The Background
Chevron’s Wheatstone Project is a multi-train Liquefied Natural Gas (LNG) and domestic gas plant located on the Pilbara Coast, Western Australia. The Wheatstone Project involves processing gas from various fields located offshore and the installation of gas gathering, export and processing facilities in water and on land. The gas is transported to the Wheatstone LNG plant from subsea wells through a trunkline, several kilometres offshore. The last kilometre of the trunkline is sent in from the shoreline through a protective microtunnel. This project was located in an environmentally sensitive area, in close proximity to a whale shark breeding ground, which proved a challenge.
The Challenge
During tide changes, a grout plug is required inside the tunnel annulus extending 70 meters inside the microchannel to block water flow. The challenge was to anchor the last 70 meters of the trunkline within the micro tunnel to shore with a precision grout plug. Since the placement of the grout had to be done underwater with low visibility, the team had to develop a new design concept for grout movement, placement and mixing. Considering the close proximity of the project to the shark breeding ground, environmental factors had to be taken into consideration to ensure zero environmental impact.
Our Solution
A new grout delivery system was designed to overcome some of the challenges. This included a unique trolley system that carried the delivery line and inflatable grout bags down the 70-meter microtunnel underwater. The grout and water temperature was reduced to 4 degrees Celsius for 48 hours before use, using several refrigerated containers. The design of the delivery trolley also assisted temperature control by enabling rapid product placement. Best practices were employed for working in environmentally sensitive areas that had zero tolerance for any spills.
Project Facts at a Glance
The project was in the design phase for almost two years, and the actual placement of the grout was completed in 36 hours.
Two mock-up trials were also conducted before the final application of the grout.
The project now boasts the first-ever microtunnel plug installed worldwide.
Product Facts at a Glance
MasterFlow 700 is a Class A grout generally used in applications requiring a grout thickness between 10mm and 100mm.
It is a ready-to-use premixed grout that only requires the addition of mixing water on-site
It is economical due to its ease of use and flowable properties.It has a low water/cement ratio therefore reducing drying shrinkage and increasing durability.
The Customer's Benefit
A difficult project was delivered on time and within budget.
The on-site costs to the customer were reduced due to the speed of the pour (36 hours non-stop).
The grout plug provided the trunkline with an anchor that was impermeable to tides and intermittent water and air ingress, improving the durability and life cycle of the structure.
The solution reduced the possibility of future corrosion costs.
The Wheatstone Project is located in close proximity to an important whale shark breeding ground, meaning various environmental factors need to be considered when developing Master Builders Solutions' grout delivery system.
Image source: Chevron Australia