India's Pioneer High Pressure Air Injection Process Design: An Evaluation of its Efficacy for Enhanced Oil Recovery

Abstract

Abstract High Pressure Air Injection (HPAI) is one of the most versatile EOR processes and offers several advantages over other processes in low permeability light-oil reservoirs. The current study illustrates a HPAI pilot design process for an onshore light oil field of India having permeability in the range of 1-15mD. Study included screening of the field, combustion tube tests to establish technical feasibility & spontaneous ignition, modelling of lab results to validate kinetics and pilot design through simulation. Laboratory study was conducted on Combustion Tube (CT) System at IRS, ONGC, Ahmedabad. Here one-dimensional reservoir of ~2m length was created to physically represent reservoir condition in the CT and air was injected at high flux rate. To develop comprehensive kinetic model involving Thermal Cracking, LTO and HTO, the target oil was characterized based on maltenes and asphaltene. Further lab results were modelled using thermal simulator to validate the developed comprehensive kinetics. Later, the pilot was designed through field scale simulation study using the validated kinetic model. A fine scale Geocellular model prepared with block dimensions 50*50 was used for pilot design. In CT combustion front could be created, sustained and propagated. The average peak temperature of the stable zones was ~415°C with a temperature of ~600°C in the zones packed with native core, coke and shale. High peak temperature was observed due to catalytic effect of clay & coal present. Air requirement was 188 m3(ST)/m3, fuel consumption was 18.40 kg/m3, air to fuel ratio of 10.21 m3/kg and apparent H/C ratio of 1.21. Ignition was achieved within 12 hours of commencement of air injection at reservoir temperature (101°C) in second CT test confirming spontaneous ignition. The combustion tube model using comprehensive kinetics showed satisfactory match of oil rates, combustion front velocity, and peak temperature. Typical combustion characteristics such as formation of coke, and change in viscosity with temperature were successfully captured in the tube run. The temperature profile just ahead of the front showed the LTO reactions taking place in that region. In simulation, after history match, prediction variant was run with two inverted five spot patterns for pilot design. Simulation indicates average air injection rate of ~50,000 m3/d during the project life of 8 years. Envisaged incremental oil from the pilot area was ~12% above BAU case of the target STOIIP. Based on the study, India's first High Pressure Air Injection project is to be implemented in the tight light oil field by April 2024. The comprehensive design of the process via laboratory, simulation and process optimization would lessen the uncertainty of the process and would pave the way for improving recovery from tight light oil field. Also, confirmation of spontaneous ignition in such reservoirs reduces the number of factors influencing the success of the process.