Abstract
Lost circulation problems are often encountered when drilling or cementing highly permeable formations (e.g., sandstones), naturally fractured formations (e.g., limestones), or through depleted zones. Curing these problems is critical if the operator is to control the well and drill and complete it effectively. Failure on a primary cement job due to lost circulation not only increases well costs but also can jeopardize well integrity.
The use of cement plugs to cure the losses is well-known, and these plugs are often used as a last resort. Lost circulation materials (LCM) are usually added to the cement slurry to maximize the chance of successfully stopping the losses. LCM can also be added to the cement slurry during a primary cementing job if losses are expected in a particular well section. However, the design of such cement slurries is not obvious and may not completely solve the problem. It is often uncertain whether the use of an LCM will help to completely cure the losses. Lastly, the appropriate LCM is often difficult to identify.
This paper shows that it is possible to formulate effective cement slurries to solve most lost circulation problems. The technology can be used either for a cement plug or during primary cementing operations by adding specifically designed fibers in a controlled manner. A laboratory setup was built to evaluate the fibers’ efficiency in this application. We present the main results obtained and discuss the mechanism of action of the fibers. We also show that the combination of an enhanced particle size distribution cement slurry with this specific type of fiber allows the use of ultralightweight slurries, which leads to even better control of the losses and therefore increases the likelihood of success. These systems can be pumped with the standard cementing equipment used for typical primary cementing jobs. Several recommendations are made on the most effective way to use the fibers. We present Case histories that demonstrate improved slurry placement in traditionally difficult situations.
