Summary The Fuyu oil field is a typical shallow, low-temperature, low-permeability reservoir. At present, the oilfield composite water cut is 95%, artificial fractures interlace with natural fractures, and the distribution of ineffective circulation channels between wells is complex. This paper found that after reducing the permeability of the original fracture, refracturing can effectively improve the longitudinal extension range of the new fracture through numerical simulation. Therefore, a controllable permeability temporary plugging agent is studied, and controllable permeability refracture technology is proposed. The controllable permeability temporary plugging system is composed of elastic particles, quartz sand, and quick-soluble elastic enhancers, which are based on elastic particles that do not age, and long-term plugging can be achieved. Through physical experiments, 0.5–1-mm elastic particles with 70–140 mesh and 16–30 mesh quartz sand were used in different ratios (i.e., 5:5, 6:4, and 7:3). According to the closure pressure and the permeability of the fracturing layer, the ratio chart of elastic particles and quartz sand is established. The controllable permeability refracture technology can select the ratio of the quartz sand and elastic particles according to the closure pressure and the control requirements of the fracturing horizon permeability. Through field applications, we found that, compared with the conventional refracturing technology, the average daily fluid gain per well decreased from 5.0 to 3.9 tons, and the daily oil gain increased from 0.3 to 0.6 tons. The controllable permeability fracturing technology could reduce the permeability of the original fracture and improve the vertical production degree of the reservoir after refracturing. In addition, this method ensures that the original fracture has a certain conductivity and that the high-permeability layer reserves are not lost due to temporary plugging agents, thus expanding the planar sweep volume and effectively improving reservoir recovery. Nevertheless, the chart established is mainly suitable for shallow reservoirs, and the closure pressure is 3–15 MPa in this paper. Further testing and research are needed for deep reservoirs.

Nanoparticles are added to clean fracturing fluids to formulate nanoparticle-modified clean fracturing fluids, compared with ordinary clean fracturing fluid, it has the advantages of good temperature resistance, low loss of filtration, and so forth, and has good application prospects in coal-bed methane. However, the current research on nanoparticle-modified clean fracturing fluids is mostly focused on the study of their rheological properties. The mechanism of nano-fracking fluid influence on methane adsorption−desorption characteristics is not clear. Therefore, this study chooses Jiulishan anthracite coal (high-rank coal), Pingdingshan coal (medium-rank coal), and Geng village mine long bituminous coal (low-rank coal) of the three rank coal samples. Using indoor experiments and molecular simulation methods, a study on the influence of methane adsorption and desorption capacity and diffusion ability of coal samples provides a modified fracturing fluid formulation of 0.8% CATB + 0.2% NaSal + 1% KCl + SiO 2 . The experimental results show that nanofracturing fluid-treated coal samples compared to clean fracturing fluid treated coal samples, both methane adsorption and desorption capacities, were increased to some extent. Construction of methane adsorption systems with different apertures and calculation of isosteric heat of adsorption, indicating that the interaction force between methane and coal molecules is smaller after nanofracturing fluid treatment, which facilitated methane desorption. A simulation study of methane diffusion in coal samples treated with two systems of fracturing fluids at different aperture was carried out using molecular dynamics methods, indicating that nanoparticle-modified clean fracturing fluids can reduce the damage of clean fracturing fluids to the desorption−diffusion ability of coal reservoirs. Comparison of 6 MPa as the most suitable pressure for nanofracturing fluids to function provides a basis for the future development of nanofracturing fluids and their popularization.