Abstract
The use of lightweight cement systems to plug loss zones, reinforce wells in weak formations, and enforce zonal isolation is well established. Performance failure is costly and undesirable. Remedial work could result in both high costs and nonproductive time. In extreme cases, an entire well could be lost. Performance of a lightweight cement system is limited by its design strength, which directly affects the maximum placement depth. Conventional water-extended cement slurries are not considered adequate for unconventional reservoirs such as shale and sandstone. Use of ceramic microsphere and glass beads in cement formulations with reduced slurry densities has steadily increased over time. However, in cases where formulation stability is compromised, field application of these slurries is challenging because of the limits in operational latitude. In fact, density segregation due the use of glass beads is one cause of formulation instability.
Locally available raw materials have been found to combine with carefully selected glass microspheres in lightweight cement tested at nearly double the mechanical strength of a conventional control formulation. The resulting slurry showed improved rheology and fluid loss control for optimal performance in the well under bottomhole conditions. Because the combined material improves predictability of downhole density, complete circulation can be achieved when deploying this slurry. The new slurry design should enable placement of lightweight cement in deeper wells, with improved pumpability and on-location rheology and set time control.
This paper describes the formulation, lab test results and postulates the mineralogy differentiation through use of XRD testing.
