Saudi Arabia faces a complex security problem in the face of obvious danger from domestic terror groups. Even the state oil company (Aramco) is seen at risk. While it is thought that most terrorists would not attack the oil facilities themselves (which would be hugely unpopular with most Saudis), the thousands of expatriates working for Aramco are seen as a likely target. Actually, a militant minority of Saudis believe the oil money is a bad influence and advocate destroying the wells and returning Arabia to the good old days of Islamic virtue (and an average lifespan of 42 years, which is what it was before the oil money arrived.)
Most Aramco facilities are in the Eastern Province (along the Persian Gulf coast.) The Expatriates, and many Saudis, live in these compounds (basically gated communities), which contain Western style housing, and no religious police. Saudis who live in the compounds often have non-Saudi wives, or acquired a taste for Western style living while studying or working overseas. Religious Saudis, particularly religious radicals, see the housing compounds as foreign pollution, full of women walking around in short dresses and no veils, and men drinking illegal booze and holding Christian prayer services. All of that is true, but the government tolerates it as long as it stays on the compounds. But the 1800 or so foreigners (plus about as many wives and children) working for Aramco are seen as particularly offensive to Islamic radicals. The oil is considered God's gift and must not be defiled by presence of infidels working to extract and export it. Actually, Saudi Arabia has been steadily replacing foreigners with Saudis. But it's realized that replacing s skilled foreigner with an unprepared Saudi just causes more problems. So the "Saudization" process at Aramco is expected to go on for another decade or so. Faced with the likelihood of more attacks, and not wanting Aramco to suffer an exodus of it's expatriate workers (all hard-to-replace technicians and managers), security has been increased around the 40 or so compounds where the expatriates live. The Aramco administrative facilities (the ones not directly involved with pumping or moving oil) have always been heavily guarded. But the security has been increased even further. A successful terrorist attack on Aramco, or Aramco employees would be seen by Saudis, and the government, as a more direct attack on the Saudi government. Not quite as bad as an assault on the holy places or senior government officials, but close. And Aramco provides a lot more targets.