Injection of Acid Gas Mixtures in Sour Oil Reservoirs: Analysis of Near-Wellbore Processes with Coupled Modelling of Well and Reservoir Flow

Abstract

The reinjection of sour or acid gas mixtures is often required for the exploitation of hydrocarbon reservoirs containing remarkable amounts of acid gases (H 2 S and CO 2 ) to reduce the environmental impact of field exploitation and provide pressure support for enhanced oil recovery (EOR) purposes. Sour and acid gas injection in geological structures can be modelled with TMGAS, a new Equation of State (EOS) module for the TOUGH2 reservoir simulator. TMGAS can simulate the two-phase behaviour of NaCl-dominated brines in equilibrium with a non-aqueous (NA) phase, made up of inorganic gases such as CO 2 and H 2 S and hydrocarbons (pure as well as pseudo-components), up to the high pressures (∼100 MPa) and temperatures (∼200 • C) found in deep sedimentary basins. This study is focused on the near-wellbore processes driven by the injection of an acid gas mixture in a hypothetical high-pressure, under-saturated sour oil reservoir at a well-sector scale and at conditions for which the injected gas is fully miscible with the oil. Relevant-coupled processes are simulated, including the displacement of oil originally in place, the evaporation of connate brine, the salt concentration and consequent halite precipitation, as well as non-isothermal effects generated by the injection of the acid gas mixture at temperatures lower than initial reservoir temperature. Non-isothermal effects are studied by modelling in a coupled way wellbore and reservoir flow with a modified version of the TOUGH2 reservoir simulator. The described approach is limited to single-phase wellbore flow conditions occurring when injecting sour, acid or greenhouse gas mixtures in high-pressure geological structures.

Intentional salt clogging: a novel concept for long‐term CO2 sealing

“…Salt scaling issues due to pressure decrease are especially likely for mature depleted gas fields and will therefore become more important in the future . Salt precipitation as a consequence of evaporation is expected for injection of dry gas for applications including natural gas storage, pressure maintenance or enhanced oil recovery (EOR) . In the context of CO 2 storage, dry gas injection is expected to induce salt precipitation by the same mechanism.…”

“…11 Salt precipitation as a consequence of evaporation is expected for injection of dry gas for applications including natural gas storage, pressure maintenance or enhanced oil recovery (EOR). [15][16][17] In the context of CO 2 storage, dry gas injection is expected to induce salt precipitation by the same mechanism. Th is has been shown by generic simulations of CO 2 injection in both saline aquifers, [18][19][20][21] and (less studied) for depleted gas fi elds.…”

Modeling brine leakage to shallow aquifer through an open wellbore using T2WELL/ECO2N

“…Battistelli et al (2011) used both the EPM and the conventional wellbore flow model and made a comparison of the two approaches. However, the effectiveness of the EPM approach for simulate the flow in wellbore is rarely evaluated.…”

Transient Flow Modelling of Start-up CO2 Injection into Highly-Depleted Oil/Gas Fields

“…It therefore introduces a thermal aspect to the reservoir fluid migration process, because many fluid properties, such as viscosity and density, are strong functions of temperature [7]- [9].…”