METHOD OF INCREASING LONGITUDINAL STABILITY OF WELL STRUCTURE IN PERMAFROST

FIELD: oil and gas industry. ^ SUBSTANCE: invention refers to oil and gas industry and can be used particularly at making decision on construction process, on wells structure and on measures to be taken to increase their longitudinal stability in thawing out with subsidence, and cavernous permafrost rocks (PFR). Method includes well boring, control over heat mode of construction and operation of well, lowering of thermometric pipes (TMP) beyond the outer column into a well head zone while the annular space (AS) of the latter is subject to cementing, then lowering into TMP seasonally operating cooling devices (SOCD) to reduce intensity of PFR thawing out and provide support to the well structure onto surrounding rocks maintained in frozen condition. Then well caliper survey is performed, an upper cavernous with subsidence interval of PFR with length Lcl is determined, and critical length (Lcr) of maintaining longitudinal stability of a well structure is calculated. When boring, a borehole adjacent to the surface is reamed with a reamer of diameter Dr taking into consideration cavernosity of a borehole up to depth Lcl; also embedding of a borehole with reaming into rocks, stable at thawing out and deposited below depth Lcl, is performed. Diameter of the reamer Dr is determined from a reduced mathematical expression in a formula. Cementing of the well borehole is carried out, and by means of TMP control over quality of cementing, stabilisation of the well and assessment of longitudinal stability of the structure is performed. There are revealed cryolite zones with subsidence, cavernous PFR, and caverns not filled with cement beyond the outer column, overlapping PFR. There are determined dimensions of gaps near surface and at depth around the well including their diameters and depth, also of gaps between the cement ring around the outer column and rock in AS. On base of obtained measurements and on radii of thawing out of PFR there are determined the summary lengths of upper and lower subsidence zones, lengths (extensions) of caverns, adjacent to them, and cavernous intervals; on reduced expressions the summary volumes of gaps are determined. Further there are determined maximum continuous intervals, lengths Lg of not filled gaps, caverns, not filled with cement, in PFR with subsidence, cavernous PFR, in the upper adjacent to the surface interval of cryolite zone, which can be filled, and in lower interval, where filling has not reached. At that Lg must not ex