Application of Diamondoids as Maturity Indicators for Condensate from Drava Depression, Croatia

Abstract

Diamondoid hydrocarbons were investigated in gas-condensates reservoirs from the Drava Depression, Croatian part of the Pannonian Basin, to define thermal maturity of condensates. The largest gas and gas-condensate fields in Croatia are Molve, Kalinovac, and Stari Gradac, located in the northwestern part of the Drava Depression. This area has extremely complex structural, lithological, and stratigraphic features that have resulted in the specific physical characteristics of the discovered hydrocarbon fluids. Bulk properties reveal that samples have high concentration of light aromatic hydrocarbon (BTEX) and low sulphur, and some of them are waxy; Stari Gradac and Severovci. Origin and maturity parameters of condensate were investigated and correlated based on gas chromatography (GC) and gas chromatography coupled to mass spectrometry (GC-MS) techniques. The value of diamondoid based maturity parameters, like methydiamantane index 40–50 % indicate high level of thermal maturity corresponding to vitrinite reflectance 1.1–1.6 %. Condensate samples were not biodegraded, as shown by high API density values and the absence of unresolved complex mixture (UCM).

Keywords

• diamondoid hydrocarbons
• condensate
• drava depression
• maturation