CO2干法加砂压裂技术研究与实践

Experimental studies of CO_2/sand dry-frac process

CO2干法加砂压裂是以CO2代替常规水力压裂液的一种无水压裂技术，国外（美国和加拿大）的实践成果表明：该方法对低压、低渗透、强水锁／水敏储层的压裂改造效果十分明显。为此，就其增产机理、压裂液体系、密封混砂装置及压裂工艺开展了一系列的试验研究，获得了一系列成果：①CO2提黏技术使超临界CO2黏度提高了240～490倍，改善了CO2压裂液的携砂性和造缝性，是实现CO2干法加砂压裂的一项关键技术；②CO2密闭混砂装置的研制实现了对CO2干法加砂压裂关键装置的配套，能够满足CO2干法加砂压裂作业的施工需要；③CO2干法加砂压裂实现了完全自主返排；④CO2干法加砂压裂利用CO2代替水基压裂液，能够大量节约压裂作业的耗水量，实现循环经济；⑤CO2干法加砂压裂工艺是可行的，对低压、低渗透、强水锁伤害储层具有较好针对性，表现出了良好的增产效果。

The CO2/sand dry frac process involves a waterless fracturing technology with CO2 replacing the conventional hydraulic fracturing fluid. The application of the teehnoiogy in foreign countries （the USA and Canada） show its strong performance in low- pressure and low-permeability reservoirs with high fluid-block and strong water sensitivity. A series of experimental studies were conducted of stimulation mechanism, fracturing fluid system, pressurized closed system sand blender, and fracturing process. The following achievements were made. First, the CO2 viscosity enhancement technology is successfully developed, increasing the CO2 viscosity by 240 - 490 times and improving the sand-carry and fracture making capacity of CO2 fracturing fluid, so it is served as a key technology to achieve the CO2/sand dry frac process. Second, the development of CO2 pressurized closed-system sand blender realizes the allocation of critical devices for the CO2/sand dry-frac process. Third, absolute automatic flowback is also realized. Fourth, CO2 is used to replace the water-based fracturing fluid, saving a great amount of water consumed in fracturing to make the recycling and low cost both realized. Fifth, the CO2/sand dry-frac process is feasible and will obviously improve the stimulation in low-pressure and low-permeability reservoirs with serious fluid block.