Geol 404 1st Edition Lecture 18 Outline of Last Lecture I. HydrocarbonsII. Gas PhaseIII. Oil PhaseIV. Shale Pore Diameters and Oil ExpulsionOutline of Current Lecture V. Secondary MigrationVI. Migration PathwaysVII. Shadow ProblemsVIII. Migration DistancesIX. Pore ScaleX. Mechanics of MigrationXI. Water Wet/Oil WetXII. BuoyancyXIII. Capillary DataXIV.ComplicationsCurrent LectureV. Secondary Migrationa. For it to occur there needs to be some source rocki. Definition of Terms1. Primary2. Secondary3. TertiaryVI. Migration Pathwaysa. Source rock matures in a certain area, and then is carried through the permeable beds with microfractures, and it all gathers and forms a reservoir.b. Since the driving force behind secondary migration is buoyancy, petroleum will tend to move in a homogeneous carrier bed in the direction of the steepest slope.c. Buoyancyi. is the density contrast between petroleum and the subsurface brines. d. Once expelled from the source, the petroleum moves upwards until a seal arrests migratione. Ortho ContoursThese 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.i. a good way of visualizing the direction of migration. ii. They are lines constructed on a map at right angles to the depth structure contours. Instead of displaying areas of equal depth they depict lines of maximum dip. f. The Buoyancy effect dictates the rising petroleum. g. Clearly some areas have a better fetch polygon with hydrocarbons concentrated by the ortho contours while others have a disperse fetch polygon. h. Ortho Contour maps illustrate the focusing and defocusing effects of structural features in prospect drainage areas. i. It's important in PLAY ASSESSMENT to recognize those parts of the fairway. VII. Shadow Problemsa. 3 primary migration basinal areas have been identified capable of generating oil. b. Ortho Contour flow vectors have been sketched in, to show possible secondary migration routes. c. Finally, three prospects and two or more leads have been identified. Prospects are defined on something seismic or very big. d. Whereas leads are more theoretical. VIII. Migration Distancesa. The distance from the petroleum source rock to the trap may be as large as many hundreds of kilometers. b. The outermost field defines the he limit of the Petroleum System for that particular source pod. c. U.K. North Sea Fields 20-30km from source rocks whereas Western Cadadian Basin Field is 400-500km from it's source. IX. Pore Scale a. The hydrocarbon molecule size and pore throat diameters are dealing in nanometers, a billionth of a meter. b. The ease with which hydrocarbons move through the stratigraphic section is controlled by the physical properties of the pore system, the mineralogy of therock, and the properties of the hydrocarbon. c. Pore throats act as molecular sieves allowing particles smaller than the orificeto pass and retaining larger particles. d. If seals were uniformly composed of the same pore throats, they would be perfect seals for compounds larger than the pore throat apertures. X. Mechanics of Migrationa. As an oil molecule travels up through a water wet carrier bed in the subsurface environment, it needs to pass through the pore throats. b. Capillary pressure opposes the buoyant force until the radius of the curvature inside the distorted oil globule is equal at its lower and upper ends. c. Oil globulae then passes through the pore throat.XI. Water Wet and Oil Wet Reservoirsa. Pore spaces on most reservoir rocks, are presumed to be initially filled with water from the moment of their deposition. b. When oil invades the rock, a film of water is left on the surface of the grain or pore opening. c. This film has a high surface adhesion and consequently makes the bound water very difficult to move. d. The larger grains will have thicker layer skin than the smaller grains. e. The bound water also occupies the smallest pore channel while the oil is in the larger channels. f. This determines oil and water wet reservoirs and can be measured using he angle the drop of water makes. i. 0-70 degrees - Strongly water wetii. 70-110 degrees - Intermediate wettabilityiii. 110-180 degrees - strongly oil wetXII. Buoyancy Forcea. Buoyancy is the vertically directed force caused by the difference in pressure between some point in a continuous petroleum column and the adjacent pore water. b. Transport of larger molecules while possible through the large sand silt shale pores, becomes increasingly less likely as the path traversed through the carrier. c. Reservoir and carrier beds can be subjected to capillary pressure tests to quantify their capacity. d. A non wetting fluid such as mercury is injected into a core plug to determine this Cp. e. The mercury first saturates the largest pores and with continued pressure the mercury invades the smaller spaces until in the end only those pores are bound with water remain uninvaded. XIII. Use of Capillary Dataa. With enough measurements, you can plot the data vertically to find the sand and shale bars. It can create a geologic cross section. XIV. Water Wet Systems Complicationsa. Diegetic materials can also fill the pore spaces. These can range from kaolinite to illite, being attached to the pore lining and pore bridging habits of these minerals. b. For drilling mud engineers and production engineers these clays are a headache. Notes:Primary oil recovery is affected by the wettability characteristic of the system. Oil moves easier in water wet rocks than in oil wet rocks, a water wet system willexhibit greater primary oil recovery and a water wet system will have greater oil