RIASSUNTO
Abstract
The drilling of multi-lateral wells is an established process, but the selective entry, and reentry of single, or multiple, lateral wellbores is an engineering problem that is still being addressed. The economic rewards from multi-lateral wells have not been reliably understood due to the unpredictable nature of overall costs versus performance. Poor capabilities for reservoir surveillance contribute to the difficulties in evaluating production performance and drainage efficiency from individual zones. Performance evaluation can be M e r complicated by effects of cross flow from adjacent heterogeneous zones.
This paper presents a completion system that allows recovery of considerable reserves from the 'A' and 'B' zones of the Shuaiba reservoir in the Idd El Shargi North Dome Field, while providing cost effective reservoir surveillance of zones drilled with horizontal multi-lateral well technology.
Introduction
The Idd El Shargi North Dome Field (ISND) is situated in the Arabian Gulf, 90 kilometers east of Doha, Qatar (Fig 1). The discovery well for ISND, IS-2, was drilled in 1960. Production began in 1964.
Initial production from the field was from Jurassic Araej and Uwainat Formations. Production was later achieved from the Jurassic Arab Formation and Cretaceous Shuaiba Formation. The majority of production is from the Arab 'C', Arab 'D', and Shuaiba Formations. About 2.0 billion bbls of the ISND Fields 4.2 billion bbls OOIP are in the Shuaiba Formation. Still, the reservoir is relatively undeveloped. The Shuaiba is a carbonate formation with reservoir top at about 4500 feet subsea and capped by the Nahr Umr Shale. A 600 ft oil column is divided into 4 geologic zones, the Shuaiba 'A', 'B', 'C', and 'D'. The Shuaiba 'A' and 'B' intervals, with average porosity of 24% and permeability of 5 md, hold 82 percent of the Shuaiba OOIP. The intervals are separated by a tight layer in many areas of the field. With an existing infrastructure already in place, the low permeability Shuaiba 'A' and 'B' intervals are prime candidates for horizontal multi-lateral development that can optimize use of remaining well slots and production facilities.
Well IS-76 was selected as the first horizontal multilateral completion candidate. The main borehole was drilled to a horizontal orientation in the Shuaiba 'B' interval, and 9- 518"" casing cemented in place. The casing string included an oriented predrilled casing exit window. This was run in the casing string at the depth where the lateral borehole was to be drilled into the Shuaiba 'A' interval. The orientation of the pradrilled casing exit window was to the high side of the casing (to prevent any debris entering the lateral bore at a later date). After cementing the casing in place, and subsequent clean out work, a drilling whipstock was run in the well.