Study on Proppant Transport in Fractures of Supercritical Carbon Dioxide Fracturing

Abstract

Supercritical carbon dioxide (SC-CO 2 ) fracturing is a promising stimulation treatment in the unconventional oil and gas industry, which combines the utilization of greenhouse gas and the development of energy resources. Aiming to study the proppant transport in fractures, which is one of the most important issues in this technology, a generalized and pragmatic numerical method coupled with multiphase flows, physical property models of CO 2 , and heat and mass transfer in the formation rock has been established to calculate the proppant transport in fractures of SC-CO 2 fracturing. Experimentally, experimental validation of the proppant transport was conducted, which verifies the accuracy of the simulation results. Combining experimental and simulation results, the flow condition of proppant−CO 2 two-phase flow was divided into a stationary layer, a rolling layer, a saltatory layer, a suspending layer, and a pure liquid/gas layer. Numerically, movement laws of proppant beds in fracture and influence factors on the distribution of proppant beds were analyzed. Proppant bed was formed near the inlet of the fracture at the initial stage of fracturing, and the height and length of the bed would increase concurrently until reaching a steady state. The equilibrium height has positive correlations with the injection temperature, proppants' volume fraction, density, and diameter and negative correlations with the injection pressure and displacement. Nevertheless, the equilibrium time has negative correlations with all these factors except pressure. Additionally, the proppant transports of SC-CO 2 and water were compared, which indicated that water has better proppant-carrying capacity with lower proppant bed height and longer proppant bed length at the same fracturing time. The distribution of the proppant bed with the structure of a nozzle inlet is relatively homogeneous in the near-wellbore zone of the fracture compared to the cuboid structure, which could reduce the risk of fracture closure in the near-wellbore zone. Results obtained in this paper could provide references for SC-CO 2 fracturing design which would promote the development of this technology.

Effects of a Viscoelastic Surfactant on Supercritical Carbon Dioxide Thickening for Gas Shale Fracturing

“…The proppant-carrying capacity of Sc-CO 2 is relatively weaker than that of the conventional fracturing fluid and slick water due to its low viscosity. Increasing the viscosity of Sc-CO 2 will enhance its proppant-carrying capacity and it will go one step further in the implementation of Sc-CO 2 as an alternative to the conventional fracturing fluid.…”

Full-Sample X-ray Microcomputed Tomography Analysis of Supercritical CO2 Fracturing in Tight Sandstone: Effect of Stress on Fracture Dynamics

“…Although fractures are relatively narrow in aperture, the presence of several fracture branches tends to facilitate the development of conductive fracture networks. In field applications, proppants are pumped to keep the fractures open and further enhance oil and gas production. , …”

“…The significant decline in the production of conventional oil and gas reservoirs around the world has led to the commercial development of unconventional resources, such as tight sands. However, the efficient development of these resources still faces numerous challenges. − As of this writing, the commercial development of unconventional oil and gas reservoirs typically involves the multistage hydraulic fracturing of horizontal wells by injecting a mixture of water and chemical additives (known as slickwater) at high pressures . This inevitably leads to problems such as clay swelling (in formations with clay minerals), environmental contamination, and formation damage, among others. − Therefore, various researchers have considered the use of other fracturing fluids that minimize formation damage and are more environmentally friendly.…”

Supercritical Carbon Dioxide Utilization for Hydraulic Fracturing of Shale Reservoir, and Geo-Storage: A Review

“…69,92 For monitoring the fracturing process like fracture initiation, propagation and closure in the specimen, acoustic emission (AE) a nondestructive testing tool is used when shale specimens are under compressive load. 21,82,93,94 After fracturing, the study of the morphology of fracture network created by Sc-CO 2 a nondestructive high-energy computed tomography (CT), digital radiography (DR) (applicable when specimen breaks into 2 pieces) used for visual observation of fracture surface, type, and propagation. 50,95 While Stylus and Optical Profilometry define the roughness and complexity of fracture.…”