|Intermediate spool inserted below the Chrtistmas tree; spool provides a profile for landing the control line hanger and hydraulic penetration to allow control on WCS Safety Valve|
Weatherford’s Brian Marr, Scott Carline and Scott Deyoung discuss how the Renaissance WDCL system enabled the retrofitting of a new control line inside existing tubing to reestablish connection with a surface-controlled subsurface safety valve (SCSSV). The installation, which was performed without a workover rig, improved production at a significant cost savings.
The well, an offshore oil producer in the Middle East, was required by law to include a SCSSV. Like all downhole safety valves, SCSSVs act as a failsafe to prevent the uncontrolled release of reservoir fluids in the event that surface wellhead integrity is lost. These valves are popular well control options in the industry due to their ease of operation, which consists of hydraulic control from the surface. Hydraulic pressure is applied down a control line connecting the valve to surface. During normal well operation, the continuous application of this hydraulic pressure keeps the valve open. When hydraulic pressure is removed during a wellhead integrity event, the valve is forced shut, thus acting as a failsafe to isolate the wellbore.
However, SCSSVs are prone to malfunction, which is commonly caused by piston failures, leaks within the valve body or some type of control line failure such as crushing, leaking or blocking by an obstruction. Such a control line failure occurred in the offshore Middle East well, which forced the valve closed and shut in production.
The conventional remediation method calls for bringing in a workover rig to pull the tubing, replace the blocked control line and then redeploy downhole. While this option is relatively cost-effective and easy to implement in an onshore well, the logistics, cost and complexity of performing a workover offshore make this a time-consuming and expensive operation. Even a relatively simple workover of an offshore well in the Middle East might cost upwards of US$6 million, according to estimates from the operator. Weatherford collaborated with the operator to develop an alternative process— an intervention that would restore functionality to the SCSSV by retrofitting a new control line and inserting a new valve within the existing well architecture. The operator required the intervention to be performed without killing the well, pulling the tubing or incurring the time delays and costs that commonly come with a major workover.
A Renaissance in well revival
Upon review of the well parameters and intervention requirements, the operator decided to deploy Weatherford’s Renaissance WDCL system, a wirelineretreivable subsurface safety valve that allows both the control line and the safety valve to be replaced in a straightforward retrofit procedure. The system has a modified packing mandrel and wet connection, and a valve-and-lock assembly that can be installed in an existing tubing-mounted safety valve or safety-valve landing nipple. A capillary line is then run from the surface inside the tubing and connected to the valve to provide control. The retrofit process for this offshore well was performed from a jackup rig, and began by modifying the wellhead to provide the correct profile for the capillary hanger and gain access for the new capillary control line. A wireline crew set plugs in the well to keep the well isolated, after which the tree was pulled and a spool piece containing a hanger profile was installed. The tree was then reinstalled and after the wellhead was pressure tested, the wireline crew went back in and pulled the plugs.
Another trip downhole was conducted to lock open the existing tubing-retrievable safety valve, after which a new subsurface safety valve was deployed and landed inside the previous valve. Once the new valve was set, the capillary control line was run down the center of the tubing to a pod on the valve.
A weighted and centralized stinger placed at the end of the capillary string was used to join the capillary to a mating connection on the valve. This was a wet-connect assembly, which was hydraulically locked in place by applying pressure to the capillary string. The wet connect contains unique design features, including the ability to be mated and unmated should the capillary need to be removed, and dual-back check valves that prevent backflow through the capillary line as an additional safety feature.
The top end of the capillary was then landed into the new spool piece below the tree through a specially designed, 4-in. control-line hanger. A Type-H profile was provided above the hanger to allow for the installation of a backpressure valve, which would be required to secure the well during future wellhead maintenance.
|Picture of the WDCL Subsurface Safety Valve in the closed position (flapper shown in gold), the blue highlights the flow path of hydraulic fluid to function the valve.|
The entire installation took only two days of rig time, allowing the well to be brought back into production much sooner than a conventional workover. This helped to significantly lower the risk of formation damage or lost production that may result from extended well downtime. The installation was also conducted at a fraction of the price of a full workover, coming in at less than 10% of the estimated US$6 million workover cost.
The installation in the first well successfully proved the viability of this technology, and it has been running without issue since May 2013. The operator was pleased with the ease of installation of the system, the significantly lower rig time and the fewer number of trips required. The new SCSSV system also eliminated the need for a storm choke, which was prone to repeated tripping and caused production interruptions.
The operator was able to restore the well to full production once the SCSSV was fully operational, and now plans to install this solution on a number of additional wells suffering from the same control line blockage issues. These issues are not unique to this operator, or to the Middle East; Weatherford is actively working with other operators to install similar SCSSV systems in offshore wells throughout the world.
The Renaissance WDCL was installed without incident, allowing the operator to bring the well back to full production quickly, while adhering to offshore safety regulations in the region.
A new spool piece was placed below the lower master valve on the wellhead. The spool piece was custom-built with a profile to lock the control line hanger in place, and polished bores for the seals.
images courtesy of Weatherford