Abstract
Recoverable oil reserves remain trapped in fractured reservoirs of dual porosity with very low permeability rock matrix blocks, 0.10 md or less, and a fracture system. Conventional secondarty methods cannot be applied to this type of reservoirs because injected fluids channel though the fractures bypassing oil trapped in the matrix blocks. Spontaneous water imbibition is an spontaneous mechanism that could be applied. The process exchanges oil inside the rock matrix for surrounding water filling the fractures. However, the process is very time dependent. Oil distribution inside carbonated rock samples, and the effects of introducing CO2 into the water being imbibed were studied using Magnetic Resonance Imaging or MRI. Oil saturation profiles and longitudinal images along the sample were used to monitor water imbibition. A high pressure core holder suitable for MRI and CT applications was developed using commercial fiber glass tubing. Development of the new tool permitted imbibition of unadulterated and carbonated water to be studied at a reservoir pressure of 2000 psi. Different cases were studies: (1) Imbibition of unadulterated water, (2) Imbibition of CO2 - enriched water, and (3) Cyclic CO2 - enriched water imbibition and pressure depletion. Introduction of CO2 into the water being imbibed showed improvements in oil recovery rates during early times of the process. Pressure depletion caused expansion of gas dissolved into the imbibed water. This mechanism probed to cause a substantial oil increase. Oil recovery by CO2 - enriched water imbibition and pressure depletion were combined to develop a cyclic method that integrated the beneficial effects encountered at early times and gas expansion caused by pressure depletion. The cyclic method reduced recovery time to nearly one third of the time needed to produce similar amounts of oil by pure water imbibition.
Pe�rez Cardoza, Jorge Mario (1991). MRI study of imbibition flooding using carbonated water. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1250374.