Evaluation of the Performance of a CO₂ Water Based Compound Fracturing Fluid

CO₂ dry fracturing operation has to be performed in a closed environment and the fracturing fluid additives need to be added under pressure. These requirements result in high operation cost, low sand ratio, low operation scale, as well as high operational difficulties. To deal with these problems, ZHENG Yan et al. presented and tried a quasi-dry CO₂ fracturing technology. In the quasi-dry fracturing operation, the accurate control of the parameters of the liquid is key to the success of this technology, and the parameter control needs to be optimized repeatedly. This study was focused on the use of a fracturing fluid mainly formulated with CO₂ (> 70%, a water based CO₂ fracturing fluid) with conventional equipment in atmospheric pressure. Main factors affecting the ratio of the components and the thickening performance of the fracturing fluid were studied. The fluid was formulated with a visual CO₂ sampler, and by observing the settling of the ceramsite the thickening of the liquid CO₂ can be understood. The interaction of the water and the liquid CO₂, the effects of the ratio of the water component and temperature on the thickening of the CO₂ water based fracturing fluid were studied. The results of the study show that 2% AF-2 CO₂ and 2% AF-6 water based thickening agent can be used to thicken the liquid CO₂ and water, rendering them stable sand suspending ability. The two thickening agents can be used together in one fracturing fluid with no negative interactions. A CO₂ water based compound fracturing fluid at 30% or less water content and at temperatures less than 5 ℃ can be thickened fast, and has stable sand suspending ability. The fracturing fluid formulated was used successfully in field operations, with the highest sand content of 35%.