Diamondoid hydrocarbons as maturity indicators for condensates from Southern Indus Basin,Pakistan

Diamondoid hydrocarbons have been examined in condensates reservoired in the southern indus basin using gc-ms. bulk properties reveal that samples are waxy and low sulfur with the exception of pakhro and gopang which are nonwaxy. tic show bimodal distribution of n-alkanes along with high abundance of c 20+ n-alkanes indicating substantial contribution of terrigeneous om in these samples. cpi close to one is consistent with mature nature of oils. the samples show two ranges of pr/ph ratios. those within the range of 2.2-2.7 reflect marine depositional settings for om while others with pr/ph >3 may have originated from terrestrial om deposited under marine oxic conditions. the cross plot of pr/n-c17 versus ph/n-c18 indicate type iii kerogen as main source of om deposited under marine to marine oxic conditions. the values of diamondoid based maturity parameters,like methyladamantane index 54.1-75.8% and methyldiamantane index 34.9-56.3% indicate high level of thermal maturity corresponding to vitrinite reflectance 1.1-1.6%. no biodegradation is observed in any of these samples as shown by methyladamantanes/adamantane 3.99-5.52 and methyldiamantanes/diamantane 2.16-2.99 and supported by high values of api gravity (45.13°-60.02°) and absence of ucm. © 2013 shagufta nasir and tahira fazeelat.