加重液在高温高压气藏增产作业中的盐析伤害及预防措施

Saltout damage resulting from weighting drilling fluid and countermeasures in the stimulation operations of HTHP gas reservoirs

对高温高压气藏使用加重压裂技术存在潜在的储层盐析伤害,降低和防止加重液盐析伤害对提高该类气藏的储层改造增产效果意义重大。为此,采用加重液压后返排过程中盐浓聚变化模拟、现场返排液分析和岩心流动试验,对高温高压气藏增产作业中加重液盐析及其伤害进行了研究。结果表明:①加重液在高温高压气藏增产压裂后返排中存在盐浓聚及其导致的盐析伤害现象,严重时将影响气井增产效果;②产生盐析的主要原因包括加重剂类型及其加量、地层返排温度、压力以及返排速度;③盐析主要发生在压裂缝壁附近和近井裂缝附近;④加重压裂液与普通压裂液交替注入可有效防止和降低盐析产生,采用活性水裂缝闭合清洗可有效解除地层盐析伤害。

Saltout damage will easily occur when the weighting drilling fluid is used in fracturing treatment for high temperature and high pressure(HTHP) reservoirs.Thus,to mitigate and prevent such damage is of great significance to enhancing the stimulation efficiency of HTHP gas reservoirs.In view of this,the simulation is made on the concentration variation of salts in the backflowing weighting fluid after frac treatment,meanwhile the backflowing fluid analysis and core flow experiments are conducted.The following results are achieved.(1) The salt concentration found in the backflowing weighting drilling fluid will be high enough to cause damage to the reservoirs,which will badly affect the stimulation result.(2) The saltout phenomenon is mainly caused by types and amount of weighting agents,temperature,pressure and velocity of backflowing fluids.(3) Saltout will easily occur near the fractured well wall or near wellbore fractures.(4) The alternative injection of the weighting frac fluid and the normal frac fluid will effectively prevent the saltout;the active water fracture closure can be used to remove the saltout damage on the formations.