| dc.description.abstract | Johan Sverdrup is one of the largest and most profitable oil fields ever to be discovered on the Norwegian continental shelf. The extraordinarily high permeability of the intra-Draupne formation is one the main reasons for the excellent reservoir quality but it has also been a source of drilling related challenges.
The aim of this work was to experimentally assess whether the drilling fluid used on Johan Sverdrup could be modified to reduce fluid loss and lost circulation, while also minimizing damage to the formation. To conduct the analysis, it was important to first estimate the pore-sizes in the higher-permeability parts of the intra-Draupne formation. Thereafter, samples of laboratory mixed fluids and field fluids were tested on a range of permeabilities, with and without exposure to wear, to assess the effective sealing ranges of the fluids.
The results show that the reason for lost circulation primarily is related to the formation pore-sizes in parts of the formations being larger than the effective sealing limit of the fluid. A solution was found using cellulose based particles which did not degrade during the exposure to wear and thus maintained effective sealing under all tested conditions. Furthermore, a finer cellulose additive was found to reduce fluid loss and formation damage in the medium to low permeability parts of the reservoir.
The overall findings thus suggest that lost circulation may be prevented and thereby reduce time and cost of drilling and improve the productivity of each well. | |
