Abstract

Subsurface drilling waste injection has been proven as an environmentally safe and cost-effective alternative for drilling waste disposal in remote and environmentally sensitive areas. This has resulted in the rapid expansion of waste injection operations into major E&P regions throughout the world, and thus, the dramatic increase in total drilling waste volume injected in recent years.

Despite the outstanding milestones that have been achieved and the millions of barrels of drilling waste successfully injected, there are significant subsurface risks involved with any waste injection project, such as breach to surface, intersection with near-by wells or natural faults and well plugging. Limited understanding and characterization of those risks could potentially have a significant environmental impact and jeopardize the pre-defined project execution plan. Therefore, continuous injection monitoring and pressure interpretation coupled with a proactive subsurface assurance process is the key to mitigate those risks and ensure environmentally safe and seamless waste injection operations. Complexity of fracturing systems created during multiple waste injections render it imperative to monitor and characterize the waste domain in real time through corresponding pressure behavior interpretation.

This paper presents the unique and technically challenging injection monitoring and pressure interpretation experience attained in different waste injection projects in the CIS region, where the in-depth interpretation of fracture behavior and waste domain monitoring helped to minimize subsurface risks and to provide an adequate level of subsurface assurance. Continuous monitoring of injection data and parameters by a group of geo-mechanical experts in close collaboration with the operational team helps to identify and minimize the sub-surface risks and generate appropriate recommendations and mitigation procedures to avoid potential injectivity failures. Currently more than one and a half million barrels of drilling waste have been successfully contained through various waste injection projects in the CIS region.

Introduction

In the early 1990s, Waste Injection emerged as a new technology that could provide an environmentally safe and economically sound solution to the disposal of drill cuttings and other drilling associated wastes for environmentally sensitive and remote operations. It was identified as one of the few technologies able to provide a complete drilling waste disposal solution that eliminates the need to accumulate, store and haul cuttings to shore for treatment. The technology was first pioneered in Alaska and California, but the first trial was carried out from a fixed platform in the North Sea, which was demonstrated, with proper subsurface engineering and sound injection procedure in place, the process is a safe, efficient, and effective drilling waste disposal technique, and received regulatory approval in both the UK and Norwegian sectors of the North Sea.

Waste injection operations also have been successfully implemented in the CIS region, first in the Caspian Sea since 2002 and in Russia since 2003.2 On Russian's Sakhalin Island these operations have been offshore deployments and are driven by challenging climatic conditions with limited ice-free windows for drilling and with no established logistics and infrastructure for drilling waste management onshore. In the Caspian Sea region, waste injection operations have also been introduced successfully in spite of complex subsurface environment and tectonics that presented significant technical challenges and required comprehensive subsurface design analysis before injection commenced, along with vigilant subsurface pressure monitoring as injection progressed.8 This was critical to ensure the safe, long-term containment of the waste planned for injection.

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