The pressure of a reservoir is one of the most important parameters that is needed to calculate the hydrocarbon accumulation. Once the reservoir pressure is estimated, the fluid properties can be obtained via different correlations. Combined with the reservoir bulk volumes, the hydrocarbons in-place and recovery factor can be easily calculated. Consequently, if the estimate of the reservoir pressure is not accurate enough, it will be extremely difficult to determine the type of fluid we are dealing with; either saturated or undersaturated oil reservoir. In addition, it will be very challenging to accurately forecast production performance.    
During the last decades, the technology of Hydraulic fracturing plays one of the most important rule in the petroleum industry. It has become the magic tool for many companies to change the fields' status from non-economic to economic. The objectives of fracturing low permeability reservoirs and high permeability reservoirs are variant and defined by reservoir parameters. Besides that, hydraulic fracture provides a new method to determine reservoir pressure and to estimate reservoir permeability, this method is called After Closure Analysis (ACA) Technique. ACA is one of the two analyses that are obtained by performing a Calibration Test, which is usually done before executing main hydraulic job. The two main analyses of Calibration Test are Pre-Closure analysis, which is used to optimize the fracture design, and ACA to determine reservoir pressure and estimate reservoir permeability.
This paper illustrates some real cases that show the reasons why ACA is considered a very reliable technique to accurately determine the reservoir parameters with no considerable amount of funds compared to other counterparts' traditional techniques; like wireline formation testing (WFT) and pressure transient analysis (PTA). Also the paper shows how extra cost and non-productive time can be avoided if the right parameters are gotten on the rig site.