Abstract

Shale has presence of large amount of clay minerals and thus its instability is a major problem while drilling. The main factors contributing to this are the hydrostatic Pressure, Chemical and Thermal. The Thermal factor deals with difference in temperature of drilling fluid and reservoir and contributes mainly to the cause of instability. The use of mud at normal temperature results in high temperature difference between the reservoir and drilling fluid hence adding to the instability of shale.Wellbore stability is very critical for a successful drilling operation. Heating can enhance tensile failure in shale while cooling lowers its tensile stresses. This paper adduces a novel idea to ameliorate the shale stability by using low temperature drilling fluid and a cost effective thermoelectric nanomaterials and Ni-Fe nanomaterial to alter the mud temperature. Thermoelectric nanomaterial reduces the mud temperature as electricity is applied while Ni-Fe nanomaterial helps in increasing the mud temperature. While drilling, mud temperature becomes greater than formation temperature due to which stress on wellbore increases and therefore wellbore stability reduces. Apart from this the pore pressure increases and the fracture pressure decreases. Improved shale stability can be achieved if the difference between temperature of mud and formation temperature is reduced to an optimum value. This optimum temperature difference is found by considering values of pore pressure, stresses on formation and fracturing pressure for different temperatures. In case of practical purposes, stress test can be carried out at different temperatures which help in deciding the optimum temperature difference. It has been discovered that the less expensive and readily available thermoelectric nanomaterials can be used to reduce the mud temperature. The upper hand of this technique is the low dosage requirements. Moreover the nanoparticles used are innocuous and environmentally safe.

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