bluuebunny/crossref_metadata_2025 huggingface dataset:
New Capillary Pressure Models for Parameter Estimation to Interpret Centrifuge Data
Authors: Chen Zhigang , Liu Huiqing , Yao Jun
Published: December 2007

Many interpretation methods have been proposed to convert experimental data from a centrifuge into capillary pressure curves. Of all these, Bentsen's parameter estimation technique appears superior to others. However, Bentsen's capillary pressure model (Model I and Model II) may not have the flexibility to describe the downward bending section of the capillary pressure curves when Sw approaches unit, which is sometimes a typical feature of such curves. We propose in this paper two new capillary pressure models which can be used in the parametric estimation method to consider the downward bending feature of capillary pressure curves. The new models take the following forms: Model I:Sn=exp[b*(Pc−a)c]Model II:Sn=[1+b*(Pc−a)c]−1

where Sn is the normalized wetting phase saturation, a.b.c are the estimation parameters. When c=l, the Model 1 as presented will be reduced to Bentsen's Model I, which is the common form used previously. Comparisons are made between the results of the new models and Bentsen's models and those obtained from Skuse et al's method for various core sample data. Our results show the great flexibility of new capillary pressure models.
Determining Accurate Bottomhole Circulating Temperature for Optimum Cement Slurry Design
Authors: Kabinoff K. B. , Ekstrand B. B. , Shultz Steve , Tilghman S. E. , Fuller Darryl
Published: December 2007

A recently developed bottomhole circulating temperature (BHCT) memory recorder is capable of recording downhole temperatures during circulation before cementing, squeezing, or plugback operations. Conventional methods for determining downhole temperatures have primarily relied on (1) cooldown correlations obtained from published API circulating temperature schedules or (2) temperature measurements acquired during drilling and workover operations. In many cases, a temperature gradient may be estimated from temperature surveys performed in similar wells previously drilled and completed in the same field. Caution is necessary when relying on temperature data that may not provide evidence of temperature anomalies or changes in temperature gradient below some given depth. The capability of the BHCT recorder to obtain actual bottomhole circulating temperatures without delaying normal drilling operations provides essential information needed when designing cement slurries for critical primary cement jobs.

The temperature memory recorder can be tripped into the well with pipe or wireline and can be dropped down the drillstring or tubing. Retrieving can be accomplished by tripping the temperature gauge out with pipe or wireline/slickline equipped with a retrieving head. Temperature data obtained with BHCT recorders are representative of true bottomhole circulating temperatures and can provide an accurate assessment of downhole temperature conditions before critical cementing operations are performed.

This paper presents a brief description of the temperature recording gauge and describes methods and techniques used to investigate the effect of a horizontal wellbore on bottomhole circulating temperatures. Results obtained from four temperature memory recorders placed at varying depths in a horizontal well during various stages of completion are also presented.
A Unique Laboratory Gas Flow Model Reveals Insight To Predict Gas Migration in Cement
Authors: Dean G. D. , Brennen M. A.
Published: December 2007

This paper will give an overview of a laboratory gas flow model and testing procedure that allow real time measurement of gas migration during the transitional period of setting cement. Key parameters are continuously monitored and plotted on a Personal Computer such as: fluid loss, column hydraulics, matrix stability and set time. Repeatable results indicate potential gas migration even when proper slurry parameters are met which include low gelation, low fluid loss, minimal free water and short transition period. Three case studies from different West Coast fields, each of which showed improved bond logs, are reviewed to support the new testing procedure.
Steam Injection Well Falloff Analysis for Monarch Zone, MOCO Steamdrive, California
Authors: Al-Khatib A. M. , Ramey H. J. , Busby J. P.
Published: December 2007

The effects of the unswept zone mobility (kh/µ) on steam inject1v1ty were Investigated. Six falloff tests were run in a steamflood near Maricopa, California. The tests were analyzed using the radial composite model with the aid of the Barua-Horne and the Kappa Saphir well test analysis software packages.

Computer aided matching of the radial composite model with steam injection well falloff data provided remarkable agreement between field data and model simulation. It was possible to find skin, well bore storage, steam zone mobility and compressibility, and the mobility and compressibility of the zone ahead of the steam front. Low mobility ahead of the steam zone was found to limit steam injectivity in several field cases.
A Subsurface Safety Valve Specifically Designed for Jet Pump Applications
Authors: Williams C. R. , Bayh R. I. , O'Dell P. M. , Robertson Thomas
Published: December 2007

This paper describes the development and field testing of a wireline-retrievable, subsurface safety valve tailored for jet pump production systems. An examination of earlier safety system components adapted to hydraulic pump enhanced production systems is provided to show the evolution of design features involved in this new valve. From conceptual design stages to the actual field implementation and operation, a versatile pump power fluid-operated safety valve specifically designed for jet pumps is presented.
A Pattern Steamdrive Model for Personal Computers
Authors: Hsu Chia-Fu
Published: December 2007

For years, reservoir engineers have used analytical or semi-analytical models to obtain quick estimates of steam drive performance. Although such models, which consist of little more than an energy balance, can give reasonable predictions of cumulative oil-to-steam ratio, they can also yield very poor forecasts of oil production vs time. The reason for the latter is the lack of coupling between reservoir heating and fluid flow near wells. To improve upon this drawback, a new steam drive model for personal computers has been formulated. This model can predict the performance of pattern steam drives with accuracies comparable to those of more expensive full-blown simulations. The formulation of this model is based on the material and energy balance across a moving steam front. The steam zone shape is determined by a modified van Lookeren theory which incorporated the effect of ky/kh. In this paper, the physical and mathematical backgrounds of this model are presented. Capabilities of the model are demonstrated by comparisons with simulator predictions for a wide range of input parameters: reservoir thickness, kv/kh, steam vent rate, pump location, initial oil viscosity, and well pattern. Comparisons with field data are also highlighted.
Prediction of CO2/Crude Oil Phase Behavior Using Supercritical Fluid Chromatography
Authors: Stadler M. P. , Stessman A. N. , Orr F. M.
Published: December 2007

In this paper, we describe a method for characterization of crude oils for predictions of phase behavior of CO2 /crude oil mixtures with an equation of state (EOS). The method includes the use of supercritical fluid chromatography (SFC) with CO2 as the carrier fluid. Pressure-composition diagrams calculated using the the Peng-Robinson EOS and this characterization scheme agree well with PVT observations.

The advantage of this technique is that it produces predictions of the phase behavior of CO2/crude oil mixtures with much less experimental effort than is required to perform PVT experiments.
Comparison of Polyacrylamide Retention in Field Application and Laboratory Testing
Authors: Zettlitzer Michael , Volz Hartwig
Published: December 2007

Since 1975, RWE-DEA has carried out numerous successful polymer field projects. In the reservoir units where injection had been initiated in the late seventies, production is close to being terminated- or can be estimated rather precisely by extrapolation of the concentration-versus-time profile. Polyacrylamide loss is calculated on the basis of injection and production data and amounts to 15 to 24 pg/g- or 25 to 53 μg/m2, respectively. Taking into account several correction factors, characteristically specific field retention values are in the range of 8 to 14 μg/g- or 13 to 28 μg/m2, respectively.

Field retention values are compared to polymer retention values determined in laboratory flood tests on packs of crushed reservoir core material and surface sands. As a general trend, polymer losses observed in laboratory tests are higher than those experienced in field applications. Possible interpretations are discussed.
Fluid Characterization of Three-Phase CO2/Oil Mixtures
Authors: Khan S. A. , Pope G. A. , Sepehrnoori Kamy
Published: December 2007

The formation of three phases with CO2/oil mixtures at temperatures below about 120°F is well established. Several West Texas crude oils form three phases at CO2 concentrations higher than about 55% and pressures ranging between 900 and 1300 psia. These phases include an oleic phase (L1), a gaseous phase (V), and a CO2-rich liquid phase (L2). Although some authors have published equation-of-state (EOS) calculations of this type of behavior and used parameter tuning to match their experimental data, they did not give a methodology for characterizing these fluids. This paper presents a reservoir fluid characterization scheme for three-phase CO2/oil mixtures. An analytical procedure has been developed to generate mole fraction and density distributions for the heavy oil fraction. These distributions are then used for calculating EOS properties of heavy fraction components and for lumping into pseudocomponents. A new correlation for CO2-hydrocarbon binary interaction coefficients was required to make accurate predictions of three-phase (L1-L2-V) regions as well as the liquid-liquid (L1L2) region at higher pressures. Results for four West Texas crude oils are presented to validate the fluid characterization scheme. The first two cases, at 83°F and 94°F, exhibit large three-phase regions and the pressure-composition behavior has been predicted with good accuracy. The other two cases, at 105°F and 110°F, exhibit small three-phase regions and very good agreement has been obtained between the experimental and predicted pressure-composition diagrams and between compositional simulations and slimtube displacement experiments. Furthermore, this fluid characterization scheme has been implemented on a workstation using an expert system shell and is fast and easy to use.
Differences in Gas/Oil and Gas/Water Relative Permeability
Authors: Berry J. F. , Little A. J. H. , Skinner R. C.
Published: December 2007

Correlations used to predict three phase relative permeability from two phase data often assume gas relative permeability is a function of gas saturation and not dependent on the liquid phase displaced. To test the validity of this assumption and to investigate the applicability of ambient condition gas/liquid relative permeability data, unsteady state displacements were conducted at ambient and reservoir conditions. All tests were performed on a composite constructed from four reservoir sandstone core plugs with similar lithological and petrophysical properties.

In-situ saturation monitoring, used throughout the ambient condition experiments, provided distributed saturation histories along the length of the composite. Good agreement between experimental observations and numerical predictions of pressure, effluent production and saturation histories indicates history matching via coreflood simulation is a valid method to obtain drainage gas/liquid relative permeability data free of sample scale capillary pressure end effects. Also, increased confidence may be placed in the results of history matching the reservoir condition displacements where distributed saturation data are not available.

History matched relative permeability data from ambient and reservoir condition tests show gas/water relative permeability data are suppressed compared to gas/oil data over a similar liquid saturation range. The good agreement between history matched ambient and reservoir condition gas/liquid data suggests ambient condition unsteady state displacements provide similar drainage relative permeability data when interpreted using coreflood simulation incorporating capillary pressure and the appropriate boundary conditions.
The Use of Well-to-Well Tracer Tests To Determine Geostatistical Parameters of Permeability
Authors: Ghori S. G. , Heller J. P.
Published: December 2007

Tracer tests have been widely used in the petroleum industry to determine qualitative information about underground reservoirs, such as the existence of flow barriers, directional flow paths, etc. This paper describes how well-to-well tracer tests can be used to obtain quantitative information about the geostatistical parameters (variance and correlation scale) of permeability. Both theoretical and experimental results are presented.

In the theoretical work, a catalog of tracer production curves for different sets of geostatistical parameters for five-spot flooding patterns is produced. This catalog is computed with the help of a new numerical technique that is stable and devoid of any numerical dispersion. The effects of variance of the natural logarithm of permeability (ranging from .14 to 2.25), dimensionless correlation scale (ranging from .2 to .5), and of numerous realizations are quantified. The general effect of areal heterogeneity is that multiple peaks appear in the output tracer concentration curve, even when the flow is confined to a single layer. An increase in variance generally increases the number of prominent peaks in the output concentration profile, decreases the time between the emergence of peaks, and increases the time span of the occurrence of the tracer. An increase in correlation scale generally decreases the number of peaks. By using a sufficient number of permeability realizations, an attempt is made to assess variance and correlation length of the permeability field from the tracer and output concentration curves.

In the experimental work, a slab of rock (Arizona flagstone) representing a quarter of a five-spot pattern was selected. A simple minipermeameter was used to measure areal permeability on grids of points on both the top and bottom surfaces of the rock. A tracer test was performed and the tracer output concentrations were measured at six intervals along the depth of the rock at the production well. Six different types of concentration curves were obtained, showing that downhole sampling of the tracer would be important in achieving adequate information about the reservoir rock. Permeabilities measured with the minipermeameter were used as input into the simulator and the numerical production curves were compared with the experimental profiles. The occurrences of similar patterns of multiple peaks confirms the numerical technique and strongly suggests that well-to-well tracer tests in oil fields and aquifers could be used to estimate the geostatistical parameters of the permeability field.
Early CO2 Flood Experience at the South Wasson Clearfork Unit
Authors: Burbank D. E.
Published: December 2007

This paper describes the implementation and performance of the industry's first Clearfork CO2 flood - Shell's South Wasson Clearfork Unit (SWCU) located in the Permian Basin of West Texas. CO2 injection began in 1986 using a high water-alternating-gas (WAG) ratio (8:1), low volume (8% hydrocarbon pore volume) flood,- or "CO2 augmented" waterflood. The intent of the flood was to increase our understanding of the Clearfork formation before committing to a larger scale CO2 flood.

The performance of the "CO2 augmented" waterflood has met expectations. After 3-1/2 years of CO2 injection, enhanced oil production had increased to 450 BOPD,- or 7% of Unit production. CO2 injectivity was comparable to water injectivity, and no significant decrease in the WAG water injectivity was observed. Encouraged by the success of the CO2 augmented waterflood, a 2:1 WAG CO2 flood was approved and implemented in the northern half of the CO2 flood area in the spring of 1990.

Through 1991, roughly 3% of a hydrocarbon pore volume of CO2 has been injected at SWCU, and the cumulative enhanced oil recovery matches the- original projections. The performance of the CO2 flood to date has been influenced by reservoir heterogeneity, injection pattern modifications, waterflood operating practices, and gas processing constraints.
Interpretation of a CO2 WAG Injectivity Test in the San Andres Formation Using a Compositional Simulator
Authors: Roper M. K. , Cheng C. T. , Varnon J. E. , Pope G. A. , Sepehrnoori Kamy
Published: December 2007

It has been well documented that tertiary carbon dioxide WAG cycle injectivity during displacements above the minimum pressure for dynamic miscibility cannot be reliably predicted on the basis of viscosity ratios and waterflood injectivity performance alone. Approximate analytical models based upon gravity-free displacement with nondispersive plug flow of constant composition slugs in noncommunicating radial layers have been used to interpret injectivity during reservoir tests as a function of relative permeability, flow geometry, effective wellbore radius, and layering. We examine compositional simulation as an alternative for incorporating the additional effects of phase behavior, dispersive mixing, gravity, capillary forces, viscous instability, crossflow, and more realistic representations of reservoir heterogeneity in injectivity calculations for field test interpretation. We show how simple modifications can be made to an existing finite-difference equation-of-state simulator to allow for detailed modeling with these mechanisms of reservoir-scale cross-sections that incorporate geostatistical representations of reservoir heterogeneity and radial flow near injection and production wells.

The compositional model is applied to simulate and interpret an injectivity test conducted in the Mabee Field in the San Andres Formation, Martin County, Texas. Injectivity during the field test was significantly greater than initial waterflood injectivity during all WAG cycles, increased during each CO2 cycle, and was greater than would be anticipated from other field tests in the San Andres formation- or from available laboratory data. Compositional simulation of the field test indicates that the reservoir response during the first cycles of CO2 and brine injection, including the initial increasing CO2 injectivity trend and higher brine injectivity after the first CO2 cycle, are consistent with measured relative permeability, phase behavior, and reservoir characterization data, but that the observed injectivity increase during the second cycle of CO2 injection cannot be attributed to either the near-wellbore condition of the reservoir at the start of the test- or to the presence of thief zones that are statistically consistent with measured core data and well logs. Injectivity is a key variable in determining the economic incentive associated with a proposed CO2 project, and an important implication of this study is the validation of compositional simulation as a means for interpreting field tests and developing improved predictions of reservoir injectivity performance. Another important conclusion is that geostatistical techniques can be used successfully to characterize high heterogeneity in carbonate reservoirs for injectivity calculations.
Steamdrive in a Layered Reservoir: An Experimental and Mathematical Study
Authors: Gümrah Fevzi , Palmgren C. T. S. , Bruining Johannes , Godderij R. R. G. G.
Published: December 2007

We have studied steamdrive in layered reservoirs with scaled laboratory experiments. In spite of the frequent occurrence of stratification we have found no reference to previous laboratory studies of steamdrive in thin layered structures. The scaled transparent model was designed to investigate the influence of viscous, gravitational and capillary forces as well as the heat transfer mechanisms. Temperatures are measured by thermocouples and an infrared camera. Heat transfer rates to adjacent formations are measured by heat flux sensors. Visual observations make it possible to follow the evolution of the steam condensation front (SCF), which separates the steam zone from the liquid zone.

We have interpreted the results with an interface model. The interface model combines heat losses to the adjacent rock and fluid flow without the introduction of empirical relations for the SCF, which is essential to describe the behaviour in layered systems. For gravity stable situations the interface model is not valid but in this case a simpler model is adequate. We show the agreement between theory and experiments.
Some Insights Into the Low-Temperature and High-Temperature In-Situ Combustion Kinetics
Authors: Moore R. G. , Belgrave J. D. M. , Mehta Raj , Ursenbach Matt , Laureshen C. J. , Xi Kejia
Published: December 2007

The classical concept of in situ combustion kinetics assumes the high-temperature combustion of a coke-like phase which has been deposited by thermal cracking reactions occurring ahead of the high-temperature front. Although this model appears adequate to describe the behaviour of low-pressure, high-air flux tests on most oils under dry and normal-wet conditions, its limitations are apparent when evaluating the performance of most high-pressure experiments, especially those carried out at high oxygen concentrations and low oxygen fluxes. A comprehensive program on low- and high-temperature oxidation kinetics was therefore undertaken with the aim of understanding the mechanisms associated with in situ combustion.

Accordingly, the highlights of findings from a ramped-temperature oxidation study on Athabasca Oil Sands is presented in this article. The results have significantly expanded the knowledge of in situ combustion kinetics, but perhaps the most important observation arising from the work is the recognition of the significance of the low-reaction rate region existing at the temperatures intermediate between those associated with low-temperature oxidation and high-temperature combustion reactions. The kinetics in this temperature range are characterized by decreasing oxygen uptake and energy generation rates with increasing temperature. This behaviour is analogous to the negative temperature gradient region described in conventional combustion literature. The ability of an oil to transcend the negative temperature gradient region appears to dictate its ultimate in situ combustion behaviour, and it appears that many field projects and tests utilizing high pressures and oxygen-enriched air operate in the low-temperature oxidation mode because of this phenomenon.
Gel Placement in Heterogeneous Systems with Crossflow
Authors: Sorbie K. S. , Seright R. S.
Published: December 2007

Early water breakthrough can be a serious problem during waterflooding of heterogeneous reservoir formations. One possible remedy to this problem is to place a gel block in the high-permeability layer, thus diverting displacing brine into the less-permeable layers in- order to sweep the remaining oil from these zones. In such a treatment, the gelant material must be placed in the correct location within the reservoir so that gel does not impair reservoir performance. In this paper, we study the dynamics of gel placement in heterogeneous (stratified) reservoir systems. The details of the gel placement are strongly affected by the level of communication between reservoir layers, which is characterized by the closeness of the system to vertical equilibrium (VE) conditions. We show that in viscous-stable injection of gelant in systems close to vertical equilibrium, considerable volumes of injected material can crossflow into the low-permeability layers, and subsequent gel formation can seriously reduce the performance of the continuing waterflood. Results from a range of experimental displacements in well characterized layered beadpacks are presented, along with supporting numerical simulations, which help to understand the mechanisms and benefits when performing gel treatments in reservoir systems with free crossflow. The central role of viscous crossflow in such systems is demonstrated. Since we consider only viscous forces in this work, the layered experimental packs are scaled only by the viscosity ratio (displacing to displaced), the geometry of the packs, the aspect ratio and the degree of vertical communication (closeness to VE). Thus the conclusions from the experimental and simulation results are directly applicable to similarly scaled viscous-dominated systems at the reservoir scale. Some analysis is also presented of the mechanism of disruption of slugs by viscous fingering in layered systems.
Twenty-Five Years of Oil Recovery by Steam Injection
Authors: Khan Jamaludin , Parag Dhanpaul
Published: December 2007

Thermal oil recovery was first started in 1966, in Trintopec's operations, with a small cyclic pilot project in the Palo Seco field. Twenty-five (25) years of thermal recovery, comprising cyclic and flood operations, have witnessed vigorous growth and dynamic expansion to the extent that, by 1991, the thermal recovery statistics are as follows:

Steamflood operations exist in all the Company's major land fields, viz., Palo Seco, Central Los Bajos, Guapo, North Fyzabad and Apex-Quarry/Coora/Quarry. Total production from thermal recovery averages 9100 bopd, representing 55% of Trintopec's current land production. A total of approximately 40000 bspd is being supplied by 23 steam generators to more than 150 steam injectors.

This paper presents highlights of Trintopec's experiences in the design, implementation and operation of thermal oil recovery schemes. New concepts, innovations, modelling and monitoring techniques over the past twenty-five (25) years are outlined, and, in addition, projections for the future are indicated.
North Cross (Devonian) Unit CO2 Flood: Status Report
Authors: Mizenko G. J.
Published: December 2007

The North Cross (Devonian) Unit CO2 flood, Shell's first, began in 1972. While fairly small by West Texas standards, the project provides an example of a successful, mature CO2 flood. Seventy-eight billion cubic feet (BCF) of pipeline CO2 have been injected into the reservoir. Recycled produced gas has augmented this to bring cumulative CO2 injection to 128 BCF- or nearly 70% of the hydrocarbon pore volume. Production performance has been excellent. Unit oil production increased from approximately 1400 barrels per day (BOPD) when CO2 injection began to its peak of over 2600 BOPD in late 1978 before declining gradually to approximately 1900 BOPD by the end of 1991. An estimated 11 million barrels of enhanced oil have been recovered through 1991 and ultimate EOR is expected to double to over 22 million barrels.
Country Risk Analysis: A Probablistic Approach
Authors: David Amiel
Published: December 2007

The oil industry has been an internationally based industry that has been heavily dependent on outside financing sources. Historically, financing came from investment houses that, in most cases, participated in the projects as equity investors. However, investment companies can no longer satisfy the capital requirements of the current high level of exploration and development activities. The current trend is to involve commercial banks on a purely lending basis. Commercial banks, by their nature, are risk averse. In the case of oil and gas exploration and production they are asked to take not only technical risk and price risk but geopolitical risk as well. Methods have been developed by commercial banks to reduce technical and price risks to a point which enables them to be comfortable with a loan. However, geopolitical risks are more difficult to assess. The risks associated with many countries are the nationalization of the investment, new tax restricitions, restriction of currency movements, and/or revisions to the production sharing agreements.

Private and public services that rate country risks are available to the industry. The risk factor is used by the industry to determine whether or not to enter into activities in a certain country. Risk indices are based on political, economic and commercial factors, and are deterministic in nature. This paper shows that probability distribution analysis can better describe the risks and provide a more continuous rating system. The probablity approach can be incorporated into probablity reserve determination resulting in economic projections for specific countries or regions.
Applying Rigorous Decision Analysis Methodology to Optimization of a Tertiary Recovery Project: Rangely Weber Sand Unit, Colorado
Authors: Wackowski R. K. , Stevens C. E. , Masoner L. O. , Larson J. L. , Aslesen K. S.
Published: December 2007

The intent of this study was to rigorously look at all of the possible expansion, investment, operational, and C02purchase/recompression scenarios (over 2500) to yield a strategy that would maximize net present value of the C02 project at the Rangely Weber Sand Unit. Traditional methods of project management, which involve analyzing large numbers of single case economic evaluations, was found to be too cumbersome and inaccurate for an analysis of this scope. The decision analysis methodology utilized a statistical approach which resulted in a range of economic outcomes.

Advantages of the decision analysis methodology included: a more organized approach to classification of decisions and uncertainties; a clear sensitivity method to identify the key uncertainties; an application of probabilistic analysis through the decision tree; and a comprehensive display of the range of possible outcomes for communication to decision makers. This range made it possible to consider the upside and downside potential of the options and to weigh these against the Unit's strategies. Savings in time and manpower required to complete the study were also realized.
Economics of Reusable Facilities
Authors: Antia D. D. J.
Published: December 2007

Some of the different economic development strategies that can be used for reusable facilities in the UK, Norway, Netherlands and in some production sharing contracts are outlined. These strategies focus on an integrated decision analysis approach which considers development phasing, reservoir management, tax planning and where appropriate facility purchase, leasing, or sale and leaseback decisions.
Risk and Reward: The Relationship between Prospectivity and Fiscal Regimes
Authors: Kellas G. K. , Hodgshon S. G.
Published: December 2007

This paper looks at the problems facing the international oil explorationist and host Governments in 1992, under a cloud of low oil prices and falling company profits, yet with more quality acreage available worldwide than for many years, especially with the emergence of the CIS states as prospective ‘hunting grounds’ for the western oil company.

Given the extent of the spread of opportunities available to companies and recognition of the increasing need to justify, on economic grounds, progress with any licence application this paper suggests two approaches that companies can adopt to rank the opportunities available, and maximise the value, on an after risk basis, of their (limited) international exploration budget: subjective rating by factor or the Risk/Reward balance.

Both of these approaches include measures of prospectivity and measures of local cost and fiscal effects in providing an overall exploration rating which can be used by companies to rank the available opportunities.

Governments in 1992 are having to compete with each other to secure exploration funds, particularly as companies devote an increasing amount of time in assessing the prospects in the CIS. This paper shows how, by modifying their fiscal regimes, they can readily affect the Risk/Reward balance and provide incentives which will continue to attract exploration when the prospectivity of the country is not perceived as relatively high, yet maintain the Government take as the prospectivity improves.
Corporate Planning in the Nineties
Authors: Johnston J. S. , Parry David
Published: December 2007

Good afternoon Ladies and Gentlemen. The subject of my talk this afternoon is Corporate Planning in the Nineties.

I should explain that the particular case study I am going to describe took place in late 1989/early 1990 in the Exploration and Production arm of British Gas plc. I had been asked as an external consultant to help them consider their corporate needs for the next decade.

During the late 1980s, in the post-privatisation era, British Gas E&P had expanded dramatically through organic growth and through acquisition. This had resulted in a Corporate Structure with two operational offices, in London and Houston, managing the E&P activities across the world and a separate London based Corporate Group supporting the Managing Director and providing a Corporate Planning function. They also intended to expand further within the ‘90s in the same way. As such, it was necessary for the company to identify a control base for this growth. There were two particular requirements; firstly a corporate planning process that could fulfil this function, and secondly it required a predictive tool to be used in the corporate planning process in the form of a numerical model. It was necessary for both of these factors to include consistent standards across the company, and meet the needs of management and employees.
Reservoir History Matching Using the Method of Gradients on a Workstation
Authors: Bisseil Robert , Killough J. E. , Sharma Y.
Published: December 2007

abstract

Tins paper discusses the use of an automatic reservoir history matching process using the method of gradients on a work station. We illustrate the method's robustness and performance using a simple field example.

Traditional gradient methods have utilised perturbation methods to compute the gradients which require n + 1 simulations for n parameters and could consequently be quite expensive. To overcome the expense of making several runs of the simulator we have implemented into our simulator a method which can compute derivatives of many parameters simultaneously. We shall refer to this simulator as GRADSIM for the rest of the article. We show by numerical experiments that the additional cost of computing derivatives is highest for the first derivative, after which the cost rises by about 8 percent for each additional derivative.

We then use the gradients to minimise a so-called objective function which is a measure of the difference between the historical and simulated reservoir data. This is accomplished by passing the gradients to a constrained minimisation algorithm which calculates the changes required in various user-defined reservoir parameters to achieve a better history match. The reservoir description is then updated and the reservoir simulation and gradient calculations are repeated. The process continues in an iterative manner until the best match has been achieved.

This simple example of the application of the method of gradients shows that considerable savings in time could be obtained by the engineer for both history matching and proper parameter identification.
CASCADE: A Knowledge-Based Drilling Engineering Software Tool
Authors: Mattiello Daniela , Sansone Aldo
Published: December 2007

Casing shoe setting depths selection, and the consequent determination of geometrical and mechanical characteristics of casings, is a crucial activity that heavily influences well planning and affects both safety and economical aspects of the operation. Accurate well and casing design can significantly reduce drilling costs and risks; for that purpose CASCADE (Computer Aided Support for Casing Design), an expert system to support the choice of shoe depths and the selection of casing characteristics, has been developed. According to well data provided by the user (lithological information, gradients development forecasts, drilling problems in related wells, targets), the system hypothesizes the casing shoe setting depths and corresponding mechanical characteristics. Different hypotheses can be generated by the system, feeding design criteria with new user defined constraints, but the final choice is up to the user.

The system runs on a UNIX platform and is based on X-windows and KEE, a LISP-based object-oriented tool. It exploits an interactive, graphical interface; dialog boxes and menus guide the user.

The first version of the system is now undergoing field testing.
ODDA: An Expert System for Planning and Conducting Directional Drilling
Authors: Cayeux Eric , Overti P. O.
Published: December 2007

The Automated Mathematician (AM) of Douglas Lenat1 has discovered a very useful way of generalising concepts which is applicable in many circonstances:

If a concept is expressed as a conjunction of two or more other concepts, try to examine the new concept built by replacing the conjunction with a disjunction.1

The application of this heuristic has allowed AM to discover the concept of "prime number". Applied to the description of a complex system, this rule of thumb may be interpreted as: replace an exhaustive and sequential presentation of a complex system with a set of short views on that system.
Designing Better Decisions
Authors: Egeland Thore , Hatlebakk Einar , Holden Lars , Larsen E. A.
Published: December 2007

The computer may be considered a laboratory and experiments performed on the computer (like running ECLIPSE) may be designed and analyzed in much the same way as non-computer experiments. Experimental design methods replace traditional sensitivity studies where one input variable is varied at the time. The basic idea is to vary several input variables simultaneously and intelligently. Damsleth, Hage and Volden [1] demonstrate that the number of simulations may be reduced 30-40% without loosing information. Based on the output from ECLIPSE a relation between the response variable (‘Production after 4 years’ in our example) and the input variables (Lobes, STOOIP,…) is estimated. This relation is used as a surrogate simulator: The values of the input variables are sampled from assigned probability distributions to produce a large number of Monte Carlo simulated values for the response variable.

We extend and discuss the results of the mentioned paper. In particular we investigate the impact of dependence between the input variables. Moreover, the relevance of Geostatistical methods (kriging) are documented. By modeling dependence between different computer runs, the precision of predictions are significantly improved. The methods are demonstrated on the case study discussed in [1].
Object-Oriented Data Management
Authors: Trythall Steve , Greenlee J. N. , Martin Dawson
Published: December 2007

It is increasingly recognised that good data management is essential to the petroleum industry. Relational databases are prevalent within the exploration and production industry and are increasingly applied to the storage of exploration data.

In this paper we argue that the need to describe and manage complex exploration data is better served by the object oriented database management system. The OODBMS provides richer data modelling facilities which are important for representing the objects which are common in petroleum exploration, e.g. three dimensional volumes, images, etc. The facilities of the OODBMS will be introduced and contrasted with the relational database management system.

An example of the use of databases in spatial data modelling will be given and the object and relational implementations contrasted. A benchmark figure for the relational database (ORACLE) and the object oriented database (ONTOS) will be given. We will show that the OODBMS is superior in speed, efficiency and data modelling capabilities.
Advanced Hypermedia for the Petroleum Professional
Authors: Bisset J. B. , Trythall Steve
Published: December 2007

Scientific workstations are increasingly finding their way on to the desktops of petroleum professionals, resulting in the widespread use of a range of complex applications for tasks such as basin modelling, seismic interpretation and reservoir modelling. The increasing complexity of these programs raises serious issues of how effective on-line user support can best be provided. One emerging approach which is generating enthusiasm is the use of hypertext technology to assist the user.

In this paper, we describe the design and development of a hypertext-based intelligent help facility for a complex petroleum exploration application. We describe what hypertext is, and discuss its applicability for applications in the petroleum exploration and production (PE&P) industry, giving examples to illustrate where appropriate.

The system has been developed as part of an intervention strategy for the Hedera application. It is able to inform the user of erroneous data and inconsistent actions, as well as offering appropriate help and advice when required. As well as offering help on the application, hypertext technology can be applied to tasks such as annotation of work, and generation of reports of work undertaken during a modelling session.
A Thermal Transient Model of Circulating Wells: 1. Model Development
Authors: Marshall T. R. , Lie O. H.
Published: December 2007

A model has been developed to calculate the transient (unsteady-state) and steady-state temperatures in the wellbore, completion and formation of a well during drilling, production and shut-in. A finite difference approach, simultaneously solving all the heat transfer equations, is written with a Microsoft Windows based user interface. Predictions of bottom hole and return temperatures from this model are shown to closely agree with the presently available field data. A further publication will:

– provide detailed comparisons with results from more complete measured field data – investigate the sensitivity of wellbore temperatures to variables such as mud rheology, flow rate and rotary table power.
Process Requirements and Enhanced Economics of Helium Recovery From Natural Gas
Authors: Handley J. R. , Miller W. C.
Published: December 2007

The principal economic sources for the world's helium supply are helium rich natural gas reservoirs. Helium is found in natural gas reservoirs in concentrations ranging from 0.005% to about 8%. Typically, naturally occurring nitrogen also exists in these reservoirs. The presence of nitrogen requires processing of the gas to upgrade the heating value of the natural gas product stream.

The helium recovery process can be thermally integrated into the natural gas processing operations of natural gas liquids (NGL) recovery and/or nitrogen rejection units (NRU). The helium recovery unit (HRU) can even be added as a straddle facility.

The process requirements and the economic enhancement of helium recovery from natural gas for an NGL/NRU/HRU facility are presented. The facility process requirements covered include: –feed pretreatment for the removal of freezable components–turbo-expander process for NGL recovery–thermally integrated nitrogen rejection unit–thermally integrated helium recovery unit–feed gas and residue product compression

Facility capital cost and economic evaluations are presented for example cases with and without helium recovery. A guideline is presented to illustrate how the addition of helium recovery can create economically attractive projects from otherwise marginal opportunities.
Successful Remedial Operations Using Ultrafine Cement
Authors: Harris K. L. , Johnson B. J.
Published: December 2007

Since its initial application in 1989, ultrafine cement has been used in several hundred remedial cementing operations worldwide. Since ultrafine cement contains no large particles, it is capable of invading narrow openings that a standard cement can not access. This penetrating feature has resulted in high success rates in a variety of applications. Increased usage in the mid-continent states in the United States along with recent successes in the North Sea, Gulf of Mexico and southeast Asia testifies to the widespread acceptance and success of using ultrafine cement in remedial cement operations.

Recent literature has extensively related the properties and applications of ultrafine cement1-5. This paper intends to outline operational procedures required to ensure successful operations when using this new technology. Proper procedures pertaining to slurry design, cement mixing and placement, and well conditions are presented. Case histories are included and illustrate typical operational techniques in ultrafine remedial operations.
The Changing Face of Gas Proration: Proposed Rule 29
Authors: Foppiano R. E.
Published: December 2007

A new gas proration system has been proposed for Texas, one that may lower allowables and hence curtail gas production. This new system is embodied in the Texas Railroad Commission's proposed Rule 29, which was published in the Texas Register on January 21, 1992.1 It was also described by the Commission staff in a public meeting on April 8, 1991.2 To assess the impact on gas production, the allowables for a large gas field in Panola County were calculated under Rule 29 and compared to current allowables and production. The results clearly show that allowables may be severely reduced in some fields, with a corresponding effect on production. This paper will explain the basics of the current and proposed gas proration system. With a better understanding of gas proration, the production engineer can manage his operations more efficiently and economically.
Implementation of West Panhandle Vacuum Operations
Authors: Fort F. T.
Published: December 2007

August, 1992 marks the second anniversary of the initiation of area wide vacuum operations in the West Panhandle Field. Since August, 1990, MAXUS has placed 65 wells on vacuum operations over an area of 400 square miles near Dumas, Texas. The initial results have shown an increase in deliverability from the wells tested and the placement of approximately 8500 hp at or near the wellheads. The implementation of vacuum operations is another step in a long progression of the development of reserves in the West Panhandle Field.
Optimization of Cathodic Protection of Well Casing in the Texas Panhandle
Authors: Beyea R. O. , Pinckney K. D.
Published: December 2007

Evaluating corrosive potential and impressingeffective cathodic current levels based on surface methodologies exclusively are insufficient to effectively protect most wellbore casings. The time-honored solutions ofinhibited drilling muds, isolating primary cement jobs, squeezecementing, and material considerations do not provide a cost-effectivemeans to address downhole corrosion in the Texas Panhandle region. Accurate emplacement of cathodic protection systems is the key. The CPET* Corrosion and Protection Evaluation Tool effectively measures the corrosive profile and corrosive rates in the wellbore environment. This allows the operator to optimize his corrosion prevention expenditures.
An Overview of Exhaust Emissions Regulatory Requirements and Control Technology for Stationary Natural Gas Engines
Authors: Ballard H. N. , Hay S. C. , Shade W. N.
Published: December 2007

A practical overview of stationary natural gas engine exhaust emissions control technology and trends in emissions regulatory requirements is presented. Selective and non-selective catalytic reduction and lean bum technologies are compared. Particular emphasis is focused on implications of the Clean Air Act of 1990. Recent emissions reduction conversion kit developments and a practical approach to continuous monitoring are discussed.