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As the essential component of shale, clay minerals have a vital influence on the pore structure and the gas content of reservoirs. To investigate the compositional characteristics of coal-measure shale and its effects on pore structure, a total of thirteen Taiyuan formation shale samples were collected from the Qinshui Basin and were analyzed using a combination of X-ray diffraction analysis, X-ray fluorescence spectrometry, Fourier transform infrared spectroscopy (FE-SEM), polarized optical microscopy, and field emission scanning electron microscopy. The results show that the principal minerals of the samples are quartz, kaolinite, and illite. Most of the kaolinite was an original terrigenous detrital material with low crystallinity and a low degree of ordering, whereas the illite was mainly composed of 1Md resulting from diagenesis. Clay minerals developed slits, irregularly-shaped or multisized pores during diagenesis, which can be classed into interlayered pores, intergranular pores, and microfractures. Eight micro-morphological forms of clay minerals were summarized based on FE-SEM observations, such as compacted, parallel, bent, tilted, mutually supporting structures, etc., which are mainly formed by the mechanical compaction of clay minerals with different sizes, shapes, and contact relationships. The diversity and complexity of the micro-morphological forms of clay minerals contribute to the strong heterogeneity, low porosity and high permeability anisotropy of shale.

The Baikouquan Oilfield is entering middle and later periods of development. Casing failure, caused by the quality of cementing and casing corrosion, affects the normal production of the well. The number of wells in this situation has been increasing in recent years. Some wells with a high aquifer have no way to achieve effective plugging. The conventional measures have short validity periods and low plugging strengths. They cannot meet the requirements of subsequent fracturing operations and long-term production. Therefore, a new type of plugging agent with high strength, temperature resistance, salt resistance and micro-expansion features was designed and developed. The field test was carried out on four wells in the Baikouquan block, including three wells with a strong water-flooded layer and one well with an upper casing leakage point. A field test showed that the leakage formation was successfully plugged under the condition that the oilfield pressure test value was 30 MPa, with a 100% success rate. The average fluid volume decreases by 51.4%, and the average oil volume increases by 270.8%. The average daily oil volume per well increases by 3.2 t/d. The new plugging agent has the characteristics of no regurgitation, fast cementing speed with the new interface, high cementing strength and construction safety. The above advantages are of great significance in reducing the operation cost of oil and water well production and enhancing oil recovery.