RIASSUNTO
Abstract
This case-history paper presents accounts of several field applications of a drillable perforating system (DPS) that has been used on 400 jobs in the Gulf of Mexico, with a near-100% success rate.
Components of the drillpipe-conveyed system are both drillable and disposable. The aluminum gun is mounted below a drillable packer. After perforating, the packer and gun can be drilled out by conventional drilling methods. There are no mobilization or demobilization charges such as those associated with use of wireline units. Because no mud system is needed for the operation, clear fluids can remain in place for workover operations. Once in place, the firing head is actuated by pump pressure applied through the tubing.
The paper describes use of the system to perforate underbalanced, perform plug-to-abandon operations, perform block squeezes, and perform other operations. The DPS can be used to cement and perforate in underbalanced conditions, limited-entry in-flow testing, cementing with clear fluids, and plugging and abandoning wells.
The paper presents results that show the DPS to be an effective alternative to conventional perforation and squeezing methods now followed in the oil and gas industry. In case histories presented, significant rig time was saved, along with savings in material and time to first sale after application. DPS offers several advantages over conventional equipment and techniques.
Clear fluids can remain in place during workover operations because no mud system is needed for well control.
The DPS is a cost-effective and safe alternative to traditional methods of squeeze perforating.
The DPS assembly is a one-trip perforating, packer-placement, and squeeze-cementing method that can eliminate a great amount of rig-time expense.
Introduction and Background
Conventional, traditional wellbore perforating operations are performed ""overbalanced,"" meaning that the pressure in the wellbore (pushing down) is greater than the formation pressure (pushing up). When perforating guns are fired, the overbalance of pressure pushes into the formation, carrying perforation debris and well fluids into the near-wellbore area.
Steel perforating guns used in conventional perforating are not drillable, and perforating guns cannot be fired closer than 50 ft from the cast-iron packers/plugs without the risk of cracking the packers/plug mandrels, causing pressure leaks.
Current Perforating Technology
Development of the aluminum perforating gun and sliding-valve bridge plugs and packers with brass mandrels has enabled field deployment of a tubing-conveyed perforating system that can be drilled out easily by conventional drilling means. The system resists cracking from concussion of the perforating gun; therefore, the gun can be located as near to the packer/plug as desired.
The perforating system enables one-trip perforating, packer placement, and cementing on tubing. Well control is furnished by the packer, so clear well fluids can remain in place during workover operations. No rat-hole pressurization is required. DPS features are detailed below.
All drillable materials, including an aluminum perforating gun
High-performance perforating charges
Sliding-valve, brass-mandrel cement retainer
Adjustable firing head
Underbalanced perforating to 5,000 psi
Optional tandem guns available - 2-ft lengths
Optional gun spacers
15,000-psi gun case
10,000-psi retainer
Iron guns optional for plugging and abandonment
Set on wireline, coiled tubing, or pipe, or by hydraulic means
Operational advantages offered by the DPS
One-trip perforating, packer placement, and cementing on tubing
Block-squeeze cementing in underbalanced conditions
Clear well fluids retained during workover (packer gives well control)