Cementing the 20" surface casing in offshore Angola is associated with low fracture gradients and shallow water flows. These particular challenges require the use of lightweight slurry with both bead materials, and tight fluid loss control which was the initial approach for the section mentioned above. Due to high slurry volumes, rig site bulk logistics deployment, and budget, Foam cement was proposed. The Paper describes the design methodology and implementation of an automated foam cement system with real time monitoring. Based on the challenges presented above, Foam cement slurry has been the choice for some operators in Angola. Using a constant N2 injection rate with a foaming agent and a stabilizer that are injected into the slurry prior to it reaching the foaming "T" with variable choke bean size where N2 is injected into the slurry prior to pump downhole. Specific developed software’s, and Local training classes with in class and field training have proven to be very efficient allowing to have flawless execution pre and post job comparison and data evaluation.
The foamset cement system has shown to be very reliable and efficient on covering shallow surface areas likely to preserve fresh water aquifers. A standard slurry design was developed; thickening time adjusted depending on well conditions. The slurry was stable both at surface and downhole conditions with foam quality varying from 20% to 35%, providing required compressive strength. Since the implementation in Angola, 26 jobs have been performed successfully. This slurry can undergo a wide range of downhole pressures and temperatures variations without deforming the cement in place and or compromising well integrity.
This paper will share experience and success acquired in offshore Angola with best practices used in laboratory testing, both operations and engineering planning, execution, and post job data results.