bluuebunny/crossref_metadata_2025 huggingface dataset:
New Electromagnetic Surveying/Ranging Method for Drilling Parallel Horizontal Twin Wells
Authors: Kuckes A. F. , Hay R. T. , McMahon Joseph , Nord A. G. , Schilling D. A. , Morden Jeff
Published: December 2007

An electromagnetic source was used in conjunction with a measurement-while-drilling (MWD) survey instrument to drill two parallel horizontal wells with a vertical separation of 9 ± 2 m over a length of 600 m in Amoco's Wolf Lake field for steam-assisted gravity drainage of heavy oil. Existing wellbore survey methods are incapable of this level of precision because of cumulative survey error and associated position uncertainty. Using this new electromagnetic ranging technique, the twin wells were placed with better than 10 times the accuracy of gyro surveys.
Effects of Heterogeneity and Anisotropy on Probe Measured Permeabilities
Authors: Manrique Jorge F. , Kasap Ekrem , Georgi Dan
Published: December 2007

Numerical simulations and laboratory experiments were used to study effects of heterogeneity and anisotropy on probe measured permeabilities. Simulation results show that the geometric factors for unsteady-state flow measurements are not different from the ones obtained for steady-state. Effects of a nearby flow barrier on probe measured permeability are studied experimentally and numerically, and it is concluded that the effect of a local flow barrier is negligible when the barrier is located farther than one-half of a probe-tip diameter from the probe.

Probe measured permeability on a damaged formation is profoundly affected by the damaged zone thickness. Working with geometric factors, a methodology to obtain undamaged and damaged zone permeabilities, and damaged zone thickness is developed. To obtain such information uniquely three measurements with three different probe tip sizes are required.

The effects of anisotropy on probe measured permeability are also investigated by introducing tensorial permeability for probe measurements. Several simulation runs were performed for different anisotropy ratios at various cross-bedding angles. Results are presented in the form of dimensionless parameters that can be used to determine depositional dip angle and permeabilities in the principal directions.
Horizontal Well Acidizing of a Carbonate Formation: A Case History of Lisburne Treatments, Prudhoe Bay, Alaska
Authors: Krawietz T. E. , Rael E. L.
Published: December 2007

Stimulating horizontal wells in carbonate formations can lead to significant increases in productivity if effective fluid diversion can be achieved. Many horizontal wells are completed with slotted or pre-drilled uncemented liners throughout long producing intervals. These completions prevent effective use of conventional cased-hole diverting techniques, such as ball sealers and some particulates. Stimulation fluids can be mechanically placed or diverted with such materials as particulates, foam, and/or high-viscosity fluids. A combination of nitrogen foam and viscous emulsified acid pumped through coiled tubing (CT) has been successfully used to treat horizontal wells in the Lisburne field at Prudhoe Bay, Alaska. This paper documents treating techniques and production results of acid stimulation treatments pumped in horizontal wells that are completed with slotted or predrilled uncemented liners throughout long producing intervals. Case histories of four wells are used to illustrate treatment designs and production response.
Improved Oil Recovery Using Horizontal Wells at Elk Hills, California
Authors: Gangle F. J. , Schultz K. L. , McJannet G. S. , Ezekwe N.
Published: December 2007

Eight horizontal wells have been drilled and completed in a steeply dipping Stevens sand reservoir in the Elk Hills field, Kern County, California.

The subject reservoir, called the Stevens 26R, is a turbidite channel sand deposit one mile wide, three miles long, and one mile deep. Formation beds have a gross thickness up to 1,500 feet and dips as high as 60 degrees on the flanks. The original oil column of 1,810 feet has been pulled down to 200 feet by continual production since 1976.

The reservoir management operating strategy has been full pressure maintenance by crestal gas injection since 1976. The steep dip of the formation makes gravity drainage the dominant drive mechanism. Additionally, improved recovery is coming from cycling dry gas through the large secondary gas cap region.

The prudent placement of the horizontal wells above the oil/water contact promises to improve oil recovery and extend the operating life of the reservoir. Field results are given to compare the performance of the horizontal wells with the conventional wells. The horizontal wells produce at higher rates, lower draw downs, and lower gas/oil ratio which will extend the life of the project and result in higher recovery.
Using Fracturing as a Technique for Controlling Formation Failure
Authors: Fletcher P. A. , Montgomery C. T. , Ramos G. G. , Miller M. E. , Rich D. A. , Guillory R. J. , Francis M. J.
Published: December 2007

Conventional gravel-pack completions often reduce a well's productivity by increasing the completion skin. This paper describes a methodology backed by a systematic technique to predict the necessary drawdown, fracture length, and conductivity to prevent formation failure and remove the completion damage. This method enables the engineer to optimize the fracture dimensions while obtaining the necessary decrease in near-wellbore drawdown that would cause the unpacked perforation to fail. This technique will greatly reduce the chance for formation failure and improve the well performance without the need to gravel pack.
Multiple Realizations of the Permeability Field From Well Test Data
Authors: Oliver Dean S.
Published: December 2007

Although it is possible to generate smooth radially-symmetric permeability distributions that honor a given set of pressure data, the assumption of radial symmetry is unrealistic for most heterogeneous reservoirs. The alternative for generating two-dimensional permeability fields that honor the pressure data and a variogram, without the radial symmetry of the deterministic methods, has usually been to resort to Monte Carlo methods. In this paper I show that it is possible, using models which are linearized about the maximum likelihood point, to generate multiple realizations of the permeability field that are conditioned to well test data, point measurements of permeability, and the variogram. The proposed procedure is far more efficient than current simulated annealing or genetic algorithms and the resulting conditional simulations have no radial artifacts.
Fracture-Mechanics Analysis of the Breakdown Process in Minifracture or Leakoff Test
Authors: Detournay Emmanuel , Carbonell Roberto
Published: December 2007

The breakdown pressure—the peak pressure that is reached during pressurization of the wellbore—is interpreted in this paper to correspond to a condition of unstable crack propagation. It is shown that the classical Hubbert and Willis14 and Haimson and Fairhurst9 breakdown criteria represent a condition of fracture initiation in the limiting case of fast and slow pressurization rate, respectively; and that the breakdown pressure, pb, could be either equal to or larger than the fracture-initiation pressure, pi.
Production-Induced Compaction of the Brent Field: An Experimental Approach
Authors: Schutjens P. M. T. M. , de Ruig H. , Sayers C. M. , van Munster J. G. , Whitworth J. L.
Published: December 2007

The most attractive option to increase hydrocarbon recovery from the Brent and Statfjord reservoirs (Brent field, North Sea) is a gradual decrease of the reservoir fluid pressure. To provide laboratory data upon which estimates of the resulting reservoir compaction and surface subsidence could be made, we performed uniaxial compaction experiments at room temperature and in-situ stress conditions. Experimental observations suggest that the reloading of core samples to in-situ stress conditions closed coring-induced microcracks. Most Brent samples (porosity 6% to 30%) showed a compressibility that was constant with increasing effective stress (i.e., linear compaction) and increased with porosity. There was 30% to 75% strain recovery during unloading and an average permanent shortening of about 0.7%. Some high-porosity (25% to 30%) Brent samples showed a relatively high uniaxial compressibility that increased with stress (nonlinear compaction). Nearly all the Statfjord samples showed nonlinear compaction. The Statfjord samples from Core A, with a porosity of 8% and 20% to 22%, showed about 45% strain recovery upon unloading and an average permanent shortening of 0.6%. The Statfjord samples from Core B (porosity 22% to 28%) showed only 24% strain recovery and an average permanent shortening of 3.2%. Microscopy analysis of the Brent samples revealed no evidence for a compaction-induced change in microstructure. In contrast, the Statfjord samples from Core B (22% to 28% porosity) displayed numerous intergranular and transgranular cracks in quartz and feldspar grains, which probably triggered grain sliding and grain rotation. These inelastic brittle mechanisms, which occur together with elastic deformation of the load-bearing grain framework, seem dominant in high-porosity (Statfjord-type) sandstones and should be incorporated into predictive models of production-induced compaction of quartz-rich reservoir rock.
Deconvolution Under Normalized Autocorrelation Constraints
Authors: Baygün B. , Kuchuk F. J. , Arikan O.
Published: December 2007

In this paper we describe a time domain algorithm for determining the influence function from the measured input and output signals of the system. The deconvolution, which is a highly unstable inverse problem with measurement errors, is an important step for obtaining the system's influence function that provides insight about flow regimes normally masked by the time-dependent input signal. The algorithms presented for deconvolution in the literature are generally based on data reduction, with the exception of constrained deconvolution methods.

We propose a constrained least-squares deconvolution method to reconstruct the influence function from noisy data. The constraints are the lower bounds on the first few lags of the normalized autocorrelation coefficients of the influence function. The lower bounds may represent known or desirable smoothness properties of the function. By choosing the constraint values larger, a smoother deconvolution can be obtained. We also impose an energy constraint on the derivative of the reconstructed signal for further regularization.
Invasion Profiling With a Multiple-Depth-of-Investigation Electromagnetic-Wave Resistivity Sensor
Authors: Bittar M. S. , Rodney P. F. , Hendricks W. E.
Published: December 2007

The EWR-Phase 4SM sensor is the first measurement-while-drilling (MWD) electromagnetic resistivity tool to offer multiple depths of investigation by use of measurements made from signals originating at different distances from the receivers. As a propagating-wave resistivity device, it measures four phase shifts and four attenuations. This yields eight different apparent depths of investigation, allowing more meaningful information about the invasion profile.

With the phase-shift measurements alone, the traditional three-parameter step invasion model can be used to obtain the virgin formation resistivity, Rt; the flushed zone resistivity, RXO; and the diameter of invasion, Di. These same four measurements can also be interpreted with a ramp invasion model, a sloped-transition invasion model, and a continuous-monotonic invasion model. For more complex invasion profiles, such as an annular invasion profile, all eight measurements can be used to describe the invasion profile accurately.

Invasion profiling starts with an examination of the trends among measurements. These trends are used to select one or more invasion model(s) to use in the interpretation (step, ramp, sloped transition, continuous monotonic, or annulus). Once the form of a model has been selected, the model parameters are computed by use of a modified Levenberg-Marquardt algorithm, which minimizes the sum of the squares of the differences between the measured and reconstructed resistivities. Examples are presented that compare the results of interpreting invasion following one of the previously stated invasion profiles with one of the others as a reference model. Guidelines on the use of these models are given. Finally, some field examples are analyzed and presented.
EM Log Response to Anisotropic Resistivity in Thinly Laminated Formations With Emphasis on 2-MHz Resistivity Devices
Authors: Hagiwara Teruhiko
Published: December 2007

Anisotropic resistivity is not uncommon in electromagnetic logging environments. Many shale formations are known to be anisotropic. Thinly laminated sand/shale sequences behave as macroscopically anisotropic formations.

We analyzed the tool response to anisotropic resistivity for each type of EM logging tool: electric resistivity logs, induction type logs, and toroidal resistivity tools.

In particular, the effect of anisotropy on the logging-while-drilling 2-MHz induction-type resistivity log is discussed in detail. The effect causes differences between phase-derived and attenuation-derived apparent resistivities, between apparent resistivities from different transmitter-receiver spacings, and between apparent resistivities measured at different operating frequencies. Based on the tool response analysis, we present a method to estimate anisotropy from log data. An application to laminated sand analysis is discussed, in which the sand lamina resistivity and the net-gross ratio (N/G) are determined simultaneously.
A Technique for Faster Pulse-Decay Permeability Measurements in Tight Rocks
Authors: Jones S. C.
Published: December 2007

Laboratory pulse-decay measurements using a gas or liquid are effective for determining the permeability of rocks in the range from 0.1 md to 0.01 μd. The actual measurement time with this pressure-transient technique is fairly short, but pressure pre-equilibration sometimes requires hours. This paper shows how the total time can be reduced significantly, especially if the sample's pore volume (PV) is measured independently or estimated accurately. Permeability is calculated from "late-time" measurements. Strategies for minimizing errors and increasing sample throughput are presented.
Physical and Numerical Modeling of Hydraulic Fracture Closure
Authors: de Pater C. J. , Desroches Jean , Groenenboom Jeroen , Weijers Leen
Published: December 2007

This paper describes laboratory tests and numerical simulation of hydraulic fracture behavior during propagation and closure. The numerical results predicted the laboratory results during fracture propagation and closure. From the experiments and simulations, the paper provides recommendations for ensuring correct interpretation of field data.
Use of Resistivity Logs To Calculate Water Saturation at Prudhoe Bay
Authors: McCoy D. D. , Grieves W. A.
Published: December 2007

At the time of this work, induction- and porosity-log measurements were available in more than 180,000 ft of hydrocarbon column from 428 wells. Water saturations were determined from this areally and vertically extensive database after calibration to oil-base-core (OBC) -derived water saturations. This paper presents the method used to calibrate the log data to the OBC water saturations and reviews the methods used to derive resistivity and formation factor values. It also presents field measurements of as-received core-plug resistivity and water-saturation values from two oil-base-mud (OBM) -cored wells. Comparisons are presented with both field water saturations and "routine" electrical-property measurements on extracted plugs.
Chemical Tracer Studies To Determine Water Saturation at Prudhoe Bay
Authors: Deans H. A. , Mut A. D.
Published: December 2007

The single-well chemical tracer (SWCT) method was used to measure resident water saturation in two wells in the Ivishak reservoir of the Prudhoe Bay field. The tests, performed in 1981, were in API Wells 406 and 488, both of which had been oil-base cored through the Ivishak. The results of the tracer test in Well API 406 were interpreted by conventional SWCT simulation procedures. A three-layer simulator model was used to match the tracer production profiles measured during the test. The average water saturation obtained from the simulator match was 16 ±3% PV, in good agreement with the Dean-Stark analysis of the oil-base cores. The tracer-test results from Well API 488 were more difficult to interpret because of the very low water saturation at this location in the Ivishak. The SWCT method requires a hydrolysis reaction to take place in the formation to produce a product tracer. In this case, the amount of water present was so small that very little product tracer was formed. The interpreted Sw for this well was 2 ±2% PV, again in reasonable agreement with the oil-base-core measured value of 3.8%.
Mechanisms Controlling Filtration at the Core Bit for Oil-Based Muds
Authors: Warner H. R. , Rathmell J. J.
Published: December 2007

Laboratory half-scale coring experiments using 4-in.-diameter reservoir rock samples were conducted with field oil-based muds (OBM). The OBM were formulated to have low water content and low fluid loss to minimize the potential impact of the invading OBM filtrate on connate water saturations (SW). The OBM had been used previously during Prudhoe Bay (Alaska) field coring operations conducted to obtain connate Sw measurements. Laboratory overbalance pressure and temperature were similar to the reservoir downhole environment. The coring test data were OBM filtrate volume generated during coring, pressure in the rock beneath the bit as the bit approached, and pressure in the half-scale 2-in. core during and after the core bit passed by. Also, at the end of each test, dynamic and static OBM filtrate volumes were measured while only circulating the mud and with no mud flowing. OBM filtrate properties, viscosity, emulsifier content, water content, and interfacial tension (IFT) were measured after coring was concluded. Sw was measured before and after coring.

Conclusions from these tests are as follows.

The pressure measurements show that the OBM filter cake controls the pressure gradient both in the core and in the rock directly beneath the bit. The pressure gradient across the OBM filter cake took up almost all the pressure difference between the mud and formation pressures, even at the face of the core bit. The OBM filtrate contains approximately 10% of the carboxylate soap and water found in the whole OBM. OBM filtrate IFT is about half the reservoir oil/brine IFT. The invading OBM filtrate properties are similar to reservoir crude. The water-concentration increase in the OBM was approximately the amount expected as a result of freeing water from the rock drilled up during coring. Because of Sw variations within the rock samples, core sample Sw measurements could not be used to quantify any potential water movement in the core caused by OBM filtrate invasion.

These results mean that the pressure gradients in the core during coring are very low, so displacement of water by capillary number effects will not occur, and above the oil/water transition zone, cores taken with OBM similar to the ones used here should yield reliable in-situ Sw values.
Improved Reservoir Characterization in Low-Permeability Reservoirs With Geostatistical Models
Authors: Meehan D. N. , Verma S. K.
Published: December 2007

This paper is a field application of modern geostatistical reservoir characterization to a complex, low-permeability gas reservoir. Multiwell history matching with this approach is shown to be significantly better than those done with historical approaches. Important opportunities for additional drilling were identified; however, these additional infill locations required significantly lower well costs to be commercial.
Experiments on Bypassing During Gasfloods in Heterogeneous Porous Media
Authors: Burger J. E. , Springate G. S. , Mohanty K. K.
Published: December 2007

Mass transfer from a bypassed region to a flowing region is a very strong function of the solvent phase behavior. Diffusion, dispersion, and capillarity-driven crossflow can contribute to this mass transfer in addition to pressure- and buoyancy-driven crossflow. Our experiments indicated that the mass transfer rate increased with enrichment. Liquid phase diffusion played a significant role and capillary pumping did not contribute to mass transfer in the cases studied.
Fracture-Network 3D Characterization in a Deformed Chalk Reservoir Analogue-the Lägerdorf Case
Authors: Koestler A. G. , Reksten Kari
Published: December 2007

Quantitative descriptions of 3D fracture networks in terms of fracture characteristics and connectivity are necessary for reservoir evaluation, management, and EOR programs of fractured reservoirs. Our research has focused on an analogue to North Sea fractured chalk reservoirs that is excellently exposed near Lägerdorf, northwest Germary. An underlying salt diapir uplifted and deformed Upper Cretaceous chalk; the cement industry now exploits it. The fracture network in the production wall of the quarry was characterized and mapped at different scales, and 12 profiles of a 230-m wide and 35-m high production wall were investigated as the wall receded 25 m. In addition, three wells were drilled into the chalk volume. The wells were cored and the wellbores were imaged with both the resistivity formation micro scanner (FMS) and the sonic circumferential borehole image logger (CBIL). The large amount of fracture data was analyzed with respect to parameters, such as fracture density distribution, orientation, and length distribution, and in terms of the representativity and predictability of data sets collected from restricted rock volumes.
Reservoir Geochemistry: A Link Between Reservoir Geology and Engineering?
Authors: Larter S. R. , Aplin A. C. , Corbett P. W. M. , Ementon Neil , Chen Mei , Taylor P. N.
Published: December 2007

Geochemistry provides a natural, but poorly exploited, link between reservoir geology and engineering. We summarize some current ap-plicationsof geochemistry to reservoir description and stress that, because of their strong interactions with mineral surfaces and water, nitrogen and oxygen compounds in petroleum may exert an important influence on the pressure/volume/temperature (PVT) properties of petroleum, viscosity and wettability. The distribution of these compounds in reservoirs is heterogenous on a submeter scale and is partly controlled by variations in reservoir quality. The implied variations in petroleum properties and wettability may account for some of the errors in reservoir simulations.
Application of Chlorine Dioxide as an Oilfield-Facilities-Treatment Fluid
Authors: Romaine Jennifer , Strawser T. J. , Knippers M. L.
Published: December 2007

Both mechanical and chemical treatments are used to clean water-flood-injection distribution systems whose efficiency has been reduced as a result of plugging material, such as iron sulfide (FeS) containing sludge. Most mechanical treatments rely on uniform-line diameter to be effective, while chemical treatments require good contact with the plugging material for efficient removal. This paper describes the design and operation of a new innovative application using chlorine dioxide (ClO2) for the removal of FeS sludge from waterflood-injection distribution systems. The use of ClO2 for continuous treatment of injection brines will also be discussed.

Exxon USA's Hartzog Draw facility in Gillette, WY, was the site for the application described. A total of 4,500 bbl of ClO2 was pumped in three phases to clean 66 miles of the waterflood-distribution system. Results indicated that ClO2 was effective in cleaning the well guard screens, the injection lines, and the injection wells. The addition of excess ClO2 to the frac tanks used to collect the treatment fluids also reduced waste handling and disposal costs.
Field-Scale CO2-FIood Simulations and Their Impact on the Performance of the Wasson Denver Unit
Authors: Hsu C-F. , Morell J. I. , Falls A. H.
Published: December 2007

Recent advances in software and hardware technology have made possible the development of field-scale, fully compositional CO2-flood simulations capable of capturing areal variations in performance on an individual well basis. This paper first describes the general methodology developed, including key elements used to construct such large models, followed by the validation of this approach. Two modeling studies conducted on the Wasson Denver Unit are then presented to highlight several of the significant out-comes realized so far: high-grading the profitability of new CO2 projects, pinpointing best-well candidates to return to production, identifying infill and horizontal drilling locations, and identifying and quantifying injectant losses.
Representation of Wells in Numerical Reservoir Simulation
Authors: Ding Yu , Renard Gérard , Weill Luce
Published: December 2007

In reservoir simulation, linear approximations generally are used for well modeling. However, these types of approximations can be inaccurate for fluid-flow calculation in the vicinity of wells, leading to incorrect well-performance predictions. To overcome such problems, a new well representation1 has been proposed that uses a "logarithmic" type of approximation for vertical wells. In this paper, we show how the new well model can be implemented easily in existing simulators through the conventional productivity index (PI). We discuss the relationship between wellbore pressure, wellblock pressure, and flow rate in more detail, especially for the definition of wellblock pressure. We present an extension of the new approach to off-center wells and to flexible grids. Through this extension, the equivalence of various gridding techniques for the well model is emphasized. The key element is the accurate calculation of flow components in the vicinity of wells.
Incorporation of Western Components With Russian Drilling Operations, Case History of Ardalin Fie d Operations, Timan Pechora Basin
Authors: Brady Steve , Reyna Erick
Published: December 2007

Polar Lights Co. (PLC) is a 50/50 joint venture (JV) formed by Conoco and Arkhangelskgeologia (AG), a Russian geophysical association, to exploit reserves in the Timan Pechora Basin. Ardalin was the first field to be developed under this JV. Three Uralmash 3-D-86 rigs supplemented with western components, materials, and services were used to successfully accomplish the development drilling. This paper identifies the major Russian and western rig equipment merged on the rig and the Russian and western materials and services used during the drilling operations.
Case Histories and Applications of a New Slimhole MWD Multiple-Depth-of-Investigation Resistivitiy Sensor
Authors: Ball Scott , Yee S. P. , Maranuk Chris , Bittar M. S.
Published: December 2007

The use of measurement while drilling (MWD) resistivity tools in boreholes 8½ in. and greater in diameter has evolved over the past 10 years from a little-used, qualitative service to a routinely used quantitative service in directional, horizontal, and extended-reach wells. Today's applications include reconnaissance logging, geo-steering, pore pressure evaluation, wireline replacement, and enhanced formation evaluation.

Over the last several years, there has been an increasing trend worldwide toward drilling smaller boreholes to optimize the costs of tubulars and gain greater drilling efficiencies. Until recently, there have been no MWD resistivity tools available for logging 6-in. diameter boreholes. A new multiple-depth-of-investigation MWD resistivity sensor housed in a nominal 4$34-in. diameter drill collar has been developed for use in slimhole drilling operations.

This new MWD resistivity sensor provides eight different depths of investigation in any mud type and allows for derivation of the flushed zone resistivity, true resistivity, and the diameter of invasion across a wide range of formation resistivities. The tool is designed for boreholes larger than 5⅞ in. in diameter and can be used in medium-radius drilling applications.

Extensive operations in the North Sea, Gulf of Mexico, south Texas, Middle East, Alaska, and Australia have demonstrated a variety of applications. Slimhole MWD resistivity has been shown to have use in geosteering horizontal wells to maintain and optimize wellbore placement. Additionally, it allows determination of true formation resistivity and diameter of invasion for formations with invasion effects and provides for application of advanced modeling techniques to enhance formation evaluation and log interpretation.
Comprehensive Analysis of Buckling With Friction
Authors: Mitchell R. F.
Published: December 2007

While analytic solutions are available for a limited number of special load cases, the general solution of buckling with friction requires a numerical solution. This paper describes the formulation and solution of the helical buckling of tubulars with friction. An example application demonstrates many surprising results, especially when friction forces from previous load steps are unloaded.
Survey of Electrical Submersible Systems Design, Application, and Testing
Authors: Durham M. O. , Lea J. F.
Published: December 2007

The electrical submersible pump industry has numerous recommended practices and procedures addressing various facets of the operation. Ascertaining the appropriate technique is tedious. Seldom are all the documents available at one location. This synopsis of all the industry practices provides a ready reference for testing, design, and application of electrical submersible pumping systems. An extensive bibliography identifies significant documents for further reference.
Interpretation of Fracture Height From Temperature Logs—The Effect of Wellbore/Fracture Separation
Authors: Davis E. R. , Zhu Ding , Hill A. D.
Published: December 2007

Temperature logs commonly have been used to evaluate fracture height by locating cool anomalies that indicate the locations where cool fracture fluids were injected. Instead of cool anomalies, however, warm anomalies (called "warm noses") often occur on temperature logs run after fracture treatments. When interpreting fracture height from a temperature log, warm anomalies make it difficult to identify the top and bottom of the fracture. We believe that a plausible reason for warm anomalies is that the wellbore and the fracture are not coincident over the entire extent of the fracture; instead, away from the perforations, the fracture and the wellbore may be separated a finite distance that varies with depth. This paper investigates the effect of the existence and magnitude of the displacement between the wellbore and the fracture on wellbore temperature behavior after fracturing. The results obtained explain the "warm noses" on shut-in temperature logs run after a fracture treatment and, more generally, illustrate how fracture-wellbore separation can result in a variety of characteristic temperature log responses.

A mathematical model has been developed to simulate the wellbore temperature after fracturing for cases where the wellbore and the fracture are not coincident for the entire extent of the fracture. The study shows that the temperature behavior strongly depends on the pattern and the magnitude of the displacement. When the fracture is perfectly connected with the wellbore, the cool region on the log indicates the top and bottom of the fracture clearly. However, the cool region is much smaller than the fracture height if the wellbore deviates from the fracture at a constant angle away from the perforations—a situation that may occur in a well that is deviated slightly from vertical, for example. Furthermore, "warm noses" appear on the log if the well spirals in a helical trajectory because the spacing between the wellbore and the fracture will vary with depth for this geometry. Therefore, when evaluating a postfracture temperature log, the possibility of a deviated wellbore-fracture system must be considered to avoid misinterpreting the fracture height. Longer shut-in times are shown to improve the fracture-height interpretation.
Virtual Reserves—And Other Measures Designed To Confuse the Investing Public
Authors: Tobin J. C.
Published: December 2007

Norman Augustine, CEO of Martin Marietta, in his book Augustine's Laws,1 observed that, "Cost estimating is the first professional activity to make practical use of the mathematics of a complex number. It is easy to see the imaginary component in these estimations. The difficulty is in finding the real part."

Over the years, I believe we have seen this form of math creep into reserve estimation. In that we are once again dealing with numbers that have no resemblance to reality, I think that the appropriate label for such reserves, in keeping with the terminology of modern technology such as virtual imaging and virtual memory, is to call them "virtual reserves."
Fill-Up Pressure Buildup Test: An Effective Method for Wells With Low Initial Production and Deep Drawdown
Authors: Megyery Mihály
Published: December 2007

261 oil and 680 gas reservoirs have been explored within the territory of Hungary. Their depths and pressures range from 300 to 4500 m (1,000 to 15,000 ft) and from 3 to 85 MPa (430 to 12,000 psi), respectively. The highest temperature ever measured during our reservoir test operations was 218.3°C (425°F) at 4550 m depth in Well L-II. (1973). Some of the testing methods elaborated during the exploration and development of this large amount of reservoirs can be of international interest; the fill-up procedure, providing pressure buildup (PBU) curves equivalent to those of bottomhole shut-in tests in low-production oil and gas wells, is one of them. The paper presents and analyzes the results of 497 fill-up PBU tests with particular attention to the impacts of reservoir "reworkings" (retesting, acidizing, fracturing, horizontal drilling).
Mud-Induced Formation Damage in Fractured Reservoirs
Authors: Jiao Di , Sharma Mukul M.
Published: December 2007

A set of experiments was completed that clearly shows that drilling muds can cause large irreversible damage to fractures and dramatically reduce the productivity of wells producing from a natural fracture network. The use of sized fibers as an additive to drilling muds can significantly reduce both the depth and extent of formation damage. Granular additives (such as CaCO3) are much less effective. The use of acid soluble fibers is, therefore, recommended for reducing formation damage in fractured reservoirs.
Computer Codes for Oilwell-Perforator Design
Authors: Regalbuto J. A. , Gill B. C.
Published: December 2007

This paper presents three computer codes used to analyze and design oilwell perforators that are specifically tailored to hydrocarbon-bearing formations. The codes are a Lagrangian, finite-element code; a Eulerian, finite-difference code; and a coupled Lagrangian/analytical code.

Applications of the codes involve charge-to-charge interference effects, estimation of penetration and hole size, explanation of charge/gun-system behavior, and perforator-design optimization.

Analysis of an existing six-shot/ft system, which showed charge-to-charge interference, is presented. The solution, which eliminated the interference and increased overall performance, involved charge-case modification. Topics discussed include the following.

Initial correlations between experimental and calculated penetrations and hole size in steel and cement. The mechanism of producing burr-free holes in casing, explained by modeling the perforation system. An example of perforator-performance improvement by determination of discrete jet properties. Expanding the application of the codes by enlarging the equation-of-state database to include fluid-filled porous media.
Imaging of Sand Production in a Horizontal Sand Pack by X-Ray Computed Tomography
Authors: Tremblay Bernard , Sedgwick George , Forshner Ken
Published: December 2007

A laboratory experiment was performed to better understand how sand production can increase heavy oil recovery. A horizontal sand pack with an orifice at one end modeled the production of oil and sand into a perforation in a vertical well. The sand pack was scanned using X-ray computed tomography (CT). The CT images revealed that a high-porosity channel (wormhole) formed in the pack while sand was produced. The wormhole followed regions within the pack where the porosity was higher, and, consequently, the unconfined compressive strength of the sand was lower. This experiment suggests that wormholes will form within the weaker sands of a formation. The development of these high-permeability channels increases the drainage of the reservoir, which leads to higher oil recovery.
Pressure Transient Analysis in Horizontal Wells in Some Sole Pit Area Fields, U.K.
Authors: Gilbert C. J.
Published: December 2007

This paper presents a discussion and interpretation of a variety of transient pressure responses observed in nine flow and buildup surveys performed in horizontal wells in the Sole Pit area fields Barque and Clipper. Horizontal well pressure transient flow regimes and signatures associated with heterogeneous reservoirs are observed in the survey log-log pressure derivatives. The signatures show considerable variability and emphasize the strongly heterogeneous nature of the reservoirs. Rapidly declining transmissibilities in the vicinity of the wellbore are observed in two surveys, while other survey log-log derivative responses suggest a dual-porosity characteristic followed by horizontal well intermediate-time linear flow. Pressure transient testing contributes to an understanding of the reservoir behavior by revealing essential characteristics of a flow model that can describe flow in the heterogeneous, fractured sandstone.
Seeking Synergy Between Drawdown and Buildup Analyses
Authors: Kabir C. S.
Published: December 2007

Drawdown tests are rarely interpreted unless accompanied by instantaneous surface or downhole rate measurements. Rate variations prevent a constant-rate analysis in most situations. Unsteady wellbore dynamics precipitated by progressive formation cleanup, multiphase fluid flow, and wellbore thermal effects influencing compressible fluids, to name a few, may prevent one from obtaining a stable surface rate. This reality compels an analyst to fall back upon buildup interpretation. Thus, one typically presupposes that the rate was held constant before shut-in. Drillstem tests and long-duration exploratory well tests are cases in point. This conventional practice raises an important question: Can we calculate a variable-rate history such that the drawdown analysis will be consistent with the buildup?

This paper presents a method to interpret drawdown data whenever variable rates are encountered, either inherent in a test or induced by design, such as in a gas-lift well test. The method entails a stepwise procedure. First, buildup data are interpreted assuming a constant rate during drawdown. Second, the estimated parameters are used to compute instantaneous rate corresponding to each pressure data point by superposing constant-pressure solution with an appropriate pD model. The reconstructed rate history is then used to perform the variable-rate (convolution) analysis of drawdown data. Third, the new rate history is used to reinterpret buildup data. Parameters obtained from the two analyses provide the desired consistency.

The proposed procedure is entirely general, in that any appropriate reservoir pD model may be used to compute the instantaneous rate values. However, best results are obtained when the late-time data are free from outer-boundary effects. We present field examples from various scenarios to show the usefulness of this approach. These examples include a short-duration onshore drillstem test (DST), a gas-lift well test involving a gas-vent period, a long-duration production test with suspected pressure-sensitive rock properties, and a slug/closed chamber test. In all cases, we have shown the synergy between the results of the two tests.
Geologically Consistent Resolution Enhancement of Petrophysical Analysis With Image Log Data
Authors: Ramamoorthy Raghu , Flaum Charles , Coll Carolina
Published: December 2007

Very thin, laminated sand-shale sequences pose a challenge to petrophysical evaluation. The poor vertical resolution of the log measurements results in pessimistic estimates of hydrocarbon volumes and producibility. An earlier proposal by Flaum1 to enhance the resolution of the analysis using a high-resolution clay indicator did not account for variations in clay mineralogy and porosity with clay content. We present a technique to incorporate results of core mineralogy measurements to ensure a geologically consistent resolution enhancement of the petrophysical analysis, and we compare the results in an actual field example.
Development and Testing of a Compact Liquid-Gas Auger Partial Separator for Downhole or Surface Applications
Authors: Weingarten J. S. , Kolpak M. M. , Mattison S. A. , Williamson M. J.
Published: December 2007

In some applications, complete separation of liquid and gas is not required and removing only a portion of the gas is sufficient. One application that was developed fully is separation of gas from one well for raw gas lift of other wells. This can be done either on the surface or downhole. The auger separator is a new, patented device that was initially developed to fit inside production tubing and, thus, is an ultra-compact separator design. It differs from other separators in that it requires no complex controls or power to operate and, for most applications, has a diameter of only a few inches. The multiphase fluid enters an auger section where the pitch of the stationary auger blade causes the flow to rotate. Centrifugal forces created by this rotation cause the liquid to flow along the outer wall with the gas flowing in the center. A portion of the gas is ported through a crossover to the annulus in downhole applications or to a gas line in surface applications. The downhole separator can be placed by wireline in the tubing. The surface version is placed as a spool piece in the production line.

Equations were developed to predict performance and were incorporated into a spreadsheet for ease of design. Laboratory tests were performed to validate the predictions and to explore various design details. Following successful lab testing, the prototype separator, which was 3½ in. in diameter, was placed downhole inside 4½-in. tubing. The separated gas was ported to the annulus through a gas-lift mandrel. This test showed that the equipment could be placed in the well with wireline, that downhole separation was feasible, and that the theoretical pressure-drop calculations were accurate.

Following this test, an 8-in.-diameter auger separator was designed for separation of gas on the surface as a full-scale pilot test. This was placed in the production line from a well, and the separated gas was used to provide raw lift gas for other wells on the drillsite. These two field tests showed that partial separation was feasible with this device, and that the equations used for design were reasonable. The surface auger separator was left in place after the test and continues to provide lift gas.

This paper presents the concept, design equations, laboratory test results, and field-test results of both a downhole and a surface application. Although raw gas lift is an application that has been fully developed, other potential uses also are discussed.
Field Installation of an Acoustic Slug-Detection System
Authors: Dhulesia Hasmukh , Bernicot Michel , Romanet Thierry
Published: December 2007

A pipeline operating in the slug flow regime creates high fluctuations in gas and liquid flow rates at the outlet. The detection of slugs and the estimation of their length and velocity are necessary to minimize the upsets in the operation of downstream process facilities. A new method based on the acoustic principle has been developed by Total and Syminex with two variants—passive and active. The passive method gives the slug length and velocity, whereas the active method also gives the fluid density. The prototype of this system has been installed permanently on a 20-in. multiphase pipeline in Argentina. As this system detects the slugs and determines their characteristics approximately 2 minutes before they arrive at the first-stage separator, the operators take appropriate action in the case of arrival of an excessively long slug and, thus, avoid possible shutdowns. At a later stage, an automatic adjustment of the process control valves will be realized.
Wetting Alteration by Brine and Crude Oil: From Contact Angles to Cores
Authors: Buckley Jill S. , Bousseau Christophe , Liu Yu
Published: December 2007

Factors that affect wetting alteration of a rock upon contact with crude oil include composition of the oil and brine, temperature and duration of aging in oil, and initial water saturation. Similar factors affect contact angle measurements, but the relationship between the surface and core wetting conditions remains to be clearly demonstrated for crude oil/brine/rock systems.

An asphaltic crude oil and two sodium chloride solutions of varying pH have been used to alter wetting of flat glass surfaces, two-dimensional etched glass micro-models, and two core materials:

synthetic core composed of silica and alumina (Aerolith-10), and Clashach–a relatively clay-free sandstone.

Wetting changes on flat glass surfaces are consistent with the wetting conditions established in synthetic silicate cores; the effect on oil recovery by waterflooding is shown. In Clashach sandstone cores, wetting is less directly influenced by the brine pH; both high and low pH cores are distinctly mixed-wet.
Slug-Sizing/Slug-Volume Prediction: State of the Art Review and Simulation
Authors: Burke N. E. , Kashou S. F.
Published: December 2007

Slug flow is a flow pattern commonly encountered in offshore multiphase flowlines. It is characterized by an alternate flow of liquid slugs and gas pockets, resulting in an unsteady hydrodynamic behavior. All important design variables, such as slug length and slug frequency, liquid holdup, and pressure drop, vary with time and this makes the prediction of slug flow characteristics both difficult and challenging. This paper reviews the state of the art methods in slug-catcher sizing and slug-volume predictions. In addition, history matching of measured slug flow data is performed using the OLGA transient simulator.

This paper reviews the design factors that impact slug-catcher sizing during steady state, during transient, during pigging, and during operations under a process-control system. The slug-tracking option of the simulator is applied to predict the slug length and the slug volume during a field operation. This paper will also comment on the performance of common empirical slug-prediction correlations.
Alba Field Cased-Hole Horizontal Gravel Pack: A Team Approach to Design
Authors: Alexander Karen , Winton Suzanne , Price-Smith Colin
Published: December 2007

A 700-ft cased-hole horizontal well was gravel packed and completed in the Alba Field, central North Sea. The completion incorporated a number of new technologies adopted for a horizontal casedhole completion, including both equipment and fluids. The zone was completed in two stages using a horizontal stack-pack approach. Perforation packing was optimized by performing a staged acid prepack with the guns in the hole using a low-density synthetic gravel substitute in a shear thinning carrier fluid. This was a world-first achievement at a cased-hole gravel pack using the stack-pack approach in a horizontal well. A solids-free fluid-loss control material was evaluated and chosen for the high-permeability Alba sands (3 darcies). Extensive lab testing was performed to ensure minimal damage from various fluids. A 30-ft physical model was used to optimize annular pack efficiency. A gravel placement computer simulation was used to design pump rate, sand concentration, and gel loading to optimize annular and perforation-pack efficiency.