An assessment of the salt caprock creep impact on Pre-salt reservoir geomechanics

Abstract

Reservoir compaction and surface subsidence are widely studied consequences of hydrocarbon (HC) production. This is an important topic in the Brazilian Pre-salt, where wells cross thick salt layers to reach carbonate reservoirs. Adding knowledge on the behavior of salt as caprock is strategic, considering the upcoming demands for decommissioning and the trends for energy transition, such as carbon capture and storage (CCS). This work presents a literature review on subsidence resulting from HC production and the associated mechanical behavior of the salt caprock. A numerical study of a conceptual Pre-salt reservoir is performed to assess the combined behavior of reservoir compaction/expansion, salt caprock creep, and subsidence. The production, injection (such as CCS), and abandonment periods are considered. From the assumptions and findings of the study, two conclusions are drawn: i) the salt caprock creep contribution to the stress paths and changes in permeability is of small magnitude, while it is relevant to subsidence if the reservoir is abandoned in the depleted condition; and ii) creep prolongs the evolution or reversal of the mechanical behavior and permeability when the external loads acting in the model are reverted. This study is expected to serve as a reference for more advanced analyses in Pre-salt reservoir geomechanics, specially considering the trends for decommissioning and energy transition.