# Data-Driven Analyses of Low Salinity Waterflooding in Carbonates
## 2 Methodology  
### Data Collection and Cleaning  
Experimental studies of oil displacement by LSW in carbonates, available in the literature, were carefully studied and the relevant core flooding tests were extracted. Fluid/rock properties and experimental results were collected in an unbiased manner, from the tables and graphs in various sources [3; 17; 21; 24; 30; 31; 32; 33; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64]. Each data entry corresponds to a core flooding test. Both secondary and tertiary modes of LSW flooding in carbonates were considered in the data extraction process. The data from 145 core flooding tests were extracted and compiled. The laboratory experiments of oil displacement tests by LSW injection in limestone cores were categorized to extract information about the injection mode, injection sequences, and the controlling parameters that affect oil recovery. The rock/fluid properties, which control the performance of LSW flooding, are shown in Table 1, including the number of available data points for each controlling parameter. Because not all of the parameters were reported in every LSW flooding experiment, there is a significant number of missing data for some parameters, which affects the accuracy of our models. Table 2 shows the minimum, maximum and mean values of the controlling parameters. The low number of secondary core flooding tests in the literature indicates the greater importance of the application of LSW in tertiary mode and as an EOR approach. Hence, this study focused on analyzing data collected from tertiary core flooding experiments. There are 117 data points that show the incremental oil recovery by LSW injection in the tertiary mode. These data points range from 0 to 42% of OOIP (original oil in place), with a mean of 6.17% and standard deviation of 7.6%. Figure 1 shows the distribution of incremental oil recovery by tertiary recovery. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{3}{c}{**Number of Data Points**} \\ \cline{2-3}  & **Secondary Mode** & **Tertiary Mode** \\ \hline Porosity, \% & 20 & 112 \\ Permeability, mD & 28 & 117 \\ Initial water saturation Swi, \% & 23 & 116 \\ Formation water composition, ppm & 26 & 117 \\ Formation water salinity, ppm & 24 & 114 \\ Secondary injected brine composition, ppm & 25 & 114 \\ Secondary injected brine salinity, ppm & 25 & 116 \\ Tertiary injected brine composition, ppm & - & 112 \\ Tertiary injected brine salinity, ppm & - & 114 \\ Crude oil acid number, mgKOH/g & 7 & 87 \\ Crude oil base number, mgKOH/g & 1 & 64 \\ Viscosity of oil, cp & 16 & 106 \\ Density of oil, cp & 25 & 98 \\ Residual oil saturation S\({}_{\mathrm{or}}\), \% & 7 & 37 \\ pH of effluent brine & 0 & 27 \\ Test temperature, °C & 8 & 100 \\ Secondary recovery factor, \%OOIP & 28 & 117 \\ Tertiary recovery factor, \%OOIP & - & 117 \\ IFT, mN/m & 5 & 25 \\ Contact angle & 2 & 27 \\ Effluent cations concentration, ppm & 3 & 20 \\ Effluent SO\({}_{4}\)2\({}^{-}\) concentration, ppm & 1 & 9 \\ Pressure drop, psi & 2 & 60 \\ Zeta potential & 9 & 18 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Number of data points extracted from the literature for different rock/fluid parameters. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Parameter**} & **Min** & **Max** & **Mean** \\ \hline Permeability, mD & 0.40 & 200.60 & 32.70 \\ Low salinity, ppm & 0 & 193,230 & 22,315 \\ SO\({}_{4}\)2\({}^{-}\) concentration (LS), ppm & 0 & 9222 & 930 \\ Cation concentration (LS), ppm & 0.0 & 13,454.5 & 1416.0 \\ SO\({}_{4}\)2\({}^{-}\) concentration (HS), ppm & 0 & 4290 & 534 \\ Cation concentration (HS), ppm & 14.34 & 61,480.00 & 15,879.00 \\ AN, mgKOH/g & 0.08 & 4.60 & 0.57 \\ BN, mgKOH/g & 0.01 & 2.49 & 0.50 \\ Temperature, °C & 20 & 250 & 88 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Statistical measures of the parameters. The collected data points were organized and prepared for regression analysis.