Production campaign planned in challenging HPHT field

To increase production in a number of onshore vertical wells, an operator in China sought to perforate approximately 820 ft [250 m] of pay zone. Reservoir pressure exceeded 17,000 psi [117.2 MPa], and downhole temperature was greater than 350 degF [176.7 degC]. To prevent killing the wells after perforating, the operation required an overbalance of 800 psi [5.5 MPa], and the completion fluid was designed with a weight of 1.87 g/cm3.

Optimized perforating system designed

Schlumberger designed a fit-for-purpose tubing-conveyed perforating (TCP) gun system that uses the latest developments in HPHT downhole tool design. The TCP job and string configuration provided a flexible, modular, and highly reliable perforating system that could ensure successful operations and improved production for the campaign.

A 2 7⁄8-in HPHT gun was loaded with PowerJet Omega 2906 HNS shaped charges, which were picked based upon the operation's downhole specifications. The HPHT hydraulic-delay firing (HDF) head was used as the primary firing system for the operation. Specially designed for HPHT operations, the HDF head incorporates Chemraz^® seals with backup rings and uses an HPHTrated sealed percussion detonator, providing reliability and efficiency in extreme conditions.

Using PURE clean perforations system software, Schlumberger engineers predicted a high dynamic underbalance (DUB) because of the reservoir's naturally high pressure and the hydrostatic pressure of the wellbore fluid. The high DUB predicted with SPAN PURE was later verified with high-speed pressure data recorded in the actual job.

SPAN Rock stressed-rock perforating analysis considered the perforation tunnels' debris volumes while predicting shaped-charge and estimated the wells' productivity index. Downhole shock was also carefully considered to ensure minimal damage to downhole tools and equipment. Further analysis helped the operator decide to perform a shoot-and-pull operation without a retrievable packer.

Twelve HPHT perforating jobs efficiently performed with validated results

To date, the operator has run 12 HPHT perforating jobs without any lost time or service-quality issues, confirming the TCP confirmation's ability to reliably and consistently perform under HPHT conditions. Final production rates increased beyond what the operator initially anticipated, also confirming the performance of PowerJet Omega charges under severe downhole conditions.