Transient flow in wellbores and phase transition of CO₂ during formation supercritical CO₂ invasion

Abstract

CO2 reservoirs and high CO2 content gas reservoirs in marine sediments generally have complex pressure system, which usually encounters supercritical CO2(SC‐CO2) invasion into the wellbore during drilling process. The wellbore transient flow and phase transition along the wellbore during the drilling process has not been thoroughly investigated, because the CO2 physical properties and the reservoirs petrophysical properties could affect the transient flow of mixed fluid and phase transition of CO2 along the well. A numerical model is presented in this research to analyze the transient flow in wellbores and to predict phase transition of CO2 during formation SC‐CO2 invasion in the drilling process. The main considerations were the following: multiphase transient flow in wellbores was coupled with the non‐Darcy flow through the formation; wellbore temperature, pressure and the mixture of drilling fluid and SC‐CO2 were calculated in the method of coupling; the invaded SC‐CO2 could affect the mixed fluid physical properties in the annulus; the change of physical properties of CO2 (eg, solubility, phase transition) was considered and integrated. The research results indicate that as the mixture of drilling fluid and SC‐CO2 flows from the bottom to the surface, the invaded CO2 is difficult to be detected at the early invasion stage because of high CO2 density and solubility; the CO2 would change from supercritical to gas phase and the dissolved quantity and density of CO2 rapidly decrease near the wellhead, and further cause well‐control issues. Furthermore, the bottom‐hole pressure (BHP) would decrease and could not provide sufficient balance to the formation pressure, which could significantly increase the risk of well blowout. Sensitivity analysis was utilized to evaluate the effects of the choke pressure, drilling fluid pumping rate, initial pressure difference, reservoir permeability, and drilled reservoir thickness on the BHP and the depth of phase transition of CO2.

Study on the Effect of High-Temperature Heat Treatment on the Microscopic Pore Structure and Mechanical Properties of Tight Sandstone

“…However, it is noted that the research on tight sandstone is lacking as compared with that on conventional sandstone. Tight sandstone reservoir is the key area of unconventional resource development in the world [23,24]. Due to the complex mineral components and diverse depositional environments, tight sandstones have various pore types and intricate fractures, joints, and bedding planes.…”

Numerical simulation of temperature field in crack of supercritical carbon dioxide fracturing

“…Supercritical carbon dioxide (SC‐CO 2 ) fracturing is regarded as a promising means in the development of the unconventional oil and natural gas on account of its great advantages of environmental protection and resource conservation . CO 2 (usually reach a supercritical state when the temperature is higher than 304.1 K and pressure is higher than 7.38 MPa in the fracturing crack in deep wells) is injected into the wells as a fracturing fluid to make cracks in the formation in order to form a flow channel for oil and natural gas from the reservoir to the well in supercritical carbon dioxide fracturing . Although the conventional hydraulic fracturing has huge contributions, the great water consumption (about 2.3 ~ 5.5 million gallons per well) and serious formation pollution (lots of chemical additives which will be harmful to formation) bring great challenges to environmental protection and economic cost.…”

Characterization of the Dynamic Imbibition Displacement Mechanism in Tight Sandstone Reservoirs Using the NMR Technique

“…Tight oil is a key area of global unconventional oil development [1]. Unconventional tight oil and gas resources in China are widely distributed and have great development potential [2,3]. Tight oil and gas resources are found in the Triassic strata of the Ordos basin, Permian strata of the Junggar basin, Cretaceous strata of the Songliao basin, Paleogene strata of the Bohai-Bay basin, and other strata, which have broad prospects of exploration and development [4].…”