San Leon Energy: Vertical Success in Poland

Delivers Poland's Most Successful Shale Vertical with Breakthrough Frac Design from SIGMA³


Operator: San Leon Energy Plc (SLE)

Location: Poland, Baltic Basin, Gdansk W Concession, Lewino-1G2

Service Companies: Led by United Oilfield Services (UOS)

Photo Courtesy of United Oilfield Services

SIGMA³ Engineering Solutions: Stimulation Design, Dynamic Simulation Modeling, Onsite Stimulation Consulting


  • Effectively stimulate the upper Ordovician
  • Evaluate the formation response during the hydraulic fracture treatment
  • Identify opportunities for improving the stimulation strategy


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While some operators may have given up on the potential of shale gas in Poland, San Leon Energy (SLE) is invested and blazing a trail in the Baltic Basin, determined to find the sweet spots, optimize production, and prove commercial viability. As is typical in unconventional reservoirs around the world, the Gdansk W Concession has thick, laterally extensive source rock 3000-4000 meters deep.

The company has been performing a methodical vertical frac testing program in the upper and lower Ordovician target zones to determine the frac design that will allow commercially viable gas flow when effective stimulation is applied to future horizontal wells.

After testing two frac strategies in the lower Ordovician, both of which showed suboptimal proppant concentration, SLE's objective for the stimulation in the upper shale interval – an area not previously stimulated - was to prove the ability to fracture and enable sustained production. A key objective was to achieve a high proppant concentration, and if successful, the same strategies would then be applied to a multi-stage stimulated horizontal well in the lower Ordovician – which has superior gas saturation and porosity – with the intent to open the upper and lower intervals and deliver consistent commercial flow rates.

Stimulating the Upper Target Zone
In November 2013, the SIGMA³ Engineering team performed the stimulation design and on-site, real-time fracture monitoring on the two-stage hydraulic fracture treatment that targeted and stimulated the lower and upper Ordovician Shale.

Stage 1 was a refrac of the lower zone and its treatment design served as a starting point for refinement based on the response of the formation. Although proppant concentration improved, the results were still not viable for sustained production.

Stage 1 shows the failed treatment and resulting small and under-propped fracture geometry.


The objective of Stage 2 was to incorporate lessons learned from the frac/re-frac of the lower Ordovician interval, as well as efficiency improvements in drilling and fracturing operations that are being applied to shale wells in the US, to:

  • Effectively stimulate the upper Ordovician
  • Evaluate the formation response during the hydraulic fracture treatment
  • Identify opportunities for improving the stimulation strategy

All Went According to Plan

By analyzing the geology, reviewing lessons learned during the frac and refrac of the lower zone and drawing from experience in other shale reservoirs, the on-site team designed a plan (Stage 2) that would best match the formation's response to treatment.

Stage 2 was pumped through a new set of perforations, with a plug above the lower zone to isolate the upper Ordovician from the previously fractured lower zone. When the perforating guns were fired, frac pressure from the earlier frac stages was communicated into the wellbore through the new perforations, indicating that previous fracs grew to at least the level of the new perforations (27 meters).

SIGMA³ had a plan that enabled the onsite engineering team to adapt the treatment design quickly to match the formation's response, and SLE considers Stage 2 as proceeding exactly as planned.

Stage 2 shows a successful treatment and the resultant frac geometry.


By taking into account excessive fracture complexity, proppant type, and reducing the treatment rate, Stage 2 placed far higher proppant concentrations into the formation with little pressure increase. Frac modeling indicates this stage grew down, well through Stage 1's target, and into the lower target zone.


"SIGMA³ provided engineering expertise for the final frac campaign of the vertical well, and it went exactly as planned," said Joel Price, Chief Operating Officer, SLE. "This break-through frac design is critical to the successful shale development in Poland's Baltic Basin, as well as Europe by association. We are excited about applying these learnings to the upcoming horizontal well with the aim of achieving commercial flow rates."


Frac Also Penetrated the Lower Target Zone
SIGMA³ advised, and SLE/UOS agreed, that all sustained production is coming from the upper Ordovician zone, although simulation suggested the frac may have penetrated the lower Ordovician. The frac did not stay open most likely due to the higher clay content layer between the upper and lower target zones. To maximize the potential to connect the lower and upper targets of the horizontal well, future completion strategies will place higher conductivity and relatively wider fractures, with particular attention given to proppant type. This type of design should help avoid proppant embedment in the higher clay content layer.

Stage Set for Commercially Viable Horizontal Well
"The vertical well was the testing ground, enabling us to learn more about the well properties and change the stimulation program to achieve maximum production. We are confident that fracs can be designed in the horizontal well that will cover the entire Ordovician target zone," said Price. "SIGMA³ and the team concluded that the production from the third frac campaign is coming from the upper half of the formation. The lower interval has even better reservoir characteristics and is our primary target. There is significant upside once the horizontal well is executed."

SIGMA³ will be participating in frac design and analysis of the upcoming horizontal well, set to drill and frac later this year. The frac program will be 10 to 30 stages, similar to completions of horizontal unconventional wells in the U.S, and will build on the successful aspects of the vertical well's stimulation.

Learn more about SLE's recent success in this interview with Oisín Fanning, Executive Chairman, and Joel Price, Chief Operating Officer. Details of the SIGMA³ role at 2:40.