Tubing string is designed to transport oil and gas from the pay zone. It is compiled from tubing (pumping-and-compression pipes) by way of their consecutive screwing. Tubing may be as long as 3,000 meters and weigh up to 50 tons. There may be single and double tubing strings. Single tubing strings are usually used during pumping operations, and double strings – during flush stage and compressor lift stage when the pressure in the string needs to be lowered to assure oil and gas inflow from the reservoir.