Through-tubing rotary drilling and its cementing challenges

The main objective of primary cementing is to provide complete and permanent annular isolation from mechanical and chemical stresses during drilling and production. Through-tubing rotary drilling (TTRD) technology presents its own challenges to cementing design. Use of bicenter drill bits that achieve a larger openhole size than the pass-through diameter introduces centralization difficulties and adds complexity to drilling-mud removal before cementing. By challenging common design practices, a design was proposed that combined low- and high-rheology fluid properties to achieve the objectives for cementing a 2 7/8-in. liner.