The Potwar region of Upper Indus Basin in Pakistan is well known for its complexities in drilling because of high pressure subsurface conditions at shallow depths and presence of loss circulation zones. Lignite mud system is applicable preferentially in such conditions because of its low cost, inhibitive properties and tolerance to high mud weights. A study has been undertaken to evaluate the characteristic properties of lignite from Lakhra Coal mines, district Jamshoro, Sindh Province as drilling mud additive. The rheological properties, filtration loss and tolerance to high mud weight were investigated using API standard procedures. The results were positive.
This paper presents the characteristic properties of lignite from Lakhra for use as drilling mud additive. The study has been carried out in Mud Engineering and Cementing laboratory of Petroleum Engineering Department at NED University of Engineering and Technology, Karachi.
Lignite, also referred to as brown coal, is the lowest rank of coal and used almost exclusively as fuel for electric power generation. Lakhra coal mines are located about 190 km from Karachi and occupy a total area of 1,309 sq. Km. The coal reserves are estimated to be around 1.328 billion metric tons. Lakhra coal is associated with the Bara Formation of late Palaeocene age. The stratigraphic sequence is predominantly marine but also includes lacustrine, estuarine, deltaic and lagoonal deposits containing plant fossils and carbonaceous beds at several horizons. The coal beds at Lakhra have been gently folded into a major anticline. Nearly all the coal occurs at shallow depth of 50 to 450 meters from surface in gently dipping strata of the anticline, dissected at places mostly with normal fault of 1.5 to 9 meters displacement . Coal characteristics of Lakhra coal mine is given in table 1 .
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