bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Chrome-Free Lignosulfonate Thinner: Performance Without Environmental Concerns
Authors: Park L. S.
Published: December 2007

Chrome-free lignosulfonates are increasingly used in aqueous drilling fluids because of potential environmental concerns associated with the chromium counterparts. A basic design study of a chrome-free lignosulfonate showed three major reaction parameters affecting its performance: type and concentration of complexed metal ion, oxidation level under optimal pH, and lignosulfonate raw liquor. A new chrome-free lignosulfonate formulation based on titanium metal ion was developed and its plant scale-up was conducted. Testing of the new titanium-complexed lignosulfonate was found to give improved rheological control vs. other available chrome-free lignosulfonates in various water-based drilling fluid applications.
Optimization of Offshore Field Development to Minimize Investment
Authors: Grimmett T. T. , Startzman R. A.
Published: December 2007

Offshore oil and gas development is identified with high investment. Considerable incentive therefore exists to reduce investment and to improve field profitability. A computational method has been developed to optimize field development and to minimize investment.

Investment can be reduced through an optimal choice and arrangement of production facilities. The selection, size, and location of major facilities—such as platforms, templates, or subsea manifolds—heavily affect capital investment. The allocation of field wells to these facilities affects drilling and completion costs. An extremely large number of feasible development options exist that may result in a wide range of economic outcomes. Choosing the option that minimizes investment can be a major computational problem.

The solution of extremely large economic problems of this nature has not been reported previously. An integer mathematical programming computational tool, using a method called "zero-one implicit enumeration," was developed for modeling and solving this problem. This technique allows for efficient probletn solution on a computer.

A model of an example field development was formulated. This model contains a mathematical function representing the investment to be minimized and includes design restrictions inherent to the development project. The model contained nearly 10190 combinations of development options. The application of a branch-and-bound algorithm allowed selection of an optimum development in a relatively short time on a computer.
A Generalized Compositional Model for Naturally Fractured Reservoirs
Authors: Peng Chungshlang P. , Yanosik John L. , Stephenson Robert E.
Published: December 2007

This paper presents the formulation of a generalized dual-porosity compositional reservoir model. The model uses the implicit-pressure, explicit-saturation (IMPES) method, with semi-implicit treatment of wells, and the Newton-Raphson iteration method to solve the dual-porosity flow equations. The model was used to study the depletion performance of dual-porosity volatile-oil and gas-condensate reservoirs.
Use of Tracers To investigate Drilling-Fluid invasion and Oil Flushing During Coring
Authors: Brown A. , Marriott F. T.
Published: December 2007

This work develops a method in which chemical tracers in the drilling fluid help determine mud filtrate invasion and the degree of oil flushing during coring of steamed and unsteamed heavy-oil formations. Salts of iodide and bromide were added to the drilling fluid while Well T03 was cored through the Lombardi and Aurignac zones at San Ardo field in California. Vertical core plugs, taken from the periphery to the center of the retrieved whole core, were analyzed for tracer concentration.

Tracer analyses indicated minimal filtrate invasion in the not-yet-steamflooded Lombardi zone and complete filtrate invasion in the steamflooded Aurignac zone. Tracer and oil saturation analyses showed the Lombardi zone to be uniform from top to bottom with an average oil saturation of 42.5% and an average porosity of 31.1%. interpretation of tracer and oil saturation data permitted the construction of a layered model for the Aurignac zone. The layers ranged from an average oil saturation of 8% in the steamflooded layer to 37% in the bottom layer. The data showed that significant oil flushing (6%) occurred only in cores taken from the hot-waterflooded layer just below the steam zone.

Vertical core-plug porosities and saturations, as determined by a unique calculating scheme, were compared with conventional and Elkins-corrected values. The comparison indicated that misapplication of the Elkins method in high-temperature formations may result in significant errors.
Electrical Savings in Oil Production
Authors: Johnson J. E.
Published: December 2007

Many oil-production operations do not use electricity efficiently. Recommended models for improving electrical efficiency and reducing electric bills are (1) to install pumpoff controllers and timers, (2) to modify pumping-unit stroke length and speed, (3) to use multimode motors in low mode, (4) to use cog-type belts, (5) to improve power factor with capacitors, and (6) to use electric-rate options.
Horizontal-Well Pressure Analysis
Authors: Ozkan Erdal , Raghavan Rajagopal , Joshl Sadanand D.
Published: December 2007

This paper presents an analysis of the pressure-transient behavior of a horizontal well or a drainhole. The performances of horizontal wells and fully penetrating vertical fractures are compared. Dimensionless wellbore pressures are computed for two classic boundary conditions: infinite conductivity and uniform flux. Results are presented as pseudoskin factors and as type curves. In addition to conventional pressure-vs.-time type curves, derivative type curves from pressure/time predictions are presented. The derivative approach we discuss is applicable to a broader range of problems than that considered here.

Computations suggest that horizontal-well productivity is governed by two parameters: (1) the dimensionless well length, LD[LD=L/(2h)k2/k], and (2) the dimensionless well radius, rwD (the ratio of well radius to well half-length if the formation is assumed to be isotropic). Results indicate that horizontal-well productivity (infinite-conductivity idealization) is almost identical to that of a fully penetrating vertical fracture of infinite conductivity if LD >4.0. This result shows that horizontal wells may perform better than vertically fractured wells if nonideal aspects associated with vertically fractured wells, such as limited conductivity or height, are taken into account.

Results have been obtained for the range 0.1≤LD≤100 and for the range 10−4≤rwD ≤10−2; these ranges should encompass expected values of horizontal-well length, reservoir height, and the ratio of vertical and horizontal permeability. Pressure responses and pseudoskin factors are calculated for four different well locations within the productive interval. The pseudoskin factors are insensitive to well location.
The Performance of Perforated Completions in Gas Reservoirs
Authors: Ichara Mark J.
Published: December 2007

A finite-element program was used to study the influence of shot density, perforation length, phasing angle, formation permeability, formation anisotropy, and turbulence factor on the performance of perforated completions in gas reservoirs. The results indicate that when permeability is low (< 10 md), turbulence effects are negligible, and perforation length and phasing angle affect productivity ratio. In anisotropic formations, high shot density (≥ 12 shots/ft [39 shots/m]) with deep penetration (≤ 15 in. [38 cm]) is required for the well to perform better than an openhole completion. Turbulence effects can cause up to 75% loss in production in high-permeability formations. The nomograph presented can be used to predict productivity ratios and skin factors in gas reservoirs.
Progress in Developing Commercial Fuel Cells
Authors: Fleming D.K.
Published: December 2007

The fuel cell concept is being developed for the economic production of electricity. The 6.5:1 cost differential in favor of residentially purchased fossil fuels over electricity provides the impetus for this work. This article surveys the current status of research and development on the many types of fuel cells and includes an extensive reference list.

Introduction

A major benefit of the current space exploration program has been the "fall-out" of technical advancements in many fields, which includes fuel cell research and development. Because space officials have determined that fuel cells in the power range of 100 w to 25 kw are the most economic power sources for space missions lasting from 1 day to several weeks, they have spent over $100 million for research in fuel cell technology. One result of this research is that a commercially economic fuel cell may soon be available.

What Is a Fuel Cell?

The Gemini flights have made most people aware that fuel cells exist, but they know little else about them. The very name fuel cell is a poor choice since it is not very descriptive of the use or operation of the device. In fact, the same term is used to describe a better gasoline tank on Indianapolis race cars, and here the name fits. Considering the operation of the device, a better name for it would be a "continuous battery". The National Electrical Manufacturers Assn. defines a fuel cell as an "electrochemical cell which can continuously change the chemical energy of a fuel and an oxidant to electrical energy by an isothermal process involving an essentially invariant electrode-electrolyte system." This NEMA definition describes a continuous battery that does not run down or require recharging and that will continue to operate as long as fuel and oxidant are fed to it. Like all batteries, fuel cells convert the chemical energy of the reaction directly to electrical energy without the intervening steps of heat and mechanical energies. Because the conversion of heat is not required, the fuel cell is not limited by the Carnot efficiency. The theoretically high efficiency of a fuel cell is possible because the reaction is nearly reversible. The fuel cell, which reacts hydrogen and oxygen w make water and electricity, is exactly the reverse of the electrolysis of water with electricity to make hydrogen and oxygen. The fuel cell has been described as a continuous battery. Fig. I compares the operation of a fuel cell to a lead-acid storage battery. Both devices consist of an anode (negative terminal) and a cathode (positive terminal). Both batteries use an ion-conducting electrolyte. The method of generating electricity is the same in both-the galvanic oxidation-reduction reaction. in the lead-acid battery, metallic lead is converted to lead sulfate at the anode, and electrons go out the negative terminal.

JPT

P. 749ˆ
Further Discussion of Application of Oil Muds
Authors: Benning M. J.
Published: December 2007

After reading Bloemendal's "Discussion of Application of Oil Muds" (Oct. 1986 SPEDE, Page 395), I felt compelled to reply. I have 6 years of experience with Dresser, Magcobar in various capacities, including mud engineer, instructor in the in-house schools, and finally technical service engineer. I was first based in south Texas and later in Houston, where I spent time in the field dealing with oil-based muds in Alaska, Wyoming, North Dakota, California, Texas, and Louisiana, both onshore and offshore. I will address Bloemendal's objections in the order in which they occurred.

Shortly after the higher-fluid-loss oil muds came into use, I put together a study comparing rates of penetration (ROP's) between oil-based and conventional (usually chrome lignosulfonate) muds in south Texas. I chose wells drilled in the same area, at the same depths, and as much as possible, with the same bits. None of the wells used a polycrystalline bit. Without a doubt, the oil-based muds outperformed the water-based fluids. Bloemendal attributes the increased penetration to higher API-FL, lower effective bottomhole density, better lubricity, and more favorable rheology. Undoubtedly, he is correct in his choice of possible reasons for the increased penetration. But why question the increased ROP with oil-based muds because of these factors? They are inherent in the oil-based system, and all these attributes are used as selling points for oil-based muds. That they are simply mechanical factors in no way negates their importance.

Bloemendal mentions the possibility of an oil-based mud flipping under certain circumstances. Flipping is the sudden change from a water-in-oil emulsion to an oil-in-water emulsion. He neglects to mention that these circumstances are extremely rare and usually avoidable. In my 6 years dealing with muds, I have seen a few in bad condition, but I have yet to see one flip.
On the Modeling of Vertical Permeability Barriers in Single-Well Simulation Models
Authors: Haldorsen Helge H.
Published: December 2007

This paper presents stochastic descriptive schemes for explicit and implicit modeling of vertical permeability barriers in single-well simulation studies. The drainage volume of the well to be simulated is first partitioned into two regions: one explicit region ("explicit" because actual barriers—e.g., shales of various sizes—are placed within the grid) and one implicit region ("implicit" because the effects of the discontinuous shales are averaged into an effective vertical permeability). Second, the shales are converted into vertical transmissibility modifiers and included in the data-input stream, along with the effective vertical permeabilities calculated for the implicit regions.

The methodology developed is illustrated by application to a North Sea reservoir with a thin oil column sandwiched between a gas cap and an active aquifer. In this reservoir, trustworthy predictions of oil, gas, and water production rates through time are of fundamental importance. In fact, the field-development decision may be swayed one way or another, depending on how long the gas and water production may be suppressed (aided by shales) for a reasonably high (and sustainable) oil-production rate.
The Main Area Claymore Reservoir: A Review of Geology and Reservoir Management
Authors: Chen H. K. , Robinson T. , Harker S. D. , Maher C. E.
Published: December 2007

The Main Area Claymore reservoir (MACR) is the major reservoir of the Claymore field, located 110 miles [177 km] northeast of Aberdeen in U.K. Block 14/19, offshore North Sea. An integrated team effort by geologists, geophysicists, and engineers has led to an increase in recoverable oil for the MACR. Concurrently, the MACR production increased from 47 to 57 MSTB/D [7472 to 9062 stock-tank m3/d] from mid-1984 to the end of 1986. The MACR is of Late Jurassic Age. Fine- to coarse-grained sandstones of the Sgiath and Piper formations are succeeded by the very-fine- to medium-grained sandstones of the Claymore sandstone member (CSM) of the Kimmeridge clay formation. The CSM constitutes the bulk of the MACR and is divided into two informal reservoir units: the low gamma ray sands (LGRS) and the high gamma ray sands (HGRS).

The principal early field problems were lack of sufficient pressure support, uneven water advancement in both the horizontal and vertical directions, and a large pressure gradient across the reservoir. Thus, more offtake and selective injection points were required to improve oil recovery. Growth of geological and engineering knowledge of the MACR has resulted from infill drilling and the integration of repeat formation tester (RFT) pressures, flowmeters, well logs, detailed core studies, and three-dimensional (3D) seismic. Increased current oil production and recoverable reserves are the consequences of this work.

To improve oil recovery, a 10-slot subsea template for water injection was installed in Summer 1985. Three subsea water injectors have been drilled from this template and five platform wells redrilled as producers to downdip areas of the MACR. The recent drilling program owes its success to the combined efforts of a multidisciplinary team, which resulted in the optimum placement of wells and the adoption of selective completion to optimize areal and vertical sweep efficiencies.
Some Theoretical Results Useful in Analyzing Well Performance Under Solution-Gas Drive
Authors: Camacho-V. R. G. , Raghavan Rajagopal
Published: December 2007

This paper presents results pertinent to the analysis of well performance in solution-gas-drive systems. The characteristics of wells producing solution-gas-drive systems are documented. Procedures to correlate multiphase flow solutions with single-phase flow systems for both transient and boundary-dominated flows are presented.
Subsea Adjustable Choke Valves: A Focus on a Critical Component
Authors: Cyvas M. K.
Published: December 2007

With emphasis on deepwater wells and marginal offshore fields growing, the search for reliable subsea production systems has become a high priority. A reliable subsea adjustable choke is essential to the realization of such a system, and recent advances are producing the degree of reliability required. Technological developments have been primarily in (1) trim material (including polycrystalline diamond), (2) trim configuration, (3) computer programs for trim sizing, (4) component materials, and (5) diver/remote-operated-vehicle (ROV) interfaces. These five facets are overviewed and progress to date is reported. A 15- to 20-year service life for adjustable subsea chokes is now a reality.

Another factor vital to efficient use of these technological developments is to involve the choke manufacturer and ROV/diver personnel in initial system conceptualization. In this manner, maximum benefit can be derived from the latest technology.

Major areas of development still required and under way are listed, and the paper closes with a tabulation of successful subsea choke installations in recent years.
Failures of Nickel/Copper Bolts in Subsea Application
Authors: Wolfe L. H. , Joosten M. W.
Published: December 2007

Slow-strain-rate tests in ASTM seawater using specimens prepared from a failed nickel/copper-alloy bolt have shown that precipitation-hardened UNS N05500 (Monel K-500®) is embrittled by cathodic protection with sacrificial aluminum anodes. Some loss of ductility also occurred when annealed UNS N05500 was coupled to aluminum anodes and when the hardened alloy was coupled to steel. Brittle fractures produced by slow-strain-rate tests were intergranular and were very similar in appearance to the field fractures. While the slow-strain-rate tests were conducted on an alloy from only one source, there is no reason to assume that UNS N05500 alloy from other sources would resist hydrogen embrittlement from standard cathodic protecti.on systems.
Relationship Between Cement Slurry Composition, Mechanical Properties, and Cement-Bond-Log Output
Authors: Jutten J. J. , Guillot D. , Parcevaux P. A.
Published: December 2007

This paper describes and quantifies the influence of cement slurry composition on the mechanical properties of the hardened cement and on the cement bond log (CBL). Laboratory experiments were performed on more than 20 different cement slurry formulations with densities ranging from 1200 to 2280 kg/m3 [10 to 19 lbm/gal]. Results show that (1) CBL attenuation rate is directly related to the acoustic impedance of the cement; (2) particulate extenders like silica microspheres provide, for a given slurry density, higher acoustic impedance and CBL attenuation rate than chemical extenders like soluble silicates; (3) latex in the cement does not influence the CBL; (4) the relationship between compressive strength and velocity of compressional waves, verified for most slurries, is not valid for salt-containing slurries; and (5) a single relationship exists between Young's modulus and Poisson's ratio.
Capacitance Effects in Porous Media
Authors: Jasti Jay K. , Vaidya Ravimadhav N. , Fogler H. Scott
Published: December 2007

The velocity dependence of parameters in the Coats-Smith model for tracer dispersion and tailing in porous media was investigated. An axisymmetric pore with a step change in cross-sectional area was used as a model system to determine whether the stagnant zone resulting from variations in flow cross sections contributes to the observed capacitance (i.e., tailing) at the pore level. Numerical simulations show that eddies with recirculation flow are formed in the pockets as a result of flow separation. The tracer transport between the eddies in the dead zones and the main channel was found to be diffusion-limited. The simulations reveal that in the Stokes flow regime, the mass-transfer coefficient between the two regions is independent of the interstitial velocity, in contradiction to earlier theories.

Coreflood experiments were performed with radioactive tracers to verify the hypothesis that the capacitance effects are not the result of a change in flowing fraction. The experimental results confirm that tracer tailing is a function of the ratio of the molecular diffusivity to the flow rate. in light of these findings, we investigated the validity of the Coats-Smith model to predict dispersion and tailing in a porous medium. Our studies show that the Coats-Smith model may be used; however, certain restrictions, described in this paper, apply to the procedure for estimation of parameters.
Evaluation of Key Reservoir Drive Mechanisms in the Early Cycles of Steam Stimulation at Cold Lake
Authors: Denbina E. S. , Boberg T. C. , Rotter M. B.
Published: December 2007

A history-matched, 2D, single-well numerical model was used to evaluate the contributions of four key drive mechanisms to early cyclic-steam-stimulation (CSS) oil recovery at Cold Lake, Alta. Formation compaction was found to be by far the dominant producing mechanism. Solution-gas drive was the most important of the remaining mechanisms. Fluid expansion had a relatively minor role. Gravity drainage accounted for little of the oil produced in the first two cycles, but increased in importance in subsequent cycles.
Pressure-Transient Testing of Water-Injection Wells
Authors: Abbaszadeh Maghsood , Kamal Medhat
Published: December 2007

This paper presents an interpretation method for injectivity and falloff testing in a single-layer oil reservoir that is under waterflooding and develops analytical solutions for pressure and saturation distributions. The effects of relative permeability, wellbore storage, and skin are considered in these solutions. New field-dependent type curves for falloff tests, which exhibit features that do not appear in the currently available single-phase-flow type curves, are also presented. Matching of field data on these curves yields fluid mobilities in various banks, skin, formation permeability, and flood-front location. Field data interpretation with the new method shows that falloff tests can be used to monitor the progress of waterfloods.
Performance of Wells in Solution-Gas-Drive Reservoirs
Authors: Camacho-V. R. G. , Raghavan R.
Published: December 2007

We examine buildup responses in solution-gas-drive reservoirs. The development presented here parallels the development for single-phase liquid flow. Analogs from pseudopressures and time transformations are presented and gas-drive solutions are correlated with appropriate liquid-flow solutions. The influence of the skin region is documented. The basis for the success of the producing GOR method to compute the saturation distribution at shut-in is presented. The consequences of using the Perrine-Martin analog to analyze buildup data are discussed.
Frequency Effects in Acoustic Logging
Authors: Medlin W. L.
Published: December 2007

Variable-frequency acoustic logs were obtained in soft and hard formations by use of tone-burst driving methods with broad-band acoustic sources. Two underwater sources–a bender bar and a flexural disk device–were used as logging-tool transmitters. By driving the source with three-cycle tone bursts, we produced short-duration, monotone radiation in the wellbore at each resonance frequency. In this way, logs were run at each of many driving frequencies covering the acoustic band.

Our experiments dealt with the frequency effects of mode excitation (cutoff frequencies) and the frequency content of received waves. Fourier transforms of the waveforms were used to investigate the frequency content of received waves.
Effects of Steam/Liquid Counterflow on Pressure-Transient Data From Two-Phase Geothermal Reservoirs
Authors: Bodvarsson Gudmundur S. , Cox B. Lea , Ripperda M.
Published: December 2007

Numerical studies were performed to investigate the effects of localized feed zones on the pressure transients in two-phase reservoirs. Gravity effects were shown to affect the pressure transients significantly because of the large difference in the densities of liquid water and vapor. Production from such systems enhances steam/liquid-water counterflow and expands the vapor-dominated zone at the top of the reservoir. Subcooled liquid regions develop in the center of the reservoir as a result of gravity drainage of cooler liquid water. The vapor zone acts as a constant-pressure boundary and helps to stabilize the pressure decline in the system. The pressure transients at observation wells were shown to depend greatly on the location (depth) of the major feed zone; if this is not accounted for, large errors in deduced reservoir properties will result. At shallow observation points, pressures may actually increase as a result of enhanced steam upflow caused by production at a deep feed zone.
Simulation of Downhole Heater Phenomena in the Production of Wellbore Fluids
Authors: Sharma Yugdutt , Shoham Ovadia , Brill James P.
Published: December 2007

A model is presented for predicting the pressure and temperature profiles for gas/liquid flow in wellbores stimulated with downhole heaters. The solution algorithm consists of coupling the momentum- and energy-balance equations for the wellbore fluids with the transient behavior in the surrounding rock. The heater is treated as a source term in the energy-balance equation. The model is capable of predicting wellbore thermal effects, such as reduction of fluid viscosity and increase of free gas. It can be used to simulate temperature maintenance during well shut-in periods to prevent pour-point problems and paraffin or hydrate formation. An existing well with production problems related to thermal effects was simulated by the model. Results indicate that wellbore temperatures can be controlled by downhole heaters. Also, under certain conditions, an increase in production was predicted with such an application.
Expanding the Range for Predicting Critical Flow Rates of Gas Wells Producing from Normally Pressured Waterdrive Reservoirs
Authors: Upchurch Eric R.
Published: December 2007

The critical flow rate of a gas well is the minimum flow rate required to prevent accumulation of liquids in the tubing. Theoretical models currently available for estimating critical flow rates are restricted to wells with water/gas ratios less than 150 bbl/MMcf [0.84 × 10−3 m3/m3]. For wells producing at higher water/gas ratios from normally pressured waterdrive reservoirs, a method of estimating critical flow rates is derived through use of an empirical multiphase-flow correlation.
A Robust Prediction Method for Rapid Phase-Behavior Calculations
Authors: Varotsis N.
Published: December 2007

The success of phase-behavior calculations based on an equation of state (EOS) depends to a great extent on the quality of the selected initial estimates of the independent variables. Estimates considerably different from the final answer often lead to either trivial solutions or convergence problems.

The method presented in this paper consists of obtaining the maximum possible information concerning the vapor/liquid equilibrium of the mixture by directly solving the selected EOS before the start of the main iterative calculation. The information obtained, with minimal computational cost, is subsequently used to initiate a Newton-type iterative method that is stable and converges rapidly toward the solution when good estimates are provided.
Analysis of the Transient Production of a Thermally Stimulated Well
Authors: Bidner M. Susana , Kostiria Horacio M. , Vampa Victoria C.
Published: December 2007

This paper presents a simple mathematical model to predict the oil production rate from a cyclic-steam-stimulated well. The oil volume flowing from the cold zone is estimated by numerically solving the diffusivity equation governing the radial transient flow of a fluid with a small and constant compressibility for three outer boundary conditions—infinite medium, constant pressure, and no flow—corresponding to different reservoir types. At the interface between the cold and hot zones, pressure is calculated by means of the superposition principle. Numerical solutions give pressure distribution as a function of radius and time. They also allow assessment of the effects of transient flow and outer boundary conditions on oil production rate. The numerical response of a cycle of steam injection strongly depends on the outer boundary condition. Excellent agreement is found between model-calculated and observed field rates.
Gas Composition Shifts in Devonian Shales
Authors: Schettler P. D. , Parmely C. R.
Published: December 2007

Analysis of the gas composition of Devonian shale wells indicates that the composition of produced gas shifts during the production history of the well. Possible mechanisms to explain this behavior are examined in light of field and laboratory data. Application of diffusion theory is made to explain adsorption-like behavior exhibited by some shales.
Downhole Simulation Cell Shows Unexpected Effects of Shale Hydration on Borehole Wall
Authors: Simpson Jay P. , Dearing H. L. , Salisbury D. P.
Published: December 2007

Previous attempts to predict the effects of drilling fluids on borehole stability in shale have been unsatisfactory. This paper describes laboratory equipment capable of simulating downhole conditions to permit evaluation of drilling fluids by testing the alteration of natural shale specimens when drilled and exposed to drilling fluid under an annular flow regime for an extended period of time. The paper discusses ramifications of the shale alteration relative to such operational problems as torque, drag, and stuck pipe.
The Effect of Microscopic Heterogeneity on CO2-Foam Mobility: Part 1--Mechanistic Study
Authors: Huh D.G. , Cochrane T.D. , Kovarik F.S.
Published: December 2007

The mixing and flow behavior of a CO2/surfactant-solution/oil system in porous media depends on the pore structure. Two-dimensional (2D) flow-visualization experiments in several glass micromodels, each with a different length scale of heterogeneity, were performed at reservoir conditions. The mechanisms associated with gas permeability reduction were investigated in terms of microscopic heterogeneity, presence of oil phase, surfactant concentration, and flow rate in secondary and tertiary miscible CO2 floods. Results showed that foam can be generated by upstream and downstream snapoff. Fluid diversion was obtained not only by lamellae and foam, but also by multiple interfaces of CO2, surfactant solution, and oil. depending on the pore structure of the micromodel. The most important factors in the in-situ generation of foam, however, were the mixing of fluids and the aspect ratio of the pore structure.

Introduction

CO2 field projects have frequently experienced early gas breakthrough, and production will stop when an uneconomically high CO2/oil ratio is attained. Both high-pressure gas-foams and chemical gels are currently being considered for use as high-permeability-zone blocking agents--i.e., in profile modification--in many on-going CO2 flooding operations. This paper presents our preliminary investigation into the mechanisms responsible for CO2 fluid diversion, increased CO2 sweep efficiency, and the mobilization of bypassed oil when using high-pressure CO2-foam as a blocking agent. The capillary-tube model was used in one of the first attempts to study the generation and propagation Of a single lamella or bubble. Fried reported that in his glass-tube model, larger foam bubbles subdivided into smaller bubbles as they passed through pore constrictions. At the same time, some of the oil in the region invaded by the foam became emulsified, and the newly formed oil particles soon became immobile. He reported that this foam subdivision and emulsification could have been responsible for the resulting flow blockage.

JPT

P. 872^
Wettability: Fundamentals and Surface Forces
Authors: Hirasakl G. J.
Published: December 2007

The wetting of mineral surfaces by water and oil is described by models of surface forces that become important when two surfaces approach each other. Force components are electrostatic, van der Waals, and structural. The electrostatic force depends on brine pH and salinity, crude oil composition, and the mineral. The surface forces are expressed as a disjoining pressure isotherm, and its integral is the specific interaction potential isotherm. The specific interaction potential isotherm can be used to determine the stable and metastable film-thickness profiles at the three-phase contact region for a given capillary pressure and/or curvature of the substrate. This profile gives the contact angle.
An Analytical Solution for Wellbore Heat Transmission in Layered Formations
Authors: Wu Yu-Shu , Pruess Karsten
Published: December 2007

This paper presents a new analytical solution for wellbore heat transmission. Previous treatments of the wellbore heat-transfer problem are improved in several aspects: (1) nonhomogeneous formations are approximated as layered formations with different physical properties; (2) closed-form analytical solutions are obtained in both real and Laplace space; and (3) a more accurate formula is provided for the transient heat-conduction function, f(tD).
Pressure-Drawdown Test Analysis of a Gas Well—Application of New Correlations
Authors: Fligelman H. , Cinco-Ley H. , Ramey H. J. , Braester C. , Couri F.
Published: December 2007

A new method of drawdown-pressure test analysis is proposed that takes into consideration the non-Darcian flow as well as the skin and borehole-storage effects. Two new correlations obtained from numerically simulated drawdown tests are used and the method of application is illustrated. The drawdown-pressure results of a synthetic numerically simulated test are used to recalculate the a priori known reservoir skin and permeability. A comparison between the obtained and the "true" reservoir skin and permeability shows an excellent agreement when the proposed method is applied.

Drawdown-pressure analysis of the given examples with the conventional method shows errors > 5 % in the calculated permeability and > 50% in the calculated skin factor.
Optimizing Well Spacing and Hydraulic-Fracture Design for Economic Recovery of Coalbed Methane
Authors: Zuber Michael D. , Kuuskraa Velio A. , Sawyer Walter K.
Published: December 2007

Conventionally, proper well spacing and stimulation govern the economic attractiveness of producing natural gas from coalbeds. To provide an analytical foundation for this empirical evidence, reservoir simulation and economic analyses were conducted to gain insights into the optimum well spacing and hydraulic-fracturing treatments in typical "good" and "poor" geologic settings of the Oak Grove field in Alabama. We studied the economic benefit of gel-based fracturing treatments, the optimal well spacing for higher- and lower-permeability settings, and how to establish proper values for permeability and achievable hydraulic-fracture dimensions for optimal well spacing.
Results of a Field Test to Determine the Type and Orientation of a Hydraulically Induced Formation Fracture
Authors: Fraser C.D. , Pettitt B.E.
Published: December 2007

The planning phase of a program for expanding a shallow waterflood project was stalemated by lack of knowledge concerning the type and orientation of hydraulically induced formation fractures. Profitable development of the project is known to depend on successful fracture stimulation. To obtain in situ data about the induced fractures, a simple, downhole, impression sensing test was devised using an inflatable formation packer as the basic investigating element. A new well was hydraulically fractured, after which the formation packer, equipped with an especially sensitive rubber cover, was set in the pay interval. A perfect impression of the previously induced fracture was retained on the packer element. This impression showed that the fracture was vertical, oriented north 730 east, and present along the entire 9-ft section of impression rubber. Prior to the down-hole test, fracture orientation and type had been predicted based on published theories describing the relationship between tectonic stresses and artificial formation fracturing. The test data verify these predictions. As a sidelight, it is concluded that deep notches in the pay sand do not cause horizontal fractures in this area.

Introduction

The technical literature of recent years contains many papers which attempt to provide insight concerning the type, orientation and fluid- carrying ability of hydraulic fractures. Theoretical methods have been proposed with which the field engineer can make optimum use of artificial formation fracturing as a stimulation technique. The purpose of this paper is to describe an attempt to corroborate theoretical concepts so that combination waterflood-fracture stimulation program could he exploited to maximum advantage. The area involved is that bounded by Mobil Oil Co.'s Chalk Waterflood project which is located in the Howard Glasscock field of eastern Howard County, Tex. Production is from the 1,600-ft Queen sand of Permian age. This sand possesses an average porosity of 23 per cent, an average permeability of 57 md, an average water saturation of 35 per cent and an average gross thickness of 25 ft. The sand is very fine-grained and contains considerable amounts of gypsum, silt and clay. Geologically, the project is situated on the Eastern Platform of the Midland basin. Fig. 1 is a map showing the project area. The Chalk flood has been in operation since 1947; however, results were generally discouraging.

JPT

P. 463^
An Experimental Test of the Cutting and Rejoining Model for Representing Porous Bodies
Authors: Hancox N.L.
Published: December 2007

Previous researchers have used the cutting and rejoining model to represent a porous body when attempting to place Archie's law on a theoretical basis and calculate rock permeabilities (F = phi m, where F = formation factor, phi = porosity and m = a constant). In using the model, a porous solid is assumed to consist of sections with parallel sides containing straight, continuous pores of total porosity phi (pore to total volume or, for a homogeneous body, pore to total area). The joining of pores at an interface between two sections is assumed to be random which results in a common pore area phi. This reduced area phi is then taken as that area which limits electrical conduction or fluid flow in the body. Agreement between experimental results and results calculated using a model is not always good. Because of this, various modifications of the model are presented for instance, the random nature of the joining is questioned. Formation factor measurements on specially constructed porous specimens are described in this paper. It is concluded that the common pore area limits flow completely only if sections containing straight pores are very thin, and that, in most natural materials, the common pore area at an interface must be greater than that given by random joining. However, the model is still useful in permeability calculations, provided that the fractional area limiting flow is determined from formation factor measurements.

Introduction

Two important properties of porous media are permeability k, which describes the ease with which a fluid can flow through a porous medium, and formation factor F, defined as the ratio of the resistivity of a saturated specimen to the resistivity of the saturating liquid which describes the electrical properties of the saturated material. k is defined by Darcy's law,

(1)

where mu = liquid viscosity, q = flow rate, L = length of specimen, p = pressure across the specimen and Ae = the effective area over which flow occurs. F is given experimentally by Archie's law,(2)

where phi is porosity defined as the pore to total volume or, for a homogeneous body, the pore to total area; and m lies between 1.3 for loose sand and 2 for cemented sand. Consider a porous body of total cross-sectional area A and length L, saturated with a liquid of resistivity R and with an effective area for conduction of Ae. Then, from the definition of F given previously,

(3)

or, from Eqs. 2 and 3,

(4)

Thus, in any attempt to calculate k or F, some assumptions must be made concerning the pore structure of the body and a value derived for Ae.

To determine Ae, Childs and George and Wyllie and Gardner suggested an elementary statistical representation often referred to as the cutting and rejoining model of a porous body. The body is assumed to be composed of two or more parallel-sided sections of porosity phi, containing straight, continuous pores with a common pore area of phi at an interface between two sections. The value is given by a random joining of the pores in either section.
Deep-Set Subsurface Safety Valve Actuated by Jet-Pump Differential Pressure
Authors: Barnes John A. , Snlder Phil M. , Swafford Chuck V.
Published: December 2007

Offshore oil and gas production often requires placement of a subsurface safety valve (SSSV) in the tubing string to prevent uncontrolled flow from the well. In many wells, this requirement can preclude maximizing production through the use of high-capacity artificial-lift techniques, such as jet pumping. An innovative approach was developed and field-tested in the McArthur River field, Cook Inlet, AK, to overcome problems associated with incorporating SSSV's in jet-pump completions. This method provides surface control over the valve and does not restrict production rate. In this approach, an SSSSV was placed in the tubing string below a jet pump at 9, 800-ft [3000-m] true vertical depth (TVD) to satisfy safety requirements. The system design allows the SSSV to be controlled from the surface with no dependence on hydraulic control lines to surface. The system was later improved to allow the SSSV to be reverse-circulated from the well for repairs or remedial activities.
Marketing and Distribution of Helium
Authors: Troast David W.
Published: December 2007

Recently there have been many changes in the marketing and distribution of helium, one of the most versatile of industrial gases. New uses, equipment and systems, as well as a greater role for private enterprise, have been important factors in creating an annual $45 million market of 1 billion cu ft.

Introduction

Helium is a combination of unusual properties and characteristics that make it useful in a wide variety of applications. Notable for its extreme lightness, helium is nearly 10 times lighter than argon and about seven times lighter than air. The helium molecule is small and readily diffuses through even the smallest of openings. Helium is a good conductor of heat and sound. Other properties and characteristics include inertness, low solubility, low index of refraction, resistance to nuclear radiation and the lowest normal boiling point of all gases (Table 1).

While the product and its major sources have remained essentially the same for years, nearly everything else connected with helium has undergone recent changes.

Growth of Private Production and Distribution

A significant change in the helium industry has been development of a greater role for private enterprise in helium production and distribution. In cooperation with the Helium Activity of the U. S. Bureau of Mines, private enterprise now is engaged in producing crude helium for USBM's conservation storage program, as well as in producing pure liquid and gaseous helium for commercial sales. Private efforts also have created a new nationwide system for the distribution of large quantities of liquid helium.

Helium Demand Grows Rapidly

The over-all market for helium is growing steadily at a rate of about 15 percent annually, which is faster than the market for most gases and about on a par with nitrogen. Several factors provide the impetus for this growth. Helium is often the best and sometimes the only substance to fulfill requirements for many important applications associated with advanced technology and major governmental or commercial ventures. The most spectacular application, and the one most subject to fluctuation in the future, is the growth of the rocket and missile field that prompted creation of many new applications for helium in both federal programs and private industry.

Most advanced research and development work conducted by institutions and private industry in a wide variety of fields has some requirement for helium as a gas or liquid. One of the fastest growing areas is cryogenic research requiring liquid helium for low-temperature studies. Successful results of research and development in the past few years have created many new products and processes requiring helium.
Pressure-Transient Analysis for Horizontal Wells
Authors: Kuchuk Fikri J. , Goode Peter A. , Brice Bradley W. , Sherrard David W. , Thambynayagam R.K. Michael
Published: December 2007

In recent years, pressure-transient behavior of horizontalpressure-transient behavior of horizontal wells has received considerableattention because of the increase in horizontal drilling. This paper presentsan interpretation method for presents an interpretation method forhorizontal-well pressure-transient testing that is applied to a buildup testfrom a horizontal well in the Prudhoe Bay field. The complex flow Prudhoe Bayfield. The complex flow geometry associated with horizontal wells makeswell-test interpretation difficult. Unique determination of the systemparameters from pressure data with a short testing time (typical test times forvertical wells) and/or production time is not possible. We production time isnot possible. We must run drawdown and buildup tests and acquire the downholeflow rate with pressure to estimate the reservoir parameters accurately.

Introduction

Interpretation of well tests from horizontal wells is much more difficultthan interpretation of those from vertical wells because of a considerablewellbore storage effect, the 3D nature of the flow geometry and lack of radialsymmetry, and strong correlations between certain parameters. Also, zonalvariations of vertical permeability and shale distribution complicateinterpretation.

A well-defined flow period, comparable to that of the infinite-acting radialflow period (free from storage and boundary effects) period (free from storageand boundary effects) of a vertical well, is not apparent for horizontal wells, largely because most horizontal wells exhibit partial penetration effects evenwhen they are hilly perforated. Specific methods have been perforated. Specificmethods have been proposed to identify flow regimes and their proposed toidentify flow regimes and their durations under ideal conditions. AlthoughReiss and Sherrard et al. presented performance and production data fromperformance and production data from several horizontal wells and mentionedinterpretation of well-test data, they did not show how to extend theidentification and usage of flow regimes to the interpretation of realpressure-transient tests.

This paper presents a method for the interpretation of wells data fromhorizontal wells and analyses of pseudosynthetic and real well-test data.

Solutions With and Without Gas Cap or Aquifer

In a horizontal well, there is usually considerable wellbore volume (50 to100 bbl) below the measurement point, even if the downhole flow rate ismeasured or a downhole shut-in device is used. The storage effect with thisadditional volume typically lasts longer than that in a vertical well in thesame formation because the anisotropy reduces the effective permeability atearly times to root of kHkV.