Petroleum Development Oman in new oil discovery

Petroleum Development Oman (PDO) has struck oil again in the Shuaiba Formation in north-west Oman's Malaan area, one of the country's most productive geological formations.

This latest discovery can be attributed to three factors - revisiting the geophysical interpretation of seismic data in the area, making a bold decision that went against conventional thinking and drilling with new technology.

The Shuaiba Formation has been yielding oil for some time. It contains, for example, the reservoirs of the Yibal Field, which is now into its fourth decade of production.

The Malaan location was first targeted in 2000 as a likely place to find more oil reserves in the formation.

The first well - Malaan-1 - proved a disappointment when it failed to produce oil at an economically viable rate. Perseverance and further studies of the seismic and well data uncovered an ancient shoreline stretching along the edge of the Malaan structure.

"The analysis of the seismic and well data led to a revised interpretation of the geological setting, indicating a stratigraphic trap," said Stephen Hiebert, senior interpreter at PDO. A stratigraphic trap is a geological formation containing hydrocarbons within permeable rocks that have been sealed by impermeable sedimentary rocks deposited around it.

Unlike the more common structural traps, stratigraphic traps are not characterised by folding or faulting, which can be readily detected on seismic images. In the case of the Malaan structure, the stratigraphic trap was created by sedimentation around shoal rocks formed by ancient marine organisms, such as coral.

"The new setting suggested that we could expect better quality reservoirs and a higher oil content down the flank of the Malaan structure," Hiebert said.

"But this theory is counter to the conventional thinking of petroleum prospectors, which holds that the most likely place for good oil production is at the crest of a geological structure."

Nevertheless, PDO took the risk. In February, the Malaan-2 well, drilled horizontally around the flank of the structure, began to deliver 1,800 barrels of oil per day to the nearby Lekhwair production facilities.

In June, an appraisal well, Malaan-3, was successfully completed and tested, producing 2,600 barrels of oil per day.

This success might not have been possible without the deployment of a new drilling technology that was used in an exploration well for the first time.

Schlumberger's new Logging While Drilling (LWD) tool enabled the drillers to keep the well within the best-quality rock formation by detecting the boundary of the formation.