Unlocking a Frozen Resource: Horizontal Milestone in Permafrost Drilled at -80°Fahrenheit

Abstract

Situated on the central North Slope of Alaska along the Coleville River, Umiat is one of the most frigid places on Earth. The target reservoir, the Lower Grandstand, lies at an average depth of just 470 ft below ground level and is one of the largest untapped oil fields in Alaska bearing light, sweet crude in a low-energy reservoir. Conventional drilling and completions would cripple the development economics and make too large of an environmental impact at the surface. Developing methods to drill horizontally in permafrost, a task never before achieved in Alaska, would enhance Umiat production compared to that from conventional well geometries. However, the subsurface drilling environment presented challenges since the majority of directional drilling would be in permafrost. With limited infrastructure in place for year-round access to the region, Linc Energy built over 100 miles of snow and ice roads to gain access during Alaska's coldest months. This limits access for drilling from January through the initiation of the cold breakup in late April. During well planning, the bottomhole assemblies for high dogleg and shallow horizontal landing were optimized by applying experience drilling wells in permafrost in other areas across the North Slope. A new mineral-oil-base reservoir drilling fluid was proposed to provide formation compatibility and low mud weight while reducing friction. Close communication with the rig and office teams was established to enable critical decisions to be taken using drilling dynamics measurements to monitor tripping loads and to geosteer the well. While drilling the well, the directional drilling response was better than expected landing the horizontal. The risk of stuck pipe was greater than anticipated. As anticipated in the modeling, additional weight was added on the top of the drillstring to avoid pipe buckle and to assist with weight transfer. The new reservoir drilling fluid achieved a density just a half-pound per gallon above the pore pressure and produced sufficient lubricity to reach well depth, thus validating the accuracy of the predrill modelling. The first horizontal well in Umiat was a success, achieving an extended reach drilling ratio of 3.23 with 800 BOPD production rates and 0% water cut. The well set two important records as the shallowest horizontal well drilled in Alaska and the first horizontal well drilled and landed entirely in permafrost in Alaska. The results of these methods and processes demonstrated that horizontal wells can be drilled in permafrost as this was the first such well in Alaska. The lessons learned on this well will be instrumental for future horizontal wells drilled in permafrost and will enable future permafrost reservoirs to be drilled and produced with horizontal geometry worldwide.

Application of Design of Experiments for Well Pattern Optimization in Umiat Oil Field: A Natural Petroleum Reserve of Alaska Case Study

“…Umiat 23H, the first horizontal well drilled in Umiat field, in 2014, experienced actual Dog Leg Severity (DLS) of about 8o/100 ft (Sayers et al, 2015). In current model, we maintained similar DLS constraint while designing the wells.…”