A Cost-Effective Technique for Squeezing Perforations
Authors: Beirute Robert M. , Bugli Roberto , Rossignoli Horacio 
Published: December 2007

E&P Exchange

Amoco Argentina developed a cost-effective squeeze technique to seal off freshly opened perforations across water and/or gas zones. The method uses very little cement, a retrievable packer, and a retrievable bridge plug. The technique has been optimized to where the success ratio is extremely high (more than 95% in 1991–92).

Amoco Argentina has been operating in the Comodoro-Rivadavia area since1958. The Cerro Dragon contract area consists of about 25 fields. Since 1958,1,723 wells have been drilled with depths ranging from 3,000 to 11,500 ft. Allwells are either beam pumped or on electric submersible pumps. On average, about 22 zones are perforated per well, and about 3.4 zones per well require squeezing.

Before developing the current squeeze cementing technique, the company used about 30 sacks (7.5 bbl) of cement per zone to be squeezed. The zones were isolated between retrievable packers and drillable bridge plugs. Frequently, the cement slurry was pumped at pressures above fracture gradient from the beginning of the squeeze operation. Time was allowed for the cement to fullyset [waiting-on-cement (WOC) time] before drilling out. Because the nonproductive zones to be squeezed were very close to the oil zones, relatively littleroom usually was available between the packer and the bridge plug. This meant that final squeeze pressures often were obtained before a substantial portion of the cement slurry volume was pumped. When large volumes of cement slurry had to be reversed out, often the packer could not be unset and/or it could not be removed from the hole easily.

Amoco Argentina developed the current squeeze cementing technique by adjusting procedures to minimize or eliminate the potential causes of failures and to capitalize on the practices that produced successes. Working with the service companies as a team has contributed to the success. The zone to be squeezed is now isolated between a retrievable packer and a retrievable bridge plug. Squeezing is almost always done with exposed open perforations above the zone to be squeezed. The present procedure uses about 0.5 sack cement/3 ft of perforated interval, plus the volume of the casing (from the deepest perforation to the estimated top of cement), plus 1 bbl extra of slurry to account for contamination. The average is 12 sacks of cement per zone to be squeezed. Because of the low volumes of slurry used, all the slurry can be easily mixed in the recirculating mixer tub before the start of the squeeze operation.

Before the squeeze (Fig. 1), sand is placed above the bridge plug to prevent it from cementing up. Next, injectivity is established. At the beginning, pumping is conducted below fracture pressure. Cement slurry is pumped to the perforations at a low rate, and squeezing is started using the hesitation squeeze technique from the on set. After achieving an initial squeeze (seal) of the perforations, pressures are gradually increased to levels that exceed the zone's fracture pressure to promote complete dehydration of the slurry in the perforation tunnels (pressure holding steady). This step ensures that the cement will remain in the perforation tunnels. Often, the wash-through technique to clean excess cement slurry from across the perforations is used right after the squeeze and before the cement has had time to set completely(no allowance made for WOC time). The wash-through technique is used only when oil-productive zones are not open above the zone being squeezed.

In the Cerro Dragon area, the use of minimum volumes of cement slurry has eliminated the need to reverse-circulate excess cement, reducing operational risk and saving rig time. The use of retrievable bridge plugs instead of drillable bridge plugs has resulted in rig time savings of about 6 hours perzone, plus the cost of the permanent bridge plug. When the wash-through technique is used, it has resulted in a savings of about 14 hours of rig time perzone. Be cause of the high success achieved with the new technique, Amoco Argentina does not test a squeezed zone after the job unless the zone exhibits high gas/water rates or operational problems were encountered during the squeeze. This practice has resulted in savings of about 3 rig hours per zone. Overall, the new technique has reduced the cost of a typical squeeze job in the Cerro Dragon area by about 30%.