bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Capillary Number on the Microstructure of Residual Oil in Strongly Water-Wet Sandstones
Authors: Chatzis I. , Kuntamukkula M. S. , Morrow N. R.
Published: December 2007

Changes that occur with increase in capillary number in the detailed structure of residual oil trapped in water-wet sandstone core samples have been investigated. The technique of using a non wetting phase that can be solidified and separated from the porous medium has been applied with styrene monomer as the nonwetting phase and 2% CaCl2 brine as the wetting phase. The size distributions of residual oil blobs, obtained under various flow conditions, were measured by both image analysis and Coulter counter techniques. Specific features of blob shapes and dimensions were checked by optical and electron microscopy. The changes in size distribution and shapes of blobs provide insight into the mechanisms of trapping and mobilization of residual oil.
Comparison of Hydraulic-Fracture Orientation Techniques
Authors: Lacy L. L.
Published: December 2007

Knowledge of the orientation of hydraulic fractures can be important in determining optimum well locations in recovery from tight gas sands, waterflooding, and EOR. The diagnostic technology used to determine fracture orientation in single wells has matured during the last few years so that reliable field-proven techniques exist. Five fracture-orientation techniques have been investigated extensively in multiple wells and in several fields in east Texas and Alaska for well depths up to 12,000 ft [3600 m]. The techniques reviewed include active fracture mapping with tiltmeter arrays and a triaxial borehole seismic (TABS) tool. The active fracturing techniques are compared with the predictive techniques of stress relief, thermal expansion, and sonic velocity measurements on oriented sandstone cores. Sufficient field tests have been performed to evaluate the reliability and accuracy of the data, and the theory by which the data are interpreted. All the field and laboratory techniques investigated proved to be reliable and provided good agreement between four or five independent tests in the same wells and zones. Accuracy of the various field tests varied from 5 to 20° [0.09 to 0.35 rad], and methods for improving this accuracy are reviewed.
A Study of the Behavior of Bounded Reservoirs Composed of Stratified Layers
Authors: Lefkovits H.C. , Hazebroek P. , Allen E.E. , Matthews C.S.
Published: December 2007

A rigorous study was made of the behavior of reservoirs composed of horizontal layers, unconnected except at the well and filled with a compressible fluid. The report is presented in two parts. Part I deals with the practical implications of the results obtained; Part II contains the mathematical derivation of the solution. The main portion of Part I is concerned with application of the results to reservoirs composed of two layers. Relative rates of depletion of the layers are studied, and it is shown that differential depletion between layers exists in the transient stage of the reservoir, which generally is of an order of magnitude longer than the transient stage in a single-layer reservoir. In the transient stage, the more permeable layer is depleted faster than the less permeable. However, the reservoir approaches a steady-state situation where both layers contribute equally to production. Theoretical build-up curves from such reservoirs are presented, and the influence of a skin effect and flow into casing and tubing are also evaluated. The build-up curves are predicted to have, first, the familiar logarithmic straight-line section and, subsequently, a rising and flattened section. The results found are compared with an extension of an approximate theory, and it is found that this simplified theory is applicable over most of the life of the reservoir. Extensions to reservoirs containing more than two layers are indicated, and examples of the performance and build-up curves for three-layered reservoirs are presented. The theoretical results on build-up curves were applied to field examples of such reservoirs, and satisfactory results were obtained. From the build-up curve, the permeability-thickness product, the wellbore damage and the static pressure are obtained. However, it apparently is not possible to determine the properties of the individual layers from the combined build-up curve.
A New Approach to the Development of Fire-Resistant Wellhead Equipment
Authors: Karr Michael A.
Published: December 2007

A testing procedure has been developed that considers the response of the total wellhead system (vs. individual seal components) to fire conditions. This paper details the mechanics and results of this program for tests to 2,000°F [1100°C] flame at pressures of 3,750 psi [25.9 MPa]. Significant behavioral differences were observed during the development and testing of specially designed fixtures incorporating metal-to-metal seals for the tubing head, tubing hanger, and lower master valve. As a result, more stringent design criteria evolved for the sealing technology and structural integrity of the wellhead, because it became apparent that solving sealing and material problems in one sealing area or component invariably created new problems in other locations.

Highest priority was given to seal development because it seemed to be the most critical area of concern. It was concluded that meaningful tests could be conducted only when several related seals were allowed to interact in response to fire conditions. Tubing, annulus, and connector seals were considered appropriate seals for wellheads.
Dynamics of Subcritical CO2/Brine Floods for Heavy-Oil Recovery
Authors: Rojas G. A. , Ali S. M. Farouq
Published: December 2007

Immiscible CO2 flooding is an important, field-proven heavy-oil recovery method, particularly suited for thin, marginal, or otherwise poor heavy-oil reservoirs, where thermal recovery processes are likely to be uneconomical. This paper describes the dynamics of this recovery technique on the basis of experiments conducted in a scaled model. The experiments represent a medium-heavy oil (1032 mPa·s at 23°C [1,032 cp at 73°F]) occurring in a shallow, thin sand. CO2 was injected together with brine at subcritical conditions (5.5 MPa and 21 to 23°C [800 psi and 70 to 73°F]).

The CO2 and brine superficial velocities were varied from 0.18 to 2.9 m/d [0.6 to 9.5 ft/D]. This broad range of velocities permitted the study of the effect of the viscous, diffusive, and gravitational forces on the CO2 slug (20% HCPV) process for heavy-oil recovery. It was found that viscous forces completely dominated CO2 injection. Also, the mass transfer between CO2 and oil had a stabilizing effect on the brine injection. Although the molecular diffusion of CO2 in oil was high, it was not high enough to mobilize appreciable amounts of oil from uninvaded zones.

The scaled experiment results showed that oil recoveries at CO2 and brine breakthroughs were rate-dependent. While recovery at CO2 breakthrough decreased with increasing rate, recovery at brine breakthrough increased. Reduction of interfacial tension (IFT) between brine and oil, leading to the formation of brine-in-oil emulsions, was found to be an additional effective mechanism of heavy-oil recovery by CO2/brine injection.
Technical Advancements in Submersible-Pump Power Cable for Harsh Environments
Authors: Guzy R. , Vandevier J.
Published: December 2007

In artificial-lift systems, such as electrical submersible pumps, the power cable provides the link between the surface equipment and the pumping unit. New cable designs are constantly being introduced. This paper discusses these designs and their materials. Information on a new approach to cable manufacturing and on use of downhole materials in harsh environments is also provided.

This paper includes work on cable designs that incorporate a new, unique, elastomeric composition that resists rupture of jacketing materials used on downhole cables, eliminating the need for tape and braid. Cable history is also reviewed, classifying the cables by use temperatures and relative cost. Criteria for selecting materials suitable for the entire range of downhole environments are included.
A Comparison of Pressure-Transient and Tracer-Concentration/Time Data for Layered Reservoirs Under Injection
Authors: Mishra Srikanta , Ramey H. J.
Published: December 2007

Hypothetical tracer and pressure-transient test responses were computed for a production well in a developed, five-spot, unit-mobility-ratio injection/production pattern. The reservoir was a noncommunicating Dykstra-Parsons layered system. Layer effects were evident in tracer results, but pressure-transient results indicated a single layer of averaged properties. Conventional layer system "humps" were not present for the buildup pressure-transient data.
Response of the Carbon/Oxygen Measurement for an Inelastic Gamma Ray Spectroscopy Tool
Authors: Roscoe Bradley A. , Grau James A.
Published: December 2007

In the inelastic mode of operation, a gamma ray spectroscopy tool (GST) performs a measurement of the carbon and oxygen in the formation and borehole on the basis of a spectral analysis of gamma radiation induced by fast neutrons. The carbon-to-oxygen ratio contains valuable information concerning the location of oil-and/or gas-bearing rock. Hundreds of laboratory formation measurements have been performed to determine the partitioning between formation and borehole response of this tool. An interpretation model has been developed for the carbon-to-oxygen ratio that determines the borehole effects as a function of the following parameters: borehole size, borehole fluid composition, borehole fluid displacer size, casing size, casing weight, and formation porosity.
Design and Installation of a 20-Slot Template in the Gulf of Mexico in 760 ft of Water
Authors: Brinkmann P. E. , Barbier G. J. , Rodriguez W.
Published: December 2007

This paper describes the design, fabrication, and offshore operations associated with the installation of a 20-slot mudline drilling template for 760 ft [232 m] of water in the Gulf of Mexico. The basic design criteria, project scheduling, installation considerations, and associated engineering studies are discussed. Economics highlighting potential project cost savings is included.
Deflocculation of Fractionated Montmorillonite by Sodium Polyphosphates
Authors: Jessen F.W. , Turan Faruk H.
Published: December 2007

The gel strength and viscosity of two different suspensions of fractionated montmorillonite clay were measured by using a Stormer viscosimeter and Fann V-G meter. The amount of sodium polyphosphate (sodium hexametaphosphate, sodium tetraphosphate and sodium acid pyrophosphate) adsorbed by the clay particles was determined. A relationship seems to exist between the amount of polyphosphate adsorbed and the nature of the surface, edge or plate, assumed to be the principal sites for selective adsorption. Reduction in viscosity and gel strength was found to be directly related to the adsorption. Both chemical bonding and physical adsorption seem involved in deflocculation. Some indication of the axial ratios of particles of .1- to .04-micron average size is possible through study of the adsorption mechanism.

Introduction and Purpose

A knowledge of surface areas of clay particles in a suspension and a precise determination of phosphate adsorption should provide a basis for a better understanding of reduction in viscosity and gel strength caused by molecularly dehydrated phosphates. The purpose of this investigation was to study the adsorption of sodium polyphosphates on suspensions of fractionated sodium montmorillonite. Although there is considerable uncertainty regarding details of the structure of montmorillonite, a generally accepted one is that suggested by Hofmann, Endell and Wilm. The structure shown in Fig. 1 is an idealized one, and Marshall has postulated that it is possible for several isomorphous replacements to occur. Thus, aluminum may replace silicon, in which case an exchangeable cation would go along with the aluminum to neutralize what would otherwise be a net negative charge on the structure. There is disagreement among various investigators as to the particle size and shape of montmorillonite clays. Marshall reported the following results for the mean lateral dimensions of a Putnam clay (montmorillonite) - 3,730 A for particles having average diameters ranging from 500 to 1,000 A, and 750 A for those with an average diameter less than 200 A. The latter particles were estimated at 50 A in thickness, which would correspond to a stack of five unit cell layers. On the other hand, Shaw has interpreted micrographs as indicating that particles of montmorillonite are readily broken down to the individual cell layers by dispersion in water.
Application of a Mass Flowmeter for Allocation Measurement of Crude Oil Production
Authors: Liu K. T. , Canfield D. R. , Conley J. T.
Published: December 2007

Mass flowmeters have been used to improve crude oil measurement at individual wells throughout the Little Knife field. This type of meter uses the principle of the Coriolis effect to measure the mass flow rate of fluid. Mass measurement eliminates problems encountered by conventional volumetric flowmeters because of the presence of free gas in the liquid phase.

After 5 years of operation, mass flowmeters have proved to be a significant improvement over conventional flowmeters. Excellent agreement has been consistently achieved between the sum of the measurement from the allocation meters and the custody transfer meters, which receive the commingled oil. In addition to the performance improvement, significant capital and operating cost savings were realized compared with a more conventional oilfield approach.
Cormorant: Development of a Complex Field
Authors: Stiles J. H. , McKee J. W.
Published: December 2007

The development plan of Cormorant field exemplifies changes required as the nature of a large, complex field becomes better known. The number and locations of wells and the completion method have changed as the structural, stratigraphic, and diagenetic natures of the field became better known. A better understanding of a key development constraint—the drilling reach—has allowed changes to the development plan at significant cost savings. Close surveillance of geological results and field performance has been necessary to allow almost continuous updating. This paper discusses studies and evaluations undertaken by Esso E&P U.K. to evaluate such changes for each of the field's four fault blocks. These studies complemented work done by the operator, Shell U.K. E&P.
Influence of Shape and Skin of Matrix-Rock Blocks on Pressure Transients in Fractured Reservoirs
Authors: de Swaan Abraham
Published: December 2007

A formulation for pressure transients in terms of the intrinsic, or core, properties of the two media that compose the fractured reservoir establishes the influence of these properties on—and their corroboration from—the pressure/time relationship observed in well and interference tests. The influence of the following reservoir characteristics are analyzed: the area of fractures transverse to flow; the dimensions, shape, and properties of rectangular parallelepiped matrix-rock blocks; and permeability reduction in the block surfaces.

A restatement of the so-called quasisteady-state intermedia flow provides Warren and Root's α and λ parameters with the physical meaning they lacked and allows direct determination of the blocks' minimum dimensions.
Underbalanced Perforation Characteristics as Affected by Differential Pressure
Authors: Regalbuto John A. , Riggs Robert S.
Published: December 2007

Underbalanced, tubing-conveyed completions are increasing because of the apparent advantages of cleaner perforations, reduced completion times, and stimulation treatments. Radial-flow Berea sandstone core specimens are used to determine the perforation characteristics resulting from time-dependent pressure differentials between core pressure and wellbore pressure during the completion process.

The primary perforation characteristic studied [radial flow ratio (RFR)] is defined as the ratio of the perforated flow rate to the flow rate of the unperforated core. The perforation flow tests included pressure differentials from 500 psi [3450 kPa] overbalanced to 1,000 psi [6900 kPa] underbalanced, with immediate or delayed surging.

The RFR was affected most by the 500-psi and 1,000-psi [3450- and 6900-kPa] underbalance. The surged RFR's were from 50 to 58% greater than the no-surge RFR's.

Perforation hole volumes were increased as much as 55% by the surge, indicating some elimination of the compacted, damaged-zone material. Underbalanced surge conditions (1,000 psi [6900 kPa]) increased hole volume to four times that resulting from 500 psi [3450 kPa] overbalanced, no-surge conditions.

Underbalanced surging, either at the instant of perforation or subsequently, appears to improve the flow characteristics of shaped-charge perforations by simultaneously reducing the thickness of the low-permeability crushed zone and increasing the perforation surface area.
Additional Thermal Data for Porous Rocks--Thermal Expansion and Heat of Reaction
Authors: Somerton W.H. , Selim M.A.
Published: December 2007

Thermal expansions and beats of reaction of three typical sandstones were measured in the temperature range of 250° to 1,000°C. The significance of these data in subsurface heat-transfer calculations is discussed.

Linear thermal expansions were measured both parallel and perpendicular to the bedding planes. Volume expansions are reported as the perpendicular expansion plus two times the parallel expansion. Expansion behavior of the sandstones was found to be controlled by the expansion characteristics of the quartz content. Differential expansion of the quartz grains and other minerals included in the sandstones caused permanent de formation of the heated samples after they were cooled to room temperature. Structural damage resulting from heating is probably an important cause of the reduction of thermal conductivity of heated samples.

Measurements of heats of reaction were based on the known heat required for a-ß quartz inversion. Thermal reactions, which probably include dehydroxylation of clay minerals and decomposition of carbonate minerals contained within the samples, were found to require more than one-fourth of the amount of heat necessary to raise the temperature of the rock alone. In shales and limestones, the reaction heat could be substantially greater than that required from specific heat considerations alone.

Introduction

In earlier work, methods of measuring thermal properties were developed and thermal data for several sedimentary rock types were reported. Data included thermal conductivity, specific heat and thermal diffusivity. In addition, calculations of heat transfer in subsurface formations may require data on the thermal-expansion characteristics of rock and the heats of reaction of mineral constituents.
Thermal Conductivities of Porous Rocks Filled with Stagnant Fluid
Authors: Kunii D. , Smith J.M.
Published: December 2007

Effective thermal conductivities of sandstones filled with stagnant fluids were measured using a steady-state technique. Data were obtained for seven sandstone samples, taken from four different locations and ranging in permeability from 18 to 590 md. The measurements with gases (helium, nitrogen, air and carbon dioxide) covered a pressure range from 0.039 psia to 400 psig. Data were taken for four liquids - n-heptane, methyl alcohol, 79.8 weight per cent glycerol-water solution and pure water at atmospheric pressure.

The experimental results were used to evaluate the theoretical equations for predicting stagnant conductivities developed earlier. The low-pressure measurements permitted evaluation of the consolidation parameter hpDp/ks (necessary to utilize the theory) for the various types of sandstones. Using these characteristic values, the theoretical equations correlated well with the experimental conductivity data for the several fluids and rock samples.

Introduction

An aspect of heat transfer in solid-fluid systems of considerable current interest is the effective thermal conductivity of porous media. The stimulus for study of the subject arises from the need for sound procedures for designing thermal methods of petroleum production. The general system occurs when there exists a flow of fluid through the pores of the solid material. However, a logical starting point in developing a theory for predicting the effective thermal conductivity in the general system is to attack the special case when the porous solid is filled with stagnant fluid. Since the flow rates anticipated in thermal production processes are very low, such stagnant conductivities k are also of practical significance.
Applications of Convolution and Deconvolution to Transient Well Tests
Authors: Kuchuk F. J.
Published: December 2007

This paper presents the application of convolution and deconvolution interpretation methods. Two well-test field examples, interpreted with these methods, suggest that the downhole flow rate is crucial for system identification and parameter estimation and that the wellbore volume below the pressure gauge and flowmeter must be taken into account. A new generalized rate-convolution method is presented to obtain the reservoir pressure. This new method gives better results than both the Horner and modified Horner methods. A new formula also is presented to determine the vertical permeability for partially penetrated wells.
Temperature Profiles in Underground Combustion
Authors: Baker P.E.
Published: December 2007

Introduction

In this paper, approximate analytical expressions are derived for the temperature profile developed in the underground combustion method of oil recovery. A qualitative description of the process may be found in a paper by Tadema. The flame front is regarded as a moving source with a constant rate of heat generation. Heat transfer is by conduction and convection.

Previous publications, of which a few are cited here, have also attacked this problem and have presented solutions pertaining to different methods of approximating or idealizing the process studied. The present paper also treats an idealized case: linear flow is assumed for heat and fluids, and vaporization and condensation effects are neglected. The results obtained are similar to those derived by Bailey and Larkin, but are obtained by an entirely different procedure. The method used here should give considerably greater insight into the physics of the in situ combustion process.

Four types of cases are considered, distinguished by thermal and fluid-flow properties of the system. A constant rate of heat generation and constant rate of flame-front advance are assumed. Flamefront temperature is determined for each case using a heat balance which involves the entire temperature profile. The applicability of the different solutions to real systems is discussed after they are all presented. Again, this is done for the purpose of understanding better the physics of the process. Consideration of the nonapplicable solutions and of the reasons for their not applying is significant. In a paper by Cooperman, the only case solved is one considered here as not applicable.
Well-Test Analysis for Solution-Gas-Drive Reservoirs: Part 1—Determination of Relative and Absolute Permeabilities
Authors: Serra Kelsen V. , Peres Alvaro M. M. , Reynolds Albert C.
Published: December 2007

For transient radial flow to a well producing a solution-gas-drive reservoir, it is shown that estimates of effective phase permeabilities as functions of pressure can be obtained directly from the measured flowing wellbore pressure and the flow rates. Rough estimates of effective permeabilities as functions of oil saturation also can be obtained. It is also shown that a semilog plot of pressure squared vs. time can be used to estimate effective permeabilities and the skin factor.
Study of the Potential for an Off-Bottom Dynamic Kill of a Gas Well Having an Underground Blowout
Authors: Gillespie John D. , Morgan Richard F. , Perkins Thomas K.
Published: December 2007

This paper reports on an analysis that links expected reservoir performance with wellbore hydraulics. The dynamics of counterflow of the kill fluid and gas below the kill string can play a significant role in the expected behavior during a dynamic kill. The design concepts and techniques presented should be applicable to any well that requires the kill string to be run or snubbed into the well or one in which the string is a significant distance off bottom at the time of a blowout and cannot be lowered to bottom.
Visualization of Xanthan Flood Behavior in Core Samples by Means of X-Ray Tomography
Authors: Hove A. O. , Nilsen Victor , Leknes Jørgen
Published: December 2007

This paper presents examples of xanthan corefloods visualized by X-ray tomography. Water and aqueous xanthan solutions are distinguished from each other by addition of sodium iodide (NaI) at different concentrations. One reservoir sandstone and one outcrop (Rosbrae) sandstone core samples were used. The reservoir sample was naturally divided into two longitudinal zones differing in permeability by about 20-fold. The Rosbrae sample was homogeneous, with a permeability of 450 md. Miscible xanthan/water displacement tests were performed on both plugs. Immiscible displacement of light refined oil by xanthan was performed on the homogeneous sample.
Effects of CO2 Flooding on Wave Velocities in Rocks With Hydrocarbons
Authors: Wang Zhijing , Nur Amos M.
Published: December 2007

Compressional- and shear-wave velocities were measured in the laboratory in seven sandstones (porosities ranging from 6 to 29%) and one unconsolidated sand (37% porosity) saturated with n-hexadecane (C16H34) both before and after CO2 flooding. CO2 flooding decreased compressional-wave velocities significantly, while shear-wave velocities were less affected. The magnitude of these effects was found to depend on confining and pore pressures, temperature, and porosities of the rocks. The experimental results and theoretical analysis show that the decreases in compressional-wave velocities caused by CO2 flooding may be seismically resolvable in situ. Therefore, seismic—especially high-frequency, high-resolution seismic—methods may be useful in mapping and locating CO2 zones, tracking movements of CO2 fronts, and monitoring flooding processes in reservoirs undergoing CO2 flooding.
Assessment of a Vertical Hydrocarbon Miscible Flood in the Westpem Nisku D Reef
Authors: Da Sle W. J. , Guo D. S.
Published: December 2007

In 1981, a vertical hydrocarbon miscible flood was implemented in the Westpem Nisku D pool, one of 40 isolated carbonate pinnacle reefs in a trend located west of Edmonton, Alta., Canada. A solvent composed of methane and 15% ethane-plus components was injected into the reservoir, which is maintained at a pressure of about 4, 800 psig [33 MPa]. Positive indications of the location of the solvent/oil interface have been obtained from interface logging [pulsed-neutron-capture (PNC) logs] in a producing wellbore and from special analysis of core from an infill well recently drilled into the pool. Two types of chromatographic analysis of residual oil and a conventional core residual oil determination were done. The results show that the flood is gravity stable and has excellent volumetric conformance. The special core analysis provided information on the quantity and composition of residual oil saturation (ROS) in the miscibly swept zone. On the basis of these flood performance data, an estimate of ultimate recovery has been prepared.
Laboratory Measurements of CO2-Foam Mobility
Authors: Lee Hae Ok , Heller John P.
Published: December 2007

Mobility control of high-pressure CO2 floods by use of foam is a promising oil recovery technique. Critical information for the use of CO2 foam as a thickened displacement fluid is the ratio of the combined CO2/surfactant-solution flow rate to the pressure drop in the swept region. This foam mobility can be measured in laboratory experiments. In this work, a high-pressure apparatus was designed and carefully calibrated to measure foam mobilities at various flow rates. These measurements were made during simultaneous flow of the dense CO2 and surfactant solutions through core samples. Dependence of CO2-foam mobility on several variables was observed. The effect of aqueous surfactant concentration on CO2-foam mobility was explored thoroughly. The dependence in this case was such that foam mobility decreased steadily as surfactant concentration increased until a minimum mobility was attained at some particular concentration well above the conventional critical micelle concentration (CMC). The effect of foam volume fraction showed that mobility decreases with increasing fraction of surfactant solution. Also, it was found that the relative mobility (mobility divided by rock permeability) of CO2 foam was higher in Rock Creek sandstone than in Berea sandstone. Shear-thinning behavior was observed under some conditions in our experimental range of total flow rate.
Miscible Displacement: Recovery Tests With Nitrogen
Authors: Glasø Olstein
Published: December 2007

High-pressure slim-tube tests and phase-behavior studies were performed with reservoir fluid and three-component hydrocarbon mixtures. The amount of methane and intermediates in the reservoir fluid were varied while other parameters that affect the oil recovery were kept constant. The effects of displacement velocity, temperature, and length of the packed column on slim-tube recovery were also investigated. The results obtained show that the amount of methane and intermediates in the reservoir fluid has a significant effect on minimum miscibility pressure (MMP). The results suggest very strongly that a reservoir fluid with a low methane content needs a long path length to develop miscibility with N2 (a large fraction of the oil is bypassed in the first part of the column). The slim-tube oil recovery, and hence the average microscopic displacement efficiency of the process, is shown to increase significantly with slim-tube length when injection pressure and other variables are kept constant. The results from simulation tests of phase behavior and fluid flow in the slim tube confirmed some of the conclusions made from the experimental results obtained in this work. An N2 MMP correlation was developed from displacement test data reported in the literature and in the present study.
An In-Situ Combustion Reservoir Simulator With a New Representation of Chemical Reactions
Authors: Le Thiez Pierre A. , Lemonnier Patrick A.
Published: December 2007

Numerical simulation of in-situ combustion processes poses numerical problems related to the representation of chemical reactions in the burning zone. This paper presents a new approach to the description of the combustion front. The fully implicit thermal compositional model developed to simulate oil recovery by wet or dry forward combustion is formulated to handle three dimensions, three phases, gravity and capillary forces, heat transfer by convection and conduction within the reservoir, and conductive heat loss to adjacent strata. Two options are available. The first includes four components and one fuel combustion reaction. The second allows any number of components and several reactions. The first option emphasizes description of the combustion front with a new formulation that uses a heat-release curve to improve numerical stability and to give accurate temperature distribution with large gridblocks. The paper compares different representations of chemical reactions and includes results of a sensitivity study on the mesh size. Thermal-balance considerations are given for wet or dry combustion to provide calculated values of the peak temperature and steam-plateau characteristics. The thermal-balance results agree well with those predicted by the numerical model.
Analyzing Aquifers Associated With Gas Reservoirs Using AlF's and Type Curves
Authors: Targac Gary W. , Wattenbarger R. A. , Startzman R. A.
Published: December 2007

An aquifer-influence function (AIF) can be calculated from a gas reservoir's production and pressure histories. The AIF is unique for an aquifer and can be analyzed to determine aquifer size and other information. Two AIF type curves were developed for aquifers with partially sealing faults and then applied to 32 U.S. gulf coast gas reservoirs.
Light-Oil Steamflooding: A Laboratory Study
Authors: Sarathi Partha S. , Roark S. Doug , Stryker Arden R.
Published: December 2007

Experiments were conducted in a 2D elemental model to determine the response of light crudes to steam injection and to verify reported numerical simulation results. The results showed that light-oil steamfloods are typified by an early production response to steam injection and that recovery efficiencies are strongly influenced by the chemical nature of the crude. The data also indicated that gravity override of steam remains a potential problem in light-oil steamflooding and that as much as 65% of oil in place (OIP) can be recovered economically by steamflooding light oils.
The Effects of Shear History on the Gelation of Polyacrylamide/Chromium(VI)/Thiourea Solutions
Authors: Bhaskar Ravi K. , Stinson Jeffrey A. , Willhite G. Paul , Thiele John L.
Published: December 2007

The influence of shearing during gelation on the gelation rate of a polyacrylamide/chromium(VI)/thiourea solution was studied. Gelations were carried out under steady-state shear, oscillatory shear, and programmed shear. When shear rate was constant throughout the experiment, gels formed more slowly at high than at low shear rates. This behavior is opposite to that observed with polyacrylamide/chromium(VI)/bisulfite solutions, where increased shear rates led to faster gelations. The gelation mechanism is believed to involve at least two chemical reaction steps: reduction of chromium(VI) to chromium(III) followed by crosslinking of the polymer by chromium(III). in gelation with bisulfite as the reducing agent, chromium(III) is generated rapidly, and the rate-determining step (which may be polymer-diffiision controlled) is probably the crosslinking of polymer by chromium(III). in contrast, chromium(III) is generated relatively slowly in gelation with thiourea as the reducing agent, and the rate-determining step appears to be the redox reaction.

The conclusion that the rate of gelation and strength of the gel formed for the gelation of Polyacrylamide by chromium(III) are strongly influenced by the total shear history of the solution has important implications for design of field applications of gelled polymers in EOR. The evaluation of gel characteristics in quiescent botfle tests, a common practice, may not be sufficient to determine whether a gel of the desired strength can be obtained in situ because all gelling solutions must be subjected to considerable shearing during injection.
Application of Geological Modeling and Reservoir Simulation to the West Saertu Area of the Daqing Oil Field
Authors: Abib Osmar , Moretti F. J. , Mel Cen , Yuzhe Yang
Published: December 2007

An integrated geological and engineering study was conducted for a representative section of the Saertu and Putaohua reservoirs in the West Saertu area of Daqing, the largest oil field in the People's Republic of China. This paper discusses various aspects of the study related to reservoir geology, field development, geological and reservoir simulation modeling, production history matching, and reservoir performance predictions. Geological and reservoir simulation models developed during this study are being used routinely in Daqing as part of a plan to improve reservoir management of the West Saertu portion of the field.
Estimating Skin Decline and Relative Permeabilities from Cleanup Effects in Well-Test Data With Buckley-Leverett Methods
Authors: Larsen Leif , Kviljo Knut , Litlehamar Terje
Published: December 2007

This paper examines relationships between backflow of water from the invaded zone and changes in skin owing to reduced water saturation and the associated change in mobility for homogeneous reservoirs. Effects studied are governed by initial saturation profiles, relative permeabilities of water and the produced reservoir fluid, basic reservoir and fluid parameters, and the producing rate. Buckley-Leverett-type displacement is assumed in the skin zone, and production and skin-zone data needed to determine relative permeability characteristics by extensions of standard techniques are given. Methods to determine such characteristics by matching observed and computed skin-decline data are also presented.
An Experimental Study of Non-Newtonian Polymer Rheology Effects on Oil Recovery and Injectivity
Authors: Gleasure Richard W. , Phillips Colin R.
Published: December 2007

Pseudoplastic non-Newtonian polymer solutions were examined for their enhanced oil recovery performance. Detailed results are reported for xanthan gum (XAN), Kelzan XCD™, and a viscoelastic polyethylene oxide (PEO), Polyox OF-50™. Increases in the power-law coefficient resulted in improved displacement efficiency. Effects were also observed in the injectivity-index parameter results.
Successful Application of Drilling Technology Extends Directional Capability
Authors: Schroeter D. R. , Chan H. W.
Published: December 2007

This paper presents an operational overview of the application of measurement-while-drilling (MWD) directional equipment, polycrystalline-diamond-compact (PDC) bits, a top-drive drilling system (TDS), and low-toxicity oil-based-mud (LTOBM) technology for cost reductions in the drilling of long-reach directional wells in the South China Sea offshore Malaysia. Guidelines are provided for improved hole cleaning, for monitoring oil mud properties, and for drillstem tripping practices to minimize hole problems and costly stuck-pipe incidents.
Tubing-Conveyed Perforating: Operating Experience
Authors: Bowler G. V. , Suparman Dadang
Published: December 2007

In 1981, Huffco Indonesia, a production-sharing contractor to Pertamina, was the first company in Indonesia to use tubing-conveyed perforating (TCP) in its well completions. This paper draws conclusions on the benefits of using a TCP technique over wireline perforating techniques. Of the 75 TCP jobs done, less than 10% can be considered failures. The results achieved with various amounts of underbalance are compared with published results. TCP is considered the most effective perforating technique currently available.
A Slug-Length Distribution Law for Multiphase Transportation Systems
Authors: Bernicot M. F. , Drouffe J.-M.
Published: December 2007

A probabilistic approach is used to analyze the formation of slugs in nearly horizontal pipelines. Knowledge of the probability amplitude for a liquid bridge in the formation zone allows derivation of the slug-length distribution law. The method is suitable for simulating complex situations, including unsteady flows. For horizontal steady flows, a simple model of this probability, expected to be valid in large-diameter pipes or for long slugs (tail of the distribution), yields a Gaussian law, which is distinct from the log-normal law. Frequency, mean length, and variance depend on only one parameter, which may be predicted from theoretical study (not included here). This new length distribution law is verified against experimental data obtained with an air/water test loop (42 mm in diameter and 400 m long) installed in the Beauplan production laboratory in France and is compared with the log-normal distribution law.
Steam-Soak Performance in South Oman
Authors: Rice S. A.
Published: December 2007

With about 2 × 109 stock-tank m3 [12.6 × 109 STB] of medium/heavy oil originally in place (OOIP) in south Oman, considerable scope exists for increasing oil recovery by thermal methods. The viability of thermal recovery in south Oman was tested with a steamflood pilot in the Al Khlata sands of the Marmul field and a 2-year steam-soak project to test the applicability of steam soak in five south Oman oil fields producing heavy oil. This paper describes the performance of the latter project. The wells selected for the test program included a wide range of south Oman reservoir and oil characteristics—i.e., the main reservoir drive mechanisms of depletion, solution-gas, and edge- and bottomwater drive, the reservoir sandbody types, and oil viscosities from 80 to 4000 mPa·s [80 to 4, 000 cp]. Steam-soak operations were successful, and oil production accelerated significantly, with an average stimulated production rate twice that before stimulation. Acceleration was less marked in wells where reservoir energy is limited or where the primary (cold) water cut is more than 30%. At primary (cold) water cuts >50%, no increase in oil production rate was observed. The process was simulated numerically for several wells, with the results in close agreement with performance. Improved understanding of the process resulting from the simulation allowed the most important factors influencing performance to be identified and aided process optimization in the field test. Two small-scale steam-soak projects currently are being assessed for implementation in the early 1990's.
Effect of Gas Enrichment and Numerical Dispersion on Enriched-Gas-Drive Predictions
Authors: Stalkup Fred I.
Published: December 2007

This paper examines the effect of gas enrichment in reservoir-scale enriched-gas-drive displacements through predictions made with a compositional simulator and the Peng-Robinson equation of state (PREOS). The calculations examine behavior for a classical three-component condensing-gas drive and for a 12-component reservoir-fluid characterization that predicts condensing/vaporizing-gas-drive behavior. The predictions also illustrate behavior for two simplified reservoir analogues: a homogeneous cross section with a low vertical/horizontal permeability ratio and a stratified cross section. An important feature of this study is that the impact of numerical dispersion on the predictions is assessed through numerical sensitivity calculations. The simulations show that (1) numerical dispersion causes an abnormally large, erroneous, predicted increase in recovery with increasing gas enrichment and a predicted incremental recovery over waterflooding that could be too large by as much as a factor of two; (2) the most realistic predictions are obtained by extrapolating recoveries to a gridblock size of zero, even though the extrapolation may be imprecise and the degree of convergence to the correct answer is unknown; (3) numerical dispersion causes too large a predicted increase in recovery with gas enrichment beyond the critical enrichment; and (4) calculated oil recovery vs. gas enrichment for the 3- and 12-component fluid characterizations studied is qualitatively similar for injection gases that give displacements ranging from highly immiscible to essentially first-contact miscible (FCM), although absolute differences in incremental recovery are sometimes as large as 1 to 2% of original oil in place (OOIP).
Rheology of Gas/Water Foam in the Quality Range Relevant to Steam Foam
Authors: Vries Arnold S. de , Wit Krijn
Published: December 2007

Experimental results on the rheology of gas/water foam essentially show that if the gas flow rate is increased at an imposed water rate, the pressure gradient increases, reaches a maximum (the break point), and then decreases. A model for foam flow was formulated that explains this behavior semiquantitatively. It consists of a highly simplified model for foam in a single capillary coupled with a description for foam flow in a bundle of identical parallel capillaries. Below the break point, capillaries filled with foam occur with water-filled capillaries; above the break point, the water-filled capillaries are replaced by gas-filled capillaries.

A consequence of the model is that if one plots the results in a special way, a universal curve is obtained, dependent on only the porous medium and the fluid properties. The experimental data more or less conform to this curve, which can be used (in the same way as relative permeabilities) to predict pressure gradients for gas/water rates other than those experimentally measured. Consequences of the foam model for numerical simulation of foam flow are discussed.
Pressure-Transient Analysis of Arbitrarily Shaped Reservoirs With the Boundary-Element Method
Authors: Klkani Jitendra , Horne Roland N.
Published: December 2007

Two boundary-element-method (BEM) formulations are proposed for the solution of pressure-transient problems in homogeneous, anisotropic reservoirs. Pressure solutions in arbitrary reservoir shapes with multiple sources and/or sinks and a variety of constant and/or time-dependent boundary conditions can be generated. This technique is superior to numerical methods because it preserves the analytical nature of the solution and because numerical dispersion and grid-orientation effects are nonexistent. Procedures for the convolution and Laplace-domain solution procedures are compared, and problems illustrating the various aspects of the BEM are solved.
Barium and Strontium Sulfate Solid-Solution Formation in Relation to North Sea Scaling Problems
Authors: Todd Adrian C. , Yuan Mingdong
Published: December 2007

This paper presents the results of laboratory experiments carried out to investigate the formation of barium sulfate and strontium sulfate [(Ba, Sr)SO4] solid solution in multi-pressure-tapped cores. Two brines, one barium- and strontium-rich and the other sulfate-rich, were mixed in a core plug. Pressure differentials were measured and the changing permeability distribution along the core length was calculated. The morphology and chemical analysis of scaling crystals as shown by scanning electron microscopy (SEM) are presented. Results show a large extent of permeability damage caused by (Ba, Sr)SO4 solid solution deposits on the rock pore surface. The rock permeability decline and morphology and size of the scaling crystals indicate the influence of the supersaturations of BaSO4 and SrSO4 and the concentration ratio of barium to strontium ions.
Analysis off Gravity Separation in Freewater Knockouts
Authors: Powers Maston L.
Published: December 2007

The selection of a freewater knockout depends on the desired performance. The design criterion developed here is based on the perception that most FWKO's are installed to remove the bulk of the water from a high-water-cut flow stream so that the oil can be dehydrated economically to salable specifications and to discharge water requiring minimal treatment before disposal. Only the gravity separation process is considered; the contribution of coalescing devices is excluded. Vertical FWKO's are discussed briefly, but the bulk of this paper is devoted to horizontal FWKO's, which constitute a majority of vessels. Hydraulic similarity of horizontal FWKO's and API separators is demonstrated, and a design criterion for FWKO's is developed with the basis used in the design development for API separators. This analysis discloses that commonly used criteria overrate the ideal flow capacity of FWKO's by a factor of 4/π. It shows that maximum FWKO capacity occurs when the oil/water interface is maintained at a level of 0.769 diameters in the case of ideal vessels and somewhat higher for nonideal vessels, rather than 0.50 as commonly believed. Published FWKO residence-time distributions (RTD's) indicate nonideal flow. Consequently, a design allowance for short-circuiting and turbulence effects was incorporated into the FWKO design. The effect of vessel proportions on cost per unit capacity is analyzed and an equation is developed for determining optimum proportions.
The Effect of Viscous Fluid Properties on Excess Friction Pressures Measured During Hydraulic Fracture Treatments
Authors: Holditch Stephen A. , Robinson Brad M. , Ely John W. , Rahim Zillur
Published: December 2007

A plot of excess pressure vs. time can be used to predict fracture-growth patterns only when both the viscosity of the fluid in the fracture and the stress at the fracture tip remain constant. This paper uses laboratory data and field examples to explain how increased friction owing to viscous slurries affects the interpretation of fracturing pressures.