Investigation on flow regimes and non-Darcy effect in pressure test analysis of horizontal gas wells

Abstract

Abstract Transient pressure test of horizontal wells compared to vertical wells is more complicated due to the occurrence potential of different transient flow periods. Although various mathematical models were developed for horizontal well test analysis their evaluation in different well and reservoir conditions needs more investigation. In specific, in vertical wells non-Darcy flow which causes an extra pressure drop, has a significant impact on well test data but its impact on horizontal well test data needs more investigation. The objective of this paper is to examine transient pressure behavior of horizontal gas wells under various conditions including high velocity flow. For this purpose, a horizontal gas well in a finite rectangular reservoir with typical geometry is simulated using a commercial reservoir simulator. Synthetic well data are used to plot pseudo-pressure derivative curves which identify appeared flow regimes. Sensitivity study is done considering relative well lengths and well location with respect to horizontal boundaries as well as non-Darcy flow parameter. The results show that the appearance of elliptical and pseudo-radial flow regimes depends on relative well length and formation thickness. In addition, the effect of off-centered wells with respect to upper and lower boundaries in transient pressure data is expressed. The results also show that non-Darcy flow can cause a significant skin in transient data of a horizontal gas well. Magnitude of the skin is mainly affected by reservoir permeability and production rate of the horizontal well. Contrary to the general belief regarding negligible effect of non-Darcy flow in analysis of horizontal gas well test, this study showed that it can cause a significant error in analysis of the well test data.