Enhanced gas recovery and storage: the role of N2 during natural gas displacement by CO2 flooding in sandstone rocks
Carbon dioxide (CO2) injection and storage method for enhanced gas recovery holds enormous promise for concurrent natural gas recovery and CO2 storage from depleted gas resources. However, its potential application as part of climate friendly pilot scale research among industry and researchers is limited by the incessant mixing, while it is possible to reduce the extra length scale of CO2 mixing with natural gas. Despite the several investigations performed to decrease such a nascent mixing problem, only quite a few achieved significant methane (CH4) recovery with little mixing issues throughout the Enhanced Gas Recovery (EGR) process. Three (3) distinct sandstone core plugs (Grey Berea, Bandera Grey, and Bentheimer) with diverse petrophysical parameters were employed in this investigation. A core flooding experiment was carried out to simulate CH4 displacement by N2 injection at 1500 psig, 40 0C, and several injection rates (0.2, 0.4, 0.6, 0.8, and 1.0 ml/min). Maximum CH4 recovery was achieved at 0.4 ml/min for both core samples. The Berea recovered 18% more than Bandera grey at the same injection. To curtail the effect of incessant mixing an experiment was conducted to investigate the influence of N2 as a booster during natural gas displacement. This was done in a simulated reservoir situation with varied booster volume percent (6, 13, 19, and 29%). The experimental results indicated that the coefficient of longitudinal dispersion decline with raises in booster gas volume, hence the higher the amount of booster the less the dispersion of CO2 into CH4. The higher the booster volume the higher the sequestered CO2, especially at higher CO2 injection rates (1.0-1.2 ml/min). The maximum CO2 storage was obtained in the test at 0.13 PV of N2. The large differential pressure drops (dp) characterised this value. The maximum recovery, on the other hand, happened when the least amount of booster gas was employed and was marked by the least amount of N2 product impurity. The behaviour of CO2 and N2 during the natural gas displacement process was also evaluated. This intends to determine why CO2 has a longer breakthrough time during the EGR process with N2 gas inclusion. The experiment was constructed with varied injection rates at temperatures of 30 and 40 0C. The experiment at 30 °C recorded an extendable breakthrough time over that at 40 °C. The maximum breakthrough of 0.52 PV was recorded at 30 °C at the lowest injection velocity. The displacement efficiency of the current research outperforms traditional CO2 floods. When compared to traditional CO2 flooding, there was a 62 & 18% improvement in CH4 recovery and CO2 storage, respectively, and a 20% drop in dispersion coefficient when N2 was used as a booster gas. This study demonstrates that using N2 as a booster gas can increase CH4 recovery and CO2 sequestration, and thus can be suitable for pilot application within the oil and gas industry.
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