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

doi:10.7657/XJPG20210608

Abstract

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 and replacement during 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 and 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 and displacement to improve the recovery of the shale oil reservoirs.

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

CLC Number:

TE122.23

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(6): 702-708.

Figures/Tables 7

Table 1

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岩心样品编号	岩心直径/ cm	岩心长度/ cm	层位	岩性	孔隙度/ %	渗透率/ mD	含油性
1号 2号 3号	2.5	3.3	P₂l2-32	灰色白云质粉砂岩	9.8	0.016 5	油迹
	2.5	3.3	P₂l2-22	深灰色泥岩	6.4	0.002 9	荧光
	2.5	3.3	P₂l2-12	灰黑色泥岩	7.3	0.008 2	荧光
4号 5号 6号	2.6	3.1	P₂l2-31	灰色泥质粉砂岩	13.0	0.008 4	油侵
	2.6	3.2	P₂l2-21	深灰色石灰质泥岩	15.0	0.037 8	油斑
	2.6	3.1	P₂l2-31	灰色泥质粉砂岩	13.0	0.009 6	油侵