عنوان مقاله [English]
One of the major problems in drilling process of zone 4 of the member 7 of Gachsaran Formation in Marun oilfield is casing collapsing. This problem is investigated in this paper in view of geological prospect. To study the petrography it is used 500 thin sections and different well logs such as gamma ray, sonic, graphic well logs are applied to plot stratigraphic columns and wells correlation and also provide isochors and isobar maps. The petrographic study indicated that the main lithology of zone 4 is marl with a minor association of limestone and anhydrite. The collapse problem in marly intervals is more common while drilling program. According to isochor maps provided for zone 4 there is max thickness in the axial part, southern flank of the north eastern part and east end of the field. According to the isobar maps, high pressure points of Zone 4 are in the axial part and western end of the field and low pressure locations are in the curvature part of the anticline and northern part of the field. By comparing the stratigraphic column, the isobar and isochor maps it can be concluded that the formation pressure changes in zone 4 is affected by variation in thickness, lithology, structural shape and tensions trends exerted on Marun anticline structure.