Study on Temporary Plugging Diverted Acidification in Strong Heterogeneous Sandstone：A Case Study of the Silurian in Tazhong

Acidizing constitutes a pivotal enhancement strategy for the effective exploitation of low-permeability sandstone oil reservoirs. The Silurian reservoirs in the Tarim Basin, characterized by numerous thin layers and pronounced heterogeneity, present challenges in acid treatment; specifically, acid fluids preferentially enter high-permeability layers, resulting in inadequate stimulation of low-permeability strata. Current techniques for sandstone reservoir acid diversion remain insufficient. This study introduces a fully water-soluble and degradable clean temporary plugging powder, combined with chelating acid, to address the uniform acidizing challenge in heterogeneous sandstone reservoirs. The research employs a parallel core acidizing flow instrument to investigate the blocking characteristics of the clean temporary plugging powder and its acid diversion capabilities under various differential pressures. Laboratory experiments demonstrate that the degradation of this powder is predominantly temperature-controlled, with complete degradation occurring above 90 ℃, resulting in a clear, acidic solution and effectively enhancing core permeability by 20%. A 0.1% concentration of the plugging powder, when injected with chelating acid into the rock, forms an internal and external barrier layer, increasing the temporary plugging skin factor. The maximum sealing pressure differential achieved is 1.87 MPa, 6.7 times that of chelating acid alone. Parallel core acidizing experiments reveal that 100-mesh clean temporary plugging powder at a 0.1% concentration is suitable for reservoirs with a permeability gradient less than 15, effectively reducing the heterogeneity in permeability and improving the transformation of low-permeability cores. Moreover, in the acidizing operation of well 11-9 in the Tarim Basin, the temporary plugging and diversion technique showed a notable increase in pressure and a substantial enhancement in production post-acidizing. Field trials and applications confirm that the temporary plugging and diversion acidizing technique achieves commendable production enhancement and transformation in Silurian reservoirs, offering significant insights for the uniform acidizing of long sections in heterogeneous sandstone reservoirs.