Performance evaluation and application study of a degradable temporary plugging agent (TPA) for coal seam hydraulic fracturing

Abstract

Hydraulic fracturing has been widely used in the roof disaster management, dust control and gas control in coal mines. However, due to the influences of primary pores/fractures, significant fluid losses can occur during the fracturing, which makes it difficult to achieve desired injection pressures, and thus results in poor hydraulic fracturing effects. To solve this problem, we developed a new degradable temporary plugging agent (TPA) with a density close to that of water and good stability for hydraulic fracturing. The TPA was characterized through suspension stability testing, compression performance analysis, degradation assessment, and Fourier transform infrared (FTIR) spectroscopy. Plugging performance experiments were carried out at different fracture openings to analyze the plugging ability of the TPA. Its applicability to the practical field hydraulic fracturing was examined on the 3407 working face of Shaanxi Zhengtong Coal Industry, China. The results show that the density of the TPA is 0.92 g/cm³, close to that of water, and it can stably float in water for a long period of time. Its breakage rate shows an exponential function with pressure and is only 28.56 % under 30 MPa. The TPA undergoes spontaneous degradation under acidic or weakly alkaline conditions. The application of the TPA in the field experiment significantly increased the injection pressure and inhibited fluid loss, and caused secondary fracturing, suggesting that it could effectively plug the primary pores/fractures and improve the coal seam hydraulic fracturing effect. The TPA's superior characteristics demonstrate significant fracture-plugging potential for coalbed hydraulic fracturing applications.