Consolidation of Carbonate-Based Formation Rocks by Dissolution-Precipitation of Ground Calcium Carbonate

Abstract

Abstract Generating hydraulic fractures with good conductivity is essential for well productivity in unconventional formations. However, hydraulic fractures gradually lose conductivity with hydrocarbon production as fracture surfaces creep closer due to proppant embedment or failure of fracture asperities under increasing effective in-situ stresses and high temperatures. This work proposes adding a widely available, natural-based ground calcium carbonate (GCC) to fracturing treatments in carbonate formations to make fractures mechanically harder and enhance long-term well productivity. The GCC-based solutions with several particle sizes (PS of 5-30 µm) were prepared at 77-300 °F and tested on homogenous carbonate core samples. Several solutions (different PS) were formulated by mixing 20 gm of GCC powder in 100 ml of organic solvent. The core samples were immersed in different solutions for seven days at either 77 or 300 °F, and the samples were thoroughly characterized before and after exposure to the solutions. Rebound hammer tests were also conducted to show the effect of the solutions on the samples’ mechanical properties, such as Young's modulus and compressive strength. The test results show that the physical properties, such as the dry weight of all core samples, increased noticeably after treatment, reflecting the success of the precipitation reaction and the penetration of used GCC into the bulk of the rock samples. Rock treatment with several (PS of 5-30 µm) powder solutions led to a significant enhancement of the samples’ mechanical properties, where Young's modulus (E) and Unconfined Compressive Strength (UCS) were observed to increase by up to 10-25 % compared to untreated rock samples. Rock hardening in fracturing applications is a relatively new concept. Compared to the consolidation additives in the literature, the proposed GCC formula is ubiquitous, widely available, and inexpensive. Lastly, the GCC formula is a by-product of a few oilfield operations, making it a sustainable solution to industrial waste in the oil industry.