$re = '/((?<=Project )\d{0,2}).*?(FOAH|PRJ)(\d{1,10})/si';
$str = 'C:\\temp\\TimeSheet\\11-06-2017.txt:1:11/06/2017 18:45:56 - This 15 minutes is dedicated to PROJECT 100 FOAH18
C:\\temp\\TimeSheet\\11-06-2017.txt:2:11/06/2017 18:45:58 - This 15 minutes is dedicated to PROJECT 90 FOAH278
C:\\temp\\TimeSheet\\11-06-2017.txt:3:11/06/2017 18:45:59 - This 15 minutes is dedicated to PROJECT 80 FOAH313
C:\\temp\\TimeSheet\\11-06-2017.txt:4:11/06/2017 18:46:00 - This 15 minutes is dedicated to PROJECT 70 PRJ0031905
C:\\temp\\TimeSheet\\11-06-2017.txt:5:11/06/2017 18:46:02 - This 15 minutes is dedicated to PROJECT 60 PRJ0031909 C:\\temp\\TimeSheet\\11-06-2017.txt:6:11/06/2017 18:46:03 - This 15 minutes is dedicated to PROJECT 50 PRJ0032045';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php