Unconventional Gas in Italy: the Ribolla Basin

Bencini, Roberto ¹; Bianchi, Elio ¹; De Mattia, Roberto ¹; Martinuzzi, Alberto ¹; Rodorigo, Simone ¹; Vico, Giuseppe ¹
(1)Independent Resources plc, Rome, Italy.

CBM and Shale Gas production is growing fast and is becoming an important energy source in many countries.

CBM is methane produced directly from coal seams. Methane is found adsorbed into the coal matrix, and it is produced at low pressure by pumping away any water from the coal seam and stimulating the methane flow through the coal cleats to the well bore. Similarly, Shale Gas is natural gas that is produced by desorption from organic rich clay at low pressure, after multistage stimulation of long horizontal boreholes, often from formations that are less permeable than coal.

Independent Resources plc is developing the first unconventional gas project in Italy, at the 100% owned “Fiume Bruna” and “Casoni” exploration licences (Central Italy), where some 300 BCF of natural gas are calculated to be in place, of which 160 BCF are interpreted to be primarily recoverable from the two blocks. The gas is interpreted to be producible from both the coal and the organic rich shale that is associated with the coal seam, at an average depth of approximately 1000 m.

Results to date include knowledge that the Miocene age organic rich sequence:

- consists of one laterally continuous 9-11 meter thick seam of coal and black shale,

- is saturated with thermogenic gas,

- is dry,

- is able to produce excellent quality natural gas by desorption after stimulation,

- has a permeability of 1-2 mD,

- responds more like a gas shale than a classic high permeability coal.

Additionally, there are indications that the 70 meter thick laminated marl and clay sequence immediately above the main seam may be prospective for shale gas as well.

The initial challenges of the project are:

- characterization of the coal and of the organic rich shale, including its mineralogy and gas content, gas composition and gas productivity, and any associated water;

- identification of the best formation stimulation technique;

- technology transfer from areas where CBM and Shale Gas production is mastered with economic success;

- procurement of suitable equipment and services in a safe and value-for-money manner.

ECBM (Enhanced Coal Bed Methane) is one way to implement CO2 geological storage, by injecting CO2 in unmineable coal seams to enhance methane recovery. This technique may find application toward the end of the primary production cycle in the Ribolla basin.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.