GGU-SLUGTEST: Type curves methods - several approaches
An expansion of the solution after COOPER by five additional type curves was presented by PAPADOPULOS et al. (1973) once they had recognised that the existing values for 
were only sufficient for the evaluation of tests in layers of high permeability. PAPADOPULOS et al. (1973) also commented on the relatively large uncertainty of the method when determining the storage coefficient.
With the pressurised slug test, BREDEHOEFT & PAPADOPULOS (1980) introduced an alternative to the classical slug tests. The borehole being investigated is filled to the top with water and then a pressure impulse applied. The head of the borehole is closed by a valve and the subsequent pressure loss registered. This procedure is suitable for very low permeability layers because it allows the test duration to be substantially reduced. The storage capacity of the borehole is now no longer determined by the free water column, but by the compressibility of the enclosed volume of water.
However, this model assumes that the rock and the testing equipment are incompressible. But this is not very realistic. In reality, the compressibility of the whole system, consisting of the enclosed water volume, the rock and the measuring equipment must be known.
The skin effect was considered by RAMEY et al. (1975), adopting the COOPER et al. (1967) approach. They showed that it is possible to combine the storage constant and the skin factor to a single fingerprint parameter CD e2s for recalculation of type curves. However, their solution only applies to an infinitesimal skin zone and for curve parameters CDe2es ≥ 10 (MOENCH & HSIEH, 1985 a,b).
FAUST & MERCER (1984) investigated the influence of a finite skin zone on the determination of transmissivity in layers of low permeability, with the aid of a numerical model. According to their calculations, a positive skin factor, caused by a zone of lower permeability than the surrounding rock, can lead to an incorrect appraisal of the true transmissivity. There is a hazard here of measuring not the transmissivity of the rock mass, but that of the skin zone.
This assessment was nevertheless cast in doubt by MOENCH & HSIEH (1985 b). On the contrary, they are of the opinion that the transmissivity would be correctly determined despite a positive skin factor.
An imperfect well with wellbore storage is the subject of a model by DOUGHERTY (1989). A skin is not taken into consideration in the analytical solution.