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More shallow gas for ADX Energy at Anshof-2 well in Austria

Updated: Mar 25

ADX Energy operations in Upper Austria. Credit: File.

ADX Energy has encountered more encouraging shallow gas peaks of 2.52 and 1.27 per cent during drilling of the 8½-inch (216mm) hole section of its Asnhof-2 well in Upper Austria.

But the primary Eocene-age target still lies below as the company continues to drill in a bid to re-evaluate the field reserves, which could be as high as 26 million barrels of oil equivalent (MMboe).

The primary Eocene sandstone is an active producing unit from the Anshof-3 discovery well, which penetrated the reservoir 1.8km away. If Anshof-2 is a success, ADX will keep it as a second producing well in the field. It is expected to contribute about 300 barrels per day to total field production, with an ultimate well recovery of 0.8 million barrels (MMbbls).

The company says its drilling operations are running smoothly, with 9 5/8-inch (244mm) casing now run and cemented and the 8½-inch (216mm) drilling assembly now on bottom and making hole at about 1110m.

The hole is deviated to about a 20-degree inclination and is planned to build angle again to hit 79 degrees before entering the main reservoir target at 2318m measured depth (mMD). The hole is planned to end at 2650mMD.

As ADX waits for the main reservoir to be hit, the shallow drill gas peaks within the Puchkirchen Formation are extremely encouraging.

The company says drill gas peaks of 2.52 per cent and 1.27 per cent around 850mMD depth likely correlate with shallow gas encountered by the Anshof-3 well and represent the distal, or edge, of a shallow gas field. This “pinch-out” of the gas-bearing sand has been modelled on 3D seismic data and proves a strong well-to-seismic tie based on drilling data so far.

At about 930mMD, the character of the gas shows changes from peak to more blocky, sustained gas highs. It may represent thicker, higher-quality sandstones and is supported by mudlogs recording an increase in sandstone within cuttings at about that depth.

It is also worth noting that the hole section is being drilled with a higher mud-weight than was used for the Anshof-3 well, which was only drilled to a 35-degree inclination. Higher mud-weight, essentially a more viscous mud, is used for several reasons and in this case, ADX has alluded to borehole stability and rate of penetration optimisation for the increase.

Higher mud-weights will provide increased downhole pressure and help to keep the hole in-gauge in response to formation pressure attempting to squash the hole flat – a particular issue with inclined holes in high formation stress regimes. The viscous mud will also help with clearing cuttings from the bit and allow it to cut efficiently and maintain design rate of penetration.

The downside of a high mud-weight is that it will supress gas shows, as the increased downhole pressure fights the against the formation gas attempting to enter the hole. It is an important safety measure, but we will need to wait for logging to reveal more information about the shallow sands.

Last week, a sand encountered in the 12¼-inch (311mm) hole section gave a drill gas peak of 4.2 per cent, suggesting exploration potential exists in the imbricated clastic Puchkirchen formation of Oligocene to Miocene age, although the sand intercept was thin at the well location.

But the main focus is on the primary target – the Eocene-aged sandstone. ADX says it hopes Anshof-2 will provide data to support a reserve upgrade to as high as 26 million MMboe for the field, which represents the current combined 3P reserves and 3C resource volumes.

Management says success at Anshof-2 may also allow it to move reserves from the currently low-side gross estimate (1P) of 0.5 MMboe into the 2P classification, in addition to de-risking several follow up prospects.

Operationally, things seem to be going well for ADX, with the drillbit approaching the main reservoir. It says it will update the market on drilling operations on December 5.

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