Investigating the performance of non-damaging hybrid gel to mitigate lost circulation in fractured formations: A comprehensive study using Box–Behnken design

Abstract

Gels that have a low viscosity at the time of mixing and form a three-dimensional gel structure after some time delay can be applied successfully in controlling lost circulation. Cross-linked gels play an important role in sealing high permeable and fractured formations. This research aims to evaluate a novel gel that can mitigate lost circulation during drilling in fractured formations. The hybrid gel consists of a cross-linked polymer gel as the continuous phase and an oil as the internal phase. The purpose of designing hybrid gels is to reduce the possibility of formation damage caused by the presence of gel in the fractures. In addition, the use of an internal phase in the gel can increase the durability of the gel and reduce the final cost of the operation.This article consists of two parts, experimental investigation and empirical modeling using response surface methodology. A number of parameters such as initial gelation time, final gelation time, and cross-linking rate were defined to evaluate the gel behavior under different conditions. First, the effect of polymer type, internal phase viscosity, pH, temperature, salinity, and shear rate on the behavior of the hybrid gel was investigated. Furthermore, in order to increase cross-linking efficiency, the cross-linker was added onto the reactive nano-silica surface to achieve a nano-crosslinker, and then the performance evaluation was accomplished. Thereafter, the sealing pressure test was examined to measure the amount of pressure that the hybrid gels could withstand in the fractures to prevent further fluid loss. Finally, the amount of gel rupture in 15% and 28% hydrochloric (HCl) was studied over time at 25 and 60 °C so as to evaluate the formation damage of hybrid gels.Response surface methodology (RSM) was employed based on Box-Behnken design to determine a correlation for predicting the final viscosity of hybrid gel as a function of temperature, pH, and CaCl2 concentration. The predicted model was obtained by solving the quadratic regression model. The value of the correlation coefficient (R2 = 0.90) for the present mathematical model indicated good relation between experimental data and predicted values. Therefore, the proposed model is able to predict the final viscosity of hybrid gel adequately within the limits of input parameters being used.The experimental results show that hybrid gels, due to their flexible viscosity response, long-term stability, and non-damaging properties, can have proper performance and application in industry to combat lost circulation. Nano-crosslinker can effectively increase the cross-linking rate and final viscosity of the gel and also improve the gel performance at high temperatures. Based on dynamic sealing pressure experiments, the value of maximum sealing pressure for the guar-based hybrid gel is higher than that of xanthan. In addition, the nano-crosslinker enhances the maximum tolerable pressure of the gels to seal the fractures.