Method for Preventing Sediment Disruption due to Degassing in Coring Operations

Volume expansion of sediments in coring operations due to sediment degassing as they travel from the higher pressure subsurface to the lower pressure drilling platform is a known problem. At reasonable depth below the seafloor, the sediments do not flow like slurry as they are more consolidated and have an inherent texture that contains minute cracks and crevasses. Though these sediments may be “soft,” they exhibit a heterogenous permeability with higher permeable zones such as cracks and crevasses serving as natural flow channels to release entrained gas as the surrounding pressure decreases. The standard practice is to capture sediments within a polycarbonate liner housed within the core barrel behind the drill bit. The liner is generally open on both ends. The change in pressure often leads to sediments undesirably surging out of the core liner from one or both ends and in extreme scenarios, cause the liner to explode due to an excessive pressure buildup from the trapped gas. These complications due to degassing result in longer extraction time, lost sediment samples, equipment repairs, and other problems.

SUMMARY OF TECHNOLOGY

Researchers at OSU have developed a perforated tube-section to provide a dedicated pathway for entrained gas to escape and optionally collected while holding the core sediments in place. To enable degassing, the liner can be a perforated half-tube or tube-section with one tapered end located inside the liner and fused to its inner wall creating a wedge at one end and an open channel at the other. The tapered portion of the tube-section is not perforated and compresses the sediments as they exit the drill head (Figure 1). Other embodiments can also include: a perforated tube-section placed on one side of the liner, an interior collar within the liner, or a perforated tube suspended in the center supported by ties (Figure 1). The last arrangement can be thought of a perforated liner held firmly within the standard (nonperforated) liner through semi-flexible ties. Adjusting the perforation size will allow for safe degassing without significantly altering the sediment texture. Chemical sensors can be located between the perforated and non-perforated pieces to provide real-time feedback. This novel device allows for the preservation of sediment samples, fluidic sensing, as well as decreasing the time lost to blowouts.