Rapid Curing Environmentally Degradable Polymeric Pill for Loss Circulation Treatment

Abstract

Loss circulation is frequent while drilling in naturally fractured or depleted reservoirs, which is usually associated with high non-productive time (NPT). Moreover, naturally pre-existing fractures may propagate when fluid pressure inside the fractures exceeds the minimum principal stress. The primary objective of this paper is to investigate the operational performance of a quick applying polymeric pill to treat severe loss circulation in highly fractured formations. To strengthen the wellbore in the presence of large fractures, proper size and concentration of loss circulation materials (LCM) are required. In this paper, a crosslinked polymer comprised of inorganic crosslinker (Aluminum-Acetate) is used to cure severe loss circulation by completely sealing fractured or high permeable formations. To achieve this, the project investigated the rheological behavior, mechanical properties, gelation mechanisms, and the filtration of the crosslinked polymer through an artificial fracture. The effect of concentration, temperature, pH, and salinity on the stability and gelation process was also assessed.

The rheological properties of polyacrylamide/Aluminum-Acetate (PAM/AlAc) in aqueous solutions, with concentrations varying from 1 to 3 wt.%, were highly affected by pH, time, and shear rates, while temperature changes have less impact. The Aluminum-Acetate has a broad operational window and can form a strong gel in temperatures ranging from 75°F to 260°F. Nanosilica (NS) in small quantities less than 1% was found to enhance the stability and strength of the polymer. The results revealed that the gelation time of the Aluminum-Acetate is controllable at pH conditions between 3.5 and 8.5, and the most stable gel was formed in the temperature range from 65°F to 212°F. Fracture sealing experiments demonstrated the ability of (PAM/AlAc) to form a strong plug with sealing pressure of up to 700 psi. In general, the Aluminum-Acetate reinforced with nanosilica has great potential applications in curing severe loss circulation in high fractured formations under a wide temperature range. This paper describes a detailed method of mixing and preparing stable and functioning polyacrylamide/Aluminum-Acetate pill for curing a severe loss of circulation. The new proposed aluminum-based salt was investigated as a potential environmentally friendly replacement for the conventional chromium acetate as crosslinkers for polyacrylamide. The paper provides a good understanding of the rheological, mechanical properties, and gelation characteristics, which are important factors affecting the spotting of these pills.