Experimental Investigation on the Effects of CO2 Displacement Methods on Petrophysical Property Changes of Ultra-Low Permeability Sandstone Reservoirs Near Injection Wells

Abstract

The petrophysical properties of ultra-low permeability sandstone reservoirs near the injection wells change significantly after CO2 injection for enhanced oil recovery (EOR) and CO2 storage, and different CO2 displacement methods have different effects on these changes. In order to provide the basis for selecting a reasonable displacement method to reduce the damage to these high water cut reservoirs near the injection wells during CO2 injection, CO2-formation water alternate (CO2-WAG) flooding and CO2 flooding experiments were carried out on the fully saturated formation water cores of reservoirs with similar physical properties at in-situ reservoir conditions (78 °, 18 MPa), the similarities and differences of the changes in physical properties of the cores before and after flooding were compared and analyzed. The measurement results of the permeability, porosity, nuclear magnetic resonance (NMR) transversal relaxation time (T2) spectrum and scanning electron microscopy (SEM) of the cores show that the decrease of core permeability after CO2 flooding is smaller than that after CO2-WAG flooding, with almost unchanged porosity in both cores. The proportion of large pores decreases while the proportion of medium pores increases, the proportion of small pores remains almost unchanged, the distribution of pore size of the cores concentrates in the middle. The changes in range and amplitude of the pore size distribution in the core after CO2 flooding are less than those after CO2-WAG flooding. After flooding experiments, clay mineral, clastic fines and salt crystals adhere to some large pores or accumulate at throats, blocking the pores. The changes in core physical properties are the results of mineral dissolution and fines migration, and the differences in these changes under the two displacement methods are caused by the differences in three aspects: the degree of CO2-brine-rock interaction, the radius range of pores where fine migration occurs, the power of fine migration.

Effects of carbonated water injection on the pore system of a carbonate rock (coquina)

“…However, Drexler et al (2019) noted a reduction in weight, porosity, pore volume and permeability of the sample after injecting carbonated water (desulphated seawater saturated with CO2), while Abbaszadeh et al (2016) reported a reduction in porosity and the sample's weight, but an increase in the permeability. By contrast, Wang et al (2019) observed almost no changes in the porosity but a significantly lower permeability. Most studies noted the importance of rock dissolution as such, and the transport and deposition of fine particles (e.g., Jia, 2019;Mahzari et al, 2019).…”

Experimental Investigation of Oil Recovery Performance and Permeability Damage in Multilayer Reservoirs after CO2 and Water–Alternating-CO2 (CO2–WAG) Flooding at Miscible Pressures

“…Moreover, CO2-brine-rock interactions lead to dissolution of carbonate minerals and destruction of clay mineral structure in rocks. Metal carbonate precipitation occurs due to changes in pH and the concentration of metal ions (i.e., Ca 2+ , Mg 2+ , Fe 2+ ) in the fluid of the cores (Equations 1-3), and additional clay particles are released caused by structural instability [29][30] . It has been reported that low-permeability sandstones undergo CO2 flooding and CO2-WAG flooding, and the concentration of suspended solid particles in the produced brine ranges from 0 to 6720 mg/L with an average size of 1049.7 nm [24] .Three of the most common carbonate minerals formed in pores and capable of blocking pore throats are given by the equations CO2 + H2O + CaCO3⇌ Ca(HCO3)2,…”

A Novel Approach to Stabilize Foam Using Fluorinated Surfactants

“…Foam has different applications in oil and gas industry such as in drilling, hydraulic fracturing, and in enhanced oil recovery (EOR) [2][3][4][5][6]. CO 2 flooding is one of the most commonly used EOR method that involves the injection of compressed CO 2 [7][8][9]. In EOR methods that employ low viscous fluids as displacing slugs such as CO 2 flooding, the foam is applied to improve the sweep efficiency by controlling the gas mobility.…”