Well Clean-Up Using a Combined Thermochemical/Chelating Agent Fluids

Abstract

The well clean-up process involves the removal of impermeable filter cake from the formation face. This process is essential to allow the formation fluids to flow from the reservoir to the wellbore. Different types of drilling fluids such as oil- and water-based drilling fluids are used to drill oil and gas wells. These drilling fluids are weighted with different weighting materials such as bentonite, calcium carbonate, and barite. The filter cake that forms on the formation face consists mainly of the drilling fluid weighting materials (around 90%), and the rest is other additives such as polymers or oil in the case of oil-base drilling fluids. The process of filter cake removal is very complicated because it involves more than one stage due to the compatibility issues of the fluids used to remove the filter cake. Different formulations were used to remove different types of filter cake, but the problem with these methods is the removal efficiency or the compatibility. In this paper, a new method was developed to remove different types of filter cakes and to clean-up oil and gas wells after drilling operations. Thermochemical fluids that consist of two inert salts when mixed together will generate very high pressure and high temperature in addition to hot water and hot nitrogen. These fluids are sodium nitrate and ammonium chloride. The filter cake was formed using barite and calcite water- and oil-based drilling fluids at high pressure and high temperature. The removal process started by injecting 500 ml of the two salts and left for different time periods from 6 to 24 h. The results of this study showed that the newly developed method of thermochemical removed the filter cake after 6 h with a removal efficiency of 89 wt% for the barite filter cake in the water-based drilling fluid. The mechanisms of removal using the combined solution of thermochemical fluid and ethylenediamine tetra-acetic acid (EDTA) chelating agent were explained by the generation of a strong pressure pulse that disturbed the filter cake and the generation of the high temperature that enhanced the barite dissolution and polymer degradation. This solution for filter cake removal works for reservoir temperatures greater than 100 °C.

Complex barite filter cake removal using in-situ generated acids by thermochemicals

“…Recently, Mahmoud 40 found that using the high temperature and pressure generated using thermochemical fluid (ammonium chloride and sodium nitrate salts) was able to hydrolyze the polymer coat covering the filter cake material. According Mahmoud 40 , the exothermic reaction (Eqs. 2-4) generated temperature and pressure ensured the removal of the polymer coat around the filter cake material.…”

“…Therefore, the polymer layer of the filter cake must be dissolved prior to the filter cake washing process 15 , 38 using any of the regular polymer breakers such as α-amylase to degrade this layer 39 . Recently, Mahmoud 40 found that using the high temperature and pressure generated using thermochemical fluid (ammonium chloride and sodium nitrate salts) was able to hydrolyze the polymer coat covering the filter cake material. According Mahmoud 40 , the exothermic reaction (Eqs.…”

An Experimental Study to Reduce the Fracture Pressure of High Strength Rocks Using a Novel Thermochemical Fracturing Approach

“…Application of thermochemical is widely found in petroleum engineering applications. Recently, Mahmoud [35] used thermochemical to remove a filter cake and provide experimental evidences to clean up the oil and gas wells after drilling operations. Hassan et al [36] presented a new technique to remove condensate banking by using thermochemical.…”

Reduction of Breakdown Pressure by Filter Cake Removal Using Thermochemical Fluids and Solvents: Experimental and Numerical Studies

“…Barite has very low solubility in mineral and organic acids, compared to other weighting materials in drilling fluids. Barite also has moderate solubility in high pH chelating agents such as EDTA and DTPA [ 23 ]. The filter cake can be removed through either a single-stage or multi-stage process based on the computability of the remover fluid ingredients [ 23 ].…”

“…Barite also has moderate solubility in high pH chelating agents such as EDTA and DTPA [ 23 ]. The filter cake can be removed through either a single-stage or multi-stage process based on the computability of the remover fluid ingredients [ 23 ]. This study aims to investigate the removal of barite filter cake and its impact on the breakdown pressure of different rocks.…”