Investigation of Water-Sensitivity Damage for TightLow-Permeability Sandstone Reservoirs

摘要

Tight sandstone reservoir has been characterized by low permeability and porosity, developed micro-nanopore throats, strong capillary forces, and high content of clay minerals. It is vulnerable to damage caused by water sensitivity during the processes of reservoir development, which significantly impedes the hydrocarbon production. Hence, it is important to analyze the damage mechanism of water sensitivity to avoid the production decrease. However, the conventional steady-state method is time-consuming and inaccurate for evaluating the water-sensitivity damage in tight low-permeability reservoirs. Aiming at this problem, this paper introduced pressure transmission test (PTT), a time-saving and accurate method, to quantitatively evaluate the degree of damage by water sensitivity. Moreover, lithofacies analysis methods, consisting of computed tomography (CT) scanning, scanning electron microscopy (SEM), and X-ray diffraction (XRD), are also used to evaluate the reservoir properties, which can provide a basis for analyzing the potential damage factors. The CT scanning results show that the developedmicropore throat in the target reservoirs has poor connectivity. TheXRD results indicate that the target reservoir mainly consists ofa mixed-layer illite/smectite and smectite, which is consistent withthe observation by SEM experiments. The results of PTT show that theultimate average damage rate of water sensitivity is approximately62.94%, attributed to the medium-strong water sensitivity. Comparedwith the conventional steady-state method measuring the outlet flowof the core, this method can reduce the experimental errors merelyby recording the pressure data varying with time. Moreover, it isalso applicable for evaluating other types of formation sensitivitydamage, such as alkali and acid sensitivity damage for low-permeabilityreservoirs.