Petrobras achieves lowest cost per foot in Brazilian presalt drilling

With Halliburton Sperry Drilling’s combo solution, Petrobras was able to drill 4,984 ft (1,519 m) with an average ROP rate of 95 ft (29 m) per hour, setting the highest ROPs across the entire 17 ½-in., 16-in., and 14 ¾-in. sections. Particularly in the 14 ¾-in. section, the operator realized the lowest cost per foot/meter for a salt section. With these new drilling records, Halliburton Sperry Drilling says that it helped Petrobras maximize asset value by reducing costly deepwater well time by four days. (Courtesy Halliburton)

Petrobras has extensive experience in drilling pre-salt and sub-salt formations in deepwater areas offshore Brazil. The operator was drilling a deepwater well approximately 170 miles (274 kilometers) off the Brazilian southeast coast at a water depth of 6,900 ft (2,103 m), and the objective was to reduce well time in the presalt oil reserves in the Santos and Campos basins. This area contains large amounts of proven reserves at depths of 6,562 ft (2,000 m) below the presalt layer and the overburden. The potential for huge returns comes at a very high risk, as drilling through this much salt and rock to extract the pre-salt oil and gas can be challenging and extremely costly.

Presalt drilling

Brazil’s presalt environments have multiple challenges. Reservoirs in these salt domains are extremely difficult because of low penetration rates and the interbedded nature of the salt formations, which have different drilling characteristics. There is a high risk of stuck pipe and torsional resistance due to the shifting salt environment and salt creep, thus requiring higher drillstring rotations to achieve the required rates of penetration (ROPs) for each section in order to safely set casing.

Additionally, the corrosive environment presents a challenge because it contains significant amounts of carbon dioxide (CO2) and hydrogen sulfide (H2S), which cause a need for special cement and metallurgies throughout the drilling and completion processes. The challenge to drill a well faster requires a broad scope of solutions that feature best practices, along with lessons learned from previous Brazilian pre-salt drilling. Without these solutions, operators face longer well time due to lower ROPs and failures caused by the challenging salt formations.

Engineered drilling solution

Halliburton Sperry Drilling collaborated with Petrobras to engineer a drilling solution to reduce well time and increase drilling efficiency in the complex Brazilian presalt formation. After several rounds of planning, the teams decided to use the NAV and SHIELD solutions, from Halliburton Drilling Engineering Solutions (DES), which provided risk mitigation and drilling efficiency, respectively. DES experts also used DrillingXpert software, which consolidates proprietary information from the Halliburton Sperry Drilling, Baroid, and the Drill Bits and Services product service lines into a single platform to provide a solution for maximizing performance and maintaining safe drilling conditions.

From the operator’s office, the DES execution team provided drillstring integrity, hydraulics management, and wellbore integrity as part of real-time support. DES experts also advised to utilize the point-the-bit 9600 Geo-Pilot 50k rotary steerable system (RSS) with a drilling-on-gauge sub in order to provide higher torque capability and reduce stuck pipe risks due to salt creep.

Sperry Drilling says that it is currently the only provider that can provide an RSS with a drilling-on-gauge sub for better salt drilling performance with very limited impact on directional capability. A point-the-bit RSS is ideal for drilling in soft formations, such as salt, as this system does not rely on the formation stiffness to change directions as other push-the-bit RSSs would. With higher rotational speeds (200 rpm) and the high-strength driveshaft of the Geo-Pilot 50k RSS, Petrobras had a solid solution to overcome torsional resistance, reduce stuck pipe events, and increase salt-drilling performance with the highest-torque-rated RSS that can withstand rotary torques of up to 50,000 lbf ft.

Reduced well time

The NAV and SHIELD solutions allowed Petrobras to not only improve its planning process, but to also model all elements of the drilling systems. The results were two-fold in that the unique combination of services utilizing the appropriate technologies and higher drillstring rotation allowed the pre-salt section to be navigated and drilled in one run without any stuck-pipe issues and with reduced extreme levels of stick-slip torsional vibrations. The Geo-Pilot 50k RSS with a drilling-on-gauge sub provided rotary steering at maximum speed without any safety or performance issues.

With this combo solution, Petrobras was able to drill 4,984 ft (1,519 m) with an average ROP rate of 95 ft (29 m) per hour, setting the highest ROPs across the entire 17 ½-in., 16-in., and 14 ¾-in. sections.

Particularly in the 14 ¾-in. section, the operator realized the lowest cost per foot/meter for a salt section. With these new drilling records, Halliburton Sperry Drilling says that it helped Petrobras maximize asset value by reducing costly deepwater well time by four days.