鄂尔多斯盆地盒8段致密砂岩气藏微观孔隙结构及渗流特征

Characteristics of micro pore structure and seepage in tight sandstone gas reservoir of the 8^(th) section of Shihezi Formation in Ordos Basin,China

应用铸体薄片、恒速压汞、高压压汞、气水相渗、水锁伤害、应力敏感等分析测试技术,对鄂尔多斯盆地上古生界二叠系石盒子组盒8段储层微观孔隙结构及渗流特征进行了分析,对钻井、储层改造、气藏开发等工程工艺措施提出了针对性改进建议。结果表明:盒8气藏为致密砂岩气藏,储层孔隙半径分布曲线主峰为70~200μm,喉道半径分布曲线主峰为0.2~2.2μm,属大孔、中—细喉储层;渗透率>1×10^(-3)μm^2、(1.0~0.5)×10^(-3)μm^2、(0.5~0.1)×10^(-3)μm^2、(0.1~0.01)×10^(-3)μm^2等4个级别储层中,由半径<0.062 4μm喉道控制的孔隙体积分别占总孔隙体积的18.8%、38.4%、57.3%、71.6%,小喉道控制的孔隙体积比例高;喉道半径大小决定了储层渗透率高低,也控制了渗流特征,水锁和应力敏感是影响盒8致密砂岩储层渗流能力的主要因素;盒8气藏压力系数低,加之储层强亲水,易发生水锁伤害,气相渗透率随含水饱和度升高急剧降低;盒8段储层管束状、缩颈状喉道发育,易发生应力敏感伤害,应力敏感伤害率为40%~80%;盒8致密砂岩气藏储层改造应广泛采用体积压裂以减弱小喉道对孔隙的控制,在钻井、储层改造过程中应尽量避免使用水基工作液,多采用欠平衡作业等措施,减少或避免水基工作液侵入。开发生产过程中应尽量避免大压差生产和频繁开关井,主动排水采气,以保护储层,提高采收率。

A detailed study about the micro-pore structure and reservoir seepage characteristics was carried out on the 8^th section of Shihezi Formation of Upper Palaeozoic in Ordos Basin,based on casting thin sections identification,onstant-rate mercury injection,high-pressure mercury injection,gas water phase permeability,water lock damage and stress sensitive analytical techniques,then give the improvement suggestions about drilling and reservoir reconstruction for tight sandstone gas reservoir development technology.The results are as follows：Gas reservoir in the 8^（th） section of Shihezi Formation is tight sandstone gas reservoir.The main peak of the pore radius distribution is between 70-200μm,and the main peak of throat radius distribution is between 0.2-2.2μm,so the reservoir belongs to big hole,medium-fine throat type reservoir.The reservoir permeability was divided into four levels,such as greater than 1 millidarcy,1.0-0.5millidarcy,5-0.1millidarcy,and 0.1-0.01 millidarcy.The throats whose radius is smaller than 0.0624μm respectively takes up the 18.8%,38.4%,57.3%and 71.6%pore volumes in four lever permeability,so it is obvious that the small throats take up pore volume much higher,and throat radius size determines the reservoir permeability and also controls the reservoir seepage characteristics.Water locking and stress sensitivity are the main factors that influence the He 8section tight sandstone reservoir seepage ability.Pressure coefficient of He 8gas reservoir is low,and hyolrophilic preperty of the reservoir is stong,prone to water locking damage,gas permeability decreases sharply with the increase of water saturation.With pipe bundle and necking shape throat development,He 8 section tight sandstone reservoir is prone to stress sensitivity damage,and the stress sensitivity damage rate of He 8 section ranges from 40% to 80%.Volume fracturing should be widely used to reduce the control of small throat for pore in reservoir reconstruction of He 8 section tightsandstonereservoir.Indrilling and reservoir reconstruction process of He 8 section gas reservoir should avoid using water-based fluid and use underbalanced drilling technology,which prevent the water-based fluid invading.Indevelopment process,the tight sandstone gas reservoir should avoid great production pressure drop and frequent switch well,and active drainage gas recovery so to protect reservoir and improve gas recovery.