Schlumberger

Case Study: Operator Eliminates Trouble Time and Increases Drill Rate with MPD in DW Field

Automated MPD system enables ECD reduction and eliminates trouble-time and losses in depleted field high angle wells

Challenge: Reenter mature deepwater field after 10 years of production and avoid the previously experienced non-productive drilling time due to lost circulation, gas influx, and wellbore instability.

Solution: Engineering planning, optimized hydraulics, real-time BHP management using the DAPC system, and early kick detection using the kick detection system.

Result:

  • BHP was managed at a near constant level in a +/- 0.3 ppg window between pore pressure and fracture gradient, drilling, tripping, and making connections.
  • In three wells there was zero trouble time due to stuck pipe, lost circulation, and wellbore instability.
  • Three wells drilled in 30 days compared to the previous four wells drilled in 68 days.

Eliminate drilling problems

In their development plans for a deepwater GOM field, Stone Energy was facing the same drilling problems the previous operator faced 10 years ago: a narrow pressure margin, wellbore instability, annular loading, and ECD management.

The Drill Time Comparison chart shows the level of trouble that the previous operator encountered in the last two reentry wells drilled in the field. Neither of the first sidetracks made it to TD; both were finally drilled to TD with a second, unbudgeted sidetrack.

Ten years ago, offshore technology did not exist to manage constant bottomhole pressure in narrow margins to avoid wellbore instability and lost circulation.

Manage narrow margins

To avoid the problems of the past, Stone engineered a drilling solution using the Dynamic Annular Pressure Control (DAPC) system.

The DAPC system is an automated MPD system that manages BHP at a programmed set point in steady state conditions, when there is little or no change in flow, and dynamic transitions, when the flow rate is actively changing.

Stone used the DAPC system in three wells to manage the BHP between the pore pressure and fracture pressure. All three wells were drilled with zero trouble time, no unplanned events, at average drill rates that were double the old rates.

Performance - response time

An important measure of performance for an automated MPD system is its response time which reflects how fast it can respond to sudden changes in flow and pressure. In the first Stone well, the rig held an unannounced fire drill during which the driller turned off the rig pumps very fast without informing the MPD crew. The system automatically responded and within 20 seconds had stabilized the BHP and held it within the required limits.

Another measure of system performance is accuracy, which is reflected by how well the system controls pressure during pump transitions. For the three Stone wells the DAPC system managed the BHP on average between +/ 0.1 and +/-0.25 ppg which, for the depths in question, are equivalent to a minimum window of +/-57 psi (+/-3.9 bar) and +/-86 psi (+/-5.9 bar).

Together, system response time and accuracy determine how fast the driller can turn off the pumps during a connection while maintaining the BHP within the prescribed margin. The connection times for the three Stone wells went from 14.5 minutes in the first well to 9.5 minutes in the third well, a 35% improvement.

Dynamic influx test

Stone also used the kick detection system to eliminate the uncertainty of the pore pressure in the target sand package before drilling too far into it. The system was used to perform a dynamic influx test which allowed Stone to make an actual determination of the reservoir pore pressure.

The test sequence was:
1. rig pump being turned off
2. spike in flow-out indicates back pressure pump turned on
3. choke closing, initial backpressure 220 psi
4. rig pump off - no flow-in
5a. backpressure being staged down
5b. ECD staged down with backpressure
6. DAPC backpressure pump turned off
7. well is static, BHP is 14.75 ppg
8. flow-out monitored, influx detected with the EnFlux QF service, flow increased from 0 to 28 gpm in 4 minutes, gain limited to 2.5 bbl
9. well shut-in with 175 psi on the annular


Download: Operator Eliminates Trouble Time and Increases Drill Rate with MPD in DW Field (0.79 MB PDF)

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