Computational Research Progress in Applied Science & Engineering CRPASE Vol. 06(01), 25-29, March 2020 ISSN 2423-4591 Development and Performance Appraisal of a New Flat Rheology Drilling Fluid System for Drilling Deep Water HPHT Reservoir Mamidi Lokesh Teja a , P. K. Mahata b a Department of Petroleum Engineering and Petrochemical Engineering, University College of Engineering(A), Jawaharlal Nehru Technological University Kakinada , AP, India b EOA & HPHT Asset, Oil and Natural Gas Corporation Ltd, Kakinada, AP, India Keywords Abstract Deep water, High Pressure High Temperature, Flat Rheology, Equivalent Circulating Density (ECD), Barite sag. Drilling fluid performs many functions in a drilling process, including the removal of cuttings, lubricating and cooling the drill bits, providing the stability of the hole and preventing the inflow-outflow of fluids between the borehole and the formation. Conventional drilling fluids experience a number of deteriorations such as gelation, degradation of weighting materials and breakdown of polymeric additives under HPHT conditions. Flat rheology profile minimizes adverse effects on ECD, lost circulation, barite sag and hole cleaning activity. This paper highlights the performance of flat rheology drilling fluid systems and their rheology modifiers with special emphasis on water-based mud systems in deep water HPHT reservoirs. Various rheological parameters are experimentally evaluated and the results indicate the constant rheological profile over a wide range of temperatures and pressures. On the basis of the study following drilling fluid system is recommended: New Nanomaterials, KCl-Glycol, low-solids, non-dispersed (LSND) polymer systems(Poly Styrene-co-Butadiene), Glycol-polymer, and Mixture of barite and Manganese Tetra Oxide, TiO2 Nanofluids, Polyol based drilling Fluid system in Water- Based drilling fluid system to provide stable rheology and fluid loss for designing an HPHT tolerant Water-Based mud with an eco-friendly formulation. The newly engineered drilling fluid system exhibits constant flat rheology even in a deepwater environment, has demonstrated promising performance characteristics in field trail. 1. Introduction There are three distinct classifications of drilling fluids; Water Base Mud (WBM), Oil-based Mud (OBM) and Pneumatic fluid. However, these drilling fluids can further be sub-classified into various other categories. Many criteria are considered for the selection of type of drilling fluid to be used for particular wellbore construction. However, three key factors usually determine the type of fluid selected for a specific well: cost, technical performance and environmental impact [1]. Technical performance of the drilling fluid include cooling and lubricating the bit, carrying cuttings to surface to keep the hole clean, and to counterbalance the overburden pressure to prevent wellbore collapse [2]. Because of a narrow safe-density window in deepwater formation, the high ECD will cause the loss of drilling fluid, thus severely affecting deepwater drilling operations and significantly increasing the cost of drilling fluid [3]. Additional properties  Corresponding Author: E-mail address: lokeshteja9063@gmail.com– Tel, (+91) 8639291197 Received: 12 January 2020; Accepted: 26 March 2020 in the development of the fluids for deepwater conditions are:  Stability to extreme temperature ranges, from 34°F to 500°F  Minimal impact upon equivalent circulating densities (ECD)  Relatively non-reactive with shales and clays  The ability to suspend cuttings and keep barite from settling (sag)  Exhibiting a flat rheological profile over a given range To meet the above-mentioned properties and fluctuation in rheological properties, many innovative techniques have been developed and applied in the field. Flat Rheology drill fluid system is found immune to these detrimental effects. It means that a relatively stable yield point as well as 10-min gel and 6 r/min reading (Ø6) of the drilling fluid in the deepwater wellbore are maintained in a wide temperature range [4]. Therefore, the ECD of drilling fluid can be effectively controlled, and the loss of drilling fluid can be