Petroceltic in association with its partner Sonatrach announced well AT-4 on its Isarene Permit (Blocks 228 & 229a) in Algeria has successfully tested gas from two zones in the Ordovician at a maximum combined flow rate of 1.35 mmscf/d and 450 bwpd on a 48" choke.
Well AT-4, the first of the current appraisal campaign of the Ain Tsila gas discovery, was drilled to appraise the previously undrilled eastern margin of the Ain Tsila field and was located with the primary objective of maximizing information about the gas-in-place rather than optimizing flow rate on testing. The well encountered a gross gas column of 155 meters with no gas-water contact interpreted within two zones of the Ordovician reservoir. This gas-down-to is deeper than the gas-water contact currently interpreted in the field. Pressure data from logs and the test indicate the continuity of the Ain Tsila gas accumulation at this location and that AT-4 therefore represents a successful delineation well of the Ain Tsila field.
The AT-4 testing program initially involved the perforation, fracture stimulation and then isolation of the lower zone with a sand plug. Following this, the upper zone was also perforated and fracture stimulated, the well cleaned out and the two zones flowed together.
The well flowed with a combined rate of 1.35 mmscf/d of gas (1593 cubic meters/hour) and 450 bwpd of water with a flowing wellhead pressure of 160 PSIG on a 48" choke. After isolation of the lower zone to reduce water production, the upper zone was flowed separately at 1 mmscf/d of gas (1180 cubic meters/hour) with an associated 250 bwpd. It is likely that the induced fractures in the well have extended below the current field gas-water contact into an underlying aquifer resulting in the volumes of produced water seen. This volume of water reduced the gas flow to rates significantly lower than anticipated from this well. Testing and sampling operations at AT-4 have been completed and the well has been suspended.
The next well in the appraisal drilling campaign, AT-5, is targeting one of several structural pop-up features in the field with the intention of carrying out multiple fracture stimulations in a horizontal well to improve productivity and ultimate recovery factor for the field. Following the successful drilling of the pilot hole, we are currently preparing to conduct logging operations prior to commencement of the horizontal section.
Brian O'Cathain, Chief Executive of Petroceltic commented, "The first well in the current Ain Tsila appraisal campaign has successfully confirmed the extension of the field to the East and increased the proven area and calculated gas-initially-in-place. While the volumes of produced water reduced the gas flow rate, the data gathered from AT-4 will enable us to refine our remaining drilling and testing program in the Ain Tsila discovery in 2011 and ensure we optimize our future plans for the field."
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