# Unconventional Wells Interference: Supervised Machine Learning for Detecting Fracture Hits
## 2 Materials and Methods  
### Data Subsets Selection  
All available data were examined for completeness. Pad 137 was selected as the reference because the most comprehensive data was available for that location. Figure 2 shows the geolocations for all wells in the area of interest (selected from several hundred wells available in the field). The data for Pads 133 and 138 were also used in the analysis. Table 1 shows the key operational information, such as the fracking dates and the date of first production (DOFP) for all Pad 137 wells. The events timeline is shown in days counted from DOFP of Well 42-329-42006, the earliest producing well in Pad 137. One can observe two subsets of wells on this pad, with distinctly offset timing of the well-stimulation batches. The first batch subset comprised the top six wells in Table 1, where fracking had started before Day 0. The stimulation was completed after the start of production at the reference well at only one of these wells. The second batch subset (the remainder of the Pad 137 wells) did not even have fracking started until at least 430 days after the start of production at the reference well. Distinct pressure spikes, an indication of a likely frac hit, were visually identified at the second batch subset of Pad 137 wells between Day 430 and Day 450, as well as between Day 530 and Day 550 (Figure 3). The latter could be attributed to interference from fracking at the other pads. For example, there was fracking at Pads 4, 25, and 133 (see Table A1) during the same time span. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Well ID** & **Frac Start, Day** & **Frac End, Day** & **DOFP, Day** \\ \hline
137-42006 & \(-\)53 & \(-\)27 & 0 \\
137-41996 & \(-\)53 & \(-\)27 & 2 \\
137-42048 & \(-\)22 & \(-\)6 & 15 \\
137-42338 & \(-\)53 & \(-\)27 & 16 \\
137-42106 & \(-\)5 & 4 & 21 \\
137-42104 & \(-\)22 & \(-\)6 & 22 \\
137-42740 & 431 & 453 & 477 \\
137-43200 & 431 & 453 & 477 \\
137-43201 & 431 & 454 & 477 \\
137-42276 & 433 & 452 & 477 \\
137-42007 & 433 & 452 & 477 \\
137-43675 & 433 & 452 & 477 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Operational time span for Pad 137 wells as days counted from the Well 137-42006 DOFP. Figure 2: Well clusters, color-coded by pad numbers. The pads of interest are pointed at by arrows. The likelihood of inter-well communication may depend on the local geology and the distance between the wells. Accordingly, Pad 133 was selected for a preliminary investigation into potential inter-pad interferences, because it was closer to Pad 137 than to Pads 4 and 25 (Figure 2). Pad 138, located between Pads 133 and 137, was then picked as the verification pad for the same case study. Eight of the twelve Pad 133 wells were stimulated between Day 91 and Day 128 (see Table 10), chronologically taking place between the first and second well-stimulation batches at Pad 137 (Table 1). The second batch at Pad 133 followed the second batch at Pad 137 and was of primary interest in the case study. DOFP data were not available for Pad 138 wells, which somewhat limited the data analysis. However, it did not critically affect the model validation and verification workflow. Well stimulation at Pad 138 was done between Day 294 and Day 327 (Table 10). Some of the relevant data were missing, but the pressure and fracking timeline data were available for all 10 wells on Pad 138 (Figure 4a), for the second batch on Pad 137 (Figure 4b), and for the second batch on Pad 133 (Figure 4c). The average treatment pressure (calculated for each stimulated well) was the lowest for Pad 138 and the highest for Pad 137. The treatment (well-stimulation) pressure data were deemed to be particularly important because higher pressure at the child well could be more likely to lead to either pressure communication with the offset wells or the loss of well control (or well blowout) whenever this pressure is transferred to wells that have less pressure integrity.