Assessment of Oil Recovery by Low Salinity Waterflooding from Laboratory Tests

Abstract

Increased secondary and tertiary oil recovery by low salinity water flooding has attracted widespread interest as a low cost improved oil recovery method. Field applications that give increased recovery by over about 2% OOIP are considered economically viable. Although the number of reported laboratory and field investigations is now approaching 200, no consistent conclusions have been reached as to the circumstances under which recovery is improved. Laboratory core floods provide a practical approach to investigation of necessary conditions for improved recovery. In seeking responsive rocks for investigation of recovery mechanisms, 19 sandstones were screened for low salinity effect (LSE) through decrease in residual oil after injection of dilute brine (LSE @Sor). The highest recovery given by a definitive bump in recovery, as opposed to small increase in oil cut, was 5% OOIP. Three rock types, Castle Gate, Berea Stripe, and Briar Hill, were selected for further study because of relatively high response. After the originally tested core plugs were cleaned and restored, two of the plugs gave robust residuals to high salinity flooding and no LSE @Sor; the third gave very high recovery by high salinity flooding but much reduced response to LS brine. Reproducibility of recovery behavior was tested for pairs of sister plugs. For all three core types, average LSE @Sor, if any, was much lower than the recoveries that led to their selection. The best performing sandstone, Briar Hill, was then tested further with sets of cores being taken from two additional quarried blocks, each weighing about 10 tons. None of the cores cut from these blocks gave significant tertiary response. The average recovery for outcrop rocks is much lower than the average for reservoir rocks. An unexpected conclusion from the study is that, because of the generally low response, outcrop rocks provide numerous examples of very little or no LSE @Sor.

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

“…Cores experimented upon by Winoto et al (namely: Berea Stripe 1, castle Gate 1, Idaho hard 1, Boise 1, Bandera Brown 1, Kirby 1, Torrey Buff 1, Leopard 1, Bentheim 1, and Cedar Creek) generally showed little responses to reduced salinity injection, even though they met the necessary conditions such as the presence of clay and mixed-wetness . There were two reasons for this: all samples are outcrop samples, and clay structures are significantly different from regularly stacked kaolinite structures, which the likes of Brady et al have observed to be crucial in LSWF.…”

“…We will exclude the results of outcrop samples from these analyses. For all cores used in Winoto et al, low-salinity water was prepared by diluting formation water 20 times, resulting in 1780 ppm, with no sensitivity analyses on dilution factor. A similar case applies to AlQuraishi et al with Saudi sandstone and Saudi carbonate, in which seawater was diluted 10 times to yield a LSW of 6835.8 ppm.…”

“…As discussed earlier, formation and injection water salinity contrast, kaolinite content, sulfate content, multicomponent ion exchange and crude oil desorption are some of these. Cores experimented upon by Winoto et al, namely: Berea Stripe 1, Castle Gate 1, Idaho hard 1, Boise 1, Bandera Brown 1, Kirby 1, Torrey Buff 1, Leopard 1, Bentheim 1, and Cedar Creek generally showed little responses to reduced salinity injection even though they met the necessary conditions such as the presence of clay and mixed-wetness . AlQuraishi et al attributed improvement of oil recoveries for Saudi Carbonate and Saudi Sandstone to MIE, sulfate presence and wettability modification.…”

A Magnetic Resonance Study of Low Salinity Waterflooding for Enhanced Oil Recovery

“…LSF increased oil recovery by 4% OOIP and 9% OOIP for the kaolinite-coated and montmorillonite-coated sand packs, respectively. The literature suggests that the oil recovery improvement with LSF can be approximately 10% in some cases but may be negligible in others. ,, Winoto et al measured LSF for a series of sandstone samples and found the highest recovery improvement from LSF was approximately 5% OOIP, while most were 1–3% OOIP. Therefore, a 4% OOIP and a 9% OOIP increase from LSF in the current work are reasonable oil recovery improvements.…”

Compatibility evaluation of modified seawater for EOR in carbonate reservoirs through the introduction of polyphosphate compound

“…Numerous laboratory studies and a few field pilots have shown that both low-salinity waterflooding (LSWF) and ion-modified waterflooding (MWF) could be potential and economic EOR solutions comparable to other chemical EOR techniques (Rotondi et al 2014;Winoto et al 2014;AlQuraishi et al 2015;Jackson et al 2016; Afekare and Radonjic 2017). The fundamental difference between LSWF and MWF is that in LSWF, the salinity and total dissolved solids (TDS) of the injected water are lowered by diluting with seawater or freshwater (Nasralla and Nasr-El-Din 2011;Shaker and Skauge 2012).…”