PRESSURE-DRIVEN PETROLEUM MIGRATION AND HEAT TRANSFER: UNDERSTANDING THE ORIGIN OF NATURAL GAS CHARGE OF THE HAYNESVILLE FORMATION IN THE SABINE UPLIFT AREA OF TEXAS AND LOUISIANA, USA

Jurassic mudstones of the Haynesville Formation in the Sabine Uplift area of Louisiana is a self-sourced natural gas reservoir with additional gas charge from downdip Jurassic source rocks, which may include the Haynesville, Bossier, and Smackover Formations. Migration of hydrocarbons and supercritical water into the Sabine Uplift from warmer, downdip, gas-generating Jurassic strata in the North Louisiana Salt Basin was investigated quantitively. Modern thermodynamic equations of state were used to model thermophysical properties of methane and supercritical water under reservoir conditions. Pressure-driven migration velocities, across pressure differentials ranging from 0 to 29,000 psi (0 to 200 MPa), were derived from Darcy flux through homogeneous isotropic porous media exhibiting a wide range of porosities (0 to 99%) and permeabilities (10 Darcys to 1 picoDarcy). We further investigated migration velocities for porous media exhibiting 11% porosity and 400 nanoDarcy permeability at 350 °F (177 °C) reservoir temperature, representative of average rock and reservoir properties for the Haynesville from the literature. Pressure-driven migration modeling through isotropic, non-fractured strata ensures the slowest route and the most conservative migration velocities.

Our findings indicate migration requires ~100,000 years for natural gas to migrate through 1.0 km of strata having representative petrophysical and reservoir properties of the Haynesville. Distance between the centers of the North Louisiana Salt Basin and Sabine Uplift is 96 miles (155 km). Given these migration velocities over this distance, 1.55 Ma is required for dry gas migration. Although 1.55 Ma is beyond the production timeframe of moving hydrocarbons from the reservoir into the wellbore, it is well within the geologic timeframe to charge a reservoir. Our studies indicate supercritical water is five times more thermally conductive than methane under these reservoir conditions; however, the relatively small volumes of migrated water likely did not transfer sufficient heat for metagenesis of dry gas. Based on these calculations, a component of natural gas that charged the Haynesville in the Sabine Uplift can be reasonably explained by updip migration from mature Jurassic source rock in the adjacent North Louisiana Salt Basin.