Secondary and Tertiary Thermally Induced Gas-oil Gravity Drainage from Oil-wet Fractured Rocks: Experiments under Reservoir Conditions

A series of reservoir condition experimental studies are presented that investigate the effects of oil production by water drive on the success of subsequent oil production by gas-oil gravity drainage in a fractured laboratory model. The experiments were performed using low permeable, oil-wet carbonate core samples. During this work, injection of N-2 gas followed by steam into the fracture was studied using two different scenarios: initial oil place at connate water saturation condition utilized for secondary oil recovery, and water flooded cores at residual oil saturation for tertiary oil recovery. The result showed that the water invasion into the fractures reduces oil production potential, and it is shown that the ultimate recovery for secondary gas injection is considerably higher than tertiary gas-oil gravity drainage for both isothermal and non-isothermal tests. Steam injection into the fractured model leads to twice more oil recovery than the preceding isothermal recovery. The results confirmed that the key oil production mechanism during non-isothermal gas-oil gravity drainage that initiates the main phase of oil production is heat transfer into the matrix blocks and viscosity reduction. In addition, results of contact angle measurements showed that wettability of the oil wet rocks after steam flooding was shifted to neutral wet condition that increase gravity drainage performance.