Full replacement of drilling mud by cement slurry can provide good-quality cementing and cement sheath integrity. Drilling of deviated and horizontal wells is often accompanied by presence of bottlenecks in the wellbore where drilling mud cannot be fully pumped down the annulus, which significantly reduces chances of good-quality cementing. The most efficient technique to solve this problem is casing movement (rotation, reciprocation) when cement slurry is placed into the borehole annulus. Casing string reciprocation has significant geological and technical constraints, while casing string rotation does not produce hydrodynamic load, providing additional cement flow turbulence and opening space to flush fluid and cement slurry. Numerous bench tests and model experiments proved that casing rotation significantly increases degree of drill mud replacement by cement slurry. However, casing rotation during well cementing jobs remains the least applied technique. This is primarily due to the lack of specialized wellhead equipment and threaded joints load limitation. The paper reviews development of casing-rotation-while-cementing technology in PJSC TATNEFT. The first casing rotation operations were performed in horizontal wells, where 245-mm casing strings with premium threads were cemented using mobile slant drilling rigs. Application of a rotating cementing head enabled continuous casing rotation with no need for shutoffs to squeeze the cement plug and significantly improved cementing quality. A unique equipment package for liner cementing in horizontal wells of Devonian formations has been developed and tested, which included a cementing rotary swivel and a disconnecting tool. A versatile rotating cementing head has been manufactured for cementing of 102-168-mm casing strings using drilling rigs equipped with a top drive or a rotor, which enabled wide application of casing rotation technique. Experience has shown that the key barrier for nonstop casing rotation during cementing jobs is torque limitation for buttress thread connections. Generally, the breakdown torque is reached when cement slurry goes behind the casing string and, at the same time, rotating resistance occurs due to concentric rotation of the casing string. Another limiting factor is the effect of torque and drag accompanied by the increased hook load, resulting in casing rotation stoppage. Nevertheless, acoustic and gamma-gamma cement-bond logs prove beneficial effect of casing rotation in obtaining a homogeneous cement sheath.
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