Perforations and stimulations of horizontal wells are technically challenging, costly and required lengthy operations time. Often, perforated and stimulated wells show non-uniform production distribution and poor production results. In case of high pressure and sour environment, HSE risk is also increasing. In one of the producing assets in the Southern Oman, a study was conducted to review the most optimum perforation option based on historical performance of horizontal wells perforations, stimulations and production.
Three perforations/completions methods reviewed:
Explosive perforations with tractor or coil tubing conveyance,
Abrasive Jetting Perforations
Abrasive Jetting perforations were shown to be the most optimum option allowing perforation of the entire horizontal section (maximum connection to the reservoir), minimizing operations time, and reducing HSE exposure and cost.
Abrasive Jetting is the process of pumping abrasive material through the specific nozzles with fluid via coil tubing. Nozzles are faced 90 degree to casing and kinetic energy from high velocity abrasive material erodes casing, cement and rock. Tests have shown that wash-down caverns can reach 1.2-1.4 meters penetration length and 0.3-0.5 meters of caverns diameter. This is about 10 times deeper than conventional perforation technique.
Since 2018, successful deployment of abrasive jetting perforations has been done on three wells out of five planned. Results to-date also shows that productivity index (PI) derived from multirate tests in first well reached 58 m3/d/bar, in second well 28 m3/d/bar and in third well 20 m3/d/bar, respectively. Reservoir permeability in first well is 10 times higher than in third. Due to low permeability in third well, it was stimulated with matrix acidizing. All three wells flowed with low GOR=250 m3/m3 for the current field. Achieved PI's is 2 to 5 times higher than in previous best well in the field to date. Previous best well had explosive perforations covering 100% of the horizontal sections and the entire horizontal section was matrix acid stimulated with coil tubing. Production logging processed with Spectrum Noise Logging (SNL), Production Logging (PLT), High Precision Temperature logging (HPT) observed uniform production distribution across the wellbore and it is fully correlatable to the reservoir properties observed across the perforated zone.
Total operations time reduced from 40 to 12 days and resulted in 4 times reduction in perforations and stimulations cost. Also due to the minimization of operations time in high-pressure sour field, operations HSE risk has been reduced and process safety improved.
This newly proposed approach of perforations and stimulations in horizontal wells is the first implementation in PDO/Oman. In high permeability conventional reservoirs due to deep jetting caverns, penetrations do not require acid stimulation as caverns penetrate to the same depth as matrix acidizing. However, in low permeability reservoirs it is recommended to acid stimulate all perforated zones.
For our wells with 600 m of horizontal section, perforations of only 25% of horizontal section by abrasive jetting caverns create 10.5 higher reservoir contact compared to explosive perforations of all 100% of horizontal wellbore, and 8.8 times higher reservoir contact than 24 Fishbones.
It is envisaged that Abrasive Jetting is beneficial for perforations of horizontal well onshore and specifically offshore with high rig operations cost.