Feasibility analysis on the pilot test of acid fracturing for carbonate reservoirs in Halfaya Oilfield, Iraq

The oil reservoir of Mishrif Formation is of strong heterogeneity vertically and laterally, and its single‐well production rate after conventional acidizing is low and declines fast. Therefore, we intend to carry out the pilot test on diverting acid fracturing so as to improve the stimulation effect of acid fracturing by enlarging the lateral and vertical stimulation range. In this paper, a series of experimental studies (eg, rock mechanics, acid rheology, acid‐rock reaction kinetics, and full‐diameter core etching diversion) were carried out to deal with the reservoir characteristics and stimulation demand of Mishrif Formation, the principal oil reservoir in Halfaya Oilfield in Iraq, the Middle East. It is shown that calcite content of Mishrif Formation reservoir is higher than 95%, indicating the strong acid dissolution. As for rock mechanics, the characteristics of “low Young's modulus and high Poisson's ratio” are presented, and the stress‐strain curves show certain elastic‐plastic characteristics. Additionally, a large number of wormholes appear on the surface of the full‐diameter cores after acid etching, so it is necessary to consider the serious filtration of acidizing fluid near the wellbore. The mechanical strength of rock plates decreases after acid etching, so it is recommended to adopt and optimize the closed acidizing technology so as to avoid excessive etching. Furthermore, the self‐support flow conductivity of etched fractures is weak, so it is recommended to adopt the sand fracturing or the combined stimulation technology of acid fracturing + sand fracturing to improve the reservoir stimulation effects. A series of experimental studies, for example, rock mechanics, acid rheology, acid‐rock reaction kinetics, full‐diameter core etching diversion, and analysis of three‐dimensional digital imaging technology were carried out on the cores of Mishrif Formation to analyze the stimulation feasibility of acid fracturing in this paper, which is seldom studied before for carbonate reservoirs in the Middle East.