bluuebunny/crossref_metadata_2025 huggingface dataset:
Computer User Groups: The Overlooked Source of Training
Authors: McGinnis B. , Flanders W. A.
Published: December 2007

Petroleum companies, recognizing the need for computer use, have invested millions of dollars in compíuter hardware, software, and training. While large productivity increases have been achieved through initial training (Phase One), even larger gains can be accomplished through the computer skill-building process called optimized training (Phase Two). Traditional sources provide excellent Phase One training, but lack the resources and format capabilities to provide complete Phase Two training.

Computer user groups (CUG's) can provide an efficient, cost-effective way to supply Phase Two training Presently, however, CUG's are not widely used for this purpose. For this to change, CUG members and their companies must cooperate to develop programs that provide this training. Increased productivity can be realized by working together.
An Integrated Three-Dimensional Wellstring Analysis Program
Authors: He Xiaojun , Sangesland S. , Halsey G. W.
Published: December 2007

A Well String Simulator (WSS) computer program has been developed to analyze well string performance in high-angle and horizontal wells. The program can calculate the axial force, pick-up/slack-off loads, bending moment, rotating torque, buckling load, and stress along the well string (drill string/casing/coiled tubing) in any well profile. The effects of well string running speed and rotating speed on the axial forces and torque can be considered in the calculations.

A menu-driven data input interface with on-line help and a graphics post processor has been integrated into the program for easily inputing data and visualizing results immediately after the calculations. Dynamic memory allocation and overlay techniques are used to minimize the memory requirements of the program. As a result, the program can run comfortably on an IBM PC with 512 KB memory.
Using Computer Graphics and Animation To Teach Petroleum Engineering Concepts
Authors: Whitman D. L. , Evers J. F. , Terry R. E.
Published: December 2007

The authors have developed a number of microcomputer-based programs that use the graphical capability of this computer to teach petroleum engineering concepts to students. Students have consistently-commented that the use of this software, both for in-class demonstration and out-of-class assignments, is very beneficial to their understanding of certain petroleum engineering problems. The programs also eliminate the tedium that is involved in many of these computations, without removing the requirement that the student must understand the concept of what the program is demonstrating.

Details on these programs have been published previously1–4 and, therefore, no detailed explanation will be presented in this paper. Brief descriptions will be given for the following microcomputer-based teaching programs:

Monte-Carlo Simulation Vapor-Liquid Equilibrium Experiment Gas Kick Control Water Flooding
Advancements in Remote Completion and Operation of Underwater Satellite Wells
Authors: Childers T.W. , Langley J.O.
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

This paper was prepared for the 43rd Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Tex., Sept. 29-Oct. 2, 1968. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Humble recently demonstrated an important advancement in subsea completion technology by remotely completing a satellite underwater well with pump-down tools. This was Industry's first known attempt to perform completion operations with the rig off location. Pump-down tools and techniques were used Pump-down tools and techniques were used to perforate and consolidate the producing sand at 10, 100 feet TVD. This pump-down completion along with onshore tests simulating other pump-down completion-workover operations demonstrates the capability to remotely perform virtually all through-tubing type well servicing operations necessary to complete and maintain satellite subsea wells. This technology, in addition to significantly lowering completion costs of subsea wells, will substantially reduce maintenance costs by eliminating the need for many vertical re-entry workovers.

The subsea wellhead, tree and control system used for completion of this well and Humble's experience in operating underwater completions in the Gulf of Mexico are reviewed in this paper.

Introduction

Several significant advancements have recently been made in underwater completion technology. These advancements include both new and improved pump-down tools and well completion systems, as well as continued successful operating experience with underwater completions. They combine to greatly enhance the capabilities, economics, and application of the underwater completions, as well as overall confidence in the system.

Specific advancements that have been made Humble are:

The development of a complete suite of pump-down production maintenance an workover tools. The development of these tools has eliminated the need for expensive mobile rigs to perform most completion well servicing, and routine workover operations. The development of an unassisted diver connection system for tubing extensions.
Acoustic Controlled Subsea Completion System
Authors: Coburn William L.
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

This paper was prepared for the 43rd Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Tex., Sept. 29-Oct. 2, 1968. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Introduction

Water depths in the recent Santa Barbara and Texas lease sales have focused attention on the need for a technique to remotely control and monitor wellhead completion systems. There is a need for a remote control system that eliminates the requirement for either fixed electric cables or hydraulic control lines linking the surface and the subsurface wellhead equipment. Physical control cables or lines are very Physical control cables or lines are very susceptible to physical damage from various sources. If these cables become severed, complete loss of control of the subsea equipment is experienced.

The use of acoustic communications as a means of reliable underwater remote control and telemetry is now a working concept. It is the only technique which can provide remote control without interconnecting cables and still maintain the required security. The AMF acoustic system was designed specifically for remote control applications where multiple commands. are required. It is secure from undesired responses to either ambient or man-made noises. This system has proved itself over the past four years in many varied underwater remote control and monitoring applications.

A prime consideration in the design of a remotely controlled subsea system is the selection of the power supply. Power can be supplied in many ways:

via a subsea primary battery system, via a subsea storage battery system trickle-charged by a subsea nuclear generator, and via a subsea storage battery system tackle-charged over a hard wire line from a surface platform.

There are numerous trade-offs in each of the above mentioned power supply systems, such as water depth, life expectancy and cost (initial and maintenance).
The Geology and Reservoir Characteristics of the Zakum Oil Field, Abu Dhabi
Authors: Fox A.F. , Brown R.C.C.
Published: December 2007

The structure and stratigraphy of the area are discussed and related to the geology of the surrounding areas. Possible correlations of the various beds penetrated with the successions in bordering territories are suggested.

The geological characteristics of the producing horizons are described and their effect on the reservoir properties discussed.

The subdivision of the oil-bearing horizons into recognisable reservoir units, their physical characteristics and influence on the methods of production currently in use are described.

Introduction

The Abu Dhabi Marine Areas Concession, originally of about 12,000 sq. miles, is held by Abu Dhabi Marine Areas Ltd. in which The British Petroleum Company has a two thirds interest. The terms of the concession were revised during 1966 and two areas totalling about 1705 sq. miles were relinquished by Abu Dhabi Marine Areas Ltd. on 10th January 1967. A map showing the area and the location of the various oilfields is at Figure 1.

Exploration has been active and continuous since the original grant of the concession by the Ruler of Abu Dhabi in March 1953. The first phase was a topographical and geological investigation of the sea bed combined with a reconnaissance gravity survey carried out from the m.v. CALYPSO under the command of Cdt. J.Y. Cousteau, by BP surveyors and geologists, and geophysicists of the Geophysical Prospecting Company's staff.

The second phase consisted of a reflection seismograph survey, the traverse lines for which were laid out in accordance with an interpretation of the previous gravity survey. This survey ran from 14th December, 1954 until 23rd April, 1955 and included 2760 miles of single cover line. Most of the traverse lines were laid out on a 10 mile grid but indications were sufficiently conclusive for a location for a test well to be selected at Umm Shaif the results from which have already been described.
Reliable Deepwater Structural Casing Installation Using Controlled Jetting
Authors: Beck R. D. , Jackson C. W. , Hamilton T. K.
Published: December 2007

This paper presents a method for installing structural casing from floating drilling vessels in a manner such that the casing is proof loaded and will not settle when other casing is landed later. The method borrows from geotechnical principles and pile installation observations. In addition to structural casing installation, this method can be used to install lightly loaded piles (e.g., anchor piles) in clay soils.
Shaker Screen Characterization Through Image Analysis
Authors: Cutt A. R.
Published: December 2007

The labelling of shaker screens has been a problem. Existing mesh count designations do not adequately describe a shaker screen's potential separation performance. Consequently, it is difficult to make an informed decision when selecting shaker screens. The establishment of a standardized, performance-based designation system has been hindered largely by the time, expense and difficulty in deriving absolute screen separation efficiencies from full-scale laboratory testing.

This paper introduces a technique which overcomes this problem by relating the separation efficiency potential of a shaker screen to a volume-equivalent distribution of its hole sizes. Magnified, computer-enhanced visual images of screen apertures were measured using a PC-based image analyzer system. An equivalent volume distribution was then derived from this data to yield a curve corresponding to a grade efficiency or percent-separated function. These equivalent volume distributions were compared to experimental percent-separated values for square, oblong and layered mesh screens to confirm the viability of the image analysis technique.
Visualization and Numerical Studies of Bubble Growth during Pressure Depletion
Authors: Li X. , Yortsos Y. C.
Published: December 2007

Bubble nucleation and bubble growth during pressure depletion in porous media is an important problem encountered in solution gas-drive. The problem was recently analyzed by Yortsos and Parlar (1989) who proposed a theoretical model valid at low decline rates. In this paper we continue their work using both experimental and numerical methods.A numerical pore network model is developed to simulate the process under various conditions. The model includes gas expansion, concentration gradients and finite size effects, previously neglected. Emphasis is placed on the determination of the critical gas saturation, Sgc, and on effects of the rate of pressure decline. Experiments similar to Yousfi et al. (1990) are also carried out in glass micromodels and Hele-Shaw cells. The nucleation of bubbles in various places and their subsequent growth are recorded. As previously predicted, bubble growth occurs from various nucleation sites, which are activated at different stages of the process. In the micromodel, bubbles grow as ramified clusters, which have the general features of a percolation process (e.g., similar to drainage). This is in contrast to Hele-Shaw cells, where growth of compact clusters is observed. Numerical simulation with the use of the pore network model gives results in good agreement with the experiments.
Large-Scale Averaging of Drainage at Local Capillary Control
Authors: Yortsos Y. C. , Satik C. , Salin D. , Bacri J. C.
Published: December 2007

Present continuum models for large scale averaging rely on volume averaging and homogenization methods, typically under the premise of capillary control. However, such methods are intrinsically unable to provide the local saturation distribution, which is needed for the computation of effective flow properties. In this paper, paralleling porelevel approaches, a percolation method is proposed for the derivation of large scale properties in a drainage process at low flow rates. Percolation is applied to a macroscopically heterogeneous region with a random, uncorrelated permeability distribution. We show that at conditions of local capillary control, when a local description is possible, the large scale capillary pressure curve is a non-trivial average of the individual curves. Large scale capillary trapping is predicted and a corresponding large scale trapped saturation is calculated. Large scale phase premeabilities are also derived. It is found that capillary heterogeneity renders a system more strongly wet in a macroscopic sense.
Phase Behavior In Miscible Systems Of Solvent, Dry Gas And Oil
Authors: Meldau R.F. , Simon R.
Published: December 2007

Introduction

In solvent injection projects, the injection fluid mixes with the reservoir oil being displaced. As the project proceeds, all the possible mixtures of reservoir oil and injection fluid from pure oil to pure injection fluid will occur. If all these mixtures are single phase at reservoir temperature and pressure, then the process is a miscible displacement, and high oil recovery can be obtained from the swept regions of the reservoir.

In most cases, the injection fluid is vaporized at reservoir conditions. Therefore, for a miscible displacement, it is necessary to have a composition transition from liquid reservoir oil to vaporized injection fluid without having two phases present at any one point in the reservoir.

A series of phase behavior experiments was conducted which showed the event which occur during the transition from pure reservoir oil to pure injection fluid. These events can be illustrated by Fig. 1.

Fig. 1 shows that the addition of injection fluid to reservoir oil produces a series of bubble point mixtures, then a critical mixture, and finally, a series of dew point mixtures. A bubble point mixture is defined as one which produces a gas as the second phase when the pressure is lowered into the two phase region. A dew point mixture produces a liquid as the second phase.
A Computerized Simulation Of A Heterogeneous Aquifer Storage Formation
Authors: Reed L.N. , Henderson J.H. , Dempsey J.R. , Coats K.H.
Published: December 2007

A multi-dimensional, two-phase numerical reservoir simulator has been used to model a completely heterogeneous aquifer formation in which natural gas is stored. The mathematical model accounts for the variables which affect aquifer storage performance, such as capillary pressure, gravity effects, aquifer strength, pressure, gravity effects, aquifer strength, reservoir heterogeneity and variable fluid properties. A procedure was utilized which properties. A procedure was utilized which permits automatic history matching of the field permits automatic history matching of the field pressure response to gas injection and pressure response to gas injection and withdrawal. Results are presented which indicate that a reliable reservoir description was obtained which allowed for a satisfactory match of historical pressure-response and will serve as a basis for future reservoir studies. The usefulness of the automatic matching procedure to determine reservoir parameters procedure to determine reservoir parameters based on matching of field response is emphasized.

Introduction

A company which utilizes underground gas storage must be confident of the dependability of the facility. It is imperative that the reservoir performance be accurately predicted to insure that the reservoir is capable of delivering the withdrawal rates as required. This guarantees the satisfaction of customer demands by incorporation of the storage field performance with the more easily determined mainline capacity. While all storage facilities have unique design and operational difficulties, perhaps the most difficult is gas storage in natural aquifers. This stems in part from the many variables which influence performance, the lack of performance data prior to development, and the performance data prior to development, and the introduction of a foreign hydrocarbon into a 100% water saturated zone. The engineers responsible for the development and operation of storage fields have historically been forced to make many simplifying assumptions in order to predict a field's performance, determine optimum development schemes, performance, determine optimum development schemes, etc. This situation is not unlike the problems faced by reservoir engineers concerned with the depletion of natural-occurring hydrocarbon reserves. The availability of high-speed digital computers and mathematical reservoir models offers a means to more rigorously study various gas storage problems incorporating the many variables which must be considered. This paper describes the approach we are taking to more accurately predict aquifer storage reservoir performance.
A New Approach to Modelling of Multicomponent Two-Phase EOR Processes With Interphase Mass Exchange
Authors: Brusilovsky A. I. , Zazovsky A. F.
Published: December 2007

A new approach to the analysis of multicomponent EOR processes with interphase mass exchange is proposed. It’s based on the splitting of mass exchange and flow problems corresponding to two-phase displacement in porous media. On the first stage phase and composition behavior of system inside the zone of mass exchange is investigated by means of simulation of various composition paths. All these paths, as it was found, are realized in a very strong narrowing of compositional space for every fixed compositions of displacing and displaced fluids.

This is very useful on the second stage when hydrodynamic calculations are worked out. Such an approach substantially reduces the expenses connected with repeated calculations of phase behavior for compositional models and it extends the application range for analytical methods.

The main features of new approach are illustrated for gas-drive EOR processes. The general form of cubic EOS is used for description of phase behavior in terms of real composition. Hydrodynamic calculations are fulfilled after the reduction of a real system to a three-component one. Generalization of common composition path simulation for immiscible oil displacement by gas agents is proposed. The results for methane and smoke gas injections in Tengiz and Surgut fields are presented.
Mechanisms of Miscible Oil Recovery: Effects of Pore-Level Fluid Distribution
Authors: Stern D.
Published: December 2007

A series of tertiary multiple-contact miscible CO2 corefloods have been carried out to study effects of flow rate, core length, oil viscosity, wettability, WAG ratio, and initial water saturation on displacement mechanisms. The goal of these experiments was to identify important recovery mechanisms that influence performance of reservoir-condition, multiple-contact miscible floods.

In these experiments, a bank of miscibly-displaced oil is produced first, followed by oil that is initially lighter than the original oil, and becomes increasingly heavy as the flood progresses. The implication is that some oil is initially bypassed and later recovered by extraction.

The amount of bypassing is not sensitive to flow rate or core length, but increases as the solvent/oil viscosity ratio decreases. Based on these results, it is concluded that pore-level effects such as capillarity-induced bypassing and dispersion are major bypassing mechanisms. Microvisualization experiments, in which fluids are hardened in-place, provide direct confirmation that pore-level bypassing takes place.

Viscous fingering (macroscopic bypassing) may also take place, but it is not thought to be the dominant bypassing mechanism under the conditions of this study.

Wettability also has a significant effect on coreflood performance, particularly at high WAG ratios. High WAG ratios result in less oil recovery by extraction. In water-wet rock, this is a large effect, with almost no extraction at high WAG ratios. In mixed-wet rock, however, the effect of WAG ratio is much smaller, and significant quantities of oil are recovered by extraction regardless of WAG ratio. This is likely the result of wall-coating oil films in the mixed-wet rock, which improve contact between oil and solvent.
Analytic Solutions for Elliptical Finite-Conductivity Fractures
Authors: Riley M. F. , Brigham W. E. , Home R. N.
Published: December 2007

The purpose of this study is to develop exact analytic solutions for the pressure response of a finite conductivity fracture. This model should be able to verify the existence of various flow regimes found in earlier studies. It is hoped that this solution could be modified to give simplified expressions for well pressures for all times and all fracture conductivity ranges.

The present work poses and solves the problem of a vertical finite conductivity fracture of elliptical cross-section. The flow within the fracture is assumed to be incompressible and the reservoir is assumed to be infinite. The elliptical fracture geometry was chosen to facilitate the expression of fracture and reservoir pressures as eigenfunction expansions.

The solution is obtained by expressing the reservoir pressure as a series of Mathieu functions, and the fracture pressure as a series of cosines. The coefficients in these series satisfy an infinite set of linear relations, termed Fredholm sum equations. Exact solutions to these sum equations are obtained in forms which resemble continued fractions of summations, or equivalently, which require iteration of rational forms. A great deal of effort has been expended to speed the calculation of the solutions, however, only partial success has been achieved.

The solutions become increasingly difficult to compute as time decreases. So, approximate solutions for well pressures are given for extremely low values of time. These solutions indicate that behavior of an elliptical fracture is essentially the same as that of a rectangular fracture. Indeed, the well pressures calculated in this work are quite close to those for a rectangular fracture. Generally applicable simplified well solutions have not been found.
Electrical and Petrophysical Properties of Carbonate Rocks
Authors: Wang Zhijing , Hirsche W. K. , Sedgwick G. E.
Published: December 2007

Electrical and other petrophysical properties were measured in the laboratory versus pressure in 54 carbonate core samples from 11 oil-producing reservoirs. The measured electrical and petrophysical properties include formation factor F, cementation exponent m, and saturation exponent n, porosity φ, permeability K, grain density ps, capillary pressure Pc, residual (irreducible) water saturation Swr, and sonic velocities. In the measured cores, systematic relationships exist between formation factor and porosity, permeability and porosity, permeability and residual water saturation, saturation exponent and residual water saturation, and formation factor and sonic velocities, although the data are significantly scattered. The formation factors were best-fit to Archie’s equation so that the coefficient a and cementation exponent m were obtained. The empirical equations allow for calculation of porosity from formation factor, permeability from porosity and residual water saturation, and saturation exponent from residual water saturation, or vise versa.
Reservoir Heterogeneity at Seventy-Six West Field, Texas: An Opportunity for Increased Oil Recovery From Barrier/Strandplain Reservoirs of the Jackson-Yegua Trend by Geologically Targeted Infill Drilling
Authors: Hamilton D. S.
Published: December 2007

Seventy-Six West field, in northwest Duval County, South Texas, produces from the uppermost Jackson Group at depths of 1300 to 1400 ft [396 to 426 m]. Reservoir geometry is highly complex, consisting of strike-oriented beach ridge, channel, and sand-poor lagoonal facies, which are modified by dip-oriented tidal-inlet fill and washover sands. Production trends mirror the beach ridge and channel facies but are also influenced by dip-oriented facies and by small normal faults. The reservoir is heterogeneous and has an estimated 6 MMBbl [9.5 × 105 stock-tank m3] of remaining mobile oil trapped in untapped compartments and poorly swept zones. Results of detailed reservoir characterization identify these compartments and provide targets for infill drilling. Results at Seventy-Six West field are applicable to nearly 300 similar South Texas fields.
Application of the Pulse Decay Technique
Authors: Gilicz A.
Published: December 2007

In recent years the pulse decay technique became a frequent tool for the fast and convenient measurement of permeability and porosity of mostly tight rocks. The method is superior to conventional steady state methods as it is much faster and easier to perform. So far it was applied to linear cores (plugs) only. In the last years radial models appeared widely as they show some advantages over linear models, so the need emerged to apply the method for radial cores. Experimental apparatus and mathematical models have been developed to solve the problem. The current paper describes experimental set-up, analytical solutions of the governing equation and applications of them to performed measurements.
A Model for the Simultaneous Generation of Core-Controlled Stochastic Absolute and Relative Permeability Fields
Authors: Tjølsen C. B. , Damsleth E.
Published: December 2007

During the last few years, a two-stage stochastic model for 3-D modelling of reservoir architecure and absolute permeability1 has been developed and utilized in field development studies. The scope of this paper is to present a new, important extension of this model: The possibility of generating relative permeability curves with stochastic spatial variation. Absolute permeability can be measured on cores as well as in analogue outcrops, using a field minipermeameter. Relative permeabilities, however, are in general time consuming and expensive to measure. For this reason, they are usually measured on a very limited number of core samples. Relationships or interdependendencies among petrophysical variables are required as input to the stochastic model. Based on a unique set of core data containing relative permeability curves measured on 85 core plugs from one single well in the North Sea, correlations between relative permeability curves (represented by endpoints and Corey-exponents), absolute permeability and depositional environment have been developed2. Utilizing these correlations, the paper demonstrates a co-kriging procedure for simultaneously generating absolute and relative permeability fields.

An example based on data from a North Sea reservoir is given to illustrate the model and its application. To evaluate the effect of different relative permeability curves in each grid cell, flow simulations were performed. The same grid was used for the flow simulations as for the stochastic realizations, to avoid the problem of homogenization of the relative permeability curves. The results indicate that in the cases studied, the introduction of stochastic variation in the relative permeability curves has no significant effect on the shape of the production profile, when compared to the case with a constant relative permeability curve.
Stochastic Heterogeneity Models of Thin, Laterally Continuous North Sea Sandstones and their Influence on Simulated Reservoir Performance
Authors: Aasen J. O. , Høye T. H. , MacDonald A. C. , Grindheim A. O. , Jacobsen T. , Storvik G. , Holden L. M.
Published: December 2007

The paper presents an application of a stochastic reservoir description simulator to the modelling of two sections of a coastal-deltaic reservoir, the Tarbert Formation in the Gullfaks Field. The description simulator, called DESIRÈ, models reservoir architecture by an ordered sequence of widespread facies types on which are superimposed bodies or infinitely thin barriers. Petrophysical variables are simulated conditionally on architecture. The reservoirs display features of a coastline progradation and a sandflat sequence, interspersed with bodies of tidal origin and calcite cemented zones. Contoured- and flow unit models have been constructed for the reservoirs, and sets of realisations from the models have been simulated. Production simulations of water injection have been performed on all realisations. The production results show that with the data available for analysis, significant uncertainty remains in predicted behaviour irrespective of the comparatively simple structure of the reservoirs under study.
Fractional Dimension Analysis of Constant-Pressure Well Tests
Authors: Doe T. W.
Published: December 2007

This paper presents a discussion of spatial dimension and applies a generalized dimension approach to interpreting constant-pressure well tests. The spatial dimension of a well test is determined by the power by which either the surface area or reservoir properties change with distance from the source. The dimension equals the power of variation plus one. Fractional dimensions arise when the power of variation is not an integer. Fractional dimension behavior may indicate either fractal reservoir geometries or non-fractal geometries which are not space-filling. The dimension of a well test is distinctive in logarithmic plots of flow rate versus time. For dimensions between 1 and 2, the flow rate declines along a straight line with a slope equal to n/2-1 where n is the dimension. Determination of reservoir properties is complicated by uncertainties in the space-filling proportion of the reservoir, conducting surface areas of the reservoir, and the effective radius of the well.
Numerical Construction and Flow Simulation in Networks of Fractures Using Fractal Geometry
Authors: Acuna J. A. , Yortsos Y. C.
Published: December 2007

Present models for the representation of naturally fractured systems rely on the double-porosity Warren-Root model or on random arrays of fractures. However, field observation in outcrops has demonstrated the existence of multiple length scales in many naturally fractured media. The existing models fail to capture this important fractal property. In this paper, we use concepts from the theory of fragmentation and from fractal geometry for the numerical construction of networks of fractures that have fractal characteristics. The method is based mainly on the work of Barnsley [1] and allows for great flexibility in the development of patterns. Numerical techniques are developed for the simulation of unsteady single phase flow in such networks. It is found that the pressure transient response of finite fractals behaves according to the analytical predictions of Chang and Yortsos [6], provided that there exists a power law in the mass-radius relationship around the test well location. Otherwise, finite size effects become significant and interfere severely with the identification of the underlying fractal structure.
Quantifying Horizontal Well Logs in Naturally Fractured Reservoirs—I
Authors: Svor T. R. , Meehan D. N.
Published: December 2007

Horizontal wells have been applied in many types of reservoir conditions with a variety of applications. The most successful of these has been exploiting the very large horizontal permeability anisotropics associated with naturally fractured reservoirs. Log analysis has always been difficult in naturally fractured reservoirs; very little has been published regarding horizontal well logs. This paper summarizes Union Pacific Resources (UPRC) experience logging dozens of horizontal wells in several different naturally fractured reservoirs, summarizes the improved information resulting from this experience, contrasts various well logs applicable in such areas, and describes a method for categorizing fracture apertures used to quantify the total horizontal well fracture index CRH).

UPRC has logged dozens of horizontal wells in the Bakken, Niobrara, Austin Chalk, Buda, Georgetown, and Second White Specks formations with oriented microresistivity devices (FMS), borehole acoustic televiewers (BATV), four and six arm dipmeters, and sonic logs. Formation evaluation objectives have included determining the depth of most intensely fractured intervals, identifying and quantifying number and aperture of fractures encountered, locating faults and bed boundaries, determining fracture azimuths, and for use in subsequent production operations. The use of vertical and 45 degree ‘pilot’ holes is compared, showing significantly superior results using a 45 degree well to detect the fractured intervals. The applicability of the various tools are described with examples of each being presented. The UNIX-workstation based methodology for approximate quantification of fracture azimuths into aperture-based categories is described, along with the procedure to determine the RFI. A horizontal well log presentation is discussed that illustrates difficulties in mud log interpretation.
Revival of the van der Waals Classical Theory via Silberberg Constant
Authors: Lawal A. S.
Published: December 2007

Starting from the state equation reported by Hirn in 1863 and the experimental studies of Andrews (1863), plus over a century and twenty years of efforts on the van der Waals classical theory, the search for a predictive equation of state led to reexamination of the work of eight Nobel Laureates and revised value of van der Waals’ gas constant for the Silberberg constant. The use of the Silberberg constant provides a better basis in theory for the development of the predictive equation of state than the purely empirical definitions used by earlier investigators. The perceived confusion of the van der Waals gas constant, which hitherto has been assumed to be synonymous to the constant of the gas laws, has also been resolved with the Silberberg constant.

The question of why van der Waals theory of the cubic equation of state was in error is an intriguing one, and its answer provides dramatic proof of the human side of science. This paper uncovers the source of the error and pin-points the Nobel speech of van der Waals as the fruitful source of resolving the two oversights of his earlier works. A reformed van der Waals equation of state is used to demonstrate the solution for two important and often puzzling areas of active research: improvement of the predictive power of the equation of state for complex hydrocarbon molecules and the prediction of critical points of disparate molecules from their constituent components.
A Study of Fractured Wells in Bounded Reservoirs
Authors: Chen Chih-Cheng , Ozkan E. , Raghavan R.
Published: December 2007

This work is a rigorous evaluation of vertically fractured well responses producing fractured reservoirs. Detailed evaluation of plausible responses to be expected from short-term tests are provided. New diagnostic rules, analytical procedures, and working curves are presented. The effect of fracture length on flow patterns in the reservoir is documented. Practical issues that the analyst must be cognizant of are documented.
Two-Phase Flow Interporosity Effects on Pressure Transient Test Response in Naturally Fractured Reservoirs
Authors: Al-Bemani A. S. , Ershaghi I.
Published: December 2007

Complexities related to multi-phase flow in naturally fractured reservoirs have been somewhat addressed in numerical models used for performance prediction purposes. This paper examines the concept of the two-phase (oil and water) flow in analytical modeling of pressure transient response in naturally fractured reservoirs.

Under the condition of the two phase flow in both the matrix rock and the fractures, the capillary pressure and the relative permeability characteristic associated with prevailing saturation conditions are integrated into the pressure transient models.

Characteristic shape of the transition portion of pressure response curve, for naturally fractured reservoirs, is influenced by the specific assumptions made about the nature of matrix-to-fracture flow. The analytical solution presented here describes the effect of two-phase interporosity on the transition portion of the pressure response. The interporosity parameter is modified to incorporate the contribution of the relative permeability and capillary pressure effects associated with countercurrent flow.

Our studies show that without proper consideration of two-phase flow, and the saturation conditions, the estimated values for interporosity coefficient, estimation of the shape factor and block sizes are subject to errors.

With independent measurements from cores and well logs, to ascertain the wettability and fluid saturation conditions in both fractures and matrix rock, the proposed model allows improved estimation of the interporosity flow parameter, shape factor and block sizes for history matching purposes.
Using a Multiarray Induction Tool to Achieve High-Resolution Logs with Minimum Environmental Effects
Authors: Barber T. D. , Rosthal R. A.
Published: December 2007

Over 30 years ago Poupon proposed using several simple induction arrays, each measured separately, and combining them to produce an induction log with improved characteristics. The response of each simple array becomes a "basis function" that can be combined with the others without introducing unwanted interactions. This approach has been used in the Array Induction Imager Tool (AIT*). The AIT tool consists of eight three-coil arrays, six of which are operated simultaneously at two frequencies.

By treating the response of each measurement as a basis function, an optimization technique has been developed to combine all the raw measurements into logs with vertical, radial, and two-dimensional (2-D) response properties that are not achievable with conventional fixed-focus induction arrays. Using this approach, a set of logs has been developed with a 90% vertical resolution width of 1 ft and a reasonable rejection of borehole rugosity effects. Additional log sets are available that have different resolution-cave effect tradeoffs. A log set with a vertical resolution of 2 ft has less cave effect than conventional induction logs with 8-ft resolution, and a 4-ft resolution set has virtually no cave effect. The effectiveness of this response shaping technique has been demonstrated in case studies with both computed and field logs over a wide range of environmental conditions.
Practical Solutions for Interactive Horizontal Well Test Analysis
Authors: Ohaeri C. U. , Vo D. T.
Published: December 2007

This study presents new approaches to solve problems of flow to horizontal wells. It documents a procedure to obtain solutions to problems of single phase liquid flow to horizontal wells. This procedure, which couples the source function approach with a real space Laplace inversion algorithm, gives very accurate results for a wide variety of wellbore and reservoir conditions including constant wellbore pressure, wellbore storage, skin and fluid phase redistribution. This approach is valid during both transient and boundary-dominated flow periods. Furthermore, the solution technique is very fast and is ideal for interactive well test analysis and design. This paper presents a complete analysis of well test data using an interactive type curve matching procedure and the solutions derived in this study.
Interdependence Between Geology and Well Test Interpretation
Authors: Massonnat G. J. , Bandiziol D.
Published: December 2007

This paper shows the leading role of geology in the choice of a well test interpretation model and in the selection of the best solution; at the same time the results coming from well test interpretation contribute to improve the geological model. Three field cases are discussed: The first case evidences the need of a good sedimentological analysis, in order to choose among the different reservoir models that match properly the derivative plot: Radial Composite, Homogeneous with two parallel or three boundaries. Geology indicates that the reservoir was deposited in the median part of a deep-sea fan, and that the perforated interval belongs to a channel layer. The model retained is therefore the homogeneous reservoir with two parallel boundaries, which gives a channel width of about 400 meters, in accordance with sedimentology.The second case deals with a shaly formation with few sandbodies. Regional geological knowledge allows to divide this formation into two main units with different sandstone sedimentological origin: fluvial or lacustrin. Interpretation of the well tests performed in the different sandbodies emphasizes the differences between the two sedimentological units, and allows to locate their limitIn the case of the fractured reservoir some input parameters were affected by a high degree of incertitude, and interpretation led to a too big range of possible values for the output parameters (permeability, vertical permeability anisotropy). Geological studies allow to decrease the incertitudes.

A multidisciplinary approach with repeated information exchanges between geologist and reservoir engineer seems to be the best way to deal with well test interpretation problems.
Collection, Analysis, and Integration of Discrete Fracture Data From the Monterey Formation for Fractured Reservoir Simulations
Authors: Gale J. E. , Schaefer R. A. , Carpenter A. B. , Herbert A.
Published: December 2007

Fracture orientation, trace length, termination mode, spacing and other surface and shape data have been collected, using scanline and areal mapping techniques, on approximately 1600 fractures from surface outcrops of the Monterey Formation in western Santa Barbara county. Trace lengths for each cluster or set of fractures appear to follow a log-normal distribution with mean values that vary by up to a factor of five between clusters in the same area and rock type. Spacing values also appeared to follow a log-normal distribution. However, mean spacing values differ only by a factor of up to two between clusters in the same rock mass. Correcting the raw data for censoring and truncation produced a significant change in the distribution statistics.

These fracture statistics have been used to create both 2-D and 3-D stochastic fracture network models that have been analyzed using discrete fracture flow codes to determine the effects of fracture geometry on reservoir permeability. Comparison is made to other work in which fracture geometry and hydraulic data have been integrated, using 3-D discrete codes, in order to provide 3-D reservoir properties that have compatible flow and transport properties.
Geomechanical Evidence for Shear Failure of Chalk During Production of the Ekofisk Field
Authors: Teufel L. W. , Rhett D. W.
Published: December 2007

The Ekofisk Field is a naturally-fractured chalk reservoir in the Norwegian Sector of the North Sea that has been producing hydrocarbons for over 20 years. In situ stresses in the field have been constantly changing because of the decline in pore pressure that has occurred in the reservoir as a result of production. The effect of production and pore pressure drawdown on the minimum horizontal in situ stress in the Ekofisk Field has been determined from shut-in pressure data from 37 hydraulic fractures conducted during the past 15 years. The effective stresses in the reservoir increase linearly with pore pressure drawdown, but at different rates. The reservoir stress path, defined as the ratio of the change in effective minimum horizontal stress to the change in effective overburden stress, is approximately 0.20. Laboratory experiments, which simulate the stress path followed by reservoir rock during the production history of the field, show that shear failure has occurred during compaction of high porosity chalk as the shear stress increased with pore pressure drawdown. Shear failure during depletion will increase fracture density and reduce matrix block dimensions in the fractured reservoir, thereby maintaining reservoir permeability as the apertures of older natural fractures are closed with increasing deformation. It is suggested that the shear failure process may account for the continued good producibility of the Ekofisk Field, in spite of compaction.