Establishing a homogeneous and stable sand pack to study parameters during spontaneous imbibition
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Spontaneous imbibition is an important process for oil production during water flooding in porous media and has been widely studied for decades to understand the physics of the process for different boundary conditions. This thesis study spontaneous imbibition in unconsolidated sands, where experimental protocols have been improved to mitigate challenges associated with displacement processes in such systems. An initial focus was to establish uniform and stable sand packs that enable tests to be repeated without changes in permeability and porosity due to poor packing or loss of sand. Homogeneous sand packs allow for reproducible tests to compare the influence of initial water saturation on spontaneous imbibition. Sand packs were also used in spontaneous imbibition tests with different wetting fluid viscosity, where brine viscosity was increased by adding glycerol or an HPAM polymer powder. This enabled a systematic investigation of wettability alteration by polymer solutions in unconsolidated sands. A new sand packing method in glass tubes was developed where the sand was compressed by pressure to achieve a narrow pore size distribution. End pieces that enabled flow in and out of the sand packs were redesigned to eliminate the need for threaded glass tubes, leading to less leakage and glass tube shattering. The presence of an initial water saturation reduced recovery efficiency and production rate during spontaneous imbibition conducted in sand packs: average recovery factor without initial water (RF=79%OOIP) was 40% higher than with initial water (RF=56%OOIP). Spontaneous imbibition with HPAM polymer added to the brine yielded 3% higher recovery than spontaneous imbibition with a glycerol solution. This contradicts earlier findings where a 5% higher recovery was observed with glycerol compared to HPAM polymer. Unlike earlier studies, the polymer solution used in this thesis was filtered to remove microgels and other multimolecular structures. By filtering the solution, retention in the filter was prevented, and the polymer solution could imbibe freely. In addition, measurements of the Amott-Harvey wettability index (I_AH) indicated that the HPAM polymer altered the wettability of the sand. Average I_AH for sand packs where HPAM polymer had been present was 0.92, whereas, for sand packs where it had not been present, the value was 0.97.