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Elastic-wave velocity characterization of gas hydrate-bearing fractured reservoirs in a permafrost area of the Qilian Mountain, Northwest China

机译:中国西北祁连山永久冻土区燃气水合物裂缝储层弹性波速度特征

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There are two types of gas hydrate-bearing reservoirs in the permafrost area of Qilian Mountain. Most of the gas hydrates occur mainly in the fractured mudstone reservoirs and rarely in the pores of the sandstone reservoirs. In this study, for the acoustic velocity characterization of the fractured gas hydrate reservoirs of the Qilian Mountain permafrost area, some mudstone core samples were collected for physical rock experiments, such as the acoustic experiment and the porosity and permeability experiment. An acoustic velocity numerical simulation of gas hydrate reservoirs was performed according to the Biot theory and the differential effective medium theory, with the conditions of multiple gas hydrate occurrence models, including the suspension model, the semi-cementation model and the cementation model, and considering both infinite and penny-shaped cracks. Fracture porosity was added to the core samples that only contain matrix porosity. With fracture porosity ranging from 0.01% to 5%, the variation laws between acoustic velocity with fractured porosity and hydrate saturation are obtained: (1) In the case of an infinite crack, if the fractured porosity is 0.01%-1%, the P-wave velocity decreases rapidly in the case of the three occurrence models. If the fractured porosity is higher than 1%, the acoustic velocity decreases gradually. If the crack shape is a penny-shaped crack, the P-wave velocity decreases almost linearly with increasing fracture porosity. (2) If the hydrate occurrence model is the suspension model, the P-wave velocity increases slightly with increasing hydrate saturation. If the occurrence model is the semi-cementation model or the cementation model, when the gas hydrate saturation of the infinite crack ranges from 0 to 80%, the acoustic velocity increases approximately linearly, whereas when the gas hydrate saturation ranges from 80% to 100%, the velocity increases rapidly. If the crack is a penny-shaped crack, the velocity increases almost linearly with increasing gas hydrate saturation from 0 to 100%. (3) It is found that the fractured gas hydrate reservoirs of the Qilian Mountain permafrost area contain both penny-shaped and infinite cracks, of which the infinite crack is the main crack shape. The gas hydrate occurrence in the Qilian Mountain permafrost area mainly follows the suspension model. This has significance for the seismic exploration and log evaluation of gas hydrate-bearing fractured reservoirs in the permafrost area of the Qilian Mountain in studying the acoustic velocity characterization, the crack shapes and occurrence models of gas hydrate reservoirs in the study area. (C) 2016 Elsevier Ltd. All rights reserved.
机译:祁连山多年冻土区有两种燃气水合储层。大多数天然气水合物主要发生在碎泥岩储层中,并且很少在砂岩储层的毛孔中。在这项研究中,对于祁连山永久冻土区域的裂缝气水合物储存器的声速表征,收集了一些泥岩核心样本,用于物理岩体实验,如声学实验和孔隙率和渗透性实验。根据BIOS理论和差动有效介质理论进行气体水合物储存器的声速数值模拟,具有多种气水合物发生模型的条件,包括悬架模型,半胶结模型和胶结模型,并考虑无限和便士形裂缝。将裂缝孔隙率加入仅含有基质孔隙率的核心样品中。裂缝孔隙度范围为0.01%至5%,获得声速与骨折孔隙率和水合物饱和的变化定律:(1)如果裂缝孔隙率为0.01%-1%,则P在三种发生模型的情况下,波速度迅速减小。如果裂缝孔隙率高于1%,则声速度逐渐降低。如果裂缝形状是一分钱形状的裂缝,则随着裂缝孔隙率的增加几乎线性地降低了P波速度。 (2)如果水合物发生模型是悬架模型,则P波速度随着水合物饱和而略微增加。如果发生模型是半胶结模型或胶结模型,当无限裂纹的气体水合物饱和范围为0至80%时,声速大致线性增加,而当气体水合物饱和范围为80%至100 %,速度迅速增加。如果裂缝是一分钱形状的裂缝,则随着0至100%的气体水合物饱和,速度几乎线性增加。 (3)发现祁连山永久冻土区域的骨折气体水合物储存器含有一分钱形状和无限裂缝,其中无限裂缝是主要裂缝形状。祁连山多年冻土区域的天然气水合物主要遵循悬架模型。这对祁连山多年冻土面积的抗气体水合物骨折储层的地震勘探和日志评价具有重要意义。 (c)2016 Elsevier Ltd.保留所有权利。

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