Geomechanical Lessons from Oil and Gas Produced Water Injection Towards Subsurface Carbon Dioxide Sequestration
Authors: Ramos G. G. , McLennan John , Ispas Ion , Green Sidney 
Published: August 2024

ABSTRACT:
The petroleum sector, with its competencies in water flooding and produced-water re-injection (PWRI), provides complementary technologies for carbon capture and sequestration (CCS). Our objective is to identify oil & gas technologies and procedures that would be beneficial to future CCS implementations. We reviewed PWRI operations in 3 major petroleum basins. We then compared their geological and geomechanical settings, PWRI data, and induced seismicity. The most prominent impact is induced seismicity, as others have shown, the cause being the increase of pore pressure in faults. Contributing causes of rock failure and pressure communication are perturbation of the in-situ stresses, water-induced weakening, static creep, and fatigue-induced weakening. Measures for effective risk reduction are volume/pressure management, well placement, managed pumping schedules, high-resolution reservoir description, frequent monitoring coupled with laboratory programs, and strain-coupled reservoir simulation. We recommend adopting these practices learned from water-flood oil-gas operations. These would help promote gradual ramping of the reservoir pressure, a uniform CO2 flooding front, flooding profile control, and most importantly, rock stability.

1. INTRODUCTION
With growing public interest and government incentives for carbon capture, the oil and gas sectors are uniquely positioned in future implementation of large-scale carbon capture and sequestration as supercritical CO2 (sCO2 or "CCS"). The industry's experience, personnel, infrastructure, and core competencies in deep subsurface operations can immediately provide complementary technologies for subsurface Carbon Sequestration (CS).
As geo-engineers/scientists in the upstream petroleum sector, we offer practical lessons from our experience in large-scale water floods and Produced Water Re-Injection (PWRI), also called Salt Water Disposal (SWD). The multimillion-barrel daily produced water disposal operations in Texas and Oklahoma are very relevant to future high-tonnage injection of sCO2. The most prominent adverse impact is induced seismicity, because of its impact on structures and the general public. Another unfavorable effect is the contamination of freshwater aquifers. Lesser known and poorly understood effects are induced microseismicity, surface heave, loss of injectivity, and overestimation of reservoir capacity. All of these arise from combinations of factors such as: pore pressure rise, proximity to unmapped structures, perturbation of in-situ stresses leading to rock failure, injection fluids' geochemical effects, induced fatigue from pumping schedules, concentration of pressurized zones/bulbs, and perturbation of pre-existing geologic creep rate. This paper provides an overview of PWRI operations in 3 major oil and gas (O/G) fields in Texas and Oklahoma, and how seismicity may have developed. We identified other geomechanical processes that contribute to rock weakening and debilitation of rock interfaces.