Stress sensitivity and water blocking in fractured carbonate reservoir formations with low permeability were determined as the main potential damage mechanisms during drilling and completion operations in the ancient ...Stress sensitivity and water blocking in fractured carbonate reservoir formations with low permeability were determined as the main potential damage mechanisms during drilling and completion operations in the ancient buried hill Ordovician reservoirs in the Tarim Basin. Geological structure, lithology, porosity, permeability and mineral components all affect the potential for formation damage. The experimental results showed that the permeability loss was 83.8%-98.6% caused by stress sensitivity, and was 27.9%-48.1% caused by water blocking. Based on the experimental results, several main conclusions concerning stress sensitivity can be drawn as follows： the lower the core permeability and the smaller the core fracture width, the higher the stress sensitivity. Also, stress sensitivity results in lag effect for both permeability recovery and fracture closure. Aimed at the mechanisms of formation damage, a modified low-damage mixed metal hydroxide （MMH） drilling fluid system was developed, which was mainly composed of low-fluorescence shale control agent, filtration control agent, lowfluorescence lubricant and surfactant. The results of experimental evaluation and field test showed that the newly-developed drilling fluid and engineering techniques provided could dramatically increase the return permeability （over 85%） of core samples. This drilling fluid had such advantages as good rheological and lubricating properties, high temperature stability, and low filtration rate （API filtration less than 5 ml after aging at 120 ℃ for 4 hours）. Therefore, fractured carbonate formations with low permeability could be protected effectively when drilling with the newly-developed drilling fluid. Meanwhile, field test showed that both penetration rate and bore stability were improved and the soaking time of the drilling fluid with formation was sharply shortened, indicating that the modified MMH drilling fluid could meet the requirements of drilling engineering and geology.展开更多
水锁损害会对油气井产能造成极大的影响,建立一种对水锁损害进行快速预测的方法十分必要。针对低渗砂岩储层发生水锁损害的特点,选取一定数量的低渗砂岩岩心,较系统地评价了在不同的气测渗透率、孔隙度、初始水饱和度以及油水界面张力...水锁损害会对油气井产能造成极大的影响,建立一种对水锁损害进行快速预测的方法十分必要。针对低渗砂岩储层发生水锁损害的特点,选取一定数量的低渗砂岩岩心,较系统地评价了在不同的气测渗透率、孔隙度、初始水饱和度以及油水界面张力条件下的水锁损害程度,采用灰关联分析法对低渗砂岩储层的水锁损害进行了评价和预测研究,并编制了相应的计算程序。灰关联分析实际上就是分析参考序列与比较序列间曲线几何形状的接近程度,一般情况,几何形状越接近,关联度就越大,变化趋势就越接近。灰关联分析步骤为,确定比较序列(子序列)和参考序列(母序列);数据规一化处理;求关联系数;求关联度;关联度按大小排序。结果表明,利用该方法评价和预测低渗砂岩储层的水锁损害是可行的,对影响水锁损害的气测渗透率、孔隙度、初始水饱和度和油水界面张力的4种因素权值分配是合理的。经验证,预测结果有较高的符合率。该方法中的数值计算程序均使用Fortran 4.0在FORTRAN POWER STATION环境下编制而成,在实际应用中能较方便地利用该方法预测低渗砂岩储层的水锁损害程度。展开更多
基金the National Natural Science Foundation of China(No.50574061)
文摘Stress sensitivity and water blocking in fractured carbonate reservoir formations with low permeability were determined as the main potential damage mechanisms during drilling and completion operations in the ancient buried hill Ordovician reservoirs in the Tarim Basin. Geological structure, lithology, porosity, permeability and mineral components all affect the potential for formation damage. The experimental results showed that the permeability loss was 83.8%-98.6% caused by stress sensitivity, and was 27.9%-48.1% caused by water blocking. Based on the experimental results, several main conclusions concerning stress sensitivity can be drawn as follows： the lower the core permeability and the smaller the core fracture width, the higher the stress sensitivity. Also, stress sensitivity results in lag effect for both permeability recovery and fracture closure. Aimed at the mechanisms of formation damage, a modified low-damage mixed metal hydroxide （MMH） drilling fluid system was developed, which was mainly composed of low-fluorescence shale control agent, filtration control agent, lowfluorescence lubricant and surfactant. The results of experimental evaluation and field test showed that the newly-developed drilling fluid and engineering techniques provided could dramatically increase the return permeability （over 85%） of core samples. This drilling fluid had such advantages as good rheological and lubricating properties, high temperature stability, and low filtration rate （API filtration less than 5 ml after aging at 120 ℃ for 4 hours）. Therefore, fractured carbonate formations with low permeability could be protected effectively when drilling with the newly-developed drilling fluid. Meanwhile, field test showed that both penetration rate and bore stability were improved and the soaking time of the drilling fluid with formation was sharply shortened, indicating that the modified MMH drilling fluid could meet the requirements of drilling engineering and geology.
文摘水锁损害会对油气井产能造成极大的影响,建立一种对水锁损害进行快速预测的方法十分必要。针对低渗砂岩储层发生水锁损害的特点,选取一定数量的低渗砂岩岩心,较系统地评价了在不同的气测渗透率、孔隙度、初始水饱和度以及油水界面张力条件下的水锁损害程度,采用灰关联分析法对低渗砂岩储层的水锁损害进行了评价和预测研究,并编制了相应的计算程序。灰关联分析实际上就是分析参考序列与比较序列间曲线几何形状的接近程度,一般情况,几何形状越接近,关联度就越大,变化趋势就越接近。灰关联分析步骤为,确定比较序列(子序列)和参考序列(母序列);数据规一化处理;求关联系数;求关联度;关联度按大小排序。结果表明,利用该方法评价和预测低渗砂岩储层的水锁损害是可行的,对影响水锁损害的气测渗透率、孔隙度、初始水饱和度和油水界面张力的4种因素权值分配是合理的。经验证,预测结果有较高的符合率。该方法中的数值计算程序均使用Fortran 4.0在FORTRAN POWER STATION环境下编制而成,在实际应用中能较方便地利用该方法预测低渗砂岩储层的水锁损害程度。
