低渗透天然气气层损害机理及其预防

FORMATION DAMAGE MECHANISMS OF LOW-PERMEABILITY GAS RESERVOIR AND ITS PREVENTIVE MEASURES

低渗气藏通常具有束缚水饱和度高、毛细管压力高、地表面积大等特点 ,使得低渗透气层在钻井、完井和开发过程中引起的损害更具特殊性。文章研究了低渗透气藏在气层打开后主要产生的损害特点和损害机理 ,并对预防各种损害的方法进行了探讨。研究结果表明 ,液相滞留、应力敏感性、水敏性和反向自吸效应损害是气层损害的主要特点。在预防和治理气层损害问题时 ,应综合考虑 ,系统运筹。

The particularity of the formation damage caused in the processes of the drilling,completion and development of low-permeability gas reservoir is more evident than that of oil reservoir,because of the small flowing pores,poor permeability,large percolation resistance and strong interaction of solid-liquid interface and gas-liquid interface in the low-permeability gas reservoir.It is an effective preventive basis to recognize correctly the formation damage mechanisms of the low-permeability gas reservirs.On the basis of investigating widely the relevant documents,four main factors of causing the formation damage for low-permeability gas reservoir,i.e.liquid retention,stress sensitivity,water sensitivity abd reverse natural suction effect,are generalized;their damage mechanisms are analyzed;and the methods of preventing various formation damages are discussed in the paper.Through research,it was shown that the liquid retention damage is the first and fundamental damage factor;and caused by the stress sensitivity,the change in rock permeability is irreversible.In order to prevent the occurrence of low-permeability gas reservoir′s being damaged,it is necessary to avoid using the well-entered liquids being able to cause the liquid retention and water sensitivity damages for the gas reservoirs and it should be comprehensively considered to draw up plans systematically according to the conditions of the gas reservoirs.