RIASSUNTO
ABSTRACT
Debris management is a major concern for producers. Wellbore debris is responsible for many of the problems and much of the extra cost associated with extreme water depths and highly deviated holes. This paper discusses procedures and tool systems developed to optimize the efficiencies and economics of debris removal. Issues pertinent to deepwater wellbore cleaning will be discussed, along with the problems associated with removal of debris caused by perforating, milling, etc. The authors will outline techniques for removal of this debris and discuss a tool system that is a workable solution for these problems.
This paper will focus on the use of a Vectored Annulus Cleaning System to remove debris from areas of the wellbore that have normally proven very difficult. The system has been shown to be effective in removing debris from problem areas such as above liner tops or where casing size changes, areas with a loss of annular velocity, and inwells with little to no circulation. Case histories from the Gulf of Mexico and the North Sea will demonstrate how this technology has reduced problems of debris removal while saving rig time by eliminating trips.
INTRODUCTION
Debris in any form can create a problem not only during the completion of an oil or gas well but also during the drilling and workover stages of a well.During the completion phase the most common form of debris is originated by perforating guns. Many wells are shot across multiple zones and usuallyhave a retrievable bridge plug or packer plug below the area that will be perforated to isolate the different zones. Once the guns are fired and removed the majority of thegunand perforating debris will fall down around the retrieving headsof the packer plugs or bridgeplugs.Debrisisoneof the main causes of difficulty that prevents retrieval of the packer plug. Although the packer plug retrieving headisprovided with milling teeth and fluid passages to mill awayanysandor settlings from around the control bar, experience has shown that metal shavings and junk do not permit full engagement of the J-pin in the internal slot. Also,oncethepackerplugis retrieved, there is a high probability of debris falling into the lower completion.This can become costly andcanbetime consuming, often requiringmore than one trip to recover the plugs.
Some of the debris will be suspended in the wellbore either in the fluid, casing collars or liner tops. This debris, if not removed, will cause problems later during the running of the completion string. In spite of precautions taken to keep the production equipment as clean as possible, it is common to find problematic metal debris and shavings in the production string after the completion is run. This can cause difficulty during subsequent slickline operations to gain access to equipment further down the well. Furthermore, the risk of slickline tools and equipment becoming stuck is increased, often necessitating costly fishing operations.
The use of coiled tubing and its ability to circulate fluids is very often used to address the debris problems once they are recognized. This requires more costly coiled tubing runs involving cleanout fluids and downhole tools to cleanthe production tubing. Coiled tubing is also used to perform cleaning followed by manipulation of flow control devices such as shifting sleeves, and recovery of isolation plugs. Although less likely than wireline, coiled tubing also carries a risk of becoming stuck in a debris laden completion, particularly in larger completion sizes where annular velocities may be limited by size and flow capacity of the coiled tubing.
During workover operations where a permanent packer has to be removed by means of milling, the debris may cause all sorts of unforeseen problems. It may create damage to the casing wall while milling, cause the milling string to become stuck. On the deepwater floating rigs debris can get logged in the sub sea BOP stack and may hinder the operation of the BOP's. Debris can also create similar problems as above when running the new completion string.