Pressure Drop in Perforated Pipes: Experiments and Analysis

Abstract

SPE Members Abstract The total pressure drop in horizontal wells is considered to consist of reversible (acceleration) and irreversible (wall friction, perforation roughness, mixing effects) pressure drop. The fundamental equations for pressure drop are presented along with relationships used for pipe junction flow. Experiments on a perforated pipe with 144 perforations, geometrically similar with wellbore casing (12 SPF, 600 phasing), are presented and analyzed. The results are applied to a typical horizontal oil well in the North Sea. It was found that the total pressure drop consists typically of 80 percent wall friction, 15 percent mixing effects (including perforation roughness) and 5 percent pressure drop due to acceleration. Introduction The total pressure drop in horizontal oil wells is dominated by frictional effects, but not gravitational effects as in vertical wells. And because more and longer horizontal oil wells are being drilled around the world, a better understanding of the factors affecting the total pressure drop is required. Increased knowledge about the total pressure drop will make it easier for petroleum engineers to optimize completion designs. Almost all papers dealing with the performance of horizontal wells consider only the wall friction part of the total pressure drop. Pressure drop in horizontal wells has been studied by such authors as Dikken, Asheim et al. and Landman. Dikken assumed that the total pressure drop was due to wall friction. Landman formalized the approach of Dikken and added the pressure drop through the perforation tunnel. Asheim et al. included the effect of acceleration in their estimation of the total pressure drop. Su and Gudmundsson considered the pressure drop due to perforation roughness. We are carrying out pressure drop experiments in perforated pipes that are geometrically similar to perforated liners used in horizontal oil wells. In the experiments we are using liquid water at wellbore and perforation conditions typical for horizontal wells in the North Sea. The work reported in this paper is from the second phase of our on-going studies on the pressure drop in perforated pipes. This paper follows an earlier paper on the friction factor of perforation roughness in pipes, where there was no flow through the perforations. PRESSURE DROP EFFECTS We find it convenient to divide the total pressure drop in horizontal wells into reversible pressure drop and irreversible pressure drop. The reversible pressure drop is that due to the acceleration as more fluid enters the wellbore through perforations. The magnitude of this acceleration term in calculations depends on whether the momentum or energy equation is used, as will be discussed. Another way of expressing the meaning of the acceleration pressure drop is to say that the momentum of the fluid is changed from one state of momentum to another (higher) by the action or process of acceleration. The irreversible pressure drop is that due to pipe wall friction, perforation friction and mixing effects. P. 563^