Diamondoid Hydrocarbons as Maturity Indicators for Condensates from Southern Indus Basin, Pakistan

Abstract EN

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 C20+ 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.