Iranian Journal of Oil and Gas Science and Technology
Quarterly Publication

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

Document Type : Research Paper

Authors

Mahdi Najafi 1
Abbas Bahroudi 2
Ali Yassaghi 1
Jaume Vergés 3
Shahram Sherkati 4

1 Department of Geology, Tarbiat Modares University, Tehran, Iran

2 Department of Engineering, University of Tehran, Tehran, Iran

3 Group of Dynamics of the Lithosphere (GDL), Institute of Earth Sciences “Jaume Almera”, ICTJA-CSIC, Lluís Solé i Sabarís s/n, 08028 Barcelona, Spain

4 National Iranian Oil Company, Exploration Directorate, Tehran, Iran

https://doi.org/10.22050/ijogst.2014.5797
Abstract
A synthesis of well logs was carried out and drilling mud weight data were analyzed to figure out anomalous high fluid pressure within the Triassic evaporitic cap rock (the Dashtak formation) and study its impact on the geometry of anticlinal traps in the gas rich Gavbandi province located in the southeast part of the Zagros Mountains. The results indicated that the location of anticlinal traps at the depth in which the Permian Dehram Group reservoir unit exists is horizontally displaced with respect to surficial crest of many anticlines within the Gavbandi area. This crestal shift may be induced by abnormally high fluid pressure in the “A evaporate” member of the Dashtak formation, detected in many exploration wells across the area. When fluid pressure increases due to compaction during shortening, the higher shaliness could probably cap more fluids and consequently increase the fluid pressure within the Dashtak formation. Anomalous high fluid pressure decreases internal friction and shear strength of rock units and facilitates fracturing and faulting within the Dashtak formation, which consequently causes crestal shift of anticlinal traps. This should be taken into account when planning a new exploration well in Gavbandi area in order to prevent trap drilling.

Keywords

Evaporitic Cap Rock
Fluid pressure
Anticlinal Trap
Crestal Shift
Gas Exploration Well

  • Receive Date 08 September 2013
  • Revise Date 26 November 2013
  • Accept Date 24 December 2013

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