乳化钻井液条件下高温高压气井气体扩散研究

GAS DIFFUSION IN HPHT HORIZONTAL WELL USING EMULSION DRILLING FLUID

高温高压下甲烷在油里的溶解度大,水包油乳化钻井液中存在油相,钻井作业中钻井液静置期间如起下钻、工具故障抢修等时间过长,储层中的甲烷气体会扩散到井眼里。在钻高含硫化氢及二氧化碳气井时,高温高压条件下天然气更有可能到达与油完全互溶的状态。文章将储层内的水平段井眼的气体扩散区域划分为4个区,外滤饼区、内滤饼区、滤液滞留区、滤液未污染区,根据外滤饼区、内滤饼区、滤液滞留区不同计算参数条件,计算预测了在使用水包油乳化钻井液情况下,储层中天然气通过扩散穿过3个区后,进入储层内井眼段环空导致的环空含气质量浓度变化,对环空内含气质量浓度随扩散时间、含油浓度因素的变化进行了定量计算。用伽略金有限元方法求解,计算表明,气体扩散量随钻井液静置时间延长而增加,水基钻井液加入油后与不加油的钻井液相比增大了气体扩散量。

Since methane has great solubility in oil under high temperature and pressure, and there is oil phase in oil-in-water emulsion drilling fluid, the methane gas from the reservoir will diffuse into the borehole when the drilling fluid is undisturbed for a long time to make a trip or repair a tool's failure. The natural gas with high H2S and CO2 contents may completely inter-solve with oil under high temperature and pressure while drilling the gas wells with high H2S and CO2 contents. The gas diffusion region of the horizontal borehole in the reservoir is divided into 4 zones, including the external filter cake zone, the inertia filter cake zone, the filter fluid residence zone and the filter fluid un-pollution zone. According to the different calculating parameters of the external filter cake zone, the inertia filter cake zone and the filter fluid residence zone, the gas-bearing concentration variation in the annulus caused by the natural gas from the reservoir diffusing into the borehole section of the reservoir through the 3 zones is predicted while using oil-in-water emulsion drilling fluid. It is quantitatively calculated the gas-bearing concentration variation in the annulus changes along with such factors as diffusion time, oil-bearing concentration etc. Through Galerkin Finite Element Methods, the calculation shows the volume of gas diffusion increases as the time prolongs of the drilling fluid being undisturbed and gas diffusion in water-based drilling fluid with oil is larger than that in water-based drilling fluid.