Currently, many producing formations are carbonates and/or depleted sands that are characterized by highly permeable flow paths or vugs. Severe-to-total loss of drilling fluid in these formations is a major concern from both the drilling and reservoir damage perspectives. Conventional particulate lost circulation materials (LCMs), such as acid-soluble ground marble, might not effectively cure severe losses. Furthermore, because the application is in a producing formation, avoiding reservoir damage is a major criterion that any potential solution should satisfy. The "band-width" of available solutions that are both efficient and reservoir friendly is narrow, leading to both high cost and potentially risky drilling practices.
A possible solution is using an acid-soluble right-angle-setting composition (RAS-Co) that was developed to provide the industry with a more efficient solution for plugging and isolating producing zones that have high drilling fluid loss rates. RAS-Co is formulated from inorganic, nonhazardous powders and fluids mixed in fresh water or seawater. RAS-Co is engineered to be a low-viscosity (18 to 30 cp) fluid containing small particulates, which allows it to be mixed at the rigsite and pumped through any drillstring configuration. It is designed to react at a specific bottomhole circulating temperature (BHCT) in a consistent and controllable manner with a "right-angle" set. Once it is spotted/placed in the suspected loss zone, it helps eliminate further fluid losses and formation damage. The small particle size distribution acts as a pore-bridging material while in the fluid state, and the right-angle-set characteristic makes the material non-invasive to the formation and allows it to be easily drilled or removed with acid. It can be used in zones with up to 300°F circulating temperature and tolerates up to 50% contamination with water or drilling fluids.
This paper describes attributes of RAS-Co along with successful field applications that illustrate it is an effective solution for controlling reservoir damage by helping to stop severe lost circulation events.