bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial Distribution of Oil and Water in Horizontal Pipe Flow
Authors: Soleimani Arash , Lawrence C. J. , Hewitt G. F
Published: December 2007

In this paper we report a series of experiments to quantify the spatial distribution and identify the flow pattern of liquid-liquid flow in a horizontal 25.4-mm (nominal 1-in.) tube. Experimental results are presented for kerosene (EXXOL D80) and tap water at room temperature. Two different measurement techniques (a high frequency impedance probe and a gamma densitometer system) were applied for measuring the volume fraction distribution across the tube and to obtain tomographic results for phase distribution. The use of the gamma densitometer system to obtain the tomographic results in liquid-liquid cocurrent flow is believed to be the first in this field. These methods are more precise than other techniques such as visualization and help to distinguish certain differences in flow patterns for different superficial velocities and liquid fractions. The two sets of measurements were compared and it was concluded that the gamma densitometer system was a more reliable method by which to measure the volume fraction. Two important phenomena in liquid-liquid flow were observed: oil encapsulation by water at low mixture velocity and droplets concentrated at the center of the pipe in the dispersed flow regime. Some possible explanations are given regarding these phenomena.
Field Applications of Abrasive-Jetting Techniques
Authors: Ousterhout R.S.
Published: December 2007

Interest in abrasive-jetting techniques for perforating and cutting well casings, cement and formation rocks has increased rapidly since 1958. This renewed interest in an old process has been due mostly to the development of a jetting tool of longer life and higher efficiency. Present-day jet-orifice nozzles are made of extremely hard materials that have a working life of more than three hours, compared to several minutes in the early days of abrasive jetting. Also, new efficient nozzle design has greatly increased jet speed and depth of penetration.

These improvements in design and materials of construction, coupled with improved operating techniques, have resulted in many widespread and varied applications of abrasive jetting. Jobs have been performed, using this process, that would have much more expensive or even impossible with conventional methods.

Several case histories are presented in this paper to illustrate applications and performance of abrasive jetting.
Correlations for Fluid Physical Property Prediction
Authors: Vasquez M. , Beggs H.D.
Published: December 2007

Introduction

The evaluation of physical properties of hydrocarbon mixtures is an important step in the design of various stages of oilfield operations. The fluid properties, which change as pressure and temperature change, must be evaluated for both reservoir engineering and production design operations. For example, the production design operations. For example, the calculation of two-phase flowing pressure gradients occurring in piping systems requires prediction of fluid properties such as dissolved gas, formation volume factor (FVF), oil compressibility, and viscosity at various locations in the pipe, Even though laboratory measurements of these properties may be available as a function of pressure, the measurements usually are made at reservoir temperature only. The behavior of these properties with temperature change usually is predicted empirically.

Increasing emphasis is being placed on the necessity of having accurate estimates of fluid physical properties in advance of laboratory PVT physical properties in advance of laboratory PVT analyses of the reservoir fluids. Many times these properties are required at a time when the only properties are required at a time when the only information available consists of oil and gas gravities and reservoir pressure and temperature. The purpose of this study was to utilize a large base of laboratory. measured PVT data to develop improved empirical correlations to replace those commonly in use. Many of the presently used correlations were developed many years ago from limited data and are being used beyond the range for which they were intended.

JPT

P. 968
Screenless Completions: Cost-Effective Sand Control in the Adriatic Sea
Authors: Pitoni E. , Devia F. , James S. G. , Heitmann N.
Published: December 2007

Many gas reservoirs in the central Adriatic Sea, offshore Italy, are formed of laminated, low-permeability, dirty sandstones, with as much as 50% clay content. Initially, wells were completed with gravel packs, but the nature of the formations caused productivity to decrease in some gas fields because fines plugged the gravel packs. In the past few years fracpacks have been used to alleviate the fines migration problem. However, there are many gravel-packed wells which are either sanded up and shut in or underperforming because fines have plugged the gravel-pack screens. These wells do not currently justify the expense of an immediate full rig workover.

A candidate zone was selected to evaluate the viability of a screenless completion technique for competent sand control. We placed a highly conductive tip-screenout fracture in the zone, using recent innovations in fracturing fluid technology and proppant flowback control additives, to eliminate sand production. Successful implementation of this technique was confirmed by posttreatment production more than 2.5 times the normalized rate of the initial gravel-pack completion. No formation sand or proppant was produced back to surface during production. The screenless completion technique provided a cost-effective and reliable rigless rehabilitation technique.
Observation of Asphaltene Destabilization at Elevated Temperature and Pressure
Authors: Wang J. X. , Brower K. R. , Buckley J. S.
Published: December 2007

An optical observation cell was added to a mercury-free pressure/volume/temperature apparatus to extend studies of the onset of asphaltene precipitation to elevated temperatures and pressures. Observations for asphaltic, paraffinic, and light-to-medium gravity crude oils are reported as a function of temperature, pressure, and mixing time. Precipitants ranged from heptane to propane.

Studies at ambient conditions have shown that the refractive index at the onset of precipitation is an important characteristic of oil/precipitant mixtures. Calculated values of refractive index as a function of temperature, pressure, and composition are being correlated to observations of asphaltene separation at elevated temperature and pressure, as a predictive test.
Temperature Effect on Formations During Jet Perforating
Authors: Robinson Reginald L.
Published: December 2007

An investigation into the thermal reactions during jet perforating has been conducted over a period of years. Theoretical considerations have been investigated and correlated to experimental laboratory tests. The tests have been conducted under a variety of simulated well conditions and into sandstone, limestone, and dolomite cores. Various well fluids were used in the tests. Jet charges contained in steel guns and self-contained or directly exposed jet charges were both used in this investigation.

Introduction

For almost a decade now jet perforating has been used in well completions. With the introduction of this radically different tool, misconceptions as to its method of penetration arose. In some instances it was thought that the jet stream itself burned its way through the casing, cement and into the formation. This, of course, was a misconception. Numerous surface tests have indicated no burning action. The mechanics of penetration of a formation or target is altogether a different subject and is not covered in this paper.

A direct mathematical explanation of the thermal aspects of jet perforating, especially the heat transfer relations, is very complicated. It is probably for this reason that very little work has been done on this problem. With the ever increasing use of jet perforating, the question of what happens to the formation during perforating is of interest to the petroleum industry.

Theoretical Considerations

The nature of an explosion or decomposition of a high explosive is a complex phenomena and entails unusual heat flow conditions.

Actual well conditions present many variables that vastly complicate the calculations by having multiple explosions occurring with the jet charges cased in various materials in both dry and in fluid filled holes. These extremely complex conditions result in laboratory measuring methods as a practical approach to temperature reactions.

Types of Jet Perforators

A conventional jet perforating carrier has a number of ports or holes in a hollow steel tube with a jet charge arranged to shoot through each port. At the time of firing, all charges in a gun are detonated, resulting in an explosion in each jet charge.
Thermal Reservoir Simulation Model of Production From Naturally Occurring Gas Hydrate Accumulations
Authors: Swinkels Wim J. A. M. , Drenth Rik J. J.
Published: December 2007

Reservoir behavior of a hydrate-capped gas reservoir is modeled using a three-dimensional thermal reservoir simulator. The model incorporates a description of the phase behavior of the hydrates, heat flow and compaction in the reservoir and the hydrate cap. The model allows the calculation of well productivity, evaluation of well configurations and matching of experimental data. It shows the potentially self-sealing nature of the hydrate cap.

Production scenarios were also investigated for production from the solid hydrate cap using horizontal wells and various ways of dissociating the gas hydrates. These investigations show the role of excessive water production and the requirement for water handling facilities. A data acquisition program is needed to obtain reservoir parameters for gas hydrate accumulations. Such parameters include relative phase permeability, heat capacity and thermal conductivity of the hydrate-filled formations, compaction parameters and rate of hydrate formation and decomposition in the reservoir.
Realistic Numerical Models for Fractured Reservoirs
Authors: Gurpinar O. M. , Kossack C. A.
Published: December 2007

Characterization and forecasting in fractured reservoirs is one of the most challenging topics in the oil and gas industry. Managing such reservoirs requires construction of representative reservoir models that can handle both fracture and matrix systems, and their interaction, correctly. Data integration from all disciplines is required for construction of these reservoir models.

Commercial numerical models capable of handling flow in fractured reservoirs have been present in the industry for quite some time. However, the correct application of those simulators for representative reservoir models is not easy. This paper will discuss parametric ways to improve construction of representative reservoir models. Discussion will focus on transition from single-porosity representation to dual-porosity models and pseudoization of capillary pressure process employed in between.

A fractured reservoir undergoing a waterflood is simulated with a single-porosity formulation, where the matrix blocks are subdivided into core-plug-size gridblocks and the fractures are subdivided into even smaller blocks. The results from this fine grid are considered the "solution" to the displacement in the fractured reservoir. The grid is coarsened and the effects of scale-up are observed. Pseudos are developed for a coarse grid so that the results match the solution. The reservoir is then simulated with a dual-porosity simulator. The sensitivity of the dual-porosity results to the refinement of the numerical grid is studied.

A comparison is made between the solution and the dual-porosity simulator results. Several of the advanced features found in commercial dual-porosity models are tested to see how well they improve the comparison. A scale-up pseudoization is determined that allows the dual-porosity simulation to match the solution. A larger sector model is then simulated with the pseudocapillary pressure to investigate the robustness of the scale-up pseudoization. Recommendations are provided that describe a procedure for using the dual-porosity model to simulate displacements in a fractured reservoir in a more accurate way.

The scale-up process discussed in this paper is just the first step of a two-step procedure. The next step is to scale-up these curves to a field-scale gridblock (i.e., 100×100×20ft or m). If one uses nested matrix blocks for this first step of the scale-up process: the numerical computation problem is much more difficult and expensive and the next step scale-up calculation is confusing and difficult. Thus, this process is preferred in the final analysis.
Alkaline-Surfactant-Polymer Flooding of the Cambridge Minnelusa Field
Authors: Vargo Jay , Turner Jim , Vergnani Bob , Pitts Malcolm J. , Wyatt Kon , Surkalo Harry , Patterson David
Published: December 2007

The Cambridge Minnelusa field alkaline-surfactant-polymer (ASP) flood was an economic and technical success, with ultimate incremental oil of 1,143,000 bbl at a cost of $2.42 per barrel. This success was due to an integrated approach of the application, including: reservoir engineering and geologic studies, laboratory chemical system design, numerical simulation, facilities design, and ongoing monitoring. This paper discusses how each of these was used in the design and evaluation of the Cambridge ASP project.
Discussion and Comparison of Horizontal-Well Performance in Bouri Field
Authors: Jafar A. S. , El-Ageli I. S. , Al-Attar H. H.
Published: December 2007

Seven horizontal wells were drilled in Bouri field, offshore Libya, and put on production between 1989 and 1992. This paper presents the experience gained in producing and monitoring these wells over the past few years. Comparison of well basic characteristics and performances with offset conventional wells indicates their higher productivity and general superior performance. Different monitoring activities conducted on these wells are discussed, including transient test analyses and production logs. Free gas production was found to be related to the combined phenomena of coning and fracture flow mechanism. These discussions show that, in most of the cases, production of water and gas is inevitable as long as economic oil rates are to be maintained. The targets set for these wells in terms of recovery increase and production troubles reduction were at least partially fulfilled.
Advanced Rheological Techniques for Optimizing Borate-Crosslinked Fracturing Fluid Selection and Performance
Authors: Power David J. , Paterson Lincoln , Boger David V.
Published: December 2007

The complex rheological behavior of crosslinked fracturing fluids is a function of shear history, temperature, and chemistry. Understanding the relationship between these variables and the downhole properties of the fracturing fluid is a challenging task. Rheological measurement techniques are presented that unravel some of the mystery associated with crosslinked fracturing fluids. The concept of a physical gel-point for fluids undergoing crosslinking is introduced and shown to correlate strongly with the proppantcarrying ability of the fluid. The gel-point variation with temperature and chemistry is discussed. This variation can be studied in the laboratory to provide an in-situ field performance evaluation without the need for expensive proppant-transport flow loops. The limitations for newly developed, low-concentration polymer fluids are also discussed. The fluid system chosen for analysis was the pH-activated, borate-crosslinked hydroxypropylguar (HPG) fluid.
Processing of Multi-Acquisition NMR Data
Authors: Slijkerman W. F. J. , Looyestijn W. J. , Hofstra P. , Hofman J. P.
Published: December 2007

Crucial issues in formation evaluation are the determination of porosity, permeability, hydrocarbon volumes, and net-to-gross ratio. Nuclear magnetic resonance (NMR) logging provides measurements that are directly related to these parameters. The NMR response of fluids contained in pores is governed by their T2- and T1-relaxation times, diffusion coefficient, and whether or not they wet the rock. In the case where fluids possess a sufficiently large contrast in these properties and NMR data have been acquired with suitably chosen acquisition parameters (i.e., wait times and/or inter-echo times) a separation of water, oil, and gas NMR responses can be made. From these separate NMR responses the hydrocarbon volumes, porosity, and permeability estimates are subsequently calculated. Key in these applications is the ability to include all the acquired log NMR data into the processing towards the desired end result.

Methods exist to derive hydrocarbon volumes from T2 distributions or from echo decay data. However, these are all methods in which the difference between just two acquisitions that only differ in either wait time or inter-echo time are considered. Over the past years we have developed, tested, and employed an alternative processing technique named multi-acquisition NMR (Mac-NMR). MacNMR takes any number of log acquisitions (wait time and/or inter-echo time variations) and simultaneously inverts them using a rigorous forward model to derive the desired water and hydrocarbon T2 distributions. In this paper, we discuss the concepts of MacNMR and demonstrate its versatility in NMR log processing. An example will illustrate its benefits.
Well Formation Characterization by Residual Hydrocarbon Analysis
Authors: Maness Mabre
Published: December 2007

JFT Forum articles are limited to 1,500 words including 250 words for each table and figure, or a maximum of two pages in JPT. A Forum article may present preliminary results or conclusions of an investigation that the author wishes to publish before completing a full study; it may impart general technical information that does not warrant publication as a full-length paper. All Forum articles are subject to approval by an editorial committee.

Letters to the editor are published under Dialogue, and may cover technical or nontechnical topics. SPE-AIME reserves the right to edit letters for style and content.

Introduction

Information supplied by current wellbore evaluation methods often is insufficient for optimum well completion. Recent developments indicate that additional data useful for this application may be obtained from the composition of residual hydrocarbons in drill cuttings. As early as the mid-1950's, Smith and Evans demonstrated that residual hydrocarbons could be used to characterize some geologic formations. The general principles involved later were extended by Reed and Warren and Scrima to oil shale formations using pyrolysis techniques and thermal chromatography. In pyrolysis techniques and thermal chromatography. In 1974, Baker expanded their work to include petroleum source-rock evaluations. Other investigators during this period experienced only limited success in modifying the technique for use in wellbore evaluations. This paper describes a pyrochromatographic analysis that has proved useful when characterizing the producing potential of certain types of wells. potential of certain types of wells. Description of Method

Our method involves the premise that not all hydrocarbons in bits of formation rock are lost when these samples are brought to the surface during normal drilling procedures. Phase behavior and formation permeability procedures. Phase behavior and formation permeability phenomena responsible for residual hydrocarbons in these phenomena responsible for residual hydrocarbons in these samples have been well documented. Relationships between residual hydrocarbon saturations and formation production potential also have been well established. Our method potential also have been well established. Our method uses these relationships to correlate characteristics of test sample hydrocarbon with well production potential.

The analyzer used was composed of a low dead-volume pyrolysis unit attached directly to a flameionization gas pyrolysis unit attached directly to a flameionization gas chromatograph. A large pyrolysis chamber (1 m1 in volume) was developed to allow the testing of larger, more representative formation samples.

Fig. 1 - Carbon-number distribution for nonproductive formation.

Fig. 2 - Cumulative percent curve for nonproductive formation.

JPT

P. 118
Time-Lapse Ultrasonic Measurements of Laboratory Hydraulic-Fracture Growth: Tip Behavior and Width Profile
Authors: Groenenboom J. , van Dam D. B. , de Pater C. J.
Published: December 2007

We performed acoustic measurements in a time-lapse sequence in scaled laboratory tests. The advantage of time-lapse measurements is that the fracture response can be separated from the background signal. As a consequence, not only can the hydraulic fracture be detected, but its shape and geometry can be measured during its growth. This application requires the combined information of both compressional- and shear-wave measurements. We apply this technique to propagation, flowback tests, and reopening of hydraulic fractures.

Acoustic waves excite diffractions at the fracture tip. These diffractions are used to locate and to characterize the fracture tip. The acoustic measurements indicate that we can distinguish between a dry tip and the fluid front of the fracture.

Shadowing of shear-wave transmissions allows estimation of the moment of fracture initiation. The width profile of the fracture is determined with compressional-transmission measurements. This application is based on the fact that the attenuation and time delay of compressional transmissions are proportional to the fracture width. Analysis of a flowback test shows that the fracture closed at the wellbore but remained open farther away from the wellbore.
Comparison of Period- or Height-Dependent, Sea-State Parameters From a Theoretical Model With Observation at Sea
Authors: Arhan M. , Ezraty R. , Laurent M.
Published: December 2007

A joint theoretical probability density for individual wave heights and periods, originally developed to describe storm conditions, is compared with about 2,000 routine wave recordings in the Bay of Biscay. From this joint probability density, all other mean sea-state parameters (HT 1/3, - TH 1/3, T 1/3 . . .) can be computed using H 1/3, T, and, the spectrum width parameter. The systematic discrepancy existing between theory and observation can be corrected empirically if necessary.

Introduction

Cartwright and Longuet-Higgins predicted the height of sea waves and computed the significant wave height, h 1/3, or similar variables, h 1/n, as well as the expectancy of the maximum, E(h max), of a given number of waves. They started with mo and, the total energy and the width parameter of the spectrum, respectively.To describe a sea state, a characteristic period and characteristic height are necessary. In the "zero-up-crossing" wave analysis the following periods usually appear: (1) T 1/3 is the mean of the periods usually appear:T 1/3 is the mean of the highest third of the zero-up-crossing periods,TH 1/3 is the mean of the periods connected to the waves used to compute H 1/31 andThis the mean of the zero-up-crossing periods.In the same way, T 1/n and TH 1/n also can be defined.

Wiegel found empirical relationships between these characteristic periods, based on observation at sea. Our theoretical model is based on the theory of Gaussian noise as established by Rice and leads to an explicit formula for the joint probability density of wave heights and periods. probability density of wave heights and periods. This density is fixed when given these parametersa characteristic height, a characteristic period, and epsilon. Then, by appropriate integrations, we can relate the different average heights to the associated average periods that describe a given sea state. Although the narrow-band spectrum hypothesis is not always satisfied, computed values of mean quantities from observations at sea remain close to their theoretical equivalents. Any systematic discrepancy can be corrected if necessary.

THE THEORETICAL MODEL

A model was developed using as a starting point, the joint probability density for a Gaussian noise signal with a maximum value, 1, and a second derivative with respect to time, 3, as

........................................(1)

We have assigned to each positive maximum a sinusoidal wave with amplitude 1 and period T given by

SPEJ

p. 233
Evaluation of the M-Site B-Sand Fracture Experiments: Evolution of a Pressure Analysis Methodology
Authors: Gulrajani Sunil N. , Nolte Kenneth G. , Romero Jean
Published: December 2007

The most comprehensive hydraulic-fracturing data including the first objective measurements of fracture height, length, and width are acquired from the Gas Research Inst. (GRI)/Dept. of Energy (DOE) Multiwell Site (M-Site) tests. In spite of the availability of extensive and reliable fracturing data, significant deviation between predicted and microseismic-determined fracture geometry was reported. The purpose of this study is to provide a consistent analysis of B-sand experiments by applying a systematic methodology for fracture-treatment evaluation.

For this analysis, fracture parameters are estimated initially from laboratory data, well logs, and calibration tests. These parameters are refined by matching simulated pressures to field-measured fracturing pressures recorded during the first linear gel injection. These fracture parameters then are used to compare predicted- and measured-fracture pressures on all subsequent injections. Although general agreement for the fracturing pressures was obtained, a discrepancy was noticed between zone stresses estimated by evaluation and their variation as indicated on published stress logs. Stress data were reinterpreted and an acceptable pressure match was established.

Fracture parameters resulting from this study are in agreement with independently inferred estimates. In addition, an apparent difference between closure pressure and microfrac stress is resolved. Finally, good agreement between predicted fracture geometry and microseismic readings is observed for each injection test considered in this study. This study shows that fracture pressures and geometry can be predicted consistently with good accuracy using elementary analysis techniques, without a reliance on ad hoc physical explanations.
Proppant Transport Characterization of Hydraulic-Fracturing Fluids Using a High-Pressure Simulator Integrated With a Fiber-Optic/Light-Emitting-Diode (LED) Vision System
Authors: Shah Subhash N. , Asadi Mahmoud , Lord David L.
Published: December 2007

Slurries of selected hydraulic-fracturing fluids such as 40-lbm/Mgal hydroxypropyl guar (HPG) linear gel and borate-crosslinked 35-lbm/Mgal guar gel were evaluated to characterize their proppant transport properties using 6-lbm/gal 20/40-mesh sand. In addition, fluids such as water, 40-lbm/Mgal HPG linear gel, and borate-crosslinked 35-lbm/Mgal gel were evaluated to determine their relative ability to remove the fluidized layer lying along the top of settling proppant bed and subsequently to erode more compacted layers below. The experimental study used a unique high-pressure parallel-plate flow cell, simulating a down-hole fracture, integrated with a fiber-optic vision system and LED.
Silica Micro-Encapsulation Technology for Treatment of Oil and/or Hydrocarbon-Contaminated Drill Cuttings
Authors: Quintero Lirio , Limia Jose M. , Stocks-Fischer Shannon
Published: December 2007

Silica micro-encapsulation (SME) is a new technology that has significant economic and environmental value because it allows disposal of oil- and/or hydrocarbon-contaminated drill cuttings, either onshore or offshore, in an environmentally safe manner.

SME is a process by which the oil attached to the drill cuttings is removed by emulsification and then physically encapsulated within an insoluble matrix of amorphous silica. The process consists of the addition of an emulsifier in an acidic environment, followed by the addition of water-soluble silicate.

Specific emulsifiers are selected to cover hydrophilic-lipophilic balance (HLB) requirements for a broad range of oils used in drilling fluids, including synthetics, mineral oil, diesel, crude oil, and bitumen.

Laboratory and pilot tests of the SME technology show that, using environmentally acceptable emulsifiers, oil-based mud present on drill cuttings is removed and forms a stable oil-in-water emulsion. These results led to development of a process for SME treatment of drill cuttings that could be environmentally acceptable for offshore applications, as described in previous publications.1,2
Electrical Measurements in the 100 Hz to 10 GHz Frequency Range for Efficient Rock Wettability Determination
Authors: Bona Nicola , Rossi Elio , Capaccioli Simone
Published: December 2007

This paper summarizes an experimental and theoretical study conducted to investigate the effect of rock wettability on the electrical response of water- and oil-saturated core samples in a wide frequency band. The aim of the study was to evaluate a technique not previously applied to wettability determination as a practical alternative to conventional tests, and to ascertain the consequent economic and technical benefits in reservoir appraisal.
Effect of Discontinuous Shales on Reservoir Performance During Horizontal Waterflooding
Authors: Jackson M. D. , Muggeridge A. H.
Published: December 2007

We investigate quantitatively the effect of inclined and intersecting discontinuous shales on horizontal waterfloods, using generic, dimensionless two-and three-dimensional models. We focus upon whether the shales alter the sweep efficiency. We find that they have a significant effect only if they are continuous over large areas of the bedding surfaces and are steeply inclined to the flow, or if the displacement is highly unfavorable. We also find that two-dimensional simulations can significantly overestimate the effect of intersecting shales, because they assume that the shales are entirely continuous in the third dimension.
Improved Oil Recovery in Carmópolis Field: R&D and Field Implementations
Authors: Mezzomo Roberto F. , Luvizotto José M. , Palagi Cesar L.
Published: December 2007

Carmópolis field, in northeastern Brazil's Sergipe/Alagoas basin, is the country's largest onshore oil accumulation at 253 × 106 m3 original oil in place (OOIP) and a current total oil production of 2880 m3/d. Discovered in 1963, it was quickly put into primary production. Waterflooding followed in 1971 at the central portion of the field. The combination of adverse fluid mobility ratio, reservoir heterogeneity, and the lack of proper selective injection led to the quick decline of production; however, a major program of selective plugging, stimulation, and selective injection was able to stabilize production immediately. Waterflooding was then extended to the entire main block of the field. The well pattern was changed from five- to nine-spot arrangement, with a corresponding downsizing in well spacing and injection rates. Carmópolis also was subjected to an intense improved oil recovery (IOR) campaign with pilot tests on polymer flooding, steam-flooding and in-situ combustion. The history of Carmópolis field and the significance of waterflooding to oil production in Brazil, with approximately 2000 × 106 m3 OOIP currently submitted to this method of recovery, led to the selection of Carmópolis as the target for one of the projects in the PRAVAP (Petrobras Strategic IOR Program) portfolio. The scope of this project included a review of the waterflooding operation through improved reservoir characterization and flow simulation, as well as the investigation of other IOR methods that might reverse the declining production trend. This paper reviews the IOR history of Carmópolis field and summarizes the outcome of the PRAVAP project that led to the approval of field implementations worth U.S. $34 million net present value (NPV).
Miscibility Variation in Compositionally Grading Reservoirs
Authors: Høier Lars , Whitson Curtis H.
Published: December 2007

Minimum miscibility conditions of pressure and enrichment (MMP/MME) have been computed with an equation of state (EOS) for several reservoir-fluid systems exhibiting compositional gradients with depth owing to gravity/chemical equilibrium. MMP/MME conditions are calculated with a multicell algorithm developed by Aaron Zick, where the condensing/vaporizing (C/V) mechanism of developed miscibility is used as the true measure of minimum miscibility conditions when it exists. The Zick algorithm is verified by detailed one-dimensional (1D) slimtube simulations with elimination of numerical dispersion. The miscibility conditions based on the traditional vaporizing-gas-drive (VGD) mechanism are also given for the sake of comparison, where it is typically found that this mechanism overpredicts conditions of miscibility.

Significant variations in MMP and MME with depth exist for reservoirs with typical compositional gradients, particularly for near-critical oil reservoirs and gas-condensate reservoirs where the C/V mechanism exists. An important practical implication of these results is that miscible displacement in gas-condensate reservoirs can be achieved far below the initial dewpoint pressure. The requirement is that the injection gas (slug) be enriched somewhat beyond a typical separator gas composition and that the C/V miscibility mechanism exist. This behavior results in many more gas-condensate reservoirs being viable candidates for miscible gas cycling than previously assumed, and at cycling conditions with lower cost requirements (i.e., lower pressures) and greater operational flexibility (e.g., cycling only during summer months).
Synergy Is Essential to Maximum Recovery Michel T. Calls for Full Coordination Of Petroleum Engineers and Explorationists
Authors: Halbouty Michel T.
Published: December 2007

You call for full coordination of geologists, geophysicists, and petroleum engineers to advance petroleum exploration, development, and production. Does this require a revolutionary change in the way each discipline and industry managers think of their responsibilities?

Absolutely not. In fact I think that it is the duty and responsibility of industry managers to encourage full coordination of geologist, geophysicists, and petroleum engineers to advance petroleum exploration, development, and production. Any petroleum exploration, development, and production. Any supervisor or manager who does not encourage such coordination is a liability to his company and should be dismissed. Do you see the team approach as basic to most exploration, development, and production work, or useful in limited but vital areas?

The team approach is definitely basic. Not only to most. but to all exploration, development, and production work. This coordination should not be limited in any manner.

How essential is the synergy idea to future petroleum reserves and production?

Very essential. Without it I doubt that we will be able to find the future petroleum reserves which I think exist in this country and require extensive drilling to find.

Do economics already indicate a basic need for a new approach in the petroleum sciences and engineering?

Yes - because costs to explore. drill, and produce are so high that every effort should be made to reduce these costs by coordination of the three disciplines. You would be surprised how this coordination can reduce costs. In our shop we have definitely proven, without any doubt whatsoever, that costs are reduced when geologist, geophysicists, and petroleum engineers get together and discuss every phase of the exploration, drilling, and production effort. This eliminates the "I told you so" chiding if a mistake is made by a particular discipline.

Does the combined effort apply equally to exploration and development in new as well as old areas?

Yes. The combined effort should apply to new as well as old areas. In fact, this combined effort is particularly productive in old areas.

What role does the team approach play in finding new reserves near producing reservoirs?

Traditionally, explorationists seek and find and petroleum engineers develop and produce.

P. 750
A New Approach for Log Analysis of the Pulsed Neutron and Resistivity Log Combination
Authors: Aqivlera Robert
Published: December 2007

JPT Forum articles are limited to 1,500 words including 250 words for each table and figure, or a maximum of two pages in JPT. A Forum article may present preliminary results or conclusions of an investigation that the present preliminary results or conclusions of an investigation that the author wishes to publish before completing a full study; it may impart general technical information that does not warrant publication as a full-length paper. All Forum articles are subject to approval by an editorial committee.

Letters to the editor are published under Dialogue, and may cover technical or nontechnical topics. SPE-AIME reserves the right to edit letters for style and content.

Introduction

A current technique for evaluating the pulsed neutron-resistivity combination involves crossplotting the capture cross-section, Sigma, as read from the log vs true formation resistivity, Rt, on an inverse-square-root scale. The data points must be from clean zones with a limited range of points must be from clean zones with a limited range of porosities. The Sigma - Rt crossplot generates a clean porosities. The Sigma - Rt crossplot generates a clean oil-water straight line with a slope equal to a R w (Sigma w - Sigma hy). Values of water saturation can be determined directly from this straight line.This paper presents a different approach for evaluating clean zones of a single lithology using the pulsed neutron-resistivity combination. The method has the same capabilities as the technique mentioned previously, plus the following advantages. plus the following advantages. 1. This method permits analysis in the presence of porosity variations. porosity variations. 2. The value of the porosity exponent, m, does not have to be assumed as 2.0.3. Under favorable conditions, the method allows us to estimate the value of the water saturation exponent, n, from logs alone.The procedure discussed here is inspired by the pattern recognition approach introduced by Pickett.

Theory

The fundamental equations for log analysis are

(1)

(2)

(3)

The basic equation for quantitative analysis of clean formations from pulsed neutron logs is

(4)

Solving for porosity we obtain

(5)

Combining Eqs. 2, 3, and 5 and taking the logarithm of both sides leads to

(6)

where

(7)

Analysis of Eqs. 6 and 7 indicates that a log-log crossplot of Rt vs Sigma - Sigma ma for zones that are 100% saturated with water must result in a straight line with a slope equal to -m, provided the values of a, R w, m, Sigma ma, and Sigma w are constant. If the value of Sigma ma is not known, this type of analysis allows us to determine Sigma ma by trial and error. In fact, if the value of Sigma ma is incorrect, it is impossible to obtain the desired straight line, and only curves result.Once the 100% water-bearing trend is established, we can create a family of parallel lines, each representing a value of water saturation.

JPT

P. 415
The Use of Resistivity-at-the-Bit Images and Annular Pressure While Drilling in Preventing Drilling Problems
Authors: Rezmer-Cooper Iain , Bratton Tom , Krabbe Helle
Published: December 2007

The cost of well construction can exceed budget dramatically if drilling operations are plagued by wellbore-instability problems and excessive time and resources are needed to free stuck pipe, regain circulation, or clean the hole efficiently. Annular pressure while drilling has been recognized recently as one of the key downhole measurements for aiding real-time diagnosis of the condition of the wellbore and drilling fluids. In addition to conventional drilling-mechanics measurements, time-lapse logging-while-drilling (LWD) documents the dynamic change in measured properties during well construction. This can be essential in diagnosing wellbore failure, and the mechanism of failure, in addition to dynamic processes such as cuttings buildup.

An example from a horizontal well in the North Sea is used to illustrate how LWD resistivity images can be used in conjunction with annular-pressure-while-drilling measurements to detect the onset of drilling-induced fractures. Although the majority of azimuthal images have been acquired to understand the geology and petrophysics of reservoirs, the images usually contain features resulting from geomechanical processes.

Analysis of these features reveals important information for optimizing drilling and understanding the geomechanics of the well. Coupling resistivity images to the pressure measurement enables problem identification and correct remedial actions to optimize the drilling operation, for example, ensuring that swab and surge pressures are kept to a minimum, and correct hole-cleaning procedures are used to prevent irreversible formation breakdown.
Multiple Proppant Fracturing of Horizontal Wellbores in a Chalk Formation: Evolving the Process in the Valhall Field
Authors: Norris M. R. , Bergsvik L. , Teesdale C. , Berntsen B. A.
Published: December 2007

Oil production from this chalk field has been improved significantly over the last 3 years using multiple proppant fractures placed from horizontal completions. Following early successes, the engineering effort focused on increasing value through engineering innovation and increased productivity. This paper describes, through case histories and field data, advances made in the design and execution of these completions over 13 wells in the Valhall field.

Wellbore completion activities and stimulation are performed now as a stand-alone process. Using specialized large-diameter coiled-tubing (CT) equipment allows ongoing drilling operations to be performed concurrently. This has reduced daily spread costs significantly while bringing wells on production in a much-reduced time frame. This lower cost environment also has allowed innovative field procedures to be developed resulting in further improvements such as proppant plugs for isolation between stimulation zones, novel bottomhole assemblies (BHA's) for perforating, and treatments using recycled proppant to minimize waste.

Productivity is the driver for economic success. Treatmentdesign requirements have evolved through laboratory testing to account for longer-term downhole-operating conditions below the bubblepoint while also improving initial conductivity. Field data to date through production logging operations have confirmed the hydrocarbon contribution from each fracture. This is used to validate the effectiveness of each treatment. Normalized well productivities continue to improve and the challenge is to maintain the rate of evolution through the improved application of new and existing technologies.
Review of Air and Gas Drilling
Authors: Cannon George E. , Watson Ralph A.
Published: December 2007

Experimental work with compressed air or gas as drilling fluid has been carried on by Humble in West Texas, South Texas, North Texas, and New Mexico with beneficial results in nearly all instances. During the past three years, gas has been used at certain stages in drilling seven wells and air in nine wells. Penetration of lost returns sections has been facilitated by this method of drilling and, in addition, drilling rates have been greatly increased.

Air or gas may be used to advantage with rotary drilling in areas where formation water is limited, the formation does not slough, and where pressures of fluids which may be encountered are sufficiently low to snake safe operation possible. An injection pressure as low as 65 psi is sufficient when the hole is dry, much higher pressure being required for handling formation water influx, however. Although its application is limited, as mentioned, progress is being made in developing techniques for handling formation water encountered in conjunction with air or gas drilling.

Introduction

The drilling industry in the United States during the past five years has effected a remarkable improvement in footage drilled with no basic or revolutionary changes in method of operation; average footage per rig year has risen from 35,369 ft to 45,200 ft. The average well cost and average footage cost have not been reduced, however, because of increased costs of materials and services. A possibility for reducing over-all costs lies in the further development of new techniques. It is the purpose of this paper to set forth benefits which have been possible through the use of air or gas as a circulating medium in rotary drilling, a technique which is creating considerable interest throughout the industry.

Rotary drilling with air or gas can greatly facilitate operations in wells penetrating sections in which drilling mud would be lost, by effecting reductions in rig time, mud, and casing costs, in many cases being more effective than cable tools. Damage to producing formations can be averted by eliminating contact with drilling mud. Great benefit is also derived, however, from markedly increased penetration rates and bit life as compared to drilling with mud. The following discussion is limited to Humble's experience with air and gas drilling.
Pseudosteady-State Flow Equation and Productivity Index for a Well With Noncircular Drainage Area
Authors: Odeh A.S.
Published: December 2007

Most reservoir engineering flow-equations and calculations assume radialgeometry. Radial geometry implies that the drainage area of a well is circularand the well is located at the center. In many cases, the drainage area of awell is rectangular, triangular, or some other noncircular shape. Applicationsof equations based on radial geometry to noncircular drainage area could leadto appreciable error. In many wells, pseudosteady-state flow occurs during mostof their productive life. The productivity index (PI) concept is used in apseudosteady-state, depletion-type reservoir to predict the oil wellsperformance as a function of the difference between the average reservoirpressure and expected flowing bottom-hole pressure of the pressure and expectedflowing bottom-hole pressure of the well. The PI concept is not used for gaswells. The most common equations used by the reservoir engineer to describepseudosteady-state flow and productivity index are

.....(1)

.....(2)

and

.......(3)

where

qo = oil production rate STB/D qg = gas production rate, Mscf/D k =effective permeability, md h= thickness, ft
Handil Field: Three Years of Lean-Gas Injection Into Waterflooded Reservoirs
Authors: Gunawan Sugianto , Caié Didier
Published: December 2007

The giant Handil field comprises more than 500 hydrocarbon accumulations in structurally stacked and compartmentalized fluvio-deltaic sands. Most of the accumulations consist of a large column of saturated oil underlying a gas cap, trapped in reservoirs with good rock properties, and produced by water injection or strong natural waterdrive.

In 1995 five reservoirs representing nearly one-fifth of the field's total original oil in place (OOIP)—and which had reached their final stage of waterflood development (58% of the total oil in place had already been produced)—were submitted to further development with lean-gas injection to increase the ultimate oil recovery. To date, after 3 years of gas injection, the recovery factor for these five reservoirs has increased by 1.2% of the oil initially in place, and the project is considered both a technical and an economic success.

The predominant drive mechanism with lean-gas injection has been confirmed by field data. The previous decline of oil production has been stopped, and the oil rate is now stabilizing. The main monitoring challenge has been the control of gas cycling for most of the producers, particularly during periods of higher injection rates, to compensate for low injection periods imposed by gas availability.

The very close monitoring of well and reservoir performance, the numerical simulation, and material-balance studies have helped provide a better understanding of the mechanisms involved and have led to a revised and more efficient policy to maximize oil production.

The experience gained and the analysis of this 3-year-old project gives us the confidence to pursue the extension of the lean-gas injection development to other Handil field reservoirs.