An Investigation of Abnormal Fluid Pressure within an Evaporitic Cap Rock in the Gavbandi Area of Iran and its Impact on the Planning of Gas Exploration Wells

A synthesis of well logs was carried out and drilling mud weight data were analyzed to figure outanomalous high fluid pressure within the Triassic evaporitic cap rock (the Dashtak formation) andstudy its impact on the geometry of anticlinal traps in the gas rich Gavbandi province located in thesoutheast part of the Zagros Mountains. The results indicated that the location of anticlinal traps at thedepth in which the Permian Dehram Group reservoir unit exists is horizontally displaced with respectto surficial crest of many anticlines within the Gavbandi area. This crestal shift may be induced byabnormally high fluid pressure in the An evaporate member of the Dashtak formation, detected inmany exploration wells across the area. When fluid pressure increases due to compaction duringshortening, the higher shaliness could probably cap more fluids and consequently increase the fluidpressure within the Dashtak formation. Anomalous high fluid pressure decreases internal friction andshear strength of rock units and facilitates fracturing and faulting within the Dashtak formation, whichconsequently causes crestal shift of anticlinal traps. This should be taken into account when planninga new exploration well in Gavbandi area in order to prevent trap drilling.

کلیدواژه ها:

Evaporitic Cap Rock ، Fluid Pressure ، Anticlinal Trap ، Crestal Shift ، Gas Exploration Well