ISOTOPIC AND MINERALOGIC PROPERTIES OF PYRITE AS INDICATORS OF THE GENESIS OF HYDROGEN SULFIDE IN PRODUCTIVE STRATA OF THE DAULETABAD-DONMEZ GAS FIELDS

Abstract

The Dauletabad-Donmez gas field is in the southern part of the Amu Dar'ya oil and gas province. The identification of the origin and sources of H2S in gases of the Dauletabad-Donmez field is very important, particularly for its further exploration and subsequent development. To definitively establish the source of H2S in gases of this field the authors studied the mineralogy of pyrite in productive strata, identified its different generations, analyzed the sulfur isotope distribution (SID) in them and compared the resulting data with the SID in H2S, both free and dissolved in interstitial and condensed water, as well as in sulfates present in the rocks and the interstitial water. Study methods and results are discussed. The data on the mineralogy of pyrite and of the SID in it support the assumption that the H2S present in free gas in the Dauletabad-Donmez field originated in Upper Jurassic deposits and, therefore, migrated from them. These data suggest, too, that H2S found in condensed and interstitial water in the pool zone with sweet free gas is a chemical reduction product of sulfates in Cretaceous red beds themselves.