Improved oil recovery by raw water injection
Thi Kin Phuong Nguyen, Andrew James Hage
Engineering Honours Degree 2009
University of Adelaide
Injectivity formation damage with waterflooding using sea/produced water has been widely reported for North Sea, Gulf of Mexico and Campos Basin. Formation damage occurs due to the capture of solid particles and the formation of external filter cake, resulting in permeability decline. Yet, moderate injectivity decline does not damage to the same extent in the case of long horizontal injectors, with high initial injectivity. The injection of raw or poorly treated water would save cost on water treatment, which can be significant on sea platform or sea-bottom-placed filters.
In this paper, we investigate the effect of injected water quality on waterflood using horizontal wells. It is found that induced injectivity damage results in increased sweep efficiency. The explanation of the phenomenon is as follows: injectivity rate is distributed along horizontal well non-uniformly; water advances along some intervals faster than others resulting in early breakthrough; the injectivity damage plugs the most permeable channels during flooding and homogenizes the injectivity profile along the well. The sweep efficiency is increased compared to the treated water injection. To test this theory, a combination of Excel and ECLIPSE 100 models has been run.
The results for several injection and production well configurations, in reservoirs with different heterogeneity have been produced. These results show that an increase in skin will increase the overall recovery factor at a set volume injected, for example after one pore volume injected. The results also show that at any point in time, the water cut is lower when skin is induced compared to the injection of treated water. The results suggest that the injection of untreated or raw water can be analogous to the injection polymers into the reservoir. Thus, the application of raw water injection can deliver a significant decrease in water treatment cost.