Abstract
Horizontal wells can present special challenges for cementing operations. Extended-reach lateral sections, unconventional mineralogy, and high-pressure/high-temperature (HP/HT) environments can cause failures during and after the cement job. The high clay content and ductility of these formations force operators to use oil-based mud (OBM) to drill the curve and lateral section. A narrow pore-pressure/fracture-gradient window and tight annular clearance create higher than usual equivalent circulating densities (ECDs) and can affect mud displacement efficiency and cement placement. As unconventional reservoirs become more prevalent, increased focus on the cementing process will be vital to the long-term success of the well. New theories and proper planning will help decrease the probability of an irregular cement job and increase the chances of having zonal isolation for the life of the well.
In this paper, many aspects of the cement job design are discussed and recommendations are provided for horizontal cementing in unconventional reservoirs. New testing methods and additive composition help ensure the compatibility and thermal stability of the cementing fluids while creating more realistic wellbore hydraulic modeling and job optimization. Improved casing attachments and plug sets help increase displacement efficiency, while formation-specific cement designs increase effectiveness of the stimulation method. As multistage sliding-sleeves completion tools become more prevalent and increase efficiency, the cementing operation should align with the overall goal of the completion procedure. With the entire lateral section in one formation, it is not only critical to isolate the target formation from shallower zones but to also create a good annular seal between fracture stages. Without isolation, communication between stages can cause fracture treatments to migrate to unwanted areas. Modeling the expected temperatures, forces on the formation, displacement efficiency, and stress on the set cement sheath allows for a design that meets the expectations during the life cycle of the well. Complex temperature profiles create unfavorable design criteria, so accurate temperature determination is an important element to the cement design. With a renewed focus on the fundamentals of cementing, sufficient planning, and new technology, these unconventional reservoirs can become a manageable and sustainable resource for many years.
