| Title | Bulalo 99 Workover: Complex Zonal Isolation |
|---|---|
| Authors | Angelito C. Torres and Wilhelmino Q. Lim |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | peripheral fluids, zonal isolation, marginal recharge, downflow, annulus casing packer |
| Abstract | A major problem encountered by mature geothermal fields is the influx of cooler peripheral fluids into the production area. This tends to reduce the productivity of the field by curtailing steam flash. After 30 years of commercial operation, some wells in the Mak-Ban Geothermal Field, Philippines are affected by cooler edge fluids which invade the two-phase region of the reservoir. Cooler fluids tend to short-circuit deep into the reservoir through wellbores of affected wells and eventually invade the production zones of nearby wells. This causes their steam production to drop and leaves their signature in terms of chloride dilution and increasing non-condensable gases in case of steam wells. With this damaging reservoir problem, there is a need to isolate and cement the unwanted zone. A workover employing zonal isolation addresses this problem. The complexity of this workover is further enhanced when the unwanted cool zone lies between two productive zones. In order to solve the problem, the existing perforated liner was cut below the cool zone and retrieved. A high temperature annulus casing packer was run together with stage cementing tool and blank liner to isolate the cool zone. The top of this blank liner was in uncased open hole. The blank liner was set to ensure that the productive zones, above and below the cool zone, will not be blocked. The blank liner was cemented across the cool zone followed by running perforated liner from top of cemented blank liner up to casing shoe. The cement inside the blank liner and the float was cleaned out to open the lower production zone. This provided access to the upper and lower steam zones while isolating the cool zone. Subsequent tests have shown the cool zone isolation to be mechanically successful. This paper details the original planned operation, the obstacles and difficulties encountered while executing the plan, the steps taken to reach a successful completion and the lessons learned to enhance future execution of similar work. |