The area
The RotliegendesThe Rotliegendes sandstone is a world class gas play sourced by underlying Carboniferous rock and sealed by overlying Zechstein salt. The sandstone is a fossil desert sandstone formed in the Permian 270 to 300 million years ago. Because desert sands are clean and rounded, most Rotliegendes gas fields have good productivity as the gas can flow easily around the sand grains.
In some areas however the sandstone has been considerably altered over geological time and in many areas the spaces between the sand grains have become filled with chemicals deposited by circulating underground water. This makes the trapped gas difficult to produce – ‘tight gas’.
Technology transfer
- Fracture stimulation of tight Rotliegendes began in late 1970s
- MFHW1 is now the technology of choice
- 100+ horizontal and 300+ slant wells across 50 fields drilled in the Rotliegendes to date
- Aurelian operates the first multi-frac well in Poland
- Ultimate recovery to date in the Rotliegendes Basin is estimated as 211 tcf2
- Polish Rotliegendes is an underexplored region that Aurelian is exploiting using technologies that are well-known and widely used elsewhere
- These technologies have been used successfully throughout the German and Dutch Rotliegendes, the southern North Sea and extensively in North America
1. Multi-Frac Horizontal Well.
2. The volumes are the ultimate recovery calculated from data taken from the websites of the Mines Dept. or equivalent in Germany, Poland UK and Netherlands.
The Zechstein plays
The Zechstein formations are rock salt, anhydrite, dolomite carbonates and shales deposited in a shallow Permian sea 250 to 270 million years ago. Poland has a long history of successfully exploring for oil and gas fields within these Zechstein sediments. The hydrocarbons are sourced from the shales and are frequently discovered within dolomite reservoirs.
Initially the exploration target was for reservoirs deposited in shallow water and located primarily on the edges of thick anhydrite platforms. Over the years a significant number of oil and gas fields have been discovered within this geological setting. More recently, exciting exploration successes have been made on the basinward side of the anhydrite platforms.
The first of these was the Sulecin oil field. Here, oil was discovered within slump and/or low-stand deposits located within the deeper water setting at the foot of the anhydrite platform slope.
Recent exploration success has been aided by technological advances in seismic acquisition and processing techniques. PGNiG discovered several oil and gas fields near Gorzów to the north of Cybinka/Torzym in 2003. The largest are the Międzychód and Lubiatów oil fields containing 7 billion m3 of gas and 30 million barrels of crude oil. Other discoveries include Sowia Góra, Grotów and Sieraków deposits, each containing several billion m3 of gas.