Wellbore and Reservoir Thermodynamic Appraisal in Acid Gas Injection for EOR Operations

Abstract

This study provides insights into the experience gained from investigating the thermodynamic behavior of well and reservoir fluids during acid gas injection (AGI) in a hydrocarbon field to enhance oil recovery (EOR) and to reduce greenhouse gas emissions. Unlike conventional water and natural gas injection, AGI involves complicated phase changes and physical property variations of the acid gas and reservoir fluids at various pressure-temperature (P-T) conditions and compositions, and both constitute crucial parts of the EOR chain. A workflow is developed to deal with the reservoir fluid and acid gas thermodynamics, which is a key requirement for a successful design and operation. The workflow focuses firstly on the development of the thermodynamic models (EoS) to simulate the behavior of the reservoir fluids and of the injected acid gas and their integration in the field and in well dynamic models. Subsequently, the workflow proposes the thermodynamic simulation of the fluids’ interaction to determine the Minimum Miscibility Pressure (MMP), yielding the dynamic evolution of the fluids’ miscibility that may appear within the reservoir. Flow assurance in the acid gas transportation lines and in the wellbore is also considered by estimating the hydrate formation conditions.

Automated Equations of State Tuning Workflow Using Global Optimization and Physical Constraints

“…Subsequently, the GPS optimizer was tested on a reservoir oil with a H 2 S concentration of 31.43%. Note that this composition represents the reservoir fluid of an oil field in Northern Greece [31,32], the high H 2 S content of which poses a significant challenge in EoS model tuning due to the polar nature of H 2 S. The developed EoS model will be utilized for simulating an Enhanced Oil Recovery (EOR) process that includes acid gas (primarily comprising H 2 S and CO 2 ) injection. According to the workflow outlined in Section 2, the heavy end was split into single carbon number (SCN) fractions which were further lumped into three pseudo-components to maintain the number of components as low as possible.…”

Prospects of an Acid Gas Re-Injection Process into a Mature Reservoir

“…Sour resources refer to hydrocarbon reservoirs characterized by a significant presence of H 2 S and, to a lesser extent, CO 2 , which must be removed at onshore gas plants before the treated gas can be utilized onsite for operational needs or transported to the sales line [9][10][11]. To achieve this, the sour gas undergoes a process commonly known as "sweetening", during which its H 2 S and/or CO 2 components are separated in amine units, enabling the resulting natural gas product to meet the necessary specifications for transportation to various end users.…”

“…However, SRUs do not significantly contribute to revenue due to the unattractive market price of sulfur, and their installation is primarily driven by environmental compliance. Additionally, the tightening of air emission standards and regulations places growing economic pressure on oil and gas companies, prompting them to seek environmentally sustainable and cost-effective alternatives for handling acid gases produced alongside sour natural resources [9,11].…”

“…This approach offers several advantages, including cost savings from deactivating Claus units, reduced sulfur emissions into the atmosphere, and increased oil recovery [10]. Acid gases primarily consist of H 2 S and/or CO 2 , water vapor resulting from the sour gas sweetening process, and other impurities, including methane and heavier hydrocarbons [11,13]. In a typical AGI process (Figure 1), the sour gas produced undergoes a one or two-stage absorption, during which it comes into contact with an amine solution.…”

“…High-pressure acid gas is transported through pipelines to the well site, where it reaches the wellbore in a dense-fluid state (either liquid or supercritical) before being injected into the reservoir through the well tubing [15]. Depending on the composition and operator specifications, it may also be necessary to dehydrate the acid gas to prevent hydrate formation within the pipeline and wellhead and to mitigate corrosion [11,16,17].…”