Running perforation guns with coiled tubing conveyance is an effective method of oil and gas wells perforation. Since other services like acidizing and well stimulation can also be carried out by coiled tubing, this method can be considered economical and efficient in several cases. Precise depth determination and perforation precision have been continually controversial issues from the beginning of coiled tubing perforation in the region. Since it is not possible to perform wire line logging through coiled tubing, and compare the achieved log results with initial open hole base log, the classic method of depth correlation by the use of a pip tag in the perforation string is out of question. For this reason, currently, if perforation operation is supposed to be carried out with coiled tubing conveyance, the depth correction is determined by tagging the LDC (Latch Down Collar) during a dummy run (Coiled tubing with MHA and empty guns) and applying corrections on the coiled tubing counter based on the drillers depth of the LDC.
Two major errors occur in this method: 1-Final well depth is approximated by drilling pipes and their approximate length in the well. This lacks required precision for perforation operation.
2-In some cases, required depth for perforation operation is widely different from final well depth which affects the precision of the operation further. In the absence of a precise method, the coiled tubing perforation operation depth precision has been continually questioned. Petro Danial Kish Company with the support of its clientâ€™s (Petro Pars and Pars Oil and Gas Company) has lately managed to gain high precision in perforation for the first time in Iran:
According coiled tubing perforation operation manual, a dummy gun is carried out before the main coiled tubing runs. As mentioned above in this run , coiled tubing , MHA, firing head and Dummy (Empty) guns are run in hole to make sure the well path is clear and there is no possibility that coiled tubing gets stocked with live guns. Also during the same run the LDC is tagged and mechanical depth correlation (which was described as non accurate) is carried out. The innovative method proposed here is to utilize wireless gamma ray sensors working with batteries during the same dummy run. Now the new precise correlation method is based on placing these sensors in empty perforation guns of the dummy run and by comparing the values gained by gamma ray and CCL sensors with values of the base open hole log, exact depths can be determined.
According coiled tubing perforation operation manual, a dummy gun is carried out before the main coiled tubing runs. As mentioned above in this run , coiled tubing , MHA, firing head and Dummy (Empty) guns are run in hole to make sure the well path is clear and there is no possibility that coiled tubing gets stocked with live guns.
In this method: First, gamma-depth log of executed operation by coiled tubing is achieved through the comparison between gamma-time logs of sensors in empty perforation guns with depth-time log of coiled tubing device. After comparing this log with the basic open hole log which perforation depths have been determined based upon, differences are captured and depth modification is carried out. Additionally, this method prevents the need for E-coiled tubing units which in turn can add to the complexity of the operation and might also be considered uneconomical. According to the mentioned instructions, the depth of perforation in South Pars gas field has been considerably modified. It is notable to mention that in the absence of such method, the existing technology is not capable of depth modification so precisely. It is now considered crucial to apply this method in almost any coiled tubing perforation operation