Feeling the Pulse of Drill Cuttings Injection Wells—A Case Study of Simulation, Monitoring, and Verification in Alaska

Abstract

In April 1998, a program for continuous deep disposal of drill cuttings and open pit materials was initiated on the North Slope of Alaska. This ongoing injection project is commonly referred to as GNI, or "Grind and Inject." Accumulated drilling cuttings and mud slurry are injected into a receptive Cretaceous soft sandstone in three wells: GNI-1, GNI-2, and GNI-3. Typical operations involve injecting slurry into one of the three wells continuously for a number of days and then switching injection to another well. The average injection rate is approximately 30,000 B/D. As of 30 September 2002, project injection has included 12.7×10 6 bbl of water, 30.9×10 6 bbl of slurry containing 2.0×10 6 tons or 2.2×10 6 cubic yards of excavated frozen reserve pit material and drilling solids, and 1.31×10 6 bbl of fluid from ongoing drilling operations.Knowledge of the fate of the drilling and open-pit materials during injection is paramount to assure the safe containment of the disposed materials without harm to the environment. Numerical modeling, well testing (including step-rate and pressure-falloff testing), and logging surveys were performed periodically to assess the operational integrity of the disposal wells and to ensure the safe containment of the disposed waste slurry. The high-volume capacity of these injectors highlighted the mechanisms for slurry being accepted by multiple and branched fractures-part of the slurry went to previous fractures during subsequent batch injections. This paper will detail how to integrate numerical simulations, well testing/monitoring, and operational data to estimate storage capacity and construct a clear representation of what was happening underground during this GNI operation. The work has implications on other large drilling-waste injection projects worldwide.

Coupled discrete element modeling of fluid injection into dense granular media

“…[3] In engineering practices, subsurface fluid injection has been widely employed for applications such as grouting for ground improvement to reduce the liquefaction potential of cohesionless soils, to raise the ground elevation, or to compensate the volume loss due to ground surface settlement [Mitchell and Katti, 1981;Au et al, 2003;Woodward, 2005;Germanovich and Murdoch, 2010]; construction of permeable reactive barriers for soil remediation [Hocking, 1996]; injection of carbon dioxide for geological storage [Bachu, 2000;Hovorka et al, 2004;Lucier et al, 2006] or for enhanced oil or coalbed methane recovery [Orr Jr. and Taber, 1984;Blunt et al, 1993;White et al, 2005]; subsurface disposal of liquid or slurrified solid waste such as drill cuttings [Moschovidis et al, 1998;Schmidt et al, 1999;Keck, 2002;Clark et al, 2005;Guo et al, 2007;Tsang et al, 2008]; and hydraulic fracturing and waterflooding for hydrocarbon recovery [Ayoub et al, 1992;Morales and Marcinew, 1993;Economides and Nolte, 2000;Hustedt et al, 2008;Khodaverdian et al, 2010]. Although the engineering objectives vary in this list of applications, they share a common operation procedure in that clean fluid and/or slurry is injected into the subsurface via a circular wellbore over a certain interval.…”

Deep Underground Injection of Waste from Drilling Activities—An Overview

“…Although subsurface injections of waste materials from drilling activities is a well-known and successful technology whose effectiveness has been confirmed through time, there are many challenges, such as frequent changes in regulation, selection of suitable geological formation, monitoring and verification of injection process, design of the whole process, etc. [41].…”

“…Although the slurry waste is traditionally injected by a positive displacement plunger or piston/liner-type triplex mud pumps, new laboratory research and a field trial conducted by Newman et al [34] indicate that multistage centrifugal pumps could be advantageous in some situations. In some situations, as in the case of oil and gas exploration and production waste injection in polar regions, it is necessary to heat up the waste slurry preparation water because of frozen waste material in the reservoir pits [41] or to apply winterized measures for the entire unit to assure a minimal internal temperature of 17 °C [50,52].…”

“…In Figure 2, the waste slurry and disposal unit are shown in detail, as well as all options for adequate deep underground disposal [53]. In some situations, as in the case of oil and gas exploration and production waste injection in polar regions, it is necessary to heat up the waste slurry preparation water because of frozen waste material in the reservoir pits [41] or to apply winterized measures for the entire unit to assure a minimal internal temperature of 17 • C [50,52].…”

Colorado Drill-Cuttings-Injection Pilot Results

“…Other land-based drilling-waste-injection operations have been described previously [e.g., at Wilmington field, California (Hainey et al 1997)], but they differ with regard to the logistical treatment of cuttings. In the North Slope of Alaska, land-based processing occurs either on site at single-well installations or at a central location in which reclaimed cuttings from existing pits are processed (Guo et al 2007). The process described here differs because it deals with the logistics of transporting and processing cuttings from multiple drillsites at distances of several miles from the processing-and-injection site.…”