With the discovery of deepwater pre-salt reservoirs offshore Brazil, national operator Petrobras began complex drilling operations to uncork the massive hydrocarbon reserves under these salt layers, which acted as seals, preventing the oil and gas from escaping. Drilling in the pre-salt can be daunting, with heterogeneous rock layers and a thick salt crust to be negotiated before reaching the reservoir rocks. In some pre-salt plays, hydrostatically over-balanced drilling methods encounter problems.
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Rotating control device for MPD. From Weatherford. |
While looking for solutions to their pre-salt drilling woes, Petrobras partnered with Weatherford to test the viability of using managed pressure drilling (MPD), which has been used in shallow plays for years, to safely and efficiently drill the deepwater pre-salt formations. MPD had been successful in making drilling viable in plays where the margin between pore pressure and fracture gradient is very narrow.
Weatherford
Petrobras has experimented with pressurized mudcap drilling and other forms of MPD since 2005, beginning onshore and in shallow water. With Petrobras experimenting in deeper waters for the last few years, the company used MPD successfully on wells at the Franco South, Iara and Lula North fields. Petrobras is now targeting three or more fully MPD-capable ultra-deepwater rigs for the Libra field.
The technology proved to be very efficient in the complicated deviated entrances to pre-salt reservoirs, making these difficult wells viable and reaching targeted depth, where other drilling technologies may have failed. MPD has proven to also be capable of increasing productivity, improving drilling safety and possibly even giving the operator new options for circulating gas kicks. As drilling moves into deepwater, this combination of global and local experience is driving the application of MPD methodologies. Initial successes in shallower waters and deepwater clearly demonstrate how flexible MPD methods will contribute to the growth of deepwater drilling. “We have been reaching bottom depths on wells that probably could not have been drilled otherwise,” said Emmanuel Franco Nogueira, senior petroleum engineer for Petrobras, during an industry seminar in 2014.
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Aker managed pressure operations equipment. From Aker Solutions. |
The MPD system constitutes several skids containing manifolds, valves, and sensors that penetrate into the drilling rig mud circulating system, creating a closed atmosphere in the wellbore, allowing MPD technology to achieve a target equivalent circulating density (ECD) by adjusting surface backpressure across the wellhead. Once the target ECD is reached, stable bottom-hole pressure is established. Using Weatherford MPD technology including the BTR 7875 rotating control device, Petrobras safely reached total depth in a previously abandoned well. Since the operation, the operator earns US$2 million/d from the well.
Gas leaks are also a major concern. In a 2013 Drilling Contractor article entitled,"MPD provides precise prevention, handling of gas influxes in risers," Brian Grayson, Director of Pressure Control Systems for Secure Drilling Services at Weatherford, said: “MPD ideally prevents riser gas from occurring in the first place and, in fact, this is the case with many wells where the technology has detected and mitigated kicks that could have otherwise resulted in riser gas incidents."
A few years ago, Weatherford developed a dedicated subsea rotating control device (RCD) integrated with the riser below the tension rig. Locating the RCD below the tension ring improved riser integration and overall performance of the MPD system, while unburdening the drilling rig, which was one of Petrobras’ requests, as the earlier RCDs had the tendency to unbalance the rig. Petrobras is relying heavily on MPD systems for its deepwater wells, to the point where they are demanding that MPD systems be installed in all the deepwater drillers it contracts. Weatherford is currently developing a fully integrated MPD solution that can be incorporated into most deepwater MPD systems. The next generation of Weatherford’s MPD system is expected to be delivered in 2015.
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MPD enhances well integrity by creating a secure closed-loop drilling. From Weatherford. |
Aker/MPO
When Aker Solutions acquired Managed Pressure Operations in 2013, it became a provider of next generation continuous circulation and MPD systems. The MPD system being introduced by Aker/MPO is fully automated and simple to operate, needing few people to run the equipment
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Aker managed pressure operations. From Aker. |
An important part of the MPD system is the riser safety systems and riser gas handling system. According to Aker, the deepwater riser safety system (RSS) has been developed to enable safe handling of gas entry into the riser. In order to allow for easy installation on the rig, the RSS is designed to be installed below the tension ring. The two main components are the quick close annular and the flow spool, both of which will pass through a 49.5in rotary table. With this system in place, an influx can be safely routed from the riser, through the RSS manifold and out the ultra mud gas separator with no discharge to the environment.
Another important safety aspect of the MPD system is the deepwater kick detection system, because the conventional methods of kick and loss detection and subsequent well control procedures are inadequate for today’s ultra-deepwater drilling requirements. Well control event detection and subsequent control measures are time critical. The longer the event detection time, the greater the consequential problem especially in the increasing risks of pre-salt drilling with fractured carbonates and higher pressure reservoirs. The deepwater kick detection and riser safety system used together is what Aker calls an open system. This system protects the rig 24 hours per day during every operation from when the riser is run until the riser is pulled and offers instant closure of the well once influx has been detected. The system can reduce kick volumes by a factor of five.
Aker Solutions' subsidiary Managed Pressure Operations has inked its first MPD contract in Brazil, where it will deliver MPD systems and riser gas handling services to Repsol Sinopec Brazil. Repsol will use the equipment at an ultra-deepwater operation in the Campos Basin.
"This contract will demonstrate the unique capabilities of our riser gas handling safety system and introduce the first deepwater application of our riser drilling device into an offshore MPD system below the tensioner on a rig," says Charles Orbell, head of Managed Pressured Operations.
The riser gas handling system helps control wellbore fluids during offshore oil and gas drilling. It detects an influx of gas into a drilling riser and diverts the gas to prevent a blowout. In addition to the increase in safety as a result of wellbore stability gained from MPD, well economics improve greatly making managed pressure drilling a highly selectable application.
To see Weatherford’s video illustration of MPD:
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