Schlumberger

Case Study: Geostopping Allows Safe Drilling in Hazardous Java Carbonates

Proactive real-time intervention and casing point selection using zero-offset resistivity measurements avoid lost circulation and costly contingency casing

Challenge: Select correct casing point to avoid drilling hazards and costly contingency casing when drilling through overburden shale formations into pinnacle-shaped, low-pressure reef carbonate reservoirs.

Solution: Use zero-offset resistivity measurements from geoVISION imaging-while-drilling service to guide geostopping decisions.

Result:

  • Correctly identified casing point in eight well sections despite geologic uncertainty.
  • Avoided drilling hazards and cost of contingency casing.

Select correct casing point

Indonesia’s national oil company was drilling wells in Java that passed through overburden shales, which had a relatively high pore pressure, into pinnacle-shaped low-pressure reef carbonate reservoirs. The pinnacle shapes made it nearly impossible to predict the depth of reservoir tops through well-to-well correlation, so casing point selection was a challenge.

Failure to set casing at the top of the carbonate had resulted in total loss of circulation and could have led to kicks—or even blowouts—if the mud column had fallen farther. To avoid those risks and the need for a costly contingency casing program, the company wanted to be able to precisely detect the boundary between the shale overburden and the carbonate reservoir top.

Measure resistivity at the bit

The geoVISION imaging-while-drilling service provided real-time measurement of resistivity at the bit for proactive geostopping. This accurate zero-offset measurement gave the earliest possible indication of the resistivity contrast as the wellbore approached the carbonate reservoir top, allowing confident casing point selection.

The geoVISION service can make electrode resistivity measurements—and near-bit azimuthal gamma ray measurements—in both water-base and oil-base drilling fluids. In conductive drilling fluids, the service also provides a focused deep ring resistivity measurement and high-resolution images.

Clearly identify reservoir top

In eight wells drilled using the geoVISION service to provide zero-offset resistivity measurements at the bit, the reservoir top was identified correctly—at depths as much as 105 m shallower than anticipated. These real-time measurements enabled the drilling team to geostop well sections at the correct casing point, avoiding the cost of contingency casing.


Download: Geostopping Allows Safe Drilling in Hazardous Java Carbonates (0.83 MB PDF)

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