bluuebunny/crossref_metadata_2025_split huggingface dataset:
Use of Fluorochemical Surfactants in Nonaqueous Stimulation Fluids
Authors: Clark Henry B. 
Published: December 2007

This paper discusses a fluorochemical surfactant that is surface-active in hydrocarbon liquids such as kerosene and xylene and can function as an effective foaming agent for these liquids. A new apparatus for evaluating foaming capability in the laboratory is described, and data for hydrocarbon liquids foamed with this surfactant using this apparatus are presented. Field tests are described.

Introduction
Various types of foamed aqueous stimulation fluids have found considerable use in the oil field, but in many instances water can damage a formation, and foamed hydrocarbon liquids would be preferable. In addition, there are cases where foaming of hydrocarbon solvents would make them more efficient and where condensate removal by foaming would be desirable.A fluorochemical foaming agent has been developed which is capable of foaming nonpolar hydrocarbon liquids such as kerosene, xylene, and condensate for a variety of oilfield applications. This fluorochemical, identified as FC-C in this article, is a mixture of nonionic fluorochemical surfactants belonging to the chemical class of fluorinated alkyl esters. Other fluorinated alkyl esters were less effective in foaming nonpolar hydrocarbon liquids, but some showed greater surface tension reduction in hydrocarbons and some foamed alcohols. Laboratory foaming data on FC-C, and three field tests illustrating various applications of this foamer, are discussed.

Laboratory Experiments
To study the foam-generating capabilities of this fluorochemical surfactant, a foam generator was constructed; the apparatus and experimental procedure for its use are discussed in detail in Ref. 4. This equipment and procedure appear to provide a valuable and reproducible method for determining the foaming characteristics of liquids.Using this apparatus, the procedure to test foam consists of placing a liquid in a suitable vessel so it can be subjected to a constant pressure of 150 psi (1 MPa), passing the liquid through an aspirating inline generator, and collecting the foam in a tared graduated cylinder for measurement of foam quality and half-life. Foam quality is defined as percent by volume of gas phase in the foam, and half-life is defined as the time required for one-half of the liquid in the foam to drain from the foam, regardless of whether the foam actually breaks or simply drains.Using this procedure, hydrocarbon liquids were foamed using FC-C, and foam data are summarized in Table 1. For comparison, this table includes equivalent data for an aqueous foam generated by this same procedure, using a well-known aqueous foamer (Adofoam BF-1(TM) from Nalco Chemical Co.). It is evident that under these conditions, FC-C at 0.1% (solids) foams kerosene and diesel oil about as effectively as the aqueous foamer foams water at 0.5% (solids). It also produces good foam in xylene and fairly good foam in 55 degrees API gravity (0.75-g/cm3) condensate but does not foam hexane.
JPT
P. 1695＾
Gannet E Subsea ESP: The Application of Technology in Practice
Authors: Harrall S. J. , Nevelsteen D. 
Published: December 2007

Summary
The Gannet E single-well subsea electric submersible pump (ESP) development has been onstream since January 1998. This is the first such installation in the North Sea and only the third development of its kind in the world. At a 14-km step-out from the Gannet Alpha platform, Gannet E represents a world record in terms of electrical transmission distance for such developments. Since startup, flow rates of 18,000 barrels of oil per day (BOPD) have been sustained while valuable operating experience has been acquired in a relatively short time. During the project planning and execution phases, emphasis was placed on anticipating potential operational pitfalls that could jeopardize the overall success of the development. Areas of concern lay in the fields of
ESP control and run life. Control of the platform facilities. Electrical power transmission. Data gathering. ESP flexibility with respect to flow rates and required delivery pressures. Reservoir-related uncertainties. Well completion installation.
This paper describes the technology and techniques applied to maximize the safeguards in the overall system integrity and to deliver a robust development. Actual startup and running experience is discussed in relation to the planning effort. Attention is paid to trip analysis and evaluating operability limits over the whole system. Major learning points that are being carried into further projects of this nature are also presented.
Effect of Viscosity on Downhole Gas Separation in a Rotary Gas Separator
Authors: Lackner G. , Doty D. R. , Shirazi S. A. , Schmidt Z. 
Published: December 2007

Summary
Electrical submersible pump (ESP) installations are commonly used in the oil industry to aid fluid flow from the reservoir to the surface. As with any pump, the presence of free gas at the pump intake can adversely affect the operation of an ESP. One method of reducing the amount of free gas the pump has to process is to install a rotary gas separator.
In this work, the effect of viscosity on the separator's performance is investigated. New experimental data were gathered that covered a broad range of operational conditions in terms of pressures, liquid flow rates, gas-liquid ratios (GLRs), and rotational speeds. The experiments were conducted on a field-scale experimental facility with a commercially available separator. The working fluids were water, two mineral oils, and air. An existing mechanistic model (based on physical principles) predicting the bottomhole gas-separation efficiency in ESP installations was then evaluated with the data. Based on this investigation, improvements were implemented in the model to better capture the influence of viscosity on the downhole gas-separation process.
The results of the study indicate that there are two regions of separation efficiency with a pronounced transition between them: one region in which the rotary gas separator is very effective (separation efficiencies between 80 and 100%), and the other in which it is not effective at all (separation efficiencies between 30 and 55%). The transition location depends on the fluid physical properties, operational conditions, and geometry of the separator. The mechanistic model can predict this behavior and agrees well with the data that are obtained during this investigation. Fluid viscosity in the range of investigation (1 to 50 cp at 100°F) is found to have only little influence on gas-separation efficiency. This may indicate that the effects of turbulence at high rotational speeds dominate the behavior of flow inside the separator.
A Case History for Massive Hydraulic Fracturing the Cotton Valley Lime Matrix, Fallon and Personville Fields
Authors: Kozik H.G. , Holditch S.A. 
Published: December 2007

Summary
This report summarizes the results of an active stimulation program on the Cotton Valley Lime as evaluated using reservoir production and pressure transient data. Using standard economic parameters and reservoir permeabilities determined by history matching, a detailed study was made to determine the well spacing and fracture length radius necessary for optimum development of the Fallon and North Personville fields.

Introduction
Considerable emphasis has been placed in recent years on recovering gas from "tight-gas" basins. One step that shows promise for unlocking tight gas is massive hydraulic fracturing (MHF). A case in point is the evolution of the stimulation in the Cotton Valley Lime at Fallon and North Personville fields, about 10 miles southeast of Mexia in Limestone County, TX (Fig. 1).The Jurassic Cotton Valley group on the west flank of the East Texas basin generally consists of a succession of about 1,000 ft of terrestrial and marine sands and shales, 800 ft of dark (Bossier) shale, and 300 to 500 ft of limestone at the bottom known as the Cotton Valley Lime or Haynesville. The group covers more than 250,000 sq miles in the East Texas basin and adjacent parts of Louisiana and southeast Arkansas.The Cotton Valley Lime in the Fallon and North Personville area has been a known gas area since its discovery in 1969. However, its poor permeability pay at a depth of about 11,000 ft had produced at rates too low for commercial development under the price schedules and technology of the past decade. Due to fracture porosity, beginning rates were moderately good (1 to 4 MMcf/D), but the natural fracture system was not sufficient to maintain the high rates of flow; consequently, the rates dropped to 0.200 to 0.500 MMcf/D in less than 2 years.Lately, advances in stimulation technology and improved economic incentives renewed interest in this area. Conventional acid stimulations and small fracturing jobs brought some improvement. Bigger fracturing jobs brought further improvement, but MHF appears worthwhile.These are the objectives of this report:1. Document the evolution of stimulation technology of the Cotton Valley Lime at the Fallon and North Personville fields.2. Using a computer reservoir simulator, history match the production and pressure transient data of the Muse No. 1 well before and after MHF and determine the uniqueness of this solution.3. History match the production of the Muse-Duke No. 1 after a super-MHF treatment.4. Optimize the development of the Cotton Valley Lime reservoir with respect to fracture length and well density using reservoir data and economic guidelines.5. Document the design of a super-MHF job (see Appendix).

Reservoir Characteristics Rock Parameters
The Cotton Valley Lime formation is generally gray, massive, oolitic to pistolitic, and finely crystalline to micritic. The better porosities appear to be related to the oolitic zones, ranging from 2 to 12% with some local thin zones of 14%.
JPT
P. 229^
Analysis of Dynamic and Static Foam Behavior
Authors: Lord D.L. 
Published: December 2007

Summary
An equation of state describing pressure, volume, and temperature interactions of compressible foam is presented. Also shown is how this equation of state, when used in a unique solution of the mechanical energy balance for compressible-fluid flow, permits prediction of static and dynamic foam properties. A fracturing-treatment case history is presented for illustration.

Introduction
Low-permeability gas reservoirs are noted for their retention of water-base stimulation fluids within the matrix following treatment. In addition to retaining treatment fluids, many low-permeability formations are underpressured and water sensitive, creating other possibilities for matrix damage from exposure to water-base treatments. Such conditions indicate the need for a stimulation fluid, other than a hydrocarbon, which has a low water content. Foam has fulfilled that need because, on a volume basis, it is composed of a larger percentage of gas than liquid. Typically, foams used for fracturing and fracture acidizing contain 65 to 80 vol% gaseous nitrogen. Several foam fracturing treatments have placed proppant using a liquid phase composed of a 50/50 mixture of water and methanol. Such treatments further limit matrix exposure to a possibly damaging water phase. Compressible fluids, as a class, normally are considered gases; gases are considered Newtonian fluids. If corrections are made for acceleration losses and provisions made for variable density, it is found that gases follow Newtonian-fluid laminar and turbulent flow relationships. Gas viscosity changes are small compared with density changes that occur with changes in pressure. Foam is composed of gas bubbles, which are dispersed uniformly throughout a continuous liquid phase, and can be treated as a homogeneous fluid with both variable density and viscosity. When considered such a homogeneous fluid, foam is probably the only known compressible non-Newtonian fluid.

Theory
This section presents a state-of-the-art report on equations of state and flow equations for foam. Very few references to an equation of state for foam appear in the literature. However, a number of available references provide methods of estimating dynamic foam behavior.

Equation of State
Ross proposed an equation of state for foam in the following form.
(p ............(1)
Eq. 1 offers little from an engineering viewpoint because it is difficult to determine values for such parameters as Pgf, and . However, this equation does provide considerable understanding of foam physical properties. For example, if Eq. 1 is rearranged to the form
...(2)
we find that interfacial area per unit volume is determined uniquely by (1) the average excess pressure of gas within the foam above that of the surroundings and (2) liquid surface tension. In addition to this equation of state, Ross provides a guide to other foam behavior and to foam morphology.
JPT
P. 39^
The Effect of Fluid Leakoff on Gel Placement and Gel Stability in Fractures
Authors: Ganguly S. , Willhite G. P. , Green D. W. , McCool C. S. 
Published: December 2007

Summary
Chromium acetate-hydrolyzed polyacrylamide gel systems are applied in fractured reservoirs for conformance control. A portion of the gelant leaks off into the adjoining matrix during placement of the gelant in the fracture. This paper describes an experimental study on the effect of fluid leakoff on the performance of a gel treatment. The stability of a gel that is placed in a fracture and is subjected to a pressure gradient was also investigated.
Physical models of a fracture were developed to conduct displacement experiments. The models were fractured Berea sandstones designed to permit leakoff of the gelant into the matrix on the sides of the fracture. A polyacrylamide-chromium acetate gelant was injected into the fracture under conditions in which there was leakoff and no leakoff into the matrix. A gel did not form, and the gelant was easily displaced from the fracture by subsequent brine injection when the gelant was placed without leakoff. When the gelant was placed with leakoff, a gel formed in the fracture after placement and provided significant flow resistance. It is hypothesized that the lack of gelation in the absence of leakoff was caused by diffusion of chromium from the fracture to the matrix. Diffusion reduced the chromium concentration in the gelant to levels at which gelation would not occur when the gelant was placed without leakoff.
It was discovered that gels that were formed in a fracture ruptured when a brine pressure was applied at the inlet. The pressure where rupture occurred was determined for gels placed in tubing of various lengths and diameters. The rupture pressure was proportional to a length/diameter ratio.
Some Results From Continuum Mechanics Analyses of the Hydraulic Fracturing Process
Authors: Hanson M. E. , Shaffer R. J. 
Published: December 2007

Abstract
We are developing and applying theoretical, numerical models to analyze the hydraulic fracturing process. Applications include fracturing near interfaces, effects of existing fractures near interfaces, pore-pressure effects, and stress-field changes due to embedded lenses. For a well-bonded interface, the calculations indicate that the stress-intensity factor of the leading crack tip decreases as the crack approaches a higher modulus material. As the tip crosses the interface into the higher modulus material, the stress-intensity factor abruptly increases to a higher value than it had in the lower modulus material. When the situation is reversed, the intensity factor increases as the tip approaches the interface and then abruptly decreases when the tip crosses the interface. Further calculations show that when existing cracks are present near the interface, the effects of the change in material properties across the bonded interface are reduced. In addition, our analysis shows that increases in pore pressure due to leakage of fluids from the fracture into the surrounding media causes the stress-intensity factor to drop; a decrease in the stress-intensity factor means a reduction in the tendency to break. In other calculations we analyzed the stress-field disturbance caused by lenses of one material that are embedded in another material. These calculations show that in regions that are not tectonically relaxed, the stress field is modified by the lenses. We conclude that the fracture geometry is modified by the presence of embedded lenses under these conditions.
Interpretation of Radioactive Marker Measurements To Evaluate Compaction in the Northern Adriatic Gas Fields
Authors: Ferronato M. , Gambolati G. , Teatini P. , Baù D. 
Published: December 2007

Summary
The radioactive marker technique (RMT) appears to be a promising tool to evaluate the in-situ uniaxial vertical compressibility cM of deep producing gas/oil reservoirs. However, when the field consists of multipay layers with the porous-medium heterogeneity scale smaller than the marker spacing (10.5 m), great care must be exercised in the interpretation of an RMT survey. If the monitored depth interval incorporates thin clayey layers or the measurement is made in an active pumping well, cM can be grossly underestimated. Moreover, rock may expand, with the expansion correctly recorded by RMT. In the present paper, a set of RMT measurements made by Eni-E&P over the past decade in three deep boreholes of the Northern Adriatic basin are simulated with the aid of a 3D poroelastic model solved by finite elements (FEs). Use is made of the much detailed lithostratigraphies of the test holes and the cM constitutive equation derived from a previous statistical analysis of the marker data. The modeling results show that the measurements also can be reproduced satisfactorily from a quantitative viewpoint, and they indicate that an efficient marker installation requires that the monitored depth interval be made mostly from an entirely depleted sandy unit, with the markers placed possibly far from a producing well and approximately 10.5 m apart (i.e., the distance between the gamma ray detectors that monitor the marker position). The cM constitutive law used in the numerical analysis is realistically accurate from 2500 to 3000 m depth, while it appears to be underestimated by a factor of 2 between 800 and 1500 m. The measured expansions allow for the assessment of the reservoir cM under unloading conditions. This turns out to be 2.5 times smaller than cM in virgin loading conditions.
An Experimental and Theoretical Investigation of Upward Two-Phase Flow in Annuli
Authors: Lage Antonio C. V. M. , Time Rune W. 
Published: December 2007

SummaryA steady-state mechanistic model is formulated to predict the mixture behavior for upward two-phase flow in concentric annuli. It consists of a procedure for flow pattern prediction and a set of independent models for calculating gas fraction and pressure drop in bubble, dispersed bubble, slug, and annular flow. Some aspects of churn flow are also discussed.Experiments are performed in a 1278 m vertical well and in a small-scale U-tube, which comprises a descending pipe and an ascending annulus. Small-scale data available in the literature were also collected and catalogued.The model is validated against the database. The performance of the model is compared with the performances of other models from the literature. It shows that the proposed model is more accurate than the alternatives.
A Parallel Multiblock Black-Oil Model in Multimodel Implementation
Authors: Lu Qin , Peszynska Malgorzata , Wheeler Mary F. 
Published: December 2007

Summary
In this paper we discuss the multiblock algorithm for an implicit black-oil model as implemented in the multiphase simulator framework of IPARS (Integrated Parallel Accurate Reservoir Simulator). The multiblock algorithm decomposes the simulation domain into multiple nonoverlapping subdomains, or blocks, according to the geometric, geological, and physical/chemical properties, and well distribution. Each block can have its own grid system, and the grids of the neighboring blocks can be nonmatching on the interface, which allows for local grid refinement, or discrete fault or fracture modeling. Adjacent blocks are coupled across the interface by a set of conditions imposing a continuity of both primary variables and component mass fluxes that is realized through the use of special interface mortar variables. The resulting system is solved by an interface Newton procedure. Regularization techniques and preconditioners are proposed to improve the performance of the solver. The multiblock technique is effective and scalable, as shown by our numerical experiments. In addition, we present how the multiblock black-oil model has been used in the coupling of different physical models.
Nonlinear Regression: The Information Content of Pressure and Pressure-Derivative Data
Authors: Onur Mustafa , Reynolds Albert C. 
Published: December 2007

Summary
It is shown that commonly used procedures for estimating parameters by regressing on pressure-derivative data are based on incorrect covariance matrices and thus violate the underlying statistical basis for nonlinear least-squares parameter estimation. Although the resulting estimates of model parameters may be reasonable, calculated confidence intervals are meaningless. Here, we show how to compute the correct derivative data covariance matrix that should be used for estimating parameters by nonlinear least squares. It is also shown that the information content of derivative data cannot be greater than the information content of pressure data, in the sense that regression on derivative data with the proper covariance matrix does not yield smaller confidence intervals than those obtained by regressing on pressure data only. In fact, we prove that matching a data set, including all interior derivative data plus two appropriate pressure points, yields exactly the same estimates and confidence intervals that would be obtained by regressing on pressure data only.
Simulation of Dynamic Foam-Acid Diversion Processes
Authors: Cheng L. , Kam S.I. , Delshad M. , Rossen W.R. 
Published: December 2007

SummaryA new simulator for foam-acid diversion is described. The simulator explicitly accounts for the first time for the effects of gas trapping on gas mobility in foam and in liquid injected after foam and for the effects of pressure gradient on gas trapping. The foam model fits steady-state foam behavior in both high- and low-quality flow regimes and steady-state liquid mobility after foam. Previous laboratory experiments suggested that a relatively slow transition between steady states during foam and acid injection may control the diversion process in the field. The simulator fits this transition period in laboratory corefloods qualitatively with no additional adjustable parameters.Simulations and new data agree that the transition is faster at higher pressure (with lower gas compressibility) and that response to a shut-in period depends on how much gas escapes during the shut-in (i.e., on how long the shut-in lasts). Simulations and data suggest that a dead volume present upstream of the core in previous studies strongly affects the transition period seen in those experiments.