Estudo do efeito da saturação de óleo na acidificação de carbonatos

Abstract

Carbonate acidizing is a well stimulation technique used to increase oil production. This technique aims to inject acid into the formation below the fracture pressure, creating paths of high conductivity resulting from the dissolution of the rock by the acid. In the laboratory, most experiments are performed on rock samples saturated with water, due to the assumption that there is only water in the formation, after preflush and previous drilling and completion operations. However, different saturation conditions can occur in the formation due to its petrophysical characteristics and history of operations. One scenario is oil saturation in the porous medium. This work proposes to carry out physical experiments and evaluate the influence of oil saturation on the acidizing of carbonates. Reactive flow experiments were carried out using acid systems, with HCl 0.5M and HCl 15%, in rocks saturated with ultra pure water and liquid paraffin. The carbonate rock samples are from the Indiana Limestone outcrop with 3 in length and 1.5 in diameter. For oil saturation, a high flow rate of 20 mL/min was used for the two acid systems at room temperature (25°C); and with HCl 15%, the study was deepened with a temperature of 45°C at flow rates of 1 and 20 mL/min. The x-ray microtomography technique was used to image the samples to visualize the wormhole morphology. Through it, the influence of oil on the structure of the wormhole and the value of PVBt was compared, highlighting the impact of oil for each acid concentration. The PVBt curve of HCl 0.5M has values above those presented using HCl 15%, in samples saturated with water. This effect is due to the lower concentration promoting a lower dissolution power of carbonates. The analysis of the wormhole area and the porosity distribution after acidizing show that the oil influenced an efficient propagation of the wormhole and lower consumption of acid. PVBt values are lower when the sample is saturated with oil in all scenarios. The use of HCl 15% in the sample saturated with oil and at a temperature of 45°C. In this scenario, the value reduces by about 54% when using HCl 15% at 20 mL/min.