bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Method of Obtaining Injection Profiles in Short Radius Horizontal Wells
Authors: Wallace T. F. , Garrett K. D. , Guillot S. N.
Published: December 2007

An oxygen activation log was modified for use in obtaining injection profile sun'eys in four short radius horizontal injection wells. The tool was run inside a workstring that was temporarily placed in the lateral. Injection was established down the well annulus and the tool measured flow rates at points in the annulus between the workstring and open hole lateral. From this data, a distribution of injection along the lateral could be determined. Three different stimulation techniques were used on the horizontal wells and the profile results provided valuable insight into the effectiveness of these techniques.
Identification and Distribution of Hydraulic Flow Units in a Heterogeneous Carbonate Reservoir: North Robertson Unit, West Texas
Authors: Davies D. K. , Vessell R. K.
Published: December 2007

A model is developed of a heterogeneous carbonate reservoir based fundamentally on measurement of pore geometrical parameters. Pore level reservoir modeling results in improved accuracy in the prediction of rock types, permeability and identification of flow units. Pore geometrical attributes are integrated with wireline log data to allow for I) log-based identification of intervals of rock with different capillary characteristics, and ii) field-wide, log-based prediction of permeability. Twelve hydraulic flow units are identified through integration of data concerning rock type distribution and depositional environments. Maps of permeability thickness (kH) for each flow unit reveal significant stratigraphic compart-mentalization. Future development drilling using uniform well spacing patterns is not appropriate. The location and design of infill drilling patterns should be geologically targeted for prudent, cost-effective field development.
Flow Units Vs Depositional Cycles In Field Development, Reeves San Andres Field, Yoakum County, TX
Authors: Danielli H. M. C.
Published: December 2007

Geological reservoir layering for simulation and development usually models depositional sequences. Another approach looks for flow units, i.e., rock units with uniform flow properties. The two are not always identical and should be distinguished. Numerical core descriptions show that porosity and permeability in Reeves Field are determined by both depositional and diagenetic parameters. Flow units defined in this way cut across depositional cycles and cannot be traced between wells with 40-acre spacing. High oil cuts are obtained from 20-acre infill wells despite a long-term waterflood. Reservoir behavior is controlled by the geometry of these flow units, not by depositional cycles.
A Case Study of the Development of the Sundown Slaughter Unit CO2 Flood Hockley County, Texas
Authors: Folger L. K. , Guillot S. N.
Published: December 2007

This paper describes the design of the miscible CO2 flood on the Sundown Slaughter Unit. The 8,700 acre unit was a mature waterflood in the San Andres formation surrounded by seven active CO2 floods. CO2 injection commenced on the Unit in January of 1994. The project benefited from the available technology on CO2 flooding and particularly information on other CO2 projects in the Slaughter field. The paper summarizes methods used in the geologic description, reservoir characterization, pattern selection, CO2 flood predictions, and field preparation. The CO2 injection plan and actual performance to date are also presented.
Dollarhide Devonian CO2 Flood: Project Performance Review 10 Years Later
Authors: Bellavance J. F. R.
Published: December 2007

The Doilarhide Devonian CO2 miscible flood has demonstrated substantial production increases in Phases 1, 2, 3 and 4 of the 5 Phase project. To date, incremental recovery is estimated at 15.8 MMBBLS. The field has now produced 63.7 MMBO and is presently under a program of accelerated depletion. In view of the detrimental effects of the WAG cycles on injectivity, water injection has been limited to areas of severe breakthrough. Production currently averages 3080 bbls/d. A total of 66.5 BCF or a 11.2% HCPV of CO2 has been injected into the reservoir and less than 15% has been produced. CO2 breakthrough has not been a problem in the Devonian hence, a WAG process is not warranted at Doilarhide.
Pump-in/Shutdown Tests Key to Finding Near-WelIbore Restrictions
Authors: Hyden Ron E. , Stegent Neil A.
Published: December 2007

Hydraulic fracturing treatments are often significantly impacted by near-wellbore flow regimes that are not anticipated and usually unaccounted for. Identifying the existence of these unusual flow restrictions and quantifying their magnitude has been described in previous work done by Cleary et al.' This paper presents case histories showing the value of simple pump-in/shutdown tests before large-scale hydraulic fracture treat-ments to evaluate such near-wellbore formation restrictions as tortuosity, existence of multiple fractures, and perforation fric-tion, based on the previous work of Cleary et al. These case history evaluations have led to more predictable job outcomes. Testing includes step-down rate tests, water-hammer effects, and fluid efficiency test analysis. These tests are all conducted and analyzed before the treatment, on the day of the treatment.
Water and Gas Coning in the Oil Reservoirs With Steady State and Transient Flow (Part I: Vertical Wells)
Authors: Azar-Nejad F. , Tortike W. S. , Ali S.M. Farouq
Published: December 2007

This paper examines fluid flow mechanism in an infinite rectilinear reservoir with bottom water and/or gas cap. The water-oil contact (WOC) is treated as a no-flow moving boundary while the initial WOC is kept at a constant pressure. The potential distribution around the partially penetrating wellbore is a solution of Laplace or difiusivity equation with uniform potential inner boundary condition (1BC). A new dimensionless variable is introduced. Dimensionless Density, as a function of reservoir geometry, reservoir anisotropy, fluid properties, production rate and the difference of the densities of two fluids. This paper reports the existence of a Critical Dimensionless Density, CDD. above which cone is stable. The results of this study show that for large v alues of Dimensionless Density the cone height is very small and the well pressure response is almost identical to that of the reservoirs without bottom water or a gas cap. Therefore for reservoirs with a high Dimensionless Density a solution of no-flow boundary at the initial WOC level seems more accurate with respect to solution with constant potential boundary. CDD indicates that 1) in anisotropic reservoirs, smaller the vertical permeability the larger is the critical production rate or time of breakthrough. 2) Heavy oils, at equivalent conditions, have smaller critical production rate or time of the breakthrough due to higher viscosity. Thus thermal processes such as steam stimulation reduce the cone height and consequently increase the time of the breakthrough.
Development and Application of Unique Natural Solvents for Treating Paraffin and Asphaltene Related Problems
Authors: King S. R. , Cotney C. R.
Published: December 2007

Paraffin and asphaltene related problems including solid deposits, stabilization of emulsions and sludge production1,2,3continue to plaque the oil and gas industry. Condensates and refined aromatic solvents are popular treatments for dissolving and/or controlling paraffin and asphaltene related problems. These treating fluids are typically used as a quick fix with little regard for formation damage consequences and long term effectiveness.

Testing, blending and refining of unique condensate feedstocks has resulted in unique natural multi-component hydrocarbon solvents. These unique solvents will dissolve a broad carbon number spectrum of organic deposits and keep them in solution under extreme conditions. These natural solvents maximize solvency, demulsifying properties and natural wettibility tendencies without the addition of chemical additives. These natural solvents offer economic alternatives and enhancement to common treatment practices including condensate treatments, hot oiling, chemical treatments, stimulation and production treatments.
Studies on Fracturing in Carbonate Formations in Mexico
Authors: Porres A. , Samudio M. , Pacheco C. , Castrejón F.
Published: December 2007

The study of fracturing in carbonate formations has become a critical factor for the exploitation policies for the main oil and gas producing reservoirs in Mexico, since a great percentage of hydrocarbons production is associated with this kind of reservoirs.

In this paper a methodology that integrates diverse sources of information at different spatial scales is proposed, the range of spatial scales goes from the microscopic level study of thin section of rocks and cores to the megascopic level where fracturing is determined with seismic information.

To define reservoirs fracturing it has been utilized information derived from cuttings samples, cores, well logging, wellbore images, well testing and seismic interpretations.

Given that the fractures are not isolated phenomena in nature, the studies herein described, target to know their origin, in this way, fractures and their spatial relations are identified with the purpose of defining fracture system, principal stresses and their association with major tectonic features such as folds and faults; letting know the fracturing pattern and its association with the geologic model of the area.

Fracture parameters are estimated by means of core analysis and well log information using indices derived mainly from resistivity and porosity logs, on the other hand, fracture orientation is determined from dipmeter information, wellbore images and its correlation with cores.

The application of this method and its results in two fields of Mexico are shown, these results allowed to establish models at well and reservoir levels. Also from these it was possible to estimate preferential fracture orientations in areas not yet drilled, which is of great importance for the optimum field development.
Rock Cutting By Laser
Authors: Carstens Jeffrey P. , Brown Clyde O.
Published: December 2007

Introduction

A recent study of laser-assisted mechanical rock tunneling, conducted at the United Aircraft Research Laboratories under Department of Transportation sponsorship, had as a goal the investigation of laser-assisted mechanical rock fracture for use in tunneling machines boring in extremely hard rock. The results of this study, which are reported in Ref. 1, indicate that the use of the laser in a low-power-density mode to preweaken the rock without causing malting of the rock surface is indeed a feasible mode of weakening hard rock, which does allow a reduction in the energy required for subsequent mechanical removal of the rock. However the system studies undertaken in Ref. 1 indicate that the amount of strength reduction achieved by the laser or any other type of heating system would not be sufficient to justify economically the addition of an expensive heating system to a hard rock tunneling machine.

One avenue toward employing concentrated heat energy which appears to have a potentially greater efficiency in reducing potentially greater efficiency in reducing the strength of hard rock was identified in the Ref. 1 study. This concept involves using highly concentrated thermal energy to form very narrow melt cuts in the rock. This mode of rock weakening has two advantages relative to the use of the low-power-density heating mode in which rock melting is not allowed to occur. For one thing, the use of an extremely high-power-density energy beam allows penetration of the heat into the rock at substantially higher speeds than the nonmelting case, in which penetration speeds are based on the speed of thermal diffusion into the solid rock. Secondly, there are indications that the deposition of heat at depth in the rock could allow removal of a much greater rock volume than the same amount of heat if it were allowed simply to heat-weaken an entire surface area. Careful use of a very highly concentrated heat tool could allow weakening of rock along specific planes, with subsequent removal of relatively large pieces of rock bounded by these planes.
Tailoring the TLP – Evolution and Adaptation of the Concept
Authors: Stokes Edward G. , Koon J. Ray , Thompson Dwight A.
Published: December 2007

A generic characteristic of the Tension Leg Platform (TLP) concept is the interdependencies between the elements of its design, Ref. 1. For example, a change in deck layout and/or weight can affect the center of gravity, which affects platform dynamics, tether tensions, and so on. An important attribute of the concept is its insensitivity to water depth while providing direct access to wells for maintenance.

TLPs can be configured in a variety of ways to achieve different objectives. Hutton1, Jolliet, and Heidrun are three unique applications of the concept, Ref. 2, Fig. 1. The authors' company has through the design evolution and operation of these units, and through studies of other similar TLP concepts, continued to focus on ways to improve its adaptability in different location, environments, water depths and reservoir sizes. Based on the best practices and lessons learned from the existing developments, the advances in related technologies, and knowledge gained from other studies, an even broader range of cost-effective TLP solutions will be possible in the future.

This paper discusses the similarities and differences in three TLPs and the factors that influenced their evolution and adaptation. The paper also reviews the history of the concept, TLP principles, project and operational learnings from each application, and other adaptations of the TLP concept.
Minimum Attractive Rates of Return Associated to Different Risk Levels: A Methodology Applied to Production Projects of The Brazilian Petroleum Industry
Authors: Asrilhant B. , Ensslin L.
Published: December 2007

The use of the maximization of net present value (NPV) associated to a single discount rate as a criterion of evaluation and selection of resources allocation projects tends to direct the investments portfolio up to a situation of high risk, and possible endangering economic position. This inappropriate situation may, however, be manageable through the use of the risk-return rule as assumed criterion. First of all, a compound factor which associates risk due to the market environment, obtained by the Capital Asset Pricing Model (CAPM), to risk related to the project liquidity, identified by the concept of securities duration is introduced. Finally, a factor, pointed out by the Prospect Theory, which carachterizes the losses aversion is incorporated. When the available information is difuse, the risk related to the cash flows estimation is added. Thus, one adjusts the minimum attractive rate of return of a project to its global risk, whose NPV adjusted to the global risk calculation allows a comparison among projects of different risk levels, through a single objective criterion, which incorporates the three risk factors judged significant. Finally, the methodology will be applied to production projects of the Brazilian petroleum industry.
On the Exploitation Conditions of the Akal Reservoir Considering Gas Cap Nitrogen Injection
Authors: Arévalo—V J. A. , Samaniego—V. F. , López—C. F. F. , Urquieta—S. E.
Published: December 2007

This paper presents the results of a study performed to evaluate nitrogen injection in the offshore Akal oil reservoir. It includes a geological description, measurement of physical properties, model development, mechanistic studies, and three dimensional compositional simulations. Nitrogen injection is being evaluated as a way to accelerate and increase oil recovery, through an improvement of the gravity drainage, main producing mechanism in this reservoir, and by pressure maintenance purposes.
Synthetic-Based Fluids Enhance Environmental and Drilling Performance in Deepwater Locations
Authors: Zevallos Manuel A. Legendre , Candler John , Wood J. Hooker , Reuter Larry M.
Published: December 2007

Deepwater drilling in the Gulf of Mexico is a challenging opportunity for drilling fluid performance. Synthetic-based muds (SBMs) applied in the Gulf of Mexico have overcome performance shortfalls of currently available water-based and oil-based muds. This paper will compare environmental, health, and drilling performance factors of polyalphaolefins (PAO) and internal olefins (10) SBMs with emphasis on rheological profiles, acute toxicity, benthic toxicity, bioaccumulation, and biodegradation rates. Field case histories of PAO and 10 SBMs used in deepwater projects are compared to water-based muds (WBM) and oil-based muds (OBM).
Prediction of Rheological Behavior of Ester-Based Drilling Fluids under Downhole Conditions
Authors: Hemphill Terry
Published: December 2007

The accurate prediction of drilling fluid rheological behavior under downhole conditions has become increasingly important, especially on highly-deviated and extended-reach wells drilled with invert emulsions. On these wells, hole cleaning and cuttings suspension parameters should be maintained within optimum ranges for best results, and firm control over unnecessary increases in annular pressure losses and Equivalent Circulating Densities (ECDs) must be exercised. Rather than calculate downhole hydraulics using surface data, more accurate simulation of fluid properties downhole should be used.

Rheological tests that simulated field conditions were run in the laboratory on an ester-based drilling fluid from the field. The rheological behavior of the fluid was tested under varying ranges of temperature, pressure, and ester/water ratios. A predictive downhole rheological model of the ester-based drilling fluid was constructed using over eight hundred (800) fluid viscosity measurements. Using the surface rheological measurements and downhole temperature and pressure, the computer algorithm rapidly calculates fluid properties under the specific downhole conditions.
Design and Application of Brine-Based Drilling Fluids
Authors: Swartwout R. , Pearcy R.
Published: December 2007

The oil & gas industry has evolved a new class of drilling systems designated for the drilling of the pay-zone sections of wells. In addition to high angle drilling operations, these fluids are now being utilized for underreaming and workover type operations where formation protection is of major concern. As compared to typical drilling fluids, these fluids are unique in that they are brine based and designed to not only fulfill requirements desired for drilling operations but are also essentially non-damaging to the production zone.

Brine based drilling fluids have become one of the most widely utilized systems for the drilling of the productive interval due to their ability to protect the formation while drilling.1 These fluids are formulated with a brine as the liquid phase, selected bridging solids and polymers. The brine liquid phase may be composed of NH4Cl, KCl, KBr, HCOOK, NaCl, HCOONa, NaBr, CaCl2, CaBr2 and ZnBr2 as single or multiple salt solutions. Bridging solids can be water soluble or acid soluble. Selected polymers are added to provide proper suspension and desired Theological properties.

Criteria used to properly design brine based fluid for specific drilling operations will be discussed. Proper formulation of a selected drilling fluid will take into consideration well hydraulics, formation compatibility and completion strategy. Proper selection of the base brine, bridging solids and polymers should result with an optimum drilling fluid that minimizes formation damage.
Downstream Gas Opportunities in Mexico
Authors: Flores Eduardo E.
Published: December 2007

Speaking for myself and on behalf of Mr. Ignacio Pichardo, the Secretary of Energy, I would like to extend to you a warm welcome to Mexico and to this beautiful and historical city of Villahermosa, Tabasco.

As you probably know, the natural gas industry in Mexico was managed and operated by the State with very limited access to the private sector. What this meant was that there was neither private ownership of pipelines nor distribution systems, very limited private investment and restrictions on free trade of the commodity.

As of June, 1995, we have new regulations regarding transportation, storage, and distribution of natural gas with private ownership of pipelines and distribution systems explicity allowed. There are no longer any restrictions on imports of natural gas, thus ending the Petroleos Mexicanos monopoly in this particular area.
Environmental Cost Criteria for Exploration and Production
Authors: Parums A. M. , O'Leary H. E.
Published: December 2007

The objective of this study is to assemble, in a rational, comparable format, typical costs per tonne for reducing E&P emissions and discharges to the environment.

The aim of the study was to provide a rationale for helping BP's upstream business to target spend most efficiently in response to environmental, concerns. Economic evaluation is only one of the factors in deciding whether to implement an environmental improvement – other considerations may include regulatory compliance, community concerns and operational benefits.

The environmental issues covered are (i) oil discharges to sea from produced water and drill cuttings (ii) hydrocarbon emissions to air – VOC's & Methane (iii) combustion emissions – NOx and CO2.
Optimizing Cuttings Circulation in Horizontal Well Drilling
Authors: Martins A. L. , Sá C. H. M. , Lourenço A. M. F. , Campos W.
Published: December 2007

The action of stopping drilling to circulate the cuttings out of the well is always a point of controversy among oilfield teams. The practice of circulating periodically the hole may avoid several operational problems during the drilling of a horizontal well. On the other hand, if hydraulic minimum requirements for the cuttings bed removal are not achieved, circulation can be ineffective, time consuming and, in some cases, detrimental to wellbore stability. This paper presents a series of large scale lab experiments which aimed at the investigation of the erosion of a cuttings bed deposited on the lower part of a horizontal annular section. A group of correlations, based on the experimental data, was developed to predict bed height and critical flow rate for bed removal as functions of several independent variables. The proposed methodology, coupled with a cuttings transport numerical simulator, is an useful tool for programming effective circulation of a cuttings bed.
A Method for Simplifying Field Application of ASP Flooding
Authors: French Troy R.
Published: December 2007

An injection strategy that should simplify field application of the ASP (alkali/surfactant/polymer) process was developed. Additionally, this procedure should be useful for increasing oil recovery from on going polymer floods. Process design was accomplished with computer simulations which were supported with laboratory experiments. Small slugs of concentrated alkali and surfactant, which were diluted by in situ mixing, produced suitable conditions for ultra-low IFT (interfacial tension) at the leading edge of a larger polymer slug.

Computer simulation was used to determine diffusion/dispersion parameters so that the degree of in situ reservoir mixing of small chemical slugs could be predicted. A three-dimensional, three-phase, reservoir simulator was used for simulation. The derived diffusion/dispersion coefficients were used for chemical flooding simulations, and the simulation predictions were verified with laboratory core floods. Coreflood effluent compositions matched computer simulation predictions.

When followed with polymer, injection of small, concentrated, slugs of alkali and surfactant mobilized as much oil as injection of larger, more dilute, slugs of alkali/surfactant. This procedure should simplify field application of ASP flooding because very small slugs of alkali and surfactant can be easily handled and injected in an oil field. It was also shown that injection of small slugs of alkali and surfactant during an on going polymer flood should improve oil recovery significantly. An additional 23% PV of oil was recovered when small alkali and surfactant slugs were injected during polymer flooding.
World-Wide Applications of Microbial Technology for Improving Oil Recovery
Authors: Bryant Rebecca S. , Lindsey Rhonda P.
Published: December 2007

Microbial enhanced oil recovery (MEOR) technology has advanced, since 1980, from a laboratory-based evaluation of microbial processes, to field applications internationally. In order to adequately support the decline in oil production in certain areas, research on cost-effective technologies such as microbial enhanced oil recovery processes must be focused on both near-term and long-term applications. Many marginal wells are desperately in need of an inexpensive improved oil recovery technology today that can assist producers in order to prevent their abandonment. Microbial enhanced waterflooding technology has also been shown to be an economically feasible technology in the United States. The 5th International Microbial Enhanced Oil Recovery Conference and Related Technology for Solving Environmental Problems was held in September 1995. Various papers were presented from companies and researchers all over the world on field applications using microorganisms. This paper will compile pertinent information and results from those papers to provide an overview of the state of the art of microbial technology with specific emphasis on current field applications.
Evolution of Conformance Improvement Efforts in a Major CO2 WAG Injection Project
Authors: Fullbright G. D. , Hild G. P. , Korf T. A. , Myers J. P. , O’Toole F. S. , Wackowski R. K. , Smith M. E.
Published: December 2007

The Rangely Weber Sand Unit is giant oil field located in northwestern Colorado currently under miscible CO2 and water flooding operations. Field development has evolved through many stages, including infill drilling, waterflood expansions, and CO2 injection. Conformance improvement has become a major strategy as the CO2 project matures and production and oil cuts decline.

The success of a conformance improvement effort requires development of links to the business objectives of the field's operating teams. The effort to improve conformance, although not new, has taken on significant strategic importance to insure continued strong economic performance and maximum oil reserves.

A multi-disciplinary team was developed to focus on this issue. As with any effort attempting to change the focus of an operation, conformance improvement required a detailed study to scope the potential benefits, and to communicate those benefits to decision-makers. This paper summarizes the Rangely Conformance Improvement Team's efforts, including: Organizational approach to the effortStrategic alignment of conformance improvement with operating team prioritiesAssessment of the state of conformance and the tools developed for problem identification and opportunity rankingConformance improvement method selectionResults to dateFuture conformance improvement efforts and challenges.
New Insight into Aluminium Citrate/Polyacrylamide Gels for Fluid Control
Authors: Stavland Arne , Jonsbråten Hilde Carlsen
Published: December 2007

Aluminium citrate/polyacrylamide gels are found to be more sensitive and less robust than similar chromium systems. The main motivation for investigating aluminium based systems is the environmental constraints. This paper summarize the status on research of aluminium citrate gels. Several field experiments have been carried out, some of them claimed to be a success but yet the gelation mechanisms has not been fully understood. This paper demonstrates one possible gelation mechanism, where oligomerisation of the aluminium citrate complex is essential. The variation in gelation kinetic observed and to some extend gelation mechanisms for the different sources of aluminium is mainly because of the difference in oligomerisation.

The ratio between aluminium and citrate is critical. In seawater, precipitation of aluminium is observed at low amount of citrate (2:1) and precipitation of calcium citrate at ratios above 1:2. Within this window robust gels may be formed as long as pH is below 6 and hydrolysed polyacrylamide are used. In core flopds gel is formed if the sources to polymer degradation is removed. At aluminium to citrate ratios of 1:1 no precipitation and face plugging, that is a severe problem at lower citrate concentrations, have been observed.
Economics of Light Oil Air Injection Projects
Authors: Fassihi M. R. , Yannimaras D. V. , Westfall E. E. , Gillham T. H.
Published: December 2007

Several papers have been recently published1,2,3,4,5 discussing the process of air injection for light oil recovery and describing the criteria for a successful project. The performance of some light oil air injection field projects has also been discussed in these papers.2,5 However, the economics of this process have never been fully addressed before. This paper discusses the economics of a successful on-going project, the Medicine Pole Hills Unit (MPHU, ND), and a new project underway at West Hackberry, LA. The economics of air injection in low pressure fault blocks for repositioning and producing the oil rim are discussed as well.
Putting Technology to Work for Independents
Authors: Rowell D. , Benton J. H.
Published: December 2007

To exploit the remaining resources in the lower 48 states, independent operators need access to new technologies that reduce the costs of finding, drilling, and producing oil. The problem is that new and existing technologies are often beyond the reach of independents, who have not engaged in research and development (R&D). These exploration and production (E&P) companies must gain access to available technologies if they are going to survive in today’s changing industry conditions.

The Petroleum Technology Transfer Council (PTTC) has been formed by the E&P industry as a national non-profit organization to address the technology needs of US companies, mainly independents. Its mission is twofold: (1) to facilitate and accelerate the effective flow of technology information from R&D organizations to the US upstream industry, and (2) to provide a feedback mechanism through which operators can inform the R&D community about their priority research and technology needs. The PTTC receives funding from the Department of Energy (DOE), several state governments, industry, the Gas Research Institute (GRI) and other sources.

Although it has only been in existence since 1994, the PTTC has made great strides in identifying and prioritizing the industry’s technical problems, and assessing which technologies provide possible solutions. Technology workshops are being held around the country to transfer information to the actual users of the technology in the field. Regional resource centers have been opened in many areas to provide producers with access to computers, analytical software, databases, referral services and technical assistance. The PTTC has established various forms of outreach, including a national electronic information system on the Internet, that links its national Home Page with ten regional Home Pages. Through its function as a national clearinghouse, the PTTC is successfully transferring the latest advancements in exploration, reservoir characterization, drilling, production, offshore, and environmental technologies.
Reservoir Characterization and CO2 Pilot Design in the Naturally Fractured Spraberry Trend Area
Authors: Schechter David S. , McDonald Paul , Sheffield Tom , Baker Richard
Published: December 2007

The Spraberry Trend Area in West Texas encompasses a productive area greater than 2,500 mi2. Spraberry was once deemed, "The largest uneconomic field in the world." The marginal economics and low recoveries of producing in Spraberry are well documented and have effectively prevented comprehensive reservoir characterization yet the Spraberry Trend Area continues to produce nearly 60 Mbopd from more than 7,500 wells and has produced 700 MMbbls during the life of the reservoir. Many wells have been abandoned due to low productivity and many more face the same fate unless new technology becomes available which will improve recovery over the current low value. Spraberry Trend Area reservoirs originally contained some 10 Bbbls OOIP of which less than 10% has been recovered. Obviously, the oil remaining in place represents a tremendous EOR target.

Many of the large Spraberry Units which were once operated by major oil companies have been acquired by independent oil companies. Development of these units has resulted in extensive in-fill drilling from 1991 through 1995. The consolidation of large tracts of unitized Spraberry production under one operator combined with a plentiful, local and relatively inexpensive supply of CO2 has raised some interesting questions. This paper addresses the necessary background and future plans for a proposed CO2 pilot in the Upper Spraberry.

The work in this paper also demonstrates the value of consolidating old data from several operators aud integrating with more recent data as a necessary step towards comprehensive fracture characterization, a precursor for developing all possible process options before vast numbers of Spraberry wells are plugged and abandoned.
3-D Seismic Texture Classification
Authors: Vinther R. , Mosegaard K. , Abatzis I. , Andersen C. , Vejbaek O.V. , Nielsen P.H.
Published: December 2007

Statistical recognition of seismic reflection patterns is a useful aid to seismic data interpretation. The seismic texture classification classifies and recognizes seismic data into a limited number of categories each characterized by a distinct style of reflectivity. The basis in the recognition is a set of reference windows (2D) or blocks (3D) representing all major types of reflectivity from the sections of interest.

The seismic data is analysed as 2-D windows each modelled as a Markov random field, where the probability distribution of small patterns in the window is used to characterize the seismic texture. In 3-D the seismic block is represented as a collection of 2-D windows, where the average probability distribution of small patterns in the windows characterize the seismic texture of the block. The recognition of the seismic texture uses a linear projection where the seismic texture is projected onto categories of reflectivity. This makes the method computationally efficient.

The information obtained by the seismic texture classification is most easily seen in the vertical display as illustrated on small extractions from 2-D and 3-D offshore dataset.
Effective Flow Parameters for 3D Reservoir Simulation
Authors: Pickup Gillian E. , Carruthers Dan
Published: December 2007

With the increasing use of detailed full-field 3D reservoir models, the issue of the correct determination of multiphase flow functions in three directions arises. Reservoir engineers are relatively familiar with the use of kv/kh ratios, but the correct kx/ky/kz functions for multiphase (or even single- phase) flow are less easily estimated. In this paper, we describe a model for a 3D sedimentary structure and we derive directional flow functions using a development of the geopseudo approach.

In order to incorporate the effects of 3D lamina structure, a new method of upscaling has been devised. In this method, the laminae are modelled as a series of plane surfaces. The effective permeability of these planes may be calculated analytically, and then a numerical simulation may be performed to obtain the effective permeability for the whole bed. This method can be used to calculate tensor permeabilities for either single-phase or two-phase flow. In this way we can generate 3D pseudo-functions which may be used as input for larger-scale simulations.

Using both the new method and the traditional Kyte and Berry pseudo-ising approach we have calculated the pseudo relative permeabilities for a model of a fluvial trough crossbed. We show that oil recovery may be significantly influenced by the 3D laminar structure. In particular, the nature of the bounding surfaces of the beds has an important effect on capillary trapping. In beds with high permeability contrast in the laminae, crossflow may be important indicating the need for full tensor upscaling methods.
Connected Volume Calibration For Well-Path Ranking
Authors: Gutteridge P.A. , Gawith D.E.
Published: December 2007

Presented here is a method by which we are using a shared earth model in the planning of development wells. The latest 3D modelling packages give us the ability to design non-conventional well trajectories interactively, inside a 3D geological model. This means that we can easily generate a number of possible well paths designed to penetrate particular features of the reservoir. Final well placement decisions are normally based on performance predictions from a reservoir simulator, but the time required to run the simulator for all possible wells would be prohibitive. There is clearly a need for a rapid screening or ranking technique to identify the well paths most likely to be suitable, and we describe here some recent work to meet this need.
Modelling Injection Strategies for a Reservoir with an Extreme Permeability Contrast: IOR Qualification
Authors: Surguchev Leonid M. , Hanssen Jan Erik , Johannessen Hege M. , Sisk Carl D.
Published: December 2007

Considerable hydrocarbon reserves are associated with heterogeneous stratified reservoirs. Many of these reservoirs demonstrate poor recovery efficiency, due to the low vertical and lateral sweep, if produced traditionally by depletion or waterflooding. Modern Improved Oil Recovery (IOR) methods have significant potential for such formations.

A Norwegian sandstone field was evaluated in this study. This field is characterized by extreme contrasts in reservoir properties. Horizontal permeability in the formation varies from 2 - 20 mD in the lower reservoir to more than 2000 mD in the upper reservoir. The sweep is accordingly very low in the lower reservoir, which contains 60-70% of oil in place.

A 3D model of the formation was constructed in order to investigate, in detail, potential IOR processes. The selection of the model area was conducted by a cross-discipline team. It was decided that a full field model was too resource intensive and a generic model would be too simplistic. A third alternative called, average pattern approach, was utilized. The cross-discipline team looked over the field and made a group decision to choose a specific area. A portion of the field that had average properties and well completion history was modelled. The area was large enough to capture different development schemes. The reservoir model reflects the main characteristics of the formation and, in particular, the high permeability contrast between the upper and lower reservoirs, interlayer communication and presence of faults. Actual operational and reservoir information was available for the selected pattern. This approach gives validity to predictions and evaluation of IOR processes and also minimizes the resources and time required for modelling.
Hydraulically Fractured Horizontal Well Simulation
Authors: Hegre T.M.
Published: December 2007

Simulation of hydraulically fractured horizontal wells is discussed in detail. Horizontal wells intercepted by both transverse and longitudinal fractures are evaluated. It is shown that fractured horizontal well representation in simulation models is dependant on the study objectives. For single well studies of the early pressure transient behaviour it is in general necessary both to explicitly model the fracture with small highly conductive grid cells, and to specify relatively small grid cells in the near fracture area. The effect of both grid cell size and fracture conductivity on the transient pressure behaviour and computer time is demonstrated by several examples. Based on these examples it is possible to construct a grid system which satisfies the accuracy required. For reservoir management purposes, reasonable accurate results may be obtained utilising the equivalent effective wellbore radius concept or the transmissibility corrected method presented in this paper. The effective wellbore radius concept is a simple way to model fractured horizontal well behaviour in a full field model. The fractured horizontal well is modelled as a standard vertical well with an equivalent effective wellbore radius. The effective wellbore radius can be derived from analytical solutions. This method is applicable only if the effective wellbore radius is smaller than the pressure equivalent radius of the grid cells. Generally this restriction requires that the horizontal wellbore with its hydraulic fractures are completely located within a single areal grid cell. A more flexible method is to compute both corrected transmissibilities and well connection factors for a coarse grid which gives the same long term pressure behaviour as a fine grid model. This procedure to adjust coarse grid model transmissibilities and well connection factors based on fine grid simulation results is also simple. In general, it is however required to have a simulation model where it is easy to include local grid refinement and which automatically computes adjusted transmissibilities and well connection factors that can then be applied for coarse grid simulations. The main part of this paper is devoted to single phase problems. However, it is demonstrated that the equivalent wellbore radius concept can be applicable also for multiphase problems.
Direct Inversion for Porosity of Post Stack Seismic Data
Authors: Rasmussen K. B. , Maver K. G.
Published: December 2007

3D seismic data is inverted directly for porosity by implementing a non-linear, globally optimised seismic inversion scheme. The technique takes into account the lithology dependent relationship between porosity and acoustic impedance without requiring the user to make a detailed interpretation of the seismic data and specifying the correlation between acoustic impedance and porosity for each lithological unit. For comparison seismic inversion for acoustic impedance is also carried out.

Seismic inversion directly for porosity is implemented by utilising that the correlation between acoustic impedance and porosity has a negative slope which is often approximately constant and not lithology dependent.

A wavelet is derived that inverts directly for porosity reflectivity and the absolute level of porosity is defined by constraining to a low frequency porosity model which is specified from available well logs.

To invert the seismic data a non-linear globally optimised seismic inversion technique is used. This full 3D multi trace technique does not directly include well logs or seismic horizons and therefore unbiased results are generated from post-stack, migrated seismic data. The seismic inversion is performed by utilising an estimated wavelet, a low frequency model and by specifying 5 inversion parameters.

The seismic inversion for both acoustic impedance and porosity is illustrated by a 3D seismic survey. The seismic data was acquired in the Danish part of the Central Trough with the main target being the Chalk Group which includes Upper Cretaceous-Danien chalk reservoirs. 7 wells are used in the study in order to invert a time window from 1.5 to 2.5 sec TWT, that includes a total of 456,000 traces covering an area of 71 sq km.

The results show that the technique is a fast and reliable method for estimating porosity directly from seismic data. However, the match between the porosity log and the inversion result is not as good as the correlation between the acoustic impedance log and the corresponding inversion result. This is attributed to the non-unique correlation between acoustic impedance and porosity.
Optimisation of Production Strategies using Stochastic Search Methods
Authors: Harding T.J. , Radcliffe N.J. , King P.R.
Published: December 2007

This paper describes the application of stochastic search techniques to the production scheduling of a group of linked oil and gas fields. The goal was the maximisation of total net present value and a genetic algorithm using problem-specific crossover operators was particularly successful in this respect.

Introduction

Reservoir engineers must decide upon a "best" management strategy for the exploitation of each petroleum resource, typically the strategy which will maximise economic return. In particular, a production schedule, specifying rates of extraction over the lifetime of the reservoir(s), must be chosen. From this, decisions about the construction of processing facilities and pipelines will follow. A quantitative approach to the search for the "best" production schedule requires the construction of a mathematical model, which must capture enough characteristics of the reservoir(s) to predict the costs and benefits of any given schedule.

Even when a single independent field is under consideration, finding the "best" schedule can be a non-trivial problem, as all but the simplest models are likely to be non-linear and contain discontinuities. BP has a number of multi-field potential developments world-wide. In such cases, the problem is more difficult still. The total number of production rates is of course proportionately larger, but extra complexity arises from the inter-dependence of the fields. There are extra degrees of freedom, namely the respective timing of each field, and in addition the costs associated with each field depend on the sum of the production rates from some or all of the other fields.

If possible, the reservoir engineer will also wish to ensure robustness of the choice of extraction strategy in the presence of uncertainty in the economic model - the most obvious source of uncertainty in this case being the reservoir characterisations.

This paper describes how several techniques - genetic algorithms in particular - were used to search the space of possible production schedules based on an indicative data set from one multi- field development. The techniques show potential ways to achieve significant increases in net present value, which were consistent with traditional discrete analysis.