Water production reduces oil recovery

Water control was fundamental to efficient oil recovery in Chevron's PetroBoscan field in Venezuela for several reasons. First, the surface facilities were unable to handle the amount of water the wells were producing. In addition, the PetroBoscan reservoir was underpressurized and required artificial lift for production. The older wells were completed with gravel-packed slotted liners, and the more recent wells were completed with gravel-packed stainless-steel stand-alone screens. The conventional method of dual injection to control water production presented a high risk of damaging the oil-producing zones. Chevron planned to abandon some of the wells because they were not economical.

Design of innovative solution shuts off water

Schlumberger developed and implemented a new sand control screen and shutoff solution for the gravel-packed completions. The process included an operation placement technique that used existing Schlumberger gel and cement products: PROTECTOZONE* fluid for temporary zone plugging, ZONELOCK* permanent zone sealing fluid system, and SqueezeCRETE* remedial cementing solutions. The new technique isolated the oil zone before the main treatment with a temporary blocking gel. The primary treatment included squeezing a permanent rigid gel followed by a microfine cement slurry system into the water zone.

For the gravel-packed slotted liner completions, PROTECTOZONE fluid was placed into the open-hole wells as a balanced gel plug so that the underpressurized formation absorbed the fluid. This process isolated the entire lower completion as though it were a cemented production zone making a permanent seal.

After the oil zones were isolated, the main treatment to abandon the water zone was performed as a conventional squeeze using a cement retainer. The water zone was perforated, and the ZONELOCK sealing fluid was injected deep into the formation to prevent water from breaking through into the oil zone. After the ZONELOCK system injection, SqueezeCRETE cement was used to penetrate a near-wellbore formation and to maintain a permanent seal around the wellbore.

The treatment for the stand-alone mesh screen completions was the same as for the gravel-packed slotted liner completions, except that the PROTECTOZONE gel was engineered and modified to allow it to pass through the mesh of the sand control screen.

Production increases while operating costs are lowered

Using the new water shutoff method increased oil production, reduced lifting costs, improved optimized recovery, extended field life, and revived old watered-out wells. Soon after treatment, data indicated that water was reduced by 55%, lifting costs were lowered by 44%, and the average oil production increased by 3,000 bbl/d.