Abstract:
Nanofluid flooding in the petroleum industry has generated growing interest because of its
potential to greatly improve oil recovery. However, studies have reported that injection of
nanofluid could lead to impaired permeability due to adsorption of nanoparticles on
reservoir rocks thereby incurring high costs. The use of single Nanofluid Flooding (NF) has
not appreciably reduced permeability impairment. This study was therefore, designed to
investigate the technical and economic viability of Nanofluid-Alternating-Brine Flooding
(NABF) for enhanced oil recovery in Niger Delta reservoirs.
Eight sandstone core samples obtained from Niger Delta, were characterised for porosity
and permeability using Helium-Porosimeter and Permeameter, respectively. Densities and
viscosities of crude oil samples and brine (Salinity: 32.2g/L) were determined using
pycnometer and viscometer, respectively. Core samples were initially saturated with brine
and drained with crude oil, to determine the initial Water Saturation (SWi). Silica
nanoparticles of size: 20-70 nm, were dispersed in brine at concentrations ranging from 0.01
to 3.00 wt%. Interfacial Tensions (IFT) between oil and nanofluids were measured. Brine
Flooding (BF) of core samples was conducted at 2.00 cm3/min. The Optimum
Concentration (OC) and Optimum Injection Rate (OIR) during NF were determined by
injecting each nanofluid concentration at 0.50, 1.00, 2.00 and 3.00 cm3/min. The NABF was
carried out at OC and OIR. The Oil Recovery Factors (ORF) for all experiments were
computed using material balance. The images of pre-flooded and post-flooded core samples
were obtained using Scanning Electron Microscope. Nanoskin factors (Sn) were determined
for NF and NABF and compared with the analytical model developed from Darcy’s
equation. The ORF obtained were upscaled for field application and evaluated for Threshold
Oil Price (TOP). Risk analysis with varying ORF, Capital Expenditure (CAPEX) and
Operating Expenses (OPEX) was carried out using a commercial software. Data were
analysed using ANOVA at 𝛼0.05.
Porosity and liquid permeability for the samples were 17.0-30.0% and 1.1x10-8 -1.6x10-8
cm2 (1104.9-1584.0 md), respectively. The densities of crude oil and brine were 0.88 and
1.02 g/cm3, while their viscosities were 3.0x10-4 kgms-2 (3.0 cp) and 1.0x10-4 kgms-2 (1.0viii
cp), respectively. The SWi were 11.0-18.4%. The IFT were 1.9x10-2 -2.3x10-2 N/m (18.5-
23.0 dynes/cm) while the OC and OIR for NF were 2.00 wt % and 2.00 cm3/min,
respectively. The ORF for BF, NF and NABF were 68.9-73.1, 63.8-66.2 and 83.8-86.2%,
respectively. The pre-flooded cores had evenly distributed grain matrices void of external
particles while permeability impairment was observed for NF. Permeability impairment
reversal was observed during NABF. The predictive model for Sn agreed with the
experimental result. Economic analysis revealed that for unit CAPEX (N13,985.56/bbl;
$34.00/bbl) and OPEX (N1,867.48/bbl; $4.54/bbl), at discount rate of 10.0%, TOP was
N20,196.79/bbl ($49.10/bbl). Risk analysis on profitability showed that TOP for proved,
probable and possible ORF were 33,400.81, 19,197.24 and N12,545.87/bbl (81.20, 46.67
and $30.50/bbl), respectively. The order of impact of the economic variables on profitability
was ORF>CAPEX>OPEX.
Improved oil recovery in Niger Delta reservoirs was achieved using nano-alternating-brine
flooding with minimal permeability impairment. The method is also profitable within the
stipulated oil price regime.
