Challenge: Barla field is located in Arges
County, Center-South Romania, and together with the Bacea and Surdulesti
fields, is known for partial-to-total losses in a relatively shallow and loose
Meotian shaly sand formation. Many wells drilled in these fields encountered
significant losses; blind drilling had to be employed in some of the most
severe instances. A new drilling campaign was initiated in 2007 to drill
several production wells in the depleted fractured limestone Inferior
Cretaceous formation that lies below the loose Meotian. The operator requested
a solution that would first prevent or minimize lost circulation but still
sustain directional drilling. Also, the Meotian formation was not as thick as
expected; medium-reactive clays had to be drilled at the same time as the thief
zone, demanding a system with superior inhibitive characteristics. In addition,
the field is in an environmentally sensitive area requiring minimum waste.
Solution: The EMS-2700 system was chosen
because of its well-documented abilities to control losses and
cuttings-carrying capacity even at reduced circulation flow rates. These
characteristics (combined with elevated low-shear-rate viscosities) to reduce
erosion of the mechanically weak Meotian formation were considered essential to
enable fast drilling, very good hole cleaning in the directional section, and
most important, to reduce/eliminate lost circulation that could result in
lengthy remedial operations. The EMI-795 inhibitor facilitated trouble-free
drilling of the clay interval while supporting high efficiency of the
solids-control equipment and reduced generated waste.
Results: 1. The EMS-2700 system allowed
drilling the interval without mud losses and reduced drilling time and costs.
2. The interval reached TD ahead of time with a 36.4% reduction versus planned
days. 3. The new system, in addition to preventing losses, enabled faster
drilling, improved hole stability and reduced interval costs. 4. Using the
EMS-2700 system, the total interval cost, including chemicals, engineering,
solids-control equipment and waste management, was 37.1% less than planned,
enabling significant savings to the operator. 5. The system’s inhibitive
nature resulted in hole stability and improved solids-control equipment
efficiency (80% versus 75% planned). 6. The actual disposal factor was 1.77
m3/m3 hole volume compared to 2.12 m3/m3 planned hole volume, resulting in 155
MT less generated waste and reduced disposal costs.
