Abstract

Fine migration is considered to be the primary factor leading to the production decline of the unconsolidated sandstone formations. Micro-fracturing technology is regarded as a practical approach to solving these problems for improving the permeability near the wellbore. However, no detailed and comprehensive research has investigated the blockage-removing mechanism upon microfracturing. Therefore, a comprehensive simulation method is proposed in this study, capable of simulating the permeability evolution and the mechanical responses of the unconsolidated sandstone during the micro-fracturing. Afterward, the blockage-removing mechanism of micro-fracturing and the associated mechanical deformation are analyzed in a field case. Furthermore, the simulation results were classified using digital method and made into a predictive chart. The results show that the permeability damage caused by a blockage in an unconsolidated sandstone can be treated by micro-fracturing. The underlying mechanisms can be summarized in three aspects. First, the hydraulic effect can mitigate the permeability damage caused by particle deposition. Secondly, the increase in pore throat radius due to pore dilation can disrupt the structure of the particle bridging. Third, the blockage caused by size exclusion is diminished due to an increase in the effective pore radius. These results elucidated the mechanism of blockage removal by microfracturing and provided valuable guidance for field engineers to improve the subsequent stimulation work.

Introduction

In recent years, more and more oil and gas resources are found in unconsolidated sands or weakly consolidated sandstones, such as the Gulf of Mexico, Athabasca (Canada), Orinoco (Venezuela), and Bohai Bay Basin of China (Xiong et al., 2018; Wang et al., 2021). These resources include conventional oil and gas reservoirs and unconventional reservoirs such as oil sands. The loss of permeability caused by fines migration in the reservoir is always considered a significant factor responsible for productivity decline. Due to unconsolidated cementation, fines migration almost occurs during the whole process of oil and gas reservoir development, such as drilling, fracturing, water injection, or liquid production. Due to the high fluid velocity near-wellbore, it is essential to note that fines migration and blocking always occur near the wellbore. Various approaches have been proposed to alleviate the adverse effects of fines migration on reservoir permeability, including nanofluid clay stabilizers, and polymers. (Huang et al., 2008; Yuan et al., 2016; Zhang et al., 2015). However, these methods are not only costly and effective for a short period, but are mainly preventive in focus.

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