疏松砂岩气藏泥砂堵塞机制研究

Mechanism of mud and sand plugging in unconsolidated sandstone gas reservoirs

疏松砂岩气藏具有埋藏较浅,储层岩石疏松,气水分布复杂等特征,生产过程中地层易发生边底水侵、微粒运移和泥砂堵塞问题,导致井筒产水、出砂现象发生,影响气田的正常生产。选取柴达木盆地涩北气田疏松砂岩气藏为研究目标,基于生产工程因素分析与堵塞机制理论研究,探究产水、出砂以及地层泥砂堵塞的主要影响因素,进行不同压实作用下的泥砂堵塞机制模拟实验,并通过压汞法毛管压力曲线、粒度测试分析和X-射线衍射分析等手段研究泥砂微粒堵塞机制及其对疏松砂岩渗流能力的影响程度。结果表明,生产压差、地层压力和边底水侵是气井出砂的主要影响因素;生产压差越大,地层压力衰减越快,压实作用越强,导致地层出水加剧;当储层发生边底水侵后,水侵与压实效应导致岩心渗透率迅速下降,最大渗透率损失率达到77.40%;岩心水化分散导致泥砂微粒粒径变小,释放出的石英、长石等非膨胀性颗粒将发生运移,运移泥砂微粒粒径(Dp)与孔喉直径(df)满足3df<Dp<10df的桥堵规则,导致地层泥砂微粒堵塞;当围压达到12 MPa后,运移泥砂微粒粒径与孔喉直径满足df>1/3Dp的匹配关系,泥砂微粒直接堵塞孔喉。因此,在开发中不建议采用过高的生产压差,对于地层压力降低的储层宜采取增压开发的方式,对地层进行能量补充。

The unconsolidated sandstone gas reservoirs are characterized by shallow burial depth,loose reservoir rock,and complex gas-water distribution,and the formation is prone to the problems of edge and bottom water invasion,particle migration,and mud&sand plugging during the production process,resulting in water and sand production in the wellbore,which affects the normal production of the gas field.In this study,the unconsolidated sandstone gas reservoirs of Sebei Gas Field in Qaidam Basin were selected as the research target to study the main influencing factors of water production,sand production,and formation mud&sand plugging based on the analysis of production engineering factors and the theoretical study of plugging mechanism.The simulation experiments of the mud&sand plugging mechanism under different compaction conditions were carried out,and the plugging mechanism of mud&sand particles and its influence degree on the flow capacity of unconsolidated sandstones were studied by means of mercury injection capillary pressure curve,particle size test analysis,and X-ray diffraction analysis.The results reveal that the main factors influencing sand production in gas wells are production pressure difference,formation pressure,and edge-bottom water invasion.The faster decaying formation pressure and the stronger compaction result in increased formation water when the production pressure difference increases.The permeability of the core decreases rapidly due to the effect of water invasion and compaction when the invasion of edge and bottom water occurs in the reservoirs,and the maximum permeability loss rate reaches 77.40%.The hydration dispersion of the core leads to the smaller size of the mud&sand particles,and the released non-expansive particles such as quartz and feldspar will migrate in the formation.There is a bridge blinding rule of 3df<Dp<10df between the grain size(Dp)and pore throat diameter(df)of the transported mud and sand particles,which causes mud&sand plugging in the reservoir.When the confining pressure reaches 12 MPa,there is a matching relationship of df>1/3DP between the grain size and pore throat diameter of the transported mud&sand particles,and the mud&sand particles are directly plugged in the pore throat.Therefore,it is not recommended to adopt too high production pressure difference during the production process.For the reservoirs with reduced formation pressures,it is advisable to adopt pressurized development to replenish the energy of the formation.