【摘要】 通过研究温度、压力、pH值等因素对CO2、CaCO3垢溶解度的影响,分析高含CO2天然气藏储集层的结垢机理。CO2的溶解度随温度升高而降低,随压力升高而升高,随地层水矿化度的升高而降低;CaCO3在水中的溶解度随温度升高而降低,随压力的升高而升高,溶液pH值升高会促进CaCO3的生成。结合吉林油田典型含CO2天然气藏储集层特征进行了结垢预测,认为钻井液滤液侵入储集层后,储集层近井地带存在结CaCO3垢的可能。针对气藏储集层埋藏深、井底温度高、地层压力系数低、裂缝发育等特点,优选了水包油及甲酸盐无固相两种欠平衡钻井液体系,CO2侵入、动态污染实验评价表明,两种钻井液均具有很好的抗CO2污染能力,储集层保护效果显著。两种欠平衡钻井液体系已分别在龙深2井和龙深3井进行了现场应用,效果良好,现场钻井液的岩心渗透率恢复值均在85%以上,满足欠平衡钻井的要求。更多还原

【Abstract】 Factors affecting the solubility of CO2 and CaCO3,including temperature,pressure,salinity of solutions,and pH value have been studied and then the mechanism of scale deposition in gas reservoirs with high CO2 content has been analyzed.The solubility of CO2 reduces with the increase in temperature and salinity,whereas it increases with the increase in pressure;the solubility of CaCO3 reduces with the increase in temperature,it increases with the increase in pressure and increase in pH value can promote the formation of CaCO3.Taking the typical formations of high CO2 content in Jilin Oilfield as an example,the prediction of CaCO3 scaling was conducted,indicating that there might be scale deposition after the drilling fluid filtrate invaded into the formations.Since the gas reservoirs was characterized by deep embedding,high temperature,low pressure coefficient,fracture developing,etc.,two kinds of drilling fluids,oil-in-water drilling fluid and formate drilling fluid with no solid phase,were selected for the underbalanced drilling.The anti-pollution test and dynamic damage tests showed that they all exhibited excellent anti-pollution performance to CO2 and remarkable formation protection.The field applications in Longshen No.2 and No.3 wells proved that the two drilling fluid systems worked well and the restored permeability of the field drilling fluid to cores was more than 85%,which met the demands of underbalanced drilling.更多还原