When designing a hydraulic fracturing intervention, the selection of the interval to be perforated is critical in order to maximize oil production and to avoid unwanted gas/water breakthrough from neighboring layers.
While on new wells the perforation interval can be selected carefully analyzing logs and CBL, it can be challenging to design a workover where the HF targets a zone that is right in the middle of a large existing perforated interval (125 meters).
Leaving exposed too many perforations during a fracturing treatment could result in operational issues such as early screenout and/or uncertainties on the fracture initiation point. Zonal isolation could be obtained by cementing part of the perforations but this would mean in permanently losing part of the level.
This paper will describe a successful workover carried on a shut-in oil well, onshore Congo, where a single stage fracturing treatment was performed leaving exposed only few meters of the existing perforations and without permanently losing the remaining intervals.
This result was obtained using a multi-stage ball drop frac completion setting the packers across the perforated interval. The downhole equipment was able to withstand the treating pressure during the fracturing treatment and production was obtained through the frac sleeves.
This workover resulted in a significant oil production from a well that never produced until that moment.
In the last decade, hydraulic fracturing has been widely used in Congo for the development of tight reservoirs: since 2007, more than 180 stages have been pumped on 9 different fields with almost one third of these jobs pumped offshore.
All of these treatments have been performed in a wide range of scenarios including: both sandstone and carbonate reservoirs, low to high temperature formations, field rejuvenation and exploration wells.
While applying this technology throughout the years, tailored solutions have been put in place to maximize oil recovery through frac design optimization. This learning curve included:
Job design optimization (SPE 151860-MS)
Fracture height detection (IPTC 16581-MS)
Waterless fluids (IPTC 16640-MS)
Completion Strategy and Operations (OTC 19455)
Proppant flowback prevention (SPE 169959)
With the encouraging results obtained from the use of hydraulic fracturing, this technology has become the standard completion for tight reservoirs. When dealing with new wells, all aspects of well design, from well trajectory to perforation and completion strategy, are planned in order to optimize the hydraulic fracturing treatment.
