By Colin Rice
Colin Rice Exploration Drilling Advisory - www.colinrice.co.za
Despite the very clever innovations that have been introduced to reduce the risks associated with wireline retrieval, the industry still experiences accidents related to wireline operations. This article explores one further safety device that can be used to further reduce risk.
This is the second article in Part 2 of our Technical Series on Wireline Retrieval Operations. Click here for an outline of the entire Technical Series on Wireline Retrieval Operations.
Prior to the introduction of safety overshot systems that positively lock the lifting dogs onto the spearhead point, many contractors adopted a "safety chain" system to prevent the inner-tube from falling in the event that the inner-tube de-latched from the overshot.
These systems generally connect the inner-tube head assembly to the overshot assembly via a chain or nylon rope or wire rope. This became an industry standard and contractors have made several modifications to the basic idea in order to improve its effectiveness. An example of one of these systems is shown in the photograph.
Although the safety chain system was a vast improvement and undoubtedly saved many injuries, it is not fool-proof. In many systems the upper point of attachment is the jar staff of the overshot and if the jar staff becomes detached from the overshot head then it would be rendered useless. The other disadvantage is that if the inner-tube de-latched it could still swing around and cause injury - obviously the longer the attachment the more it could swing around.
Notwithstanding these potential issues or the overshot system used, it is recommended that all contractors use a secondary safety device during wireline retrieval operations.
The next article provides some recommendations as a first step in mitigating the risks of wireline retrieval.