四川盆地中部地区致密河道砂岩气藏高产井地震模式及井轨迹设计

Seismic model and wellbore trajectory design for high-yield wells of tight channel sandstone gas reservoirs,central Sichuan Basin

四川盆地中部地区中侏罗统沙溪庙组气藏为典型致密气次生气藏,勘探开发潜力大,是中国石油西南油气田增储上产的重要领域之一。前期单纯依据河道的刻画成果部署井位,获得的产能与预期存在明显差异。为明确沙溪庙组致密气高效开发井位部署模式,在多手段河道刻画基础上,综合实钻井岩心、测井、地震预测成果,开展致密河道储层产能主控因素分析及地震响应特征研究。研究结果表明:①川中地区沙溪庙组河道储层总体表现为低孔、致密特征,孔渗具有明显正相关关系,属于孔隙型储层,气井产能主要受河道砂岩优质储层发育程度、储层富气程度以及压裂改造三大因素控制。②沙溪庙组优质河道砂体越厚、泥质含量少、储层厚度越大、物性越好,砂体底界波峰反射越强;利用河道砂“亮点”波峰最大振幅能量属性能有效区分优质砂体储层分布位置,并与实钻井具有较好的对应关系。③地震正演结合实钻井分析建立了浅层致密河道气藏高产井模式为“强振幅‘亮点’+低泊松比+垂直(大角度斜交)最大主应力方向”,利用该模式部署试采井实钻,强振幅区内Ⅰ、Ⅱ类储层钻遇率超过80%,测试单井平均无阻流量由2018年的31.8×10^4 m^3/d提高到84.5×10^4 m^3/d。

Most gas reservoirs of Shaximiao Formation,central Sichuan Basin,are typical secondary tight gas reservoirs with great exploration and development potential.And they are one of the most important domains for PetroChina Southwest Oil&Gasfield Company to realize dual increase in reserves and production.In the early development stage,well deployment is simply just based on channel characterization,resulting in obvious deviation compared to the expected productivity.In order to determine the deployment mode for an efficient development in tight gas of Shaximiao Formation,the main factors controlling the productivity of tight channel reservoirs were analyzed and the seismic response characteristics were studied on the basis of multi-means channel characterization,combined with some data from drilling core,logging,and seismic prediction.Results show that(1)the channel reservoirs of Shaximiao Formation,central Sichuan Basin,are generally characterized by low porosity and tightness.There is an obvious positive correlation between porosity and permeability.They are porous reservoirs.The productivity of gas wells is mainly controlled by three major factors,including development degree of high-quality channel sandstone reservoirs,gas enrichment in reservoirs,and fracturing stimulation;(2)the thicker the high-quality channel sandbody of Shaximiao Formation,the less the shale content,the greater the reservoir thickness,the better the physical properties,and the stronger the peak reflection at the sandbody bottom.The peak maximum amplitude energy property in certain"highlight"of channel sand can be used to effectively distinguish the distribution position of high-quality sandbody,and it has a good correspondence with actual wells;and(3)combined seismic forward with actual drilling analysis,one high-yield well mode of tight channel gas reservoirs in shallow layers is established,i.e,strong amplitude"highlight"+low Poisson's ratio+maximum vertical(large-angle oblique)principal stress direction.When this mode is applied to deploy production test wells,the drilling rate of TypeⅠandⅡreservoirs in high-amplitude area exceeds 80%.The average absolute open flow per well is increased to 84.5×10^4 m^3/d from 31.8×10^4 m^3/d(in 2018).