Shale Gas Flashcards
The gas accumulated on the surface of a solid material, such as a grain of areservoirrock, or more particularly the organic particles in ashalereservoir. Measurement of adsorbed gas andinterstitial gas, which is the gas contained inporespaces, allows calculation of gas in place in a reservoir.
adsorbed gas
Predictable variation of a property of a material with the direction in which it is measured, which can occur at all scales. For a crystal of amineral, variation in physical properties observed in different directions is aeolotropy (also known as anisotropy). In rocks, variation in seismic velocity measured parallel or perpendicular to bedding surfaces is a form of aeolotropy. Often found where platy minerals such as micas and clays align parallel to depositional bedding as sediments are compacted, aeolotropy is common in shales.
aelotropy
An example used for comparison. In oil and gasexploration, geoscientists and engineers compare new prospects and fields with fields and surface exposures thought to be similar indepositional environmentandreservoircharacterto guide predictions. Wide variations inshalereservoirs create doubt about the utility of analog comparisons.
analog
Having directionally dependent properties. For a crystal of amineral, variation in physical properties observed in different directions is anisotropy. In rocks, variation inseismicvelocity measured parallel or perpendicular to bedding surfaces is a form of anisotropy. Often found where platy minerals such as micas and clays align parallel to depositional bedding as sediments are compacted, anisotropy is common in shales.
anisotropic
Predictable variation of a property of a material with the direction in which it is measured, which can occur at all scales. For a crystal of amineral, variation in physical properties observed in different directions is anisotropy. In rocks, variation in seismic velocity measured parallel or perpendicular to bedding surfaces is a form of anisotropy. Often found where platy minerals such as micas and clays align parallel to depositional bedding as sediments are compacted, anisotropy is common in shales.
anisotropy
The direction in which a deviated or horizontal well is drilled relative to magnetic north. Most horizontal wells inshalereservoirs are drilled in the direction of the minimum horizontalstress. This allows for the creation of multiple hydraulic fractures that arenormalto the wellbore.
azimuth
A depression in thecrustof the Earth, caused by plate tectonic activity and subsidence, in which sediments accumulate.Sedimentarybasins vary from bowl-shaped to elongated troughs. Basins can be bounded by faults.Riftbasins are commonly symmetrical; basins along continental margins tend to be asymmetrical. If richhydrocarbonsource rocks occur in combination with appropriate depth and duration of burial, then apetroleum systemcan develop within the basin. Most basins contain some amount ofshale, thus providing opportunities forshale gasexplorationandproduction.
basin
The fraction of naturally occurring, inflammable organic matter that is extractable from rock using organic solvents. Manypetroleumprecursors are composed of bitumen, but most are formed fromkerogenin the process of petroleumgeneration. Bitumen includes hydrocarbons such asasphaltandmineralwax. Typically solid or nearly so, brown or black, bitumen has a distinctive petroliferous odor. Laboratory dissolution with organic solvents allows determination of the amount of bitumen in samples, an assessment ofsource rockrichness. Burial and heating of kerogenyieldbitumen, thenliquid hydrocarbons, and thenhydrocarbongas. Understanding organic content is especially important inshalereservoirs because the shale is both the source rock and thereservoirrock in thepetroleum system.
bitumen
Aflow crossinstalled on top of afrac treewheretreating ironis connected andtreatment fluidenters the frac tree.
buffalo head/ frac head/goat head
The physical and chemical alteration of sediments andporefluids at temperatures and pressures higher than those ofdiagenesis. Catagenesis involves heating in the range of 50° to 150°C [122° to 302°F]. At these temperatures, chemical bondsbreakdown inkerogenand clays withinshale, generatingliquid hydrocarbons. At the high end of this temperature range, secondarycrackingof oil molecules can generate gas molecules.
catagenesis
A trailer in which fracturing engineers can monitorformation pressuresand other critical information pertaining to thefracturingprocess.
command trailer
A generic term used to describe the events and equipment necessary to bring a wellbore intoproductiononce drilling operations have been concluded, including but not limited to the assembly of downholetubularsand equipment required to enable safe and efficient production from an oil orgas well. Completion quality can significantly affect production fromshalereservoirs.
completion
A prediction of how effectively rock may be stimulated usinghydraulic fracturing. Completion quality (CQ) is an engineering assessment of factors that determine the effectiveness of hydraulic fracture treatments and includes the ability to initiate and create an inducedfracture network, the degree ofreservoircontact of the newly createdfractures, the level of connection to thenatural fracturesystem of those created fractures and ability of the stimulated reservoir to deliver gas or oil into the well.
completion quality (CQ)
Afrac treein which multiplefrac valvesare contained in a single large body such that the overall height of the frac tree is reduced.
composite frac tree
A type of areally extensivereservoirthat containshydrocarbonthroughout, rather than containing a watercontactor being significantly affected by a water column or a definedstructuralclosure. The areal extent of a continuous reservoir, such as ashalereservoir, can be as large as the extent of thesedimentary basinin which the shale was deposited.
continuous reservoir
Areservoirin which buoyant forces keep hydrocarbons in place below a sealing caprock. Reservoir and fluid characteristics of conventional reservoirs typically permit oil ornatural gasto flow readily into wellbores. The term is used to make a distinction fromshaleand other unconventional reservoirs, in which gas might be distributed throughout the reservoir at thebasinscale, and in which buoyant forces or the influence of a water column on the location of hydrocarbons within the reservoir are not significant.
conventional reservoir
Laboratory study of a sample of ageologicformation, usuallyreservoirrock, taken during or after drilling a well. Economic and efficient oil and gasproductionis highly dependent on understanding key properties of reservoir rock, such asporosity,permeability, andwettability. Geoscientists have developed a variety of approaches, including log andcoreanalysis techniques, to measure these properties. Core analysis is especially important inshalereservoirs because of the vertical andlateralheterogeneityof the rocks. Core analysis can include evaluation ofrock propertiesandanisotropy; organic matter content,maturity, and type; fluid content; fluidsensitivity; and geomechanical properties. This information can be used to calibrate log andseismicmeasurements and to help in well andcompletiondesign, well placement, and other aspects of reservoir production.
core analysis
The total amount of oil and gas recovered from areservoiras of a particular time in the life of thefield. Cumulativeproductioncan be referenced to a well, a field, or abasin.
cumulative production
The intentionaldeviationof a wellbore from the path it would naturally take. This is accomplished through the use of whipstocks,bottomhole assembly(BHA) configurations, instruments to measure the path of the wellbore in three-dimensional space, data links to communicate measurements taken downhole to the surface,mudmotors and special BHA components and drill bits, including rotary steerable systems, and drill bits. The directionaldrilleralso exploits drilling parameters such as weight onbitand rotary speed to deflect the bit away from the axis of the existing wellbore. In some cases, such as drilling steeply dipping formations or unpredictable deviation in conventional drilling operations, directional-drilling techniques may be employed to ensure that the hole is drilled vertically. While many techniques can accomplish this, the general concept is simple: point the bit in the direction that one wants to drill. The most common way is through the use of a bend near the bit in a downhole steerable mud motor. The bend points the bit in a direction different from the axis of the wellbore when the entiredrillstringis not rotating. By pumping mud through the mud motor, the bit turns while the drillstring does not rotate, allowing the bit to drill in the direction it points. When a particular wellbore direction is achieved, that direction may be maintained by rotating the entire drillstring (including the bent section) so that the bit does not drill in a single direction off the wellbore axis, but instead sweeps around and its net direction coincides with the existing wellbore. Rotary steerable tools allow steering while rotating, usually with higher rates of penetration and ultimately smoother boreholes. Directional drilling is common inshalereservoirs because it allows drillers to place theboreholeincontactwith the most productivereservoirrock.
deviated drilling
The physical, chemical or biological alteration of sediments intosedimentaryrockat relatively low temperatures and pressures that can result in changes to the rock’s original mineralogy and texture. After deposition, sediments are compacted as they are buried beneath successive layers ofsedimentand cemented by minerals thatprecipitatefrom solution. Grains of sediment, rock fragments and fossils can be replaced by other minerals during diagenesis.Porosityusually decreases during diagenesis, except in rare cases such as dissolution of minerals anddolomitization. Diagenesis does not includeweatheringprocesses.Hydrocarbongenerationbegins during diagenesis. There is not a clear, accepted distinction between diagenesis andmetamorphism, although metamorphism occurs at pressures and temperatures higher than those of the outercrust, where diagenesis occurs.
diagenesis
The intentionaldeviationof a wellbore from the path it would naturally take. This is accomplished through the use of whipstocks, bottomhole assembly (BHA) configurations, instruments to measure the path of the wellbore in three-dimensional space, data links to communicate measurements taken downhole to the surface,mudmotors and special BHA components and drill bits, including rotary steerable systems, and drill bits. The directional driller also exploits drilling parameters such as weight onbitand rotary speed to deflect the bit away from the axis of the existing wellbore. In some cases, such as drilling steeply dipping formations or unpredictable deviation in conventional drilling operations, directional-drilling techniques may be employed to ensure that the hole is drilled vertically. While many techniques can accomplish this, the general concept is simple: point the bit in the direction that one wants to drill. The most common way is through the use of a bend near the bit in a downhole steerable mud motor. The bend points the bit in a direction different from the axis of the wellbore when the entiredrillstringis not rotating. By pumping mud through the mud motor, the bit turns while the drillstring does not rotate, allowing the bit to drill in the direction it points. When a particular wellbore direction is achieved, that direction may be maintained by rotating the entire drillstring (including the bent section) so that the bit does not drill in a single direction off the wellbore axis, but instead sweeps around and its net direction coincides with the existing wellbore. Rotary steerable tools allow steering while rotating, usually with higher rates of penetration and ultimately smoother boreholes. Directional drilling is common inshalereservoirs because it allows drillers to place theboreholeincontactwith the most productivereservoirrock.
directional drilling
The amount of oil and gas expected to be economically recovered from areservoirorfieldby the end of its producing life. Estimated ultimaterecoverycan be referenced to a well, a field, or abasin.
estimated ultimate recovery
An area in which hydrocarbon accumulations or prospects of a given type occur. For example theshalegas plays in North America include the Barnett, Eagle Ford, Fayetteville, Haynesville, Marcellus, and Woodford, among many others. Outside North America,shale gaspotential is being pursued in many parts of Europe, Africa, Asia, and South America.
exploration play/ play
The measurement and analysis offormationand fluid properties through examination of formationcuttingsor through the use of tools integrated into thebottomhole assemblywhile drilling, or conveyed onwirelineordrillpipeafter aboreholehas been drilled. Formation evaluation is performed to assess the quantity and producibility of fluids from areservoir. Formation evaluation guides wellsite decisions, such as placement of perforations and hydraulicfracturestages, and reservoirdevelopmentandproductionplanning.
formation evaluation
Also known aslogging while drillingorLWD, the measurement offormationproperties during the excavation of the hole, or shortly thereafter, through the use of tools integrated into the bottomhole assembly. LWD, while sometimes risky and expensive, has the advantage of measuring properties of a formation before drilling fluids invade deeply. Further, many wellbores prove to be difficult or even impossible to measure with conventionalwirelinetools, especially highly deviated wells. In these situations, the LWD measurement ensures that some measurement of the subsurface is captured in theeventthat wireline operations are not possible. Timely LWD data can also be used to guide well placement so that the wellbore remains within the zone of interest or in the most productive portion of areservoir, such as in highly variableshalereservoirs.
formation evaluation while drilling/ logging while drilling
Pressureabove which injection of fluids will cause therockformationtofracturehydraulically.
formation fracture pressure/ fracturing pressure
An abbreviation forfracturing fluid, a fluid injected into a well as part of astimulationoperation. Fracturing fluids forshalereservoirs usually contain water,proppant, and a small amount of nonaqueous fluids designed to reduce frictionpressurewhile pumping the fluid into the wellbore. These fluids typically includegels, friction reducers, crosslinkers, breakers and surfactants similar to household cosmetics and cleaning products; these additives are selected for their capability to improve the results of the stimulation operation and the productivity of the well.
frac fluid
Another term forhydraulic fracturing, astimulationtreatment routinely performed on oil and gas wells in low-permeabilityreservoirs. Specially engineered fluids are pumped at highpressureand rate into thereservoirinterval to be treated, causing a verticalfractureto open. The wings of the fracture extend away from the wellbore in opposing directions according to the natural stresses within theformation.Proppant, such as grains ofsandof a particular size, is mixed with the treatment fluid to keep the fracture open when the treatment is complete. Hydraulic fracturing creates high-conductivitycommunication with a large area of formation and bypasses anydamagethat may exist in the near-wellbore area.
frac job
