A New Approach for Optimization of Long-Horizontal-Well Performance

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 18372, “A New Approach for Optimization of Long-Horizontal-Well Performances,” by Abdullah Al Qahtani, Hasan Al Hashim, and Hasan Al Yousef, King Fahd University of Petroleum and Minerals, prepared for the 2015 International Petroleum Technology Conference, Doha, Qatar, 7–9 December. The paper has not been peer reviewed. Copyright 2015 International Petroleum Technology Conference. Reproduced by permission. Initially, it was believed that a horizontal well should be drilled with as much length as possible. However, field experience and flowmeter surveys in long horizontal drainholes revealed that the frictional pressure loss in the wellbore is an important factor hindering the full use of the entire length of the horizontal well. This paper presents a new approach to maximize the use of the full length of long horizontal drainholes. Introduction Horizontal-well drilling allowed the drilling of different well architectures and made it possible to offset well costs and productivity limitations. Intuitively, drilling longer wells will maximize exposure to the producing formation and yield higher flow capacity. Paradoxically, however, some wells were drilled longer than the optimal horizontal-section length and the extra length did not yield additional flow. Therefore, it is important to determine the optimal horizontal-section length that would achieve flow contribution along the whole section. Experience has revealed that long horizontal wells suffer from frictional pressure losses. This fact is exacerbated in the presence of highly productive formations; these would require low pressure drawdowns that may well be similar to the frictional pressure losses, which would therefore hinder wellbore flow ingress. Thus, some horizontal wells are equipped with downhole flow-choke systems to optimize well productivity. Finite-Conductivity Horizontal Wells Horizontal wells are initially deemed to be infinite-conductivity wellbores; this thesis was made on the basis of the fact that the magnitude of the pressure drop in the wellbore is negligible. Practically speaking, however, production data proved otherwise; frictional pressure losses in horizontal wellbores hinder flow influx to different degrees along the horizontal section. This issue is of great importance under conditions in which the magnitude of the pressure drop in the wellbore is small when compared with the magnitude of the pressure drop in the reservoir. Therefore, given the fact that horizontal wells are often proposed and justified on the premise that high production rates can be obtained by small reservoir pressure drops, and the fact that flow developed at reasonably high production rates should cause increased wellbore pressure losses, the use of the infinite-conductivity assumption for horizontal wells may not be valid.