柴达木盆地涩北二号生物气田砂体产能分类评价

从柴达木盆地涩北二号气田砂泥薄互层滩坝相高孔-中低渗细粒储层特征出发,以气层产能为评价目标,在分析其内涵的基础上,选取孔隙度、渗透率、含气饱和度、有效厚度和泥质体积分数5个地质参数,厘清各参数的影响方式,并建立层次结构模型;以单砂体为基本单元,将消除生产压差影响的"视无阻流量"作为比较参数,采用相关分析结合层次分析法确定参数权重;结合现场生产实际从产能角度将气层分为3类。结果表明:气层分布特征与实际气井产能趋势吻合较好,气层产能分布不但受控于含气丰度、储层条件及原始地层压力,同时也受隔层质量及构造位置的影响。纵向上,由深至浅各气层组的气层数量逐渐增多,但高产能级别气层比例逐渐降低;气层组内部普遍具有气层下少上多,气层产能级别下高上低的特征。平面上,高产能级别气层较多分布在构造高部位即含气面中央部位,向构造边部逐渐过渡为低产能级别气层。通过评价气层产能潜力,可全面了解气层产能分布状况,便于优化调整部署方案。

Productivity Evaluation Method of Single Sand Body Gas Reservoir in Sebei-2 Biogenic Gas Field,Qaidam Basin

The fine-grained reservoir in Sebei-2 gas field is interbedded by the thin sand-shale beach and bar facies with the characteristics of high porosity and moderate-lower permeability.Aim to evaluate the productivity of gas reservoir, the authors analyzed the connotation of gas productivity.Five geological parameters were selected, including porosity, permeability, gas saturation, effective thickness,and clay content;and their influences on gas productivity were clarified.A single sand body was taken as the basic unit, and the "apparent open flow potential", which eliminates the effect of production pressure drop, was applied as a comparative parameter in combination with the correlation analysis and the analytic hierarchy process (AHP).The weight of each parameter was determined.The threshold values of gas reservoir classification criteria were defined with regards to the actual productive requirement;on which the gas reservoirs were divided into 3 categories.The predicted distributions of gas reservoir productivity are coincident with the trend of the actual gas reservoir productivity.The distributions of the gas reservoir productivity are controlled not only by the gas abundance, the reservoir condition, and the original formation pressure, but also the interlayer quality and structure position.Vertically, the quantity of gas reservoirs increases upwardly and gradually, while the proportion of high level productive gas reservoirs reduces gradually;more gas reservoirs occur in the top gas layers than at the bottom within one group of reservoirs, and the productivity level of gas reservoirs at the top is lower than the ones at the bottom.Horizontally, the high level productive gas reservoirs are distributed in the central and high structural section, and the productivity level reduces gradually and transits to the edge of the plane.The research results can provide some references for a fine adjusting development plan so as to improve the enhanced field gas recovery.By this evaluation, the distribution of gas reservoir productivity can be predicted;and this, in turn, can provide support for optimization of a development plan.