Case Study: Implementing Continuous Circulation and Managed Pressure Drilling Techniques to Drill in the Challenging Perla Gas Field in Offshore Venezuela

Abstract

Abstract The Perla Gas Field is a naturally-fractured carbonate formation in offshore Venezuela that often requires advanced technology to complete and optimize drilling operations while also minimizing nonproductive time (NPT). To overcome the challenges and reduce NPT demonstrated on a well drilled in 2010 in the Perla field, continuous circulation and managed pressure drilling (MPD) technologies were used to drill two subsequent wells in 2016. Drilling in the Perla field is a challenge because of its narrow pore pressure and fracture pressure window, which increases the potential for issues such as lost circulation, kicks, wellbore instability, and connection gas. To overcome challenges encountered in 2010 while also decreasing NPT, a combination of MPD and continuous circulation technologies were selected to drill the wells. To navigate the tight drilling windows, MPD was selected for this campaign, with continuous circulation implemented to supplement the MPD process by removing any transient time or pump cycling effects during connections. Continuous circulation allows the operator to circulate fluid downhole during the drill pipe connections. The system includes a manifold connected into the standpipe that performs the diversion, and subs installed onto the top of each stand of drill pipe, creating two independent flow paths for drilling an open hole section. MPD creates a closed loop system and allows the operator to safely add or remove backpressure at the surface in order to control bottom hole pressure (BHP). In Perla, a well was drilled in 2010 with significant losses as a result of an unexpectedly narrow drilling window of 0.5 ppg equivalent mud weight between pore and fracture pressures (9.8 to 10.3 ppg, respectively). In 2016, the new combined solution enabled drilling of the lateral in both wells by maintaining a constant BHP during all phases, mitigating influxes or losses, removing static mud pressure spikes (breaking gels), reducing connection gas, and improving hole cleaning. A statically underbalanced 9 ppg fluid was used while targeting a 10.2 ppg equivalent mud weight throughout the length of the 8½ in lateral on more than 150 drill pipe connections to decrease tripping time, get liner to depth, and improve the estimated time to total depth, decreasing overall risk, NPT, and cost. In exploratory and development wells, risks increase when different than expected well conditions are encountered during drilling. This case study provides an example of the viability of combining MPD and continuous circulation, a solution which is highly applicable in offshore Latin America, including but not limited to Venezuela.