Changes

Freezing core is often done to minimize the loss of the volatile hydrocarbons, to preserve the fabric and structure of unconsolidated cores, and to immobilize the fluids in pressure cores.<ref name=Torsaeter_1985>Torsaeter, O., 1985, The effect of freezing of slightly consolidated cores: [[spe:14300|SPE paper 14300]], 60th Annual Technical Conference and Exhibition, Las Vegas, NV, Sept. 22-25.</ref> The most common method of freezing core is with dry ice. However, light hydrocarbon fractions are not maintained at dry ice temperatures ([[temperature::-78.5&deg;C]]), thus liquid nitrogen temperatures ([[temperature::-195.8&deg;C]]) are required.

Freezing core is often done to minimize the loss of the volatile hydrocarbons, to preserve the fabric and structure of unconsolidated cores, and to immobilize the fluids in pressure cores.<ref name=Torsaeter_1985>Torsaeter, O., 1985, The effect of freezing of slightly consolidated cores: [[spe:14300|SPE paper 14300]], 60th Annual Technical Conference and Exhibition, Las Vegas, NV, Sept. 22-25.</ref> The most common method of freezing core is with dry ice. However, light hydrocarbon fractions are not maintained at dry ice temperatures ([[temperature::-78.5&deg;C]]), thus liquid nitrogen temperatures ([[temperature::-195.8&deg;C]]) are required.

The exact effects of freezing on the rock and its petrophysical properties are still unknown. A variety of studies examining the effects of freezing on porosity and permeability show contradictory results.<ref name=Wisenbaker_1947>Wisenbaker, J. D., 1947, Quick freezing of cores preserves fluid contents: Oil Weekly, v. 124, n. 9, p. 42-46.</ref> <ref name=Lebeaux_1952>Lebeaux, J. M., 1952, Some effects of quick-freezing upon the permeability and porosity of oil well cores: Journal of Petroleum Technology, v. 4, n. 11, p. 19-20.</ref> <ref name=Kelton_1953>Kelton, F. C., 1953, Effect of quick-freezing versus saturation of oil well cores: Petroleum Transactions, AIME, v. 198, p. 312-314.</ref> <ref name=Torsaeter_1985 />). The freezing process may affect the rock structure due to ice formation and may affect the wettability due to precipitation of hydrocarbons onto pore surfaces. To minimize damage by ice, the cores should be frozen quickly to reduce ice crystal growth.

The exact effects of freezing on the rock and its petrophysical properties are still unknown. A variety of studies examining the effects of freezing on porosity and permeability show contradictory results.<ref name=Wisenbaker_1947>Wisenbaker, J. D., 1947, Quick freezing of cores preserves fluid contents: Oil Weekly, v. 124, n. 9, p. 42-46.</ref> <ref name=Lebeaux_1952>Lebeaux, J. M., 1952, Some effects of quick-freezing upon the permeability and porosity of oil well cores: Journal of Petroleum Technology, v. 4, n. 11, p. 19-20.</ref> <ref name=Kelton_1953>Kelton, F. C., 1953, Effect of quick-freezing versus saturation of oil well cores: Petroleum Transactions, AIME, v. 198, p. 312-314.</ref> <ref name=Torsaeter_1985 /> The freezing process may affect the rock structure due to ice formation and may affect the wettability due to precipitation of hydrocarbons onto pore surfaces. To minimize damage by ice, the cores should be frozen quickly to reduce ice crystal growth.

Sublimation from the core surface must be prevented during storage. One method is to quick freeze a layer of brine on the surface of the core. The brine does not enter the frozen core; subsequent sublimation comes from this layer, not the core.

Sublimation from the core surface must be prevented during storage. One method is to quick freeze a layer of brine on the surface of the core. The brine does not enter the frozen core; subsequent sublimation comes from this layer, not the core.