Oil Reservoir Sensitivities to Various Exposures

The properties of Hongnan 2 block T₁ oil reservoir in Xinjiang oilfield were analyzed in terms of petrological characteristics, rock granularity, clay composition, and other aspects. Experiments based on these results studied the sensitivities of the reservoir to velocity, acidity, alkalinity, stress, and water. The results showed moderate velocity sensitivity damage with an index in the range 42-56% and a critical flow velocity in the range 0.25-0.30 mL/min. Moderate and strong water sensitivities with indices varying from 52 to 65% and critical salinities from 5,000 to 10,000 mg/L were found. Water injected into a well should have salinity ≥ 10,000 mg/L to avoid water sensitivity damage. Weak sensitivity to alkalinity with an index varying from 31 to 36% with a critical pH of 8 was observed. Moderate and strong sensitivity to acidity was found for HCl fluid (15%); extremely strong, HCl (12%) + HF (3%); extremely strong, HCl (10%) + HF (3%) + HBF₄ (8%); and no sensitivity, HCl (10%) + HBF₄ (8%). The reservoir could be acidified by using HCl (10%) + HBF₄ (8%). Significant changes in the reservoir core structure were not observed with large pressure differences. The critical pressure varied from 2 to 3.5 MPa. The permeability damage rate ranged from 13.33 to 18.68%. The stress sensitivity was weak.