Various logging tools deploys into borehole to gather various reservoir properties before steel casing run. Some logging tools which use electric signals to measure reservoir properties must be run in open hole. The logging tools can not be used in cased hole due to restriction of steel casing. Reservoir properties such as water saturation and porosity must be concluded from the logging data as initial condition of the reservoir.
Casing is run subsequently to secure the hole wall from collapsing, steel casings are used mostly. Then cement is placed between casing and borehole to isolate productive zones hydraulically. The casing and cement are perforated at productive zone to allow reservoir fluid flowing into the well.
In horizontal well, slotted liner is more preferable than casing tubular since the leg (horizontal section) is only connected to one reservoir . The slotted liner is required to prevent the borehole from collapsing and the slots are design to prevent sands flowing into well.
During the well life, fluid saturation around the well or between wells is changing. Re-running electrical logging tools to measure fluid saturation are impossible. Pulsed neutron logging which measures carbon-oxygen ratios is run to assess the changing. But this method has shallow depth of investigation and low accuracy in low porosity reservoir.
The question comes up whether there is any possibility to pass electric signal (EM signal) through slots and measure reservoir properties as done in open hole logging. The answer is yes. Now, the challenge is to make the slot through casing and run suitable electric logging tools.
The inventors protect their idea in the form of method (procedures) and system (tools). Making the opening (slots) is a very important part of the method and the system. The slots can be pre-installed on the casing before running or made using mill-cutter, perforating gun, sandblast cutter or other means. At least one transmitter and one receiver is required, more is better.
Figure 1: Pre-installed slots on casing
Figure 1 shows pre-installed slots on casing. The insulator which is made from material that transmits EM radiation covers the slots to provide isolation during cementing.
Figure 2: Logging in water coning well
Re-logging producing wells can give information about fluid distribution behind casing or between wells. Re-logging periodically to monitor the resevoir will give information any changing during the life of the well. Sometimes, in high water cut wells, oil is still unproduced due to water saturated zone. Figure 2 shows the logging result. Instruments B and C gives difference results for deep and shallow surveys which conclude oil left due to water blocking around well. Immediate remediation can be taken accurately to allow oil flowing into the well.
Filed under: Production & Operation, Reservoir Evaluation & Engineering Tagged: | electric log, logging, mill-cutter, paten, patent, reservoir monitoring, resistivity log, sandblast cutter, saturated water zone, slotted liner, water coning, well completion
