Analysis of the Influence of Wellbore Deposits on Wireline Well Intervention Operations
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Well intervention activities are crucial for maintaining well performance and integrity throughout the whole lifecycle of oil producers and injectors. Typical operations involve perforation, logging, setting and pulling plugs, milling, broaching, brushing and work on side pocket mandrels and downhole safety valves. Common for all interventions is that sufficient access is needed to fulfill work downhole. It has been experienced that various deposits develop in the wellbore, inhibiting intervention access. It is well known these deposits are causing extra time and cost to well intervention operations, but there is limited systematic tracking of the problem. An improvement project related to wellbore deposits was defined in Statoil to get a better quantified understanding of the problem and suggest improvement in practices for future operations. The work from this thesis became an input to the project. To investigate deposit problems a data gathering based on operational reporting was performed. A set of parameters was defined to depict the problem. The scope of the collection was limited to all wireline intervention activities that were performed by Statoil on the NCS in 2014. An analysis was performed to describe the extent of the problem and look for potential trends. It was found that about 40% of all wireline operations encountered deposits (including only those registered in operational report). The impact of the deposits, in terms of time lost and time used removing the problems, has a significant contribution to the time and cost of well intervention operations. In addition, it can be inferred that the overall impact of these deposits on well performance and production is very substantial. The biggest single contributor to cost was scale removal associated with the downhole safety valve, which will also be the activity with greatest saving potential. Scale was found to be a problem mainly related to oil producers (~20%) while black amorphous deposits, commonly referred to as Black Sticky Stuff (BSS) were found on ~30% of the water injectors. Removal of scale was in many cases very time consuming, but achieved the objective in most cases, while for BSS, the outcomes had variable success. This study acts more as a benchmarking of deposit problems and impact on well intervention operations rather than presenting any breakthrough in understanding their appearance in the wells. This work depicts the complexity of deposits and the amount of work that needs to be done to enhance comprehension. There are many observations done in this work that cannot be explained, based on the relatively limited data set and the complex nature of the subject. Implementing sample taking, classification and better experience transfer system for wellbore deposits, can enhance future prediction and treatment procedures.