已发表: 11/09/2021
已发表: 11/09/2021
The operator wanted to eliminate losses in a challenging 6-in openhole production section. The narrow pore-pressure window and fracture gradients impose formation instability, leading to severe lost circulation problems during the construction phase and compromising zonal isolation objective of the well. The 4 1/2-in production liner on the first appraisal well was cemented with total losses, requiring the revision of the cementing strategy. Mitigation measures of strengthening the formation or adding lost circulation material (LCM) would be insufficient. The first attempt was made in the next well, where the production liner was cemented.
A mud weight reduction from 1.2 to 1.05 sg was proposed prior to cementing. MPD equipment including RCD 3 rotating control device system and SUPER AUTOCHOKE high-pressure drilling choke control system maintained constant bottomhole pressure. With the assistance of VIRTUAL HYDRAULICS drilling fluid simulation software, the operator created a well displacement schedule with the required surface backpressure adjustment. CEMENTICS zonal isolation software determined the optimal pumping and backpressure schedule to maintain the cementing ECD within acceptable range and obtain effective mud displacement. To further reduce the risk of loss circulation, CemNET advanced loss-control fiber technology was proposed to further reduce the risk of lost circulation.
By varying the surface backpressure according to the calculated schedule, ECD was constantly maintained within a safe pore-pressure window and fracture gradient during the entire operation. While the team drilled the 6-in openhole section and upon reaching the total depth, an MPD static formation pressure test (SFPT) and MPD dynamic formation integrity test (DFIT) defined the safety window for ECD.
VIRTUAL HYDRAULICS software indicated each 0.02 sg of circulation density reduction was compensated by a surface backpressure increase of 5 atm [73.5 psi] increment per step, enabling maintenance of a constant ECD value of 1.25 sg. To enhance mud displacement, the liner was rotated at 15 rpm before activation of liner hanger. During cementing, operation-specific backpressure and pumping schedules were applied as defined by
CEMENTICS software to keep ECD in a safety window. CEMENTICS software optimized fluids volume, density, rheology requirements, and centralizer placement, ensuring effective mud displacement. CemNET technology treated the 1.90-sg cement slurry to further minimize the lost circulation risk. This approach helped obtain full returns during prejob circulation and reduce the total losses during cementing less than 1 m3. Surface cement returns during postjob circulation above the liner confirmed that cement slurry covered the liner overlap section.
An operator in Chepakovskoe Field in Russia used a combination of technologies to drill and cement the production liner in a geologically challenging area without complications.
