An Experimental study on usage of hollow glass spheres (HGS) for reducing mud density in low pressure reservoirs and lost circulation zones

Arı, T. Çağrı
Drilling fluid is a fluid mixture that is used in oil and gas drilling operations. Generating hydrostatic pressure, carrying cuttings to the surface and maintaining wellbore stability is essential for a drilling fluid with its other important functions. For low pressure reservoirs, hydrostatic pressure that drilling fluid generated should be low. To achieve that, drilling fluid density should be lowered. However, use of drilling fluids with higher density than required could cause partial or complete loss of drilling fluid into the formation which may cause serious problems. To obtain lower mud densities, methods such as air/dust drilling can be used or oil based muds can be preffered. But for enviromental reasons and cost issues, Hollow Glass Spheres (HGS) is a serious alternative. This study aims to find proper HGS type with a convenient composition in a water based mud. In this study, HGS is used to obtain a density as low as 6.88 ppg which is needed to balance the formation pressure in a low pressure reservoir. Among HGSs with different pressure resistance, HGS5000 and HGS8000X are tested because of the maximum pressure to be encountered in the well is lower than 5000 psi. HGS is selected based on its improved mud properties such as fluid loss, rheological properties, filter cake quality, pH and gelation. After selecting the proper HGS type, laboratory tests are conducted with different water based fluid systems such as KCl-Polymer mud, Polymer based mud and Flo-Pro mud with different concentrations of HGS. Polymer based mud with HGS at rating of 5000 psi showed the best performance in cuttings carrying capacity which can be interpretted from rheological properties. Polymer based mud with HGS5000 has the lowest fluid loss value by optimizing CaCO3 concentration and has the best filter cake qualities: thin and impermeable. Gelation and pH values of the selected drilling fluid are observed. Polymer optimization for the selected drilling fluid with selected HGS is conducted and particle size analysis is also in the content of this study.