A Practical Drill-Stem Testing Technique, Combining High Shot Density Underbalanced Perforating With Full Bore Test Tools

Abstract

Abstract Since 1976 Gulf Canada Resources Inc. through partnership arrangements, has participated in several offshore exploratory wells drilled and tested from artificial islands and drillships in the Canadian Beaufort Sea. As an operator since 1980, Gulf has drilled and evaluated a number of additional offshore wells to depths of 4800 m (15,750 ft) in as much as 30 m (98 ft) of water. Drilling and testing procedures have been refined through years of operating in the hostile Arctic environment to maximize information obtained and to minimize rig time. This paper chronologically reviews the offshore drill-stem testing techniques utilized by Gulf during 1982 when three Beaufort Sea wells were evaluated: two from an artificial island, one from a drillship. Future well tests by Gulf will incorporate many of the concepts illustrated here, as well as some recently improved tool technology. Introduction The Beaufort Sea is one of the harshest yet most sensitive environments in the world where oil and gas exploration activities occur. The Canadian Beaufort Sea extends west from Banks Island (125 ºW) to the Yukon I Alaska border (141 ºW) and north from the coastline (69 ºN). Figure 1 shows geographically where Gulf Canada Resources Inc. has current exploration agreements, and several well locations in which Gulf has an interest. Gulf interest acreage encompasses water depths from 20 m to 100 m, with the major portion occurring between the 20 m and 50 m bathymetric contours. Environment Typical environmental conditions are as shown in Figure 2, illustrating seasonally the hours of daylight available, air temperatures, ice cover/ice concentration, precipitation and visibility. A typical drillship operating season extends from 80 to 120 days between July 1 and October 31, with artificial islands in most cases operating all year long. Governmental regulations prohibit floating drilling operations below risk hreshold depth any later than September 25; extensions however, an be granted dependent upon ice conditions. Cased hole testing has been allowed up to early November for drillship operations. Island operations have fewer restrictions, requiring suspension of activities only when environmental onditions are severe enough to affect island stability or for relief well considerations. Well Schedule Figure 2 also shows the well schedule for the Gulf-operated wells during 1982. Two different units were used to drill and test the three wells discussed in this paper. The Canmar Beaufort Island Rig No.1 was installed on Tarsiut Island in the fall of 1981 and drilled the Gulf et al. East Tarsiut N-44 vertical well during the winter of 1981–82, and the Gulf et al. East Tarsiut N-44A directional well during the summer of 1982. The Canmar Explorer 1 drillship was used on the Gulf et al. Kiggavik A-43 vertical well, also during the summer of 1982. The major difference in the two operations was the use of a land wellhead and surface BOP stack on the two island wells, while the A-43 well used a subsea wellhead and BOP stack located on the seafloor.