Process of Releasing a Stuck String Using Static Dissolvable Coating Layers
Authors: Althowiqeb Ibrahim 
Published: March 2023

Stuck-pipe incident identified as when planned operations are suspended due to the affection of downhole forces which restrict and prevent the drill string movement and rotation. It is considered as one of the most undesirable incidents while drilling oil & gas reserves. It usually leads to massive delays and obstructions during operational actions, which would result in tremendous amount of loss in cost and time. There are three main mechanisms contributed for causing a stuck-pipe incident, include differential sticking, hole pack-off, and wellbore geometry sticking. The prospective of this paper is to address a competent solution to reduce differential stuck-pipe incidents at sandstone formations particularly. Differential sticking described in general as when a portion of the string embedded or sink into the filter-cake that has been formed or consolidated across the wellbore. It could result because of the differential pressure exerted by the mud column being greater than the pressure of the formation fluids on that particular section. Also, it could result due to various reasons such as poor filtration control and deficient filter cake quality. It can be also a result of excessive overbalance when a high mud weight is required to hydrostatically control a high-pressure zone which also includes lower pressure or depleted zones in the same hole section. High ECD could be a contributed factor as well due to poor mud condition, poor or inadequate hydraulics respectively. Addition to that, excessive rate of penetration that resulting in increased of annular mud weight due to the cuttings overload, leading to poor hole cleaning in sequence. As a Drilling Engineer, this should be a major subject to think about actively and try to look after feasible solutions for troubleshooting this matter and trying to control its frequency of occurrence. There are many solutions that could be approached to resolve a stuck-pipe incident, depending on the mechanism encountered. One of the most effective methods of which, is to pump acid downhole around the string. Pumping acid considered as the most common method of freeing a stuck string in general, and yet the last resort to be approached in some of the cases. The mechanism I have been mainly studied and focused to develop a solution against, is differential sticking at sandstone formation. A proactive solution has been formulated of introducing a static dissolvable coating layers of CaCo3 based element, that can be deployed and attached initially around the outer body of the drilling BHA, so it can be dissolved by the action of HCL acid. This will help for creating a beneficial clearance between the coated BHA and the filter-cake to be able to release the string after the dissolvance of the pre-installed composite coating layer. The product of this reaction between HCL acid and the CaCo3 coating layers, will introduce Co2 which will actively help to weaken the bonds between the coated BHA and the filter-cake, in addition of creating a slippery medium to be able to mechanically rotate and release the string with a supportive force applied from surface. The overall objective of this idea crystalized a concept of introducing the carbonate element physically inside the sandstone formation, to ensure that once the HCL acid pumped, we can guarantee ending up with very good results to free the string. This is based on the experimental results which have proven earlier a high success rate of using HCL acid in carbonate formation, with limited success achived at sandstone formation in counterpart. So, this advantage has been taken into considerations for designing this Engineering solution of stuck-pipe avoidance and release mechanism. The HCL can be pumped through normal circulation from inside the drillstring typically, or it can be pumped through another supportive feature proposed in the embodimient of this solution. This feature proposed to pump the HCL acid through channels that can be constructed on the sideways of the drillpipes, which are eleigible for inserting acid resistant tubes connected together to transfer the acid all the way from surface to the targeted spot of action. This feature simulating a similar concept of utilizing wired drillpipes for obtaining real-time data while drilling, as it introduces these connected cavities to transfer the acid to the stuck area. This also will help to minimize the contact of the acid with the drillstring metallic components, resulting in longer life for the tools along with achieving the objective. It can be activated once the normal circulation method cannot proceed effectively, or if we can locate the stuck depth clearly. The working principle of this Engineering method start by introducing the coating layers to be imbedded around the drilling BHA at earlier time in town. This step achieves the proactive tendency of the solution. After that, the coated BHA will be presented at the rig site to be picked-up prior to drilling a hole section. The coated BHA will be included within the drillstring configuration along with the drilling bit assembled in the last order. As far the drilling operations moving forward, hole sections will be developed. Once a differential stuck incident encountered, the process can be activated through delivering the HCL acid as the dissolving solution to be then release the drillstring as a determinet result.