Liquid Trapper™ provides the means to accurately determine oil saturation. A quality core is vital to proper analysis but contains a shortcoming in accurate determination of fluid types and volume for quantifying residual oil volumes. During the core pull out trip to surface, the hydrostatic pressure decreases gradually allowing gas to come out of solution inside the core. During its escape from the core, expanded gas drives the formation fluids expelling oil and/or water out of the core’s pore spaces. Using standard core barrels, the expelled core fluids are completely lost and cannot be used to properly quantify fluid parameters.
This issue has always been considered a shortfall of conventional coring techniques, particularly in situations where oil or water saturations are critical. The industry has made many attempts to overcome this challenge but the technologies developed so far have failed to provide a reliable, cost-effective solution. Liquid Trapper™ technology overcomes the challenge and provides the means to contain the expelled fluid for further analysis and quantification.
Liquid Trapper™ technology is designed to trap fluids escaping from the core on its assent from the wellbore. The technology is applicable where the identification of pore fluid type and volumes are critical. The most obvious cases include secondary and tertiary recovery projects. A sample of the fluid is collected with one meter resolution. The fluid volume is directly measured on site and the sample can be sent for compositional analysis.
As pressure drops during the trip to surface, gas is liberated from the oil and expands in accordance with Boyle’s law. The gas drives out a portion of all liquids present in the core depending on reservoir properties and fluid characteristics. The liberated fluids flow freely out of the core and disappear within the mud system in traditional systems. Liquid Trapper™ captures these fluids for volume quantification and further analysis.
The Liquid Trapper™ consists of a specifically designed liner assembly which utilizes an inflatable seals which “trap” the liquids escaping from the core. The Liquid Trapper™ inner barrel system may be pre-saturated with a selected fluid before it is run in hole. This saturating-fluid is selected depending on the information targeted from the core. The saturating fluid can eventually be doped using a mud tracer and is maintained inside the inner tube using a ceramic plug. The plug disintegrates once the assembly reaches bottom. Coring proceeds as normal and the saturation fluid reduces mud contamination of the core inside the inner barrel.
The inner barrel of the Liquid Trapper™ consists of stacked, one meter modules which represent closed ‘cells’. Once activated, these cells provide a barrier around the core via innovative seal joints which impede fluid movement. The captured fluids separate naturally based on their specific gravity. The seals will allow core gases to escape upward, thus eliminating a trapped-gas hazard at surface.
Within the closed cells, fluids expelled from the core are trapped in the annulus between the inner and outer cell wall. On recovery, the core is laid down normally using proper core cradles. The Liquid Trapper™ cells are cut into 1m sections between the individual seals. The trapped fluid is recovered and the core is readied for transport as normal.
In the lab, the fluids are analysed. Whole core analyses are conducted and actual material balance is re-built, based on core and fluid volumes. The collected oil (or water) bleeding from the core is reconstituted into the core porosity to correct the fluids saturation for bleeding. The combined amount of oil in the core and Liquid Trapper™ is converted to in-situ conditions by applying the current oil formation volume factor while pore volume is adjusted for compaction using the stress correction factor.