Theory And Technology Research Of Carbon Dioxide Foamed Fracturing

For the low pressure, low permeability and water sensitive formations, the stimulation performance of common hydraulic fracturing technology is not ideal, even may fails. Due to the following properties: visbreaking, antiswelling, friction reducing, cleanup and high carrying capacity, small filter loss, swift flowback, low damage, carbon dioxide foam liquid is fit for fracturing these formations, while for the heavy damage oil layer, low water ratio, heavy oil well or primary fracturing layer, the performances are better than that of common fracturing.However, the study on carbon dioxide foam fracturing is being in exploration stage in the domestic, and still has many problems. It mainly displays as follows: lacking of theory research, especially there is no agreement on the reheology model of foam fracturing fluids under the circumstances of room temperature and pressure, not to mention the case of high pressure/high temperature; no report of fracture propagation model for the foam fracturing. It needs developing and improving the relevant theories quickly. For these reasons, it's necessary for us to study the theory and technics of carbon dioxide foam fracturing.Based on the formers' researches, we studied the following aspects and draw the corresponding conclusions in this paper:1. Studied the reheology model of foam fracturing fluids under the circumstances of high temperature and pressure by virtue of the large-scale, high-parameter foam fracturing fluids flow loop; Studied the influence law of the parameters such as shear rate, foam quality, temperature, pressure et al on the rheological parameters and fitted the rheological parameters expressions for the carbon dioxide foam fracturing fluid based on guar fluid. The following conclusions were concluded: (1)When the foam quality is smaller than 0.9, the reheology model of foam fracturing can be depicted by the power law model; When the foam quality is larger than 0.9, it can be depicted by the Bingham model. (2)Carbon dioxide fracturing fluid is a shear thinning and temperature thinning fluid. (3)The effect of the foam quality and temperature on the rheological parameters is in index law, while the effect of the pressure is little. (4)As the foam quality increases, n decreases and k increases; As the temperature increases, k decreases and n increases.2. Studied the flow of carbon dioxide foam fluids in the wellbore and established the hydrostatic column model and the friction calculation model for the carbon dioxide foam fluids. The case calculation showed that: as the foam quality increases, the friction loss along the tubing increases, but the larger the foam quality is, the smaller the increment is; the smaller the foam quality is, the larger the increment is. As the foam quality increases, the gravity pressure drawdown diminishes the variation trend of the gravity pressure drawdown diminished.3. Considering the effect of friction energy, we calculated the wellbore temperature field, and analyzed the effect of foam quality and discharge rate on fracture. The results indicated that temperature obviously influences carbon dioxide state in the wellbore. The compressibility of foam fracturing fluid shouldn't be omitted in the foam fracturing design.4. Established a pseudo-3D fracture propagation model for the foam fracturing fluid behaved as power law fluid on the basis of special attributes of foam fracturing. The model is mainly made up of pressure drawdown equation, fracture width equation, fracture height equation, continuing equation, and state equation which depict the fluid flowing in the fracture.5. Deduced the pressure drawdown equation in the fracture when carbon dioxide foam fracturing fluid behaves as Hershel-Bulkley fluid, and established 2D fracture propagation model. The concrete solution was given, and the field instance calculation was conducted.6. Assessed the performance of common proppant and technology, launched rockcore mechanical test and studied core microproperty, established the experimental method of foam fracturing, simulated and analyzed the effect of fracturing fluid sensitive parameters on foam fracturing design, established foam fracturing design method and quality control system in the field, formed carbon dioxide foam fracturing technology whose traits are as follows: clear stimulation mechanics, definite well & layer selecting principle, perfect technique, high adaptability.7. Carbon dioxide foam fracturing technology was used in low permeability oilfield of Jilin, high condensate pool of Liaohe, and gas reservoir of Sinopec Northeast bureau. It was used in 26 layers of 22 wells; the success ratio was higher than 95%, and with obvious stimulation performance.8. Based on the carbon dioxide foam fracturing model and design methods, we compiled a convenient operating and friendly interface engineering design soft of carbon dioxide foam fracturing.