Geol 404 1st Edition Lecture 19 Outline of Last Lecture I. Secondary MigrationII. Migration PathwaysIII. Shadow ProblemsIV. Migration DistancesV. Pore ScaleVI. Mechanics of MigrationVII. Water/Oil WetVIII. BuoyancyIX. Capillary Data X. ComplicationsOutline of Current Lecture XI. Trap and SealXII. Good/Bad SealsXIII. Types of TrapsCurrent LectureVIII. Trap and Seala. The logs usually include SP curves and Resistivity curves.b. The logs help differentiate the zones, and can give us the Gross Reservoir Sections.c. They name the Oil Pay Zone, Gas Pay Zone, Transition Zone with water, and Free Water Zoned. Pressure Gradientsi. The main driving force behind secondary migration into a trapping position is buoyancyii. The pressure increases as the height of the structure increasesiii. A water filled structure would have a normal water gradient but an oil gas filled structure will have a new pressure gradient reflecting the buoyancy of the hydrocarbon.iv. The free water level occurs where buoyancy pressure is zero in the reservoir system.e. Sealing Elements Begini. A capillary seal is when the capillary pressure across the pore throat isgreater than the buoyancy pressure of the migrating hydrocarbonsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.ii. Capillary entry pressure is proportional to interfacial tensioniii. Greater interfacial tension the greater the seal capacityiv. Smaller pore throat = higher capillary pressureIX. Good/Bad Sealsa. Good Sealsi. Petro physically has small pore throats without large connected poresii. Homogeneous both vertically and laterallyiii. Laterally continuousiv. Thick to reduce the number of pathwaysv. Has no bypass system, faultsvi. Water wet to increase capillary pressuresb. Bad Sealsi. Large pore throatsii. Lithologically variableiii. Discontinuous layeringiv. Thin bedsv. Fractured and faultedvi. Hydrocarbon wetX. Types of Trapsa. Subsurface Watersi. Meteoricii. Connate Wateriii. Juvenile Wateriv. Mixed Waterb. Trap Typesi. Structuralii. Stratigraphiciii. Combinationiv. Hydrocarbonc. Gravitational Structuresi. Roll over anticline into a listric growth faultii. Due to instability in the sediment pile and its movement under gravityd. Sealing Faultsi. Faults themselves can act as lateral barriers even though the displacement can have reservoir quality rock laterally juxtaposed.ii. Fault gouge can be clay smeared along the fault such that the more clay, the more the capillary pressure is created and the better the seal qualitye. Piercement Trapsi. Diapiric traps are produced by the upward movement of sediments that are less dense than those overlaying themii. The sediments tend to be dragged upwards by the diapir and in doing so, form a diverse series of hydrocarbon trapsf. Stratigraphic Trapsi. Buried depositional relief macroformsii. Positive relief of trap due to depositional controlled reservoir thickness varies.iii. They are actual dunesiv. Carbonate traps can include barrier, patch, and pinnacle reefsv. They may need to rely on as many as four sealing elementsvi. Two up top and two on the sides.vii. If the buoyant force of the hydrocarbon column exceeds the resistant force of the displacement pressure, oil and gas could leak laterally updip through the displacement pressure barrier and continue to migrate updip through the reservoir carrier bedsg. Leaky Lateral Sealsi. Structural (spill) differential entrapment of oil and gasii. For a series of traps that spill updip, gas will be differentially entrappeddowndip from oiliii. Stratigraphic (leak) differential entrapment of oil and gasiv. For a series of traps that leak updip oil will be differentially entrapped downdip.h. Sub Unconformity Trapsi. Play in the giant Gohta Fieldii. Play in the Angila Fieldi. Hydrodynamic Trapsi. If pore water flow in a sedimentary basin is strong enough, the oil water contact may deviate from the horizontal because of the hydrodynamic shear that is set up.ii. In some cases, oil may accumulate without closure.iii. Flow of fresh water down through oil bearing rocks commonly results in biodegradation of the
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