Flow behavior of N2 huff and puff process for enhanced oil recovery in tight oil reservoirs
In the present work, the potential of N2 huff and puff process to enhance the recovery of tight oil reservoir was evaluated. N2 huff and puff experiments were performed in micromodels and cores to investigate the flow behaviors of different cycles. The results showed that, in the first cycle, N2 was dispersed in the oil, forming the foamy oil flow. In the second cycle, the dispersed gas bubbles gradually coalesced into the continuous gas phase. In the third cycle, N2 was produced in the form of continuous gas phase. The results from the coreflood tests showed that, the primary recovery was only 5.32%, while the recoveries for the three N2 huff and puff cycles were 15.1%, 8.53% and 3.22%, respectively.The recovery and the pressure gradient in the first cycle were high. With the increase of huff and puff cycles, and the oil recovery and the pressure gradient rapidly decreased. The oil recovery of N2 huff and puff has been found to increase as the N2 injection pressure and the soaking time increased. These results showed that, the properly designed and controlled N2 huff and puff process can lead to enhanced recovery of tight oil reservoirs.
Miscible oil recovery utilizing N2 and/or HC gases in CO2 injection
Abstract Carbon dioxide miscible injection is one of the non-thermal effective enhanced oil recovery (EOR) methods. In the Middle East, particularly Abu Dhabi, pilot testing is already implemented in the Rumaitha Field for CO 2 miscible injection. This paper investigates the means of improving CO 2 miscible injection by enriching it with N 2 and HC gases. The emphasis is on identifying CO 2 solvent mixtures with reduced MMP to achieve miscibility at reasonable injection pressures in Abu Dhabi fields. The minimum miscibility pressure (MMP) of targeted oils from Abu Dhabi carbonate reservoirs with mixtures of N 2 , CH 4 , C 2 H 6 , and HC rich gases of varying composition with CO 2 injection gas are evaluated through simulation. The first contact miscibility (FCM) and the multiple contact miscibility (MCM) of injected gases/oil mixture under reservoir temperature have been determined using WINPROP module of the Computer Modeling Group (CMG) simulator. In addition, the corresponding oil recovery factors for various N 2 /CO 2 content displacements were calculated by 1-D compositional simulation of slim tube using BUILDER and GEM module of CMG Simulator. Results show that miscibility is predicted to occur with multiple contact miscibility (MCM): vaporization and/or condensation mechanisms. The increase of C 2 H 6 concentration in the CO 2 injected gas reduced MMPs for targeted Oil 1 by 100 psi/10 mol%. However, N 2 , CH 4 and HC rich gas increments in CO 2 injected gas increased the MMPs for targeted Oil 1. MMP was observed to be 2300 psi for pure ethane with Oil 1. In addition, MMPs for targeted oils with N 2 /C 2 H 6 and N 2 /CH 4 injected gas mixtures are assessed. This study can open possibilities for future enriching of CO 2 and N 2 miscible injection to improve miscibility and recovery of oil.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.