An Experimental Study on Usage of Hollow Glass Spheres (HGS) for Reducing Mud Density in Geothermal Drilling

Abstract

Successful drilling is a key factor in developing geothermal fields. Generating hydrostatic pressure, carrying cuttings to the surface and maintaining wellbore stability is essential for drilling fluid with its other important functions. For low pressure reservoirs, hydrostatic pressure of the drilling fluid should be low. To achieve that, mud density should be lowered. However, use of drilling fluids with higher density than required may fracture the formation and could cause partial or complete loss of drilling fluid into the formation that may cause serious problems. To obtain lower mud densities, methods such as air/dust drilling can be used. But for environmental reasons and cost issues, HGS are a serious alternative. This study aims to find proper HGS type with a convenient composition in a water based mud. In this study, hollow glass spheres (HGS) are used to obtain a density as low as 6.88 ppg which is much lower than the water density (8.33ppg). HGS are selected based on their pressure resistance and improved mud properties such as fluid loss, rheology, 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® with different concentrations of HGS at two different temperatures. Polymer based mud with HGS at rating of 5000 psia showed the best performance in filter cake properties and carrying capacity proving their effectiveness in horizontal and deviated wells. It has been also observed that HGS added lightweight drilling fluid also works well at high temperature. It has been observed that homogeneity (i.e. particle size distribution) of hollow glass spheres is greatly affects the results.