Abstract
Slickwater fracturing has become one of the most leveraging completion technologies in unlocking hydrocarbon in unconventional reservoirs. In slickwater treatments, proppant transport becomes a big concern because of the inefficiency of low viscosity fluids to suspend the particles. Many studies have been devoted to proppant transport experimentally and numerically. However, only a few focused on the proppant pumping schedules in slickwater fracturing. The impact of proppant schedules on well production remains unclear. The goal of our work is to simulate the proppant transport under real pumping schedules (multi-size proppants and varying concentration) at the field scale and quantitatively evaluate the effects of proppant schedules on well production for slickwater fracturing.
The workflow consists of three steps. Firstly, a validated 3D multi-phase particle-in-cell (MP-PIC) model has been employed to simulate the proppant transport at real pumping schedules in a field-scale fracture (180 m length, 30 m height). Secondly, we applied a propped fracture conductivity model to calculate the distribution of propped fracture width, permeability, and fracture conductivity. In the last step, we incorporated the propped fracture geometry and conductivity distribution into a reservoir simulation model to predict gas production.
Based on the field designs of pumping schedules in slickwater treatments, we have generated four proppant schedules, in which 100-mesh and 40/70-mesh proppants were loaded successively with stair-stepped and incremental stages. The first three were utilized to study the effects of the mass percentages of the multisize proppants. From schedules 1 to 3, the mass percentages of 100-mesh proppants are 30%, 50%, and 70%, respectively. Schedule 4 has the same proppant percentage as schedule 2 but has a flush stage after slurry injection. The comparison between schedules 2 and 4 enables us to evaluate the effect of the flush stage on well production.
The results indicate that the proppant schedule has a significant influence on treatment performance. The schedule with a higher percentage of 100-mesh proppants has a longer proppant transport distance and a larger propped fracture area. However, fracture conductivity after fracture closure decreases. Then, the reservoir simulation results show that both the small and large percentages of 100-mesh proppants cannot maximize well production because of the corresponding small propped area and low fracture conductivity. Schedule 2, with a median percentage (50%) of 100-mesh proppants, has the highest 1000-day cumulative gas production. For schedule 4, the flush stage significantly benefits the gas production by 8% because of a longer and more uniform proppant bed along the fracture.
This paper, for the first time, provides both the qualitative explanation and quantitative evaluation for the impact of proppant pumping schedules on the performance of slickwater treatments at the field scale, providing crucial insights for the design of proppant schedules in the field slickwater treatments.
