Improving Drilling Mud with Soda Ash (Sodium Carbonate, Na2CO3) and Barite (BaSO4) | An Original Research
On the 6th through the 9th of August 2019, I was opportune to attend the Nigerian Society of Engineers (NSE Uyo Branch) 2019 Tech-Innovation Engineering Conference and Exhibition. It is usually an impactful and interesting gathering of engineers all over the state.
So last year's edition of the conference had the theme to be “Local Content Innovation in Engineering for Sustainable Economic and Industrial Development of Akwa Ibom State and beyond.” Thus the entire focus of the meet up was being centered upon the need for local content sourcing and development in all respective engineering fields.
It is believed that the conference theme came up considering the fact that almost all, if not all of the equipment and materials being used for operations in Nigeria (especially in the Petroleum sector) are being imported whereas some of these materials are readily available in the nation and could be quite useful, if harnessed and developed upon appropriately.
This then gave the drive and motive to undertake this very research project on improving Nigeria local clays so as to serve as a substitute for the imported Bentonite in drilling fluid applications. For this reason, local clay was obtained fro Uyo and drilling fluid formulated using it as well. The density and pH value was measured and recorded accordingly. Also, barite and soda ash were added in various proportions to the formulated mud; their effects on the mud pH and density was also recorded.
The results of the research will be quite beneficial to petroleum engineering students, research institutes and indigenous oil and gas companies in Nigeria. In a case where the results of the research prove that the addition of these additives to the local clay will help improve it, indigenous companies will have the confidence to start utilizing and harnessing local contents.
From the foregoing, there is a great need to develop local contents for use in the oil and gas industries in Nigeria as it is necessary for the sustainability of the sector. One cannot afford to keep buying what he has as it is a total waste of resources.
THE SODA ASH EFFECT ON LOCAL CLAY
Drilling fluid or drilling mud is simply the combination/ mixture of chemical, fluid (water or oil) and clay materials. Drilling fluid is however very vital and necessary for successful rotary drilling operations. Imagine someone trying to dig a hole down the earth; it will definitely be a tedious task if the person in question does not try to soften the ground first by applying some water on the ground.
The water will therefore help in making the ground soft for easier digging. In the same vein, that is the role of drilling fluid in drilling operations; it serves as a lubricating agent and thus enhances drilling. The Wyoming Bentonite has been mostly used for this purpose.
It is worthy of note that one of the main reasons Nigeria local clays are not being employed in the formulation of drilling mud is because of their high acidic content/ nature compared to how strongly alkaline bentonite is. This assertion is thus proven in the results gotten below:
Table 1: pH Values of Bentonite Versus Local Clay
The results in Table 1 above show that the local clay is highly acidic (5.12) while the standard bentonite is strongly alkaline (10.6) in nature. The result further shows that there is a low concentration of sodium cations in the local clay which explains its low pH value. From Chemistry, pH scale helps in measuring the acidity and alkalinity of a solution or substance. Basic or alkaline water-based solutions tend have a high pH while acidic solutions have lower pHref..
It is the alkalinity of bentonite that makes it the most preferred in drilling fluid applications as it poses no threat to equipment. On the other hand, employing the use of this local clay as it is (acidic) for drilling operations will end up corroding the drill rig components such as drill strings, drill pipes, casings, drill bits etc resulting in an unproductive operation. This then explains the avoidance of local contenting by companies in this area.
However, Soda Ash (Sodium Carbonate, Na2CO3) comes into play here. Soda ash is an inorganic compound that gives moderately alkaline solutions when mixed with water. It is a very useful additive whenever the pH of a mud is to be improved upon. Thus, it is quite useful for mud engineers. When added to the mud, it aids in reducing the acidity of the mud rendering it suitable for use.
In view of the above, soda ash was being added in different concentrations (proportions) to the formulated drilling fluids using the local clay. The drilling mud was formulated using 25 grams of local clay against 350 milli litres of water, following the American Petroleum Institute (API) specification. Summary of its effect on the pH of the local clay is shown in the results presented below:
Table 2: Effect of Soda Ash on Local Clay
|Local Clay||Sample A||Sample B||Sample C||Sample D||Sample E||Bentonite (Reference)|
|Soda Ash Content (g)||2||4||6||8||10||Nil|
Research have shown and proven that the presence and absence of sodium cations (Na++) is a factor that affects the rate of ions exchange in clays. Thus from the results obtained, it is evident that there was a very low concentration of sodium cations in the local clay which resulted in their its low pH value (5.12) initially - Table 1.
But from Table 2 above, the addition of soda ash to the said local clay caused an increase in the pH value. Meaning that there was an increase in the concentration of sodium ions as a result of soda ash's addition. Also, its introduction drastically reduced the acidity of the clay. Therefore, as the soda ash content increased, the more alkaline the formulated drilling fluid becomes.
Still to note is that the mud pH increased from an initial value of 6.28 to 9.79 (about 56%) at a concentration of 10g of soda ash (Na2CO3) to 350mL of the local clay mud. The results further revealed that the yield point, plastic viscosity and apparent viscosity increased by about 169%, 43% and 70% respectively. The graph below depicts the effect of soda ash content on the pH value of the local clay mud.
The Soda Ash Effect
Thus, from the results obtained, the pH of the local clay mud improved drastically with increase in soda ash content.
THE BARITE EFFECT ON LOCAL CLAY
Barite (BaSO4) is a known additive whenever mud density is to be increased. Low mud density could cause a kick which could eventually lead to a blowout in the well. This is so because when the mud density is low, the hydrostatic pressure in the column of the well will be low and hence, would not counterbalance the formation pressure. When the formation pressure is therefore higher than the hydrostatic pressure in the column of the well, a kick (or blowout) is inevitable. No driller or oil company wants a blowout occur as it is highly destructive.
A kick is a forceful flow of fluid into the wellbore. A blowout on the other hand could be said to be an uncontrollable release of oil and/or gas from the formation or simply put an uncontrollable kick ref..
On the other hand, high mud density could lead to what is called 'Lost Circulation.' This is the loss of drilling mud to the formation. This happens when the hydrostatic pressure is greater than the formation pressure in the well and this is greatly attributed to the mud density. It is thus necessary to always keep the mud density in check.
The control of the formation pressure during drilling operation with drilling mud is a direct function of the density of the mud.
From the results of the experiment below, Nigeria local clays possess very low mud density and hence cannot be used for drilling fluid formulation as they could increase the chances of a blowout. The mud balance was used to measure the density of the local mud and that of bentonite. The result is given below:
Table 3: Mud Density of Bentonite and Local Clay
|Property, Unit||Standard Bentonite||Local Clay|
From the above results, the local clay has a low mud density when compared to bentonite. In order to increase or improve the mud density, barite was being added to the formulated drilling mud as a wighting agent. The effect of barite is thus seen in the results below:
Table 4: Effect of Barite on Local Clay
|Local Clay||Sample A||Sample B||Sample C||Sample D||Sample E||Bentonite (Reference)|
|Barite Content (g)||2||4||6||8||10||Nil|
From the result in Table 4, it is evidenced that the density of the local clay mud improved significantly with increase in the barite content. The results obtained further show that the local clay density increased from an initial value of 8.20lb/gal to 8.95lb/gal (about 9%) at barite content of 10g to 350mL of the local clay mud. More so, the figure below depicts the effect of barite on the density of the local mud.
The Barite Effect
This development then implies that barite (BaSO4) can be used as weighting material in the formulation of drilling fluid using this local clay.
The local clay possessed low mud density and low pH (acidic) in its natural state which makes it unsuitable for use. However, at considerable concentrations of barite and soda ash, the local clay showed suitable mud density and pH when compared with those of bentonite. Thus, these additives enhance and improve the performance of the local clay thereby showing a possibility that drilling mud could be formulated using it.
(PS: This is an original research work conducted by the author @Tomlee. All experiments were carried out at the University of Uyo Petroleum Engineering Laboratory. Images are from the author except otherwise stated.)