Decipher - [Bottom Hole Pressure Condition Indicators]
Zone-1: 5600 ft
Zone-2: 5750 ft
Zone-3: 6000 ft
Zone-4: 6050 ft
> Downhole pressure readings. This window is used to monitor downhole pressure conditions as they occur at different depths within a wellbore. ACTive downhole pressure data can be combined with user input regarding fluid types to obtain feedback on downhole pressure conditions. Although this display shows four zones, the operator can actually monitor up to six different depths at a time. The background of each dial changes color to represent real-time pressure conditions seen at a particular zone. While the dial presents a snapshot in time, a bar graph below each dial displays pressure conditions during the entire job. These readings can be easily referenced in real time during the job or can be saved for postjob analysis.
Talisman’s experience, along with perforating records and production analysis, indicated that the higher the underbalance, the more effective the removal of perforation damage. However, in neighboring fields, guns had sanded in as a result of excessive drawdown. After evaluating core and log data, the TML reservoir group deter mined that a 1,000-psi [6.9-MPa] initial underbalance would be sufficient to remove perforation damage while avoiding failure of the perforation tunnels and fluid invasion beyond the new perforations. The group chose deep-penetrating
charges to bypass drilling damage and increase effective wellbore radius.
TML planned to perforate several intervals that were just 2 to 3 m [7 to 10 ft] in length. A high degree of depth accuracy and a means to confirm gun detonation were therefore required. TML also wanted flexibility to use the CT for other applications such as fill cleanout, if necessary. Size and weight were also considera - tions because the job was to be performed without a rig; crane capacity on most of the
platforms was only about 16 metric tons and deck space was limited. TML’s plan called for displacing wellbore fluid with nitrogen to achieve the required under - balance of 1,000 psi in this 3,200-psi [22-MPa] reservoir. As nitrogen pumping progressed, ACTive real-time bottomhole pressure measure - ments prompted the operator to displace an additional 50 bbl [5.8 m3] of fluid from the well to achieve the desired underbalance. Real-time measurements following this additional displace - ment confirmed a bottomhole pressure of
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