The Carupano Basin is located in northeastern offshore Venezuela. This area is characterized by the interaction between the Caribbean and the South American Plate. It has two structural highs, the Los Testigos High located in the northern limit of the basin and the Patao High, which is between the Caracolito subbasin and the Paria subbasin. In the latter are located the main gas fields.

The generated gas is characterized by low maturity, and it has been attributed to biogenic processes because of its carbon isotopic signature. Nevertheless, gas compositions show that a thermogenic signature predominates with an increase of gas maturity from the east to the west, where condensates were found associated with gas.

To understand the origin of the gas, the total organic carbon (TOC)_SR methodology was used to define continuous TOC profiles from sonic and resistivity wirelogs. As a result, we have shown that the whole column from the Eocene to the Pliocene consists of a poor source rock, except the middle Miocene that could be considered as a good source rock. The average TOC content of the middle Miocene can reach values around 2.5%. The kerogen is mostly type III continental–derived organic matter.

The thermal calibration and the basin modeling study shows that the bottom of the Paria subbasin has reached the oil window, whereas the bottom of the Caracolito subbasin has reached the gas window. Nevertheless, simulations of fluid-flow migration conducted using default type III kinetic parameters were not able to fill any of the known fields.

We conclude that the default kinetic parameters used for basin modeling are not able to reproduce the nature of these fluids. Indeed, in our study, the main part of the fields drainage area is in a low-maturity domain where the vitrinite reflectance (R_o) is less than 0.6%, but the kinetic parameters used were calibrated with kerogen samples for which R_o was taken to be approximately 0.6%.

Considering default type III kerogen as a starting point and using observed natural data such as gas compositions, a new set of kinetic parameters were derived to account for low gas maturity. This modified type III kerogen differs from the previous one by a 13% increase of the hydrogen index. The simulations conducted with this modified type III scheme allowed us to reproduce quite well the filling of the fields, as well as the composition of the hydrocarbons.