Relative Permeability-Dictated Huff-n-Puff Technique in Tight Reservoirs: Suitability and Limitation toward Field Implementation

Abstract

Exploiting unconventional petroleum is needed in this era, and thus more enhancement has been introduced including chemical additives to manipulate the fluid flow characteristics. Although most of the examinations were at the laboratory scale, the scaling-up to reservoir applicability is in question and needs further studies. The current study examined laboratory-derived relative permeability (k r ) at various wettabilities and the oil−water interfacial tension on reservoir-scale numerical simulation, utilizing a huff-n-puff technique, aiming to emphasize suitability and limitations of k r . The simulated results emphasized the important character of k r , which dictates the oil recovery in tight reservoirs where the huff-n-puff technique is normally implemented. Although derived from laboratory tests, such a k r character has to be taken caution when considering EOR design in field deployment at the reservoir scale since there are suitability and limitations to be concerned for each k r character as well as the economic aspect. Not all reservoir parameters or producing factors could practically induce substantial changes in oil production; hence, further techno-economic study should be executed prior to implementation toward field implementation of tight reservoirs. Simulations of primary oil production agreed with those of the experiment, confirming the model validity. Following the secondary six-cycle huff-n-puff process also yielded the same trend of oil production performances, dictated by k r as a primary fluid flow characteristic. Four influencing factors of reservoir properties and producing design were further investigated for their sensitivity to the oil production performances. At various k r investigated in the current study, the porosity factor was distinctively found to have limited suitability to low values if high oil production is anticipated, owing to the nature of tight reservoirs pe se. On the contrary, reservoir permeability likely did not have much influence since more oil was produced with higher value of permeability, albeit no sensitivity at much higher values. The shut-in period for the huff-n-puff process was not sensitive to the oil production of all fluids. Interestingly, the critical water saturation where the water phase starts to flow (k rw > 0) had a strong influence on the oil production in two approaches, either demoting the oil production or having no contribution, depending on the k rw −S w character. Although derived from laboratory tests, such a k r character has to be taken caution when considering enhanced oil recovery design in reservoir-scale deployment since there are suitability and limitations to be concerned for each k r character.