Improving Hydrocarbon Resource and Fluid Property Prediction with a Coupled Generation/Expulsion Model

The recent extensive exploration in gas shales provides unprecedented opportunities to understand the hydrocarbon retained in source rock. In a newly developed modeling method, we coupled both generation and expulsion processes for hydrocarbon in source rock. The generation processes, including both primary-cracking (generation of hydrocarbons from kerogen) and secondary-cracking (generation of light hydrocarbons from heavy ones), are well described by a group of parallel first-order reactions with kinetic parameters calibrated by gold-tube pyrolysis. The extent of expulsion processes is based on the evaluation of maximum amount of water, oil, free gas and adsorbed gas in the pore system and on the matrix surfaces of source rock.

The results revealed following interesting phenomena, which has not been paid enough attention in previous work on hydrocarbon resource evaluation:

1. There is remarkable oil and condensates retained in source rocks even at high maturity of Ro > 1.5%, which contribute to the formation of shale gas at high maturity.

2. Retained and expelled gas content is not only a function of organic matter properties, but also remarkably influenced by burial history and paleopressure profiles.

3. There is obvious compositional fractionation between retained and expelled hydrocarbon; this fractionation need to take into account for fluid property prediction of both conventional reservoirs and shale gas.

Our quantitative method illustrated that the estimation on oil/gas amount, composition and fluid property can be largely improved considering the residue hydrocarbon components retained in source rock. This is important to for both shale gas and conventional oil/gas appraisal.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California