Unconventional and mature field cementing operations in Argentina present challenges through intermediate and production sections. Typically, challenges are associated with specific formation geologic properties, e.g., naturally fractured rock combined with high-reservoir pressure and depleted sandstones. The formation gradients require better control over equivalent-circulation densities (ECD) during cementing to mitigate risk of lost circulation (LC). Such issues can lead to poor zonal isolation, sustained-casing pressure (SCP), and increased costs. Described herein is a new tailored spacer system engineered to mitigate LC during cementing and its use in a field application to reduce risks of LC and improve zonal isolation in a loss-prone formation.
Lost circulation (LC) is one of the largest contributors to non-productive time (NPT) and overall cost of well construction operations. Fluid losses may occur via natural formation thief zones, e.g. permeable, fractured, or vugular sections, through unconsolidated or highly depleted wells. LC thief zones may also be encountered when induced by exceeding fracture gradients of the formation during operations, thus breaking down the wellbore. When risks of inducing fractures are present, careful management of fluid properties and equivalent circulating density (ECD) are necessary. LC may occur under a range of conditions and loss rates, including seepage (up to 10 bbl/hr), partial (10- 100 bbl/hr), severe (100–500 bbl/hr), and total (no returns) (Nayberg, 1987; Nelson, 2006).
In drilling and cementing operations, LC is commonly encountered, and can be particularly harmful to zonal isolation. Efforts should be made to arrest LC during the drilling phase, prior to cementing; however, losses may persist. When LC is experienced during primary cementing and left untreated, zonal isolation may be compromised, and cementing objectives may not be met, including the inability to achieve planned top of cement (TOC). Not achieving TOC in cementing potentially results in a failure to isolate critical sections and/or meet regulatory specifications, leading to added operational time and cost to remediate.
Cementing slurry designs are subjected to hydraulic simulations to optimize pump rates with minimized ECD; however, additional mitigations may be necessary to reduce risks of LC during cementing. Like drilling practices, these may include use of LC materials exhibiting various sizes and morphologies, amongst other properties in fluid formulations, to plug or bridge thief zones and stop fluid losses.