New Concepts of Dual-Completion for Water Cresting Control and Improved Oil Recovery in Horizontal Wells

Abstract

Abstract The primary advantage of horizontal wells is the long penetration and small pressure drawdown. Thus, horizontal wells have been used for developing reservoirs experiencing severe water coning problems. However, several field experiences indicate that horizontal wells are also not free from the problem of water coning (otherwise known as water cresting). In some field reports, water breakthrough into horizontal wells could be quite dramatic and tend to erode the merit of high deliverability. Field experiences also indicate that the horizontal well fluid inflow profile is not uniform along the well but rather asymmetrically skewed toward the heel of the well. Thus water tends to breakthrough first at the heel (downstream end) and spread toward the toe-end (upstream end) of the well. In this paper, the authors present the result of a tool developed to effectively evaluate the problem of pressure loss in the wellbore and its effect on water cresting in horizontal wells. The tool incorporates the effects of several factors such as in-situ pipe roughness, perforation size and perforation density, axial fluid influx and two-phase oil-water flow. The results could be extended to three-phase flow by adequate gas-liquid correlations. The paper also presents a study of two innovative concepts of "smart" completions for controlling water cresting in horizontal wells: "tail pipe water sink" and "bi-lateral water sink". The technologies involve the segregated production of oil and water in a dual completion with zonal isolation. The results of this research using commercial numerical reservoir simulators indicate that dual completions are capable of reducing the incidence of by-passed oil at the toe of horizontal wells and improve oil recovery by over 7 percent. Introduction The subject of control of water cresting in horizontal wells is yet to receive much attention as in vertical wells. This is, perhaps, due to the fact that the technology is relatively new compared to vertical well. Most publications recommend horizontal wells as a solution to developing reservoirs experiencing water coning1–7. However, the experience with water cresting in horizontal wells over the past decade have prompted some level of research to understand and control the influx of unwanted water into the wellbore. One of the earliest references to the problem of water cresting in horizontal wells underlain by water was the performance test by Elf Aquitaine in 1984. The well Lacq 90, in Lacq Superieur field completed with a slotted liner produced 19 BOPD in 4 years with a watercut of 99 percent8. Chugbo et. al.9 observed that using horizontal well technology as a solution to developing thin oil columns in unconsolidated sand deposit in a deltaic environment may be erroneous and dangerous. Also, Mobil's experience with a horizontal well to mitigate water coning in the Ness field, UK sector, was reported to be unsuccessful. "In a field where average water cut from conventional vertical wells was 40 percent, the completed horizontal well showed rapid rise in water cut averaging nearly 65 percent despite all careful well planning efforts"10. They, however, attributed the performance to geological uncertainties.