An Investigation of the Factors Affecting Barite Sagging Related to Drilling Fluid Properties
Authors: Amani Mahmood 
Published: June 2019

Drilling phase is one of the most important parts of developing a field. The durability of the well and its performance is greatly related to the quality of the drilling. A good drilling will also have an effect on how fast the project can start make profits as the drilling phase become shorter and more efficient. There are number of different factors that can hinder the quality of the drilling job and in some cases stop it or damage the wellbore and cause catastrophic disasters. Barite sagging is a one of the main causes of damage in the wellbore during the drilling stage. Any drilling job needs a drilling fluid that can provide the engineers with: enough hydrostatic pressure to prevent the well from collapsing in, removing the drilling cuts to the surface, cools down and lubricates the drill bit during the drilling job, suspend the drilling cuts within itself during the drilling and when drilling is stopped,seal the permeable zones in the wellbore to prevent lost circulation, control the corrosion caused by corrosive gasses such as H2S, provide hydraulic energy to the bit to fasten and improve the drilling and finally help the engineer to the cementing and completion after the drilling was done. Barite Sag is a common phenomenon that occurs while drilling for oil and gas. Barite, BaSO4 is a weighing agent used to increase the density of drilling fluids to a desired level. It has a high density of 4.2 g/cm3. The problem that occurs in this phenomenon is that as the mud is circulated through the borehole, the barite that was dissolved in the mud starts separating from the liquid phase and settles down. This separation of barite from the aqueous phase creates an undesired density gradient and causes a lot of further problems. Barite sag can occur in both conventional and deviated wells. In vertical wells, higher density drilling fluids or barite-rich phase settles on the bottom of the well bore while the lower density fluid form layers on the upper part of the column. This usually occurs during static conditions i.e. when drilling is stopped or very low shear rate (rpm). Additionally, a very low shear-rate viscosity can also result in barite sag. However, deviated wells are more susceptible to barite sag as in deviated wells, gravity induces an additional settling effect which results in sediment beds of barite at the bottom of the borehole. In deviated wells, Boycott effect is the reason for barite sagging. In an inclined tubing, the vertical distance of the settling particles is greatly reduced as compared to that in vertical columns. Hence the process of sedimentation is accelerated. Barite sagging can cause some serious problems during drilling operations. These problems are: loss of mud circulation, well bore instability, and uneven mechanical friction which can cause pipes and tools to get stuck downhole. Barite sagging, if not controlled properly, can lead to a complete shutdown and well abandonment. Hence, this study is being conducted to look in detail at the various chemical and physical factors, that affect barite sag, so that more viable and optimal solutions can be derived to control the extent of barite sag. Barite sagging is just a general term used to describe the phenomenon of which the weighting material detaches itself from its own liquid phase and slowly settles down the wellbore. But many more specific examples of barite sagging have been looked into and researched to further expand our understanding of this phenomenon. From dynamic to static sagging, in wells that are vertical, horizontal or deviated, all of these scenarios have been heavily examined and studied. The extent of the research that has been done in regards to barite sagging is surely well deserved as barite sagging can cause major problems while drilling in the field such as loss circulation, sudden changes of density in the drilling fluid which could further escalate into a blowout. Problems with cementation, well control issues and stuck pipe, all have been encountered mainly due to barite sagging. The research papers available look into a wide range of aspects related to barite sagging, but I will mainly look at the research conducted that studies adding different substances into the drilling fluids and comparing the effects that the new substances can cause to the sagging affect. Another major topic that I will try to cover is the different methods that have been used through the years to measure barite sagging in the laboratory environments.