Copyright 2001, Society of Petroleum Engineers Inc. This paper was prepared for presentation at the SPE Asia Pacific Improved Oil Recovery Conference held in Kuala Lumpur, Malaysia, 8–9 October 2001. This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435. ABSTRACT Many horizontal wells are being drilled all over the world to increase their productivity in comparison to that of vertical wells. Horizontal wells increase reservoir contact area and thus increase productivity. Therefore, it is essential to be able to predict the horizontal well productivity. The major objectives of this investigation are to: (1) develop a comprehensive evaluation of currently- used steady-state productivity equations of horizontal well, (2) investigate the effect of horizontal well length and pay zone thickness on the productivity ratio of horizontal well to vertical well, when both having the same drainage area and under identical flow conditions, and (3) study the influence of pressure drop on production rate of horizontal wells using different steady-state flow equations. In this study, six different steady-state equations of the open-hole horizontal wells under identical conditions of flow parameters and reservoir geometry are subjected to a wide ranges of horizontal well lengths (100 to 3,000 ft), pay zone thickness (50 ft to 500 ft), and pressure drop (10 psi to 200 psi). These horizontal wells were used to calculate the productivity and to study the influences of flow rate and pressure drop on the sensitivity of these equations. The obtained results showed that all steady- state equations provide similar horizontal well productivity for horizontal well length < 1000 ft, while a remarkable difference appears and increases when well length increases > 1,000 ft. In addition, the results using all steady-state equations confirmed the recommendation of the application of horizontal well for thin formations and do not recommend it in thick ones (h> 250 ft) for wells having identical rock and fluid properties. Comparing the performance of steady-state equations showed that all of these equations are sensitive to the increase of pressure drop, which yields an increase in flow rate of horizontal well. The results of this study have important implications in reservoir simulation studies, since it evaluates some important variables including pay zone thickness, well length, and pressure drop on the performance of each flow equation. INTRODUCTION Over the past several years, horizontal well technology becomes one of the hot topics of the oil industry. The publicity of horizontal wells advantages over the vertical wells devoted the effort SPE 72121 Sensitivity Analysis of Horizontal Well Productivity under Steady-State Conditions Shedid A. Shedid, Suez Canal University, Petroleum Eng. Dept., Suez City, Suez, EGYPT. Abdulrazag Y. Zekri, United Arab Emirates University, Al Ain 17555, U. A. E. SPE Members