Dynamic Characteristic Evaluation Methods of Stress Sensitive Abnormal High Pressure Gas Reservoir

Abstract

Abstract Gas reservoirs with abnormally high pressure have been encountered all over the world. Due to unusual stress environments, a potential impact to reservoir performance is the stress-sensitive permeability. The result of skin factor will be abnormally positive if we interpret the sensitive data using traditional welltesting analysis software. Interpretation of well testing and performance prediction is a major challenge. This paper establishes a numerical well test model and develops a simulator by finite element method with consideration of stress sensitive permeability. LOG-LOG curves are obtained and their characteristics are analyzed. In the earlier period, the pressure response of sensitive reservoir is identical to that of the normal reservoir. In the latter period, the pressure reservoir reaches a semi-log straight line, but the value of the derivative curve is less than 0.5. The transitional period is controlled by sensitive permeability. For lower permeability module, the transitional period is longer. In the log-log plot, the distance between pressure and pressure derivative is larger than the normal reservoir. Permeability modulus will be obtained by log-log analysis. An evaluation method of the effect of stress sensitivity on gas deliverability is presented using the concept of permeability modulus. By combining the LIT equation with the material balance equation, the performance prediction model is also established. The tank material balance equation for gas reservoirs has been written taking into account the effective compressibility of formation. This paper presents an analysis of a flow after flow test in the Tarim abnormally, stress-sensitive gas reservoirs. The effect of stress-sensitive permeability on well test response is analyzed through numerical simulations. Permeability modulus is about 0.01MPa−1; Skin is −1.48 ( traditional software is 60.8; qAOF decrease is 14%; period of stabilized production decrease is 5.5 a; and, degree of reserve recovery decrease is 6.8%. The interpretation results show that numerical well test analysis can accurately identify gas reservoir parameters and acidizing effectiveness and that the decrease degree of gas deliverability is different and depends on the ‘permeability modulus’ in the formation on which the gas well is located.