Novel Thermal Technology Uses Two-Wellhead Wells

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 120413, ’A Novel Thermal Technology of Formation Treatment Involves Bi-Wellhead Horizontal Wells,’ by R.R. Ibatullin, SPE, N.G. Ibragimov, SPE, R.S. Khisamov, A.T. Zaripov, and M.I. Amerkhanov, Tatneft, originally prepared for the 2009 SPE Middle East Oil and Gas Show and Conference, Bahrain, 15-18 March. The Republic of Tatarstan possesses significant reserves of heavy oil and bitumen. The first pilot project on heavy-oil production through vertical wells dates back to the 1970s. A number of thermal methods were tested including in-situ combustion, cyclic-steam stimulation, and gas/steam-mixture injection. However, all these methods demonstrated their insufficiency. In 2006, a new pilot project was launched. This is a modified technology of steam stimulation through a pair of U-shaped horizontal wells. Introduction There are many applications of the steam-assisted gravity-drainage (SAGD) method in Alberta, Canada. The efficiency of the SAGD method greatly depends on the presence of water-saturated and shale interlayers in the reservoir section. In 2006, a new pilot project was launched in Ashalchinskoye field to test a modified low-pressure SAGD technology using a unique pair of U-shaped horizontal wells (two-wellhead wells) (Fig. 1). This technique overcomes some disadvantages of classic SAGD technology. This deposit occurs at approximately 78 m and has a rather complex structure. Water-saturated interlayers are found in the top and in highly oil-saturated zones of the formation, while shale stringers are found in the middle of the sequence. Both aquifers and tight, low-permeability, calcareous sandstones or a low-saturated reservoir can serve as the bottom of the formation. New Solutions To date, three pairs of U-shaped horizontal wells have been drilled in this area, with the length of horizontal wellbores from 200 to 400 m. The wells were drilled with a vertical drilling rig, hitting the surface at an angle, thus having two wellheads–vertical and slanted. Two parallel horizontal wells were completed with sand screens and were drilled one above the other at a vertical distance of 5 m between them. The process monitoring is carried out through vertical evaluation wells, and a fiber-optic cable is used for temperature measurement along the horizontal wellbore. The wells were completed by swabbing until mud and solids stopped being produced; then, steam was injected into both wells with the subsequent placing of the lower well on pump production; temperature was monitored along the wellbore length to determine lost-circulation zones and to control the profile of the wellbore heating.