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Examining Innovative Techniques for Matrix Acidizing and Acid Fracturing in Limestone Formations to Minimize Damage to Equipment and Environment

Fred Markey, Tyler Betz, Kyle Taylor, Daniel Ackwith, and Reza Barati
University of Kansas


Well acidizing is one of the most common practices in the oil industry that has been used traditionally for wellbore cleanup, matrix acidizing, and acid fracturing. Hydrochloric acid (HCl) has been used as the main acid for limestone stimulation purposes. There are several concerns with the use of HCl acids: health and safety of the field crew, corrosive nature of the acids for the flow lines and equipment, and environmental effects of the produced HCl. Moreover, fast reaction times and consumption rates of HCl makes it a less favorable option for the stimulation of long wells with long or multiple stages of fractures. UltraFrack™ is an environmentally-friendly and equipment-friendly product. It is a conversion to an organic base to maintain very low pH (0 to 2) as a vehicle for aggressiveness, along with the creation of buffers and surface tension relievers for effectiveness and safety. Low pH, slower reaction rates with limestone, small amount of residue after reaction, safety, minimum damage to equipment, and longevity are the properties of this product. The main objective of this study is to validate the application of the environmentally-friendly and equipment-friendly UltraFrack™ product for stimulation and matrix treatment of tight limestone formations and compare the performance of this product with 15% HCl.

Beaker, rheology, and core-flooding tests have been conducted to develop this new product and study possible improvements in this blend. It was observed, using inductively coupled plasma mass spectrometry (ICP-MS), that UltraFrack™ dissolves the same mass and volumes of limestone rock samples with slower reaction rates compared to HCl. However, it lasts longer during the course of reaction and leaves fewer residues. Core floods using HCl and UltraFrack™ were performed at temperatures of 25°C and 40°C. Wormhole paths were observed using CT scan imaging. The results showed that HCl performs better in cleaning the near wellbore rock while Ultra-Frack™ performs better in generating long wormholes and higher effective permeability compared to the cores that were treated using HCl.

AAPG Search and Discovery Article #90201 © AAPG Education Directorate Mississippi Lime Forum, February 20, 2014, Oklahoma City, Oklahoma