A simulation method for modified isochronal well testing to determine shale gas well productivity

A simulation method to determine shale gas well productivity is developed based on modified isochronal well testing. The method is reliable and accurate and reduces the well testing time. First, the physical properties and wellbore parameters of the reservoir are obtained using the production data analysis method or well testing method. Then the production sequence and time sequence are determined. The production sequence is estimated by the production data analysis method, which can calculate gas well production under different pressures. The testing time interval and duration are determined by using the time value of the inflection points on the curve of the productivity coefficient and the time sequence. A modified isochronal well testing simulation model is developed based on the dynamic change patterns of the reservoir and well tubing, the production sequence, and time sequence. Finally, the simulation model is solved by the conventional production well test regression method, and the well productivity and open flow potential are calculated. Using a shale gas well in the Changqing oilfield, China, as a case study, field test results and simulation result are analyzed and compared. The results confirm the reliability of the new method in a shale gas reservoir; the precision of the shale gas productivity evaluation improved and the cost and duration of the test were reduced. This method can be expanded to other unconventional tight gas reservoirs.