Sealing of rocks

Parameter improvements (reduced rock mass permeability and rock mass thermal expansion by the KTH/SKI team, and increased thermal expansion coefficient and reduced swelling pressure constant of the buffer by JNC team) -Inclusion of the sealing of rock fractures by penetrating bentonite by the KTH/SKI team, which can explain the uniform (axisymmetric) wetting of the bentonite. 

Cataclasis the fault movement has destroyed the rock matrix close to the fault plane. Individual quartz grains have been ground up creating a seal comprising of rock flour . 

To a cooled pressure autoclave are added 288 gm (4.0 moles) of isobutyralde-hyde, 150 gm of potassium carbonate, 500 ml of xylene, and 200 gm (4.4 moles) of dimethylamine. The autoclave is sealed, and rocked, or stirred for 4 hr at 100°C, cooled, vented, and opened. The liquid is distilled to afford 122 gm of a forerun, b.p. 53°-87°C, and then 216 gm (55 %) of the enamine, b.p. 87°-88°C, n d° 1.4221. Less xylene and potassium carbonate gave poor results. In addition, if the distillation is not carried out immediately after the reaction, lower yields of the enamine are possible. 

The movement of petroleum from the place of its origin to the traps where accumulations are found is believed to have occurred in an upward direction. This movement took place as the result of the tendency for oil and gas to rise through the ancient seawater with which the pore spaces of the sedimentary foimations were filled when originally laid down. An underground porous formation or series of rocks which occur in some shape favorable to the trapping of oil and gas must also be covered or adjoined by a layer or rock that provides a coveting or seal for the trap. A seal of this type, frequently called a cap rock, stops further upward movement of petroleum through the pore spaces. 

Lens-Type Traps. These form in limestone and sand. In this type of trap the reservoir is sealed in its upper regions by abrupt changes in the amount of connected pore space within a formation. A trap formed in sand is shown in Fig, 7(a). An example is the Burbank Field in Osage County, Oklahoma. This type of trap may occur in sandstones where irregular deposition of sand and shale occurred at the time the formation was laid down. In these cases, oil is confined within the porous parts of the rock hy the nonporous parts of rock surrounding it. A lens-type trap formed in limestone is shown in Fig. 7(b). In limestone formations there are frequent areas of high porosity with a tendency to form traps. Examples of limestone reservoirs of this type are found in the limestone fields of West Texas. 

Ramsay J. (1980) The crack-seal mechanism of rock deformation. Nature 284, 135-139. 

Hydrodynamic conditions influence the system of hydrocarbon migration in a basin, i.e. the volumes of hydrocarbons available for entrapment in a certain part of the basin, and the trapping energy conditions in the basin, i.e. the location of potential trapping positions and the sealing capacity of rocks and faults (Sections 5.2 and 5.3). 

Tectonic forces may affect the hydrocarbon accumulation and entrapment indirectly by changing the hydrodynamic condition of the basin (Chapter 4) and thus the sealing capacity of rocks and the holding capacity of hydrostatic traps. 

The fault sealing mechanisms considered are those which occur as a direct result of the faulting process, i.e., those due to either across-fault juxtapositions of reservoir and non-reservoir units or to the presence of sealing fault rocks, i.e., membrane seals. The diage-netic contribution to seals (Knipe, 1992) is not considered. 

Fig. 7. Fault assisted top seal leakage, (a) Probability of top seal leakage. Analytical solution for shale beds of constant thickness /, in which identical faults of maximum throw are randomly dispersed. This relationship for probability of seal leakage also holds approximately for seals in which the shale layers and fault throws are each normally distributed about the same mean t. (b) Determination of the throw-cumulative frequency relationship. Faults in a volume of rock, from a map-based statistical analysis of the fault population. Adding 1 to the slope C2 simulates the addition of the third dimension (Gauthier and Lake, 1993). Here a length/Tfnjx fst o 100 1 was used, (c) Determination of the seal risk. Comparing the number of faults required for leakage with the number of faults in the trap volume determines the seal risk. In the example shown, the probability that the seal is breached lies between 50 and 90%, For points in the sealed field, the effect of increasing fault throw on the number of faults needed for breaching is illustrated.

Case Thickness of rock salt seal (m) Methane column held (std. m /m ) Structural height (m) Porosity Max. of reservoir capacity (%) of reservoir (std. m /m ) ... 

The plot of Fig. 7 is made against the maximum depth reached by the seal. For cases C-G this is the present depth for cases A, B, M, and N this was the depth at 85 myrbp. The maximum depth of the seal has been chosen as the control on the permeabilities because a body of rock salt once exposed to a pres-sure/temperature regime largely keeps the petrophysical properties acquired at that time even if subsequently discharged and cooled due to tectonic uplift (permeability hysteresis see Borgmeier and Weber,... 

An alternative explanation, which we refer to as pressure-inhibited charge, is that downward hydrocarbon migration from sealing source rocks ceases as the pressure of the underlying stratigraphically contiguous reservoir approaches the pore-pressure of the seal. This process is consistent with capillary theory. 

Seal properties Rock seal properties are usually described in terms of their capillary pressure characteristics, primarily wettability, entry and displacement pressures, and irreducible wetting phase saturation. Wettability defines which fluids will preferentially occupy the smallest rock pores. Entry pressure is the capillary pressure at which the non-wetting phase first displaces the wetting phase, while displacement pressure is the capillary pressure at which the non-wetting phase first forms a continuous network within the pore structure. The irreducible wetting phase saturation describes the initial connate fluid saturation at the top of the capillary column. 

Over time, the primitive oceans dried up. The sand and mud that had accumulated on the ocean floors changed into rock. The natural gas and liquid petroleum that had formed on the ocean floor was trapped in the rock. It flowed through cracks in the rock until it reached porous rock that acted like a sponge and soaked up the petroleum and natural gas. These fossil fuels remain trapped in the porous rock by non-porous layers of rock that act like caps or seals on the porous rocks. 

Use of higher E (Young s modulus) and v (Poisson s ratio) of the bentonite near the heater, and use of a sealed layer of rock around the bentonite by the CNSC team. 

Jin Anzhong, Zhao Qiang, Liu Xiqiang. 1997. Result of electromagnetic radiation of rock in small seal abserved from field experiment. Acta Seismologica Sinica, 19(1) 45-50. 

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