Case Study: Conduct Successful Perforating Operations in Old Wells

Schlumberger combines technologies to reperforate an old well for Repsol in Ecuador

Challenge: Reperforate a well that may not be able to withstand the annular pressure necessary to activate annular-pressure-operated valves and hydraulic firing heads.

Solution: Protect the well and achieve maximum reservoir connectivity using a combination of the PURE perforating system for clean perforations and the eFire electronic firing head system.

Result: Proved through the success of the operation that new zones of interest in older wells could be exploited with minimal risk of damage.

Repsol wanted to reperforate an old well

Repsol wanted to reperforate an old well in Block 16, but it needed a TCP string design that would enable perforating without the use of annular-pressure-operated valves. Repsol’s concern was that the well’s integrity was insufficient to accept the amount of pressure necessary in the annulus to activate valves and hydraulic firing heads.

Schlumberger introduced a combination of perforating technologies to protect the well

Repsol accepted Schlumberger’s proposal to apply a combination of PURE system and eFire firing head.

Unlike conventional perforating, which relies on a large static pressure differential between the wellbore and the formation to remove perforation debris and crushed-zone damage, the PURE system fully exploits the transient underbalance that occurs immediately after perforating. It creates a large dynamic underbalance, then absorbs perforation debris into the gun chambers, minimizing skin and leaving an obstruction-free path for flow from the reservoir to the wellbore.

PURE software was used to specify the unique perforating system based on full consideration of the completion geometry, reservoir fluids, and formation characteristics in the older well.

eFire technology uses low-level, coded pressure pulses to communicate with the firing head. Fully controlled from the surface, the system can be armed and fired, or the operation can be aborted at any time. This flexible technology enables perforating under less rigid conditions than other technologies. To conform with Repsol standards, the perforating string had redundancy by virtue of the inclusion of a mechanical firing system.

Once the string was on depth, the eFire firing head was activated by two low-pressure through-tubing pulses via the nitrogen cushion maintaining the desired underbalance. The sequence of events was documented with slow- and fast-gauge pressure recordings from the eFire firing head.

Underbalanced perforating with the eFire firing head proved to be the optimal solution

The success of this customized underbalanced perforating operation demonstrated that the combination of the PURE system and eFire firing head could enable Repsol to exploit new zones of interest in older wells with minimal risk of damage.

Advantages of this approach include

  • elimination of primary explosives
  • minimization of operation time and related costs
  • elimination of extra pumps needed to perform firing operations
  • usability for open zones above the zone of interest
  • optimization and recording of the effect of the PURE system with the same tool.

Download: Conduct Successful Perforating Operations in Old Wells (0.94 MB PDF)

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Remove Perforation Debris & Crushed-Zone Damage

PURE Perforating System for Clean Perforations
The PURE system creates clean perforations by optimizing the dynamic underbalance that occurs after charge detonation. Visit PURE System page