Even though it has long been recognized that pressure drop along a horizontal wellbore cannot be neglected, little has been done to estimate the pressure drop with any rigor. The existing models are derived jPom pipeflow equations, neglecting, therefore, the presence of radial fluid movement perpendicular to the direction of bulk fluid flow. Recent experimental studies indicate that such a simplistic approach provides an optimistic behavior in a horizontal wellbore. This paper presents a realistic representation of the pressure drop in a horizontal wellbore. Equations are derived from rigorous experiments conducted earlier and reported in the literature. They include the effect of radial fluid movement, perforation flow, gas-oil ratio, oil viscosity, bulk flow rate, water saturation, and even the presence of asphaltenes in the crude oil. Even though the equations are based on experimental results, predictions apply to Jeld situations. This aspect is verified with certain unpublished field data from USA and Canada.
The use of horizontal wells has significantly increased in recent years. However, mathematical modeling of pressure drop in the horizontal well has been neglected in this research. Pressure drop has been found to be a very important aspect of horizontal well analysis. Aziz and Arbabi' pointed out that performance prediction in horizontal wells is considered to be a very difficult task. Ahmed and Badry2 recognized the increase in horizontal well usage and noted the effects of pressure changes on well productivity. Dikken3 concluded that the pressure drop in the wellbore cannot be neglected in order to obtain realistic prediction of field performance with horizontal wells. Also, Doan et al.4 pointed out the importance of pressure drop along the wellbore of a horizontal well, especially during initial production periods of a steam injection process (when the oil viscosity is high). Lackner and Economides5 noted the importance of pressure changes in horizontal wells by combining vertical and horizontal pressure gradient curves to predict the pressure loss in horizontal wells. However, this study was conducted over the entire length of the well and did not focus on the horizontal portion. Also, this study resulted in pictorial representations of pressure drop instead of algebraic solutions. Many studies on pressure drop in horizontal wells simplify the system by neglecting perforations and multiphase flow. Collins et al.6 reported a simplistic model for simulating flow in a horizontal well in a field. They used Darcy's law in a dual porosity representation of a horizontal well. This model unnecessarily introduces simplicity and does not deal with wellbore dynamics with any rigorousness. Jelen7 used a new technique for solving fluid flow equation in different domains independently. This method was particularly useful for modeling a horizontal well in which several domains exhibit different types of fluid flow. This paper deals with the development of simple polynomial equations that may be used to predict pressure drop in horizontal wells. By using past experimental data by Islam and Chakma8, it examines the difference between pressure drop in wells with and without perforations and it shows the important role that perforations play.