The Burgan Oil Field is made up of three main subsurface structures known as the Magwa, Ahmadi, And Burgan formation. The deeper reservoirs, namely the Lower Cretaceous Ratawi and Minagish limestones and the Jurassic Marrat Formation also contain significant oil reserves but are less substantial. The Magwa and Ahmadi formation are separated from the Burgan formation by a normal fault cutting horizontally down through the whole structure. This is known as the Burgan Graben. The role of tectonic stresses that have affected this region in Mesozoic and Cenozoic times also play a part in much of the faultings seen in the formation. Looking closer at the Burgan field the formation is made up of several radial faults that help trap the petroleum content in the formation. These faults and the Burgan graben are what cause the compartmentalization of the reservoir. This compartmentalization makes for great petroleum play and holds it in place well over a long period of time. The source rock that caps this formation is known as the Mauddad Limestone.( the above diagrams help give you a better visual on the formation as a whole)