bluuebunny/crossref_metadata_2025 huggingface dataset:
Minimum Miscibility Pressure, Rising Bubble Apparatus, and Phase Behavior
Authors: Mihcakan Metin , Poettmann F. H.
Published: December 2007

The objective of this study was to determine the minimum miscibility pressure (MMP) as a function of temperature using the rising bubble apparatus for a ternary system consisting of CO2, normal pentane, and normal hexadecane. The MMP's were compared and interpreted with the phase behavior of the ternary system. In addition, the MMP was determined for a dead oil of 41.7° API gravity and a live oil having a bubble point pressure of 2266 psia at a reservoir temperature of 240°F for CO2 and CO2 enriched with normal butane.

The MMP's as a function of temperature were determined using a modified rising bubble apparatus (RBA). Bubble behavior was monitored using a motion tracking optical system (MTOS) and a cell pressure data acquisition and monitoring system (CPMS). The MTOS consists of a video camera mounted on a rail table parallel to the path of the rising bubble in the sight gauge (or cell). The magnified bubble image is monitored on a screen and recorded on a video cassette for subsequent viewing. The VCR can playback the recorded image frame-by-frame or at any desired speed for detailed study of bubble behavior and shape. An image processor installed on the computer captures and digitizes selected bubble images that are printed out on a laser printer with high resolution. The CPMS records the pressure behavior in the cell as a function of time as the bubble rises in the oil column and aids in the determination of the MMP.

The MMP measured with the RBA for the ternary system agreed with the MMP as determined from the phase behavior of the ternary system. For the dead oil and the ternary system the MMP measured as a function of temperature terminates at a low temperature at the critical temperature and pressure of the injected gas for both the vaporizing and condensing systems. For the ternary system the MMP as a function of temperature for an enriched gas goes from a multiple contact condensing system to a multiple contact vaporizing system at the temperature where the enriched gas ternary system MMP curve crosses the CO2 -Ternary System MMP curve. At the cross-over temperature and pressure both the liquid composition and the enriched gas composition lie on the termini of the limiting tie line of the ternary system and thus the enriched gas is single contact miscible with the liquid.
A Polymer Thermal Decomposition Model and its Application in Chemical EOR Process Simulation
Authors: Lange E. A. , Huh Chun
Published: December 2007

Accurate assessment of the potential of high temperature chemical flood processes utilizing biopolymers for mobility control requires not only a model of polymer rheology and retention but also a model of polymer thermal decomposition. A detailed model for the thermal decomposition of a polymer flowing in a high-temperature reservoir was developed for use in simulation and several example enhanced oil recovery process simulations were conducted using model parameters obtained experimentally for xanthan biopolymer.

The model consists of three parts. First, a thermal decomposition rate expression for the decline of average molecular weight of polymer was derived from a fundamental consideration of polymer bond breakage. Second, a scheme to calculate the apparent viscosity of polymer in reservoir rock as a function of polymer concentration and average molecular weight was established. Third, a novel simulation scheme was developed that calculates the polymer concentration and average molecular weight as functions of time and position in the reservoir. One advantage of the proposed scheme is that conventional chemical flood simulators can be easily modified to account for the effects of polymer degradation.

Experimental studies to support the model development included measurements of xanthan thermal decomposition rates in brines at low oxygen concentration as well as several other xanthan physical and rheological properties. Results indicated that xanthan decomposition under anaerobic conditions could be modeled as simple random scission of the chain. Average molecular weight could then be directly related to viscosity in the low-shear-rate limit at any concentration through an expression of the Mark-Houwink form and through the empirical Martin equation. The dependence of viscosity on shear rate was described through the Carreau-Yasuda equation and the effects of temperature on the rheogram were predicted with the method of reduced variables. Finally, the viscosity as measured in a viscometer was related to flow properties in porous media through an effective shear rate correlation. Example calculations for a surfactant flood process using this model illustrate quantitatively the impact of high temperature and thermal decomposition on polymer propagation and oil recovery.
Application of Low-Toxicity Crosslinking Systems in Production of Thermally Stable Gels
Authors: Moradi-Araghi Ahmad
Published: December 2007

Earlier reports from our laboratory described a number of thermally-stable water-soluble polymers which tolerate extensive aging times in brines with high salinity and hardness levels at temperatures up to 149° C (300°F). These polymers can be crosslinked with phenol and formaldehyde crosslinking system to produce stable gels under hostile environment conditions typically defined as temperatures higher than 167° F (75° C) and brine hardness levels above 2000 ppm. The resulting gels can be used for profile modification and water shutoff treatments under hostile environment conditions.

In one paper we proposed a mechanism for the gelation of acrylamide containing polymers. This mechanism postulates the formation of salicyl alcohol as an intermediate through the condensation of phenol and formaldehyde. Formation of a thermally stable gel by direct reaction of salicyl alcohol and formaldehyde, with a thermally stable acrylamide containing polymer, is consistent with this mechanism. Concerns about the toxicity of phenol and especially the carcinogenic character of formaldehyde motivated us to search for alternative crosslinkers with lower toxicity, which can be used in place of phenol and formaldehyde to produce stable gels. Through an extensive study, we have identified and tested several compounds which can be used in place of phenol. These compounds include o- or p-aminobenzoic acid, m-aminophenol, aspirin, furfuryl alcohol, methyl phydroxybenzoate, phenyl acetate, phenyl salicylate, salicylamide and salicylic acid. The only suitable compound identified in our study, which can be used in place of formaldehyde and produce stable gels, is hexamethylenetetramine (HMTA), a precursor of formaldehyde. HMTA thermally hydrolyzes to formaldehyde and ammonia at elevated temperatures which will go on to crosslink with acrylamide containing polymers and phenol or its replacements. However, not all formaldehyde precursors can produce thermally stable gels when used in combination with phenol or with an alternative compound to phenol. No suitable gels were produced with glyoxal or 1,3,5-trioxane as formaldehyde precursors.

This paper will describe a number of low toxicity thermally stable gels suitable for applications under hostile environment conditions. The gels described here exhibit a lot of flexibility in terms of gelation time. With the choice of proper crosslinking system, one can produce gels which can set from a few hours to several months. The slower gelation systems could be used for in-depth treatments of hot reservoirs such as those in the North Sea. The bulk gels produced in synthetic seawater or brines containing up to 20% sodium chloride and 2% calcium chloride, have remained stable for several years of aging at 250° F (121° C). This study has only been directed at evaluating thermal stability of bulk gels. The performance of these gels in porous media will be the subject of future studies.
Brine-Initiated Gels: A New Water Shut-Off Agent
Authors: Whittington L. E. , Naae D. G. , Braun R. W.
Published: December 2007

There is increasing concern among domestic operators for reducing water production as fields mature. A new polymer gel, with several unique advantages over conventional gelling systems, has been developed which could serve as a water shut-off agent. The gel forms in place when a freshwater solution of a water-soluble polymer (hydroxypropylcellulose, HPC) and a surfactant (sodium dodecyl sulfate, SDS) mixes with brine. While conventional gels use a chemical initiator or activator, often a heavy metal like chromium, to form the gel, the new HPC/SDS gel uses the salinity of the connate brine to initiate immediate gel formation.

The low-viscosity freshwater HPC/SDS solution injects easily into core material. Upon mixing with the connate brine, a stable high-viscosity gel forms that effectively reduces brine permeability by over 95% in both linear and radial sandstone corefloods. The gel viscosity was measured at about 70,000 centipoise. Permeability reduction is maintained, both in the forward and reverse flow direction, even after several pore volumes of brine flow. In a parallel coreflood test, the gel diverted 90% of the fractional flow of brine.
Progress With Compositional Studies in Heterogeneous Systems for Slightly Submiscible Gas Displacement
Authors: Fayers F. J. , Aleonard Bruno , Jouaux François
Published: December 2007

In this paper we examine factors influencing the characteristics of slightly sub-miscible gas displacement of oil in a heterogeneous system. 2D fine grid compositional solutions are obtained using a fast simulator, MORE, on a Cray YMP computer for a stochastically generated heterogeneity distribution. It is shown that only four pseudo-components are needed to represent the phase behavior adequately and that although fairly low interfacial tensions are obtained, there is not a discernible need to modify the immiscible relative permeabilities. Comparisons are made with heterogeneous results based on the simpler first contact miscible assumptions often used in two-component high resolution simulations of viscous fingering. The fully compositional flow is less unstable than its miscible counterpart, but it is found that the latter can be made to reproduce a compositional solution through reducing the mobility ratio from M = 20 to M = 5. A method for determining this effective mobility ratio is described. Cases with gravity give moderate agreement using M = 5, provided an ad hoc adjustment is also made to the gravity number.
Experimental Study of the Parameters Affecting Cutting Transportation in a Vertical Wellbore Annulus
Authors: Belavadi M. N. , Chukwu G. A.
Published: December 2007

Transportation of cuttings is a mechanism which is a vital factor for a good drilling program. Though many researchers have studied different parameters affecting the transportation of cuttings, a system of equations completely describing the mechanism has not been arrived at. Experimental observation of cutting transportation has been the most effective and accurate method to explain the behavior of cuttings and fluids in the cutting transportation mechanism to a realistic degree of accuracy.

To better understand the effects of some of the parameters affecting the cutting transportation, a well simulation unit was constructed and the transportation of cuttings in the annulus was observed in a test section. The effects of fluid and cutting densities, fluid viscosity, cutting size and pipe rotation were studied using Bingham Plastic fluids of four different densities. The data collected were graphically correlated in the form of non-dimensional units with transport ratio, which was used as a measure of the transportation efficiency.

Analysis of the results showed that the ratio of the density difference between the cuttings to the fluid viscosity had a significant effect on the transport ratio. The effect of density alone on the transport ratio was significant but was not as profound as the density to viscosity ratio. The graphical correlation of transport ratio to the drag coefficient helped to illustrate the magnitude of the effect of drag coefficient on transport ratio.
Sunray Gas Plant: A State-of-the-Art Gas Plant Designed for Today's Environment
Authors: Norton D. G. , Maloney J. J.
Published: December 2007

Maxus Energy Corporation's Texas Panhandle Sunray Gas Plant (70 miles north of Amarillo) is unique, in that it utilizes practically every unit operation available to the gas processing industry (Table 1). This permits extensive processing and operating flexibility, and compliance with tighter environmental criteria, while minimizing operating expenses.
An Economic Assessment of Artificial Lift in Low-Pressure, Tight Gas Sands in Ochiltree County, Texas
Authors: Brady C. L. , Morrow S. J.
Published: December 2007

A review of 289 completions in Ochiltree County, Texas, shows 137 classified gas completions currently produce with the aid of artificial lift. Two methods of artificial lift, beam pumping units and plunger lift, were identified in the review. The study revealed that 130 gas wells produce with the aid of a plunger lift, while only 7 gas wells produce with the aid of a beam pumping unit. This paper reports on historical results obtained from using plunger lift systems. The historical results are compared to published methods for predicting liquid loading and plunger lift production responses. An evaluation of the historical plunger lift production responses and installation workover costs show that an impressive 32 BCF of reserves were added at a cost of less than $0.06/MCF.
How To Conduct an Environmental Audit
Authors: Dancy J. R. , Snell G. A.
Published: December 2007

Environmental legislation enacted over the last several decades has produced a complex matrix of regulations. Environmental compliance now represents a significant cost of doing business, both in terms of the cost of compliance and in terms of the possible penalties and fines which could be incurred as a result of non-compliance.

When making informed corporate decisions involving the acquisition and divestiture of oil and gas properties environmental audits can be used to evaluate the compliance status of a facility.1
Advancements in Two-Phase Slug How Modeling
Authors: Fabre J.
Published: December 2007

Since it was presented by Wallis1 the unit cell model for slug flow has proved its superiority in predicting the phase fractions and pressure gradient with a reasonable accuracy. However it relies on some crucial assumptions and on the choice of four closure laws. These fundamental issues are addressed in the present paper.

On the one hand, the closure laws guarantees the accuracy of the model. The scientific papers provide abundance of these laws whose physical value is unequal. The effectiveness and weakness of some of these laws are discussed from a comparison with existing data. Their critical role for certain ranges of flow rates is emphasised.

On the other hand, some specific assumptions limit the potentiality of the model. In particular the fully developed flow assumption in long bubble and liquid slug is discussed. A route to improve the model is explored.
Barriers to Flow in Tidal Sandstone Reservoirs, Sun Ranch Field, Wyoming
Authors: Tillman R. W. , Pittman E. D.
Published: December 2007

Tidal1y deposited valley-fill sandstones, when sourced from the sea, as is the case in Sun Ranch field, Wyoming, generally form sand bodies which contain smaller pores, (finer grained) and contain significantly more pore throat plugging by detrital (and diagenetic) clay than most superficially similar fluvial or distributary channel sandstones. The detrital clay occurs as thin beds, drapes, clasts and "grains." Calculated log porosities are significantly lower where clay occurs in otherwise high quality reservoir sandstones. The quality of the reservoir is commonly masked on logs by the effect of the clay clasts.

Individual tidal valley-fill deposits are demonstrably separable laterally and generally have several locally continuous horizontal shaley beds which form baffles or barriers that slow or prevent vertical flow. These very thin horizontal beds are: (1) dominantly clay and fine sand and silts deposited during marine to brackish flooding events; (2) are easily recognizable in core but not on most logs; (3) have very low porosity and permeability; (4) prevent or deter vertical flow between reservoir compartments and act as baffles to flow; and (5) are the focus of diagenetic clay formation. Because of the significant amounts of clay present in some tidal and tidally-reworked fluvial valley fills, they have significantly lower porosity and permeability and smaller "port sizes" than most fluvial and deltaic deposits.
PDC Bits: What's Needed To Meet Tomorrow's Challenge
Authors: Warren T. M. , Sinor L. A.
Published: December 2007

When polycrystalline diamond compact (PDC) bits were introduced in the mid-1970s they showed tantalizingly high penetration rates in laboratory drilling tests. Single cutter tests indicated that they had the potential to drill very hard rocks. Unfortunately, 20 years later we are still striving to reach the potential that these bits seem to have. Many problems have been overcome, and PDC bits have offered capabilities not possible with roller cone bits. PDC bits provide the most economical bit choice in many areas, but their limited durability has hampered their application in many other areas.
New and Expected Developments in Artificial Lift
Authors: Lea J. F. , Winkler H. W.
Published: December 2007

Artificial lift is a broad subject. This paper discusses some of the new developments in the major areas of artificial lift. These are (1) Beam Lift, (2) Electrical Submersible Pumping, (3) Gas Lift, (4) Hydraulic Pumping and (5) Miscellaneous Topics.

The beam lift discussion concerns a new rod material, downhole measurements for rod loading, unit design and some miscellaneous topics. The ESP (Electrical Submersible Pump) section includes a discussion on solids handling, downhole sensor technology, new motor temperature limitations, motor efficiency, and other topics. The gas lift discussion includes mention of coiled tubing with gas lift valves internal, a surface controlled gas lift valve concept, and gas lift valve testing and modeling. Hydraulic pumping Is used in many locations with deep pay and fairly small production rates. New hydraulic developments include a wider availability of power fluid pumps other than positive displacement pumps, and small jet pumps specifically designed for de-watering gas wells. Some miscellaneous developments include an insertable PC (progressing cavity) pump and improved plunger lift algorithms and equipment.
Avoiding Hydrates in the Petroleum Industry: Kinetics of Formation
Authors: Christiansen R. L. , Bansal Vibha , Sloan E. D.
Published: December 2007

Natural gas hydrates significantly impact the economics of development of off-shore hydrocarbon resources in deep water. Methods for avoiding hydrates that depend on kinetics of hydrate formation may replace thermodynamic methods. Hydrate growth rates measured on a quiescent drop of water were found to agree qualitatively with rates measured in a vigorously stirred reactor when normalized with respect to the area of contact between the gas and the liquid, or liquid suspension of hydrates. The Gibbs free energy change for hydrate formation is shown to be a good estimate of driving force for hydrate growth. Hydrate growth rates per unit area correlate with the driving force. Driving force calculations suggest that hydrate structures other than the thermodynamically favored structures may form.
Rock Mechanics Characterization of Deep Formations: A Technico-Economical Overview
Authors: Santarelli F. J.
Published: December 2007

Rock mechanics is a central component of many oil industry problems. The correct rock mechanics characterisation of formations in terms of behaviour is thus of paramount technical and economical importance. State-of-the-art characterisation relies upon core testing. After emphasizing the limits of such methods two field cases are used to show that the operational timing of the characterisation is of fundamental importance. To ensure the characterisation efficiency, it is suggested: i. to use data sources normally available during operation as part of a risk prevention policy; ii. to develop new measuring methods compatible with field practice. For both areas, specific examples are given.
Elastic Moduli In Porous Rocks: A Comparison Of Differential, Poroelastic and Semi-Empirical Models
Authors: Ravalec M. Le , Gueguen Y.
Published: December 2007

Computations of effective elastic moduli of porous/cracked rocks have been performed by using three distinct theories. The first one, the differential scheme, accounts at best for fluid content, crack interactions and connectivity. When compared with the second one (poroelasticity), it gives consistent results for round pores. For a crack porosity, there is also a good agreement for the bulk modulus, but not for the shear modulus. The differential scheme shows that this last modulus depends on fluid properties. The third theory is a semi-empirical model (Bound Averaging Method) which can be calculated explicitly from the differential scheme.
Effects of Rock-Fluid Interactions On ohe Petrofabric and Stress-Strain Behaviour of Mudrocks
Authors: Amanullah M. , Marsden J. R. , Shaw H. F.
Published: December 2007

Uniaxial compression tests and SEM analyses were conducted on Tertiary and Jurassic outcrop mudrocks after exposure to different water- and oil-based fluid phases. The tests were conducted as part of an investigation into the role of rock-fluid interactions on drilling and wellbore problems. It was found that increasing intensity of rock-fluid interactions led to a decrease in brittleness of the mudrocks as well as reductions in their strengths and stiffnesses. Interestingly, on exposure to the most reactive fluids (water and 4% NaCl brine), the more competent Jurassic mudrock experienced a greater percentage reduction in strength than the Tertiary material, even though its clay content comprised a lower proportion of swelling minerals. It was demonstrated that behaviour similar to that seen for the mudrocks in their natural states could also be achieved using selected water based systems as well as oil-based muds.
Experimental and numerical study of crack propagation in sandstone
Authors: Schlangen E. , Van Mier J. G. M.
Published: December 2007

A combined experimental and numerical approach is adopted to investigate crack propagation in sandstone. Experiments on two types of sandstones show a similar behaviour as found in tests on concrete specimens. The heterogeneity of the material in combination with the stress situation, as a result of the applied load, governs the direction of crack propagation. Cracks that develop axe not continuous, but overlaps exist mainly around the grain particles in the material. A simple lattice model, in which the material is schematized as a network of small beams, is adopted to simulate the experiments. Using the simulations caxried out with the lattice model, stable four-point-shear tests were designed. The crack patterns obtained with the model are in good agreement with the experimental observations. However further study is needed to predict the load-displacement response more accurately.
The effect of temperature on rock mechanical properties and fracture mechanisms in source rocks – Experimental results
Authors: Lempp Ch. , Natau O. , Bayer U. , Welte D. H.
Published: December 2007

Triaxial compression tests were carried out on Toarcian source rocks (Lias ε) from South Germany under various temperatures between 20 °C and 300 °C and under drained and undrained conditions. The behavior of the source rocks with high total organic carbon (TOC) is strongly temperature dependent and predominantly plastic at elevated temperatures. Microfracture systems are generated which resemble natural assemblages. The fractures are of tensile nature and related to internal pressure built-up in the pore fluid. The experiments provide new aspects to compaction and fluid expulsion from source rocks.
Size dependency of hollow-cylinder stabiliy
Authors: van den Hoek P. J. , Smit D. -J. , Kooijman A. P. , Bree Ph.de , Kenter C. J. , Khodaverdian M.
Published: December 2007

The hollow-cylinder (HC) test is an important means of assessing openhole stability during drilling, completion and production. This paper reviews experimental and theoretical work aimed at quantifying the size dependency of hollow-cylinder stability. The strength of the size effect appears to depend largely on the initial failure mechanism (whether splitting or shear). The preference for one or the other failure mechanism, in turn, depends not only on the type of material but also on hole size. Quantification of such a preference, as a function of size and material, is considered one of the major challenges in this line of research.
Nonlinear effects in the study of borehole stability
Authors: Pellegrino A. , Sulem J. , Barla G.
Published: December 2007

The purpose of the paper is to describe a damage constitutive model adopted for the description of the nonlinear mechanical behaviour of brittle rocks subjected to different stress paths. The main feature of the model consists in the introduction of a damage tensor which allows for representing stress induced anisotropy effects related to anisotropic crack development and propagation.

The model is used first for the simulation of testing of a hollow cylinder, loaded from the outer boundary. Then, consideration is given to borehole stability, when studying the creation of a circular cavity in a rock mass under a hydrostatic stress field. In both cases, the solution of the problem is attained by using a numerical procedure for the integration of the equilibrium equations. It is shown how the results are dependent upon the stress path associated with the specific problem being analyzed.
X-ray Tomographic Study of the Influence of Bedding Plane Orientation on Shale Swelling
Authors: Cook J. M. , Goldsmith G. , Bailey L. , Audibert A. , Bieber M. -T.
Published: December 2007

X-ray tomography (CT scanning) has been used to monitor, in real time, the damage produced by chemical interaction between drilling fluid and Pierre shale in a model wellbore geometry, under downhole stress conditions. This shale is moderately anisotropic, and the experiments examine the effect of the angle between bedding and wellbore. The swollen zone around the wellbore becomes increasingly asymmetric as the angle between bedding plane normal and wellbore axis increases. Swelling and strength tests on the shale at different orientations are described, and the results related to the damage seen in the wellbore experiments.
Role of Hydration State of Shales in Borehole Stability Studies
Authors: Onaisi A. , Durand C. , Audibert A.
Published: December 2007

When in contact with water-based muds, shales can absorb water and ions that causes serious wellbore stability problems. An efficient stability model should combine together mechanical and chemical effects, but to run such a model, shale mechanical properties and hydration tendency as function of mud composition have to be identified. Characteristics would be determined while shale is under hydration and stress states representative of downhole conditions. A laboratory methodology has been developed to restore initial rock hydration state. Modelling of such experiments points out the existence of a suction pressure that can be wrongly assimilated to a swelling pressure. This paper will contribute to specify the representative experimental conditions and show how rock behaviour can be affected if such conditions are not respected.
The Mechanism of Mud Support Reduction Due to Mud Pressure Penetration
Authors: ETan C. , Rahman S. S.
Published: December 2007

This paper describes the fundamental concept and a mathematical model of the mud pressure penetration mechanism and the associated mud support reduction as the drilling mud invades the rock material. The variation of breakthrough pressure with cumulative pore size distribution of a Cretaceous shale from the North West Shelf of Australia has been quantified for a polyacrylamide, an ester-based and an oil-based mud systems. The results indicate that the improvement in the stability of reactive shale sections drilled with ester-based and oil-based muds may not be due solely to the muds inhibiting the hydration and loss of strength of the shale but also due in part to the comparatively better mechanical support provided by the muds.
A Novel Technique for the Investigation of Drilling Fluid Induced Borehole Instability in Shales
Authors: van Oort E.
Published: December 2007

A new experimental technique for the investigation of drilling-fluid induced borehole instability in shales is introduced. Pressure transmission transients are used to study pressure penetration in shales, the latter being a main shale-destabilising mechanism. The pressure transmission method provides a powerful tool for the fundamental study of shale-fluid interactions and for the development of improved water-based mud formulations to promote borehole stabilisation in shales. The capabilities of the method are illustrated by permeability measurements made in low-permeability shales. In addition, a wide range of conventional and new mud systems is screened and the shale-stabilising performance of these systems is assessed. It is argued that the strategy for promoting borehole stability in shales through improved mud formulation should be based on maintaining pressure isolation between wellbore and formation.
Experimental Study of Sand Production Processes Near an Orifice
Authors: Yim K. , Dusseault M. B. , Zhang L.
Published: December 2007

An experimental study was performed using Ottawa sand and a produced sand. A 3-D semi-analytical flow model was developed to analyze the experimental data. The results show that the ratio of sand grain size and outlet hole size, grain size distribution, and angularity are the most important factors affecting the sand arch stability. Pressure increase mode and pressure magnitude also affect arch stability.
A Model for Borehole Breakouts in Brittle Rocks
Authors: Germanovich L. N. , Roegiers J. -C. , Dyskin A. V.
Published: December 2007

A 2-D model of the mechanism of borehole instability due to crack propagation parallel to the free surface is considered. Pre-existing cracks start to grow under the action of the compressive stress concentrations at the borehole boundary. The interaction with the boundary eventually makes the crack propagate unstably and separate a thin rock layer which subsequently buckles. This initial step of failure slightly moves the borehole boundary, enabling the next crack to propagate. Such a process repeats itself until the change in the borehole shape is sufficient to suppress the unstable phase of crack growth. This is regarded as the ultimate extent of the failure. The smaller the sizes of the pre-existing cracks, the larger the extent. This implies that in the cases when the considered failure mechanism prevails, larger failures can be expected for less microcracked rock masses.
Review of Recent Developments in Fracture Mechanics with Petroleum Engineering Applications
Authors: Shlyapobersky J. , Chudnovsky A.
Published: December 2007

Basic concepts of fracture mechanics are discussed to analyze their applicability in modeling fracture initiation and propagation during hydraulic fracturing and waterflooding. Recent advances in modeling fracture initiation and quasi-equilibrium growth are reviewed. Special attention is given to the role of the process zone in fracturing. Process zone observed in laboratory and field hydraulic fracture experiments may explain the discrepancies between simulated and measured net fracture pressures. Process zone is revealed to be the common critical element for proposed mechanisms used for calibrating hydraulic fracture models. Deterministic and probabilistic mechanisms in fracture phenomena are addressed. Scale and rate effects are discussed.
Reorientation of Propped Refracture Treatments
Authors: Wright C. A. , Conant R. A. , Stewart D. W. , Byerly P. M.
Published: December 2007

Refracture treatments have been effectively used for production enhancement for decades. Typical motivations for refracture treatments include: restoring the fracture conductivity to the (possibly) "damaged" proppant pack of the initial fracture treatment; achieving a longer propped fracture by placing a much larger volume of proppant; or simply achieving a more effective proppant pack through the use of vastly improved fracture design procedures1. This paper describes tiltmeter hydraulic fracture mapping field studies which conclusively document a significant additional motivation for refracture treatments, namely: refracture reorientation. Reorientation of propped refracture treatments allows contact with undepleted reservoir from older existing wellbores, which can restore production to near initial rates.
Coupled Geomechanical, Thermal and Fluid Flow Modelling as an Aid toIimproving Waterflood Sweep Efficiency
Authors: Heffer K. J. , Koutsabeloulis N. C. , Wong S. K.
Published: December 2007

Generic studies, involving coupled geomechanical, thermal and flow modelling, together with empirical field data, have elicited the concept that preferred directionality in oilfield waterflooding is stress-related and progressive with time. Specific field applications have illustrated the importance of mechanical and hydraulic interactions between wells, and of the characteristics of natural fractures.
Propagation/Recession of a Penny-Shaped Fracture in a Permeable Diffusive Formation
Authors: Abousleiman Y. , Yuan Y. G. , Roegiers J. -C.
Published: December 2007

This paper examines the poromechanics-related aspects in the propagation/recession of an axi-symmetric hydraulic fracture. Using a penny-shaped geometry, the fluid leakoff is modelled as a pressure-dependent phenomenon coupled with the poroelastic stresses induced by changes of the porepressure. The system of equations that couples the formation poroelastic response with the flow of a Newtonian or power law fluid in a fracture is described. The fracture model is formulated in a moving coordinate system and solved using a pseudo-explicit finite difference scheme. The programme, "McFrac," has the following features: (i) a fixed mesh for a propagating/receding fracture, (ii) the capability for fluid flow-back, and (iii) a pressure-dependent fluid leakoff. The numerical simulation indicates that poroelastic processes coupled with the fluid leakoff affect not only the pressure history at the wellbore, but also the fracture's dimensions.
Experimental Modelling of Casing Deformation in a Compacting Reservoir
Authors: Veeken C. A. M. , Wahleitner J. P. , Keedy C. R.
Published: December 2007

The deformation of casing in a compacting reservoir has been simulated in model experiments to assist with the design of compaction-tolerant completions installed in deep-water, unconsolidated sandstone reservoirs.

Compaction causes severe casing buckling if the lateral casing support is insufficient. Vertical casing with adequate support has been compacted 10% without developing excessive dogleg. Compaction of deviated casing results in casing ellipticity and bending. The model test results are confirmed by field observations (borehole televiewer data). The experimental results indicate that casing damage in a compacting reservoir can be reduced by providing adequate lateral support, by changing the wellbore deviation and by using thick-walled casing.
Application of Seismic Tomography to Induced Seismicity Investigations
Authors: Maxwell S. C. , Young R. P.
Published: December 2007

Two case studies are presented, which highlight the potential application of seismic velocity imaging to induced seismicity investigations. Velocity images may be produced using data currently recorded with seismic monitoring arrays. Comparisons of velocity images and induced seismicity have shown that both natural and induced earthquakes cluster in regions of high seismic velocity, while low-velocity regions predominantly lack seismicity. An interpretation of seismic velocity imaging and induced seismicity can be used to interpret the state of stress throughout a rockmass and identify potential problem regions. Examples are given of using this combined seismic interpretation to validate numerical stress models.
The Use of a Genetic Algorithm for the Optimal Design of Microseismic Monitoring Networks
Authors: Jones Robert H. , Rayne Christopher M. , Lindblom Ulf
Published: December 2007

The quality of microseismic location data from a volume of interest is dependent on the three dimensional geometry of the monitoring array. When the volume of interest contains an arbitrary shaped cavity not all the sensors will detect all the seismic activity. The performance of the array can be modelled so its configuration can be optimised.

A genetic algorithm is used to steer the search for the optimal array of sensors. Various fitness functions were tested in the genetic algorithm and the minimax criterion was found to be the most satisfactory.
Acoustic Emission and Temperature Changes in Hard Coal During Carbon Dioxide Sorption-Desorption
Authors: Majewska Zofia , Majewski Stanislaw , Moscicki Wlodzimierz , Zietek Jerzy
Published: December 2007

The effect of carbon dioxide sorption – desorption on hard coal on acoustic emission (AE) and temperature (T) changes have been carried out on granular coal samples. The study was conducted primarily in order to answer the following questions: Do measurements on AE and T changes provide a good indication of the proneness of coal to outbursts? Is it possible to find correlation between AE and T characteristic and petrographic structure of a coal? Data are presented as plots of AE and T parameters versus time.

The experimental data presented lead to the following conclusions:

– AE and T versus time plots show that they provide a very good measure of the proneness of coal to gas and coal outbursts. – There is a direct influence of porous structure and petrographic composition of coal on its behaviour during carbon dioxide sorption – desorption – AE and T measurements have been shown to be promising for predicting outbursts. – The results obtained in this study are also relevant to coal – methane system.
Computational Modelling of the Thermal and Mechanical Behaviour of Rock Mass Subjected to Cryogenic Temperatures
Authors: van den Bogert P. A. J. , Kenter C. J.
Published: December 2007

A finite-element model has been developed to simulate the behaviour of rock mass to be utilised for underground storage of liquefied natural gas (LNG). The model will be used to assess the technical and commercial viability of LNG storage in unlined rock caverns for different geotechnical conditions. The numerical model includes interface elements to describe the mechanical behaviour of joints. The smeared-crack approach is employed to simulate cracking in intact rock.

The numerical model is validated against large-scale site experiments which are being carried out in cavern B at the Röda Sten Rock Laboratory (Göteborg, Sweden). In an exploratory experiment carried out in 1992, the temperature was lowered to −40°C using a cooling machine. In a subsequent experiment liquid nitrogen will be used to cool the same unlined cavern to −162°C. The paper describes the validation of the model against the exploratory experiment at −40°C. The calculated temperature and strain distribution in the rock mass compare well with the measurements. The results demonstrate an encouraging prospect in adequately simulating the relevant phenomena in jointed rock mass at low temperatures.
High Pressure Storage of Gas in Lined Shallow Rock Caverns — Results from Field Tests
Authors: Stille H. , Johansson J. , Sturk R.
Published: December 2007

At the Grängesberg Research Plant field tests have been performed regarding storage of gas at very high pressures in lined shallow rock caverns. The surrounding rock mass (granite) has proven to be very capable of withstanding loads at levels far above the initial rock stresses. No tendency of vertical uplift has been recorded. At an internal pressure of 52 MPa the maximum registered radial deformation in the rock was 5.65 mm, corresponding to a tangential strain of 2 per mille. The combined construction element liner-concrete-rock has fulfilled its main purpose, i.e. to confine the gas, throughout a tough load history. Leakage tests at high pressures have indicated that even a large failure in the liner can be controlled without any severe consequences.
The Micro Mechanical Description of Rocksalt Plasticity
Authors: Fokker P. A. , Kenter C. J.
Published: December 2007

The constitutive behaviour of rocksalt is explained from micro mechanical concepts. Rocksalt plasticity (or primary creep) can be well explained by a dislocation glide mechanism, where gliding becomes increasingly hindered by dislocations (in fact dislocation pairs or dipoles), disturbing the glide paths. Such dipoles are both the main source for hardening, as well as the main source for time dependent behaviour. From such a description a deformation model can be derived that relates strain rates to stresses, strains and the temperature. The resulting creep curve bears great similarity with the Lemaitre and the Menzel-Schreiner deformation law. However, different from these curve fitting laws, primary creep here is based on proper micro-mechanical considerations and moreover can cope with the transient effects as occurring when load or strain rate increments are suddenly changed.
Recent Results of Geomechanical Field Measurements in the TSDE Test at the Asse Salt Mine
Authors: Schneefuss J. , Droste J. , Heusermann S. , Sonnke J.
Published: December 2007

The German reference concept for the final disposal of spent fuel elements comprises their emplacement in Pollux casks in backfilled drifts of a repository in salt rock. Since 3,5 years the Asse salt mine is the location of a large scale trial to demonstrate this storage technology and is intended in particular to allow assessment of long term thermomechanical behaviour of backfill and rock mass. As a result of heating to a maximum 200°C a considerable increase was measured in rock mass deformation and drift closure. Substantial thermally induced stresses result in the rock mass. The backfill pressure shows a steady increase, which is however far below the initial stress state in the host rock.
Re-Injection of Produced Water – Field Experience and Current Understanding
Authors: Paige R. W. , Murray L. R.
Published: December 2007

This paper reviews field experience of produced water re-injection. Recent improvements in understanding the processes which control reinjection are described, demonstrating the key role of rock mechanics in enabling successful reinjection of large volumes of dirty water via waterflood induced fracturing. Methods for predicting injection well behaviour using models which couple reservoir simulation with rock mechanics, and tools for investigating fracture geometries are presented.
Safe Injection Pressures for Disposing of Liquid Wastes: A Case Study for Deep Well Injection
Authors: Abou-Sayed A. , Thompson T. W. , Keckler K.
Published: December 2007

The determination of maximum injection pressures is an important component of planning and permitting for deep well disposal of liquid wastes. In the United States, safe injection pressures are defined as those that do not initiate or propagate fractures. The maximum injection pressures are often based on the closure pressure at the wellbore; however, higher pressures can sometimes be demonstrated to be safe. This was the case during the recent preparation of a nomigration petition and permit applications for deep well injection at the BP Chemicals Inc. Lima, Ohio, facilities. In this case, a substantial database existed, which included core mechanical properties, in situ stress tests and transient pressure tests on a specially drilled Stratigraphie test well, as well as about 20 years of injection flow and pressure history. These data were used to provide the required assurances to the regulatory agencies that injection over the closure pressure could be adequately defined. This analysis was complicated by the stress dependance of the injection formation permeability and the pluggage of the near wellbore region due to fines in the injection stream. This paper describes the database used and the analyses conducted to demonstrate that injection above closure pressure at BP Chemicals' facilities at Lima, Ohio, does not initiate or propagate fractures in the injection zone and that the injected fluids will be contained in the injection zone for at least 10,000 years.
Finite Element Analysis of Compaction and Subsidence — Experience Gained from Several Chalk Fields
Authors: Plischke Bertold
Published: December 2007

For North Sea chalk fields, finite element models are used to evaluate the reservoir compaction and the associated seafloor subsidence. The present paper addresses aspects of the calibration of the stress strain laws to be used for the chalk and the overburden. Results of laboratory tests do not reflect the large scale deformation behaviour. The calibration is therefore mainly based on the back analysis of measured formation movements. Another topic is the coupling with reservoir simulation models, which provide the reservoir pressure. This coupling should be improved, if a local compaction cannot be derived from a simultaneous change in reservoir pressure at that location.
Recent Advances in Laboratory Automation Programming
Authors: Mahmood S. M. , Olsen D. K.
Published: December 2007

Petroleum laboratories greatly benefit from automation because tests often involve rapid transient behavior, e.g., in determining unsteady-state relative permeability; and/or long slow processes such as capillary tests. Many smaller laboratories are not fully automated due to the high cost of developing custom-made software or modifying commercial software for their specific use.

This situation is rapidly changing with the emergence of a new generation of object-oriented computer languages. These new languages allow novice programmers to develop sophisticated systems with unprecedented ease and speed. This paper introduces the concepts behind this new generation of languages and their use for petroleum laboratory automation.

A public domain, general-purpose laboratory/pilot plant automation program, "LabWARDEN," developed at the National Institute for Petroleum and Energy Research (NIPER) for the U.S. Department of Energy is presented as a case-example. This menu-driven, user friendly program for data acquisition/control/analysis/presentation is a valuable tool for laboratories where test requirements change frequently. Its features include: run-time system setup reconfiguration; built-in constraints to eliminate operator errors; real-time graphic display of current and previous data with editing and smoothing; data export to other applications for report generation or animation such as automatic 3-D rotation; pictorial display of test status for quick trouble-shooting; error and out-of-range audio/video warnings to designated users on the network; automatic resetting of instrument(s) to rectify minor problems; and automatic shut-down in emergencies when the operator does not respond. Configuration of a high-temperature high-pressure steamflood oil displacement laboratory is described.
Seplant: An Expert System for Process Plant and Gas Lift Well
Authors: Patrício A. R. , da Rocha A. F. , Morooka C. K.
Published: December 2007

Oil production is very sensitive to disturbances on process plant and/or well installation. Identification problem in gas-lift wells involves mainly symbolic reasoning, since gas surface card provides important information but not all data required for decision making. A variety of well problems can occur with this system. Neural nets were used to developed SEPLANT, an expert system whose purpose is to support the intelligent control of gas-lift and process operation by helping operators in making the correct decisions in contingency situations, in an effort to avoid problems and production losses.