Permeability Microstratification in Natural Sandstones

American Institute of Mining, Metallurgical and Petroleum Engineers, Inc. This paper was prepared for the 42nd Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Tex., Oct. 1–4, 1967. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Spherical flow tests in sandstones indicated a strong tendency for flow to follow the natural bedding planes. These results suggested that a cylindrical flow pattern be studied in the same rock. The latter tests for the ten samples studied, showed an unexpected type of microstratification. The flow took place in thin (0.1 inch thick) horizontal laminae. The apparent permeability of adjacent laminae varied widely in many cases. It is believed that this type of microstratification—if continuous—would cause premature breakthroughs and poor performances in gas cycling and miscible displacement projects. Introduction Darcy's law has always been the basis of reservoir engineering methods. In its infancy, reservoir engineering consisted mostly of predictions of fluid production as a function of the amount of drawdown in the production well. For this purpose, Darcy's law could be used in its simplest form— which points out that the flow rate of any fluid through a porous medium of any type or geometry is directly proportional to the pressure drop across the system. Later attempts to study problems such as water coning and the effects of well bore damage required the use of Darcy's law as a differential equation of flow at a point: (1)