Drilling exploration wells aim at reaching the reservoir in safe and efficiency way. The broad framework of drilling activities is set out by pressure window boundaries. Drilling operating margin is represented as the lowest limit by the formation fluids pressure in open hole and as the upper limit by the fracture pressure the wellbore can withstand without incur in uncontrolled mud losses.
Deep HPHT wells in remote area locations are considered critical not only for the known narrow margin between pore and fracture gradients but even for several logistic reasons and conventional equipment reliability.
In the case study presented the reservoir section of an HPHT well was planned to be reached by applying the ENI near balance drilling technique (e-nbd™).
The reference well was abandoned after several attempt without reaching the proposed target due to pressure management reasons.
The application of e-nbd™ technology allowed to reach and secure for production the proposed explorative targets in an extremely narrow PPFG window overcoming the technical difficulties encountered.
The use of the MPD system to run and cement the 4 ½″ liner ensured a good quality of cement job with a satisfactory zonal isolation of the sand layers.
The drilling performance has been enhanced, no main hole problems were encountered and only 2hrs NPT was related directly to MPD/ECD system allowing to complete the well in the planned time schedule.
Drilling exploration wells aim at reaching the reservoir in safe and efficiency way. The broad framework of drilling activities is set out by pressure window boundaries. Drilling operating margin is represented as the lowest limit by the formation fluids pressure in open hole and as the upper limit by the fracture pressure the wellbore can withstand without incur in uncontrolled mud losses.
Safety is accomplished in conventional conditions, by drilling through pressures margin with appropriate kick tolerance and MAASP.
Moreover, the operating efficiency may require a deeper analysis to avoid inappropriate mud weight, which might result in loss of drilling fluid into formation or to induce drilling complications such as ballooning effect, differential sticking, reservoir damage and well bore instability.
