Effectiveness and sensitivity analysis of solution gas re-injection in Baikouquan tight formation,Mahu sag for enhanced oil recovery

To address the fast productivity decline of the horizontal wells and low oil recovery during natural depletion in Baikouquan formation,the approach of solution gas re-injection was proposed with the primary objective of further developing this formation.Herein,a field-scale numerical compositional reservoir model was built up based on the formation properties and then the effects of permeability,fractures and formation stress on the production dynamics were thoroughly investigated.A sensitivity analysis,which can correlate the oil recovery with these parameters,was also performed.The results showed that the re-injection of solution gas could remarkably retard the production depletion of the horizontal wells thereby improving the oil production.The oil recovery rate increased with permeability,fracture half-length,fracture conductivity,and formation dip.With regard to the fracture distribution,it was found that the interlaced fracture outperformed the aligned fracture for the solution gas re-injection.The influence of the formation stress should be carefully considered in the production process.Sensitivity analysis indicated that the formation dip was the paramount parameter,and the permeability,fracture half-length,and fracture conductivity also played central roles.The results of this study supplement earlier observations and provide constructive envision for enhanced oil recovery of tight reservoirs.

Influence of supercritical CO_(2)on the physical property of tight sandstone

In low-pressure gas reservoirs,water-based fracture fluid is difficult to flowback,which is unfavorable for several tight sandstone gas reservoirs in the Sichuan Basin with low pressure and high permeability geological characteristics.Supercritical CO_(2)possesses a number of remarkable physical and chemical features,including a density near to water,a viscosity close to gas,and high diffusion.Supercritical CO_(2)fracturing is a new type of non-aqueous fracturing method that is favorable to fracturing flowback in low-pressure tight sandstone and has a wide range of applications.To discuss on whether supercritical CO_(2)fracturing with low pressure tight sandstone is feasible.Tight sandstone cores from the Jinqiu gas field in the Sichuan Basin were used to study the influence of supercritical CO_(2)on the physical properties of sandstone reservoirs.Supercritical CO_(2)was used to interact with tight sandstone samples,and then the changes in porosity,permeability,and rock microstructure of tight sandstone were observed under various time,pressure,and temperature conditions.After the interaction between tight sandstone and supercritical CO_(2),new dissolution pores will appear,or the original pores will be increased,and the width of some natural fractures will also be increased,and the porosity will increase by 1.09%-8.85%,and the permeability will increase by 2.34%-21.26%,quantifying the influence of supercritical CO_(2)on physical properties of tight sandstone,and further improving the interaction mechanism between supercritical CO_(2)and tight sandstone.This study improves in the understanding of the tight sandstone-supercritical CO_(2)interaction mechanism,as well as providing an experimental foundation and technological guarantee for field testing and use of supercritical CO_(2)in low-pressure tight sandstone gas reservoirs.