초록 ▼

An insulated well casing is described that includes an inner tubular member and an outer tubular casing member joined together at their ends by a weldment, typically formed into a thrust cone suitable for joining strings of insulated casings to insulate and encase the entire depth of a well for deli

An insulated well casing is described that includes an inner tubular member and an outer tubular casing member joined together at their ends by a weldment, typically formed into a thrust cone suitable for joining strings of insulated casings to insulate and encase the entire depth of a well for delivery of steam, for example, into a producing formation. A key element of the invention is pre-stressing the integrated casing by tensioning the inner tubular member at a level less than the yield strength of the tubular material prior to joining the weldments of the unit together. The resulting integrated casing includes a tensioned inner tubular member and an outer member that is in compression. The tensioning load is selected such that at well operating temperatures and pressures, the compressive stresses exerted upon the casing at the bottom of the hole approach the compressive yield strengt of the inner tubular member, but leave a desired margin of safety. The casing of the invention permits injecting high-temperature steam at 450°-700°F. adjacent the insulated casing and recovering product from the formation through a central annular uninsulated tubing. The temperature and stress experienced by the outer tubular casing member, grouted to the wellbore are such that the adhesive bonds between the casing and the formation remain intact and the casing is not significantly deformed. The insulated casing of the invention reduces heat loss from the injected steam to the surrounding formations to less than 1%.

대표청구항 ▼

An insulated wellbore casing adapted to be cemented to the surrounding earth of a wellbore, comprising: an outer tubular member adapted to be cemented to the surrounding earth of the wellbore; an inner tubular member, concentrically spaced from said outer tubular member, having terminal ends substan

An insulated wellbore casing adapted to be cemented to the surrounding earth of a wellbore, comprising: an outer tubular member adapted to be cemented to the surrounding earth of the wellbore; an inner tubular member, concentrically spaced from said outer tubular member, having terminal ends substantially adjacent said outer tubular member and providing an insulating annular cavity therebetween; insulation material filling said annular cavity between said inner and outer tubulars; and weldments that join said outer and inner tubular members with said insulation held therebetween, said weldments joined while said inner tubular member is tensioned, whereby an integrated casing unit is formed that is pre-stressed to accommodate linear thermal expansion of said inner tubular member at well-operating temperatures.