ABSTRACT:

Acid fracturing, a conventional and effective stimulation method, has been widely used in sandstone reservoirs. Due to serious acid leakage and rapid acid-rock reaction rate resulting from high temperature and high closure stress in deep sandstone, the conventional acid may acquire the limited length of effective acid etched fracture and the low acid fracture conductivity. Therefore, a novel chelating acid fracturing with slow reaction rate and no precipitation, was proposed to improve the stimulation performance. However, the conductivity of chelating acid fracturing has been rarely studied. Aiming at this problem, this paper conducted a research on the acid-etched fracture conductivity by acid fracturing conductivity evaluation system. First, conventional mud acid and chelating acids with different acid-rock contact times were tested to analyze the effects of acid type and acid-rock contact time on the conductivity. Next, the effect of acid injection rate on the conductivity was also investigated. Finally, long-term conductivity was measured up to 168 hours to analyze the impact of fracture creep on conductivity. The results show that the conductivity of chelating acid fracturing in ultra-deep sandstone is about 10 percent higher than that of conventional acid. First, the conductivity of sandstone is the highest when acid-rock contact time is about 4h. Then when the injection rate is 15ml/min with the total injection amount 3.6L unchanged, the conductivity is highest. At last, after the long-term test, there’re only 20% decline on the conductivity of chelating acid comparing to 50% decline of conventional acid. The research on chelating acid fracturing conductivity can provide effective guidance for field application.

1. INTRODUCTION

At the later stage of oilfield development, effective exploitation of low permeability sandstone reservoir becomes more and more important. In the petroleum industry, for reservoir with low permeability and reservoir with medium and high permeability that were polluted near wellbore, in order to achieve certain production targets, it is necessary to carry out reservoir reconstruction technology such as acid fracturing.

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