Unconventional gas reservoirs are basically reservoirs having very low permeability and high anisotropy, which demands particular recovery processes compared to the conventional performing practices. These reservoirs include tight gas, shale gas, and coalbed methane deposits. Production optimization of these reservoirs requires drilling of horizontal wells and applying hydraulic fracturing technique. Well test analysis for unconventional reservoirs is one of the most important methods for analyzing and evaluating these reservoirs. In addition, Gas wells deliverability tests are very important for analyzing the production data of unconventional gas reservoirs. This paper presents the results and analysis of flow after flow test which was conducted on a horizontal well located in tight gas carbonate reservoir in Apollonia formation, Western Desert, Egypt. This reservoir has an original permeability of 0.1md. Horner plot, MDH plot, pressure-difference plot and derivative function were used to analyze the pressure buildup data after performing eight hydraulic fracture stages. The analysis depicts that the permeability and skin factor are improved to 5.5 md and -4.5 respectively. According to the analysis of diagnostic plot, there is a high wellbore storage value of 0.224 bbl/psi and no skin hump. The analysis of middle time region shows a radial flow; however, the late time region shows a linear flow due the performed eight hydraulic fracture stages. The analysis of deliverability plot depicts that the absolute open flow is 5.5 MMSCF/D and the production performance coefficient is 0.0014 MSCF/D/psia2 . This work proves the success of the 8 stages hydraulic fracture stimulation job that has been done. In this paper also, a new spread sheet program was developed to perform all required plots and calculations. The results of this program are compared with the results of two commercial softwares (Pansystem and Saphir) and give the same results. The developed spread sheet program accurate, easy to run and not expensive.