San Leon to test tight sands, shales in Poland Carboniferous

By OGJ editors

San Leon Energy PLC expressed encouragement and is shooting a 3D seismic survey around the Siciny-2 well in Poland’s Carboniferous basin after having evaluated the quality of five prospective zones for unconventional shale and tight gas accumulations in the well.

San Leon drilled Siciny-2 to 3,520 m in February 2012 and cut more than 265 m of continuous core in three prospective intervals previously identified in the Siciny-IG1 well drilled by the Polish Geological Institute in 1972. Siciny-2 had continuous gas shows throughout the Carboniferous interval.

Several previously undrilled, high-potential Carboniferous fractured tight gas sandstone intervals were encountered below 2,870 m and will be the focus of initial testing. The well was cased for future operations including pressure testing of the prospective zones, a dynamic formation integrity test, and possible vertical fracture stimulation and production testing across several intervals.

San Leon’s NovaSeis subsidiary is shooting 220 sq km of 3D seismic surrounding Siciny-2. Here are San Leon’s petrophysical descriptions of the promising zones encountered:

Zone 1, 3,200-3,520 m, Carboniferous tight sandstone (A sand) is a highly gas-saturated sandstone with more than 151 m identified as potential net pay. Petrophysical analysis of the calculated pay indicates porosities of 3-7% and averaging 3.86% and permeability of nanodarcies with an average of more than 100 nd. The A sandstone has low water saturation and an average 74% free gas saturation.

The interval’s mineralogical composition suggests it is well suited for hydraulic fracturing with average clay content less than 33%. Petrophysical analysis indicates that the sandstone contains potentially extensive natural fracturing that will further enhance the existing porosity and permeability of the interval.

The company believes the primary source of the gas is from deeper Carboniferous shales with some input for organic matter in the interval. Calculated free gas in place for the interval is estimated to be 163 bcf/sq mile with total gas estimated at 193 bcf/sq mile. Based upon gas samples and mud log shows the gas is estimated to be primarily dry gas.

The company plans to perform pressure tests, a DFIT, and possible vertical fracture stimulation and production testing across the lower 100 m of this interval in late 2012.

Zone 2, 2,870-3,110 m, Carboniferous tight sandstone (B sand) is a thick tight gas-saturated interval of sandstones and interbedded shales. Over the 240-m gross interval more than 32 m are identified as net pay with potential net pay of 188 m. Petrophysical analysis of the calculated pay indicates porosities of 3-9% with an average effective porosity of 3.58% and permeability of 20-300 nd and averaging more than 115 nd.

The B sandstone has low water saturation with an average 62% free gas saturation. The interval’s mineralogical composition suggests that it is well suited for hydraulic fracturing with average clay content less than 37%. Petrophysical analysis indicates that the sandstone contains potentially extensive natural fracturing that will further enhance the existing porosity and permeability.

The interval does contain dispersed organic material with estimated average total organic carbon of 1.48-2.14% within the shales over the gross interval. The company believes the primary source of the gas is from within the interval and potentially deeper Carboniferous shales. Calculated free gas in place for the interval is estimated to be 64 bcf/sq mile with a total 97 bcf/sq mile. Based on gas samples and mud log shows the gas is estimated to be primarily dry gas.

Zones 3-5, upper shale gas zones. The well encountered three potential prospective, highly fractured, organic-rich shale intervals with a total gross thickness of 430 m between 2,065 m and 2,610 m. San Leon took 250 m of whole core over three of the intervals.

Tight rock analysis on the core, integrated with petrophysical analysis of the logs, indicates total porosity of the intervals range between 1.4% and 8.5% and permeability averages 80-100 nd. TOC values are 1.2% to 3.25%, and maturity (Ro) values between 1.2-1.5.

Analysis of the TOC data suggests the shales are gas prone Type III source rocks that are in the dry gas window.  Gas saturations range between 30% and 80%. Based on gas samples and mud log shows, the gas is primarily methane with a small fraction of ethane and propane.

Given the highly fractured nature of the shales, the company is looking at further analysis of the core and petrophysics to fully understand the reservoir properties, particularly porosity and permeability, and long-term production potential of the zones. Future testing and potential fracing of the intervals is pending testing of the deeper tight gas zones that are believed to have much higher potential for commercial production.

San Leon said Siciny-2 was the first modern well to test the basin’s Carboniferous potential and has proven very real potential in the play. The company plans flow testing in 2012 and continued drilling in 2013 across its extensive position including concessions acquired as part of the joint venture with Hutton Energy.

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