Abstract
One of the largest oilfields experienced calcite scale depositions on downhole tubing and surface equipment. The incumbent solution is a conventional precipitation-type scale inhibitor squeeze. However, the chalk reservoir features calcium-rich formation waters and strong binding affinities to the selected inhibitor. Such factors often challenge the squeeze design with brine incompatibility, water-loading, and low inhibitor return concentrations in the flowbacks, leading to higher frequency of treatments especially when higher inhibitor MECs are required.
This study details four squeeze optimization approaches for chalk-type formations: 1) Screening of new inhibitor chemistries to provide equivalent inhibition performance and better high-salinity brine tolerance through static bottle and dynamical scaling loop methodologies; 2) Optimizing the main-treatment pH for carbonate formations; 3) Investigation of a newly developed flush-additive squeeze enhancement technology; and 4) Inhibitor-rock adsorption modifiers to boost the inhibitor return profile. Items 2-4 were evaluated through carefully designed dynamical core flood techniques with great data reproducibility.
Through a comprehensive screening of 18 products, one scale inhibitor chemistry was identified demonstrating excellent calcite inhibition and superior brine compatibility. Furthermore, the inhibitor adsorption/desorption profiles showed that the carbonate matrix responded significantly differently to the inhibitor pH. With a normalized inhibitor MEC of 2-ppm, the core lives were 1200, 1800, and 650 PV under the same treating parameters with the main-treatment pH at 2.5, 4.5, and 7, respectively. Besides adopting the optimal pH, the treatment live was further increased to 2,800 PV using 2% squeeze enhancer in the preflush. Different from the flush-additive enhancer, the adsorption modifier was directly applied with the inhibitor. Synergistic effects were observed as the treatment lasted 2000, 2400, 2700 PV for 1%, 2%, and 5% modifier in the inhibitor package. The next steps are to conduct cost analysis among the options for an optimization, followed with formation damage evaluations using the reservoir core plugs from the formation depths. The data will be used to design the field trials.
This study shows how different parameters and chemistries can be utilized to improve the inhibitor squeeze lives for chalk reservoirs. The treatment design methodology for the chemical additive application is outlined and presented.
