bluuebunny/crossref_metadata_2025 huggingface dataset:
Well Tests in a Complex Sandstone Reservoir
Authors: Towler B. F.
Published: December 2007

The Mereenie field is a large complex sandstone reservoir and the well tests have some pecularities which, though not fully understood, have considerable bearing on the well test interpretation.

The first of these are diurnal pressure variations caused by gravitational effects which particularly affect interference tests. Secondly, because of the high gas-oil ratio, phase segregation in the well bore causes a hump in the Horner plot on some of the build-ups.

Thirdly, in one of the sands in one area of the field there is a marked discrepancy between drawdown and build-up results which is attributed to stress dependent permeability. Also core permeabilities in general do not agree with build-up permeabilities.
Oil and Gas Relative Permeabilities Determined From Rate-Time Performance Data
Authors: Fetkovich M. D. , Guerrero E. T. , Fetkovich M. J. , Thomas L. K.
Published: December 2007

This paper presents a method of determining kg/ko, oil relative permeability, kro, and gas relative permeability krg, using oil and gas rate-time performance data from individual wells and from a total field. Advanced decline curve analysis is used to obtain original oil in place, N, and thus saturation; the Δp2 form of an oil inflow performance equation is used to determine kro below the bubble point pressure.

The procedure was used on production data from several wells in a North Sea naturally fractured limestone volatile oil field. Results indicate the calculated oil and gas relative permeabi1ity curves differ from laboratory and correlation calculated curves. By analyzing the oil and gas relative permeability curves of each of the seven wells in the field, it was found that the degree of natural fracturing of a specific well influences the position of the oil and gas relative permeability curves. The results expressed as kg/ko curves appear to be consistent with the field case history findings of Arps for limestone reservoirs – i.e., as the degree of fracturing increases, the kg/ko curves become more unfavorable with respect to oil recovery.

Initial pressure surveys on-each well determine its degree of fracturing while a later field-wide pressure survey confirms the oil-in-place calculated for each well using rate-time decline curve analysis.

Pressure-time data to make these calculations is seldom available for all wells in a field or, when available, is much less frequent than rate-time data. In contrast, the principal calculation methods shown in this paper use rate-time data, thus taking advantage of the most frequently collected and the most widely available information.
Hysteresis of Methane/Coal Sorption Isotherms
Authors: Bell Gregory J. , Rakop Karen C.
Published: December 2007

Methane production from coal seams has been actively pursued in the U.S. since the mid-1970's. This resource is regarded as an unconventional natural gas supply due to several unique characteristics of the reservoir, including: two-phase (water and gas) flow, low effective permeability to gas, and the majority of the methane being held in an adsorbed state on the internal surfaces of the microporous coal structure rather than as compressed or dissolved gas within the pores.

In a virgin coal reservoir with ideal conditions the adsorbed methane concentration is in equilibrium with the initial reservoir pressure. Production of gas from the coal bed depends on the release of this adsorbed methane to a free state, which then flows through the natural fracture system of the coal towards the wellbore. Release of the adsorbed methane is accomplished by dewatering the reservoir which decreases the local pressure and thereby upsets the equilibria.

In the past, researchers have utilized laboratory-measured adsorption isotherms to model the gas concentration/reservoir pressure equilibrium relationship. In the current study both adsorption (pressure increasing) and desorption (pressure decreasing) isotherms were determined for several coal samples. It was found that there are hysteresis effects which cause the two sorption modes to be different. The desorption isotherms were more non-linear than the adsorption isotherms. In terms of reservoir performance this means that coalbed reservoirs must be drawn down to pressures lower than those indicated by adsorption isotherms to achieve the same degree of methane release.

This paper presents a review of methane/coal adsorption phenomena and compares results of the present work with those of previous investigators. Experimental procedures are given along with error analyses and substantiation of repeatability. Variability of gas content within the coal seam is determined for a deep western coal from the Piceance Basin in Colorado. The effect of moisture content on methane sorptive capacity is investigated for an eastern coal from the Black Warrior Basin in Alabama. All samples and funding were provided from Gas Research Institute's R&D field sites.
Mud and Cement for Horizontal Wells
Authors: Zurdo C. , Georges C. , Martin M.
Published: December 2007

High-angle and horizontal well bores raise many questions concerning the characteristics of mud and cement. This paper is a summary of our knowledge and work on these two subjects.

For all research carried out, large or full-scale laboratory test plants were used.

Cutting transport is not only a problem in horizontal conditions but hole angles of 25 to 65° can be even more critical when parameters such as mud rheological properties and velocities are not optimized.

Drilling a long horizontal drain creates a dynamic annulus pressure unbalance. This can lead to a loss and kick situation. Two test benches were thus used to obtain a good understanding of the inefficiency of conventional plugging methods and of the difficult ies of gas migration control in subhorizontal well bores. High concentrations of LCM, high rheological properties of fluids and low flow rates increase the chances of solving the first problem. The results of the second bench demonstrate the difficulties of annulus gas evacution for angles varying from 90 to 100 degrees, or from over-gauged sections in horizontal holes.

Cementing horizontal casing strings is still a fairly new practice. However a good casing/formation cement bond is certainly the best means of obtaining correct well productivity. A successful horizontal cement job should prevent the formation of mud, water and gas channels and of a free water channel on the upper part of the drain hole.

Therefore, several full-scale test benches (25 to 300 m in length) were set up in order to study the following cement placement parameters: casing-hole eccentricity, drilling fluid rheological behaviour, hole geometry, spacer design (rheology and density), flow rate, etc. Furthermore, slurries without free-water were studied for varying downhole conditions.
Successful High Angle Drilling in the Statfjord Field
Authors: Wilson R. C. , Willis D. N.
Published: December 2007

The original drilling design criteria for Statfjord field development set an upper limit on wellbore inclination of 60°. This figure was derived by considering the special drilling problems found on Statfjord and technological limitations.

By developing engineering operational procedures and introducing new technology, wells can be drilled routinely at sail angles between 60° – 70°.

This paper, therefore, elaborates upon the special drilling problems encountered in the area and describes engineering and operational solutions which were developed to extend the maximum reach of wells. In addition, it describes the evolution of drilling on Statfjord and documents the impact of advances.
Wellbore Inertial and Frictional Effects on Drillstem Tests From Naturally Fractured Reservoirs
Authors: Saldana M. A. , Brigham W. E. , Ramey H. J.
Published: December 2007

A mathematical formulation is presented in this paper which includes wellbore inertial and frictional effects during a slug test or the flow period of a drillstem test from naturally fractured reservoirs. This formulation is obtained by coupling a wellbore equation and the diffusivity equation for double-porosity reservoirs. The wellbore equation represents a transient momentum balance relating liquid level in the wellbore and bottomhole pressure. Wellbore storage and skin effect are considered in the coupling conditions. A simplified formulation resulting from the assumptions of a small slug and friction losses for laminar flow in the wellbore is solved by applying the Laplace transformation with numerical inversion.

Solutions obtained in this study show a distinctive double-porosity behavior for some naturally fractured reservoirs. For those naturally fractured reservoirs with double-porosity behavior, an estimate of the interporosity flow parameter, λ, and of the storativity ratio, ω, can be obtained in addition to fissures transmissivity, kfh/µ, and skin effect factor, s. On the other hand, during the practical range of time, the response of other naturally fractured reservoirs follow either the response for a single-porosity reservoir with the properties of the fracture system or the response of a single-porosity reservoir with the combined properties of the fractures and matrix blocks.

Criteria to estimate the magnitude of wellbore inertial and frictional effects for practical systems are developed from an analysis of results obtained in this study. Also, the solution method proposed in this paper can be used to forecast or match bottomhole flowing pressures during a drillstem test from estimates of the properties that describe a naturally fractured reservoir.
A North Sea Application of Slug Testing for Quick Reservoir Analysis
Authors: Waller H. N. , Krase L. D.
Published: December 2007

The application of slug testing in the Valhall Field, a North Sea reservoir, is presented. Specific field examples are given which show this pressure transient testing method to be a quick and reliable way to determine reservoir flow capacity and wellbore skin factor. Some of these examples show confirmation of a channel behind pipe that was indicated by a cement bond log. A review of the theoretical basis of the method is also given.

Although this method has found wide application in ground water hydrology, it has been used on a very limited basis in the petroleum industry. As applied here, the test is conducted on an isolated zone at the time of perforating underbalanced with the well filled with diesel. The primary advantage of this test is the extremely short time required to collect sufficient data for analysis, even when permeability is relatively low or skin factor is high. The test also eliminates problems associated with wellbore storage. Therefore, both required rig time and the production deferred due to data collection are minimized. This advantage is especially important in costly offshore applications and should lead to use of the technique in many other fields worldwide.
A Combined Condensing/Vaporizing Mechanism in the Displacement of Oil by Enriched Gases
Authors: Zick A. A.
Published: December 2007

Experimental observations, combined with equation-of-state predictions, indicate that a combined condensing/vaporizing-gas drive mechanism, rather than the traditionally believed condensing-gas drive mechanism, may be responsible for displacements of reservoir oil by enriched gases. Apparent minimum miscibility pressures and minimum solvent enrichments are observed with this mechanism, even though true miscibility is probably not developed.
CO2 Huff-Puff Simulation Using a Compositional Reservoir Simulator
Authors: Hsu H. -H. , Brugman R. J.
Published: December 2007

Increased field application of the CO2 Huff-Puff process has resulted in increased laboratory and numerical simulation activity. This paper focuses on numerical simulation of the CO2 Huff-Puff process in a light oil reservoir, using a fully-compositional reservoir simulator.

A simulation model is first validated by successfully history-matching production data from two huff-puff cycles. A performance prediction is then conducted for a third cycle. A number of parametric runs are performed to determine oil recovery as affected by: The number of cycles,The timing of injection, soak and back-production operations, andThe quantity and composition of the injected sol vent.

The following conclusions can be made based on the results of the CO2 Huff-Puff simulation: The simulation of a CO2 Huff-Puff process is possible through the use of a compositional reservoir simulator. A successful history match of oil, water, and GOR was conducted for two cycles of a CO2 Huff-Puff project in Paradis Field, Louisiana. The model is suitable for design, evaluation and prediction of a CO2 Huff-Puff project. It can also assist engineers in gaining insight into the oil recovery mechanisms in a CO2 Huff-Puff project.The simulation results from the Paradis project indicate that, The primary CO2 effects on oil recovery appear to be vaporization of intermediate components, oil viscosity reduction and oil phase swelling,A significant drop in incremental oil recovery occurred between the first and second cycles for this particular project. A third cycle would probably not be attractive,Variation in soak time from 5 to 40 days has little effect on oil recovery,The most important parameter affecting oil recovery appears to be the quantity of injected solvent, andContamination of a pure CO2 solvent with up to 20 mole percent N2 or CH4 has little effect on oil recovery.
General Spectral Theory for the Onset of Instabilities in Displacement Processes in Porous Media
Authors: Scheidegger A.E.
Published: December 2007

The problem of penetration of a fluid into a porous medium containing a more viscous liquid is investigated. It is known that the displacement front may become unstable in this case because it may break up into "fingers". The problem of inception of fingers has been treated previously in the literature by describing the displacement front in terms of its Fourier transform. In the present paper, we generalize earlier procedures by making allowance for an arbitrary elemental growth law. Furthermore, we assume that the phenomenon of fingering is not solely governed by the prevailing flow potentials, but also by the spectrum of heterogeneities in the porous medium. This is achieved by introducing a constant characteristic of the frequency of the heterogeneities in the porous medium. It then turns out that the maximum rate of growth as a function of wave length is considerably shifted from that predicted in the literature. At the same time it is also shown that the difficulty encountered by other workers, which consists of small wave lengths growing at an infinitely high rate, is being avoided.

Introduction

When a fluid enters a porous medium displacing a more viscous liquid, an interesting kind of instability may occur at the displacement front. Protuberances may arise which shoot through the porous medium at relatively great speed, leaving behind the large amounts of the liquid intended to be displaced. This phenomenon is commonly referred to as "fingering".

The problem of fingering is an extremely involved one owing to the complexity of the phenomenon. To treat it theoretically, drastic simplifications have to be made. One way to do this is to confine one's attention to the very beginning of the occurrence of the instabilities. The displacement equations can then be linearized, the displacement front can be described by its Fourier transform and the growth law for each spectral component can be deduced.

An attempt along these lines has recently been published by Chuoke, et al., who showed how the prevailing flow potentials affect the various spectral components of a displacement front on the verge of instability. Chuoke's formula contains a capillary pressure term as an essential feature; if the limit is taken with this term being set equal to zero, a disconcerting difficulty arises. The spectral components with the smallest wave lengths are found to grow at the fastest rate; in fact, the rate becomes infinite for the wave length approaching zero.
Gas Well Decline Analysis Incorporating Real-Gas Behavior and Non-Darcy Flow
Authors: Schmidt S. H. , Caudle B. H. , Miller M. A.
Published: December 2007

Through the application of the real gas potential and non-Darcy flow analysis, type curves have been developed which model decline behavior of real gases producing from a closed drainage volume. It was determined that both reservoir permeability (in relation to the turbulence factor) and initial average reservoir pressure at the start of the decline period significantly contribute to type curve response and should not be neglected from gas well decline analysis.

The result is a simplified and improved method for forecasting gas well performance and for estimating gas in place. Using the same dimensionless variables as those derived by Fetkovich1, a direct comparison of type curves, including the effects of varying reservoir parameters, is presented. Results from several case studies involving both single well and whole field data are also provided.
Application of Superposition and Pseudo-Steady State Concepts to Thermal Recovery Pressure Tests
Authors: Onyekonwu M. O. , Ramey H. J. , Brigham W. E.
Published: December 2007

The liquid flow equations have generally been adapted for use in gas flow applications even though the gas flow equations are non-linear. This follows from earlier studies in which it was concluded that although superposition is correct only for linear partial differential equations, nevertheless there is a close check between linearized real gas solutions and the liquid flow solutions. However, these earlier studies were carried out at uniform reservoir temperature.

This paper discusses the application of superposition and pseudo-steady state concepts to gas reservoirs with non-uniform temperature such as thermal recovery systems. The paper is in two parts. The first part discusses verification of the finite-difference thermal simulator used for this study while the second part discusses application of the superposition and pseudo-steady state concept to thermal oil recovery falloff tests.

Results from this study show that effective pressure, compressibility and temperature are required for interpretation of thermal oil recovery falloff tests. The effective pressure is the same as the average pressure while the effective temperature is usually lower than the average temperature based on an energy balance. It may also be inferred from this study that non-linearity in the equations due to non-uniform temperature effects may be mild. This is because linear equations were successfully used to analyze cases with non-uniform reservoir temperature.
Field Application of Lignosulfonate Gels to Reduce Channeling, South Swan Hills Miscible Unit, Alberta, Canada
Authors: Wagner O. R. , Weisrock W. P. , Patel C.
Published: December 2007

Following initiation by Amoco in 1973 of a secondary miscible (WAG) flood in the South Swan Hills Unit, tracer performance indicated severe channeling of solvent and water, particularly in the northwest quarter of the Unit. In 1975 and 1977, problem zones at 9 injectors were isolated and selectively treated with chrome-lignosulfonate time-set gels in an attempt to reduce solvent and water cycling. The treatment volumes varied between 8500 and 14,000 bb1s (1350 and 2225 m3) per well.

As part of an evaluation of the gel treatments, incremental oil production responses observed at a number of the 56 producers offset to the 9 treated injectors were examined. The responses which could not be explained by other contributory factors, such as the drilling of infill seam injection wells, well workovers (e.g. acid jobs and asphaltene treatments), casing repairs, and pump changeouts, were considered to be the result of improved sweep due to the gel treatments.

Thirteen of the 56 offset producers (23%) were found to have responded to the gel treatments, and these were rated as to the duration of response. Response durations of up to 18 months were rated as "good," and those lasting longer were rated as "excellent."

Although a detailed economic analysis was not performed, a comparison of the total cost of the 9 injector gel treatments with the gross revenues generated by the total calculated incremental oil from the 13 responding producers indicates that the treatments were an economic success.
Drillstring Torsional Vibrations: Comparison Between Theory and Experiment on a Full-Scale Research Drilling Rig
Authors: Halsey G. W. , Kyllingstad A. , Aarrestad T. V. , Lysne D.
Published: December 2007

This paper presents a mathematical method for the computation of torsional resonance frequencies in a drillstring. The torsional resonance frequencies in a drillstring are readily calculated from the nominal drillstring dimensions. A high degree of accuracy is achieved when a correction factor to the torsional propagation velocity in drillpipe due to the offsets at the drillpipe joints is incorporated into the calculations. The theory and computer program were tested against data recorded in a 1000m deep, nearly vertical well. Torsional spectra were recorded with the bit off bottom at 450m, 550m, and 1000m and while drilling. Well defined torsional resonances were observed for frequencies up to 40 Hz. The calculated resonance frequencies are in very good agreement with all experimental data.
Front-Tracking of Three-Dimensional Piston-Like Displacements in Porous Media
Authors: Kocberber S. , Miller M. A.
Published: December 2007

In this study, a front-tracking method for three-dimensional piston-like displacement is described. Many reservoir processes develop distinct fronts (discontinuities) that move through the reservoir. When the width of the discontinuity is smaller than realistic computation mesh sizes, standard methods are not always adequate. By tracking frontal movement, accurate representation of the front location is provided.

This is accomplished by approximating the flow domain as regions of homogeneous properties separated by sharp, distinct fronts. Flow is treated as a succession of steady-states based on incompressible fluids. With these assumptions, the potential equation is solved by finite-element methods, and the front moved accordingly. Elements are originally aligned with streamlines based on single-phase flow so that mesh orientation effects are minimized. As the front moves, elements are reformed to represent the discontinuity at the front accurately.

The validity of the model is tested against data available in the literature. The model provides an inexpensive and accurate solution for problems such as coning, gravity under- and over-ride, fluid displacements, and movement of chemical reaction or gas condensation fronts, in which movement of the front is of primary concern. The method is applicable to two fluids of any mobility and density contrasts.
An Investigation Into the Application of Expert Systems to Matrix Treatment Design
Authors: Cram R. S. , Hendrickson A. R.
Published: December 2007

The design of a Matrix Treatment can be an involved procedure requiring considerable knowledge and experience in order to maximize return on investment and improve the success of the treatment.

Some of the major decisions which must be made during the design process include the selection of the optimum base fluid followed by the choice of the required additives and the size of the proposed treatment. All of these decisions are crucial to the success or failure of the treatment and a great deal of expertise is required to ensure that the best choices are made.

The total number of possible combinations of base fluids and additives available to the design engineer are numbered in the hundreds. In many cases however certain additives are either not compatible with other additives or they are not compatible with materials in the formation. This can result in the total failure of a matrix treatment in the event that such a possibility is overlooked.

The introduction of expert system shells has made it possible to develop expert systems which can be used to guide and advise design engineers in selecting the best type of treatment for a given set of circumstances so reducing the possibility of important factors being overlooked. This can lead to reduced costs and an increase in the assurances of a successful job. A second advantage for large corporations lies in the fact that, since many of the expert systems can be run on relatively inexpensive micro computers, headquarters engineering personnel can be sure that all of their location technical staff can have the same guidelines to follow for treatment design.

This paper examines several different types of expert system shells and includes examples of how the different systems lend themselves to establishing guidelines in selecting the best fluids (acid and non-acid base) in treatment design.
Drag Bit Performance Modeling
Authors: Warren T. M. , Sinor A.
Published: December 2007

Models for the forces required to remove a fixed volume of rock with a single cutter have been applied to different polycrystalline Diamond Compact (PDC) bit designs. The integration of the forces for each cutter over the bit face gives the torque and weight-on-bit (WOB) required for a particular rate-of-penetration (ROP).

This paper presents the results of comparing such a model to laboratory drilling tests for four radically different bit designs in four different rocks. The geometry of each cutter on the bit was determined by detailed measurements of the bit with a 3-axis coordinate measuring machine.

Drilling tests were conducted by "reaming" rock with an 8-1/2" bit that had been previously drilled with a 6-1/4" bit. Only the peripheral cutters engaged the rock during the reaming. Additional tests were conducted where the WOB and torque were recorded while drilling a pilot hole into the top of a flat rock and drilling through two different bed boundaries with constant ROP. The model predictions compared well to the measured data for both the reaming tests and the pilot hole tests.
Type Curves for Analyzing Naturally Fractured Reservoirs
Authors: Petak K. R. , Soliman M. Y. , Anderson M. F.
Published: December 2007

A solution representing flow at the wellbore in a naturally fractured reservoir is presented in this paper. The model used to develop this solution assumes unsteady state interaction between the fractures and the matrix. Wellbore storage and skin are considered in determining the boundary conditions for this model.

A new set of type curves for analyzing pressure transient data from naturally fractured reservoirs is presented. Each type curve within the set is for a different value of CDe2S. Each type curve presents one radial flow solution with the associated family of curves approximating behavior at intermediate flow times. Each curve within a family is for a different ω′λ′e-2S product, where ω′ and λ′ depend upon fracture/matrix storativity and permeability ratio, respectively. Ambiguity is eliminated when a simultaneous match of data against the dimensionless pressure curves and the differential dimensionless pressure curves is performed. Reservoir and well parameters including permeability, skin, dimensionless wellbore storage, ω′, and λ′ can be calculated from this match. Truer matches against actual natural fracture pressure transient data are obtained by using these curves instead of existing type curves.

The principal advantages of using these curves are discussed. The first advantage is that when sufficient transition period data is measured, Horner data does not have to be available for an analysis to be performed. Actual pressure buildup data is used to illustrate this. Secondly, after reviewing many actual well tests, the upper practical limit on values for permeability ratio has been expanded. Values for λ′ > 10-3 can now be calculated.

Use of these curves is explained in detail. Applicability of the curves is demonstrated by successfully matching actual pressure transient data against the curves.
Cenomanian Stratigraphic Traps in Western Abu Dhabi, U.A.E.
Authors: Loutfi G. , Baslaib S. M. , Abul Hamd M.
Published: December 2007

Cenomanian rocks in western Abu Dhabi comprise a sequence of shallow and deep marine carbonates with terrigenous shales and sandstones. Four rock units, in ascending order; the Shilaif, the Tuwayil, the Ruwaydha and the Mishrif are recognized within the sequence.

The Shilaif Formation is represented by pelagic carbonates, deposited in anoxic intrashelf basin, developed in central Abu Dhabi during the Cenomanian. It proved to be the source rock of the oil reservoired in the overlying Mishrif.

The Tuwayil, consists of shales and sandstones, and represents a period of terrigenous clastic influx, which has formed a large tongue protruded into the Shilaif basin. It includes four sandstone units, which are found oil bearing in some localities. The Ruwaydha represents the last basinal depositional phase of the Cenomanian in the area.

The Mishrif Formation is a thick shallow marine carbonate sequence, exhibiting minor cyclic deposition reflecting periodic oscillation of sea level. It represents deposition on epicontinental shelf, with its margin prograding eastward into the Shilaif basin. It is a good reservoir, known to be oil productive in east Abu Dhabi and offshore Dubai from rudist reefal build-ups and/or accumulations.

Large oil and gas accumulations have been found in the area, mainly in structural traps of the Middle and Lower Jurassic, with moderate oil accumulations in Middle and Lower Cretaceous rocks.

A transitional zone between the Mishrif and Ruwaydha/Tuwayil exists in the area. The width of this transitional zone appears to extend along few kilometres. However, interfingering of the Tuwayil, the Ruwaydha and possibly the Shilaif appear to extend into the Mishrif reflecting possible occurrence of localised paleo-embayments at the Mishrif shelf margin.

Seismic-stratigraphic investigation, helped to define facies limits, patterns and occurrence of prospective stratigraphic traps in both the Mishrif and the Tuwayil Formations. The Tuwayil sandstone and Mishrif carbonate clastics pinching out against structural highs, are prospective localities for stratigraphic hydrocarbon entrapment. In addition, areas where the Mishrif develops possible carbonate build ups and/or rudist reefal accumulations are also of interest and could have hydrocarbon potential.

The sequence of seismo-stratigraphic/facies definition procedure, presented in this paper, were applied to define stratigraphic traps in the Mishrif and Tuwayil Formations.
Design, Implementation, and Interpretation of a "Three-Dimensional Well Test" in the Cormorant Field, North Sea
Authors: Bunn G. F. , Yaxley L. M.
Published: December 2007

This paper describes the design, execution and interpretation of a pair of distributed pressure interference tests in a North Sea Reservoir. The tests were performed in two new development wells which were located some 1500 feet from an existing producer.

The results of the tests were interpreted by numerical simulation and have yielded an improved description of the vertical and horizontal transmissibilities of individual layers, and an improved understsanding of the significance of faulting in the region around the wells.
Reserve Definitions – An Attempt at Consistency
Authors: Keith D. R. , Wilson D. C. , Gorsuch D. P.
Published: December 2007

An alternative system for the categorisation of volumes of hydrocarbons in place and reserves is proposed. The system uses criteria based on level of confidence to define Proven, Proven + Probable and Proven + Probable + Possible categories of fluid in place and reserves. The proposed definitions are compared with the systems of definitions currently in general use and the advantages are outlined. The methods of application of the proposed definitions are detailed and their application to prospects, discoveries and producing fields are discussed.
A Driller's HAZOP Method
Authors: Comer P. J. , Fitt J. S. , Østebø R.
Published: December 2007

A method has been developed for performing Hazard and Operability studies of drilling systems and procedures. The need for such a technique is explained and its development and application are described. Although the Drillers' HAZOP uses the same basic method as the traditional "process" HAZOP, novel features have been introduced for the analysis of those drilling operations which are essentially sequences of mechanical and manual handling operations by teams of people. For these cases, a new type of master document, the Multiple Activity Chart, has been developed and refined to be the basis for critical study by deviation analysis. It has been found that the set of guide word-variable combinations used in the classical HAZOP study is not suitable for analysis of Multiple Activity Charts; an alternative set has been developed and is described. The experience gained in development of the new method through a programme of case studies, and by virtue of its first practical application, is reviewed. This experience has demonstrated that use of the method can result in improved safety and efficiency in drilling operations. Finally, the authors discuss their plans for the future use and development of the technique.
A Probabilistic Strategy for Subsea Inspection of Steel Structures
Authors: Carr P. , Clayton M. , Busby P.L. , Dobson J.
Published: December 2007

A strategy has been developed for determining the relative effectiveness of differing underwater inspection and maintenance regimes (type of inspection, inspection intervals and the policy for responding to defects when found). policy for responding to defects when found). The strategy requires knowledge of inspection records, fatigue test data and jacket analysis results, including redundancy studies. These data are combined using Bayesian statistics, risk analysis methods and a Monte Carlo simulation technique.

Introduction

Safe and economic operation of structures offshore depends on structural integrity. Structural integrity in turn depends on corrective maintenance as decided by regular inspections of condition. Welded joints can present a particular problem in this respect present a particular problem in this respect because of the lack of objective answers to the following questions:Which joints should be inspected?What inspection method should be used?Should the inspection method be the same for all the joints?What should be the maximum interval between return visits to the same joint?When weld defects are detected during inspection, what corrective action should be taken?

In an attempt to provide objective responses to the above questions, a probabilistic strategy has been developed. Essentially, this strategy involves understanding structural behaviour and NDT capabilities, then modelling the processes of decay and inspection/maintenance by means of mathematical models. By analysis of these models, the effectiveness of various inspection and maintenance regimes can be compared and the optimum regime selected for implementation.

Development of a rationale for welded joint inspection and corrective maintenance can be expected to reduce maintenance costs without lowering safety standards. This is achievable by making sure that the right items are inspected using the most cost-effective techniques and return intervals, and by adopting an appropriate response when defects are detected.

INSPECTION AND MAINTENANCE STRATEGY

Offshore installations in UK waters must satisfy the requirements of Statutory Instrument No 289. The Department of Energy have issued guidance notes to clarify the legislation. The requirements of these documents include:a major underwater survey preceding recertification;an additional underwater survey two years after the major survey;an annual above water survey.

Although defining the types of survey required, neither document is specific as to the answers to the questions posed in the introduction to this paper. paper. P. 187
Miscible Gas Drive in Unit 1 of the Statfjord Reservoir
Authors: Broekers M. P. , van Dorp W. G.
Published: December 2007

Miscible flooding with hydrocarbon gas is being applied on a pilot basis to the Statfjord Unit 1 reservoir of the Northern Fault Block of Shell/Esso's Brent field. This is expected to increase the recovery by 14 MMstb (2.2 Mm3) above the 39 MMstb (6.2 Mm3) expected from water flooding this unit.

Simulation studies were undertaken to confirm that the gas drive in the Unit 1 reservoir would be adequately separated from the concurrent water drive in the underlying units. Also critical production/injection rates for cusping have been investigated. The feasibility of this project will continue to be scrutinised.
Deepwater Hydraulic BOP Control Systems
Authors: Vujasinovic A. N. , McMahan J. M.
Published: December 2007

Relatively simple and economical hydraulic blowout preventer (BOP) control systems must be replaced by complex and expensive multiplex electric systems at depths where the hydraulic signal, traveling at the speed of sound, becomes too long for the function to be executed within the prescribed time period.

In subsea applications, the total time to operate (close or open) a BOP can be split into two parts: signal time and fill-up time. The signal time is the time required for the pilot signal from the surface to reach the corresponding valve in the subsea control pod. The fill-up time is the elapsed time between activation of the subsea pod valve and full execution of the BOP function.

This paper deals with innovative approaches to improve both the signal and fill-up time; the result is a hydraulic BOP control system capable of operating in depths approaching 4,000 ft.

Methods to shorten the hydraulic signal time include "fast relief" and "biased" systems. To improve the fill-up time, emphasis is placed on use of the Energy Saving Valve (ESV) system described in general terms in IADC/SPE paper 11379 presented in New Orleans in 1983. This system utilizes the differential area between opening and closing sides of BOP hydraulic operators to shorten the closing time and to substantially reduce the fluid volume used during the closing process.
Methods for the Alleviation of Slug Flow Problems and Their Influence on Field Development Planning
Authors: Shotbolt K.
Published: December 2007

Alternatives for medium-depth marginal and deepwater field developments include subsea wells with floating process facilities, or total subsea developments with multiphase export lines. Hydraulics considerations of productivity, slug flow, wax, hydrates and emulsions need to be assessed together with capital and operating costs when deciding a field development plan. Unexpected slug flow problems have previously caused reductions in productivity.
Situational Drilling and Completion Practices in the Stoney Point Field: A Subnormally Pressured and Fractured Trenton/Black River Reservoir
Authors: Browne B. L. , Parker E. F.
Published: December 2007

The Trenton/Black River has provided Michigan's only giant oil and gas field, the Albion–Scipio Field, and favorable economics at most oil price levels. A recent Trenton/Black River field discovery has again renewed interest in this play. There are reservoir characteristics, however, that do not lend themselves to easy or standard analysis in trying to locate, drill, complete and produce hydrocarbons from this horizon. The Stoney Point Field wells identify these characteristics and show how the actual well conditions encountered while drilling can determine the drilling and completion procedures. Individual well case histories are given to show some of the situational considerations.
Practical Well Test Analysis Methods for Hydraulically Fractured Wells in Dual-Porosity Reservoirs
Authors: Lancaster D. E. , Gatens J. M.
Published: December 2007

Successful analysis of post-fracture well test data in dual-porosity reservoirs is essential to the design and evaluation of stimulation treatments in these reservoirs. Many methods have been presented for analyzing post-fracture well test data from hydraulically fractured wells in single-porosity reservoirs. Little information is available, however, to assist the engineer in analyzing pressure transient data from a well completed in a dual-porosity reservoir which has been fracture stimulated.

As part of a study we are conducting of the Eastern Devonian Gas Shales, a reservoir which is usually described as dual-porosity, we have analyzed post-fracture well test data from a number of wells for the purpose of estimating propped fracture length and fracture conductivity. The purpose of this paper is to present how we have applied available analytical techniques in our analysis of post-fracture well tests for hydraulically fractured wells in a dual-porosity reservoir. Simulated and field examples are presented to illustrate our approach. Guidelines for conducting and analyzing post-fracture well tests in dual-porosity reservoirs are also presented.
The Optimization of Gas Reservoirs
Authors: Van Goldfracht T. , Perrotti G. , Gorini G.
Published: December 2007

This paper was prepared for the 41st Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Dallas, Tex., Oct. 2–5, 1966. 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 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.

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.

A simplified method for the optimization of the exploitation of gas reservoirs based on technical and economic considerations has been developed.

It predicts the present-worth value profit of a project by the use of a functional relationship between pertinent variables.

The optimization of the exploitation of a gas field is indicated by the maximum present-worth value of the profit when the rate of production and the number of wells are optimized.

The optimum number of wells is to be considered as the optimum drilling program since, besides the number of wells, the optimum timing of the drilling program is also predicted.

In order to allow a general use of this method, a dimensionless relationship was written and plotted in graphical form. By the use of this graph, simply knowing the so-called C "payout time" 0 =, the optimum rate

qiL 365 of production and the optimum drilling program are quickly obtainable.

The uncertainties on the reliability of reservoir data in the early life of a field have been corrected by the use of a risk factor.

The importance of this risk factor is shown by the higher sensibility of the profit-to-investment ratio.

A sample calculation is given at the end of the paper for a better understanding of the rapidity of the method.

Introduction

In recent years the sales of natural gas and associated products increased commensurate with the increase of energy consumption. This has been evidenced by more intensive exploration and exploitation of deep and low-permeability gas reservoirs, which before were considered uneconomic.

Although reservoir engineering methods for analyzing and predicting the performance of gas reservoirs and gas wells have long been available, it appears that these methods must be applied with economic criteria early in the history of the reservoir in order to give a usable tool for quick and sound decision-making on investment. The aim of this paper is to develop a simplified procedure for fast and accurate prediction of gas production and drilling program in optimum operating conditions.
Production Decline Type Curves for Gas Wells Producing Under Pseudo-Steady-State Conditions
Authors: Aminian K. , Ameri S. , Hyman M. D.
Published: December 2007

Predicting the production rates from a given gas well is of considerable interest in the natural gas industry. The conventional method to predict the performance of the gas reservoirs require a number of data which are often unavailable. This is especially true for low permeability reservoirs. In many cases, the production data is the only available information on the gas wells. In such cases, the production decline type curves have been utilized to predict the future production rate based upon the past production data. However, the published type curves have been generated with certain assumption(s) which limit their applications. These assumptions include consideration of only Darcy flow, use of constant gas viscosity and deviation factor, as well as ignoring the skin factor.

This paper presents a set of new production type curves for gas wells (production forecasting) without any of the above mentioned assumptions. The type curves are generated by utilizing a simple reservoir model which accounts for variations in gas deviation factor and viscosity as well as non-Darcy flow. The results of this study are presented in the form of dimensionless rate-time and cumulative production-time type curves.

The type curves presented in this study can be utilized to estimate the reserves and forecast future production of a given gas well. In addition, the application of the developed type curves was found to be significantly easier than those previously published. Finally, the developed type curves were verified using actual production data obtained from the gas wells in the Appalachian Basin.
Estimation of Reserves and Recovery Performance in Highly Complex Naturally Fractured Reservoirs
Authors: Owusu L. A. , Ershaghi I.
Published: December 2007

A new approach for estimation of oil recoveries from extremely heterogeneous naturally fractured reservoirs under water influx or water injection is developed. A fully-implicit and versatile simulator was developed and used to obtain recovery predictions. Based on model studies conducted, correlations were obtained for the estimation of recoveries and producing water—oil ratios as a function of reservoir properties. Important reservoir characteristics identified include matrix permeability, maximum capillary pressure for the matrix and fracture density.
New Method of Mini-Frac Analysis Offers Greater Accuracy and Enhanced Applicability
Authors: Lee W. S.
Published: December 2007

A new method of pressure decline analysis has been developed in three geometry models, Perkins and Kern, Christianovich and Zheltov, and Penny. This new method greatly expands applicability of the analysis. The results obtained from the new method agree more closely with field observation. The method improves on the existing approach in the following areas:

In the existing method, calculated closure time often does not agree with field observed value. In the new method, fluid loss calculation is evaluated from the beginning of pumping to field observed closure time, thus ensuring better accuracy. In the new method, the total fluid loss is set equal to the pumped volume minus bulk volume of proppant, therefore, it is suitable for full scale fracturing treatment with proppant. The existing method is not suitable for such treatment because the calculated created volume may be less than the bulk volume of proppant. The new method can handle early time pressure rise and fall caused by pressure and temperature effect near wellbore. The existing method is unsuitable for such fluctuation because type curve matching is frequently impossible. Formulas required to determine fracture parameters such as fluid loss coefficient, fracture extension and fluid efficiency have been derived which are simple to use and can be implemented on desk calculators for real-time application.