Horizontal well in carbonate gas reservoir required dynamic perforating
technique
An operator was completing a gas well in a field that has particularly
challenging characteristics, including long horizontal laterals and high
concentrations of H2S. The operator wished to perforate a 3,000-ft
interval in the field with a technique that could maximize productivity while
ensuring safer operations in the high-H2S reservoir.
An existing openhole lateral in communication further added to this
job's complexity; the presence of the openhole lateral prevented using any
pressure pulses down the annulus side to actuate tools, including a TCP firing
head. Also, care is required to monitor fluid levels at surface while the guns
fill after shooting because a lowered fluid level decreases hydrostatic
pressure, which could result in well-control issues.
Underbalance perforating technique planned
After consulting with the operator about its perforation and production
goals, Schlumberger ran SPAN Schlumberger perforating analysis to predict the
performance of gun systems at downhole conditions. PURE system planning
software was used to determine the optimal shot density of PowerJet charges and
the PURE system. It was recommended to use a fit-for-purpose TCP system that
combined a 4 1/2-in, 72° phase gun loaded with PowerJet deep-penetrating
shaped charges at approximately 4.84 shots per foot (spf) and PURE system
charges at approximately 0.15 spf. The PowerJet charges’ shot density was
close to maximum, an important requirement in this job.
Over 7 days, 143 guns were loaded at a Schlumberger gun shop and
transported to the wellsite. After assembly, the guns were run in hole as a
drillpipe-conveyed TCP system with a pressure-operated valve, keeping the
tubing isolated until after shooting. Using a hydraulic-delay firing head,
every gun fired correctly. Extreme care was taken to condition the mud
thoroughly to remove any traces of H2S while the guns were
retrieved.
After the guns were retrieved, a trip was made with debris catchers and
magnets to recover any debris left in the well from the perforating process. A
total of 48.5 lbm [22 kg] of debris was recovered, some of which is
perforation-related debris. This amount was less than predicted; the low debris
volume may be a side benefit of the PURE system design, which kept much of the
perforating debris inside the gun string to then be retrieved at surface.
Effective perforation performed with efficiency and safety
This large and complex TCP job was executed precisely as planned with
two perforating jobs successfully completed using the PowerJet charges and PURE
system. The 3,000-ft interval was shot in a single trip. All shots fired
successfully with minimal gun debris left in the well after shooting. During
gun retrieval, special care was taken to ensure no residual H2S
remained in the fluid column, and several circulation trips were made while
monitoring for H2S at the pits. The operator was pleased with the
results of the operation—the largest 4 1/2-in 5 spf TCP job completed in
the region.
