Importance of Cement Fluid Loss Additives

Owning to the fluid loss behavior of cement slurry, two stages come into question. Firstly, a dynamic one corresponding to the placement and secondly, a static one, the waiting on cement.

During the first period, the slurry flow eroded the filter cake as it grows and thus a rapid steady state is reached, due to which filtration occurs and through a cake of constant thickness, the slurry loses water but no solid particle, along with its density increases in line along with the fluid loss rate.

During the second period, which is known as the static, the cake grows as a result of absence of flow. It may grow to a point where it locally and completely fills the annulus; the bridging takes place and the hydrostatic pressure can no longer be transmitted to the deeper zones.

In the dynamic state, the maximum acceptable value of the total volume of the fluid is lost during the cement placement and it can be easily calculated from an upper density limit. As the basic slurry properties, which include the thickening time and rheology, which are greatly dependent on density, they may be hence used to define this limit. In order to convert the total amount of the fluid loss into the API fluid loss value, three parameters are essential, these include the mudcake thickness, the permeable formation area and its permeability.

Depending upon a typical mudcake resistance, the estimation in dynamic and static conditions could cause fluid loss and in some conditions it can be reduced to an API value, an order of magnitude lower than what is usually considered as a fair control of fluid loss.

Experts believe, there is still very little known about the effects of mechanical aids, cement, spacers and washes on the mudcake state.