CHAPTER 04 CHAPTER 04 SEAL SEAL ( ( ROOF ROOF OR OR CAP CAP ROCK) ROCK) Definition Definition : : Seal is impermeable rock that forms barrier Seal is impermeable rock that forms barrier on top of the reservoir rock of an oil and/or gas on top of the reservoir rock of an oil and/or gas reservoir. reservoir. [...]... •KEROGEN – RICH SHALES ° •CLAY SHALES ° •SILTY SHALES ° •CARBONATE MUDSTONES ° •CHERTS (most ductile lithologies at top of column) THICKNESS ° A few inches of ordinary clay shale are theoretically adequate to trap very large column heights of hydrocarbons (particle size of 1 0 -4 mm have 600 psi ≅ 915m of hydrocarbon column) ° •Unfortunately, there is a low probability that a zone only a few inches thick... sizable accumulation STABILITY ° STABILITY IN LITHOLOGY ° STABILITY IN THICKNESS QUESTION TO DISCUSS Determine the type and characteristics (petrographic content, thickness, colour, main minerals, rock facies, original, tectonics) of below seal rock (Cuu Long Basin) ... Hydrocarbon type ° The characteristics of the water filled pore, network of the contacting seal ° Time available for diffusion 4. 4 MACRO CHARACTERISTIC OF SEAL ° LITHOLOGY ° DUCTILITY ° THICKNESS ° STABILITY LITHOLOGY ° Almost effective seals are evaporite, fine grained classtics, and organic-rich rocks ° These lithologies are seen as seals because:      Have high entry pressure Are laterally continuous... ductile Are a significant portion of the fill of sedimentary basins DUCTILITY ° Ductility is a rock property to deform and flow without visible fracturing that varies with pressure and temperature (burial depth) as well as with lithology ° Ductile lithologies tend to flow plastically under deformation, whereas brittle lithologies develop fractures ° The evaporite rock group make good ductile seal under . but faults ( Figure Figure 1 1 , (b )) and , (b )) and stratigraphic stratigraphic traps ( traps ( Figure Figure 1 1 , ( , ( c,d c,d )) must be sealed both )) must be sealed both vertically. ( In the case of anticlines ( Figure Figure 1 1 , (a )) , only a vertical seal, , (a )) , only a vertical seal, or or caprock caprock , is required; but faults ( , is required; but faults ( Figure Figure 1 1 ,. CHAPTER 04 CHAPTER 04 SEAL SEAL ( ( ROOF ROOF OR OR CAP CAP ROCK) ROCK) Definition Definition : : Seal is impermeable rock that forms