Application of In-Depth Gel Placement for Water and Carbon Dioxide Conformance Control in Carbonate Porous Media

摘要

This paper presents the results of an investigation on the application of gel placement in an attempt to reduce the permeability of a carbonate porous medium to water and supercritical carbon dioxide, as encountered in the CO_2 flooding of carbonate reservoirs. A 7500 ppm high molecular weight polyacrylamide polymer with 300 ppm chromium (III), as crosslinker, was used for this study. Since sodium lactate is commonly used for increasing gelation time at elevated temperatures, additional experiments were conducted by adding sodium lactate to the gel solution with a ratio of polymer to sodium lactate equal to one. The other gel system tested was composed of 5 percent low molecular weight polyacrylamide with a ratio of 1:12 chromium to polymer. Experiments were conducted at 1200 psi and 40 deg C, with and without the presence of residual oil in order to investigate any role the residual oil might play in the performance of gel. Performance and stability of above gel systems for reducing the permeability of the carbonate medium to the injected water and carbon dioxide was tested in a series of flow experiments by alternatively injecting several pore volumes of water and carbon dioxide into the porous media in several cycles. The porous medium used was crushed carbonate with initial permeability of over 10 Drcies. For all experiments the presence of S_(or) led to lower residual resistance factors (RRF). Nevertheless, RRFs were between 100 and few thousands for all experiments conducted. The results obtained are clear indication of the effectiveness of these gel systems for conformance control purposes during carbon dioxide flooding projects in carbonate reservoirs.