Traps

Anticlinal structural traps

The main exploration targets for hydrocarbons in Latvia, as well as in the whole Baltic region, are anticlinal structures within the Middle Cambrian sandstone reservoir.

Based on present knowledge, structural anticlinal traps are numerous within the Liepaja-Saldus Ridge crossing the Baltic Syneclise - from central Latvia to middle Baltic, as well as within Gdansk-Kura depression. The average size of most of the identified structures is several tens of km² with vertical closures of 25 to 50-60 m, reaching over 100 m in larger structures.

All the Cambrian hydrocarbon accumulations of the Baltic Basin are associated with such structural traps, for example, the Lithuanian ones, and the Kuldiga oil deposit in Latvia. In all the cases, Lower Ordovician clay serves as the seal for the Cambrian reservoir while lateral sealing along faults is usually provided by Silurian or Ordovician rocks.

Stratigraphic traps

There are possibilities for other potential traps, which associated with Ordovician and Silurian carbonate (Reefs, Inter-Reefs and Back-Reefs), as well as Cambrian Pinch-out and Onlap deposits. However, their definition relies on high-resolution seismic data that are not available in the area so far.

Ordovician organic reefs, reefoid structures and build-ups represented a group of seismic anomalies that can be traced to the Gotland reefs. The island of Gotland is the best reference area; there reefoid structures form traps, from which oil has been produced for decades. The size of each individual reef does not exceed 1-3 km². Some of seismic data indicate a large seismic anomaly - strong intra-Ordovician reflection (see B seismic section),  in the Ordovician sequence, which could be interpreted as carbonate buildup (much larger than the Gotland reefs), possibly representing fringing or barrier reefs. Recently, this seismic anomaly has been interpreted (in the preliminary manner) as the presence of oolites within the Ordovician carbonate body.

On stable carbonate platforms, conditions that prevailed in parts of the Baltic Region during Ordovician and Silurian, shallow marine conditions dominated. Within this carbonate setting, reefs and organic build-ups were periodically partly exposed and eroded. The eroded materials were redeposited off the organic structures, often associated with bioclastic and oolitic deposits. These off-reef Oolitic and bioclastic deposits are known reservoirs in western Latvia.