Investigation of Dissolution Effects on Dolomite Porous Media under Carbonated Water Injection CWI

Abstract

To investigate the effects of carbonated water injection (CWI) on dolomite porous media, a set of two coreflooding experiments were performed on outcrop samples. The results allowed the identification of the effects of dissolution on porosity and permeability on outcrop dolomite samples. Experiments were carried out at 70 °C, injection pressures of 8500 and 7500 psi, and a constant injection flow rate of 2 cm3/min. The experimental setup was assembled and commissioned arranging two coreholders connected in series, each one containing a rock sample, to improve result acquisition. The injected fluid was carbonated water made from synthetic sea water (salinity of 38 kppm) saturated with 21.5% of total solubility in CO2 X-ray Computed Tomography (CT) provided image acquisition allowing the evaluation of porosity evolution throughout the tests. Experiments showed a tendency for porosity increase for the sample in the first coreholder, possibly associated with rock dissolution. The spatial porosity profile from the CT scan for the first coreholder showed porosity variation in the first centimeters of the rock sample inlet. In the second coreholder, porosity remained unchanged during the entire test, indicating that the dissolution effect promoted by carbonated water injection was most notable in the first sample when compared with the second. The amount of dissolved moles afforded the behavior regarding dissolution phenomena. Permeability behavior was analyzed through the pressure drop values from the sample for the entire experiment, registered by pressure transducers installed in each coreholder. Results showed consistent permeability behavior for the first coreholder samples, despite the tendency of the porosity to increase. The samples placed in the second coreholder presented lower permeability because minerals dissolved in the first sample were transported to the second sample and likely precipitated and so related to the porous media blockage.

The effect of CO2-enriched water salinity on enhancing oil recovery and its potential formation damage: an experimental study on shaly sandstone reservoirs

“…This paper investigated the influence of CWI and WF on oil recovery improvement and induced formation damage in various low salinities. The result of CWI on permeability in sandstone media can be quite different from dolomite (observed by Nunez et al) (Nunez et al 2017). However, the following conclusion can be proposed from this study:…”

“…They also concluded that acid solutions could be considered to work as a clay stabilising agent (Musharova et al 2012). Nunez et al reported some percentage increase in permeability during CWI in dolomite cores (Nunez et al 2017). In contrast to their investigation, permeability tends to decrease in the sandstone rock.…”

“…Nunez et al investigated dolomite dissolution phenomena of CWI. They reported that porosity and permeability are increased in the near-wellbore region, but they have an opposite trend far from wellbore (Nunez et al 2017). Ross et al investigated CO 2 -brine dissolution effect on sandstone cores.…”

Mechanistic study of the carbonated smart water in carbonate reservoirs

“…The studied rock's heterogeneity has an important effect on mineral dissolution, as Nunez et al 11 concluded. They reported that the mineral dissolution increases in the higher porosity region and decreases in the lower one.…”

“…Carbonated low salinity water (CLSW) is a combination of low salinity water and CO 2 (supercritical), coexisting in the same phase at p > 1072 psi and T > 87.8°F. 10,11 CLSW takes advantage of the high CO 2 solubility in the low salinity water (salting-in phenomenon), which ensures a high mass transfer of CO 2 from the CW to the oil, based on 3-7 times higher affinity of CO 2 to be dissolved in oil than in water. [3][4][5] CW had an enhanced sweep efficiency compared to the other CO 2 -EOR methods such as CO 2 injection and water-alternating-gas (WAG) due to oil viscosity reduction and CW's ability to overcome the shielding effect.…”