压裂液对碳酸盐岩储层裂缝的伤害特征研究

STUDY ON THE CHARACTERISTICS OF FRACTURE DAMAGE IN CARBONATE RESERVOIR CAUSED BY FRACTURING FLUID

针对塔河油田碳酸盐的储层特征和储集体性质,研究了HPG植物胶水基压裂液对地层岩心的伤害规律,并评价了线型胶、冻胶、破胶残液等对碳酸盐岩裂缝的伤害程度。随着围压的增加,裂缝逐渐闭合,水测渗透率呈幂指数降低;而压裂液及其冻胶、破胶残液对裂缝的伤害用滤失量进行表征,它们在裂缝中的滤失明显地分为两个阶段,第一阶段t1≤4s。两个阶段的滤失特性与裂缝本身的渗透率及液体的黏度有关。冻胶体系在初始阶段的滤失量极低,后期阶段其滤失量急剧增大。研究结果表明,初始起压阶段,储层较低的渗透率不仅可以产生较低的滤失,而且有助于形成高的破裂压力;压开后的破胶时间对裂缝的导流能力影响很大,即压开后破胶时间越短则对裂缝的倒流能力影响越小。

According to carbonate reservoir characteristics and reservoir body properties in the Tahe Oilfield,the damage laws of water base vegetable gum fracturing fluid HPG to formation cores were studied.And the fracture damage degree of carbonate rock was evaluated when linear guar solution,gel and its breaking liquid were separately used.With the increasing confining pressure,fractures were gradually closed and their permeability to water showed exponential decline.Filter loss was used to characterize the fracture damage degree of fracturing fluids,gels and gel breaking liquid.The filtration process could be separated into two phases,the demarcation point of which was about 4s.The filtration characteristics during the two periods were related to the permeability of the fracture and liquid viscosity.The filter loss of gel was fairly low in the initial period while it increased drastically in the later period.It was indicated that the lower formation permeability in the initial pressure-rising period could not only result in lower filtration loss,but also was beneficial to the formation of high fracture pressure.Additionally,the breaking time after fracturing influenced greatly on fracture conductivity.The shorter the time of gel breaking after fracturing was,the weaker the influence on fracture conductivity would be.