Effective Zonal Isolation in Horizontal Wells: Mitigating Negative Impact of Mud Channels
Currently, hydraulic isolation of wells drilled with nonaqueous fluids
(NAFs) relies heavily on the elimination of mud from the annuli before the
placement of cement. Failure to expel all NAFs will result in residual fluid
channels that will compromise well integrity and can even serve as
nonproductive communication pathways during subsequent stimulation treatments.
To mitigate this risk, an interactive cementing system is presented that is
designed to reduce conductivity of the residual mud channels.
Although mud removal remains an integral part of the cementing process,
this new cement formulation was developed to improve zonal isolation in the
case of poor mud removal. The unique cement system reacts with the hydrocarbons
present in NAFs, leading to a reduction of channel permeability and mobility.
This significantly improves the likelihood of hydraulic isolation. Specialized
testing protocols were developed to enable the demonstration of the
capabilities of this new system. In addition, API testing methods and
analytical techniques were used to optimize the slurry.
The development of the new cement system focused on the optimization of
the active component concentration to give a favorable interaction with NAF,
and at the same time, minimize the effect on cement rheology and mechanical
properties. Procedures developed in-house demonstrated that the new system
effectively reduces hydraulic conductivity of microannuli as well as channels
up to several tenths of inches in size. Zonal isolation laboratory experiments
were extrapolated to predict whether the modified channels can withstand the
range of differential pressures typically seen between neighboring fracturing
stages. This is the most critical operation that the cement sheath would be
Field tests are on-going at the time of writing this manuscript, and the
preliminary results will be presented and discussed in this paper.