Schlumberger

Case Study: Increased Survey Frequency Avoids Costly Sidetracks in ERD Project Offshore Asia

TVD survey optimization reduces depth uncertainty to avoid oil/water contact, enable geosteering in thin reservoir

Challenge: Drill extended-reach well in crowded development field, staying in zone through thin reservoir with stratigraphic faults.

Solution: Use WellDefined drilling survey services for TVD survey optimization to increase accuracy of survey data for geosteering, avoiding gas/oil contact (GOC) and oil/water contact (OWC).

Result:

  • Drilled extended-reach well in zone for maximum reservoir exposure.
  • Corrected survey data for magnetic interference and BHA sag to increase accuracy of TVD data.
  • Used 3-m survey frequency to avoid GOC and OWC in new development well.
  • Discovered errors in legacy field data acquired at 30-m intervals, indicating 6-m difference in TVD for previous wells.

Improve survey accuracy to drill in development field

An operator offshore Asia planned an extended-reach drilling (ERD) project in an already crowded development field. At the time of planning, there were 13 multilateral wells drilled in close proximity in the field—with lateral sections extending as far as 2,000 m. There were survey data available from some of the previous wells, which had been acquired at 30-m intervals. The long intervals between measurements left quite a bit of uncertainty for the drillers targeting what was known to be a thin reservoir, ranging from 3- to 20-m thickness, with an aquifer lying just beneath it.

Increase survey frequency to 3 m for precise geosteering

Schlumberger performed TVD survey optimization to ensure accurate data for geosteering the new extended-reach well and for collision avoidance. TeleScope high-speed measurements-while-drilling service was used to acquire continuous direction and inclination while drilling. And because the development field was known to contain stratigraphic faults and dips, the team selected the PowerDrive Archer high build rate rotary steerable system (RSS) for maximum steerability control in drop zones that had caused loss of directional control in previous wells.

The TVD survey optimization interpolated the continuous data acquired while drilling with the previous static data from the field to create high-definition surveys with 3-m intervals. This service corrected for drillstring magnetic interference and BHA sag, which can cause misalignment of the directional sensor, to provide accurate TVD to the drillers on surface. The plan was to drill at high ROP; therefore prejob planning and real-time data were essential to enable fast geosteering decisions.

Drilled lateral within shallow target zone using accurate TVD data

By using TVD survey optimization, the operator gained precise understanding of the wellbore position and landed the development well on target, keeping the lateral section in zone to avoid GOC above and OWC below. The PowerDrive Archer RSS provided optimal directional control while drilling the drop zones and maintained high speed. This saved drilling time and prevented the need for costly sidetracks as the system was able to maintain control and stay in zone.

The static survey data acquired at low frequency in previous operations was corrected as well and indicated other wells to be as much as 6 m TVD shallower than originally thought. The 30-m surveys had not registered a build, resulting in GOC above the reservoir. This correction of historical data added to the operator’s confidence that WellDefined drilling survey services improve the accuracy of well placement in ERD operations.


Download: Increased Survey Frequency Avoids Costly Sidetracks in ERD Project Offshore Asia (0.27 MB PDF)

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WellDefined TVD corrections to 30-m survey data showed previous wells to be 6 m shallower than expected.
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