CONSTRUCTION METHOD OF WELL OF SMALL DIAMETRE Russian patent published in 2010 - IPC E21B7/00 E21B33/138 

FIELD: oil and gas industry.

SUBSTANCE: borehole sinking, lowering and attachment of casing and production strings is performed. The first part of the well bore - direction is drilled with diametre of not more than 300 mm by using clay drilling solution with density of 1.12-1.20 kg/m³, the second part - conductor is drilled with diametre of not more than 220 mm, and the third main part is drilled with diametre of not more than 160 mm. As drilling solution, when drilling the conductor and the third part, there used is service water with density of 1.00-1.09 kg/m³. Flow rate of service water is determined with lost circulation zones exceeding the service water absorption. After the caving zone is opened and the bottomhole is deepened below the caving zone by 10-15 m, the well bore is washed with service water in the volume of 1-2 of the well volume, layout with the bit is lifted, layout with open end is lowered below caving zone, washing is performed for 1.5-2.5 hours with water for caverns to be formed in he caving zone, layout is lifted above the caving zone by 10-30 m, process exposure is performed during 0.5-1 hour for the soil to fall from caverns, layout is lowered and the caving value is determined as per the varying depth of the bottom-hole. In case of caving the end of pipes reaches the bottom-hole with washing. Layout is lowered and the caving interval is filled in the following way: clay solution is pumped with density of 1.12-1.25 kg/m³ in volume of 1 to 5 m³, fresh flush fluid to cut the clay solution from cement solution in volume of 0.5-1 m³, cement solution with addition of 1 - 3% setting calcium chloride agent in the volume equal to 1.1-1.3 of the design one to shutoff the caving zone. Flushing with service water is performed. Layout is lifted from the well, process exposure is performed for waiting on cement during 4-6 hours, drilling assembly by means of which the well bore has been drilled is lowered, cement bridge is drilled within the interval of the caving zone and the well drilling is continued to the design depth. When cement solution is being pumped, tubes are rotated with rotation frequency of 10 to 60 rpm, and when cement solution is flushed with water, reciprocation of pipe string is performed by the value of 8-12 m with frequency of 1 to 4 lifts per minute.

EFFECT: reducing the costs for well construction and well flushing in cavern formation and caving conditions.