Gas Injection EOR Screening by Laboratory Experiment and Sector Modeling in Carbonate Reservoir

Abstract

Hydrocarbon gas injection projects are undertaken in order to maintain reservoir pressure, produce oil through swelling and reduce residual oil saturation by decreasing the interfacial tension (IFT). Along with local displacement efficiency, macroscopic sweep efficiency plays a dominant role in the success of gas injection projects, as recovery from the field depends strongly on reservoir geology and petrophysical properties.In this paper, a procedure to screen the best injectant for implementation of a successful gas injection pilot project is discussed. To determine the microscopic sweep efficiency, PVT experiments and coreflood tests are conducted. First, minimum miscibility pressure (MMP), oil solubility and IFT values are measured through PVT experiments, which is followed by unsteady-state coreflood experiments on 200 cm long cores to evaluate the sweep efficiency at miscible and immiscible conditions. Data from the experiments are used to evaluate oil recovery in a sector model extracted from the full field model. The sector model analysis for different injection scenarios provides sweep efficiency and guidelines for the implementation of the gas injection pilot project.The coreflood experiments show improvement in recovery in immiscible conditions due to oil swelling and reduction in IFT, while higher recovery is achieved in miscible conditions due to multiple-contact miscibility. Evaluation of the macroscopic sweep efficiency in the sector model highlights the issue of gas override, and suggests improving the sweep by gas enrichment, as well as water-alternating-gas injection (WAG).

A Case Study on Miscible and Immiscible Gas Injection Pilots in Middle East Carbonate Reservoir in an Offshore Environment

“…PVT experiments showed that the minimum miscibility pressure (MMP) is around 4500 psia, which is higher than initial reservoir pressure; but the crude oil has a strong swelling effect (swells by a factor of 1.45 once saturated with gas). Unsteady-state coreflood experiments performed with a 200 cm long core showed recovery of 70% for immiscible flood while recovery of 92% for miscible flood (Kumar et al, 2015).…”

“…Moreover, local grid refinement allowed more accurate representation of well trajectories, which was difficult in large gridcells of full field model. A value of 5% residual oil to miscible flood (S orm ), obtained from coreflood experiments (Kumar et al, 2015), was used to restrict the vaporization of oil components into gas phase below the user defined residual oil saturation in a grid block (Hiraiwa et al, 2007;Bourgeois et al, 2011).…”

A review of development methods and EOR technologies for carbonate reservoirs

“…Laboratory experiments should be carried out to determine the feasibility of hydrocarbon injection before field implementation. Kumar et al (Kumar et al 2015) conducted pressure/volume/temperature (PVT) experiments and core displacement experiments of natural gas in combination with hydrocarbon gas injection projects of carbonate reservoirs. The results show that the minimum miscible pressure (MMP) of injected natural gas is somewhat higher than the initial reservoir pressure, but crude oil has a strong swelling effect (once saturated by gas, the swelling rate can reach 1.45 times).…”

Development of a Giant Carbonate Oil Field, Part 2: Migration from Pressure Maintenance Development to Sweep Oriented IOR Development

“…Down-flank gas injection pilot Gas injection pilots (GIP) were implemented in the north-west area of the field to assess the secondary and tertiary gas sweep efficiency in down-flank area for long term development plan. The injected gas was the 1 st stage separator gas of which minimum miscibility pressure is higher than the field initial pressure (Kumar et al, 2015a). The pilot results are summarized as (a) gas movement in the pilot area was dominated by pressure gradient of the peripheral water injection, (b) significant gas override was observed, (c) high recovery occurred when injected gas achieved miscibility and (d) asphaltene precipitation was observed in one of the pilots (Kumar et al, 2015b).…”