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For a mine section comprising 100 different stoping activities, there are ~10158 different possible stoping sequences to explore in the mine schedule optimization search and this figure is indicative of the challenge posed in maximising profitability through mine schedule optimization. Any viable excavation timetable must satisfy all conditions that will constrain feasible sequences. In general, consideration of additional constraint will tend to reduce profitability. Geomechanical constraints on mine schedules, introduced with the aim of avoiding excavation instabilities, can be established for underground mine schedule optimization processes but, currently, this is done only rather crudely; precedence relations between excavation activities (stoping or development) are encoded to produce particular stope sequence patterns (e.g. ‘chevron’ or pyramidal sequences).
The work reported aimed to investigate automated processes for formulation of such geomechanical constraints. The timetable optimization approach to the problem precipitated a fresh look at time dependent, and excavation sequence dependent, deformation. Abundant evidence emerged that supported the notion that any methodology developed that failed to account for such time and sequence dependencies was itself bound to failure. Yet, it was also recognised that any deviation at all from an assumption of linear elasticity for geomechanical numerical modeling, adopted to inform geomechanical constraint formulation, would rapidly lead to impractical levels of computational effort.
Thus the approach presented here represents a compromise: the elastic stress fields induced by individual mining activities are computed for each activity, independently considered within a computational domain identical to that of all other activities. These are stored in a database. Instability risk for a specific sequence of mine activities can be assessed through superimposition of stress fields drawn from the pre-computed database. Time stamps allocated to events corresponding to the excavation processes permit the conversion of the sequence of elastic stress fields into a time table of stress fields. For specific locations within the computational domain, the aggregate effect of the sequence of mine activities leads to stress-time histories having a castellated appearance, a result of the near instantaneous response of an elastic medium to the excavation perturbations. Time dependent deformation responses are crudely allowed for through the re-profiling these castellated histories through graphical construction of curved responses, where the curve gradients are related to a viscous parameter. Such curves form the basis for a geomechanical constraint formulation to be adopted for mine schedule optimization.
Natural gas engineering entails production, processing, storage and transportation of natural gas. A good handling of the gas requires a sophisticated understanding of how its density, compressibility, pseudo-pressure, and specific heat capacity varies with the gas condition. While petroleum & gas journals and a host of scholastic materials have presented varieties of means to evaluate other properties, they neglected or underscored the need for same for specific heat capacity of natural gas. The only available mathematical relation for this property only predicts its value at 1500F- not at other temperatures.
Samples of natural gas collected from Bell field, Sabine field, Bacon lime and paradox formation were used as data source. The variation of the respective specific heat capacity of the components and the effect of the composition on the specific gravity and overall specific heat capacity of the gas was taken into consideration giving rise to a robust correlation that reads in the individual composition of the gas, its density and temperature to generate the specific heat capacity of the gas.
The result yielded 98.3% accurate result compared to the method of isentropic coefficient at 1500F and an average error of 0.3% within a range of 4910R to 27400R.
The benefit of this work is that it provides a means of dealing with situation where the heat transferred into or out of a natural gas system is to be calculated over a wide range of temperature as it allows the specific heat to be expressed as an integratable function of temperature other than the isentropic coefficient method which only gives a constant value for a variable that is not constant.
Introduction and Literature Review
The specific heat capacity of natural gas is the quantity of heat required to raise the temperature a kilomole of natural gas by 1 Kelvin or a Fahrenheit (in field unit).
Maddox, Bradley Dean (ECA Holdings, L.P.) | Wharton, Molly (Halliburton Energy Services Group) | Hinkie, Ronald Lee (Halliburton Energy Services Group) | Balcer, Brent Powell (Halliburton Energy Services Group) | Farabee, Mark (Ely & Associates Inc.) | Ely, John W.
This case-history paper presents an account of the application of expandable (swelling) packers and a hydrajet perforating stimulation technique to perform a cementless completion and hydraulic stimulation in a 350o F, openhole horizontal well of 15,700 ft total vertical depth (TVD). Resulting production was more than three times that of an offset vertical well.
The first Wilcox Meek 2 well in the Brazos Bell Prospect Area was drilled and completed to test the effectiveness of horizontal well technology in tight-sand formations. This paper presents the cementless completion process and explores the effectiveness of horizontal-well technology in tight sands by comparing initial horizontal-well production rates to those of offset vertical wells.
The well, which was the first horizontal Wilcox in the area and probably the deepest horizontal well completion for a sandstone reservoir in South Texas, used a 5 ½-in. / 3 ½-in combination string as a production string. The 3 ½-in casing was run in the openhole horizontal lateral section and extended into the 7 5/8-in liner casing. It employed five swellable packers, strategically placed on the string to facilitate isolation for optimum stimulation results. An additional swellable packer, larger than the previous five, was run on the top of the 3 ½-in casing string and was placed inside the 7 5/8-in casing to help ensure complete isolation of the annulus. The swelling packers were activated over an 18-day period by hydrocarbons present in the oil-based mud (OBM) in the annulus.
Following packer activation, four fracture-stimulation operations were conducted in a non-cemented hole using a unique fracturing technique that incorporates hydrajet perforating with coiled tubing (CT). This technique allows for (1) multiple stimulation treatments to be performed in series without the CT being removed from the hole, (2) larger stimulation stages, and (3) maximum surface-area exposure to the fracture pressure without formation damage caused by cement.
ABSTRACT: In high stress environments, as the rock mass yields and fails, fracturing is initiated through intact rock and the extension and shear failure of pre-existing fractures (joints). When close to openings these fractures are expected to be tensile in nature, but further away with increased confinement, shearing is expected to become the predominant mode of failure. Associated with this fracturing in brittle rock masses, are microseismic and seismic events. This microseismic activity, although problematic to operators, can give an indication of the state of the rock mass, in relation to fracture initiation, accumulation of damage and ultimate failure. In this paper the authors examine the use of the spatial and temporal distribution of seismicity at two mine sites over a 6 year period of progressive failure into the post-peak region, relating the seismic event density, combined with the temporal examination of the principal components analysis (PCA), to characterize the extent and trend of the yield zone, and the significant stages of the failure process.
A great amount of research has focused on the properties and behaviour of laboratory samples of hard rock up to the peak strength and into the post-peak failure region. Similarly, much research has focused on the bulk properties of in situ rock masses up to the peak strength. This is largely due to the expense and technical difficulty in performing large controlled compressive tests at the rock mass scale and from a civil engineering standpoint failure is often considered just after the peak strength, when the material no longer fulfills its engineering function. In the hard rock mining industry, at high stresses the rock mass is often driven not just to the peak strength, but often well into the post-peak until ‘complete failure’ occurs.
The initial bulk mining operation began on the 8 and 7 levels shown in figure 1, proceeding upwards from both on intermediate levels spaced 25 meters vertically. The resultant sill pillar between the 8C and 7 levels was forseen as a problem mining area. Successful extraction of this sill pillar was critical as it contained high grade ore. In addition, it was critical to document the rock mass behaviour as the sill was extracted to help in planning the extraction of a pillar to be created as the number 9 and 10 levels are mined upwards beneath the number 8 leveL The increased depth of that pillar will increase stress related problems, thus making detailed extraction planning critical. An integrated program of rock mass classification, instrumentation and numerical modelling was begun to assist in planning both pillar extractions.
ABSTRACT: Research'' in which structural mapping, microseismic monitoring and numerical modelling have been used interactively to gain a better understanding of the behaviour of a rock mass under mine induced stress was carried out at the Golden Giant Mine at Hemlo, Ontario.
The analysis shows good correlation between location of microseismic event clusters and stress concentration zones. Comparison of stress on joint planes at the location of microseismic events and structural mapping indicates that the joint set parallel to the foliation is the most probable joint set for shear slip. Mohr-Coulomb and Hoek and Brown failure criteria were used to derive friction angles based on events presumed to have occurred on the foliation joint set.
The analysis suggests that interactive studies using mapping, microseismics and modelling can be used to isolate critical joint sets where shear movement may be induced and to derive key geomechanical constitutive parameters.
RÉSUMÉ: Ce travail presente l''utilisation interactive de l''analyse structurale de factures, de donnees microsismiques et de la modelisation numerique afin d''apprehender le comportement d''un massif rocheux soumis à des contraintes induites par l''activite minière de Golden Giant Mine à Hemlo, Ontario.
L''analyse montre une bonne correlation entre la localisation des evenements microsismiques et les zones de concentration de contraintes. La comparaison des contraintes sur les plans de faiblesse preexistants, où sont localises les seismes, avec les donnees de l''analyse structurale indique que le plan parallèle à la foliation presente la plus forte probabilite de rupture par cisaillement. . Les critères de rupture de Mohr-Coulomb, Hoek et Brown ont ete'' utilises afin d''obtenir les angles de friction interne, pour les evenements localises sur le plan de foliation.
L''analyse montre qu''une etude interactive cumulant cartographie des fractures, microsismicite et modelisation numerique est Efficace pour definir les plans de faiblesse où les ruptures par cisaillement peuvent être induites, ainsi que pour obtenir les paramètre-cles du modèle geomecanique.
ZUSAMMENFASUNG: Eine Forschungsstudie, in dem wechselseitig erganzend geotektonische Kartographie, mikroseismische Überwachung und numerische Modellerstellung eingesetzt wurden, um das durch eine Mine verursachte Spannungsverhalten einer Felsmasse naher kennenzulernen, wurde bei der Golden Giant Mine in Hemlo, Ontario, durchgefuehrt.
Die Analyse zeigt eine positive Korrelation zwischen der örtlichen Lage der mikroseismischen Vorfallsaufung und der Zone der Spannungskonzentration. Der Vergleich der Spannung an Ablösungsflachen am Ort des mikroseismischen Vorfalls und die geotektonische Kartographie zeigen, daβ die parallel zur Schieferung ausgerichtete Ablösungsflache die wahrscheinlichste Flache fuer die abscherende Gleit-Verwerfung ist. Versagenskriterien nach Mohr-Coulomb sowie Hoek und Braun wurden verwendet, um Reibungswinkel herzuleiten, die auf der Höffigkeit der Ablösungs-Sets der Foliation beruhen.
Die Analyse schlagt vor, daβ man wechselseitig erganzende Studien unter Benutzung von Kartographie, Mikroseismik und Modellierung verwendet, um konstitutive geomechanische Schluesselparameter abzuleiten und urn kritische Ablösungs-Sets, wo eine Scherbewegung induziert werden kann, zu isolieren.
During the past 15 years applied rock engineering has matured into an operationally useful tool for the mining industry. The function of rock engineering personnel is to prevent unexpected failures in order to improve safety and efficiency at operations and to optimize resource recovery.
Rockbursts represent probably the most serious mode of unexpected rock mass failure and are of particular concern in deep hardrock mining. Research and development into the rockburst phenomenon has been ongoing for over 40 years. The development of microseismic monitoring systems has led to a better understanding of this phenomenon. Considerable research has been directed toward using such systems to predict rockburst occurrences in real time. The results of rockburst prediction research have generally proven to be less than satisfactory.
At the same time numerical stress analysis tools have been rapidly evolving. Initially this technology was constrained due to hardware and software limitations. Today both of the above are much less problematic and these techniques offer powerful tools for the analysis of mine induced stress redistribution and associated stability problems.
It is generally accepted by many rock mechanics specialists is that major mine induced rock engineering problems can only be realistically addressed through the design process.
The Antrim Shale, first drilled in the 1940's, is estimated to contain significant quantities of gas, up to 76 Tcf in place. However, relatively low gas production rates, coupled with an inadequate understanding of its key reservoir properties, have limited its active pursuit. Recently, a better appreciation of the merit of the Antrim Shale as a gas resource has raised operator interest. From a base of 32 Antrim Shale wells in 1986, drilling increased to 91 wells in 1987 and to over 300 wells in 1988.
While the pace of Antrim Shale drilling has clearly increased, gas production rates are still relatively low (at about 100 Mcf/day), suggesting that innovative completion and stimulation techniques are needed to increase production and, ultimately, gas reserves. This paper examines in detail two such development strategies aimed at improving Antrim Shale productivity - large volume sand fracs and improved geologic productivity - large volume sand fracs and improved geologic understanding.
Initial analysis of the Antrim Shale suggests that large, water-based stimulation treatments may increase gas flow by more efficiently removing the water in the formation thus improving relative permeability to gas. In addition proper interval selection and well spacing could improve gas recovery. A two-phase, dual porosity reservoir simulator was used to examine the well performance and gas flow rates for applying improved technology to the Antrim Shale.
The Devonian shales of the Appalachian Basin have been drilled for gas reserves since the 1900's, whereas the Antrim Shale in the Michigan Basin has seen little development. However, recent activity points to a growing interest in Antrim Shale gas. This paper examines the nature of this activity, particularly how advances in gas extraction technology could particularly how advances in gas extraction technology could support continued development of this resource.
Though gas production from the Antrim Shale began in 1940 in Otsego County, Michigan, little development took place until the mid 1980's. Drilling activity increased from 15 wells in 1985 to 32 wells in 1986 and 91 wells in 1987. In contrast, 738, 626, and 615 Devonian shale wells were drilled these years in the Appalachian Basin (Figure 1). Current drilling permits issued by the Michigan Department of Natural Resources in 1988 and 1989 reflect an accelerated pace for Antrim Shale drilling. By mid-May, 1988, the number of permits issued to drill the Antrim Shale had reached 165, nearly doubling the previous total. Over 300 wells were drilled to the Antrim Shale in 1988 (Table 1). The Michigan Oil and Gas News has projected that 1,200 permits will be issued to drill Antrim Shale wells in 1989, making this shallow Michigan gas play a nationally recognized area of activity.
Table 1 Permits to Antrim by Year Permits to Antrim by Year Well Permits Wells Drilled Year Year Total First Quarter Year Total
1985 30 3 15 1986 39 0 32 1987 98 1 91 1988(est.) >300 86 >300 1989(est.) 1,200 157 >1,000
Some of the recent interest in the Antrim Shale may be spurred by the unconventional gas tax credit. However, a review of the potential of this resource, particularly with the use of advanced/improved extraction technology and in light of the strong, local gas market indicates that the Antrim Shale may be an economic gas play, even after the tax incentive expires.
Gamma ray spectral logging devices, in addition to total gamma ray counts, record the individual contributions of potassium-40 isotope, uranium series nuclide bismuth-214, and thorium series nuclide thallium-208. Application of these data to identify fractured shale reservoirs and source-rock characteristics of argillaceous sediments is discussed.
Highly radioactive, black, organic-rich, and gaseous shales are encountered in several U.S. geologic provinces. Such organic-rich shales are not only potential source rocks but frequently owe their localized but significant production potential to natural fracture systems in an otherwise impermeable rock. These natural fracture systems normally are concentrated in the interbedded brittle, calcareous, cherty, or silty zones. Conventional logging and interpretive techniques are not adequate to evaluate satisfactorily the complex and frequently fractured shale reservoirs. Novel applications of gamma ray spectral logging data for characterizing these shale formations as to their reservoir properties and source-rock potential (SRP) are discussed here. Calcareous and silty zones, both characterized by low values of potassium and thorium but excessively high values of uranium, are located easily with natural gamma ray spectral information obtained from highly sensitive scintillation spectrometer logging tools. These interpretive concepts already have assisted in many successful gas- and oilwell completion and recompletion attempts in the more permeable and/or fractured intervals of such shale formations. Such logging information also allows a continuous monitoring of the SRP of shales in open and cased boreholes. Hence, both vertical and lateral SRP variations can be studied using appropriate mapping techniques. Gamma ray spectral data also assist in detailed stratigraphic correlations, because in addition to total gamma ray counts, individual gamma rays emitted by potassium-40 (K(40)), the uranium series nuclide bismuth-214 (Bi(214)), and the thorium series nuclide thallium-208 (TI(208)) are measured. K(40) emits gamma rays at 1.46 MeV, Bi(214) emanates gamma rays at 1.764 MeV, and TI(208) emanates gamma rays at 2.614 MeV. These nuclides are of particular interest to the oil industry because all are found, in various amounts, in subsurface formations as constituents of potential reservoir rocks. Based on an extensive literature search and on recent field observations, a data compilation has been published to document potassium, uranium, and thorium distributions in various rock types. This discussion focuses on the use of gamma ray spectral logging to interpret the reservoir pore structure present in shales.