynamic hydraulic/natural fracture behaviour under drawdown and gas coning were key processes. The models are being used for the management or existing MFH wells and for the optimisation of field development using the MFH well concept.
Reservoir Monitoring in the Development of Marginal Fields: Ivanhoe, Rob Roy, and Hamish
Authors: Carter P. J. , Morel E. H.
Published: December 2007

Reservoir management of the Ivanhoe, Rob Roy and Hamish oil fields has been greatly enhanced during the first year of production by the continuous monitoring of bottom hole pressure in the production and water injection wells. By bringing on production and injection wells in a planned sequence the major flow paths within and between the five reservoir units have been identified. Observed changes in reservoir pressure during planned and unplanned production and injection shutdowns have provided further clues to the geological model and reservoir description.

Although not all the bottom hole pressure gauges have continued to function throughout the year a very large amount of daily pressure data has been collected. This has been used to modify and update the full field simulation model of the fields. The reservoirs have been shown to be much less affected by intra-field faulting than had previously been feared, and some shaley layers originally considered to be laterally extensive barriers are in fact more local. Because of this, excellent areal and vertical sweep is expected in the Main Piper sand. Recovery from the overlying Supra Piper sand will be less and will require further infill wells.

The reservoir model has been used to optimise individual well rates and minimise the risk of premature water breakthrough, and to site wells during the post-production drilling phase. The design reservoir depletion rate of 20 percent of recoverable oil per year has been easily achieved for both the Ivanhoe and Rob Roy fields.
A Gas-Lift Optimization and Allocation Model for Manifolded Subsea Wells
Authors: Edwards R. , Marshall D. L. , Wade K. C.
Published: December 2007

The increasing need to develop marginal accumulations using subsea equipment and common facilities has highlighted the challenge of the allocation and optimum distribution of fluids within these systems. The commingling of produced fluids requires that an auditible procedure is employed to accurately back-allocate fluids produced from different fiscal regimes. Similarly, there is a requirement to optimise lift gas allocation to ensure that the available gas provides the maximum incremental oil production. A method of optimising lift gas allocation and allocating production within a manifolded subsea development has been developed for use on a portable computer. The basic requirements for the model were that it should be usable by offshore personnel and allow a quick comparison of different operating scenarios.
Horizontal Wells in the Andrew Formation: Prediction and Performance
Authors: Garlick T. , Neville G. , Smith P. J. , Webster C.
Published: December 2007

The first few months of Cyrus field production are compared with predictions of the two horizontal wells in the field.

The modelling method used is extended to the prediction of another Andrew Formation prospect (Field 2). The approach has allowed the modelling of up to ten horizontal wells in a full-field model of Field 2.
The Use of Low-Density Particles for Packing a Highly Deviated Well
Authors: Bryant D. , Hudson T. , Hoover S.
Published: December 2007

Packing the annulus and perforations with gravel in highly deviated wells, especially horizontal wells, is difficult. As well deviation increases, pump rates and carrier fluid viscosities increase to prevent particle settling. Increasing the viscosity can reduce fluid leakoff and perforation pack efficiency. Gravel-pack studies have shown that placement efficiency improves as particle density (Dp) and carrier fluid density (Dc) become closer. In an ideal system, these densities would be equal (Dp:Dc = 1). With this ideal design, no viscosity would be required to suspend the particles, thereby improving fluid leakoff and perforation packing. The use of sand as the packing material has limited the use of such a technique because of hydrostatic overbalance. The introduction of a pack material whose density (1.65 g/cc) is 40% less than that of sand makes this technique available without the overbalance concerns.

The paper provides the industry with technology which is applicable when gravel packing highly deviated (horizontal) wells. This paper describes: (1) a new method of completing highly deviated and horizontal wells using low-density particles and low Dp:Dc ratios, (2) computer simulations performed to aid in designing completion techniques,(3) printouts of the screenout pressure and pump rates, (4) schematics of the well design, (5) logs of the pack and (6) well performance.
Case History of Algyo Field, Hungary
Authors: Werovsky V. , Tromboczky S. , Miklos T. , Kristof M.
Published: December 2007

The largest oil and gas occurence of Hungary with 100×10^6 m3 OOIP and 110×10^9 m3 gas reserve is an interesting example of simultaneous exploitation of oil and gas from 76 sandstone reservoirs layering mainly above each other, between 1500 and 2600 m depth and connecting in certain degree through the aquifer. 48 reservoirs of the 76 are in Lower-Pannonian sediments of poor reservoir characteristics, so 28 reservoirs in the Upper-Pannonian sequences give the 90 % of the OOIP and 70 % of the gas reserves and are of determining production importance. The discovery of the field in 1965 allowed the Algyö hydrocarbon production to reach and maintain a 1 million tons/year oil and a 3.2×10^9 m^3 gas production rate by about 1000 wells. Seven of the oil reservoirs have thin oil edge and large gas caps where the applied technology is water injection at the GOC and the WOC depending on the natural water encroachment. Great care is applied to the limitation of free gas production from the gas cap during the main oil production period by the effective control of the actual gas oil ratio. Methods of reservoir management and results of the careful inspection are discussed in the paper.
Simulation of High-pH Coreflood Experiments Using a Compositional Chemical Flood Simulator
Authors: Bhuyan D. , Pope G. A. , Lake L. W.
Published: December 2007

This paper reports on the use of a high pH chemical flood reservoir simulator to simulate high pH coreflood experiments. The coreflood experiments include one alkaline flood, two alkaline/polymer floods under two different salinity environments and an alkaline/surfactant/polymer flood. The agreement between the experimental and numerical oil recoveries and produced chemical compositions is very encouraging and supports the validity of the mathematical model used in the simulator. The importance of the preflush brine salinity, mobility control and effective salinity gradient using a cosurfactant as observed in the experimental data are also evident from the numerical results. Most of the fundamental mechanisms known for micellar/polymer flooding also seem to apply to high pH chemical floods, especially the dominant effect of low interfacial tension. This is the first time that comparisons have been made between a mechanistic reservoir simulator and high pH coreflood experiments. Such comparisons have yielded new insights into high pH chemical flooding.
Clay Dissolution Kinetics in Relation to Alkaline Flooding
Authors: Drillet V. , Defives D.
Published: December 2007

In order to evaluate alkali consumption for oil-field processes like alkaline flooding or clay stabilization treatment, mineral dissolution rates was determined. To do this, a steady-state method was carried out, whereby a well-mixed open reactor was used to contact mineral with alkaline solution, allowing straight forward measurement of dissolution rate in well defined conditions. The method has been tested with quartz for which dissolution rates were found in line with literature's ones. Clay dissolution kinetics were next studied with kaolinite. Initial reaction rate has been found pH-independent in the pH-range 11-13. A kinetic scheme has been worked out accounting for the steep decreasing of the dissolution rate with dissolution products concentration. The model can be used so long as no new mineral precipitates, which occurs well before the theoretical solubility product of kaolinite is attained in that pH range.
The Effect of Temperature, Salinity, and Alcohol on the Critical Micelle Concentration of Surfactants
Authors: Noll L. A.
Published: December 2007

Surfactants are used at high temperatures as additives for steamfloods, and in high-temperature surfactant floods. Most surfactants must be above the critical micelle concentration (CMC) in order to have appropriate properties for forming foams or mobilizing oil. The CMC of a surfactant increases dramatically at high temperatures; thus, it is important to know this value at the temperature of application for economical engineering design.

The CMC's of a series of surfactants as a function of temperature in the range 77°-392° F (298-473 K) have been determined at high temperatures from heats of dilution, a novel application of calorimetry. Enthalpies of dilution were determined at ambient and elevated temperatures. Surface tension measurements at ambient temperatures served to confirm the assignment of CMC from the heat of dilution data.

The CMC's of a pure surfactant were determined in distilled water, in aqueous solutions of NaBr up to 10% salinity, in n-butyl alcohol solutions up to 4% alcohol concentration, and at temperatures of 122° through 347° F (323-448 K). In general, CMC increased with an increase in temperature. The presence of electrolyte at a fixed temperature lowered the CMC and increased the sharpness of the onset of micellization. At 212° F (373 K), the presence of n-butyl alcohol caused the CMC to be lowered but had little effect on the sharpness of micellization. At 347° F (448 K), the alcohol had very little effect on the CMC, apparently because of the change in water properties at high temperatures.

The CMC's and solution behavior of three commercial surfactants were determined at 77°, 257°, and 392° F (298, 398, and 473 K), with no added salt. The CMC for these commercial surfactants also increased with temperature.
Quality Control of Sales Gas and Gas Treatment Units
Authors: Thiebot B.
Published: December 2007

A major problem for the producers on a gas production site is encountered when a unit does not perform at its designed operating conditions. A consequence of this problem is, for example, a sales gas refused as not meeting specifications.

This paper illustrates that it is possible to solve this problem, i.e. to identify the faulty equipment, and to optimize the gas treatment process. This was realized for some gas fields, with the help of a small appraisal on the site completed by fluids samplings and numerical simulations of the process (Peng Robinson equation of state).

In one case, the sales gas was refused as not meeting specifications. An appraisal performed on the site by a small team showed that it was indeed the case and identified the faulty equipment.

In an other case, a quality control of operating conditions was performed on the main separators of a production unit, comparing for each separator its operating efficiency to the designed one.

In both cases, the experimental measurements justified fluid samplings on the site. Detailed analyses on the treated gas were then carried out in the laboratory, up to C18+ fraction, which permitted a quite successfull simulation of the process, especially at low liquids carry over.

The results of this study is that optimization of the process has been obtained with the establishment of operating tables. Such a table gives to the operator, for a given separator and a given value of its efficiency, the operating pressure and temperature to be run in order to give to the treated gas its commercial specification.
The Interaction of Small and Medium Scale Heterogeneities from a Shallow Marine Depositional Environment with Various Two Phase Displacements
Authors: Opdal Svein Tore , Kossack Charles A. , Lewis Jonathan J. M.
Published: December 2007

The interaction of rock heterogeneities with the two phase displacement of oil is the dominant factor in the recovery of oil. In general, reservoir simulation can describe this interaction, but due to the large grid blocks required in most field applications, the interactions of the fluid flow with small and intermediate scales of heterogeneity is neglected. The question of the importance and magnitude of this interaction is investigated in this paper. The shallow marine depositional environment was chosen for this study. A typical shallow marine deposit was dissected into five scales of heterogeneity. A numerical flow field containing small and medium scales of heterogeneity was created for the numerical simulation of fluid displacements. Two alternate numerical flow fields were created by the homogenization of this detailed description. The first "averaged" description consisted of homogeneous layers between the clay drapes. The final description was completely homogeneous. A series of displacements at various combinations of mobility ratios, viscous to gravity ratios and viscous to capillary ratios were simulated in all three numerical descriptions. A comparison of the results shows the interaction of the scales of the heterogeneity with the two phase flow of fluid and demonstrates where homogenization of the permeability variations introduces large errors in the simulation of oil recovery. This type of analysis can easily be applied to any depositional environment.
Sequential Staging of Tasks: A New Approach to Parallel Computations
Authors: Briens Frederic J. L. , Wu Ching H. , Gazdag Jeno , Wang Hsuan H.
Published: December 2007

Developing an efficient algorithm for solving a large linear system in parallel computing environments is the major problem associated with the application of parallel processing to a large-scale reservoir simulation. This paper presents a new algorithm called Sequential Staging of Tasks (SST) that fully exploits the capabilities of parallel supercomputers to speed-up the solution of a large linear system. The SST technique can use any number of parallel processors, keeps a good load balance, and preserves vector speed-up. As SST makes use of readily available iterative solvers, it also provides a surprisingly low implementation complexity. In our computer experiments, the SST technique yields a 5.6 speed-up with 6 processors when solving a 50,000-cell linear system.
A Mixing Law to Model the Dielectric Properties of Porous Media
Authors: Rodriguez Adolfo , Abreu Raul
Published: December 2007

A new mixing law has been developed to model the dielectric properties of saturated porous media. The total propagation time of an electromagnetic wave through the composite porous medium is expressed as the sum of the propagation times through each component (rock, water and oil). A power dependence is established between the propagation lengths and the volume fractions for each component, and is expressed in terms of a water saturation exponent βw, an oil saturation exponent βn, and a βg exponent corresponding to the rock matrix material. The mixing law predicts all the major features of the measured frequency (ω) dependent dielectric constant as a function of water saturation. We conclude that the rapid increase of the dielectric constant at low water saturation values is consistent with βw ~ 0.3, while a decrease at high water saturations is indicative of βn < 1. The hysteresis observed in the dielectric constant during imbibition and drainage is associated with the existence of a different βn for each process. We further show that the exponent corresponding to the water fraction is related to the Archie exponents in the low frequency limit. Reported experimental data at two different frequencies were used to establish the values of the model parameters at those frequencies.
Identification of Asphaltene Deposition in Camorim Field, Northeastern Brazil
Authors: de Andrade Brüning Inái M. R. , Martinez Ângela Vega , Travalloni Ana Maria L.
Published: December 2007

Camorim field lies on the Continental Shelf of Sergipe Basin, under 12-21 m water depth. Its oil production started in July, 1976 with 300 m3/day; in 1978 it reached 800 m3/day and slowly decreased to 400 m3/day in 1982.

In order to identify causes for the decreasing oil production, a study involving twenty-three wells was carried on. The produced oils were characterized according to their properties and composition. The oils are of paraffinic and intermediate base and their gravities range from 39 to 17 API, being all crudes extremely rich in the gasoline fraction. Asphaltene contents vary greatly from 0.13 to 11.6% by weight. Gas chromatographic fingerprints, the asphaltene contents, interfacial tension and polarity determinations identified asphaltene deposition as the main cause for the low production rates. The analyses showed that the heavier and high asphaltenic crudes were highly unstable because the intermediate fractions which should stabilize the oil were present at low contents. Furthermore, polarity determinations showed direct correlation to asphaltene contents for several oils. This result led to the conclusion that the other oil polar components, the resins, which serve as peptizing agents for asphaltenes did not contribute to the polarity effects. This fact increases the instability of the oils and provides additional favourable conditions for asphaltene precipitation.

The case of three wells which undergone several stimulation treatments is described and confirmed the asphaltene deposition.
Use of Production Data to Estimate the Saturation Pressure, Solution Gor, and Chemical Composition of Reservoir Fluids
Authors: Labedi Rafa Mohamed
Published: December 2007

This paper seeks to overcome the shortcomings of previous correlation work on PVT. More than a hundred oil samples were collected from three major oil producing countries in Africa -- Libya (97 samples), Nigeria (27), and Angola (4). PVT data on samples analyzed and correlations established.

Equations were developed using multiple regression analysis to predict the saturation pressure, the solution gas-oil ratio, and the chemical composition of oil reservoir fluids in the three countries. A new equation was developed for estimating gas gravity, which eliminates the need to know the gas gravity for predicting saturation pressure.

The developed correlations are functions of easily measurable field data such as first-stage separator pressure and temperature, producing gas-oil ratio, stock-tank oil gravity, and reservoir pressure and temperature.

They were found to adequately fit with random PVT data in the available literature and to be more practical and accurate than other techniques such as those used by Standing Glaso2, and Vasquez3. Moreover, they may be applied to other geographical areas.
Desalting Heavy Crude Oil by Counter-Flow Electrostatic Mixing
Authors: Warren Kenneth W.
Published: December 2007

Removal of salt from heavy crude oils has always been problematical due to the difficulty in obtaining sufficient mixing for proper contact between the dilution water and dispersed brine without creating emulsions too stable for separation. As heavy oil resources have become more important in meeting world oil demand, advanced catalyst systems have been developed to increase the yield of useful products from a barrel of heavy crude. However, these catalysts demand stringent salt removal specifications in order to achieve sufficient process life for economic justification. Salt levels of less than one pound per thousand barrels of crude oil are often specified. Conventional desalting techniques are marginal at best when applied in these circumstances.

Electrostatic mixing technology is now beginning to find application in heavy crude oil desalting where it can achieve suitable contact efficiency for salt removal without producing unresolvable emulsions. This technique uses electric fields to apply mixing energy to the polar aqueous phase without expending energy on shearing of the bulk oil phase. When combined with counter-current flow of the oil and dilution water, electrostatic mixing produces multiple contact stages with their associated high efficiency in a single vessel.