PROBABLE PERFORATING RECORD SET

Nederlandse Aardolie Mij. (NAM) early this year completed what is believed to be the longest producing interval ever perforated.

The 2,977-ft overall interval in the gas-producing zone of a well in Dutch North Sea waters was perforated over a length of 2,782 ft in a single trip.

A major reason for this probable record is that the producing zone was drilled with an angle of 85 from vertical. It was therefore essentially a horizontal well with an extraordinary long section of producing formation exposed.

NAM completed the well on Jan. 2 this year. NAM operates the block for a group including itself, CLAM Petroleum (owned jointly by Marathon Petroleum Netherlands Ltd. and LL&E Netherlands Inc.), Clyde Petroleum, and Orange-Nassau Energie B.V.

The completion was carried out using tubing-conveyed perforating technology and guns provided by Vann Systems. The job was handled by Vann's Ijmuiden, Holland, location.

NAM drilled the well to a measured depth of 16,600 ft in Dutch block L-13. The producing interval was cased with 7-in. liner (6 1/8-in. ID). The tubing-conveyed perforators were then run in the hole below an hydraulic setting tool and permanent packer and a section of perforated pipe. The packer was set some 600 ft above the completion interval in a section of the hole deviated 57. Fig. 1 shows the perforating and completion system.

Vann Systems centralized the 4 5/8-in. OD guns by drilling threads into the gun couplings at specified points and screwing in round-head steel screws flush with the surface (Fig. 2).

Each gun, which was 15 ft in length, was loaded with four shots/ft. There were over 11,000 charges in all.

Loading all the guns required about 5 weeks. The racks of larger guns shown in Fig. 1 are the same size and length of those run in the Dutch well.

All the guns were coupled together in lengths of two before being brought to the drill floor to be run into the well. Running time took 13 hr during a period of high seas and winds.

After all completion equipment was run and tested, the system was prepared for underbalanced perforating by displacing the tubing fluid with nitrogen. The nitrogen was then pressurized to actuate two (one backup) pressure-operated firing heads on top of each of the three perforator sections.

Each section was made up of approximately 60 loaded TCP guns.

Delay fuses were incorporated in this system to allow time to bleed off the nitrogen pressure and create the desired drawdown of 2,200 psi prior to perforting.

After firing, the guns were left in the hole. The gas enters the production tubing through the preperforated pipe.

Although extensive planning and preparation were required for this record completion, the actual job was performed without complications.