DISTRIBUTION OF INERT GASES IN DEEPER RESERVOIRS OF THE SULAIMAN FOLD BELT, PAKISTAN

Adeel Nazeer, Tabinda Tariq, Ghulam Murtaza, S. Habib Shah, and Aisha Danyal
Pakistan Petroleum Limited (PPL), Exploration Department

Natural gas in a number of gas fields in Pakistan is associated with high percentage of inert gases. Inert gases are considered to reduce the BTU value of sweet gases. Wells of Jandran and Kandra are examples where production of inert gases (mainly CO2) is a major problem in development of the fields. High inert gases also give clues to short or long distance migration. Previous workers presented a number of factors responsible for distribution of inert gases (CO2 and N2) in various basins of Pakistan; nevertheless, the issue related to the source and variable amount of inert gases is still unresolved.

Attempts were made to analyze the varying composition of inert gases along the deep seated basement faults in the Eastern Sulaiman Fold Belt  but no specific relation could be established. This was not in favor of the prevailing notion of previous workers that inert gases are associated with deep seated faults. In the same way, geothermal gradient zones were identified and distribution of inert gases in these zones was studied but again no well established relation could be tracked.

However, varying composition of inert gases in two different formations of one of the wells of Jandran established important geological factors. The CO2 in deeper Chiltan (86%) and shallower Mughal kot (3%) in Jandran indicates that the source of inert gases and hydrocarbons is not the same. Similarly, variation in amount of inert gases in Chiltan Limestone of Rodho Structure and Afiband reveals the generation of in-situ inert gases because both wells were drilled on same anticlinorium, sharing same geology and possibly the same source rock. Probably post accumulation changes play important role in generation of in-situ inert gases in varying concentrations.

AAPG Search and Discovery Article #90160©2012 PAPG/SPE Annual Technical Conference, 3-5 December 2012, Islamabad, Pakistan.