Hydraulic Fracturing Across Large Existing Perforated Interval Unlocks Reserves on Tight Sandstone Reservoir: Successful Workover Experience, Onshore Congo

Abstract

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.