碳酸盐岩储集层钻井井涌特征及井涌风险评价

摘要

以塔中顺南地区碳酸盐岩储集层为例,分析碳酸盐岩储集层钻井井涌特征,建立井涌风险定量评价方法,并进行算例分析.依据钻井地质资料,分析塔中顺南地区碳酸盐岩储集空间特点与气体侵入井筒机制,发现储集层裂缝及孔洞发育,气体主要以压差与气液置换方式侵入井筒.综合考虑气体侵入井筒机制、气体在井筒中运移规律和井筒温度-压力场,并引入井筒气相体积分数密度函数,建立了井涌风险定量评价方法和井控风险分级方法.算例分析结果表明:可采用施加井口回压法判定井底气体侵入方式;碳酸盐岩储集层孔缝洞发育特征和酸性气体对井筒气相体积分数影响较大,易引发难监测、高强度井涌;井深、井径、钻井液密度、钻井液排量、钻井液黏度和钻速对井涌风险的影响依次减弱.%The gas kick characteristics during carbonate reservoir drilling were analyzed taking carbonate reservoirs in Shunnan area of Tazhong as an example,a quantitative evaluation method for gas kick risk was established,and then a case was simulated.Looking into reservoir space characteristics and gas invasion mechanisms of carbonate reservoirs in Shunnan area based on drilling geologic data,it is found that the reservoirs are rich in fractures,pores and caves,and the gas invades into wellbore through gas-liquid replacement and differential pressure.By fully considering the gas invasion mechanism,gas migration law and wellbore temperature-pressure field,and introducing the gas volume fraction density function,a quantitative evaluation method for gas kick risk and a method for ranking well control risk were established.The case study shows that the wellhead back pressure method can be used to tell the mode of gas invasion;pore-fracture-cave and acid gas characteristics in carbonate reservoirs have stronger effect on the gas volume fraction in wellbore,and may cause hidden and severe gas kick;the effects of well depth,well diameter,drilling fluid density,drilling fluid displacement,drilling fluid viscosity and drilling rate on gas kick risks weaken in that order.