Development and application of formation damage mitigation system for heavy oil reservoir

A compound chemical system was developed to address the formation damage in heavy oil reservoirs caused by asphaltene deposition and clay swelling. The dynamic process of asphaltene deposition was simulated through laboratory experiments and the effect of clay types and their mass fractions were investigated. The extent of formation damage from these mechanisms was quantified by measuring the reduction in permeability. Sodium dodecyl benzenesulfonate (SDBS) and n-pentanol were selected as the viscosity reducer and the additive, respectively, as their combination achieved the highest viscosity reduction rate and anti-coalescence rate. Different acids were tested based on the dissolution rates of three types of clay. The mixture of 8% HCl and 12% HBF4 was found to be the most effective. The formation damage mitigation system was formulated using SDBS, n-pentanol, HCl, and HBF4 at a mass ratio of 5:2:8:12. The sandpack experiments demonstrated a significant reduction in permeability due to the combined formation damage, followed by an effective restoration of permeability after the mitigation treatment. This compound system was successfully applied to 56 wells of the Shengli Oilfield, with over 90% of the wells achieving a significant increase in oil production rate by 35% and a notable reduction in injection pressure by 42%.