A slim tube miscibility test is performed using the equipment set-up as shown. Typically
the test is performed within a 40 foot column pre-packed (glass beads or Ottawa
sand) ¼" OD length of coiled stainless steel tubing. Columns with different
lengths and packing materials can be used upon request. The porosity and permeability
of the column is measured at the beginning of each suite of analyses. The column
is cleaned, evacuated and weighed before commencing the test procedure.
A windowed PVT cell and camera can be added to the set-up to visually observe the
time at which gas breakthrough occurs. A high pressure densitometer can also be
added to measure the density of effluent fluid.
The column / lines are pre-charged with toluene and system heated to the requested
Reservoir fluid is injected into the column and toluene is displaced out of other
end by controlling the column end-pressure, using a backpressure regulator (BPR).
After 1.5 pore volume of fluid has been injected, gas and liquid collection apparatus
are connected prior to displacing further fluid. A further 10 ml of fluid is displaced
to collect fluid for liquid density measurement and GOR calculation. The data is
compared to the original atmospheric flash data on the reservoir fluid sample. When
the data agrees with the original measurements the test can commence.
The test gas is injected at an initial rate of 6 ml per hour and the evolved products
are continuously collected. The evolved gas volume, weight and residual liquid density
is measured every hour. The composition of the evolved products can be measured
if requested by the client. The gas injection rate continues at 6 ml per hour, for
6 hours and then it is increased to 8 ml per hour for the remainder of the test.
The exact point of gas breakthrough will be clearly observed by a significant increase
in GOR, decrease in residual liquid density and change in gas composition/gas gravity.
The test continues until 1.4 pore volume of test gas has been injected into the
coil. The remaining gas within the coil is "blown down" and the atmospheric volume
recorded. Any residual oil produced during this process is also collected and weighed.
The coil is then disconnected and weighed to determine the weight of residual oil
remaining at the end of the test.
The test is normally performed at between 4 to 6 test pressures. A plot of recovered
oil volume at 1.0 or 1.2 pore volumes versus test pressure will indicate the minimum
miscibility pressure of the reservoir fluid, for the selected injection gas composition.