Abstract

In the last decade, hydraulic fracturing has been successfully applied in West Africa for the development of tight reservoirs. Since 2007, more than 200 fracturing stages have been achieved in 9 different fields targeting wells characterized by a wide range of conditions: from sandstone to carbonate formations, from low to high temperature reservoirs, and from old existing completions to new drilled wells.

While applying this technology throughout the years, tailored solutions for treatments design have been continuously put in place to address the observed challenges and maximize the final oil recovery. The deployment of new technologies such as proppant flowback prevention additives, non-radioactive tracers for fracture height monitoring, and channel fracturing, to boost the fracture conductivity played a major role in achieving the desired results.

The accumulated in-depth knowledge on hydraulic fracturing built from local experience allowed Eni West Africa to rapidly approach a new offshore tight oil field development with confidence that hydraulic fracturing would be an effetive stimulation technique. This paper will describe the fracturing campaign major milestones, from the promising results obtained on the exploration wells, to the optimization actions implemented during the first development phase. Thus far, six horizontal and two vertical wells were completed, including a total of 23 hydraulic fracturing stages during a single campaign spanning less than one year.

On the first of the two vertical wells, each stimulated with a single frac stage, a non-radioactive tracer was employed for measuring the propped fracture height, and calibrating the frac model. For the horizontal wells, where 3 or 4 frac stages were implemented, a plug-and-perf (P&P) technique was selected. This method included coil tubing equipped with fiber optic, enabling precise perforation intervals placement, also providing flexibility in case re-perforation was required. Moreover, several actions were adopted to improve completion efficiency and cost-effectiveness, including perforation selection to limit near-wellbore pressure losses, and coiled tubing runs optimization for setting the bridge plug and perforating in a single trip.

Finally, particular focus will be given to the steep achieved learning curve, describing the adopted decisions, to improve both completion performance and fracture conductivity.

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