Abstract
Complex formations refer to those with abundant fractures, alternating soft and hard layers, and poor cementation, stability and strength. Coring operations in complex formations often encounter such problems as core ripping, core disengagement and low core recovery. In light of features of complex formations, a coring tool with double core catchers has been developed. With combined advantages of self-locking and pressurized coring tools, the newly-developed coring tool may effectively cut the core and properly secure it in the inner barrel during coring operations in soft formations by using the pressurized catcher, in this way, the captured core can be protected against ripping and disengagement. While in coring operations in hard formations, the self-locking core catcher can be mobilized to penetrate into and cut the core. This tool has been used in two wells in Daqing Oilfield. On-site application shows this tool, with good formation adaptability, simple operation and low costs, can effectively enhance core recovery in complex formations to ensure accuracy of lab analysis, so reliable geologic data can be provided for highly efficient oilfield development.
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