Reducing Reservoir Uncertainties Using Advanced Wireline Formation Testing (SPE 154426)

Several offshore gas fields are present in Adriatic Sea (Italy), producing since the 60s. In these assets the gas is mainly produced from multilayer metric sand reservoirs. The declining production in these mature fields is normally offset by drilling new deviated wells. Recent technology evolution shifted the focus from metric reservoirs to thinly laminated intervals (thin beds), until now not produced due to difficulties in indentifying gas bearing zones. While gas identification in metric reservoirs can be achieved with standard petrophysical measurements, thin beds are challenging since lamination thickness is half inch or less and even advanced petrophysical logs struggle in discriminating gas from water in this environment. Conventional pressure gradient approach also does not work, since thin beds are often overpressurized and pressures are supercharged due to low mobility. A new wireline formation testing approach for thin beds to discriminate gas from water zones was introduced, using a dual packer string with downhole fluid analysis capabilities, including fluid density measurement. This provided the possibility of testing very low permeability zones with high uncertainties in saturations. The possibility to verify gas presence in zones with high uncertainties saved the cost of multiple well testings, optimized the completion strategy of the different reservoirs and allowed to increase the field production and reserves. Dual packer tests were also successfully carried out in the basinal and slope facies of foreland basin, a shale formation underlying the multilayer reservoir sequence never considered before a real reservoir, revealing potential for gas production. Several gas fields today producing from metric reservoirs will be revisited in the very near future in order to start production from thin beds, until now untouched. The advanced wireline formation testing approach described in this paper will certainly play a key role in optimal exploitation of thin beds gas reserves.