Shallow Water Pre-salt Discovery to Spark More Driiling
The recente Discovery of a shallow water pre-salt reservoir by Brazilian private operator OGX has definitely raised a few eye brows. This novelty is a first in Brazil as up to now all other pre-salt reservoirs have been found in ultradeep waters off the Brazilian coast and usually very far from the coast. This new discovery which is located in BM-S-57 Block, in the Santos Basin and is less than half the distance from the mainland as other pre-salt finds in the Santos Basin, exactly 102 km from the coast of Rio de Janeiro. The wellhead is only 155 meters deep and the well was drilled down to 6,135 meters, which is the normal depth where pre-salt reservoirs are expected to be found. Also of consequence is the fact that preliminary appraisals of the reservoir show estimates of 1,8 billion barrels boe, although the company was quick to point out that further tests may uncork even larger reserves. Some industry analysis claim there is potential for up to 4 billion barrels. The OGX-63 well identified a hydrocarbon column of approximately 1,000 meters with a net pay of approximately 110 meters in the Albian section. The drilling of the well reached the Aptian section, where it identified hydrocarbons through a high gas presence.
It is well known that the pre-salt reservoirs began to be formed during the breakup between South America and Africa over 120 million years ago and as the continents drifted apart the reservoirs were covered up by a thick salt crust which has been found to be between 200 and 2,000 meters deep. The major pre-salt finds in the Santos Basin all have been found under the 2,000 meter salt crusts.
The analysis of rock fragments led to the confirmation of a microbiolite reservoir of Aptian age, in other words, the same type of reservoir rock found in the deep and ultra-deep waters pre-salt of the Santos and Campos Basins.
According to an OGX release, due to the high pressures encountered, the drilling was temporarily suspended so that OGX can replace the current Ocean Quest rig with the Ocean Star rig, also part of OGX’s fleet. The Ocean Star has the requisite specifications to continue the operation, which is expected to include logging and possibly conducting at least one drill-stem test.
This new shallow water pre-salt discovery is an important milestone as it increases industry expectations that other large shallow water pre-salt reservoirs may be located close by and possibly also in other shallow water locations up and down the coast. One of the positives aspects of this possibility is the fact that drilling for pre-salt oil in a shallow water set-up is much cheaper and less complicated that drilling over 300km offshore, beyond the range of most helicopters and especially, much, much simpler than drilling in water depths in excess of 2,000 meters. Basically the shallow water pre-salt decreases safety hazards and logistics problems at the same time it increases the company´s profit margins.
This is also good news for suppliers of equipment used in pre-salt drilling as it is probable that other operators with stakes in areas in the Santos Basin will be looking more closely at their survey data and drilling even more wildcat well in order to try to find more of these shallow water pre-salt reservoirs.
Claudio Paschoa is Marine Technology Reporter's correspondent in Brazil.