Özet:
Shallow water and lost circulation are frequently encountered problems during drilling top holes of oil and gas wells. Plenty of methods have been applied to overcome these problems. Among these methods, silicate based gels are one of the oldest. For this study, Sodium-Silicate based gel system is investigated experimentally and several aspects of the system are improved for efficient field applications. This improved gel system is deliberately delayed, multi-component system to be mixed as a uniform liquid at the surface facilities but desired to form gel structure where it is placed in the well. Gel slurries are composed of distilled water, Sodium-Silicate solution, polymer solution, lost circulation materials, weighting agent and organic initiator (initiating the gelation). In this study, effect of these components on gel time, gel quality and gel strength at room temperature is investigated as a function of their concentration. In order to compare gelation time of different compositions, a new, easy and consistent gel time determination method is developed. Being based on vortex closure time, the method can be followed easily even by basic rig laboratories. Another new method is introduced to monitor long term gelation process by measuring turbidity (NTU) of the mixtures and plotting NTU versus time curves. In addition, unique observation codes are defined to compare the gel qualities of different compositions. For gel time and quality experiments, Sodium-Silicate concentrations from 3.5% to 15% by weight in the mixture were investigated and the concentrations range of 7.5-10% were found as applicable. It is determined that, gel time is getting higher as silicate-initiator ratio (SIR) increases for these optimum concentrations. The system is improved by addition of two different polymer solutions. These polymers not only improve the elasticity of the final gels but also provide sufficient viscosity to keep weighting agent and/or lost circulation materials (LCM) in suspension. In addition, viscosity development curves obtained from rotational viscometer at various constant shear rates indicated that, gelation is accelerated by applied shear. Furthermore, HTHP filter press cell was modified by manufacturing new bottom cap with 1. mm diameter hole in center to determine the extrusion pressures of the gels and it was found that, extrusion pressure can be increased by the addition of fibrous type lost circulation materials. © 2014 Elsevier B.V.