Tom Trott for Oil & Gas I in Fall 2013
Chptr 1: History, Accumulation & Ownership
Saturday, August 24, 2013
4:49 PM
Historical Background
· (3) whale oil operated under the law of capture: a whale belonged to the whalers who could capture it & reduce it to possession
· kerosene distilled from coal less expensive but smokier than spermaceti (whale) oil
· “rock oil” developed into suitable illuminating & lubricating oil
barrels – standardized at 42 gallons
· outgrowth of real property law
Physical Background
· (4) wildcat well – exploratory well drilled in an area & into a formation that is not known to contain petroleum
o wildcatter – person who drills wildcat wells in search of petroleum
· petroleum geology – scientific search for traps that may contain oil & gas
(5) in times before drilling, oil had been recovered from surface seeps & pools
· gas, often found w/ the oil, and called associated gas, was at 1st considered a dangerous nuisance that was vented or flared at the drill site
o 1990s: valuable liquid called natural gasoline could be separated from the gas & marketed along w/ crude oil
o advances that made natural gas production viable:
· development of high-tensile steel, advanced welding, & pipe-rolling techniques in the 1920s
· nationwide natural gas delivery system
· extraction & marketing of a host of natural gas liquids (NGLs) from “wet” gas streams
Origin of Oil & Gas
Thursday, August 29, 2013
7:17 PM
Origin of Oil & Gas
Deposition
· typically marine deposit in diff rock layers
1. (5) deposit of organic material in shallow & tropical to subtropical water tens of millions of yrs ago
a. movement & collision of continents as described by plate tectonics conspired to placed N. America near the equator & under warm/shallow marine & lacustrine (lake & lagoonal) waters
b. (6) great quantities of marine plant + animal life thrived
2. accumulation began to undergo decomposition/degradation, or both
3. great tropical waters flowed forth, carrying mud, silt, and sand
4. progressive burial & resultant overburden began to provide significant pressure & higher temps around the buried organic matter
a. diagenesis:
i. process of organic material first subjected to heightened temperatures & pressures caused by burial under the 1st several hundred feet of overlying sediments
ii. compaction & passage of time, water is squeezed out of the organic material, and other chemical reactions leave a sticky reside called kerogen and a black tar-like bitumen
Generation
· catagenesis begins: thermal degradation of the kerogen to form hydrocarbons
o 3 key ingredients: time, heat, & pressure
· oil forming window represents a range of time, heat, & pressure necessary to form oil
o natural gas avenue: temperature + pressure > those found w/in the oil formation window, more complete cracking of the kerogen occurs, resulting in the formation of natural gas
o predominate theory: hydrocarbons produced from biological material altered over millions of yrs by heat + pressure
o alternative theory: hydrocarbons, gas in particular, can be generated in the absence of biological organisms at depths of 100-300 kilometers
Migration & Trapping
· (7) migration path is a pathway of rock or unconsolidated sediment w/ enough permeability to allow gas + oil to pass through along a multitude of small interconnected pathways, commonly known as pore spaces
o upward/lateral migration continues until the surface is reached or the gas venting into the atmosphere & oil pooling on the surface, or an impermeable barrier of rock is encountered, halting & trapping the migration
o hydrocarbon migration also affected by the hydrocarbon’s viscosity
· geologic trap is comprised of rock impermeable to flow (i.e. shale/salt)
Accumulation & Occurrence
Thursday, August 29, 2013
7:17 PM
Accumulation & Occurrence
· trap required, to stop the migration of oil & gas and hold it in place
o typically, below oil & gas is water (salt water mostly, needing remediation)
· salt water deposal well: pump it back where it originating
· dumping: traditional disposal
· pump it down the annulus: down the side of the well
· (7-8) reservoir is the volume of rock in which the hydrocarbons stay after the trap stops their progress, composed of 1+ traps
o subsurface rock boy w/ sufficient void space (porosity) to store hydrocarbons & connectivity b/t those void spaces (permeability) to allow hydrocarbons to flow
· reservoir geomorphology:
o commonly sedimentary, mostly comprised of grains of other rocks that have been eroded & transported by water/wind, and therefore more porous than most igneous & metamorphic rocks
· igneous & metamorphic rocks form under temp conditions that hydrocarbons cannot be preserved
· most common hydrocarbon contained rock = sandstone (porous & permeable limestone & dolomite rock follow)
o (9) saltwater presence w/in oil + gas accumulation causes wells to produce saltwater as well as oil + gas
o one way of classifying reservoirs is to group them according to their geologic source + geometry:
· structural category:
§ formed by stresses that cause deformation of the sedimentary rocks comprising the trap + reservoir
§ can form folds & faults
§ upward & lateral salt movements can form salt domes that can produce traps in overlying & adjacent sedimentary formations
§ types:
· folds & domes:
· folding subsurface rock formations (strata) usually having the shape of structural domes or upward-bent folds, or both
· elongated fold in the rock (anticline) may not provide closure adequate to act as a trap
· (10) faults:
· fracture/discontinuity in a volume of rock: sig displacement relative to the other side
· movement of rock juxtaposing an impervious rock layer over a reservoir rock could act as a trap
· typically trapping the gas but at diff depts
· (11) salt & over-pressured shale:
· subject to plastic flow over short periods of geologic time
· salt maintains a constant buoyant density as it is buried by overlying sediments
· plastic flow + buoyance = buried salt eventually pushing up through overlying sediments & flow towards the surface to form a complex structure of domes & salt walls w/ salt withdrawal basins in between
· (12) salt & shale do not normally contain recoverable hydrocarbons, but oil & gas commonly found in the sandstone formations abutting salt domes & over-pressured shale
· great for gas storage
· stratigraphic category:
§ (12) change w/in the formation itself providing the trap + reservoir
§ do not rely primarily on geological structures, thus more subtle & difficult for petroleum geologists to detect & image
§ types:
· channel sandstones/turbidites:
· most common
· sandstone/limestone sealed superior by changes in permeability or interlayering of it w/ impervious shale/mudstone
· hydrocarbons confined w/in porous & permeable parts of the ro
osed to surface conditions, such as at oil seeps
· biological degradation by bacteria results in oil that is tar-like or asphaltic
· production requires significant volumes of water and, when surface mined, results in substantial surface destruction, requiring extensive reclamation
· 1 pipe: heats oil
· pipe 2: collects & transports oil
o gas hydrates
· slush-like solids comprised of methane & water frozen in various combinations
· (21) techniques for economic development & subsequent marketing of hydrates elusive
Types of Reservoir Drives
Thursday, August 29, 2013
8:28 PM
Types of Reservoir Drives
· (21) oil + gas pushed out of the reservoir & up the well by pore pressure provided from the very same oil, gas, and water under high pressure in the reservoir
· developer hopes that internal reservoir pressure will itself drive oil + gas to the surface
o on pump
· compressor installed to assist in lifting the gas & pushing it into a gathering line system at the surface
o natural drives (reservoir-drive mechanisms)
· overburden pressure
· gas drive
§ reservoir has an internal pressure > bubble point, pressure at which gas can be contained in the oil solution w/o separating
§ gas separates out of the liquid hydrocarbon & rises b/c of its lower density
§ gas-only gas cap formed (25-50% recovery rate)
§ BEST APPROACH: drill first at the reservoir flanks to encounter the lower oil interval, reducing intra-reservoir pressure and allows the gas cap to expand & help push the remaining oil into the wells
· if no separate gas cap exists & gas is expanding in the oil itself, a solution-gas drive reservoir: typically small, compartmentalized, or otherwise laterally discontinuous so that the reservoirs are essentially closed systems (10-25% recover rate)
· water drive
§ (23) depends on release of reservoir pressure & the resultant expansion of the compressed water to provide the drive to force the hydrocarbons out of the reservoir & into wellbore over a broad front
§ particularly effective in producing hydrocarbons from porous & permeable reservoirs that are continuous over a large area
§ generally the most efficient type of drive for oil production (30-50% recovery rate)
· combination drive
§ solution drive: water is contained within the substance
· retrograde gas reservoir (gas-condensate reservoir)
§ portion of the gas converts to liquid as the gas approaches the surface
· dramatic drop in pressure + temp
§ flashing is the term for gas condensation
§ tend to be deeper & have higher pressure/temps than conventional reservoirs
§ gaseous condensate initially remains a vapor but as pressure drops, liquid drops out of gas while still in the reservoir (condensate drops = more difficult to produce & also inhibits flow through the reservoir rock)
