METHOD FOR CONTROLLING TECHNICAL CONDITION OF WELLS IN PERMAFROST ROCKS Russian patent published in 2007 - IPC E21B36/00 

FIELD: gas and oil industry, possible use, in particular, for selecting constructions of wells, controlling quality of construction and technical condition of wells during their construction and operation in permafrost rocks.

SUBSTANCE: method includes inspection of cut of cryo-litho-zone to determine ice level, subsidence of permafrost rocks and cavernosity of borehole with selection of modern and relict permafrost rocks in cut and also includes determining of quality of cementation of casing columns overlying the cryo-litho-zone. Inspection of ice level of cut of cryo-litho-zone of well is performed at temperature of permafrost rocks, which is lower in modern permafrost rocks or is equal in relict permafrost rocks to temperature of ice-water phase transition in rocks at cryo-litho-zone cut inspection depth. Watered rocks are detected when apparent electric resistance is ≤ 5-7 Ohm·m and ice level value m=0 kg/m³. Frozen subsiding rocks with ice level coefficient m ≥ 3 kg/m³ are detected on basis of apparent electric resistance value being ≥ 20 Ohm·m. Cooled down melting permafrost rocks with ice level coefficient m<3 kg/m³ are selected with consideration of apparent electric resistances lying within interval of values ranging from 7 to 20 Ohm·m. Shoe of permafrost rocks position boundary is determined on basis of ice level coefficient m=3 kg/m³. After that subsiding rocks are registered with ice level coefficient m≥180-250 kg/m³. After inspection of cavernosity of well borehole, cavernous rocks are selected, subject to cave-in during melting. Further, total thickness of cavernous and subsiding permafrost rocks is determined in upper and lower parts of cut of cryo-litho-zone of well, and also length and thickness of rocks with caverns not filled with cement. Then, total thickness is determined of cavernous, subsiding permafrost rocks, their subsiding during melting of rocks in upper and lower parts of cut of cryo-litho-zone of well, and also critical length of well construction by longitudinal stability. After that criterion of emergency danger of well is determined, appropriate for danger degree in case of possible loss of longitudinal stability by well construction, on basis of provided mathematical expression.

EFFECT: increased reliability of operation of wells in subsiding and cavernous permafrost rocks and provision of estimation of technical condition of wells on basis of longitudinal stability of construction during melting of permafrost rocks with consideration of certain deep geo-cryological conditions on basis of subsidence and cavernosity.

2 cl, 2 dwg