Abstract
Horizontal wells are frequently used in gas reservoirs to enhance the production performance by increasing the contact surface of the well with the formation. Although some methods have been presented to evaluate vertical well productivity in tight gas reservoirs, the detailed information regarding horizontal wells has not yet been deeply addressed. This study uses a modified backpressure test method based on the isochronal test to determine the correct value of the productivity of horizontal wells in a pressure-dependent viscosity anisotropic tight gas formation. To use the isochronal test calculations in the modified backpressure test, the “process conversion-flowing pressure correction” approach was used to convert the modified backpressure test process into the isochronal test. The comparison between productivity values before and after correction with the simulation results validates that how this method can successfully estimate the productivity in horizontal wells. We perform a sensitivity analysis on the error between the pseudo-pressure before and after correction and show its variation with porosity, permeability, skin, formation thickness, and temperature. This can be helpful to understand the importance of correcting pseudo-pressure under different conditions. Results validate that the proposed method of productivity analysis is needed for horizontal wells and should be applied especially in low permeable and thin (tight gas) formations to acquire the precise value of productivity.
Highlights
This work focuses on the utilization of a backpressure test to evaluate horizontal gas well productivity in tight gas reservoirs via a straightforward superpositionbased method
A modified backpressure test was performed to estimate the productivity of the horizontal gas well
The results show that the corrected data are in perfect agreement with the data calculated by the numerical model, which validates that the proposed method can successfully deliver the accurate productivity of a horizontal gas well
Summary
Dana Energy Company, Tehran, IranHorizontal wells are applicable in low- as well as high-permeability gas reservoirs (Joshi 1991; Weihong et al 2005). An experimental and theoretical investigation of multilateral/dual lateral horizontal well productivity in areally anisotropic reservoirs was presented by Yildiz (2005) These studies, did not provide an applicable incorporation of well testing and productivity estimation method for unconventional reservoirs. Clarkson et al (2012) extended the dynamicslippage concept to shale gas formations They developed a numerical model that accounts for multi-mechanism flow and modified the modern rate-transient analysis methods to include the dynamic slippage and desorption effects. Clarkson (2013) reviewed analytical, numerical and empirical methods of production analysis in unconventional gas reservoirs He provided field examples and discussed the future development of production data analysis techniques. This work focuses on the utilization of a backpressure test to evaluate horizontal gas well productivity in tight gas reservoirs via a straightforward superpositionbased method
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