Study on filtration patterns of supercritical CO 2 fracturing in unconventional natural gas reservoirs

Supercritical carbon dioxide (SC-CO 2 ) fracturing can form more complex fracture network and avoid reservoir damage, making it a lucrative alternative to hydraulic fracturing in shale gas reservoirs. This study establishes a two-dimensional dynamic filtration model of SC-CO 2 fracturing, which considers stress sensitivity, fluid adsorption, dynamic changes of fluid physical parameters, and coupled fracture propagation. According to the established model, the dynamic filtration of fracture elements and matrix pressure variation in fracture propagation are simulated and analyzed. And the influence of dynamic and static filtration model, constant and variable SC-CO 2 physical parameters, and fluid types in the filtration areas on the calculation results, as well as the effects of stress sensitivity and fluid adsorption on the filtration process are analyzed. The results show that during the fracturing process, fracture elements' average filtration rate gradually drops and finally becomes stable, while the cumulative filtration volume increases nearly linearly. The static filtration model of uncoupled fracture propagation or the simplification of fluid in the filtration areas to SC-CO 2 single phase provides the reduction of calculation results, while constant SC-CO 2 physical parameters or the fluid simplification to the methane (CH 4 ) single phase have the opposite effect. Stress sensitivity can accelerate the filtration, while fluid adsorption can slow down the filtration. The influence of stress sensitivity is maximal at the middle stage of fracturing, while the influence of fluid adsorption weakens with time. This study's findings have important guiding significance for the optimal design and field application of SC-CO 2 fracturing in shale gas reservoirs.

Section: Filtration Modelmentioning

confidence: 99%

Section: Filtration Modelmentioning

confidence: 99%

“…Based on the assumption of linear seepage, the motion equation of SC-CO 2 fracturing fluid in the intrusion area is as follows 19 :…”

Section: Filtration Modelmentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Numerical study on filtration law of supercritical carbon dioxide fracturing in shale gas reservoirs

Luo

Zhao

et al. 2021

“…Compared to other fracturing fluids, SC‐CO 2 has relatively lower viscosity, so its proppant‐carrying ability is not clear . So far, very limited research exists in the literature about the two‐phase flow of SC‐CO 2 and proppant.…”

Section: Introductionmentioning

confidence: 99%

Numerical study of supercritical CO₂ and proppant transport in different geometrical fractures

Wang

Yang

et al. 2018

Supercritical CO2 (SC‐CO2) fracturing, as a kind of waterless fracturing method, is an effective treatment in the unconventional oil and gas industry. Due to its characteristic lower viscosity, supercritical CO2 fracturing is likely to create thin and long fractures that connect pre‐existing natural fractures and generate complex fractures. It is therefore very challenging to predict how far supercritical CO2 carrying proppant can go and how proppant will be transported in natural fractures, when natural fractures are contacted or penetrated by induced fractures. In this paper, proppant transport with supercritical CO2 in fractures was analyzed using the computational fluid dynamics method. Three types of fractures – planar fractures, T‐shape fractures and crossing‐shape fractures – were modeled. Five parametrical cases were studied using the T‐shape and crossing‐shape models. Results show that, for T‐shape fracture cases, a turbulent flow regime might develop at a fracture junction, which can make proppant propagate to natural fractures. For crossing‐shape fractures, a turbulent flow takes place behind the fracture junction, which causes a little sand dune to form downstream of the induced fracture. With the reduction in the width of the natural fracture, the height of the sand bank at the thinner natural fracture is higher than that at the wider natural fracture. Using a proppant whose density and diameter are respectively less than 1540 kg/m3 and 0.25 mm, as well as a sand‐carrying fluid whose sand ratio ranges from 8% to 10% and injection rate exceeds 2 kg/s, is beneficial to prop natural fractures. Moreover, the larger the intersection angle of the crossing‐shape fracture is, the more difficult it is for proppant to enter natural fractures. This study reveals the influence of fracture geometry on proppant transport with SC‐CO2. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.

Transient temperature‐pressure field model of supercritical CO₂ fracturing wellbore with tubing and annulus co‐injection

Luo

Zhao

et al. 2021

The physical parameters of supercritical carbon dioxide (SC‐CO2) fracturing fluid are sensitive to temperature and pressure. Accurate prediction of wellbore temperature and pressure during injection is critical for the fracturing efficiency. In this paper, a transient pressure‐field model of SC‐CO2 fracturing wellbore with tubing and annulus co‐injection was established, which was adjusted to consider the Joule–Thomson effect, axial heat conduction, expansion/compression heat, and friction heat. The model predicted the variation patterns of wellbore temperature and pressure, comparing them with those under tubing injection conditions. Effects of tubing‐annulus injection ratios and endothermic mode on bottom‐hole temperature (BHT) and wellhead pressure (WHP) were analyzed in detail. Compared with pure tubing injection, co‐injection provided higher BHT and lower WHP. At constant BHP, WHP dropped with time in the processes of tubing injection or co‐injection, while the former provided a larger WHP drop. With an increase in tubing injection ratio, the difference between tubing and annulus BHT values slightly grew. When the tubing and annulus injection displacements were allocated according to their cross‐sectional area ratio, their WHP was minimal. If CO2 was assumed to absorb all the friction heat, overestimation of BHT and WHP would be observed, which was more pronounced at larger injection displacements. This study's findings are considered instrumental in the design optimization and field application of SC‐CO2 fracturing in unconventional reservoirs. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.