Perforate, Wash & Cement (PWC) is a method developed over the past few years to remediate cement behind casings, which has been widely applied to the Plugging and Abandoning (P&A) of wells. This technique can also be used to set permanent lateral barriers for slot recovery operations. However, the technique has been mostly applied to smaller casing sizes ranging from 7 – 10 ¾". In the growing slot recovery market across mature fields, the demand is increasing for a reliable and efficient method for achieving shallower lateral barriers, thus facilitating side tracks from bigger casing sizes such as 13 3/8" −13 5/8".
For the technology to be successful there are several components that need to be tailored for the specific casing size and borehole diameter. The optimal Tubing Conveyed Perforating (TCP) system needs to be in place to maximize efficiency for the washing and subsequent cementing operation. In order to reduce risk during the washing and cementing operation, it is critical that a suitable area of the wellbore is chosen for the remediation. This area is chosen based on the operational window for the Cup-type PWC technology where annular condition plays an important role. This paper describes the extensive work that has been performed to plan, execute and verify the placement of a lateral barrier across the 13 5/8" casing on the Valhall G-22 Well in the Norwegian continental shelf as part of the slot recovery program for the field.
The testing of the TCP Gun system resulted in an optimum Exit Hole Diameter (EHD) and geometry tailored to this specific application. An ultrasonic log was run prior to the PWC operation to determine the status of the annulus to be remediated. The optimal parameters for efficient cleaning of the annular space were simulated, and successfully achieved within the narrow Equivalent Circulating Density(ECD) window for the weak permeable zone below the perforated interval. The cement job was performed flawlessly with no losses, utilizing the Pump and Pull method with the Cup-type PWC system. Moreover, the actual job parameters matched very well with the simulations. The internal cement was drilled out and the annular cement was logged using an ultrasonic logging tool. The interpretation of the log showed perfect circumferential cement coverage across the entire remediated interval. With proper planning and optimized design and execution parameters, successful annular remediation can be achieved in large casing geometries using the PWC technique. This allows for more efficient and cost-effective slot recovery and P&A operations.