Improved oil recovery by low salinity waterflooding: Surface chemistry and SCAL

The objective of this project was to investigate the scopes of low salinity water injection (LSW) as an improved oil recovery method by SCAL studies and its linkage to the surface chemistry of reservoir rocks. The combination of SCAL and surface chemistry can provide an improved understanding of possible mechanisms of oil recovery during LSW. This information can also be useful while addressing the challenges during modelling of LSW process. The SCAL experimental studies were divided into following three tasks:

1. Investigation of LSW as secondary and tertiary recovery methods using various model oils.
2. Studies on effect of initial wettability conditions on performance of LSW.
3. Influence of various crude oil components such as acids, bases, and asphaltene on the recovery performance of LSW and its linkage with surface chemistry.

From the experimental results of Task 1, it was found that initial wettability of the rock has great influence on the final recovery by LSW as a secondary recovery method. The initial neutral-wet condition provides the highest recovery for both high and low salinity waterflooding of Berea plugs. From Task 2, it was found that the initial water-wet condition is not favorable for LSW. Experiments were performed on Berea plugs with low and high clay content under same experimental conditions. The initial and final wettabilities were measured for representative plugs. It was found that there was negligible change in the wettabilities after LSW which supported poor response by LSW. In Task 3, coreflooding experiments were performed on several Berea plugs with considerable clay contents. Different variations of the Heidrun crude oil such as acid free, base free, and asphaltene free Heidrun crude oils were used to study the effects of various polar components of crude oil on the performance of LSW. It was found that the plug with base free crude oil provided highest whereas that with acid free crude oil provided the lowest oil recovery. The improved oil recoveries with LSW were found to be negligible. This can be attributed to the initial fairly water-wet conditions of the core plugs.