Abstract
The Ghawar field is the largest oil field discovered in the world. It is located in the Eastern Province of Saudi Arabia. The Arab-D reservoir (Upper Jurassic) consists of high energy shallow marine carbonate sequences capped by evaporites, oolitic grainstones forming the upper part of the reservoir. From 1983 to 1990, the southern part of the Ghawar oil field (South Uthmaniyah, Hawiyah and Haradh) was mothballed due to a period of low oil demand at the international level. During this mothballing period, Saudi Aramco reservoir management team pursued its established policy of monitoring reservoir pressure and temperature.
Following a close review of these pressure data, a clear pressure drawdown was identified during the mothballing period in a few wells centered around a localized area of the Haradh production area (South Ghawar). After eliminating all possible man-made causes (e.g. production) the available data point to a geomechanical explanation of the observed pressure drawdown. Fracture re-opening and/or propagation possibly related to neotectonic activity during a period of pore pressure recovery – after an initial period of primary depletion – is the most plausible explanation. Fracture characterization and simulation indicate the existence of natural fractures. Recent seismic events recorded in and around the study area further support the proposed explanation. Implications of the proposed geomechanical link on the reservoir performance are discussed.
