The success of well-drilling operations is heavily dependent on the drilling fluid. Drilling fluids cool down and lubricate the drill bit, remove cuttings, prevent formation damage, suspend cuttings and also cake off the permeable formation, thus retarding the passage of fluid into the formation. During the drilling through induced and natural fractures, huge drilling fluid losses lead to the higher operational expenses. That is why, it is vital to design the drilling fluid, so that it may minimize the mud invasion in to formation and prevent lost circulation. Typical micro or macro sized lost circulation materials (LCM) show limited success, especially in formations dominated by micro and nano pores, due to their relatively large sizes. The objective of this thesis was to investigate the performance improvement by the usage of NPs (nanoparticles) as lost circulation additives in the drilling fluid. In the current work, a new class of nanoparticles (NPs) based lost circulation materials has been developed. Two different approaches of NPs formation, and addition, to water based and invert-emulsion drilling fluid have been tested. All NPs were prepared in-house either within the invert-emulsion drilling fluid; in-situ, or within an aqueous phase; ex-situ, which was eventually blended with the drilling fluid. The laboratory measurements included measuring mud weight, pH, lubricity viscosity, gel strength, standard API LTLP filter test and high temperature and high pressure (HTHP) test. In this work we evaluated fluid loss performance of a wide range of NPs preferably selected from metal hydroxides, e.g. iron hydroxide, metal carbonates, e.g. calcium carbonate and metal sulfate and sulfide e.g barium sulphate and ferrous sulfide respectively.
The use of improved NP-based invert emulsion drilling fluid showed an excellent fluid loss control, rheological properties together with a good lubricity profile. This thesis reports an experimental and theoretical study on filtration properties of invert emulsion drilling fluids under static conditions. Under API standard filtration test at LTLP and HTHP, more than 70% reduction in fluid loss was achieved in the presence of 1-5 wt% NPs.
The results have also shown that the filter cake developed during the NP-based drilling fluid filtration was thin (thickness less than 1 mm), which implies high potential for reducing the differential pressure sticking problem, formation damage and torque and drag problems while drilling. Moreover, at the level of NPs added, no impact on drilling fluid apparent viscosity, and the fluid maintained its stability for more than 4 weeks. Other NPs prepared by in-situ and ex-situ method also showed an excellent fluid loss control. Results of the modeling showed that NP-based drilling fluid didn’t follow the Darcy equation at the initiation of filtration and therefore the initial region was found flat and nanoparticles reduced the premeability instantly. It was also shown that nanoparticles transport in filtration was predominantly influenced by the Brownian diffusion. Compare with the drilling fluid alone and drilling fluid with LCM, increasing shear rate did not increase the same extent of shear stress in case of NP-base fluid (both ex-situ and in-situ prepared), which can be attributed to the fact that smaller particles were dispersed more effectively than the larger bulk particles and provided bridging between clay particles due to their larger surface area. Tailor made NPs with specific characteristics is thus expected to play a promising role in solving the circulation loss and other technical challenges faced with commercial drilling fluid during oil and gas drilling operation.