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天然气水合物储层颗粒级尺度微观出砂数值模拟
董长银1,闫切海1,李彦龙2,徐鸿志3,周玉刚1,尚校森1,陈强2,宋洋1
(1.非常规油气开发教育部重点实验室(中国石油大学(华东)),山东青岛 266580;2.中国地质调查局青岛海洋地质研究所,山东青岛266071;3.中国石油集团工程技术研究有限公司,天津 345000)
摘要:
构建颗粒级尺度的天然气水合物储层地层砂颗粒结构模型,在此基础上进行天然气水合物储层颗粒级尺度微观出砂过程和形态模拟,研究出砂机制和出砂形态及其影响因素。颗粒结构模型根据地层砂粒度分布曲线随机确定颗粒直径、圆球度系数及位置倾角,根据测井曲线利用随机方法表征颗粒胶结强度和水合物饱和度的随机非均质性分布和粒间应力。使用水合物强度比例系数和影响系数表征水合物分解对胶结强度的影响。根据构建的颗粒剥落判别模型,结合水合物分解模型,建立颗粒剥落孔道延伸扩展模拟及出砂形态模拟方法。结果表明:对于胶结强度较低的高水合物饱和度储层,出砂首先从孔壁边界上开始,沿胶结弱面不均匀扩展形成类蚯蚓洞形态,最终总体呈现前端类蚯蚓洞与后端连续垮塌的复合出砂形态;水合物分解会大幅度降低储层强度,生产过程中出砂前沿与分解前沿非常接近;随着初期生产延续,最大剥落出砂粒径由16 μm降低为6 μm,剥落出砂速度呈上升趋势;水合物饱和度及其分解对出砂形态和出砂速度有明显影响;水合物饱和度越低,其分解对储层总体内聚强度的影响越小,越不容易出砂;饱和度为0.4、0.3和0.18时的砂粒剥落速度分别约降低到 平均水合物饱和度0.48对应的砂粒剥落速度的80%、69%和58%。
关键词:  天然气水合物  出砂模拟  出砂预测  颗粒级尺度  出砂形态
DOI:10.3969/j.issn.1673-5005.2019.06.009
分类号::TE 257
文献标识码:A
基金项目:国家自然科学基金项目 (51774307);国家重点研发计划 (2017YFC0307304);国家海洋地质调查二级项目(DD20190231);中国石油重大专项(ZD2019-184)
Numerical simulation of sand production based on a grain scale microcosmic model for natural gas hydrate reservoir
DONG Changyin1, YAN Qiehai1, LI Yanlong2, XU Hongzhi3, ZHOU Yugang1, SHANG Xiaosen1, CHEN Qiang2, SONG Yang1
(1.Key Laboratory of Unconventional Oil & Gas Development(China University of Petroleum (East China)), Ministry of Education, Qingdao 266580, China;2.Qingdao Institute of Marine Geology, China Geological Survey, Qingdao 266071,China;3.CNPC Engineering Technology Research Company Limited, Tianjin 345000, China)
Abstract:
A sand particle structure model was built in terms of grain size scales for natural gas hydrate reservoir, and the microcosmic sand production process and morphology of gas hydrate reservoir were simulated, in which the sand production mechanism, sand production morphology and the influencing factors were studied. In the particle structure model, the particle diameter, sphericity coefficient and position inclination angle were randomly determined according to the particle size distribution of the hydrate formation sands. Particle cementation strength, hydrate saturation, inter-grain stress and their random heterogeneous distribution were characterized according to the well logging curve using a stochastic method. A hydrate strength ratio coefficient and its influence coefficient were used to characterize the effect of hydrate decomposition on the bonding strength of sands. Based on the constructed particle exfoliation discriminant model, and combined with a hydrate decomposition model. Numerical simulations of particle exfoliation channel expansion and sand production morphology were conducted. The results show that, for reservoirs with high hydrate saturation and low cementation strength, sand production can start from the boundary of the pore wall, then it can expand unevenly along the weak cementation surface to form a wormhole like path, and finally it can form a composite sand production morphology, in which the front end looks like a wormhole and the back end will continuously collapses. The decomposition of hydrate can greatly reduce the strength of the reservoir, and the sand production front and the decomposition front become very close during the production process. With the continuation of initial production, the maximum exfoliated sand particle size can be reduced from 16 μm to 6 μm, and the speed of exfoliated sand production showed an upward trend. Hydrate saturation and its decomposition have a significant impact on the size distribution of the sands produced and sand production rate. The lower the hydrate saturation is, the less impact of its decomposition has on the overall cohesion of the reservoir, and the less possible for sand out. Compared with an average hydrate saturation of 0.48, for hydrate saturation of 0.4,0.3 and 0.18, the exfoliation rate of sand particles can be decreased to about 80%, 69% and 58% of average value, respectively.
Key words:  natural gas hydrate  sand production simulation  sand production prediction  grain size scale  sand production morphology
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