已发表: 05/25/2017
已发表: 05/25/2017
The intermediate 12 1/4-in section of a deviated well in Peru was drilled conventionally with a final mud weight of 10.6 lbm/galUS. This density was necessary to maintain the integrity and stability of the wellbore. Cementing hydraulic simulations performed with CEMENTICS zonal isolation software showed that conventional cementing jobs would exceed the minimum fracture gradient. Circulating the 10.6-lbm/galUS drilling fluid and 15.6-lbm/galUS cement slurry in the reduced annular space between the 11 3/4-in and 9 5/8-in casings generated high friction losses and high equivalent circulating densities (ECDs).
To maintain ECDs below the minimum fracture gradient of 13.23 lbm/galUS during cement placement, M-I SWACO recommended displacing the actual 10.6-lbm/galUS drilling fluid with a 9.5-lbm/galUS fluid. This is less than the maximum pore pressure of 10.14 lbm/galUS, so surface backpressure would need to be applied when necessary with the MPD system to maintain the bottomhole pressure within the operating window (between the pore pressure and the fracture gradient) during the entire cementing operation. The pumping rate and surface backpressure schedule was prepared prior to the cementing job based on up-todate hydraulics simulations from CEMENTICS software. As an additional safeguard, an MPD flowmeter located at the well returns would be installed to measure the flow out against the flow in, providing early detection of any kick or loss event.
As the 9 5/8-in casing was run to the bottom conventionally, the use of a rotating control device was not necessary to perform MPC. Instead, M-I SWACO sealed the annulus with the annular BOP and applied surface backpressure using the MPC control system via the rig’s choke line.
A complete risk analysis ensured that the operation could be performed as safely as possible. Repsol and M-I SWACO also discussed contingency plans prior to the operation.
Challenge: Overcome a reduced annular flow area between 9 5/8-in casing and 11 3/4-in casing, together with a narrow pressure window, which significantly increased the risk of losses during cement placement.
Solution:
Results:
