Design of double-packer and double-retainer completion string and its application in the collapse section of Well Ze 43-12x

Well Ze 43-12x is a key development well in Ze 43 buried hill, and its target layer of Ordovician is characterized by developed fractures and pores, so total circulation loss happens when the surface of the buried hill is drilled. And consequently, the borehole in the mudstone section of cap rocks is collapsed and bridge plug is formed in the downhole. To deal with this situation, the technical casing is run in advance to carry out pressure cementing in the Tertiary strata above 3 810.77 m by using the sand bridge. However, the mudstone section of 3 810.77~3 853.61 m is not cemented, so it is faced with the risk that buried-hill reservoir is buried in the late stage.In this paper, the technical difficulties of the third spud completion were analyzed, and accordingly the design idea of double-packer and double-retainer completion string was proposed. Then, the support technologies and tools were researched. As a result, the liner hanger was selected, the pressure level of each tool and formation sealing system were designed, the integrated tool of cuttings retainer and for-mation packer was developed, multiple effective sealing of different internal diameters in different lithological strata was realized and the precise steel belt design of spring steel of retaining tool can satisfy the requirements of irregular borehole sealing, achieving automatic regulation. The successful application of this technology in Well Ze 43-12x indicates that by virtue of this technology, non-cementing packoff in the complicated hole section can be realized by one trip string. It provides the reference for the packoff of complicated hole sections in similar wells.