Safeguarding Export Gas Supply with Subsurface Disposal of Produced Water: The MXC Approach to Liquid Handling

Abstract

Unprocessed gas from the gas wells in the nearby fields is routed through the production manifolds to the processing trains in gas plants. The associated liquids from the treatment process accumulate in a stabilization tank, where it undergoes separation by gravity into condensate and water and therefore needs to be evacuated to sustain gas production. The base design strategy for MXC's export gas supply from gas plants A and B relies on two major export pipelines as the primary evacuation routes for the accumulated condensate and water. In the absence of these major export pipelines, the condensate can be evacuated by spiking via the gas export pipeline to the LNG plant. However, the only available option to evacuate the produced water was by barging to the export terminal for subsequent disposal into the sea. This option was unsustainable due to logistics, insecurity, and operating costs. Inability to dispose of the produced water would result in water level build-up in the condensate stabilization tank, which impacts the ability to spike condensate, forced reduction in gas production as much as 500MMscf/d or complete gas plant shut down with deferments as high as 1.2 Bscf/d from both gas plants. With the prevailing external context of frequent and prolonged outages of the export pipelines, resulting in gas deferment, and external regulatory requirements to limit evacuation of produced water to the sea, it became imperative to create additional options for liquid evacuation to guarantee the security of export gas supply as well as meet regulatory requirements. Produced water disposal into the subsurface was considered a critical and essential strategy for building this robustness. This paper discusses the strategy adopted by MXC to build water disposal capacity in Plant A, comply with regulator stipulations, and sustain gas supply from MXC's gas plants. It highlights the initial trade-offs and challenges in developing and managing the system and the best practices adopted to improve system reliability.