高温高压条件下泥页岩润湿性表征实验研究

Wettability is one of the key factors for the sealing capacity of shale and internal fluid displacement efficiency. However, the wettability of shale under high temperature and high pressure and its change rule with temperature and pressure are still not clear. In this paper, it would take the wettability of shale with different mineral composition, pore size distribution and content of organic petrology properties from Qikou Sag as object of study. Captive drop system which could achieve high temperature and high pressure conditions would be used to measure the contact angles under different pressure and temperature by several groups according to the maximum pressure (70MPa) and temperature (200℃) for each test sample, and coupling characterization of shale wettability and temperature/pressure would be quantitative depicted. In addition, based on determining the nature of the live oil and synthetic formation water, Yang-Laplasse formula would be used to establish quantitive models of the oil-water interfacial tension and contact angle for predicting the capillary force of shale. Through the study of this project, it would be expected to reveal the wettability variation of shales which have different rock compositions and properties in the effect of high temperature and pressure, so then the results could lay the theoretical and experiment foundation for perfecting the mechanism of shale oil and gas preservation and improving the efficiency of the development of shale oil and gas resources.

润湿性是泥页岩封闭能力及内部流体驱替效率的关键因素之一，但是高温高压条件下泥页岩润湿性及其随温压变化规律仍不清晰。本项目以歧口凹陷内具有不同矿物成分、孔径分布和有机质含量等特征泥页岩的润湿性为研究对象，采用高温高压悬滴法润湿角测试仪器，在不同的压力（1~70MPa）和温度（20~200℃）条件下测试样品的润湿角，定量刻画泥页岩样品润湿性与温度和压力耦合特征。此外，在确定原油和地层水性质的基础上，根据杨-拉普拉斯公式构建油-水的界面张力和接触角的定量模型，预测毛细管力大小。通过本项目的研究，旨在揭示高温高压条件下不同岩石成分和物性泥页岩的润湿性变化规律，为完善泥页岩的油气保存机理，提高泥页岩油气资源开发效率奠定理论和实验基础。

本项目通过渤海湾盆地内歧口凹陷和松辽盆地重点层系泥岩样品的不同条件下润湿性实验表征，明确不同岩性和微观特征的泥页岩在高温高压条件下润湿性变化规律，补充完善地层条件下泥页岩润湿性理论。此外，利用实验数据和油田实际地下条件，结合前人研究成果，设计了泥页岩模型，利用分子动力学模拟手段研究了纳米级缝隙内油气运移与吸附特征，推动了油气在泥页岩内赋存和运移理论。研究表明，泥页岩中矿物润湿性多为水湿，有机质的润湿性为完全油湿，黏土矿物对水和油都有较强的吸附能力；地层温度和压力对矿物的润湿性有一定影响，其中温度条件对矿物润湿性影响较大；地层压力对矿物的润湿性影响较小；高矿化度的水可以使石英矿物表面油湿性增强。通过分子动力学方法模拟“油-水-矿物”微观润湿性发现，温度升高，泥页岩狭缝对烃类除了正构烷烃和支链烷烃外的吸附性都有所降低；地层压力对烃类的吸附影响较小，温度升高使得烃类在泥页岩中的吸附量减小；在一定孔径大小范围内，随着狭缝孔径的增加，烃类的吸附态密度和吸附厚度都有所增加，狭缝直径达到一定值时，狭缝内的烃类吸附密度和吸附厚度都不在变化；随着正构烷烃碳数的增大，其在狭缝内的吸附密度和吸附厚度增大。