Imbibition Law of Shale Oil Reservoirs in the Lucaogou Formation in Jimsar Sag

摘要/Abstract

摘要： Shale oil reservoirs with middle-low porosity and low-ultra-low permeability are present in the Lucaogou formation in Jimsar sag, and the reservoirs are also the source rocks. These oil reservoirs have been developed with dense horizontal wells and high-strength volume fracturing stimulation. In the case of a long-term well shut-in after fracturing, the flowback rate of fracturing fluid is low, but the oil production is high. In comparison, in the case of a short-term well shut-in, the flowback rate of fracturing fluid is high, but the oil production is low. In order to understand the law of fracturing fluid imbibition displacement in the soaking period after fracturing, the reservoir wettability was evaluated using contact angle, and the spontaneous imbibition experiment was carried out using real downhole cores and NMR. The results show that the wettabilities of the upper sweet spot interval and the lower sweet spot interval in the Lucaogou formation in Jimsar sag are quite different, which are closely related to the imbibition displacement capacities. The upper sweet spot interval is hydrophilic, where small pores are dominant during the imbibition process. Initial imbibition is a rapid process and reaches equilibrium after about 160 h, and the average imbibition recovery is 31%. The lower sweet spot interval is lipophilic, where large pores are dominant during the imbibition process. The imbibition rate is slow and reaches equilibrium after about 400 h, and the average imbibition recovery is 22%. It is proposed to appropriately extend soaking time for the upper sweet spot interval, and choose fracturing fluid with surfactants for the lower sweet spot interval, so as to give full play to imbibition displacement to improve the recovery of the shale oil reservoirs.

关键词: Jimsar sag, Lucaogou formation, shale oil, wettability, imbibition displacement, imbibition efficiency, imbibition rate

Abstract: Shale oil reservoirs with middle-low porosity and low-ultra-low permeability are present in the Lucaogou formation in Jimsar sag, and the reservoirs are also the source rocks. These oil reservoirs have been developed with dense horizontal wells and high-strength volume fracturing stimulation. In the case of a long-term well shut-in after fracturing, the flowback rate of fracturing fluid is low, but the oil production is high. In comparison, in the case of a short-term well shut-in, the flowback rate of fracturing fluid is high, but the oil production is low. In order to understand the law of fracturing fluid imbibition displacement in the soaking period after fracturing, the reservoir wettability was evaluated using contact angle, and the spontaneous imbibition experiment was carried out using real downhole cores and NMR. The results show that the wettabilities of the upper sweet spot interval and the lower sweet spot interval in the Lucaogou formation in Jimsar sag are quite different, which are closely related to the imbibition displacement capacities. The upper sweet spot interval is hydrophilic, where small pores are dominant during the imbibition process. Initial imbibition is a rapid process and reaches equilibrium after about 160 h, and the average imbibition recovery is 31%. The lower sweet spot interval is lipophilic, where large pores are dominant during the imbibition process. The imbibition rate is slow and reaches equilibrium after about 400 h, and the average imbibition recovery is 22%. It is proposed to appropriately extend soaking time for the upper sweet spot interval, and choose fracturing fluid with surfactants for the lower sweet spot interval, so as to give full play to imbibition displacement to improve the recovery of the shale oil reservoirs.

Key words: Jimsar sag, Lucaogou formation, shale oil, wettability, imbibition displacement, imbibition efficiency, imbibition rate

MA Mingwei, ZHU Jian, LI Jiacheng, LIAO Kai, WANG Junchao, WANG Fei. Imbibition Law of Shale Oil Reservoirs in the Lucaogou Formation in Jimsar Sag[J]. 新疆石油地质, 2021, 42(zk(English)): 116-122.

MA Mingwei, ZHU Jian, LI Jiacheng, LIAO Kai, WANG Junchao, WANG Fei. Imbibition Law of Shale Oil Reservoirs in the Lucaogou Formation in Jimsar Sag[J]. Xinjiang Petroleum Geology, 2021, 42(zk(English)): 116-122.

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