【作者】 李松岩；

【导师】 李兆敏；

【作者基本信息】 中国石油大学 ， 油气田开发工程， 2009， 博士

【摘要】 酸化是通过酸来溶解地层基质中的颗粒堵塞物,恢复或提高油气井产量的一种有效措施。常规酸化存在布酸不均、残酸返排不彻底、酸岩反应速度太快等缺点。泡沫分流酸化对渗透率和油水层具有选择性,可以实现均匀布酸,提高酸化效果。通过单岩心和并联岩心驱替实验,得出泡沫在高低渗岩心分流的机理为:低渗岩心毛管力大,气泡容易破裂,形成气相蹿流,流动阻力小,高渗岩心相反;并得到渗透率级差小于10时采用泡沫段塞分流酸化工艺,级差为10~15时采用泡沫酸分流酸化工艺。通过实验测定了泡沫酸与石英砂和N80钢反应的溶蚀量,并与土酸进行了对比,得到泡沫酸的溶蚀量小于土酸的溶蚀量,且泡沫特征值越大反应速度越慢,温度越高反应速度越快,泡沫酸化具有缓蚀作用,能够达到较深的穿透距离,实现油井深部酸化。把热阻力的概念引入泡沫流体管流的压降计算中,推导出了泡沫流体热阻力系数的计算公式,通过计算得出无量纲加热数越大,泡沫流体的热阻力越明显。当无量纲加热数大于0.25时,热阻力大约是摩擦阻力的10%,热阻力必需考虑。建立了泡沫分流酸化数学模型,对泡沫段塞分流酸化和泡沫酸分流酸化过程进行了模拟,由计算结果得出,注泡沫段地层总表皮系数会逐渐增大,井底和井口压力都会逐渐升高;在注酸段总表皮系数、注入压力会逐渐减小。泡沫酸分流酸化比泡沫段塞分流酸化的分流效果要好,不同渗透率的小层进酸更均匀,对低渗层渗透率改善最明显,但是总作业时间长,注入压力高。由酸岩反应计算结果得出,HF在地层中作用范围只有0.5m左右,H2SiF6与HF的溶解能力相当,并且是HF的有益补充,0.5~1.1m范围内快速反应矿物的消耗主要是由H2SiF6溶解,增加了土酸的穿透深度。地层温度越高HF消耗越快;注酸排量越大,酸化穿透深度越大。建立了泡沫举升排酸数学模型,对井筒温度场和压力场进行了耦合求解,计算得到了泡沫举升过程的井筒内温度、压力、密度、流速的分布,并与氮气举升排酸过程进行了对比。提出了泡沫分流酸化选井原则和现场施工工艺,现场应用表明泡沫分流酸化能有效封堵高渗层,把酸液转向低渗层,提高油井产量,该技术适于非均质油藏油井、重复酸化老井的解堵增产增注。更多还原

【Abstract】 Acidizing is a kind of stimulating methods for oil and gas well or injection well, through dissolution of plug in formation matrix. There are some problems in conventional acidizing technology, such as uneven distribution of acid, unthorough flowback of reacted acid, bad acidizing effect, and so on. Foam fluid has selection of different formations with different permeability, and oil and water. Diverted acidizing with foam fluid can improve acidizing distribution, and acidizing effect.Through displacement experiments for single and parallel core, theory for diversion of foam fluid in cores with different permeability was gained. Capillary tube pressure is higher in low permeable core. The bubble breaks easily, which causing gas cross flow and low flow pressure loss in low permeable core. The situation is opposite in high permeable core. When permeability ratio of high and low permeable formations is less than 10, diverted acidizing with foam plug is suitable; When permeability ratio lies in 10 to 15, diverted acidizing with foamed acid is suitable. Corrosion of foamed acid to formation is meaning to site application. Corrosion of foamed acid, base fluid, and mud acid to quartz sand were researched by experimental method. Corrosion weight loss of N80 steel was tested. The affect of foam quality and temperature to corrosion were also analysised. The results show that corrosion of foamed acid is much less than that of mud acid. The lower the foam quality is, and the higher the temperature is, the faster the reaction is. Foamed acid has good corrosion resistant, which can realize deep acidizing in formation.The concept of thermal resistance was introduced in pressure reduction calculation of foam pipe flow. Thermal resistance coefficient was deduced according mass conversation, momentum conversation and energy conversation equations. The results of example calculation show that the larger the non-dimensional heating number is, the larger the thermal resistance is. Thermal resistance is compared with fraction resistance. When non-dimensional heating number is small, thermal resistance can be ignored. When non-dimensional heating number is larger than 0.25, thermal resistance is about 10% of fraction resistance, which must be considered during pressure reduction calculation in pipeline. Based on gas trapping theory and mass conservation equation, mathematical models were developed for foam diverted acidizing, which can be achieved by foam slug followed by acid injection or continuous injection of foamed acid, respectively. The mathematical models were solved by a computer program. Computed results show that the total formation skin factor, and wellhead pressure and bottomhole pressure increase with foam plug injection, but decrease with acid plug injection. Flow rate of high-permeability layer decreases. It can divert acid into low-permeability layer from high-permeability layer. It can be seen from the results that concentration of HF decreases quickly during sandstone-matrix acidizing in radical direction, and operating range of HF is less than 0.5 m. Dissolving capacity of H2SiF6 is equal to HF, which increases penetration depth. Deposition of Si(OH)4 increases with time. Reacted acid must be blowed out thoroughly after some time, otherwise secondary precipitate will be produced, which affects acidizing effect. Consumption of HF increases with formation temperature. High injection rate of acid can increase penetration depth. Differential equations for temperature and pressure distributions of foam fluid in the wellbore were established in consideration of the heat exchange between the foam fluid in the annular space and the injected fluid from tube. Coupled solution of temperature and pressure distributions using numerical method was conducted. Distributions of foam temperature, foam density, foam quality, pressure and foam velocity in wellbore were obtained.Well selection methods and operating technique were provided for diverted acidizing with foam fluid. Field applications show that diverted acidizing with foam fluid can effectively block high permeability layer, and improve acidizing effect and oil production. It is fit to heterogenous formation wells and old wells with acidizing for many times.更多还原