Design of life-cycle multi-barrier wellbore integrity in Dongfang 13-1 HTHP Gas Field

The target layer in Dongfang 13-1 Gas Field is a natural gas reservoir with high temperature (141℃), high pressure (pressure coefficient 1.90-1.94 g/cm3) and high CO2 content (14.63%-50.04%). When it is actually developed, cementing channeling, tubing and casing strength decline and corrosion occur easily, so the wellbore safety suffers from potential danger. To solve this problem, the “five-control” (lost circulation control, channeling control, corrosion control, strain control and temperature change control) aqueous resin drilling fluid system and the petroleum/gas-response self-repairing aqueous drilling fluid system were designed, depending on which, the whole wellbore cementing was realized. Besides that, six-level barrier design technology (aqueous resin drilling fluid at liner + packer at the top of liner + tieback inserted sealing + packer at the top of tieback string + self-repairing cementing + resin cementing) was proposed to provide multi-barrier safety system. Field application results show that the cementing qualities of ?177.8 mm liner and tieback sections in all production wells in Dongfang 13-1 Gas Field are satisfied. Since they were put into production, no annulus pressure has been recorded in any production well when wellhead pressure is monitored. By virtue of this technology, HTHP pay zones with high CO2 content are cemented effectively, the wellbore integrity from drilling and completion through the whole process of development and production is guaranteed and the risk of annulus pressure is mitigated.