The shutdown of Saudi Arabia's East-West pipeline stands to squeeze already-scarce crude supply for Asia's four biggest crude importers, with South Korea appearing the most directly exposed.

Saudi crude accounted for 34.1% of South Korean crude imports in July, according to the Korea International Trade Association. It's at 27.3% of imports into Japan, government data show, and 14.9% of China's imports, according to customs data. For India, the figure is 10.2%, Kpler data show.

While Asian markets' dependence on Saudi crude do not directly translate into the number of barrels exposed to the pipelines shutdown, export constraints at the Hormuz Strait have shifted a substantial volume of the Kingdom's exports westward to the pipeline-linked Yanbu port.

Thomas Luedi, Asia-Pacific head of energy and natural resources at Bain & Company, said that Yanbu had taken over the large majority of Saudi exports previously shipped through Gulf terminals.

Luedi puts the total volume of Asia-bound supply at risk at about 4 million bpd, while Oriano Lizza, sales trader at CMC Markets, estimated between 3.5 million and 4.5 million bpd once stored crude in Yanbu and Egypt run down.

The oil market will lose 120 million barrels if the pipeline is closed for a month and storage is drawn down at the Red Sea port of Yanbu, said Matt Smith, director of commodity research at Kpler. This assumes the pipeline carries 4.5 million bpd of exports and 15 million barrels are stored at Yanbu, Smith said.

Stored crude, alternative Gulf loadings or a partial pipeline restart could substantially reduce the number of barrels ultimately disrupted.

For refiners, the more immediate effect may be cost rather than a shortage of crude.

"Asian refiners feel the cost immediately and the physical shortage weeks later," Lizza said, identifying widening premiums for medium-sour grades, along with higher delivered freight costs, as the first signs of stress.

"The biggest near-term impact is likely to be on oil prices and freight costs rather than physical availability," Chokwai Lee, director of equity research, told CNBC.

The impact to crude flow is expected to be felt much later into the year.

Luedi and Lizza estimated that stored crude at Yanbu and in Egypt could keep exports moving for roughly one to two weeks. Once those stocks are depleted and if the pipeline remains closed, loadings could begin to slip, while replacement cargoes from the Americas or West Africa can take more than a month to reach Asia.

Macquarie strategists expect the impact of Saudi flow disruption to be tamped down by greater feedstock flexibility, noting that Asian refiners have improved their capabilities in processing a broader range of crude grades which will support increased flexibility in the spot market.

The duration of the disruption remains unclear, with the Kingdom providing no timeline on the pipeline's restoration. The Associated Press and Reuters reported that repairs might take between three to six weeks.

U.S. Energy Secretary Chris Wright told CNBC last week that the vital Saudi East-West crude oil pipeline would resume operations "very soon."