Releasing Shale-Gas Potential with Fractured Horizontal Wells

Erdal Ozkan
Colorado School of Mines

Abstract
In the last decade, our understanding of shale reservoirs has progressed significantly.  It is now agreed that a major factor for the productivity of shale reservoirs is the existence of a pervasice reservoir fracture network around the well.  Accordingly, a common practice is to use hydraulically fractured horizontal wells to improve the connection with the reservoir fractures.  Flow in these unconventional systems is considered linear in the fractured volume around the well and is usually interpreted with conventional reservoir engineering wisdom.  The flaw in this interpretation is an accurate accounting of the matrix contribution due to the unconventional nature of flow in nanodarcy shale matrix.

This lecture presents a discussion of the characteristics of shale reservoirs and their impact on the performance of fractured horizontal wells.  Various flow mechanisms in shale matrix and fluid transfer from matrix to fracture network are explained.  Key parameters of productivity are identified and explained.  Emphasis is given to the estimation of the extent of the reservoir fracture network, prediction of the efficiency of matrix drainage, and their impact on the estimation of well's drainage volume.  The main idea to take away from this lecture is that some of conventional reservoir engineering interpretations and practices may not be adequate (or appropriate) for shale reservoirs.  For example, hydraulic fracture conductivity is usually not a key parameter for wells in shale reservoirs.  Examples are presented to highlight practices/problems in the interpreation of well performance from fractured horizontal wells in shale reservoirs.

Biography
Dr. Erdal Ozkan is a professor of Petroleum Engineering and co-director of Marathon Center of Excellence for Reservoir Studies at Colorado School of Mines.  Previously, he was on the faculty at Istanbul Technical University.  he has BS and MS degrees from Istanbul Technical University and a Ph.D. degree from the University of Tulsa, all in Petroleum Engineering.  His research interests are horizontal well technology, pressure-transient analysis, modeling fluid flow in porous media, and shale reservoirs.

Dr. Ozkan has authored and co-authored over one hundred technical papers, co-authored a book, and contributed chapters to the well Testing Monograph and Reservoir Engineering Handbook of SPE.  He has served as the Executive Editor of SPEREE, Chief Editor of The Journal of Petroleum Science and Engineering, and the Associate Editor of JERT.  He was involved in the organization of serveral SPE conferences, forums, and workshops including the recent meetings on shale reservoirs.  Dr. Ozkan is a member of the SPE RD&D Advisory Committee and a Technical Director of the SPE Research and Development Technical Section.  He is a Distinguished Member of the SPE and recipient of the 2007 SPE Formation Evaluation Award.