Abstract
Generally, long-radius wells are kicked off in the base of the Jilh (BJD) formation in the Ghawar field, Saudi Arabia. The well profiles require 3° to 4°/100 ft dogleg severity (DLS). The two problematic formations encountered while drilling these curve sections are the BJD and the Sudair formation. Overpressure exists in the BJD, and drilling in this unstable formation often leads to kicks. The Sudair formation, which is plastic shale, has a tendency to microball the bit, leading to slower penetration rates. Higher inclination through Sudair formation generally means more contact and hence longer duration of slower rate of penetration (ROP).
Responding to domestic demand for natural gas growth, Saudi Aramco started to focus on reducing unit cost and maximizing reservoir production. After a feasibility analysis, drilling medium-radius curve wells with steerable motors was put forth as a solution; this would mean drilling vertically through problematic formations and target entry (TE) could be reached in 800 to 900 ft of vertical section which would result in increase in reservoir exposure and therefore production. Drilling a medium-curvature well with a conventional motor assembly required a minimum of five runs. Drilling with a steerable motor and rock bit combination resulted in extra bit trips, wiper trips to clean the hole, and multiple reaming trips before running the liner. In all, drilling efficiency was poor because of slow penetration rates and multiple bit trips.
After some modifications, a high build rate rotary steerable system (HRSS) was introduced in a well in a challenging deep gas environment. Deployment of the new technology allowed the kickoff point to be pushed deeper, reducing risk and cost. The section was drilled in a single run, saving 6.5 days and improving penetration rate 84% over conventional mud motor bottomhole assembly (BHA). The introduction of new technology, while significant, was not the only factor contributing to the step change in drilling performance; the success was realized by a thorough understanding of local drilling conditions, which informed bit, BHA, and well design decisions and led to superior execution.
