潞安矿区3号煤储层现代地应力特征及地质意义

Modern in-situ stress characteristics and geological significance of No.3 coal reservoir in Luan mining area

基于潞安矿区19组注入压降试井数据,系统分析了该区现代地应力平面及垂向分布特征,探讨了现代地应力对煤储层渗透率的控制作用。研究结果表明:潞安矿区3号煤储层整体为中-低应力区,应力场类型在垂向上呈非均匀分布,埋深400~610 m区域为走滑断层应力场(σH>σv>σh);埋深610~800 m区域为正断层应力场(σv>σH>σh)。潞安地区现代地应力场测压系数与埋深关系的关系式为:131.67/H+0.1659≤K≤544.72/H+0.2380,整体表现为“浅部离散,深部收敛”的特征。煤储层渗透率与水平主应力、水平主应力差和有效应力密切相关。煤储层渗透率与最大/最小水平主应力及其应力梯度存有较好的幂函数关系,煤储层渗透率都随最大、最小水平主应力及其应力梯度的增加而快速减小。水平主应力差通过控制煤储层裂隙开合来影响渗透率,当矿区应力场最大主应力方向与煤储层优势裂隙组发育方向一致时,煤储层中的裂隙受拉张作用,煤储层渗透率提高;当矿区应力场最大主应力方向与煤储层优势裂隙组发育方向不一致时,煤储层中的裂隙受到挤压,煤储层渗透率降低。因此,二岗山、文王山断层之间区域渗透率普遍高于二岗山、文王山断层之外区域渗透率。煤储层渗透率随有效应力的增加呈指数降低。在同等条件下,煤储层压力高的地区,有效应力低,渗透率一般较高;煤储层压力低的地区,有效应力高,渗透率一般较低。潞安矿区3号煤储层压力状态整体呈低压的特点可能是该区渗透率低,煤层气产气量不高的重要影响因素之一。

Based on 19 groups of injection pressure drop well test data in Luan mining area,the plane and vertical distribution characteristics of modern in-situ stress in this area are systematically analyzed,and the control effect of modern in-situ stress on coal reservoir permeability is discussed.The results show that the No.3 coal reservoir in Luan mining area is a medium-low stress area as a whole,and the stress field types are vertically non-uniformly distributed.The stress field in the buried depth within 400-610 m area is a strike-slip fault stress field(σH>σv>σh),and the stress field in the buried depth within 610-800 m area is a normal fault stress field(σv>σH>σh).The relationship between pressure measurement coefficient of modern geo-stress field and burial depth in Luan area is 131.67/H+0.1659≤K≤544.72/H+0.2380,which is characterized by“shallow dispersion and deep convergence”.Coal reservoir permeability is closely related to horizontal principal stress,horizontal principal stress difference and effective stress.There is a good power function relationship between the permeability of coal reservoir and the maximum/minimum horizontal principal stress and its stress gradient.The permeability of coal reservoir decreases rapidly with the increase of the maximum and minimum horizontal principal stress and its stress gradient.Horizontal principal stress difference affects permeability by controlling fracture opening and closing of coal reservoir.When the direction of maximum principal stress in mining area is consistent with that of predominant fracture group in coal reservoir,the fracture in coal reservoir is tensioned and the permeability of coal reservoir is increased.When the direction of maximum principal stress in mining area is not in line with predominant fracture group in coal reservoir,the fracture in coal reservoir is squeezed and the permeability of coal reservoir is decreased.Therefore,the regional permeability between the Ergang Mountain and Wenwang Mountain faults is generally higher than that outside the Ergang Mountain and Wenwang Mountain faults.The permeability of coal reservoir decreases exponentially with the increase of effective stress.Under the same conditions,in areas with high coal reservoir pressure,the effective stress is low and the permeability is generally high;in areas with low coal reservoir pressure,the effective stress is high and the permeability is generally low.The low pressure of No.3 coal reservoir in Luan mining area may be one of the important factors affecting its low permeability and low CBM production.