A Novel Technology for Providing Long Term Scale Prevention in an Alaskan North Slope Waterflood

Abstract

Most North Slope Alaska oilfields undergo waterflood for pressure maintenance and improved oil recovery. Both recycled produced water, as well as treated seawater are injected into the reservoir which then mixes with connate water in the formation. The combination of seawater with connate water in the reservoir can lead to severe barium sulfate and calcium carbonate scaling in the production wells and reservoir. The scaling is particularly severe at initial breakthrough of the waterflood front in the production wells. However, since water breakthrough timing is unknown, most scale inhibition techniques commence after observing first water production, which is often too late. This scaling can cause significant production losses, leading either to costly remediation with acid, or in the case of barium sulfate, may be impossible to repair. A novel scale inhibition technology which uses scale-inhibitor infused proppant has been applied to mitigate scale in other North American oil and gas fields. Unlike the North Slope fields, most of these wells must be inhibited from first production to prevent scale formation from the start. The technology uses a novel process whereby scale inhibitor is only released when it comes in contact with water, making it a choice option for use in North Slope fields where scale inhibitor must be in place at waterflood breakthrough, which is typically unknown. One operator elected to install this technology in the Oooguruk field in Alaska. The Oooguruk field is an undersaturated oil reservoir found on Alaska's North Slope. Development includes both production and water injection wells, arranged in a line-drive pattern. Wells are drilled horizontally and completed with multistage hydraulic fracture treatments, which are designed to create longitudinal fractures along the wellbore. Water injection is initiated in the injectors immediately after post-frac flowback operations. Based on the severe scaling observed in other area fields, engineers deemed it imperative to put a plan in place to address scaling when waterflood breakthrough occurred. Since these are horizontal wells, scale remediation is difficult (if not impossible) to perform once the scaling damage has occurred. To address this problem, the novel scale inhibitor proppant technology was incorporated in the hydraulic fracture treatments of the producers. Four wells employing these treatments were successfully completed in 2015 and 2016. Testing of the water during the fracture clean-up period showed inhibitor returns as expected, tailing off as the load water was produced. In early 2018, the first waterflood breakthrough occurred on several wells, and the produced water was analyzed and found to contain inhibitor levels above the minimum designed inhibitor concentration, thereby successfully providing immediate scale inhibition to the entire wellbore. This paper will review the proppant delivered scale inhibitor technology, document the field application including the project analysis and design, and present the inhibitor results. This is the first installation on the North Slope of a scale inhibitor technology that can effectively remain dormant, and successfully inhibit scale upon waterflood breakthrough years later. In this case history, the scale inhibitor proppant is inhibiting water that did not break through until 2-3 years after placement. This paper will be beneficial to completions and production engineers who wish to prevent the detrimental effects of scale in their production wells, particularly in waterflood operations.