反凝析作用对苏里格气田上古生界气藏开发的影响

鄂尔多斯盆地苏里格气田上古生界气藏在开发中产生一定量的凝析油,含量约为10g/m~3,属于微含凝析油气藏,如果生产初期配产过大,那压力下降就会过快。在反凝析作用下,凝析油在近井地带析出形成多相流,堵塞微孔隙和吼道,导致气相渗透率降低,使得气井产量大幅下降,部分被封闭的天然气无法采出,层内凝析对储层的伤害有可能是永久性的。为此,通过对该气藏层内反凝析机理、层内凝析影响因素的分析及室内试验.再使用新建立的三维数学模型对单井进行预测,结果表明该气藏"三低"(低孔、低渗、低产)特征加剧了凝析液对储层的伤害。同时还分析了气井产能降低的根本原因.并对气井生产管理提出了建议:①在保护开采阶段,投产初期应合理配产,以低于无阻流量的1/5~1/8配产,尽可能延长露点线以上开采时间,使凝析油尽可能不在地层中析出;②在反凝析阶段,要在系统研究的基础上得出准确的相态图,要快速通过该阶段尽早进入蒸发阶段,使已经凝析出来的凝析油再次蒸发汽化,从而降低储层污染。该研究成果对苏里格气田上古生界气藏的科学开发以及进一步提高采收率具有重要意义。

Impacts of retrograde condensation on the development of Upper Paleozoic gas reservoirs in the Sulige Gasfield,Ordos Basin

With approximately 10 g/m³ of condensate oil produced during the development of Upper Paleozoic gas reservoirs, the Sulige Gasfield can be classified as gas reservoirs with minor amount of condensate oil. High productivity allocation in early production stages may lead to a rapid decrease in pressure. Due to existence of retrograde condensation, condensate oil may generate multi-phase flows in near-wellbore areas to plug micro-pores and throats. With permeability for gases reduced, productivity of gas wells may drop significantly and parts of natural gas may be blocked in the formation and may not be produced. Consequently, condensation within the formation may generate permanent damage to reservoir formations. Analyses and lab tests were performed in terms of mechanisms and influencing factors related to retrograde condensation within reservoir formations. In addition, a newly-built 3D mathematic model was used for prediction in individual wells. Research results show that the unfavorable properties of the gas reservoir may intensify the damages to reservoirs induced by condensation. In addition, primary causes for decrease of gas well productivity were identified and the recommended practices for production management were also proposed: proper production allocations should be deployed during the early protected development stages. Production allocation should be 1/5 - 1/8 of the open-flow capacity to extend the production period above the dew point line as long as possible to minimize the condensation of condensate oil within the reservoir formation. During the retrograde condensation stage, accurate phase plot should be obtained on the basis of systematic study to quickly end this stage and to enter the evaporation stage as soon as possible. In this way, condensate oil may be re-evaporated to minimize reservoir contamination. This study may play an important role in further enhancing the recovery rate in the development of Upper Paleozoic gas reservoirs in the Sulige Gasfield.