关中盆地西安凹陷新近系砂岩热储特征研究

Study on Characteristics of Neogene Sandstone Geothermal Reservoir in Xi’an Sag,Guanzhong Basin

层状热储的微观特征及宏观展布研究是砂岩热储地热资源精细评价和规模开发的重要依据。关中盆地西安凹陷新近系自下而上发育高陵群、蓝田—灞河组、张家坡组三套砂岩孔隙型热储,本文利用凹陷内咸阳、西安、周至等地16口地热井的测录井及岩心测试资料,对西安凹陷内新近系砂岩热储特征进行系统论述,探讨储层特征对砂体产水能力的影响。结果表明:西安凹陷新近系地层整体为河流-三角洲-湖相砂泥岩互层沉积,具有下粗上细的正韵律特征。岩石类型以长石岩屑砂岩为主,储集空间以溶蚀孔隙和原生孔隙为主,整体物性较好,张家坡组热储平均孔隙度30.02%,平均渗透率451.82×10^(-3)μm^(2),属中高孔中高渗热储层;蓝田—灞河组热储平均孔隙度20.43%,平均渗透率140.7×10^(-3)μm^(2),属中高孔中低渗热储层;高陵群热储平均孔隙度17.28%,平均渗透率109.5×10^(-3)μm^(2),属中低孔中低渗热储层。热储温度随深度增加一般呈线性升高,表现出传导型地热资源特征,典型地热井温度-深度曲线可分为直线式、折线式两类形态;部分位于渭河断裂带的地热井温度-深度曲线为“局部竖直式”,表现出传导-对流型地热资源特征。热储砂体在凹陷内广泛分布,整体厚度大、富水性好,单砂厚度一般小于5 m,蓝田—灞河组和高陵群砂体发育在垂向和平面上均优于张家坡组。热储特征影响地热井的产水能力,物性是砂体实际产水与否的最重要影响因素,单层砂体的产水能力主要受到物性和泥质含量的影响,泥质含量越低,渗透率越好,单层砂体产水量往往越高。综合砂体物性、厚度、温度等因素,蓝田—灞河组是最优的开发层段,其科学可持续开发是区域地热产业发展的重要保障。

The study of the microcharacterization and macroscopic distribution of layered geothermal reservoirs is an important basis for the fine evaluation and scale development of geothermal resources in sandstone geothermal thermal reservoirs.Neogene sandstone geothermal reservoir,which is widely developed in Xi’an Sag,Guanzhong Basin,is consisted of Gaoling Group,Lantian-Bahe Formation and Zhangjiapo Formation from the bottom to the top.Based on the logging and core sample testing data of 16 typical wells in Xianyang,Xi’an,Zhouzhi and other areas in Xi’an Sag,this paper systematically discusses the reservoir characteristics and the relationship between reservoir characteristics and water-yielding capacity.The geothermal reservoir is composed of fluvial-delta-lacustrine interactive sand and mudstone deposition,with positive rhythm characteristics.The reservoir rock is mainly feldspar lithic sandstone,and the reservoir space is dominated by dissolution pores and primary pores.The average porosity of Zhangjiapo Formation is 30.02%,and the average permeability is 451.82×10^(-3)μm^(2),which belongs to the medium-high-porosity and medium-high-permeability geothermal reservoir.The average porosity of Lantian-Bahe Formation is 20.43%,and the average permeability is 140.7×10^(-3)μm^(2),which belongs to the medium-high-porosity and medium-low-permeability geothermal reservoir.The average porosity of Gaoling Group is 17.28%,and the average permeability is 109.5×10^(-3)μm^(2),which belongs to the medium-low-porosity and medium-low-permeability geothermal reservoir.The temperature is generally linearly increased with depth,showing the characteristics of conduction geothermal resources,and the typical temperature-depth curves can be divided into two types of linear and folding patterns.Meanwhile,some wells located in the Weihe Fracture Zone have partial-vertical pattern of temperature-depth curves,showing the characteristics of conduction and convection.The reservoir sands are widely distributed and well hydrated with a large overall thickness,while the single sand thickness is generally less than 5 meters.The sandbody development of the Lantian-Bahe Formation and Gaoling Group is better than that of the Zhangjiapo Formation both vertically and horizontally.Reservoir conditions affect the water-yielding capacity of geothermal wells,and physical properties are the most important factors influencing the actual water production of sand bodies.The water yield of the monolayer is mainly affected by physical properties and argillaceous content.The better physical properties and lower argillaceous content can lead to a higher water yield of monolayer sand.Considering the physical properties,thickness,temperature and other factors,Lantian-Bahe Formation is the optimal layer for development,and its scientific and sustainable development is an important guarantee for the development of the regional geothermal industry.