ABSTRACT: Acid propped fracturing is a valid stimulation technique applied in deep carbonate reservoirs and its effect mainly depends on the conductivity. However, short-term conductivity experimental data used in existing acid propped fracturing design may not be directly applicable to real case. Aiming at this problem, this paper investigates impacts of acid-rock contact time, acid etched fracture creep, proppant size and concentration on the long-term conductivity. The study shows that the acid propped fracture retained enough conductivity under high closure stress. Gelled acid fracture conductivity increases with the longer time until it reached the upper limit when the contact time is 60 minutes. The long-term conductivity experiments show that conductivity decreased sharply in the 48 hours and underwent a gradual decline from 48 hours to 96 hours followed by the steady state after 120 hours. The ideal combination of proppant size and concentration are optimized at different stress level. An acid propped fracture conductivity correlation was also developed for calculating the conductivity. This study provides an insight of optimizing acid propped fracturing design and predicting well performance.
1. INTRODUCTION
As significant domains of oil and gas exploration and development, carbonate reservoirs constitute almost 60% of the world's remaining oil and gas. Acid fracturing, as a conventional and effective stimulation method, has been widely used in carbonate formation (Amirhossein and Maysam, 2016). However, due to serious acid leakage and rapid acid-rock reaction speed resulting from high temperature and closure stress in deep well, the length of effective acid etched fracture is limited and the effective duration of acid etched fracture is short (Li Y et al., 2009; Suleimenova A et al., 2016;). Consequently, uniting the deep penetration of acidizing with proppant fracturing is a natural progression toward great effective stimulation of deep carbonate reservoirs. Acid propped fracturing, combining the advantages of propped fracturing and acid fracturing, is the technology that can not only readily carry proppant but also react with the carbonate formation to eliminate the formation damage. It also can connect natural fracture, maximizing the drainage area and the stimulation reservoir volume (SRV).
