Least squares method (LSM) is an accurate and rapid method for solving some analytical and
numerical problems. This method can be used to estimate the average reservoir pressure in well test
analysis. In fact, it may be employed to estimate parameters such as permeability (k) and pore
volume (Vp). Regarding this point, buildup, drawdown, late transient test data, modified Muskat
method, interference test, and other methods are equivalent to a separable least squares problem.
The main advantage of LSM in the well testing problems is that the results would be confident and
no trial and error is required. Furthermore, the given method requires a short time. The fast rate of
convergence and high accuracy of the LSM are demonstrated through two examples. The current
study concerns a modified Muskat method. The results of LSM combined with the modified Muskat
method are compared with the other iterative and qualitative methods. The preliminary numerical
results with both simulated and field data suggest that the method be capable of producing smooth
interpretable estimates of reservoir parameters from data.