Effects of Temperature and Interfacial Tension in Different Production Mechanisms

Abstract

Abstract The objective of this paper is to study the relative importance of two complementary production mechanisms as are the displacement with water and the natural imbibition, evaluating the influence of different temperature and interfacial tension conditions in the production rate and final oil recovery of laboratory experiments. The production mechanism by spontaneous imbibition has been associated historically with the production in naturally fractured reservoirs. However, heterogeneities and channeling effect, usually present in argentine not fractured reservoirs, indicate that imbibition mechanism contributes considerably to the oil productivity. Evaluation of both mechanisms simultaneously (imbibition and displacement) by means of laboratory experiments is difficult. Therefore, displacement and imbibition experiments were accomplished separately. The displacement experiments with water were carried out at room temperature and at 60°C, while imbibition experiments were accomplished at 60 and 80°C. Both studies were made firstly with water and then with water and surfactant, reaching low interfacial tension conditions. The experiments were designed to reproduce reservoir conditions as faithfully as possible, since the phenomena involved are highly dependent of the molecular composition of both fluids and rock. Due to this water, oil and rock of the same formation were used. The rock used for this study presents strong water wettability. The displacement experiments with surfactant were accomplished using two different methodologies:beginning the injection of surfactant from the start of the displacement,beginning the injection of surfactant after the injection of one poral volume (PV) of water. This second procedure was employed since generally, the projects of EOR are subsequent to projects of water injection. It was observed that the final oil recovery increases with the aggregate of surfactant, independently of the injection starting time. The conclusions of this study can be summarized as follows. The phenomenon of spontaneous imbibition turned out to be an important production mechanism in waterwet rocks. The use of surfactants and the increase of temperature favor the effect of the imbibition mechanism. The efficiency of the displacement mechanism also improves with the decrease of interfacial tension and the increase of temperature. A new method to characterize the degree of heterogeneity of the sample as well as the contribution of the imbibition mechanism is presented. The method is based in a cualitative analysis of Oil Recovery vs. Poral Volume (PV) experimental curves. Finally, a new method to measure the imbibition diffussivity constant to describe the imbibition as a dispersive diffussion process is developed and applied to experimental data, giving a simplified alternative to the modeling of the imbibition process. Introduction The most studied oil production mechanism is displacement, in which oil is displaced from the porous medium through the action of an external work establishing a pressure gradient. In this mechanism viscous and capillary forces are involved, but the role of the capillary forces is not thoroughly established in the current theories. The imbibition mechanism is generally studied in the bibliography related to the productivity of naturally fractured reservoirs. This mechanism, which is characterized by the spontaneous production of oil from rocks exposed to water saturation gradients, does not require an external work and always exists in waterwet rocks.