Effect of Pressure on Vapor/Oil Gravity Drainage in Fractured Reservoirs

Abstract

Summary This fundamental research is part of a larger study in determining the capability of a solvent process, referred to as vapor/oil gravity drainage (VOGD), for enhancing gravity drainage of viscous oil in fractured reservoirs by the injection of solvent. The solvent can be designed to traverse the reservoir mostly in its vapor phase at the reservoir temperature and pressure. Heated solvent vapor can also be used to facilitate the propagation of solvent vapor in low-temperature reservoirs, taking advantage of both thermal- and solvent-recovery processes. The experimental setup and corresponding acquired data were previously introduced by the authors in Anand et al. (2018), in which the effects of temperature, solvent-injection rate, and solvent type [n-butane and dichloromethane (DCM)] were investigated. Results from Anand et al. (2018) indicated encouraging high oil rates and ultimate recoveries; results also demonstrated that the oil rates and recovery were affected by diffusion and dispersion (in the form of intrinsic gas rate), asphaltene precipitation, and capillary pressure. The intent of our present work is to further study the mechanisms behind VOGD—in particular, those related to operating pressure and solvent-vapor/oil capillary pressure. The results from this work show that the ultimate recovery and oil rate are positively correlated to the operating pressure; experiments conducted at 50 and 75% saturation pressure (Psat) yielded lower ultimate oil recoveries, ranging from 33 to 68% of original oil in place (OOIP), compared with the experiments conducted at 90% Psat (recovery of 70% OOIP). Moreover, n-butane performed better than DCM, and lower asphaltene precipitation was seen at lower Psat. The main drivers for these observations were found to be lower solvent solubility and larger capillary pressure values at lower values of Psat.

Laboratory Investigations on Field Gas Huff-n-Puff for Improving Oil Recovery in Eagle Ford Shale─Effect of Operating Conditions

“…This could be related to the cylindrical shape of the core and the more gradual component concentration gradients toward the core surface . Moreover, light crude components in the mixing zone have a higher tendency to partition into the injection gas. , Additionally, the molecular diffusion of the heavy crude oil components is slower than that of the light crude oil components as a result of the mass diffusivity–molecular weight dependence. − Thus, the composition of the effluents collected during the later soaking stages is heavier.…”

“…20 Moreover, light crude components in the mixing zone have a higher tendency to partition into the injection gas. 17,21 Additionally, the molecular diffusion of the heavy crude oil components is slower than that of the light…”

Small-Scale EOR Pilot in the Eastern Eagle Ford Boosts Production

“…During the huff stage, the injection gas in the fracture invades the matrix due to a large pressure difference between the fracture and the matrix and thus creates gas-oil mixing zones in the matrix. Thermodynamic equilibration redistributes the phase and composition in the mixing zone (Anand et al 2019;Tang et al 2020). During the soaking stage, thermodynamic equilibration redistributes the components at the fluid interface in the mixing zone according to the local composition.…”

“…Also, increasing gas expansion as pressure continues to drop could carry more crude oil from the matrix to the fracture (Mahzari et al 2019(Mahzari et al , 2020. When the huff 'n' puff process is operated at high interfacial tension (e.g., below the MCP), the lower huff pressure provides less driving forces for the mass transfer between the oil and the injection gas (Tang et al 2020;Sie et al 2018Sie et al , 2019Anand et al 2019). As the interfacial tension is reduced at elevated huff pressure (e.g., above the MCP), this mass transfer is greatly enhanced.…”

Investigation of Solvent-Assisted Gravity Drainage in a Packed Hele-Shaw Cell with Liquid Toluene over Bitumen

“…These solvents are only partially miscible in bitumen and can precipitate asphaltenes above a threshold solvent content. Asphaltene precipitation leads to an upgraded product oil and can inhibit both the gravity drainage and mass-transfer mechanisms. − Condensing solvent processes have not yet been implemented on a commercial scale, but an N-Solv pilot test was conducted on the Dover lease from 2014 to 2017 and showed promising bitumen production rates and high solvent recovery. More than 125,000 bbl of 8° to 14° API-upgraded bitumen was produced, and 80% of solvent injected was recovered.…”