Methods and apparatus of adjusting matrix acidizing procedures are disclosed. An example method includes determining parameters of a wellbore fluid during a matrix acidizing procedure using at least a first sensor and a second sensor. The parameters include velocity of the wellbore fluid and a temperature difference between the first sensor and the second sensor. The method also includes, based on the parameters, determining a characteristic relative to an invasion length of a reactive fluid within the formation, the reactive fluid used in association with the matrix acidizing procedure.