Drilling horizontal intervals in dolerite hindered by severe lost
An operator developing two horizontal wells in an eastern Siberia oil
field experienced lost circulation while drilling dolerite. In the first well,
no returns occurred at a depth of 3,727 ft [1,136 m], and attempts to clear the
circulation using a conventional lost circulation pill were ineffective. Due to
the inefficiency of the pill, process water was used in further drilling
In the second well, lost circulation of 2,906 galUS/h [11 m3/h] was
observed at a depth of 4,167 ft [1,270 m], and returns stopped at a depth of
4,177 ft [1,273 m]. Due to lost circulation material (LCM) concentration and
BHA limitations on the bridging agent, drilling continued using process water
and without returns.
Deploying FORM-A-BLOK pill to eliminate complications
M-I SWACO suggested using a FORM-A-BLOK pill, a quick-acting,
cost-effective solution with high filtering capacity to eliminate lost
circulation. The pill spotting procedure was similar for both wells. While
drilling the trap-intrusion interval, a 2,114-galUS [8-m3] lost circulation
pill with a filler concentration of 1 lbm/galUS [120 kg/m3] and a total
bridging agent content of 11.4% was injected into the well.
Another 2,114-galUS FORM-A-BLOK pill and 0.83 lbm/galUS [100 kg/m3] of
chalk were injected and squeezed with process water. After retrieving the BHA
above the lost circulation pills, squeezing began with a closed BOP into the
lost circulation formation until pressure rose from 441 psi [3.04 MPa] to 588
psi [4.05 MPa].
Improving circulation in horizontal drilling operation
Deploying the FORM-A-BLOK pill eliminated lost circulation in the first
well. In the second well, circulation improved from no returns to 17,435
galUS/h [66 m3/h]. As a result, placing cement plugs on both wells was
successful on the first try. In previous wells, placing the proper isolation
barrier using standard bridging agents failed, requiring up to four plugging
operations to isolate the lost circulation zone.