Shallow cyclic steam injection wells experience severe losses
Two wells being drilled as part of a cyclic steam injection project
experienced total losses at 1,120 ft (341 m) during drilling of the 8 1/2-in
reservoir section. Drilling continued to the target depth of 1,550 ft (472 m),
with loss rates reaching 200 bbl/hr (32 m3/h). As this section was
intended to be the production/injection zone, it was important that any lost
circulation treatments neither inhibit future production nor damage the
formation.
A decision was made to mitigate losses before running (and cementing)
the 7-in casing. The objective was to avoid cementing fluids being lost to the
reservoir and to bring cement to surface. In these shallow cyclic steam
injection wells, zonal isolation is important to avoid steam leaking to surface
when the wells are on injection and to ensure the reservoir's natural
conductivity remains undamaged for subsequent production and injection.
Innovative degradable fiber solution reduces losses
As part of the Losseal reinforced composite mat pills family, the
Losseal Reservoir Fracture treatment was selected for these challenging
conditions. The fibers and solids were rapidly prepared on site within an hour.
The treatment for each well was configured at 8.6-lbm/galUS
[1.03-g/cm3] density. The pill volumes for Wells 1 and 2 were 50 bbl
and 55 bbl [8 m3 and 8.7 m3], respectively. The treatment
material was successfully mixed and pumped without issue.
The 50-bbl [8-m3] volume Losseal Reservoir Fracture treatment
for the first well was executed as designed with the density mixed within the
acceptable range of ±0.02 lbm/galUS [±0.0024 g/cm3]
and volumes verified by the rigsite manager. When the Losseal Reservoir
Fracture treatment pill entered the loss zone, a slight rise in the pump
pressure indicated the rising column of fluids into the annulus and returns
were established after displacing 7 bbl [1.1 m3]. After pulling out
200 ft [61 m] above the top of the pill, the hole was circulated with water and
returns were observed after pumping 25 bbl [4 m3]. The drillpipe was
run in hole to the top of the loss zone and circulation was established. Again,
full returns were established after pumping 3.3 bbl [0.5 m3] of
water.
The second well was also successfully treated with a single Losseal
Reservoir Fracture treatment pill with similar results. After running back to
bottom, the measured loss rates for Wells 1 and 2 were 30 bbl/h and 18 bbl/h
[4.8 m3/h and 2.9 m3/h], respectively, reducing losses by
more than 85% on average. Further treatments were deemed unnecessary, as the
loss rates for Wells 1 and 2 were mitigated sufficiently to allow casing to be
run and cemented.
