Automated MPD System: Operator Avoids Hazards While Drilling Narrow Pressure Window in Gulf of Mexico | SLB
Case Study
Location
United States, North America, Offshore
Details

Challenge: Drill reservoir with a margin of only 1.2 ppg between pore pressure and fracture gradient. Avoid lost circulation and minimize ballooning. Prevent formation break out due to cyclic pressure changes. Minimize swabbing while tripping out of hole

Solution: Install the dynamic annular pressure control (DAPC) system, coriolis meter, and the HOLD rotating control device (RCD) to maintain near constant bottom hole pressure on connections and early kick detection. Hold back pressure and strip out of hole to prevent swabbing

Results: Minimized rig time for rig up, testing, and tuning by rigging up offline prior to mill out. Services called online early to help control influx/losses cycle due to ballooning effect

Products Used

Automated MPD System: Operator Avoids Hazards While Drilling Narrow Pressure Window in Gulf of Mexico

Automated MPD system provides near constant bottom hole pressure to avoid losses and swabbing in depleted reservoir

Proactive planning to mitigate drilling hazards

W&T Offshore planned to re-enter well SS 359 A5 through a window milled in 7 3/4" and 97/8" casing, and drilling a 6 1/2" hole to access hydrocarbon reserves in the target “P" sand. It was expected that the margin between the pore pressure and fracture gradient was expected to be only 1.2 ppg.

Figure 1: Narrow margin (1.5 ppg) between pore pressure and fracture gradient
Figure 1: Narrow margin (1.5 ppg) between pore pressure and fracture gradient

Automated MPD system provides near constant bottom hole pressure to avoid losses and swabbing in depleted reservoir

Knowing the challenges that could be faced drilling through such a narrow mud weight window, W&T Offshore chose to employ a proactive managed pressure drilling approach by using the DAPC dynamic annular pressure control system to automatically manage the wellbore annular profile.

Early start up to operations

MPD operations were started earlier than planned as a result of gains and losses observed early in the hole section. Rigging up and pressure testing was done offline in order to minimize the impact on critical path rig time. Only minimal tuning and calibration were performed prior to starting MPD operations, operator experience and hydraulics modeling were able to maintain bottom hole pressure within a window of +/- 0.25 ppg.

Figure 2: Response of the MPD system during a connection | Figure 3: Near-constant bottomhole pressure while stripping out of hole
Figure 2: Response of the MPD system during a connection | Figure 3: Near-constant bottomhole pressure while stripping out of hole

Avoiding swabbing

One of the concerns drilling the well was the risk of swabbing while tripping out of the hole. In order to mitigate this risk, a fixed back pressure was applied to the well and maintained by using a back pressure pump. Optimal selection of the back pressure and mud weight required for tripping required consideration of many factors, including bottom hole pressure would allow tripping in without surging and not exceeding fracture gradient while the pipe is stationary with back pressure.

Effective planning and monitoring allowed the bottom hole pressure to be controlled within a window of +/- 0.1 ppg while tripping out of the well.

Equipment and services provided

Providing near constant bottom hole pressure required several key components. The HOLD rotating control device (RCD) allows for closed loop circulation by diverting returns through the flow control system. The RCD is remotely operated from the rig floor promoting a safe working environment and ease in changing out sealing elements. The RCD is accompanied by a hydraulic power unit (HPU) to ensure adequate lubrication is provided to the bearing assembly, high pressure seals, and to maintain a positive pressure differential across the high pressure seal section.

The dynamic annular pressure control (DAPC) system provided control of bottom hole pressure within pre-set drilling windows through independent and/or simultaneous use of redundant chokes. The system actively controls the choke position. The system can use its own dedicated pump to circulate mud and actively supply back pressure.

A coriolis type flow meter is connected to the low pressure side of the choke manifold and provides flow out data that is continuously monitored and compared to flow in data for kick and losses detection.

Drilling engineering services provided a complete MPD drilling program and assistance in addressing the requirements of NTL 2008-G07 as required for MPD wells in the Gulf of Mexico. These services included hydraulics modeling, hazard identification and operability (HAZID/HZOP) workshops, and well site training to assure the competency of involved personnel.

Figure 4: @balance Services DAPC choke manifold | Figure 5: HOLD RCD on top of annular preventer
Figure 4: @balance Services DAPC choke manifold | Figure 5: HOLD RCD on top of annular preventer
Products Used

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