Potential Of An Andrassy And Mansuli Bentonite As A Drilling Mud Material
Authors: Samsuri A. , Leyong K.P. , Abdullah H. 
Published: December 2007

Abstract
This paper presents the results of laboratory treatment works on upgrading the bentonite from two areas of Sabah, Malaysia, namely Andrassy and Mansuli for the uses in petroleum industry. Bentonite, as a common material used in water based drilling mud is the sodium bentonite. Since the Malaysian bentonite is proved to be calcium based, certain treatment is needed to convert this bentonite to sodium variety. The successfully treated bentonite will be used as a material in drilling mud, which is cheaper as compared to the Wyoming and standard bentonite. This study included two treatment processes; wet treatment and electrolysis. Several sodium sources have been studied but only the sodium carbonate can successfully be used to upgrade the bentonite. The results obtained after these two treatment processes showed improvement in cation exchange capacity (CEC), which is about 27% increment for electrolysis treatment and 22% to 29% for wet treatment, respectively. However, the treated bentonite failed to meet the API 13A Specification (American Petroleum Institute) requirements for rheological properties when used as a material in drilling mud. Thereafter, certain polymer extender had been added to improve rheological of the upgraded bentonite slurry so that it can be used as a drilling mud material. In general the treated bentonite from Malaysia can be used as a replacement for the more expensive imported bentonite especially for local petroleum industry. In addition, the methods developed can also be used to convert the similar type of bentonite from other locations, since the large deposits of calcium based bentonite can be found in Malaysia.

Introduction
In order to reduce the overall cost of bentonite used in local oil and gas industry, the feasibility study of Mansuli and Andrassy bentonite application had been initiated. Before these bentonite can be used, their physical and chemical properties and their performance as compared with the standard bentonite must be determined. If their performances are not as good of standard bentonite, treatment ought to be applied to convert the counter ion that placed between the unit clay surfaces. The type of counter ions has a great effect on the swelling capacity of the montmorillonite mineral and by far the best performance is obtained with sodium-based montmorillonite mineral, which has sodium as counter ions. If the montmorillonite mineral in bentonite contains counter ions other than sodium, the swelling properties, viscosity build-up and filter cake permeability will be adversely affected.
Three sources of samples that were used in this study, two sources namely SA5–1 and SA5–4 from Andrassy of Tawau area and the other namely M4 from Mansuli of Lahad Datu in Sabah. These bentonite are proved to be non-sodium based, which are different from the commercial sodium based bentonite according to chemical composition, chemical and physical properties such as Atterberg limits, moisture content, moisture adsorption, ignition loss, specific surface and cation exchange capacity.

Experimental Works

Bentonite Sample Preparation
Bentonite samples from the field will be dried in the oven at 55 °C for four hours until moisture content become less than 10%. Then the sample will be crushed using grinding machine till it become powder. Selection of bentonite grain size is very important to obtain optimum cation exchange. API Specification 13A showed that the needed particles size to be used should less than 74 (m, which can be achieved by using wire cloth sieve.

Mineral Composition
X-Ray Diffraction (XRD) analysis had been used for mineralogy determination and the test was done by using Siemens D-5000 fully automatic diffractometer. The mineralogical constituents within the bentonite sample can be directly characterized giving critical information as to the geological evolution of rock samples.