Rapid Evaluation of Shale Reservoirs Based on Pre-Frac Injection/Falloff Diagnostic Test

Shale gas reservoirs are characterized by extremely low permeability.Conventional build-up tests used for reservoir assessments have extremely low efficiencies due to the prolonged time required for detection of radial flows.On the other hand,pre-frac injection/falloff diagnostic test(also known as Diagnostic Fracture Injection Test,DFIT)can detect pseudo-radial flow in a short time,and consequently may quickly assess reservoir conditions.Based on that,design optimization was performed for shale gas reservoirs in the Fuling Area with consideration to equipment selection,injection flow rates,overall injection volume and properties of injection fluids.Research results showed that satisfactory test results could be obtained by using a flow-rate of 150-500L/min and by bumping for 10-30 min after formation fractured.The total volume of injection fluids should be maintained at 5-15 m3.DFIT had been conducted in 6 wells to assess the properties of shale gas reservoirs. Through G-function and ACA analysis using the acquired data,original formation pressures and effective reservoir permeability were determined and it was discovered that relevant results coincided well with formation test results. It had been verified that the DFIT could be used for rapid assessment of shale reservoirs.