Low Salinity Waterflooding: From Single Well Chemical Tracer Test Interpretation to Sector Model Forecast Scenarios

Abstract

We study Enhanced Oil Recovery (EOR) through Low Salinity (LS) waterflooding in a brown oil field. LS waterflooding is an emerging EOR technique in which water with reduced salinity is injected into a reservoir to improve oil recovery, as compared with conventional waterflooding, in which High Salinity (HS) brine or seawater are commonly used. The efficiency of this technique can be quantified at the well-scale by a Single Well Chemical Tracer Test (SWCTT), which is an in-situ method for measuring the Remaining Oil Saturation (ROS) after flooding the near-wellbore region with a displacing agent. Two SWCTTs were executed on a sandstone North African field. The tests were realized in sequence with seawater and LS water to evaluate the EOR potential at the well-scale.Here, we propose the interpretation of these two SWCTTs. They were modeled through numerical simulations because of the presence of several non-idealities in the complex scenario considered. A recently-developed tracer simulator was employed to solve the reactive transport problem. This was used as a fast post-processing tool coupled with a conventional reservoir simulator. Model parameters were estimated within an inverse modeling framework, on the basis of an assisted history matching procedure that exploits the Metropolis Hastings Algorithm (MHA). Results were scaled up on a sector model of the field, and forecast scenarios that consider a field-scale implementation of this technique were defined.The well-scale displacement efficiency gain associated with LS water, as compared with seawater, was evaluated. It was quantified as a ROS reduction of 8 saturation unit (s.u.), with a P10 -P90 range of 3-15 s.u. Reservoir-scale simulations suggest that the associated ultimate oil recovery of the EOR pilot may be increased by 2% with LS water, with a P10 -P90 range of 0.7-4.3%.Overall, the LS EOR potential for a selected field was quantified through a robust and original workflow, based on SWCTT interpretation. This state-of-the-art procedure is now available for further applications. The simulated oil recovery improvement with LS water is promising, and leads the way to the implementation of an inter-well field trial. IntroductionWaterflooding performance may be affected by the salinity of the displacing water (Rotondi et al., 2014). In particular, the injection of water with reduced salinity may improve oil recovery, as compared with conventional waterflooding, in which HS brine or seawater are commonly used. This was firstly investigated by Tang and Morrow (1999), who proposed the migration of fines theory to underpin the observed incremental oil recovery. Since then, several mechanisms, different in sandstone and carbonate reservoirs, have been proposed to explain the ensuing EOR effect, with various degrees of acceptance in the industry (McGuire et al., 2005;Pu et al., 2010;Emadi & Sohrabi, 2013). Today, the two most recognized mechanisms are based on (a) the occurrence of multicomponent ion exchange and (b) the effects of pH on the desorption from the...

From Mineral Surfaces and Coreflood Experiments to Reservoir Implementations: Comprehensive Review of Low-Salinity Water Flooding (LSWF)

“…Modeling of LSWF have been performed with black oil models, ,,, in-house industry sector models, , compositional models, , and even a 1D numerical model . The majority of the numerical black oil models implement LSE using salinity-dependent relative permeability curves.…”