Facing lost circulation in Mexico
As one of the primary causes of nonproductive time (NPT), lost
circulation is a major problem foroperators in Mexico. Operating on behalf of
PEMEX in the carbonate Costero field near Villahermosa, Mexico, Schlumberger
Integrated Project Management (IPM) experienced oil-base mud (OBM) losses of
2,000 bbl in a 5-5/8-in [14.3-cm] hole. Casing was set at 18,963 ft [5,780 m],
and losses occurred between 18,963 and 19,173 ft [5,780 and 5,844 m]. The
operator attempted to reduce the mud density from 1.12 to 1.01 relative
density, but a kick followed. The well stabilized at 0.97 relative density, but
maintaining this density would not allow drilling into deeper formations.
Furthermore, little data was available about fracture width, density,
and temperature after the losses. These complications, along with the high cost
of OBM, prompted the IPM team to seek an alternative solution.
Applying fiber system for loss circulation solution
The Losseal fiber pill was selected to reduce mud losses. This system,
applicable for natural fractures, includes a specially engineered pill that
comprises fibers and solids, which creates an impermeable grid to stop mud from
flowing through. It is pumpable through most of the BHA and does not require
any special lab tests. The water-base pill was made compatible with the OBM
through the use of surfactants.
Based on loss rate and temperature, the team determined optimal particle
size for the Losseal system in the Costero wella pill of 90 bbl [14.3
m3], with 2.9 lbm/bbl [8.3 kg/m3] of fibers and 217 lbm/bbl [620 kg/m3] of
coarse, medium, and fine solids. The Losseal pill was placed as a balanced
plug, and a squeeze pressure of 200 psi [1,378.95 kPa] was applied.
Without requiring a trip, the system created an impermeable grid that
withstood the additional pressure generated by a mud density increase, as well
as any additional pressure from future drilling or cementing operations. Also,
the lack of chemical reaction from the Losseal pill minimized the risk of the
BHA getting plugged.
Curing losses through drilling and cementing phases
Using the Losseal fiber pill, both static and dynamic losses were cured.
The IPM team was able to increase mud density to 1.15 relative density without
any losses and resumed drilling to TD. The subsequent cementing job was also
completed without losses. And because no trip was needed, time was saved and
risk was reduced.