bluuebunny/crossref_metadata_2025 huggingface dataset:
Monitoring Quality Control and Flowback of Foam Fracturing Treatments
Authors: Cipolla C. L.
Published: December 2007

A comprehensive field data set from foam stimulation treatments is presented that illustrates the use of improved instrumentation, quality control (QC) and flowback practices. The integration of the field instrumentation with computer monitoring and real-time instrument cross-checks is also presented. The field tests of the instrumentation illustrates the application of magnetic flow meters to reliably measure actual foam flow rate. Foam flowback procedures are presented that provide controlled, monitored and clean return of foamed fluid.
Well Analysis Before and After Fracture Stimulation
Authors: Economides Michael J. , Thomas Ron L.
Published: December 2007

Variables affecting the performance of a fractured well (over that of the unstimulated well) have a large impact on fracture design. The reservoir permeability and, often, the horizontal permeability anisotropy are the important variables to measure at the pretreatment state. They generally control the optimum fracture length. Predictions of fracture permeability (affected by stresses and residue damage) and fracture height (affected by the interlayer stress contrast) must also be taken into consideration.

Evaluation of the fracture job requires measurements that would lead to the estimation of actual fracture height, fracture length, and fracture conductivity. These estimations allow the forecast of fractured well performance and the rationalization of the job design. This well performance analysis before and after stimulation should be an integral part of a properly engineered reservoir exploitation strategy.
Significant Factors for Successful Matrix Acidizing
Authors: McLeod Harry O.
Published: December 2007

Successful matrix acidizing depends upon: (1). good evaluation of candidate wells using (a) completion and production histories, (b) producing well flow analysis (nodal analysis) and (c) formation composition analysis, (2). design for effective coverage of all damaged perforations, (3). selection of solvents, acids and acid compositions to prevent or reduce incompatibilities and (4). effective well preparation and job supervision.
Long-Distance Propagation of Foams
Authors: Hudgins D. A. , Chung T-H.
Published: December 2007

A series of experiments was conducted to study foam generation and propagation over long distances through porous media. To simplify the problem, they were performed in a one-dimensional physical model consisting of a 30-ft [9.14-m] -long sand-packed slim tube. All experiments were conducted at reservoir conditions of 2,000 psig [13.79 MPa] backpressure at 150° F [338.7 K]. Alipal CD-128 surfactant was used as the foamer. WAG (water-alternating-gas) ratios and injection sequences were varied and found to have a profound effect upon the foam generation and propagation, with higher WAG ratios (more water) breaking down the foam and washing it out. In some cases, the foam became immobile or very slow-moving, while in other cases, it traveled with the gas front for great distances. Crude oil's presence in the porous media was very detrimental to foaming. For comparison, similar experiments in short Berea sandstone cores without oil failed to produce any evidence of foaming.
Oil Recovery Mechanisms in Fractured Reservoirs During Steam Injection
Authors: Reis J. C.
Published: December 2007

The recovery mechanisms for steam injection in naturally fractured reservoirs and the characteristic recovery times for these mechanisms are reviewed. Laboratory studies suggest that steam injection can recover as much as 50% more oil than waterflooding in fractured reservoirs. This recovery is essentially independent of oil gravity, making steam injection equally attractive in light or heavy oil fractured reservoirs.

One of the most important incremental recovery mechanisms is the differential thermal expansion between the oil and the matrix pore volume. At high temperatures, chemical reactions within the matrix block can generate gases, which will displace oil. In matrix blocks containing organic carbon, additional oil can be generated. Oil can also be recovered during cyclic processes by dropping the pressure and flashing the water in the matrix blocks to steam. The effects of steam injection on capillary imbibition of water are less clear, although the reduced viscosity at the higher temperatures will speed the imbibition process. Other mechanisms like gravity drainage, solution gas drive, and distillation are thought to play a less important role in oil recovery.

The characteristic expulsion times for each of these recovery mechanisms are identified. Most of the oil in matrix blocks as large as 10 ft wide can be recovered within a few months.
A Full-Field Numerical Modeling Study for the Ford Geraldine Unit CO2 Flood
Authors: Lee K. H. , El-Saleh M. M.
Published: December 2007

This paper describes a full field numerical modeling study of the on-going Ford Geraldine Unit CO2 flood. A three-dimensional, miscible-type simulator was used to simulate the project area, which covers 3,850 acres and includes 212 wells. The numerical model was calibrated by matching rates, cumulative production, and pressure history, both field-wide and for individual wells.

The full field model offers the following advantages over a unit or symmetric element model: 1. Proper description of inter-well interference; 2. Honoring the production/injection and workover histories of the individual wells; 3. Preservation of the reservoir heterogeneity; and 4. No scale-up problems or assumptions.

This paper will briefly describe the simulator and the techniques used in the history matching. The effects of adjusting various parameters will be discussed, and the history match for full field and individual wells will be presented.

After satisfactory history matching results were obtained, the model is being used to assist in the Unit CO2 flood operation. Examples will be discussed demonstrating the importance of the simulator in monitoring and operating the flood.
A Comparison of 31 Minnelusa Polymer Floods With 24 Minnelusa Waterfloods
Authors: Hochanadel S. M. , Lunceford M. L. , Farmer C. W.
Published: December 2007

The Minnelusa formation in Wyoming's Powder River Basin exhibits high permeability variations and adverse mobility ratios. Polymer augmented waterflooding has been the chosen technology to overcome these conditions for the past 15 years. The idea is to first unify the permeability distribution by injecting cationic polymer, followed by anionic polymer and aluminum citrate crosslinker. Then straight anionic polymer is injected for mobility control. This paper compares the results of 31 Minnelusa polymer floods with 24 Minnelusa waterfloods.

The paper has two parts. The first part compares oil recoveries, injection volumes, flood lives, and water productions of the two population groups at various recovery efficiency cutoffs. At equal oil recoveries, the polymer floods inject less water, produce less water and recover the oil quicker than the waterfloods.

The second part of the paper determines the economics of a typical polymer flood. The cumulative injection and the cumulative oil production of each field are plotted for both the waterfloods and the polymer floods. The points are curve-fitted to yield an equation which predicts oil recovery versus injection in dimensionless form. The equation of each group is applied to the same generic Minnelusa reservoir at a fixed injection rate to yield oil production in time-rate format. Economics are run based on these two production functions.

Results show the polymer flood is economic and recovers an additional 7.5% OOIP over the waterflood. The polymer plus equipment cost is less than $2.00 per incremental barrel of oil.
Design and Optimization of Alkaline Flooding Formulations
Authors: French T. R. , Burchfield T. E.
Published: December 2007

The state-of-the-art for alkaline flooding technology is the injection of combinations of alkalis with synthetic surfactants. Surfactant-enhanced alkaline flooding formulations with low-pH alkaline agents have potential for increased oil recovery. They react less with reservoir minerals and facilitate the use of low concentrations of surfactants because surfactant adsorption is reduced in the presence of alkaline agents.

Laboratory experiments and results from field projects have been evaluated and used to establish guidelines for designing optimum alkaline floods. For a reservoir to be a candidate for alkaline flooding, the reservoir should contain little or no gypsum, the divalent ion exchange capacity should be less than 5 meq/kg, and the in situ pH should be greater than 6.5.

Two optimized alkaline systems which exhibit typical interfacial tension (IFT) behavior are described. One system was optimized with a very low acid (acid number = 0.13 mg KOH/g) crude oil from Delawâre-Childers (OK), field. The other system was optimized with an acidic (acid number = 1.59 mg KOH/g) crude oil from Wilmington (CA), oil field. A mixture of synthetic surfactant and low-pH alkali produced lower IFT and sustained low IFT longer than either reactant alone. This effect was observed with the acidic crude and the slightly acidic crude. It was concluded that surfactant-enhanced alkaline flooding with low-pH alkalis shows promise with both acidic and slightly acidic oils.

Synthetic surfactant is an expensive component of low-pH alkaline flooding formulations. Dilute (0.1 – 0.2 %) concentrations of the added synthetic surfactant are being used in some current alkaline flooding field projects. Laboratory results showed that surfactant losses by adsorption are reduced under alkaline conditions. Losses by precipitation should also be reduced due to the lowering of divalent ion concentration by alkaline preflush.

The final section of this paper is an example of how screening criteria, phase behavior tests, and corefloods can be used to design and optimize an alkaline flood for a specific oil field. The example is for the design of a low-pH, surfactant-enhanced alkaline flood in the Ranger Zone of the Wilmington (CA), field, where a high-pH alkaline flood was previously conducted. That project encountered severe problems with alkali consumption and scaling. A low-pH alkali (such as NaHCO3 or NaHCO3 + Na2CO3) in combination with synthetic surfactant should be effective for producing incremental oil in the Ranger Zone of Wilmington field. Problems associated with high pH floods, such as intractable scales and high consumption, will be mitigated.
Evaluation of Unrecovered Mobile Oil in Texas, Oklahoma, and New Mexico
Authors: Becker A. B. , Brashear J. P. , Biglarbigi K. , Ray R. M.
Published: December 2007

This paper summarizes the technical findings of a regional assessment of oil recovery potential through advanced primary and secondary processes for reservoirs in Texas, Oklahoma, and New Mexico. Intensive infill drilling, polymer-augmented waterflooding, permeability profile modification, and selected combinations of these processes show significant promise for increasing recovery and sweep efficiencies in certain geologic reservoir settings. Given the current technical development and costs of these processes, their application could be feasible in a wide range of reservoirs in the region analyzed, even at oil prices below $20/Bbl. These advanced recovery techniques are all directed at producing unrecovered mobile oil (UMO), which is displaceable by waterflooding but remains in the reservoir at the conclusion of conventional production due to reservoir heterogeneity and unfavorable mobility differences between water and oil. The analysis, which was sponsored by the Department of Energy's Bartlesville Project Office and Office of Planning and Environment, evaluates nearly 500 reservoirs described in the data base. The data base, process predictive models, and analytical methodology used in the study are described in this paper. In addition, Important case study results and comparisons to published results for key reservoirs and other detailed analyses are discussed.

The results indicate that UMO extraction has significant future potential to increase oil reserves and maintain domestic production. This potential is large even at low to moderate oil prices and utilizing existing technology. However, the key to maximizing UMO recovery is the development and wide-scale application of advanced techniques resulting from focused research and development (R&D).
Wellbore Stability: The Effect of Strength Criteria on Mud Weight Recommendations
Authors: McLean M. R. , Addis M. A.
Published: December 2007

Hole problems during the drilling phase of operations are often the consequence of mechanical wellbore instability. This leads to higher than necessary drilling costs. A linear-elastic analysis is frequently proposed for the prediction of the onset of failure, and consequently the mud weights required to prevent hole instability. However, there is no clear choice of which compressive failure criterion to use in the analysis. This paper assesses the influence of two commonly proposed failure criteria on mud weight selection. The failure criteria selected is shown to have an extremely significant effect on the computed 'safe’ mud weights. Examples related to field situations are presented which highlight the anomalies and contrary evidence relating to the suitability of failure criteria.
Laboratory Studies on the Stability of Vertical and Deviated Boreholes
Authors: Addis M. A. , Barton N. R. , Bandis S. C. , Henry J. P.
Published: December 2007

Polyaxial or true triaxial tests have been performed on weak and strong sandstones in order to investigate the stability of model boreholes. Both vertical and deviated boreholes in anisotropic stress systems have been studied. The results indicate the decrease in stability of the deviated boreholes with increasing inclination. Boreholes oriented parallel to the maximum horizontal stress direction also produces less stable boreholes compared to those drilled parallel to the minimum horizontal stress. Comparisons of the laboratory test results with simple predictions using linear elasticity, and a Mohr Coulomb failure criterion, show that the boreholes in the strong sandstones are approximately 4 times stronger than predicted; while the weak sandstones are approximately 8 times stronger than predicted.
Applications and Limitations of Composite Cutter Drill Bits in the Gulf Coast Region
Authors: Vrooman D. , Munger R. , Rawicki A. , Smith L.
Published: December 2007

First introduced to the Gulf Coast region in 1987, the composite cutter bit is the result of research involving two design enhancements that combine polycrystalline (PDC) and thermally stable (TSP) cutters on one bit.1 Each cutter type provides complete bottom hole coverage alone, and, when combined in a 60% PDC/40% TSP mixture, greatly increases the range of applications for both.2-3

The composite cutter bit is able to drill relatively hard, abrasive formations that contain large quantities of shale or shale stringers, achieving maximum penetration rates with extended bit life. Until now, neither traditional PDC nor TSP bits could successfully drill this relatively common Gulf Coast sequence of formation types unless the individual formations were relatively thick and their occurrence was predictable.4-5 Thus, composite cutter bits increase the already-proven benefits that PDC and TSP bits offer versus traditional rock bits or natural diamonds, and provide a viable drilling alternative to conventional bit selection.

Implementation of composite bits -- from the initial onshore Gulf Coast application into proven offshore applications - is described in several key case histories. Field data documents their introduction in the onshore Lac Blanc/North Freshwater Bayou fields, then details offshore successes in the Mississippi Sound, South Timbalier and Mustang Island areas. The case histories illustrate the broad range of well programs and drilling conditions in which these bits have performed. Successful application of composite bits now has spanned extreme variations in bit sizes, hydraulics, depths and lithologies.

Operating recommendations resulting from analysis of these case histories and more than 100 composite bit runs are outlined. Analysis of this information has helped more clearly define the limitations and applications of composite bits in this region.
Improved Channel Repairs with Small-Phased Circumferential Perforating Guns
Authors: Hart P. E. , Wilson L. C.
Published: December 2007

Behind-pipe communication (channeling) may lead to environmental concerns, lost hydrocarbon reserves, and additional workover costs to detect and attempt channel repairs. This case study of channel repairs compared (a) perforation phasing and placement, (b) cementing procedures, and (c) production data in 37 wells over the past eleven years in the Texas Gulf Coast and East Texas areas. An improved repair technique, which focuses on the phasing and placement of perforations and cementing procedures was implemented, resulting in an increase in the success rate of channel repairs from 37 to 89 percent.

Channeling was repaired in wells with undesired gas or water flow past shale intervals from 2 to 29 feet thick. The improved repair success rate was obtained by adding and then squeezing perforations with 15-degree phasing and at least 24 shots across an impermeable zone, where possible. The channel repair success rate of the other wells which typically had 90- or 120-degree phased perforations was only 37 percent. This significant change in success rates was largely due to the increased percentage of the cement's circumference that was perforated. Further improvement is anticipated due to a newly developed perforator with 100 percent circumferential coverage over a 6-inch length which has been tested in two wells.
Drilling Waste Disposal in the Arctic Using Below-Grade Freezeback
Authors: Maunder T. E. , Le K. M. , Miller D. L.
Published: December 2007

The disposal of waste muds and cuttings has become increasingly difficult for operators worldwide. Disposal tasks are complicated by the great variety of operating environments as well as the multitude of local, state and national regulations governing any waste disposal.

This paper describes the successful disposal method used by ARCO Alaska, Inc. (AAI), on two exploratory wells drilled on the North Slope of Alaska in early 1988. The disposal method, below-grade freezeback, involves burying waste muds and cuttings in the permanently frozen ground known as permafrost. When buried, the waste freezes, becoming part of the permafrost. This disposal method utilizes the ability of the natural Arctic environment to isolate and permanently contain the waste muds and cuttings.
A Two-Dimensional Simulator to Predict Circulating Temperatures During Cementing Operations
Authors: Bittleston S. H.
Published: December 2007

This paper describes an advanced numerical simulator for the prediction of down-hole temperatures during cementing. The novel two dimensional approach used in the simulator is detailed together with a method for calculating the dynamic heat transfer boundary conditions on the casing surfaces and the fluid formation interface. The time-dependent numerical scheme is discussed together with the implementation of the pressure and temperature-dependent fluid rheology. The paper also covers the heat diffusion calculations in the formation and the importance of considering the effects of drilling history on the temperature distribution at the beginning of cementing.

The results of the numerical simulator show that the fluid temperatures can be predicted throughout the well and as a function of time e.g. the hottest fluid temperature is not found to be at the casing shoe but some distance up the annulus and so measurements made at the casing shoe cannot be used directly as the design temperature for cementing. The two-dimensional implementation also allows the heat transfer coefficients (Nusselt numbers) for each fluid-solid interface to be examined as a function of time and position. It is shown that the heat transfer coefficients differ significantly from the analytical pipe flow constant heat flux and constant wall temperature solutions. Moreover, the values are seen to vary with time, particularly widely in the annulus. The implication derived from these results is that one-dimensional approximations, often applied for modelling circulating temperatures, may be in significant error because of the necessity to assume values for the heat transfer coefficients in such models.
Simulation to Support Interpretation of the Loudon Surfactant Pilot Tests
Authors: Huh C. , Landis L. H. , Maer N. K. , McKinney P. H. , Dougherty N. A.
Published: December 2007

A surfactant process simulator was used to evaluate the performance of a series of surfactant flood tests carried out at the Loudon field in Illinois. The process model, developed and calibrated with laboratory data, accounts for the detailed phase behavior of the injected and resident fluid mixtures, relative permeabilities and rheology of the resulting phases, the oil displacement mechanism by low interfacial tension, and the retention of surfactant and polymer on reservoir rock. When the surfactant retention is adjusted from laboratory to field levels, the process model does a reasonable job of describing the field performance. The pilot tests matched by simulation included a 0.7-ac inverted fivespot, a 40-ac pattern comprising nine 2.5-ac normal fivespots, and an 80-ac pattern with nine 5.0-ac normal fivespots.

The validity of the process model under field conditions was first tested using a simplified reservoir model — an octant of a confined fivespot pattern. Effects of various process parameters and reservoir stratification on process performance were examined. For full-pilot simulations, reservoir models were prepared from detailed reservoir description data for each pilot, including analyses of cores from 43 pilot wells, induction logs, pressure falloff tests, and pulse tests. For the small pilot, only minor corrections to the sand thickness and permeability outside of the pattern area are needed to match the production of oil, surfactant, polymer, and nine different tracers. The tracers included one overall and four quadrant tracers for the microemulsion bank and four quadrant tracers for the polymer drivewater bank. For the two multi-pattern pilots with larger pattern sizes, reasonable matches are also obtained but require more substantial permeability adjustments overall.

An important task of this effort is to understand why the oil recovery performance of the tests with larger pattern sizes was not as good as that of the earlier smaller tests. Based on the interpretation of the history matches, it is believed that the major reason for the poorer-than-expected performance of the larger tests is the failure of the polymer bank to propagate as designed. Reasons for poor polymer transport are discussed.
Pore-Level Modelling of Gas-Condensate Flow through Horizontal Porous Media
Authors: Mohammadi S. , Sorbie K. S. , Danesh A. , Peden J. M.
Published: December 2007

In order to evaluate recovery strategies from gas condensate reservoirs, it is necessary to have some knowledge of the behaviour of the gas and liquid relative permeabilities. Very little experimental work is available on this subject and the approach taken in this paper is to consider gas-condensate relative permeability from a theoretical viewpoint. The process of retrograde condensation and revaparisation by pressure depletion has been modelled in a horizontal network of pores using microscopic rules developed from micromodel observations. These rules relate both to the pore occupancy pattern of the condensate liquid and to the effect of condensate accumulation in the tight comers of the pore elements. Concepts from percolation theory have been used along with observations of condensate formation and growth in etched physical micromodels, to determine the distribution of each phase in the pores. The relative permeabilities of gas and condensate in the presence of immobile connate water are then calculated using percolation theory. Resulting relative permeabilities are compared with those that are predicted for conventional drainage/imbibition (oil/water) processes in strongly water wet porous media. A Monte-Carlo model is also developed for comparison with the analytical model. A wide range of sensitivities of the relative permeabilities to a number of governing factors is presented.
Improved Calculation of Oil Production Response to Electrical Resistance Heating (ERH)
Authors: Baylor B. A. , Maggard J. B. , Wattenbarger R. A.
Published: December 2007

Electrical resistance heating (ERH) is a thermal stimulation technique in which electrical current passes through the formation. Field testing of this process is continuing. The current work uses results generated with reservoir simulation. Two models were used to describe ERH power dissipation (heating patterns): (1) a radial power model, and (2) an r-z power model.

Wattenbarger and McDougal1 developed a hand method for estimating the heated oil production rate under ERH stimulation. The first objective of the current paper is to present improvements to that hand method. The new hand method has the following advantages: (1) downhole electrical power is estimated, (2) well damage is accounted for, and (3) accuracy of heated production rates is improved. This new hand method can be quickly and easily used for screening potential ERH projects.

The second objective of this paper is to present results from the r-z power model. The r-z power model provides a more detailed description of in situ heating patterns, including areas of intense heating (hoc spots) which occur near the ends of the electrode. These hot spots may limit the amount of power that can be used in field installations.
The Fractal Nature of Viscous Fingering in Porous Media
Authors: Peters E. J. , Cavalero S. R.
Published: December 2007

An experimental study was undertaken to investigate the fractal nature of viscous fingering. Unstable first-contact miscible displacements were performed in a two-dimensional areal model. Images of the fingering patterns were captured and analyzed with a microcomputer-based imaging workstation. Results show that the areal sweep efficiency of the unstable displacements follows a fractal scaling law with a fractal dimension between 1.9 and 2.0. These results have potential application in the mathematical modelling of unstable EOR displacements and in the scaling of laboratory displacements to field conditions.
Managerial Goals and the Strategic Planning Process
Authors: Hailey W. A. , Barnes C. W. , Ryan E. J.
Published: December 2007

The authors examine the major decision process goals and constraints that impact the investment decisions within the oil and gas industry. The goals and constraints, reported by 124 executives during a mail survey of the 1987 Oil & Gas Journal 400, were arranged in hierarchies that vary in importance from high to low. The results can serve as planning factors for goal setting and as a basis for managing by objectives.
Scaled Miscible Floods in Layered Beadpacks Investigating Viscous Crossflow, the Effects of Gravity, and the Dynamics of Viscous Slug Breakdown
Authors: Sorbie K. S. , Sheb M. , Hosseini A. , Wat R. M. S.
Published: December 2007

In this paper, certain fluid recovery mechanisms that occur in stratified systems are analysed using experimental floods in layered beadpacks. In particular, the roles of viscous and gravitational crossflow are studied in viscous stable and viscous slug type displacement processes. The results from these floods are then scaled to field processes using a combination of scaling theory and numerical simulation. The effects of smaller sub-layer heterogeneity (within the larger scale layering) on the fluid recovery mechanisms are also examined in some detail. It is found that, although the levels of smaller scale heterogeneity studied in this work does not largely affect the total recovery profiles, they do have some impact on the detailed levels of fluid crossflow in the system. However, it is stressed that the level of heterogeneity description required for a given system must depend both on the type of system, the details of the fluid recovery mechanism operating in that reservoir and also actual balance of forces (viscous/gravity etc.) that exists in that participle situation.
Steam Injection in a Low-Permeability Reservoir Through a Horizontal Well in Lacq Superieur Field
Authors: Sahuquet B. C. , Spreux A. M. , Corre B. , Guittard M. P.
Published: December 2007

After several steamdrive patterns realized in the fractured zones of the Lacq Superieur field, a high rate steam injection in a very low permeability zone through a 350 m horizontal well is presently performed in this field.

Several tests showed that steam injection through a vertical well was not efficient due to the low permeability. The use of a horizontal steam injection well was, therefore, considered. The combination of steam and horizontal wells is in fact already a reality, in tar sands in Canada for example. The particularities of the Lacq Superieur operation are that the horizontal well is used to have a high steam injectivity in a low permeability carbonated facies and that the drain location is optimized to sweep a large area delimited by existing producing wells.

In this paper, reservoir engineering studies and the drilling of the well are presented.

Numerical simulations enabled us:

– to demonstrate the advantages of a horizontal injection well with high steam injection rate, – to show the efficiency of the dynamic and thermal mechanisms involved in such a configuration, – to optimize the location of the drain between two lines of existing vertical producers with respect to both energy savings and economical aspects.

From the drilling point of view, the geometrical data restricted the drilling domain inside a parallelepiped 9 meters wide by 5 meters high. In addition, a special type of completion was needed to be designed to allow injection in the 350 meters horizontal section only.

The horizontal well was drilled at the end of 1988 and steam injection started in April 1989. In accordance to the guidelines arrived at by numerical simulation, 600 tones per day of steam were injected, without problems.

After some changes in the initial conditions of operations, due to a too sharp increase of the flowing temperatures in some wells, the results up to date show clear and promising increases of the oil production in the neighbouring wells. This increase is somewhat earlier than what was predicted by computer simulations.
Interpretation of Production Data from Cyclic Steam Stimulation at Cold Lake
Authors: Vittoratos E.
Published: December 2007

A conceptual model of the flow regimes during Cyclic Steam Stimulation indicates that the traditional reservoir flow conceptualization of bitumen and water slipping past each other according to the relative permeability curves is to a large extent inapplicable. Emulsification of water into the bitumen swells the bitumen to occupy the whole pore space resulting in single phase flow during early cycles; thus the bitumen need not compete with free water for movement to the wellbore by the reservoir pressure gradients. Pure emulsion flow is characterized by rates changing smoothly with time. In a mature CSS well, however, free water accumulates in the flow streams, resulting in erratic production rates; this also occurs during displacement and during CSS production from vertical fractures.

As a first approximation, the wellbore production during single phase emulsion flow can be viewed as the mixture of two streams, one initially heated by convection (emulsified water content about 50%) and the other by conduction (water content about 15%). Conductive heating is dominant in early cycles in high bitumen saturation zones, implying low leak-off near the wellbore.
Scaled Model Studies and Numerical Simulation of Inert Gas Injection With Horizontal Wells
Authors: Meszaros G. , Chakma A. , Jha K. N. , Islam M. R.
Published: December 2007

Gas injection is one of the oldest enhanced oil recovery techniques used for recovering light oils. Recently, there has been renewed interest of gas injection in both light and heavy oil reservoirs. It has been pointed out that in order to apply gas injection, gravity stabilization is required to avoid early gas breakthrough. In absence of natural dip, such gravity stabilization may be achieved through horizontal wells placed on top of the reservoir while producing through another horizontal well placed at the bottom of the reservoir. The possibility of such recovery technique is investigated in this paper.

A series of partially scaled 2-dimensional model studies indicated that close to 70% oil in place may be recovered by using gas injection from the top of a heavy oil reservoir of oil viscosities of 1000 and 4000 mPa.s. Due to scaling requirements, the porous medium was replaced by glass beads of much higher absolute permeabilities. Two additional runs were also conducted with 750 mPa.s and 7500 mPa.s oils using high-pressure geometrically scaled physical models. These results indicated that it is much harder to maintain a stable gas front in a geometrically scaled high pressure 3-dimensional model than in a partially scaled 2-dimensional model. In order to maintain a stable gas front, one has to operate the injection/production wells at a very low rate. While this process is found to be rather slow, oil recovery was still found to be much higher than primary recovery if a stable gas front is maintained. If the frontal stability is lost, gas injection does not increase oil production beyond that of a primary depletion case. Several tests with variable gas composition were conducted. The presence of CO2 as opposed to nitrogen improved recovery to some extent.

Finally, numerical simulation of field cases is presented. The danger of invoking an unstable displacement front is demonstrated through numerical simulation.
Impact of Reservoir Heterogeneity on Initial Distributions of Hydrocarbons
Authors: Kocberber S. , Collins R. E.
Published: December 2007

The objective of this study was to demonstrate the effects of heterogeneity on the initial distributions of oil, water and gas in sandstone reservoirs and to provide a preliminary assessment of the effects of this structure on primary recovery. This is achieved by generating realistic capillary pressure and relative permeability relations parameterized by absolute permeability. These were then employed to compute initial fluid saturation distributions in composite blocks based on capillary-gravity equilibrium. The method is also illustrated in a real geological setting by employing the spatial distribution of permeability measured in an outcrop of Page Eolian sandstone. Severe discontinuities in saturation and effective permeability are demonstrated. These effects are most dramatic in water-wet systems; the higher capillary pressures in the low permeability laminae of a cross-bedded system cause high water retention, with correspondingly low hydrocarbon permeabilities, over the entire range of average saturations. Thus such "tight streaks" literally become permeability barriers to hydrocarbon flow and create very non-uniform reservoir drainage patterns; extensive pockets of trapped hydrocarbons result.
Pressure Desuperposition Technique for Improved Late-Time Transient Diagnosis
Authors: Ehlig-Economides C. A. , Ambrose R. W. , Joseph J. A.
Published: December 2007

Diagnosing the reservoir model from a field data set is one of the main challenges in well test analysis. The loglog pressure and pressure derivative plot is now firmly established as a primary diagnostic tool. This paper provides a new derivative formulation that enhances model diagnosis and addresses techniques for reducing noise in the derivative response.

Transients initiated by a sufficiently large increase in the surface rate closely represent the ideal reservoir response. However, when a transient is initiated by a decrease in surface rate, distortions due to superposition effects from previous surface flow rate changes are frequently present in the late-time derivative and can lead to incorrect characterization of reservoir boundaries.

To improve the late-time response, the pressure data are corrected for effects of a variable surface rate history before differentiation. The resultant desuperposition derivative avoids assuming a model for the reservoir behavior by using the late-time character of a representative transient. The desuperposition derivative appears as an equivalent drawdown (injection) response regardless of the nature of the perturbation that was actually used to induce the particular transient. This technique is particularly useful in reservoir and limits tests designed to delineate heterogeneities or boundaries; it also applies to multirate and multilayer tests.

Noise in the derivative can either mask or give a false impression of the true reservoir behavior. Overly smoothing noisy data may obscure the response and lead to erroneous model diagnosis. This study addresses logarithmic filtering and sampling techniques for reducing noise in the data.
New Solutions for Two-Well Systems with Applications to Interference Slug and Constant Rate Tests and Linear Boundary Detection
Authors: Grader A. S.
Published: December 2007

This paper presents new analytical solutions for two-well systems with storage and skin in both wells. The solutions are generated by the application of the addition theorem and the Laplace transformation. Previously presented research in this area is limited to one-dimensional radial flow. In contrast, the new solutions presented in this paper are true two-dimensional, and do not make use of the superposition principle for solving the basic cases. Hence, limitations stemming from the incorrect application of the superposition principle in the presence of finite sources are overcome. The paper describes the mathematical formulation for sixteen different configurations and some calculations showing the pressure transient response of both the active well and the interference well. The results of this study show that under certain conditions, storage in the observation well may have a significant effect on the analysis procedure. The presented solutions show that an impermeable linear boundary has a significant effect on the pressure response of a slug test. In addition, the traditional constant rate test with storage and skin can also be used for linear boundary detection. However, current techniques are limited in that the boundary effects must occur after the storage effects have ended. The new solutions presented here show the combined effects of an impermeable boundary and wellbore storage and skin.
Analysis of Well Tests Affected by a Pressure Trend
Authors: Cinco-Ley H. , Macias-Chapa L. , Samaniego-V F. , Morales-Gil C.
Published: December 2007

A new methodology is presented for the analysis of pressure data measured under the influence of a reservoir pressure trend. This technique allows interpretation of information from wells in developed reservoirs, because production or injection from wells adjacent to the test well generate pressure trends that affect the reservoir behavior. Such effect becomes dominant in reservoirs with high permeability, and in some cases, is of the same order of magnitude than the pressure changes originated in a well test.

The method presented in this work consists in the utilization of type curves that eliminate the effect of the pressure trend. For the cases of interference or pulse tests the type curve is based in a function defined as: pmdp(t)=abs ((pj-p(t))-tdp(t)/dt) and the match is performed in a Log pmdp(t) vs Log t graph. For the pressure build-up case the match function is defined as pmdp(∆t)=t{ pj-pws -tp'ws }/24Q, where Q is the cumulative production for the test. The application of the above procedures is illustrated through field examples of Abkatun and Midale reservoirs.
A Complete Set of Laplace Transforms for Finite-Conductivity Vertical Fractures Under Bilinear and Trilinear Flows
Authors: Azari M. , Wooden W. O. , Coble L. E
Published: December 2007

Analytic solutions for finite-conductive vertical fractured reservoirs are developed based on bilinear1,2 and trilinear3 fracture flow models for constant-pressure and constant-rate cases with and without boundaries. These solutions include effects of linear skin on the fracture, fracture conductivity, fracture to formation height ratio, wellbore and fracture storage, fracture to formation hydraulic diffusivity ratio, and wellbore phase segregation.

A simple method for solving these calculations is used to extend the transient fracture solutions to pseudoradial flow regime for various fracture parameters. Characteristic curves relating the effective wellbore radius for different fracture conductivities, skin and wellbore storage values are presented to facilitate the transition to the pseudoradial solutions.

The provided type curves identify fracture linear, storage linear, bilinear, formation linear, and pseudoradial flow regimes. Example problems are analyzed using type curve methods, and parameters are optimized with a Levenberg-Marquardt4 regression technique.
Acquisition and Analysis of Sonic Waveforms From a Borehole Monopole and Dipole Source for the Determination of Compressional and Shear Speeds and Their Relation to Rock Mechanical Properties and Surface Seismic Data
Authors: Harrison A. R. , Randall C. J. , Aron J. B. , Morris C. F. , Wignall A. H. , Dworak R. A. , Rutledge L. L. , Perkins J. L.
Published: December 2007

Classical sonic logging employs the acquisition and analysis of data with a simple monopole source. For this type of source, physics limits shear speed determination to speeds faster than the acoustic velocity of the borehole fluid. A dipole source excites the borehole flexural mode, providing a means to determine shear speed without this limitation. Propagation models and waveforms from computer simulations of hard and soft formations with both monopole and dipole sources are presented. These simulations are then compared to laboratory scale model data. Real-world borehole data acquired with both monopole and dipole sources, along with the instrumentation employed to acquire the data, are described. In particular, a combined monopole and dipole logging instrument with a high fidelity monopole and dipole receiver array is discussed. A processing algorithm for extracting compressional, shear and Stoneley speeds from monopole and dipole full waveform data is presented. Log examples are presented for hard, soft and extremely soft formations from both monopole and dipole sources. Application of log data to evaluation of rock mechanical properties, such as Poisson's ratio, fracture evaluation, and correlation to compressional and shear seismic data, is also discussed.
A New and Innovative Technology for Cement Evaluation
Authors: Bigelow E. L. , Domangue E. J. , Lester R. A.
Published: December 2007

The Segmented Bond Tool is a new, innovative acoustic logging device that utilizes six pads and twelve high-frequency, steered transducers to accurately evaluate cement integrity both longitudinally and radially around the entire casing periphery. Two comprehensive presentations are available, both of which are easily interpreted. Several examples from commercial and test wells emphasize the versatility of this new high-tech tool design.
The Effect of Bimodal Pore Size Distribution on Electrical Properties of Some Middle Eastern Limestones
Authors: Dixon J. R. , Marek B. F.
Published: December 2007

Laboratory investigations into the causes of anomalously low electrical resistivity of drill core Samples from two Middle Eastern carbonate reservoirs revealed bimodal pore size distributions. The rocks contain abundant interparticle porosity, but saturation exponents (Archie relation) are low (median=1.45). Scanning electron microscopy and high-pressure mercury porosimetry indicate that a network of interconnected micropores is the most likely explanation of the low resistivity behavior.
Heterogeneity in a Complex Turbiditic Reservoir: Stochastic Modelling of Facies and Petrophysical Variability
Authors: Alabert F. G. , Massonnat G. J.
Published: December 2007

The paper presents an application of recently developped geostatistical conditional simulation techniques to the modelling of heterogeneity in a complex turbiditic reservoir. Heterogeneity is mainly controlled by the distribution of sandstones embedded in laminated facies. Channels and lobes account for most of the production. Their frequencies and geometries are critical factors that affect reservoir connectivity, hence oil recovery. The combined used of flexible stochastic techniques allows generating realistic 3D models of this complex architecture. The modelling strategy is multi-steps, with first a geologically constrained generation of facies distributions, and second, simulations of permeability variations within the previously generated facies distributions.
Pressure Transient Analysis of the JX-2 Horizontal Well, Prudhoe Bay, Alaska
Authors: Rosenzweig J. J. , Korpics D. C. , Crawford G. E.
Published: December 2007

Buildup analyses of the JX-2 horizontal well, Prudhoe Bay, Alaska, were carried out to determine the skin factor, vertical, and horizontal permeabilities. The analysis approach, was to attempt to match analytical and numerical simulations to the data on the Log-Log Derivative plot. Analytical simulations failed to match the data while numerical simulations incorporating the gas cap were able to match the data well. More than one numerical match was found possible even for widely different formation parameters. The non-uniqueness of match is believed to be a result of insufficient buildup duration.

Analytical and numerical parametric simulations were carried out to improve the understanding of the range of possible pressure transient responses from JX-2. Conditions under which non-unique interpretations can occur were identified. A comparison of the pressure transient response with and without the gas cap showed that gas cap effects exert a major influence during the Pseudo-Radial flow period. Additionally, gas cap influence cannot be properly modelled by a constant pressure boundary. Thus, multiphase numerical simulations are necessary for an accurate interpretation.
Advances in Slug Flow Characterization for Horizontal and Slightly Inclined Pipelines
Authors: Scott S. L. , Kouba G. E.
Published: December 2007

Current methods for characterizing slug flow behavior are examined in light of experience with their use in multiphase pipeline design. Isograms of slug flow properties, displayed on a flow pattern map, are used to examine slug flow characteristics and identify conditions under which current prediction methods perform well. Using this technique, the equilibrium film simplification is shown to not be justified for a large portion of the slug flow region. Slug length isograms on a flow pattern map are shown to be particularly useful for visualizing slug length behavior. New methods are developed for predicting the existence of slug flow, modeling slug length behavior in inclined flowlines, and for predicting pigged slug length under slug flow conditions. Methodology is developed to determine slug flow characteristics and is applied to an example pipeline connecting the Eldfisk and Ekofisk fields in the Norwegian North Sea.