南海海域天然气水合物降压开采储层蠕变对气井产能影响

doi:10.13809/j.cnki.cn32-1825/te.2023.06.012

摘要/Abstract

摘要：

南海海域天然气水合物储层岩性以弱固结泥质粉砂为主，此类储层在降压开采过程中会发生蠕变效应。针对泥质粉砂型海域天然气水合物降压开采过程中蠕变效应对储层物性、温度场、压力场、水合物饱和度场和气井产能影响不明的问题，结合室内岩心驱替实验数据，运用数值模拟方法，开展了考虑南海海域天然气水合物蠕变特征的直井降压法开采数值模拟研究。研究结果表明：直井降压法开采南海海域天然气水合物，蠕变效应降低了储层有效孔隙度和有效渗透率；压力降落主要发生在近井区域，井周温度降低幅度最大，且储层蠕变导致储层压力漏斗变得更加陡峭；水合物分解主要发生在近井区、水合物层A顶部和水合物层B底部区域。同时，蠕变效应导致水合物横向分解半径降低了66.7 %；储层蠕变降低了气井产能，气井5 a累产降低了87 %。当生产压差大于4 MPa时，储层蠕变效应占主导作用，气井累产增幅随压差的增大逐渐减小，因此长期开发南海海域蠕变储层水合物气井应控制在临界生产压差以下生产。研究为南海海域天然气水合物的高效开发提供了可靠的理论依据。

关键词: 泥质粉砂, 天然气水合物, 储层蠕变, 降压法, 气井产能, 数值模拟

Abstract:

The South China Sea's natural gas hydrate reservoirs, primarily composed of clayey silt with non-diagenetic properties, undergo creep during depressurization development. The implications of this creep on key reservoir characteristics such as permeability, porosity, pressure, temperature, hydrate saturation distribution, and gas well productivity remain unclear. To address this, a combination of water seepage experiment data from clayey-silt cores and numerical simulation methods was employed to study the development of these hydrate reservoirs through depressurization-induced vertical wells. The simulation results show that the creep effects reduce the effective reservoir porosity and permeability while developing South China Sea natural gas hydrate reservoirs using a depressurization-induced vertical well. Specifically, the pressure drop is predominantly observed near the well, accompanied by a significant decrease in temperature around the well. Additionally, the reservoir creep results in a more pronounced pressure drop funnel within the reservoir. The hydrate decomposition mainly occurs at the regions of the near-well, the top of hydrate layer A, and the bottom of hydrate layer B, and the radius of hydrate decomposition is decreased by 66.7 % due to creep effects. The reservoir creep effects reduced the gas well productivity, and the cumulative production of the gas well in five years decreased by 87 %. The creep of the South China Sea natural gas hydrate reservoir dominates while the production pressure difference is greater than 4 MPa. As the production pressure difference is larger, the increasing degree of cumulative production gradually becomes smaller. A production pressure difference lower than 4 MPa is recommended for future long-term development. This study provides a reliable theoretical basis for developing South China Sea natural gas hydrate efficiently.

Key words: clayey silt, natural gas hydrate, reservoir creep, depressurization-induced, gas well productivity, numerical simulation

中图分类号:

TE37

崔玉东, 陆程, 关子越, 罗万静, 滕柏路, 孟凡璞, 彭越. 南海海域天然气水合物降压开采储层蠕变对气井产能影响[J]. 油气藏评价与开发, 2023, 13(6): 809-818.

CUI Yudong, LU Cheng, GUAN Ziyue, LUO Wanjing, TENG Bailu, MENG Fanpu, PENG Yue. Effects of creep on depressurization-induced gas well productivity in South China Sea natural gas hydrate reservoirs[J]. Petroleum Reservoir Evaluation and Development, 2023, 13(6): 809-818.

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序号	孔隙度/%	渗透率/10^-3 μm²
1	18.62
2	17.09	13.40
3	16.24	14.03
4	15.29	8.63
5	13.90	5.60
6	10.60	3.92