Why are wells getting tight?
25.09.2015: The recovery rate in oil fields is around 20 to 40 percent using conventional methods, i.e. most of the oil remains in the reservoir rock. By injecting seawater in the water-bearing rocks below the oil, the oil field pressure can be stabilized. Moreover, the recovery rate is enhanced by 30 percent, and production can be extended. However, this technical measure is coupled to a variety of geochemical processes between the rock fluids (water and oil) and the rock itself. One consequence is that unwanted minerals form, another is that labile rock components dissolve. In extreme cases, the production wells are blocked. Up to now, the geochemical processes between the injection and production wells were unknown.
These chemical processes were subject of a joint project between Clausthal University of Technology and Helmholtz-Centre Potsdam GFZ. For the first time, it was possible to unravel the chemical processes in time and space and to quantify them. Conceptually, a new hydrogeochemical approach was applied to model the hydrochemical data of the Miller oilfield in the UK North Sea. „This oilfield is very sensitive to seawater injection, and is known for extreme oilfield scaling and production decline”, according to Hans-Martin Schulz, senior scientist at GFZ. „This approach enables us to demonstrate how, when and how much barite forms in direct vicinity of injection wells.“ The geoscientists calculated –dependent on different time scales- how the mineralization front migrates to the production well until complete tightening.
The calculated processes are mainly dependent on the amount of injected seawater. However, mixing with the original oilfield water is another control. The developed approach allows the optimization of technical measures and their targeted programming to the given situation. In summary, the new approach helps to maintain the operative manner of the oilfield infrastructure.
van Berk, W., Fu, Y., and Schulz, H.-M. (2015): “Temporal and spatial development of scaling in reservoir aquifers triggered by seawater injection: Three-dimensional reactive mass transport modeling of water–rock–gas interactions”. Journal of Petroleum Science and Engineering 135, 206-217. doi:10.1016/j.petrol.2015.09.014
