Coring Technology for Point McIntyre Wells

Abstract

Abstract Nine wells were cored in Alaska’s North Slope Point Mclntyre field to provide engineering and geological data for oil reserve estimates. The goals for this coring operation were: (1) provide high quality permeability, porosity, and water saturation core data using mineral oil base mud, and (2) achieve 100% core recovery. Low invasion coring methods were used. Coring, core handling procedures, a new core bit, a new mineral oil base coring mud, and a new chemical tracer for the mud filtrate were developed for the Point Mclntyre operation. This paper describes the bit development, coring, and handling procedures. The mud and tracer developments are documented in companion paper, SPE 26326.1 Point Mclntyre’s reservoir is lithologically complex, consisting of high permeability consolidated quartzose sandstone, low permeability highly cemented litihic sandstone, occasional lithic conglomerate, and occasional poorly consolidated quartzose sandstone. Existing core bits were not optimal for low invasion coring at Point Mclntyre. The hard rock low invasion bit developed for the Point Mclntyre project has smaller, more numerous cutters to increase bit stability and eliminate the tendency to cut undergage cores. Coring rates using the new bit were increased in the harder racks. This core bit achieved low mud filtrate invasion in the low as well as the better quality sands. Bits and core barrel lengths were selected to maximize the core recovery and minimize rig time. Cutting of core plugs occurred immediately upon arrival in Anchorage. The goal was to keep elapsed time as short as possible to minimize tracer diffusion in the core. In the first two wells, core plugs were cut and trimmed both at the well site and in Anchorage to evaluate the time dependence of tracer distribution in the core and effectiveness of preservation methods. Time dependent effects of water saturation and mud filtrate distribution were not observed. Core plugging was moved to Anchorage for the remainder of the project. The coring methods used at Point Mclntyre provided 99.6% recovery, for 3,068 feet cored with less than 2% of the cored interval having significant mud filtrate invasion in 10 md to 2,000 md pay zone intervals. Technology development for this project was accomplished rapidly and was successful. The technology applied here produced high quality data. This enabled the coring program to be reduced with substantial cost savings. Other cost savings were obtained from high quality operational planning.