Perforate, Wash & Cement (PWC) is a method developed over the past decade to help increase efficiency in plugging & abandonment of wells. The method has helped operators world-wide to save time and cost in plugging and abandonment operations by cutting down time for setting full lateral barriers.
This technique can also be used to set permanent lateral barriers for slot recovery operations, and perform well repairs on workovers where there is sustained casing pressure. The technology is used to set lateral barriers to cure the sustained casing pressure, and enable the operator to put the wells back into production. The integrity of the well is restored and significant value is generated.
However the technology has previously been limited to setting one barrier at the time. The unique challenge for this well on the Platform Alpha, offshore Malaysia was that two zones had to be isolated in one run. The distance between the two zones was almost 100 meters. A significant challenge, with a significant upside. The execution was using Hydraulic Workover Unit (HWU) and overall 14 plugs completed (for 14 wells).
The method has several critical success factors that need to be tailored to be able to produce a high quality result, especially with this unique challenge of plugging and abandoning two different zones in the same run.
Optimization of the Tubing Conveyed Perforation (TCP) System to be able to balance hole size, geometry and density in order to create the ideal communication path into the external annulus was paramount to the success of the job. The TCP needed to also take into consideration casing size, weight and metallurgy to ensure that downhole conditions are simulated as accurate as possible, increasing the chance of successfully meeting the perforation criteria that has been optimized.
Washing parameters needed to be optimized to be able to create high annular velocity for efficient hole cleaning and debris removal. This optimization takes into consideration the fluids density and rheology, ensuring that the mud system has the correct properties to suspend the debris for removal at surface. The compatibility and stability of the fluids and mud condition prior to cementing operation is also critical.
The cementing operation on this well was a unique, tailor-fit engineering project, with the end goal and intention of being able to isolate two zones approximately 100 meters apart at the same time. The cement & spacer properties were important here due to possible gas, and high chance of losses into the formation after perforating, and during washing. The volumes, operational parameters and execution were critical to get the two zones efficiently plugged and abandoned in one run.
This paper describes the extensive work that has been performed to plan and execute the successful plugging and abandonment of two independent zones using the Perforate, Wash and Cement technology; and in the process, saving several days of rig time, gaining significant value for the customer and setting a new benchmark for efficient plug and abandonment operations for the global market.
The system testing of the TCP Gun system resulted in an optimum Exit Hole Diameter (EHD) and exit hole geometry tailored for this specific wellbore size, weight and metallurgy.
The washing was efficiently carried out with high amounts of debris over the shaker system and a declining standpipe pressure was observed indicating a very successful washing of the perforations.
The cement operation was flawlessly executed according to the planned operational parameters with no losses or operational challenges. The two zones were effectively isolated in 2.5 days.
This fantastic result not only significantly lifted the efficiency of the Platform Alpha Plug & Abandonment operations, but also set a new benchmark for the Perforate Wash and Cement Technology globally.
By isolating two independent zones in one run using the Perforate Wash and Cement Method, the technology has proven that within an already established methodology, there is still capacity for further progression and evolution of the technology.
A one team effort between operator and service companies made this possible and in the process, established a solid blueprint for future efficient, safe and reliable operations.