Characterization of Next-Generation Heavy Oil of Tar Mats in Carbonate Reservoirs and Understanding its Role in Reserve Estimation and Oil Recovery Economics

The study presented here examined a Kuwaiti reservoir that is classified as a next-generation extreme heavy oil tar-mat reservoir. Successful pyrolysis experiments were performed on carbonate rock containing 33.51% total organic content (TOC). Comparable toluene solvent, water extraction, and surfactant solution extraction had successful but different hydrocarbon recovery yields under different temperature settings. The tar-mat flow was extremely viscous, with a measured °API density close to 1.34 and calculated flow mobility close to zero. Depending on the type of extracting agent applied, increasing the temperature cracked the extreme heavy oil tar-mat available in the carbonate rock, hence improving the extremely viscous nature of the solid residue and causing it to be mobile so that it could flow and be recovered. Four carbon-density flow regimes were identified in this extreme heavy oil tar-mat composition mix, including the free hydrocarbon type I composition (C1-C15), the light hydrocarbon type II composition (C15-C40), the heavy hydrocarbon type III composition (\u3eC40), and the insoluble carbon-residue type IV material (NSO). Each flow regime exhibited a unique recovery potential within the extremely viscous composition mix. A detailed characterization of this tar-mat sample confirmed that the release of trapped type I, type II, and type III compositions from the carbonate pore space was possible, while type IV residue remained resistant to flow, and hydrocarbon retention on the rock was difficult to overcome with the suggested recovery treatments