Usage of Vermiculite as Additive Material in Water-Based Drilling Muds

Drilling mud is used in drilling operations to ensure well stability and to transport the cut-offs to the surface and is generally classified as; Spud, Lignosulfonate and Polymer types. Spud Mud is the simple mud and mostly used at the beginning of drilling operations. It is mainly composed of bentonite and water. With increasing depth, It is hard to keep well stability and to carry cuttings from the bottom of hole to the surface with the basic drilling fluid. Thus, some materials are used to maintain the rheological and filtration properties of the mud. One of them is vermiculite that is a general name of the hydrated ferromagnesian aluminium silicate group. It has expanded properties when heated. Like all clay minerals, the cation exchange capacity is very high and very similar to the montmorillonites in terms of high cation exchange capacity. In this study, the usage of vermiculite as an additive material in drilling muds was investigated. Spud muds containing vermiculite in different amounts were prepared. Then rheological and filtration analysis of the muds were done according to American Petroleum Institute (API) RP-13B-1 Standard. When evaluated the results, AV reached 41cP, PV 27cP, YP 28lb/100ft 2 , 10 sec. gel strength 17lb/100ft 2 , 10 min. gel strength 26 lb/100ft 2 and filtration 9cc. The results showed that the vermiculite can might be used as a viscosifier and fluid loss reducing additive material in the drilling mud.


Introduction
Water-based Spud mud is among the mainly drilling fluids. Thus, it's mostly important for drilling operations. It provides some specific properties for drilling operation such as prevent kick fluids, carry cuttings from beneath the bit to surface, suspend solids, form low-permeability filter cake, maintain the stability of the borehole, reduce friction between the drilling string and the sides of the hole, cool and clean the bit, assist in the collection and interpretation of information available from cuttings (Caenn & Chillingar, 1996;Lyens & Plisga, 2004;Hemphill & Larsen, 1997;Knox & Jiany, 2005).
Rheological and filtration properties of the mud varies during circulation in the well and loses flow features. In order to improve rheological properties of drilling mud, different additive, chemicals and polymers are used. These are generally CMC, PAC, XCD, Modified Starch and also clay minerals as viscosifier and fluid loss reducer additive material (Dyke, 2000).
Vermiculite is a general name of the hydrated ferromagnesian aluminium silicate group. It shows similar properties with mica group minerals. Like all clay minerals, the cation exchange capacity is very high and very similar to the montmorillonites in terms of high cation exchange capacity. The layer structure is 2:1 and there are four type. These are soil vermiculite, authigenic vermiculite, metamorphic vermiculite and macroscopic vermiculite. Generally expanded vermiculite is preferred in the industry applications, because of its specific chemical and physical properties. Nowadays, there are many application area such as building, agriculture, foundry and steel factories, oil refineries, cement companies, filler material in plants and drilling mud additive material in drilling operations (Bassett, 1959;Bassett, 1963;Berker, 1992;Erseçen, 1992;Hattaway, 1955;Kuşcu, 2001;Harben, 1995;Eaton, 1997;MRE, 1989).

Bentonite
Bentonite was supplied from Eldivan-Çankırı region in Turkey. It is a sodium type vermiculite and the particle size is lower than 75μ (Fig. 1). It is also suitable in terms of the API Specification 13A standard (API, 1990). Its elemental composition is given in Table 1.

Vermiculite
Vermiculite was brought from Yıldızeli, Sivas region in Turkey. Particle size of the vermiculite was found between 0.35mm and 1mm, so it was named as super fine vermiculite (Fig. 2). The chemical composition of the vermiculite is given in Table 2.

Experiments
First, Spud mud containing 6% w/v bentonite was prepared according to API standards. Then, vermiculite was added at different amounts (0.5, 1, 2, 4, 6 % w/v) and 6 mud samples were prepared for the investigation of the rhelogical and filtration properties.
The samples were aged 16 hours. Rheological and filtration analyses such as AV, PV, YP, 10 sec. gel strength and 10 min. gel strength analyses were done according to API RP-13B-1 Standard. The filtration test was measured using a filtration device (API Filter press) according to the same standard. Each experiment was repeated three times and the average values were taken to decrease experimental errors.

Results
The data obtained from rheological and filtration analysis are given in Table 3 and the graphs are represented in Fig. 3-4-5-6-7 and 8 respectively. Evaluation of the all results showed that the vermiculite enhanced the rheological and filtration properties of the water-based mud. The values of AV, PV, YP, 10 sec. gel strength and 10 min. gel strength specifications increased while fluid loss was decreased with increasing the vermiculite concentration in the mud. recorded for 6% w/v vermiculite addition. However, the optimum value was obtained with the 4% concentration. This result is enough for nearly all of water-based drilling muds.

Fig. 4. Analysis results of YP
As known that yield point is another important factor for a pump selection and the pressure arrangement. Fig. 4 indicates that the optimum value was reached at the 4% w/v vermiculite concentration and enough for nearly all of water-based drilling muds. According to results of 10 sec. gel strength (Fig 5) and 10 min. gel strength (Fig. 6), the addition of vermiculite increased the gelation for both. Based solution value was 1 lb/100ft 2 and 2 lb/100ft 2 , respectively and these values were not enough. But as a result of this increase with 6% concentration of vermiculite, 10 sec. gel strength reached 17 lb/100ft 2 . However, the optimum value for the 10 sec. gel strength and 10 min. gel strength were determined at 2% w/v and 4%  The filtration loss of the muds decreased with increasing the vermiculite ratio into the muds. It can be explained with the super fine particle size which can penetrate into holes and decreased permeability of the mud into formations. Based solution value was 20 cc but as a result of this increase with 6% concentration of vermiculite, filtration reached 9 cc. Reached the optimum value was with the 2% concentration. This result is enough for nearly all of water-based drilling muds.

Discussion
In this study, usability of vermiculite in spud muds was evaluated. Samples containing vermiculite in different concentrations (0.5, 1, 2, 4, 6 % w/v) were prepared and aged 16 hours. Then, AV, PV, YP, 10 sec. gel strength, 10 min. gel strength and fluid loss analyses were done according to API.
When evaluated the experiments and results, it is determined that vermiculite has positive effects on the rheological and filtration properties. As a result, vermiculite can be used as viscosifier and fluid loss reducer additive material in water-based drilling muds.