bluuebunny/crossref_metadata_2025 huggingface dataset:
Pressure Behavior of Horizontal Wells with Multiple Fractures
Authors: Kuchuk F. J. , Habusky T. M.
Published: December 2007

Drilling horizontal wells to accelerate production and increase recovery efficiency of oil and gas has now become common. With the increasing number of wells, transient well tests have been conducted in many wells with different geological settings. In this paper, we present a number of analytical models for horizontal wells with multiple fractures in homogeneous and laterally composite reservoirs. These solutions are applicable to finite-conductivity transverse fractures, and infinite-conductivity transverse and longitudinal fractures. They may also be used for the fractured reservoirs where the wellbore intersects with multiple fractures.

We examine the pressure behavior of horizontal wells with single and multiple fractures in homogeneous systems. It is shown that the wellbore cannot be neglected in the modeling of horizontal wells with fractures unless the fracture conductivity is high. If the fracture permeability (conductivity) variations in different zones are moderate, compared to the formation permeability, the multiple fractures have almost no effect on the pressure behavior of the system; the horizontal well dominates the system's pressure behavior. If the conductivities are high, the intersected fractures will dominate the behavior of the system at early times. It is also shown that multiple finite- and infinite-conductivity transverse fractures may exhibit multiple linear flow regimes before the onset of the first horizontal well radial flow regime.
Experiences With Combined Analyses of PLT and Pressure-Transient Data From Layered Reservoirs
Authors: Larsen Leif
Published: December 2007

Problems and possibilities with combined analyses of PLT and pressure-transient data from layered reservoirs are discussed, with standard single-layer methods used to estimate parameters, and model verification based on matches of available PLT and pressure-transient data used to complete analyses.

For commingled reservoirs it is shown that if the total flow capacity can be obtained from a direct analysis, then the flow capacity and skin of each layer from stable and short-time PLT profiles can also be obtained by simple two-rate methods. Assuming repeatability of the data, the PLT profile after shut-in can be determined from another test. Also, the rate of crossflow after shut-in relative to the production is shown not to be relevant for the success of this approach.

The main problem with layered-reservoir data is contrasts in skin values, both for commingled and crossflow reservoirs. With severe contrasts in skin values, analyses can become highly uncertain regardless of method used. This is shown by closedform approximations of infinite-acting solutions for commingled reservoirs and illustrated with synthetic data. A field case from the Norwegian sector of the North Sea has also been included to highlight the problems.
Fluid Placement and Diversion in Matrix Acidizing
Authors: Hill A. D. , Rossen W. R.
Published: December 2007

We compare four approaches for efficient placement of acid in matrix-acidization treatments: MAPDIR, particulate diverting agents, viscous acids, and foams. For each process, we develop analytical equations for flow into each reservoir interval and resulting skin factor. We consider treatments in reservoirs with two layers of different permeability but the same initial skin factor and with the same permeability but very different skin factor. MAPDIR reduces overall skin factor fastest but at the cost of injection of large volumes of acid into the higher-injectivity layer. Particulate diverting agents and foams can both effectively divert acid to the low-permeability or more-damaged layer but at the cost of lower injection rate. In our study, particulate diverters with the continuous addition of the diverting agent to the acid solution are most efficient. However, quantitative comparisons of foam with the other processes is difficult until more data are available for predicting foam performance in the field. The equations developed here can be applied to a wide variety of other field situations and process parameters.
The Gas Market: Impact on Management and Organisation of Upstream Assets and Resources
Authors: Handley R. L.
Published: December 2007

The onshore British gas markets in their "decade of change" and the implications for the offshore business are examined. Opportunities for the industry to continue to add value are discussed followed by an examination of the changes in perspective and strategies which may create the successful and growing companies of the future.
Practical Pressure Loss Predictions in Realistic Annular Geometries
Authors: Haciislamoglu Mustafa , Cartalos Ulysse
Published: December 2007

Frictional pressure loss calculations in narrow annuli of slim-hole and coiled tubing operations require more accuracy than before. The paper describes a method to calculate pressure losses that better represents actual annular configurations.

The skewed (vertical wells, varying eccentricity) and uniformly eccentric (deviated wells) geometries are addressed. Easy to use realistic correlations are obtained for laminar, transition and turbulent flow regimes. Experimental flow loop data validate model predictions. A step-by-step procedure is included for field calculations.
Dynamic Analysis Reveals Stability of Roller Cone Rock Bits
Authors: Kenner J. V. , Isbell M. R.
Published: December 2007

The cutting structures of roller cone bits often experience catastrophic failures resulting from dynamic load variations beyond the capacity of the cutting elements. Continuous improvements to cutting structures have steadily increased penetration rates, but at the same time have elevated their sensitivity to these dynamic effects. Until recently, the causes of these failures were difficult to identify.

This paper details a series of roller cone bit tests that discovered a new explanation for cutting structure failure. In the tests, roller cone bits drilled Carthage marble under atmospheric pressure and the system response was monitored. Measurements were taken of new and dull bits, some of which incorporated unconventional cutting structures. Lateral movements of the bit included directional reversals and orbits about the hole center. Certain motions were identified that may result in cutting structure breakage. Included in the paper are examples from kinematic models that capture the essence of the motion and reveal its harmful effects.
A Magnetostatic Well Tracking Technique for Drilling of Horizontal Parallel Wells
Authors: Pratt C. K. , Hartmann R. A.
Published: December 2007

A directional surveying technique has been developed to monitor the directional drilling of two closely spaced, parallel horizontal wells. The well-tracking technique which is based on magnetostatic homing-in technology, uses the magnetic field of the casing in the first horizontal well as a reference for monitoring the drilling trajectory of the second horizontal well. For this purpose, the casing joints of the horizontal section of the first well are artificially magnetised prior to running in the hole, so that the unique magnetic field pattern can be detected in the second well with a conventional measurement-while-drilling tool. No additional tools nor acces to the first well while drilling the second well is required.

The well-tracking technique was sucessfully applied to the drilling of two horizontal wells as part of Shell Canada’s Horizontal Well Demonstration Project, of which the objective is to recover bitumen from tar sands in the Peace River Field, Alberta, Canada (See Reference 1 for definition of bitumen).
Nitrogen Drilling System for Gas Drilling Applications
Authors: Allan P. D.
Published: December 2007

This paper outlines the development of a nitrogen drilling system used by Meridian Oil on three nitrogen drilled horizontal wells in the San Juan Basin of New Mexico. The nitrogen drilling system eliminates the downhole fire risks associated with air drilling in hydrocarbon producing formations while significantly reducing costs as compared to pipeline gas (methane) drilling or trucked liquid nitrogen drilling. Typically, wells that must be gas drilled through productive intervals rely on pipeline gas, expensive trucked liquid nitrogen, or air-water injection (mist) systems. Water mist injection minimizes downhole fire potential but this method is unacceptable on horizontal wells as the extended drilling time in producing intervals greatly increases the probability of downhole fires. Data will be presented which outline the parameters for the nitrogen drilling system development including the required flowrates, the allowable oxygen concentrations, and economic analysis and justification. Actual field data will be presented, providing additional information relating to safety enhancements, cost reduction, and additional upside through the use of the nitrogen drilling system.
Slimhole Vibration Case Study
Authors: Murray P. J. , Kingman J. E. E. , Huddy R. L. , Leon J. G.
Published: December 2007

Drill string dynamics has become an important topic in recent times. This has proven to be particularly critical in slimhole drilling where the understanding and control of vibration has become essential. Conventional rigs have the strength and brawn to overcome most vibration problems and to get to TD even if not all that efficiently. In slimhole drilling, vibration can destroy the string. This paper is a case study into the experience of a major drilling contractor with severe vibration problems on their newly built slimhole rig, at the start of a multi-well contract with a major operating company to drill exploration wells in Venezuela.

The bottom hole assembly (BHA) was catastrophically damaged as a result of vibration, culminating in a number of fishing jobs and extensive repair work to the drill string and BHA. The postmortem on the damaged components and other wear indications on the string confirmed that the string had been rotating, at high speed, in a buckled mode.

This paper describes the various solutions considered and the actions taken. Particular focus is placed on the analysis of the BHA employed and the development of a new BHA design using the experience of a slimhole drilling consultant with the help of available modeling technology and how the limits to the operating parameters were set. With only theory as a guide, we needed reassurance that what had been done was the answer. What was actually going on down hole and what were the implications of our actions at the surface?

Technology currently available to measure vibration offered us the opportunity to see what was going on down hole in real time, giving us immediate feedback on the effects of our actions on surface. The standard vibration sensing equipment available consists of an instrumented tool installed in the string at surface. Unfortunately this was too big to fit under the top drive of the little slimhole rig and another approach was heeded.

The paper describes how the team from the vibration monitoring service company came up with the innovative idea of instrumenting the top drive itself to act as the tool and how they managed to achieve their objectives of providing a reduced level of their standard service to focus on the specific problem.

The paper concludes with some examples of how the monitoring system was able to tell us what the acceptable operating limits for weight-on-bit (WOB) were, by observing the growth of axial strain energy at specified frequencies. Some other valuable spin-offs have been seen and are highlighted in the paper.
BHA Design and Steerability Optimization for Extended Reach Drilling
Authors: Agawani M. M. , Maidla E. E. , Rahman S. S.
Published: December 2007

An algorithm, based on the steerability of a bottom hole assembly (BHA), has been developed which can predict the complete geometry of the most suitable BHA to drill a given section of a directional well.

The model is particularly versatile because it is applicable to rotary mode extended reach drilling, can be used to compare various BHA configurations to that predicted by the algorithm and can take full advantage of the steerability of variable gauge stabilizers.

A field case study is presented to illustrate its usefulness.
Probability Ranges for Reserve Estimates From Decline Curve Analysis
Authors: Huffman C. H. , Thompson R. S.
Published: December 2007

An estimate of the production expected from a property is frequently accomplished by extrapolating historic production data to a minimum economic flow rate. For a particular analyst, deterministic reserve estimates from decline curve analysis gives a specific answer or value for a given production data set. A method has been developed which yields probable production rates and volumes based on the analyst’s deterministic estimate of the future well performance. The objective is to quantify the uncertainty in reserve estimates from production decline curve data.

The statistical concepts of linear regression and prediction limits have been incorporated in a method which utilizes the analyst’s decline exponent (b), decline rate (Di), and production rate (qi) estimates. The method is flexible in that any portion of the historic production data may be utilized if the analyst believes the production parameters of the well have changed over the life of the well. The prediction limits yielded by the method are analogous to probability values and could be used in property value comparisons.

The method was applied to the deterministic reserve estimates made by seven practicing engineers in SPE paper 26388, "A Comparison of Probabilistic and Deterministic Reserve Estimates: A Case Study,"1 The results of this approach will be compared to the subjective probabilistic reserve estimates made by the engineers in the study by Hefner.
Reservoir Optimization in the Nineties: Is Your Company Doing an Effective Job?
Authors: Beatty T. A. , Karlen G. R. , Brown K. R. , Van’t Bosch A. L. , Grant Neal , Burkett Dan , Kissinger Tim
Published: December 2007

PanCanadian’s extensive land holdings and attractive financial position results in work efforts being generally capital related (seismic, drilling, and facilities). As. a result of this focus, Senior Management was concerned that optimization was not being given a high priority and initiated a study in June 1992 to evaluate the process within the company.

PanCanadian has undergone major structural and cultural changes in the past three years and has used process re-engineering to implement changes and increase efficiency. A product of this change is PanCanadian’s unique method of managing people functionally and managing work cross-functionally. This organizational structure is applicable to any company considering restructuring to achieve the gains associated with business units yet want to avoid their common downfalls.

A Reservoir Management Process Study was initiated with a team of seven people from various departments within the company. The study took approximately one year to complete and included over 30 interviews within PanCanadian. Twelve companies in Canada and the United States were benchmarked based on recommendations of superiority in the areas of reservoir optimization.

This paper will detail the methodology of conducting the study, the findings of the study, and will describe the major structural changes that PanCanadian is undertaking to do a more effective job of reservoir optimization.
Fate of Waste Petroleum Refinery Sludge After Deep Well Injection
Authors: Charbeneau R. J. , Ogintz Joanna , Aubert W. G.
Published: December 2007

Application of existing hydraulic fracturing technology to deep well injection of exempt and non-exempt wastes has been investigated. This new application involves disposal of wastes by controlled hydraulic fracturing of suitable deep geologic formations. The proposed process is similar to the widely accepted Class I injection, but allows subsurface placement of waste solids-bearing slurries. Subsurface slurry injection causes fracturing of injection zone rocks because solids-laden fluids (slurries) form relatively impermeable filter cakes when pumped under pressure. Reliable information on hydraulic fracture geometry and propagation has historically been lacking, and current methods of deep well disposal exclude fracture injection. For fracture injection to be accepted, a demonstration is necessary that migration of contaminants is limited to specific geologic formations or zones, or that injected materials undergo chemical transformation into non-toxic forms. This is a "no migration" demonstration, and is done by mathematically simulating transport of injected materials.

The present research involves mathematical simulation, or modeling, of deep well fracture injection of solids-bearing waste slurries. Basic analytical and numerical models were formulated for estimation of injected waste migration from a fracture system. Parameters are in ranges expected of realistic disposal conditions. Analytical and SWIFT II models address regional fluid gradients, reservoir permeability, and fracture orientation.
The Conversion to Team Based Organizations
Authors: Hagist Peter W.
Published: December 2007

Changes in technology and market conditions are driving companies to redesign their businesses from traditional functional based organizations to team based organizations that are focused on core business processes. The advantages of teams have long been recognized, but it is only now that economic forces are driving companies to make teams an integral part of the organization. The change is allowing business to work more efficiently and produce higher quality products at a lower price. For the Oil and Gas industry, team based organizations are a way to develop difficult reserves that otherwise would not be economic to exploit. Important considerations when implementing team based organizations include: J) Defining the core business processes, 2) Establishing roles and responsibilities, 3) Defining the organization, 4) Developing process measurements, 5) Development and cultivation of leadership over management or supervision, 6) Cross-training, and 7) Effective communication.
On the Calculation and Interpretation of NMR Relaxation Time Distributions
Authors: Dunn Keh-Jim , LaTorraca G. A. , Warner J. L. , Bergman D. J.
Published: December 2007

We analyzed NMR relaxation time data using a multi-exponential model. The inversion of NMR data using such a model is an ill-posed problem. The answer is often not unique and requires subjective judgement We studied two methods of regularization. One uses norm smoothing based on an article by Butler et al. We found that optimal norm smoothing depends on the input of measurement errors. The second method uses curvature smoothing which minimizes variations in the second derivative. The latter is more effective for suppressing fluctuations in the relaxation time distribution, but doesn’t directly account for data quality. We studied NMR T1 data at full and partial saturations with desaturation pressures ranging from 15 to 400 psi (air/brine). As a general guideline, we found that the relaxation time cutoff which corresponds to irreducible water saturation is about 33 ms. For a limited number of samples, we found that the T1 relaxation time distribution has very little dependence on the frequency from 200 down to 1 MHz. We also found that T2 could be correlated to permeability.
NMRI Characterization of Fractures and Multiphase Transport in Fractured Porous Media
Authors: Chen Songhua , Yao Xiaoli , Qiao Jinli , Watson A. T.
Published: December 2007

The use of nuclear magnetic resonance imaging (MRI) for characterizing fractures and flow in fractured media is investigated. A relaxation-weighted imaging technique is developed and demonstrated for use with fractured porous media. The new technique can be used to selectively highlight either fracture or porous matrix regions. Considerable advantages over standard spin-density techniques for characterizing fractured media are demonstrated. Its use to speed image acquisition is also demonstrated. MRI technique is also used to monitor imbibition and drainage displacement experiments in fractured porous media. Multislice images show that the fractures can have profound effects on the fluid distributions in multiphase flow.
Pressure-Transient Behavior for a Horizontal Well Intersecting Multiple Random Discrete Fractures
Authors: Guo Genliang , Evans R. D. , Chang Ming Ming
Published: December 2007

New analytical pressure-transient solutions for a horizontal well intersecting multiple random discrete fractures in both an infinite and a bounded reservoir are presented. The horizontal well is assumed to penetrate multiple randomly distributed vertical fractures. The infinite reservoir containing the horizontal well is bounded at the top and at the bottom. For the case of a bounded reservoir, all exterior boundaries are non-flow boundaries. New source functions for a random vertical fracture are first derived. The pressure-transient solutions are then obtained using the derived source functions, as well as superposition principles. A uniform flux is assumed along all fracture faces. An averaging technique is used to approximate the wellbore pressure.

The new solutions provide a theoretical basis for the analysis of the pressure transient behavior of a horizontal well intersecting multiple random discrete fractures. Different flow regimes are identified. The effects of fracture characteristics, such as fracture orientation and length, on the pressure transient behavior of a horizontal well are investigated. New evaluation techniques using the derived pressure-transient solutions can be developed to determine reservoir properties and fracture characteristics from horizontal well test data.
New Insights in Pressure-Transient Analysis for Stress-Sensitive Reservoirs
Authors: Zhang M. Y. , Ambastha A. K.
Published: December 2007

Deep-seated low-permeability petroleum or geothermal reservoirs usually exhibit stress-sensitive permeability. For such reservoirs, pressure-transient analysis based on constant rock properties, especially permeability, can lead to significant errors in parameter estimation. Recently, an approximate analytical solution has been published to analyze pressure-transient tests in stress-sensitive reservoirs using the concept of "permeability modulus". However, because of the non-linear character of the partial differential equation for stress-sensitive reservoirs, application of superposition to model buildup tests is not straightforward.

Using the concept of "permeability modulus", this study presents numerical solutions for stress-sensitive reservoirs. Pressure transient solutions with wellbore storage, skin, permeability modulus, and outer boundary effects have been studied in detail. Both drawdown and buildup solutions have been investigated. Solutions presented in this study also include multiple permeability modulus values for a given situation, where permeability modulus changes with respect to stress level in the reservoir in a stepwise mode.

This study has pointed out inaccuracies involved in previous analytical solutions, especially for wellbore storage and skin effects, and buildup tests. Previously, it has been stated that stress-sensitive permeability effects can cause wellbore storage early-time unit slope line to be masked. This investigation shows that, irrespective of the severity of stress sensitivity, wellbore-storage-dominated unit-slope line always appears at early time. We also show that the use of multiple permeability modulus values to study pressure-transient analysis for stress-sensitive reservoirs is consistent with available laboratory measurements of permeability as a function of stress.
Improving Formation Evaluation by Resolving Differences Between LWD and Wireline Log Data
Authors: Jackson C. E. , Heysse D. R.
Published: December 2007

Wireline logs and logging-while-drilling (LWD) logs are important pieces of the formation evaluation puzzle. They are often the basis for the initial economic evaluation of a prospect and serve as references for monitoring reservoir depletion. As the data from the LWD devices approaches wireline quality, it becomes feasible for oil companies to consider replacing wireline data with LWD data.

Unfortunately, these logs are not directly interchangeable. In addition to differences in basic tool responses, changes in logging environment between LWD and wireline logging runs can cause significant variation between similar measurements (resistivity, density, neutron, gamma ray) that affect subsequent reservoir evaluation. The importance of resolving these differences cannot be overemphasized. Small errors in petrophysical parameters can result in a multimillion dollar difference in the calculation of economic reserves.

This examination of the differences between LWD and wireline logs and consideration of how these differences affect formation evaluation focuses on the following topics: Differences in sensor physicsBasic reference standardsEnvironmental correctionsFiltrate invasion effectsFormation alteration

The outcome is a consistent procedure for making meaningful comparisons between these logs.
Case Histories of MWD and Wireline Density Log Comparisons: An Improved Understanding of Density Log Response
Authors: Spross R. L. , Ball M. S. , Zannoni S. A.
Published: December 2007

With the advent of Measurement-While-Drilling (MWD) density tools in 1987, a new alternative to wireline for obtaining formation bulk density was introduced. As with any such introduction and evolution, comparative evaluations were made in order to assess the quality and quantitative nature of the MWD density data.

Analysis of MWD and comparable wireline density data show that the two can have different responses for several reasons. These include differing instrument designs, different logging environments, and evolving reservoir conditions. MWD and wireline density responses may also differ due to standoff, mudcake, mud density, hole rugosity, drilling dynamics, formation exposure time, and time dependent invasion profiles. Comparative evaluations show that without careful analysis, mis-interpretation of the data can frequently occur.

The ability to obtain and understand quantitative MWD density data greatly enhances the value of Formation-Evaluation-While-Drilling (FEWD) with resulting well cost savings and increased operational efficiency. While a case may be made for wireline replacement applications, it is often true that obtaining data in the MWD and wireline time domains may provide complementary views of changing reservoir conditions thereby enhancing the characterization of the reservoir.
Stochastic Description of Multiphase Flow in Heterogeneous Porous Media
Authors: Chang Y. C. , Mohanty K. K.
Published: December 2007

Typical field simulation grid-blocks are internally heterogeneous. The objective of this work is to scale-up multiphase flow properties of field simulation grid-blocks from core-scale properties and represent them by flow equations involving stochastic terms, if necessary. Heterogeneity is modelled here as a correlated random field parameterized in terms of its variance and two-point variogram. Variogram models of both finite (spherical) and infinite (fractal) correlation length are included as special cases. Local core-scale porosity, permeability, capillary pressure function, relative permeability functions, and initial water saturation are assumed to be correlated. Capillary pressure and relative permeability hysteresis are modelled at the core-scale. Water injection is simulated and effective flow properties (not pseudo-functions) and flow equations are calculated. Conditions under which stochastic terms are necessary and the form of the stochastic term are identified. For strongly water-wet media and small variance in permeability, flow can be described by an effective relative permeability without including a stochastic term. A stochastic term is, however, needed to describe multiphase flow in water-wet grid-blocks of large permeability variance; effective relative permeabilities can describe the average front movements. In fractal media, effective relative permeabilities cannot even describe the average front movements. In oil-wet systems, the saturation front movement is less stabilized and has more fluctuations than similar water-wet cases.
The Effects Of Sedimentary Heterogeneities On Production From A Shallow Marine Reservoir - What Really Matters ?
Authors: Kjønsvik Dagrun , Doyle James , Jacobsen Torgrim , Jones Alistair
Published: December 2007

This paper investigates the impact of sedimentary heterogeneities on performance of waterflooding in shallow marine reservoirs. Reservoir simulation models are developed from detailed geological models based on a four-level sedimentary architectural hierarchy ranging from sedimentary structures (wave ripples, hummocky cross-stratification) up to parasequences. Single- and two-phase flow properties are upscaled to capture the effects of small scale heterogeneities on performance. The relative influence of 12 heterogeneity factors is determined using experimental design and analysis of variance. The analysis identified large scale features (parasequence thickness and stacking patterns) to be of primary importance for waterflood performance. These features control the relative proportion of fades belts in the reservoir, which correlates with recovery. Other important, though secondary, heterogeneities include interfingering of facies belts, and small scale bedding.
New Correlations To Predict Non-Darcy Flow Coefficients at Immobile and Mobile Water Saturation
Authors: Frederick D. C. , Graves R. M.
Published: December 2007

Several empirical correlations were developed relating the inertial, sometimes called the non-Darcy flow, coefficient (β) to permeability, porosity and water saturation. The correlations were developed using 407 data points taken on 24 cores over confining stress which was varied from 1000 psi to 5000 psi. The permeability range investigated was from 0.00197 to 1230 md. Previously published work1 on proppants extend the correlation to 350,000 md with a coefficient of determination of 98%. Water saturation has a significant effect on the coefficient. Confining stress effects are accounted for in the porosity and permeability values which decrease at elevated stress.
The Influence of Stress Anisotropy on Horizontal Well Performance Predicted Via Special Core Analysis Under True Triaxial Conditions
Authors: Crawford B. R. , Smart B. G. D.
Published: December 2007

For optimisation of recovery, a thorough understanding of reservoir heterogeneity and anisotropy on as detailed a scale as possible is a prerequisite. Despite recent developments in probe permeametry enabling quantification of sedimentary heterogeneity down to the lamina-scale, no parallel advance has been evident in the field of core analysis with regard to improving the realism of the applied stress field. The conventional "triaxial" method can only achieve vertical stress anisotropy and is limited to axisymmetric uniform radial pressure. Thus it is incapable of adequately simulating the in situ rock stress field, σv≠σH≠σh. Accordingly, a new true triaxial cell and servo-control system has been developed which is capable of applying independent and unequal radial stresses to the curved surface of a cylindrical core plug. Pulse decay permeability experiments have been conducted on three reservoir sandstone analogues showing different degrees of geological heterogeneity. Permeabilities were measured under both true triaxial and conventional "triaxial" conditions, for the purposes of comparison. In terms of mean stresses, (σv+σH+σh)/3, stress-sensitive permeability profiles were very much influenced by lithology. Complex interaction between stress anisotropy and rock fabric resulted in a non-systematic variation in permeability with mean stress for the laminated, heterolithic rock type. For the scenario of a horizontal wellbore drilled parallel to the minimum principal stress, σh, the measured permeabilities were used to calculate β-factors (β=kh/kv) for simple productivity evaluation. This sensitivity analysis indicated that well performance curves were also susceptible to the degree of stress anisotropy. The effect was evident in discrepancies of up to several hundred feet in calculated horizontal wellbore lengths required to achieve desired levels of productivity.
Laboratory Investigation of Constitutive Property Scaling Behavior
Authors: Tidwell V. C.
Published: December 2007

Property scaling becomes an issue whenever heterogeneous media properties are measured at one scale but applied at another (i.e., data is collected at the core scale but analysis is conducted at the grid block scale). A research program has been established to challenge current understanding of property scaling with the aim of developing and testing models that describe scaling behavior in a quantitative manner. Scaling of constitutive rock properties is investigated through physical experimentation involving the collection of gas-permeability data measured over a range of discrete scales. The approach is to systematically isolate those factors that influence property scaling and investigate their relative contributions to overall scaling behavior. Two blocks of rock, each exhibiting differing heterogeneity structure, have recently been examined. The two samples were found to yield different scaling behavior, as exhibited by changes in the distribution functions and semi-variograms. Simple models have been fit to the measured scaling behavior that are of similar functional form but of different magnitude.
An Application of Idealized Carbonate Depositional Sequences for Reservoir Characterization
Authors: Shao Hongbin , Brimhall R. M. , Ahr W. M. , Wu C. H.
Published: December 2007

This paper presents an application of idealized carbonate depositional sequences in reservoir characterization for the San Andres/Grayburg reservoirs of the Central Basin Platform (CBP) and the Northern Shelf (NS) in West Texas. The ramp and shelf sequences represent two typical carbonate deposits. An idealized progradational ramp sequence with a progressive ramp sequence leads to develop a ramp reservoir model for characterizing the reservoirs of CBP. An idealized progradational shelf sequence with a progressive shelf sequence leads to develop a shelf reservoir model for characterizing the reservoirs of NS. The reservoir models explain variations in the lumping lateral depositional energy, recovery efficiencies, and vertical variation of reservoir permeability.
Velocity and Turbulence Intensity Profiles for Newtonian Annular Flows and the Effect of Mechanical Aids on These Profiles
Authors: Buckingham J. C. , Grimley T. A. , Buckingham J. P.
Published: December 2007

Primary cementing operations, especially those associated with horizontal wells, have encountered many problems that have resulted in poor cementing. During the cementing operation, the complete removal of drilling mud, drill solids, and filter cake (left in the wellbore annulus from the drilling operation) is of utmost importance. The oil industry has attempted to solve the problems of displacing the mud, solids, and filter cake by many means, including the use of mechanical aids attached to the casing. The objective of these aids is to modify the flow in the wellbore annulus to provide a better distribution of the wash material or cement around the casing, and thus better displace the contaminants.

The objective of this joint industry program was to establish, through flow visualization and flow measurements (using non-intrusive, laser Doppler velocimetry techniques), the change in annular flow characteristics produced by various mechanical aids for various casing positions, flow regimes, and fluid types. The initial testing was to be performed with a Newtonian fluid (water), and the most promising mechanical aids were tested with a non-Newtonian slurry with Theological properties similar to typical cements.

This paper summarizes the Newtonian fluid testing effort, including a description of the full-scale annular test facility, measurement of the baseline characteristics of the test facility, and the results of the mechanical aids screening tests.
Parametric Study of Gas Entry into Cemented Wellbores
Authors: Sabins Fred , Wiggins Michael L.
Published: December 2007

A cement slurry is placed in a wellbore to harden into an impermeable mass that seals the annulus from fluid flow and protects the casing from corrosion for the life of the well. If fluid flow does occur in the form of gas migration, expensive remedial squeeze cementing techniques are generally required.

The objective of the work covered in this paper was to study the parameters that affect entry of gas into a cemented annulus. This research incorporated a detailed study of the factors that contribute to gas influx from the time of initial placement of the slurry, through the gelation or transition state of the slurry, to the set condition. Based on the understanding of the processes involved in gas entry, a simulator was developed that can predict the amount of gas that enters a cemented wellbore and can identify the critical parameters that affect the gas entry.

This study concerns itself with a portion of the gas flow problem: the entry of gas into a cemented annulus only—not the flow of the gas up through the cement and the formation of a gas channel.

This study will provide insight to the following issues: What cement properties are important to minimize gas entry?What role does fluid loss play in minimizing gas influx?What well parameters affect gas entry?
Hydrates Formed in Unprocessed Wellstreams
Authors: Tohidi Bahman , Danesh Ali , Burgass R. W. , Todd A. C.
Published: December 2007

Production and transportation of unprocessed wellstreams is economically an attractive option and may significantly enhance the development of many marginal oil and gas fields. These pipelines may however be prone to hydrate formation which potentially can block the pipe and lead to serious operational problems. These can be avoided by either preventing hydrate formation or allowing the formation of hydrates, but preventing their aggregation and transporting them as slurry.

The first approach is the current practice in the industry and it can be more cost effective by determining the hydrate phase boundary more reliably. In the oil and gas industry, n-butane is generally regarded as the heaviest hydrate forming compound, and anything heavier than that as a non-hydrate former. Oil and gas condensate systems contain a significant amount of intermediate/heavy hydrocarbon compounds which recently have been found to be hydrate formers. The water produced with oil also contains dissolved salts which inhibit hydrate formation to some extent. If the formation of hydrates is to be avoided, information on the effect of heavy compounds and salts on the hydrate boundary is required.

Recent studies suggest that some chemicals at low concentrations may modify the growth of hydrate crystals, preventing their aggregation and hence allowing their transportation as slurry. If the use of crystal growth modifiers are to be considered, it is required to determine the amount of hydrates to be transported as a slurry.

This paper reviews briefly the effect of electrolyte solutions, benzene, and methyl cyclo-pentane (MCP) on the hydrate free zone and concentrates on new methods and equipment for measuring the amount and composition of different phases in hydrate forming conditions. An in house numerical model was successfully used for prediction of the hydrate free zone and compositional data. The developed model can be used as an engineering tool to determine the hydrate free zone for transportation of unprocessed well streams in sub-sea pipelines and gathering networks and also the amount of hydrates to be transferred as slurry where the use of growth modifiers is considered as an option.
Wax Deposition of Waxy Live Crudes Under Turbulent Flow Conditions
Authors: Hsu J. J. C. , Santamaria M. M. , Brubaker J. P.
Published: December 2007

Laboratory test methods have been developed to measure wax deposition of waxy live crudes under turbulent flow conditions. This high pressure wax deposition turbulent flow loop is rated up to 1500 psia and from 32 to 240 °F. The apparatus has been used to study impact of flow regimes, oil composition, water, and paraffin inhibitors.

Under turbulent flow conditions the pseudoplastic non-Newtonian behavior of a cold waxy crude significantly affects wax deposition rate. Wax deposition from a waxy crude can be reduced significantly under turbulent flow conditions. The flow turbulence depresses the temperature at which maximum wax deposition rate occurs.

The sloughing effect generated under turbulent flow conditions has significant impact on wax deposition rate and can not be neglected in wax deposition modeling.

Oil composition is a factor affecting wax deposition. Usually, wax deposition rate decreases with increasing oil bubble point pressure under turbulent flow conditions.

The wax hardness and carbon number of the wax deposited on the pipe wall increase with retention time.

The high pressure wax deposition turbulent loop has been used to evaluate wax inhibitors, and study optimum flow conditions and oil compositions to prevent wax problems for designing subseapipelines in the North Sea. The results are critical for potential cost savings derived from optimum design for waxy crude transport conditions.
Electronic, Fiber-Optic Technology: Future Options for Permanent Reservoir Monitoring
Authors: Botto Giovanni , Maggioni Bruno , Schenato Adelmo
Published: December 2007

According to current trends, it is likely that in the near future the oil & gas industries will have to choose between electronic and fiber optic systems for the continuous measurement of down-hole pressure and temperature (permanent reservoir monitoring).

The aim of this paper is to give a view beyond the facade of the up-to-date electronic and fiber optic technology in order to provide a critical evaluation of the degree of maturity of both technologies from an operator’s point of view and to define some realistic prospects of application in the short/medium term period.
Flow in Horizontal Wellbores with Influx through Porous Walls
Authors: Ihara Masaru , Kikuyama Koji , Hasegawa Yutaka , Mizuguchi Keiichi
Published: December 2007

Experimental investigation is presented on the channel flow with mass transfer through porous walls, which has continuous influx into a horizontal wellbore configuration from the oil reservoir. This has been recognized as one of the unsolved, yet most important problems in the production operations because of the complicated interaction between the wellbore and the reservoir.

The pressure was measured along the test channel with rectangular cross section, when the turbulent single-phase liquid flow was introduced into the channel. The fluid velocity distribution in the rectangular cross section was also measured to investigate the effect of influx on the pressure drop.

From comparison with a one-dimensional momentum exchange model, the model agreed with the experimental data for relatively large Reynolds numbers and described reasonably the flow behavior in a horizontal wellbore configuration.
Tip Screenout Designs in Low Permeability North Sea Chalk Reservoirs
Authors: Ennis B. K. , Britt L. K.
Published: December 2007

The Valhall Field is located in the Norwegian Sector of the North Sea and produces from a series of low permeability chalk formations. The wells have historically been completed with a variety of stimulation techniques including propped hydraulic fractures to increase recovery and inhibit inflow of the unstable chalk formation.

This paper will review critical stimulation design considerations, treatment redesign and execution, and post appraisal of the fracture stimulations performed in three wells in the Valhall Field. In the stimulation design portion of the paper, the effects of proppant embedment on post fracture well performance is reviewed. In addition, fracture fluid and proppant selection is evaluated. During the execution phase, fracture stimulation design methodology is reviewed. This methodology includes the use of minifrac pressure decline analysis to redesign stimulations. Finally, post fracture well performance is evaluated and compared to analytical predictions.
A Field Demonstration of Hydraulic Fracturing for Solids Waste Injection with Real-Time Passive Seismic Monitoring
Authors: Keck R. G. , Withers R. J.
Published: December 2007

This paper documents the findings of the Deep Well Treatment and Injection (DWTI) field research project to demonstrate the use of hydraulic fracturing for non-exempt solids waste disposal. This test involved injection of a large quantity of simulated waste into a porous rock formation at a depth of 4500 feet. The inert material injected was designed to match appropriate properties of actual solid wastes. A total of 4 million pounds of sand and bentonite clay, plus 50,000 bbls of water, were pumped in four batch injection cycles spanning five days of operations.

Fracture diagnostic tools used to measure the created fracture geometry included temperature and R/A tracer logs, hydraulic impedance, tiltmeters, and a new real-time passive seismic monitoring and analysis system. Seismic data was measured in two dedicated monitor wells offseting the predicted fracture azimuth. Each well contained 75 geophones that provided 700’ of vertical coverage. Over 2000 seismic events were obtained and analyzed for fracture height; 250 of these were analyzed further for three-dimensional fracture location.

The fracture geometry was predicted in advance with a new computer model developed for this waste injection application. Results showed excellent agreement between the fracture height predicted and that measured by the seismic system, but that other diagnostic techniques were not sufficiently accurate. Good agreement between the maximum predicted fracture length and the length from the seismic system was also observed.