This paper describes the first field application of a high-pressure/high-temperature (HP/HT) organophilic clay-free invert emulsion fluid (OCF IEF) weighted with small-particle-sized (SPS) barite, qualification of which was achieved through extensive laboratory investigations (described elsewhere). The paper describes detailed observations of the fluid performance during first use (i.e., “critical first well application”) on a Statoil-operated HP/HT field in the North Sea.
In the well selected for first application, finger-printing was performed so that behaviors of the 1.96-specfic gravity (sg) invert emulsion fluid (IEF) could be examined and recorded before entering the open hole. When in the open hole, observational tests were continued throughout the well. Before and after trips, fluid behavior and properties were monitored and recorded. Additionally, extensive fluid testing was conducted on the rig (rheology, HP/HT fluid loss, particle plugging test [PPT] static sag, and viscometer sag shoe test [VSST]). Before running stand-alone screens (SAS), screen flow-through tests were performed.
Extensive tests showed acceptable fluid performance within stringent, defined criteria at all times. When re-initiating circulation on several consecutive connections, pump ramp-up time was gradually reduced. No pressures above drilling equivalent circulating density (ECD) were observed at any time. While drilling, the ECD values were maintained well within the required values. No barite sag was observed on any occasion, even after 90 hours static or during a slow circulation rate test performed to simulate conditions likely to induce dynamic sag. Fluid loss control (PPT) was maintained within specifications through the addition of ground marble. A decrease of approximately 60% in fluid treatments compared to a conventional HP/HT IEF resulted in a reduction in chemical and logistical costs and manual handling. The well was drilled well ahead of plan, resulting in saved rig time. No issues were observed when running screens to total depth (TD) with the IEF. The well was easily brought on production after ∼30 days, with the IEF being produced back to surface, consistent with expectations from the qualification laboratory testing undertaken at Statoil's laboratory facilities. Highly acceptable production rates were achieved, indicating minimal productivity impairment.
The efficient drilling of the well, along with being able to complete the well in the same IEF and not displace to brine, as was previously performed, resulted in substantial cost savings compared to other qualified solutions. This successful first application demonstrated that the well could be drilled and completed in the same fluid with an enhanced drilling performance and highly acceptable productivity outcome.