Collaborative Approach Overcomes Cementing Challenges in Narrow Pressure Window Environment

The collaborative approach used for cementing the production liner in an onshore development well in Russia is presented. The reservoir has a narrow window between pore and fracture pressures, which has previously caused formation instability and severe lost circulation issues during well construction, compromising zonal isolation objectives. Total loss of fluids experienced while cementing the 114.3 mm production liner in the first appraisal well in the field led to revising the cementing strategy. Collaboration among various parts of the drilling department and the opportunity to define a new approach resulted in a decision to introduce managed pressure drilling (MPD) to address the challenges associated with a narrow pressure window and uncertainty in pore pressure while drilling and cementing. This enabled implementing the optimal mud weight and adjusting equivalent circulating density (ECD) during cementing with minimum overbalance. Reducing the mud weight from 1.20 SG to 1.05 SG eliminated losses after running the liner and while cementing it. As a result, pre-job circulation rates and pumping rates during cementing could be increased, improving mud removal efficiency and achieving top of cement at the required depth. The constant-bottomhole-pressure mode of MPD was used to maintain the same ECD during displacement of the well to a lighter fluid and during cementing, avoiding well influx during pumpoff events by compensating for the annular friction pressure loss with surface backpressure. This first onshore managed pressure cementing operation executed within the same field in Russia (later named as field A) was completed flawlessly, with no safety or quality issues, zero nonproductive time, and achievement of the required zonal isolation across the challenging production section. The collaborative approach used was a novel strategy, with the mud weight program strategically adjusted before and during the cementing operation to achieve zonal isolation objectives.