bluuebunny/crossref_metadata_2025 huggingface dataset:
Precession of Rotary Drillstrings Should be Eliminated
Authors: Zhang Y. L. , Xiao Z. Y. , Duanmu G.
Published: June 2014

Results obtained using a scale model of several hundred metres of a drill string are presented. The model has shown that the rotary drilling process is dominated by precession of the drill string. The nature of this motion is explained, along with its relationships to bending stress and torque. It is suggested that high speed precession contributes significantly to bending fatigue of drill strings; and eliminating the precession is the approach to prolong the service lives of rotary drill string components and to carry out high speed safe drilling.
Pressure Transient Testing of Methane Producing Coalbeds
Authors: Kamal M. M. , Six J. L.
Published: June 2014

A new analysis method for pressure transient testing in coal degasification projects is presented. The results from this method show that transient testing can be used to characterize methane producing coalbeds. Formation permeability, reservoir pressure, and wellbore skin can be calculated using the proposed method. Use of conventional single phase analysis produces different results.

The current practice calls for testing coalbeds by a series of water pump-in and falloff tests upon completing the wells to ensure a single phase system. Once gas production starts, a multi-phase system raises serious concerns about the validity of conventional pressure transient analysis in coal degasification projects. However, testing of methane producing coalbeds is important because in addition to the need of monitoring the pressure and wellbore conditions, the cleat system permeability may change as the pressure is decreased.

Therefore, a new analysis method has been developed for these systems. The method is based on a pseudo pressure function that uses the adsorption isotherm and relative permeability relations of the reservoir. The method enables the interpretation engineer to calculate the absolute permeability at any time even when both gas and water are being produced. The method was verified by successfully analyzing simulated tests from a rigorous coal degasification numerical simulator. The method was then used on field buildup data taken shortly after gas production began from a well. The same absolute permeability was calculated as that from the water pump-in and falloff tests which were run in the same well upon its completion. Results from field tests on another well also are included in the paper.
Analysis of Steady-state, Vapor-Liquid Concurrent Flow
Authors: Parlar M. , Zeybek M. , Yortsos Y. C.
Published: June 2014

Steady-state methods are commonly used for the determination of the relative permeabilities of single component vapor-liquid systems, such as steam-water. Even though such experiments are performed under adiabatic conditions, the interpretation of results has proved to be difficult. Reasons involve phase change, heat transfer, capillarity and rate considerations.

This paper presents a systematic study of the saturation and temperature distributions in steady-state, vapor-liquid flows and examines their sensitivity to parameters such as injection rate, permeability and core length. Two sets are analyzed, one pertaining to the simultaneous injection of a two-phase mixture (Sanchez and Schechter, 1987) and another involving phase change (liquid to vapor) within the core (Miller, 1951). End effects and, in general, effects associated with capillary heterogeneity are also analyzed.

Solution trajectories in the temperature-saturation plane are constructed. They allow a unified approach to the two problems (two-phase or single-phase injection), which are shown to lie on different parts of the same trajectory. Minimum conditions for the development of in-situ evaporation are developed. Then, the process sensitivity to parameter values is examined for steady-state two-phase injection and relative permeability estimation. It is found that a plateau region develops, within which the inlet saturation is approximately constant, although corresponding saturation profiles are not necessarily flat. Numerical estimates show that the estimation error involved increases with decreasing enthalpy and decreasing permeability.
A Laboratory Investigation of Viscosified CO2 Process
Authors: Bae J. H. , Irani C. A.
Published: June 2014

Supercritical CO2 was thickened using a commercial silicon polymer and toluene as cosolvent. The pressure range for polymer solubility in CO2 was determined, and the viscosity of the thickened CO2 measured. The viscosified CO2, increased by two orders of magnitude in viscosity, was used in corefloods in Berea and carbonate reservoir cores. The oil recovery obtained with the viscous CO2 was compared with the results obtained using neat CO2, WAG(1:1), and CO2 with a cosolvent without a polymer. The results show clearly that oil recovery is enhanced and CO2 breakthrough retarded significantly with viscosified CO2.
Evaluation of the High-Speed Centrifuge Technique for Determining Capillary Pressure at Low Wetting-Phase Saturations
Authors: Melrose J. C. , Mallinson J. E.
Published: June 2014

Recent experimental studies of the high-speed centrifuge technique have indicated that the method, if properly used, yields results which are in accordance with other methods. These studies have also shown that the concept of an irreducible wetting phase saturation is not valid. In the present paper work is reported in which these previously presented results are extended to both higher and lower capillary pressures. Air/liquid data have been obtained with n-decane as the wetting phase and are compared with new data (as well as with the previously reported data) for the air/brine system. The study involved 242 days of centrifugation and utilized 10 different Berea plug samples and 5 different high permeability plug samples taken from a producing reservoir.

The linear relationship between log Pc and log  (or log Sw, as observed in previous work) was confirmed for Berea samples over the average saturation range from about 30 percent down to 10 percent. For lower average saturations, the saturation data are not sufficiently precise either to (1) demonstrate conclusively the persistence of this relationship, or (2) prove the breakdown of the Hassler boundary condition. For three of the five producing reservoir samples, it was found that two different linear segments characterized the log Pc versus log  relationship, with a rather sharp transition occurring in the 30 to 40 percent average saturation range.
Chemical Properties of Chromium/Polyacrylamide Gels
Authors: Lockhart Thomas P.
Published: June 2014

Experimental studies on aqueous Cr+3/polyacrylamide (HPAAm) gels have led to new insight into their structure and chemical properties. In particular, Cr+3 is shown to form molecular crosslinking complexes with HPAAm, and to display chemical reactivity typical of inorganic coordination complexes. On the basis of ligand-induced de-gelation reactions, a new hypothesis regarding the bonding between HPAAm and Cr+3 is formulated. Comparisons are made between the chemistry of HPAAm gels prepared with chromium acetate complexes and those with inorganic Cr+3.
Spectrophotometric Determination of Acrylamide Polymers by Flow Injection Analysis
Authors: Taylor Kevin C.
Published: June 2014

Flow injection analysis has been applied to the analysis of acrylamide polymers to provide an automated determination at the rate of 90 samples/hour. The method is suitable for use with acrylamide polymer samples obtained from enhanced oil recovery operations, given a constant degree of polymer hydrolysis. An N-bromo amide is formed, which subsequently oxidizes iodide to iodine. Iodine is measured spectrophotometrically as the starch-triiodide complex. The method is applicable in the range of 0.5 to 75 mg/L polyacrylamide. Relative standard deviation of less than 1.5% was obtained. Detection limit (S/N=3) is 0.2 mg/L. The problems of a non-zero intercept and surfactant interference, which occur in the manual starch-triiodide method, were corrected.
Vectorízation and Parallel Processing of Models with Local Grid Refinement
Authors: Quandalle Ph. , Moriano S.
Published: June 2014

This paper discusses the vectorization and parallel processing of numerical simulation using discretization grids with completely flexible grid cell connections.

Until now, local grid refinement has been considered as an obstacle to the efficient vectorization of reservoir simulation models. Highly vectorized codes have long been available for models which have a regular underlying discretization grid, ie. with no local grid refinement, no faults, and no pinchouts, and the same discretization scheme is used all over the grid. These codes exhibit a large speed up between their execution in scalar and vector modes. However, when the same codes are adapted to handle irregular matrix structures, their high performances on vector processors drop dramatically. In this case, the inner loops of the calculation kernel are indexed on the number of neighbours a given cell has rather than the overall number of cells. This is why the corresponding codes have a poor degree of vectorization. To get better performances, a greater transformation of the codes is necessary.

To the best of our knowledge, this is the first paper to describe how a reservoir equation solver, which accounts for local grid refinement, has been restructured to facilitate vectorization and parallel processing. This solver uses the ORTHOMIN procedure [1], and the BSOR method (Block Successive Over Relaxation) [2] as préconditionner. The result is a general code which runs on vector processors with about the same efficiency whether or not the underlying grid includes local refinement. Based on explicit to fully implicit, black-oil and compositional simulations, the speed up of the linear equation solver, due to vectorization, ranges between 5 and 9, depending on the simulation and the vector computer. The performances are thus comparable to those of a more specific code specially designed for regular grids.
LPG Storage at Mont Belvieu, Texas: A Case History
Authors: Ratigan J. L. , Vogt T. J.
Published: June 2014

The Barbers Hill salt dome contains 124 solution-mined, liquified-petroleum-gas (LPG) storage wells with a capacity of 200 × 106 bbl. A geomechanics evaluation of the facility is described that includes mechanical testing of salt and caprock core, structural evaluation of the storage and brine disposal wells, and development of a subsidence evaluation network.
Optimal Control of Steamflooding
Authors: Liu Wei , Ramirez W. Fred , Qi Yu Feng
Published: June 2014

A system science approach using optimal control theory of distributed parameter systems has been developed to determine operating strategies that maximize the economic attractiveness of the steamflooding processes. Necessary conditions of optimization are established by using the calculus of variations and Pontryagin's Maximum Principle. The objective criterion is to maximize the difference between oil revenue and injected steam cost. A stable and efficient numerical algorithm is developed.

The performance of this approach is investigated through various two–dimensional steamflooding problems. The effects of reservoir properties and heterogeneity on optimal policies as well as the sensitivity of the control variables are studied.

Results show this method yields significant insight into the steamflooding process. The improvement of economic objective is significant under optimal operation.
Optimization of Well Rates under Gas Coning Conditions
Authors: Urbanczyk Christopher H. , Wattenbarger R. A.
Published: June 2014

This paper develops a method for optimizing well rates when wells are coning gas and field rates are constrained. Since each well's GOR depends on its rate, then well rates must be individually specified. This method maximizes field oil rate when gas rate is fixed and minimizes field gas rate when oil rate is fixed. The method can be used for (1) field operation, (2) reservoir simulation forecasting, or (3) simple material balance applications (as shown in the paper).
The Simultaneous Measurement of Interfacial Tension and Oil Viscosity at Reservoir Conditions for Prudhoe Bay Fluids by Surface Laser Light Scattering Spectroscopy
Authors: Dorshow Richard B.
Published: June 2014

Surface laser light scattering spectroscopy is a well-suited method for the measurement of crude oil/hydrocarbon gas interfacial tension and crude oil viscosity at elevated pressures and temperatures. The results reported herein are the first measurements of these properties in crude oil/gas systems at reservoir conditions using surface laser light scattering, and are the first reported measurements of interfacial tension for Prudhoe Bay fluids at reservoir conditions.
Water Flooding of Gas Condensate Fluids in Cores Above and Below the Dew-Point
Authors: Henderson G. D. , Danesh Ali , Peden J. M.
Published: June 2014

Water-wet cores saturated with gas condensate were flooded with water above and below the dew-point at different rates and pressure levels. The rates of gas, condensate and water recovery, and the residual saturation of fluids have been measured and the results are presented. The conclusions are relevant to the overall management of gas condensate reservoirs.
The Application of Simulated Annealing to Stochastic Reservoir Modeling
Authors: Deutsch Clayton V. , Journel Andre G.
Published: June 2014

Stochastic reservoir models must honor as much data as possible to be reliable numerical models of the reservoir under study. Traditional stochastic modeling techniques are ill-suited to reproduce complex geological/morphological patterns. The simulated annealing technique offers promise as a complementary tool to incorporate such information.
Corrosion Problems Associated with the Use of Copper-Based Corrosion Inhibitor Intensifier in Acid Stimulation Treatments
Authors: do Carmo Marques Luiz Carlos , Mainier Fernando B.
Published: June 2014

The results of a laboratory study carried out to investigate copper deposition and localized corrosion on API N-80 carbon steel are presented. Hydrochloric acid-based stimulation fluids and a recovered worn-out acid sample from the field were used in the tests. To all the tested fluids a copper-based corrosion inhibitor intensifier was added. The tests performed, which also included Scanning Electronic Microscopy and X-rays Fluorescence analysis, showed that the galvanic corrosion promoted by copper deposition on steel is evident and the corrosion process caused by the recovered worn-out acid might be severe.
A Model to Design the Foam Cement Job
Authors: Martins André Leibsohn , Campos Wellington
Published: June 2014

Foam cement is a well proved technique to perform cementing jobs across weak or fractured formation without losing circulation. This work reviews basic aspects of the technique and presents a mathematical model, based on static calculations, for planning purposes. The use of the model enables the performance of a sensibility analisys of the parameters involved. An optimum design requires careful planning of ideal number of fluids to be foamed, gas nature, number of stages, density of base slurry and use of backpressure.
A New Model for Pressure Transient Analysis in Stress Sensitive Naturally Fractured Reservoirs
Authors: Celis V. , Silva R. , Ramones M. , Guerra J. , Da Prat G.
Published: June 2014

The most commonly used methods to describe the transient flow behavior in porous media are based on the assumption of constant rock properties. Nevertheless, these methods are not strictly applicable to reservoirs that undergo changes in the rock properties due to variation in pore pressure. A frequent characteristic of fractured reservoirs is sensitivity of permeability and porosity to effective stress.

This paper presents a new analytical model, for interpreting pressure transient test. The model considers the flow in a naturally fractured stress sensitive reservoir, that is to say, the dependency of rock properties on pressure is established (dependency of permeability on pore pressure is measured by the permeability modulus parameter), and makes that the flow equation be strongly non linear. Likewise, the theory is developed under unsteady- state or pseudosteady-state conditions, and considers that the fracture is uniformly distributed, matrix geometry is the so called stratum and flow contribution from the matrix to the fracture is described by the term source proposed by De Swaan.

The problem stated is solved through an analytical approach for different boundary conditions and different permeability modulus values, thus obtaining type curves that can be used for the analysis of pressure buildup and drawdown tests.
Capillary Pressure, Water Relative Permeability, Electrical Conductivity and Capillary Dispersion Coefficient of Fractal Porous Media at Low Wetting Phase Saturations
Authors: Toledo Pedro G. , Novy Robert A. , Davis H. Ted , Scriven L. E.
Published: June 2014

Transport properties are critical for many reservoir engineering calculations. This work describes recent progress in modeling transport properties of natural porous media at low saturations of a wetting phase, i.e. when total wetting phase saturation Sw is the sum of thin-films and pendular structures inventories. Capillary pressure Pc, wetting phase relative permeability krw, electrical conductivity σw, and capillary dispersion coefficient Dc have been observed to obey power laws in the wetting phase saturation. We relate power-law behavior at low wetting phase saturations, i.e. at high capillary pressures, to the thin-film physics of the wetting phase and the fractal character of the pore space of natural porous media. If wetting phase inventory is primarily pendular structures, and if thin films control the hydraulic resistance of wetting phase we deduce the power laws X=SwbX, with X = Pc, krw, σw and Dc, where for capillary pressure bPc=−1/3−D, for wetting phase relative permeability bkrw=3/m3−D, for electrical conductivity bσw=1/m3−D, and for capillary dispersion coefficient bDc=3−m4−D/m3−D, where m is the exponent in the relation of disjoining pressure and film thickness and D is the fractal dimension of the surface between the pore space and grains or matrix. Recent experimental work lends support to these scaling laws in the cases of natural sandstones and clayey soils. Recent displacement experiments show anomalously rapid spreading of wetting liquid during imbibition into a prewet porous medium. We explain this phenomenon, called hyperdispersion, as viscous flow along fractal pore walls in thin films of thickness h governed by disjoining forces and capillarity.
Reservoir Engineering Study of CO2 Enhanced Oil Recovery for the Nipa 100 Field, Venezuela
Authors: Almeida Jaime , Espinoza Carlos , Mosquera José , Todd Michael R.
Published: June 2014

The J2L interval in the NIP-103 reservoir is comprised of a thin, uniform, high permeability sandstone. Well spacing is about 120 acres/well in the miscible-flood target region. The well configuration is non uniform. Oil saturation in the miscible flood target area is expected to be near initial at the start of CO2 injection. These characteristic distinguish this application from the majority of existing miscible floods.

In order to study the interaction of the CO2 miscible flood process with the J2L reservoir characterization, a numerical simulation study was conducted. First, a set of one dimensional simulations was made in order to examine linear displacement features. Then, multi-dimensional pattern flood simulations were conducted. Finally, a numerical simulation of the J2L CO2 pilot project was undertaken. This part of the simulation work included the construction of a field model, calibration of the field model through history-matching previous field performance, and examination of the CO2 miscible flood process as it might be implemented in the J2L.
Modeling and Optimization of Plunger Lift Assisted Intermittent Gas Lift Installations
Authors: Chacín J. , Schmidt Z. , Doty D.
Published: June 2014

A novel mechanistic model for the design of plunger assisted intermittent gas lift installations is presented. The model considers the complete production cycle: accumulation of reservoir fluids in the wellbore, annulus pressure build-up, plunger/liquid slug rise, liquid production into flowline. It is based on the fundamental mass balance and conservation of momentum equations and considers all important parameters: reservoir pressure, inflow performance, tubing and flowline characteristics, plunger characteristics, available injection pressure, surface injection choke design, gas lift valve design and performance, etc.

The model solution requires numerical techniques, and it is implemented as a computer program for personal computers and mainframe workstations. One of the most innovative characteristics of the model is that it incorporates, as part of the dynamic numerical simulation, experimental plunger rise data relating instantaneous plunger velocity to instantaneous liquid slippage past the plunger. As a result, liquid "fallback"losses can be estimated and need not be assumed.

The model and computer program has been verified and validated both qualitatively and with field data. Comparisons of model predictions versus field data are included. To the best of the authors knowledge, this the first published work in which a full model of this type of artificial lift installation is undertaken.

Finally, it is shown how the model can be used to obtain an optimum design of a new installation, considering both gas consumption costs and crude recovery. Furthermore, examples are included to show how to use the program to effectively optimize existing installations.
The Role of Pressure Transient Analysis in Reservoir Characterization - An Integrated Approach
Authors: Alvarado Ramón W.
Published: June 2014

Most reservoirs exhibit complex variations of sand continuity, thickness, structural patterns, and pore space attributes (permeability, porosity, and capillary pressure properties). The most effective way to identify and quantify rock framework and pore-space variations, is through the deliberate and integrated use of engineering and earth-science technology. The development of the pressure derivative technique of well test interpretation, has greatly improve the identification of features that are often not evident on a Horner plot. This paper illustrates, with several field cases, how an adequate model of the reservoir can be diagnosed by complementing the transient response analysis, based on the pressure derivative method, with the existing geological, openhole, core analysis and performance data.
An Experimental Compositional Approach to Study Dynamic Miscibility in Nitrogen Injection in Light Crude Oil
Authors: Alcocer Charles F.
Published: June 2014

Laboratory research was conducted to study displacements of crude oil by high pressure nitrogen injection. The objective of this study was to design and build a physical reservoir model able to simulate reservoir temperature and make possible the collection of sampling during displacement to track the phase compositional changes taking place during the process of building up dynamic miscibility in high pressure nitrogen injection in light crude oil. The reservoir model was a stainless steel tube 125 feet long and 0.435 inches in diameter, packed with sand consolidated to give an average permeability of 930 md. The model was provided with five sampling valves to collect vapor samples during actual nitrogen displacement. Continuous sampling during displacement provided material for chromatographic compositional analysis, construction of profiles of component by component to establish their role in the building up of dynamic miscibility, construction of ternary diagrams to follow the process and way to predict the so-called multicontact miscibility in high-pressure nitrogen injection. Results of 4 dynamic tests are presented. All tests were performed above the minimum miscibility pressure using 42 API petroleum fluid. The analysis of the results shows very clearly that the composition approach to explain the three different zones that are created in a displacement of this nature is technically sound. The first zone was identified by analyzing produced fluids. The second zone was identified as a two-phase flowing zone and is the result of nitrogen being initially immiscible with reservoir light crude oil. Analysis of the shape of compositional profile curves suggested that vaporization is very strong at the beginning of the process and at the leading edge of the second zone. The slope of straight lines of composition profiles are direct consequence of vaporization rate. The third zone is one-phase flowing zone. If miscibility is built up it would be created in the leading edge of zone two of the displacement. This was the case for all tests run in this study.
Cement Bond Logging - A New Analysis to Improve Reliability
Authors: Gai H , Lockyear C F
Published: June 2014

Since the CBL tool came into use over 30 years ago, Bond Index (BI) has been the most important parameter in interpreting a valid log. In recent years, more and more engineers started disbelieving the CBL because they found that the BI did not often tell the truth. Several investigators have been tackling this problem, but its complexity seems to have been overwhelming.

Fundamental studies have been carried out in the BP Research centre, Sunbury UK. It was found that the BI was obscured by the "engineering treatment" of attenuation rates which does not have correct theoretical grounds or physical intuition. This paper analyses BI and its related topics, and derives the Bond Percentage Index (BPI) which is accurate and reliable in predicting the bond conditions. It is concluded that BPI is the correct description of reality and BI, being derived on false basis, should be abandoned.
A Correlation for Miscible Flood Displacement Efficiency in the San Andres With NMR Relaxation
Authors: Hazlett R. D. , Furr M. J. , Navarro R.
Published: June 2014

A set of San Andres crystalline dolomite cores was examined for the relationship between pore attributes discernible from NMR relaxation and miscible flooding displacement efficiency. A strong correlation was observed between the inferred abundance of long relaxation time components and laboratory measured residual oil to a multicontact miscible displacement process. NMR relaxation time distribution proved to be a simple, noninvasive, nondestructive indicator of flow performance in the 12 San Andres dolomite samples examined.

Spin-lattice relaxation measurements were conducted on clean, brine saturated core end pieces from plugs taken adjacent to those used for flow displacement studies. Sample data were deconvoluted into a distribution of relaxation times, which is intimately related to surface-to-volume ratio distribution. The median relaxation time was determined to be the most sensitive statistic to convey flow performance. Residual oil saturation was adequately represented by a power law function of the median relaxation time.

Relaxation time is recognized to be a function of pore size, shape, surface roughness, and mineral composition. It was determined through direct observation by scanning electron microscopy that variation between samples was principally due to pore size distribution. Samples with larger mean pore size were observed to be less efficiently swept. Larger pores within a distribution are envisioned to bias individual fluid flow pathways, causing significant stranding of oil.
Interfacial Tension Measurement of Oil-Water-Steam Systems Using Image Processing Techniques
Authors: Huygens R. J. M. , Boersma D. M. , Ronde H. , Hagoort J.
Published: June 2014

To study the assumed correspondence between increasing spreading coefficients and decreasing residual oil saturations during steamflooding, knowledge of the spreading behaviour is essential. In this paper, the emphasis is on the accurate measurement of interfacial tensions (IFTs) that are required for the determination of spreading coefficients. With the pendant drop method in combination with image processing techniques, which considerably improve the quality of the measurements, we examined several calculation methods for determining the IFT from processed drop images. A new direct calculation method is less time-consuming than existing methods, but more sensitive to the quality of the experimental data. We applied the experimental procedures to three oil-water and oil-steam systems. The results show that the interfacial tensions of these systems tend to decrease with increasing temperature. Calculation of the spreading coefficients shows that accurate IFT-measurements are of paramount importance and that n-tetradecane spreads on water in the presence of steam in the temperature range investigated.
Polymer-Enhanced Foams Part 2: Propagation Through High-Permeability Sandpacks
Authors: Sydansk Robert D.
Published: June 2014

In this Part 2 paper on the initial laboratory study and development of polymer-enhanced foams (PEFs), the performance (effective viscosity and mobility control), propagation, and stability of relatively small (0.2 PV) PEF banks (slugs) were studied as they were flooded through long (20 ft), slim-tube-type, high-permeability sandpacks.

The objective of this study was to investigate the performance of PEFs under more demanding experimental conditions than the laboratory studies reported in the Part 1 paper of this series. Another explicit goal of this work was to study the performance of PEFs in the presence of crude oil.

Results of constant-differential-pressure flooding experiments, conducted at ambient conditions, showed that small (0.2 PV) PEF banks were propagated, were stable, and promoted relatively large effective viscosities and good mobility control during flow through the entire length of the 20-ft-long sandpacks. The high-permeability sandpacks were intended to be a one-dimensional model of a propped fracture. The standard PEF formulation of this study was shown, during these flooding experiments, to perform much better, to be much more propagatable, and to be much more stable than its counterpart conventional foam. The PEFs were also shown during these experiments to be much more stable and functional in the presence of the studied crude oils than their counterpart conventional foams.

Aging in a sandpack for 20 days after the PEF bank had been initially injected had little impact on the performance, propagation, and stability of the standard PEF. The PEFs were shown during these flooding experiments to be able to effectively mobilize and recover crude oil, especially a viscous (440 cp) crude oil. Relatively good performance, propagation, and stability of PEF banks during these flooding experiments were observed for PEFs formulated with, respectively, carbon dioxide, nitrogen, and methane. Carbon dioxide PEFs were exceptionally effective at promoting large effective viscosities and good mobility control. In addition, they were especially effective at mobilizing and recovering crude oil. For the PEFs of this study, the minimum effective polymer and surfactant concentrations for effective performance in the presence of a crude oil were determined. Minimum polymer and surfactant concentrations required for effective performance were greater in the presence of crude oil, than in the absence of crude oil.
Scleroglucan Gels for Profile Modifications in High-Temperature Reservoirs
Authors: Fjelde Ingebret , Stavland Arne
Published: June 2014

It is found (hat Cr3+ cannot form gel with scleroglucan. Using dichromate, Cr2O72−, it is found that dichromate has to oxidize alcohol groups on the scleroglucan molecule to carboxyl groups, before Cr3+ crosslinking is possible. The thermal stability of these gels is a function of the amount of dichromate added, because less thermal stable carboxyl groups are formed on the scleroglucan molecule.

Melamine-formaldehyde resins crosslink polyols like scleroglucan without any derivatisation of the polymer.
A Note On Pressure-Transient Analysis Of Fractal Reservoirs
Authors: Chang Jincai , Yortsos Yanis C.
Published: June 2014

In a recent paper1 we introduced a novel approach for the identification and description of a fractal reservoir using concepts from fractal geometry. However, the analysis presented in Ref. 1 was unduly restrictive and suffers from two drawbacks: First, it is based on the use of a generalized diffusivity equation, the validity of which has been the subject of recent debate.2 In that formulation, the diffusivity was taken to be position-dependent. This reflects the long memory associated with random walks (diffusion) on fractal objects. Alternative approaches in anamalous diffusion have also been used, e.g. with time-dependent diffusivity, or with the use of an integro-differential equation (see Ref. 3 and references therein). Second, as in all formalisms, the underlying assumption is that of a single source (well) in an unbounded medium. As a result, the equation cannot be directly extended to many wells and variable rates as is the case with normal diffusion. Although generalized diffusivity equations have also been used in other fields involving fractals4 it appears that alternative approaches based on Green's functions are more appropriate. It is the purpose of this note to provide such an alternative and to clarify certain issues related to the description of single-phase, slightly compressible fluid flow in fractal reservoirs.

We emphasize from the outset that as in Ref. 1, finite effects are not considered in this note. This presupposes a reservoir which is fractal over a wide range of scales, such that upper and lower cutoffs are greatly separated. The implication is that effects of boundaries are absent. Our recent numerical results5 have demonstrated that finite size, namely boundary, effects affect significantly the late-time behavior and must be carefully differentiated from the purely fractal response. Nonetheless, developing the proper formalism for an unbounded (theoretical) fractal is still desirable to serve as a guide for the more realistic finite size cases. In fact, it is only outside of boundary effects that a fractal response can be clearly identified.

In theory, fractals obey power-law scaling around an arbitrary point. In particular, properties, such as permeability, are scale-dependent with the same exponent at any location. Consider then the pressure response in such a fractal reservoir at location x due to n wells located at x_i(i =1, 2, …, n), and producing at rate qi(t) (where qi may also be negative). The solution of this problem can be obtained in terms of the free space Green's function g(ξ_−ξ_′,   t−t′), which represents the response at point ξ_ and time t due to an instantaneous point source at point ξ_′ and time t′. Because of the linearity of the process, a simple superposition gives the result
On-Site Real-Time Analysis Allows Optimal Propped Fracture Stimulation of a Complex Gas Reservoir
Authors: Johnson D. E. , Wright C. A. , Stachel Alfred , Schmidt Holger , Cleary M. P.
Published: June 2014

In order to increase gas production in an under-producing formation, the German utility/eneigy company RWE-DEA stimulated the Wardboehmen Z1 well with a propped fracture treatment on December 6, 1991. Two days prior to the main fracture treatment, a step-rate test and mini-fracture were pumped for the purpose of evaluating more accurately the characteristics of the reservoir, including closure stress, leak-off rates, and permeability (and stress) profile. This information was then used to substantially improve the originally proposed design, provided by the service company, in order to create an effective/optimal propped fracture in this reservoir, incidentally also producing major savings in job cost. For the first time in Germany, electronic bottomhole pressure-measuring equipment with surface readout was used, during the minifirac. Availability of the bottommhole pressure data in the minifrac and repeated abrupt flow-rate changes, including shut-ins of about one minute, during both the minifrac and main fracture treatment allowed realistic simulation of fracture development with an on-site real-data 3D simulator. It was possible to determine the continually changing friction losses in the near-wellbore vicinity of the perforations: this tortuosity was very high initially but reached acceptable values after pumping the re-designed pad volume. This finding was important because it minimized the risk of a premature nearwellbore screen-out resulting from the planned proppant concentrations, up to 1,250 g/1 (10 ppg). The fracture treatment led to a consistent four-fold increase in the gas production rate. This success was due, at least partly, to careful planning and use of novel technology in the fracture treatment, which allowed the on-site determination of actual reservoir conditions, with growth influenced by extremely variable permeability as against idealized models used for initial design.
Darcy Flow Dissipation in Petroleum Reservoirs and the Productivity Index
Authors: Inayat-Hussain A. A. , Buckingham M. J.
Published: June 2014

The conventional definition of the productivity index is ambiguous under some conditions. Similar difficulties have long been resolved, for the case of electrical conduction in continuous media, in terms of a dissipation function. Consideration of the energy dissipation in steady Darcy flow in a reservoir yields a new and more general definition of the productivity index (PI) as the ratio of the square of the petroleum production rate to the total energy dissipation in the reservoir. This definition leads to an unambiguous interpretation of the flowing pressure which appears in the conventional definition of the PI. The dissipation approach also yields the conditions which maximize the PI for production from a single well and from multiple wells in a reservoir.
Novel Approaches to the Determination of Archie Parameters I: Simplex Method
Authors: Chen D. S. , Fang J. H. , Kortright M. E. , Chen H. C.
Published: June 2014

The Nelder-and-Mead simplex method is employed to obtain optimal sets of parameters (m, n, a) used in the commonly used form of Archie's equation. This derivative-free optimization method avoids trapping by local optima. We have found that the method is very effective, highly efficaceous, and easily implemented on a PC. The agreement between the results obtained from this method and those from the nonlinear least-squares approach is remarkable. A comparison paper addresses the same problem via fuzzy regression.
Application of Human Health Risk Assessments in Oil and Gas Production
Authors: Ulrich G. A. , Agnew W. W. , Proctor D. M.
Published: June 2014

This paper illustrates the use of a health-based risk assessment in the investigation and closure of surface impoundments at an oil and gas production site. The risk assessment demonstrated that removal of contaminated soils would not be required to protect human health under future use conditions. As a result, the regulating state agency agreed that soil removal was not required, which resulted in significant cost savings over previously proposed remedial action plans.
A Laboratory Study of New, Surfactant-Containing Polymers for High Salinity Reservoirs
Authors: Uhl J. T. , Ching T. Y. , Bae J. H.
Published: June 2014

To overcome the deficiencies of partially hydrolyzed Polyacrylamides, viscosity loss at high salinity and poor injectivity at high injection rates, terpolymers having ionic surfactant side chains were synthesized. It was conceptualized that brine tolerance can be obtained by a salt-induced, surfactant side-chain aggregation mechanism. Experimental results show that these new polymers develop higher solution viscosities and screen factors than conventional Polyacrylamides in 0.5 to 30 wt% NaCI brines. These polymers have better injectivity due to their shear-thinning properties and lack of the viscoelastic effect at high injection rates.
Asphaltene Precipitation and Crude Oil Wetting
Authors: Buckley Jill S.
Published: June 2014

Precipitates that form as the result of interactions between an asphaltic crude oil and low molecular weight paraffin solvents can remain suspended in the oil phase, rather than being adsorbed onto solid surfaces. Adsorption may be restricted to surfaces made oil-wet by oil/brine/rock interactions prior to precipitation. Visual observations show that the wateirflood displacement mechanisms after asphaltene precipitation are similar to the mechanisms of displacement of the unprecipitated crude oil. Trends of wettability alteration in a Berea sandstone core, as measured by the Amott method, are shown to be similar, whether the test is performed with the crude oil or with a low-molecular weight paraffin oil with which the crude oil may be incompatible.
Transient Analysis of Variable Rate Tests for Solution Gas-Drive Reservoirs
Authors: Camacho R. , Vésquez M. , Roldan J. , Padilla R. , Macías L.
Published: June 2014

Most of the work on variable rate-variable pressure tests that is available today is related to single-phase systems. The purpose of this study is to examine variable rate-variable pressure tests (VRT), during the transient period, considering multiphase flow effects in the reservoir for solution gas-drive systems.

The only procedures present today to evaluate VRT run under multiphase flow conditions use either pressure drop, pressure squared, or pseudopressure function. The first two approaches are empirical in nature and their use is restricted. The direct use of pseudopressure approach is more general but it requires the availability of representative relative permeability data.

This paper presents methods that permit the determination of the mechanical skin and sandface effective permeabilities. These methods are derived from the pseudopressure function but they require only traditional information, i.e. rate and wellbore pressure versus time. The expressions developed in this study are useful for both single-phase and solution gas-drive systems. Synthetic and field data are analyzed to illustrate the use of the techniques developed in this work.

Rate normalization, using pressure and pressure squared drop, and the use of superposition principle are analyzed, and their advantages and limitations under multiphase flow conditions are compared to the methodology presented in this study.
New Approaches for Robust Nonlinear Parameter Estimation in Automated Well Test Analysis Using the Least Absolute Value Criterion
Authors: Rosa Adalberto J. , Horne Roland N.
Published: June 2014

In this study new robust algorithms for automated well test interpretation are proposed. The robustness of the new procedures lies in the fact that the techniques can handle well cases in which the errors do not follow the usually assumed Gaussian distribution or cases in which outliers are present, as opposed to least-squares minimizations. Also, the proposed methods are robust due to the fact that they can converge faster and from initial estimates for which previously reported methods would diverge.

The first method presented in this study is referred to as the MLAV (Modified Least Absolute Value) method. It consists of an iteratively reweighted nonlinear least-squares, where in each iteration the weighting factors are the inverses of the absolute values of the residuals obtained in the previous iteration. This procedure was found to be resistant to outliers and also to converge from poor initial estimates for the unknown parameters. One defect of this technique, although not a major concern in well test applications because usually the computational time is small, is that it tends to behave like a steepest-descent type of method, producing large decreases in the objective function during the first iterations but requiring many iterations before converging to the minimum of the objective function.

Because of the relatively large number of iterations required by the MLAV method, a second approach is suggested in this work. This second technique uses the reweighted nonlinear least-squares (MLAV method) during the first few iterations, and the LAV (Least Absolute Value) criterion thereafter. This combined approach is referred to as the MLAV-LAV method.

Examples of application indicated that the second proposed method (MLAV-LAV) combines the robustness of the least- squares type of methods, in terms of convergence from poor initial estimates, with the robustness of the least absolute value criterion, in terms of low number of required iterations and resistance to outliers in the data.
Oil/Water Relative Permeability Estimation From Fall Off Tests
Authors: Puntel de Oliveira E. A. , Serra K. V.
Published: June 2014

A methodology to design and analyze fall off tests based on works presented in the literature is proposed. Moreover, analytical solutions and pseudo-skins of three injection models are compared, and a new method to estimate relative permeability curves from fall off tests is presented
Enhanced Oil Recovery Pilot Project, Catriel Oeste Field
Authors: Gagliano A. J. , Lasalle D. D. , Olivo J. A. , Sabas R. A. , Ali S. M. Farouq
Published: June 2014

In terms of improving oil recovery in Catriel Oeste Field, a project was undertaken to determine the feasibility of applying an Enhanced Oil Recovery process by Polymerflood. A pilot was selected in two productive reservoirs projecting to start with polymer injection on August 1993.

This paper describes the studies made for the pilot design and the conditions in which it will set, taking into account aspects as reservoir characteristics, present conditions, laboratory testings and a brief description of the facilities.
An Integrated Approach To Interpret and Quantify Cusiana Hydrocarbon System
Authors: Lee S. T. , Gomez P. A. , Toczylkin L.
Published: June 2014

This paper presents PVT properties and phase behaviour of Cusiana hydrocarbon system. The interpretation and quantification of the hydrocarbon system was made possible through an integrated program involving fluid sampling, laboratory fluid analyses as well as equation-of-state (EOS) prediction. In the light of the complex fluid system encountered, it was found important to have a developed EOS to guide welltesting, perforation selection and laboratory programs.

The Cusiana hydrocarbon system contains favourable thermodynamic factors (composition, pressure and temperature) for a gas injection process to improve hydrocarbon recovery. Laboratory fluid work, including swelling, multiple-contact and gasflooding in reservoir cores, demonstrated that efficient recovery can be achieved through a vaporization mechanism. EOS compositional simulations were also conducted to validate the EOS model and to further investigate the recovery mechanisms.