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 make it a less favorable option for the stimulation of long wells with long or multiple stages of fractures. FF-01 is an environmentally-friendly and equipment-friendly product. It is a conversion to an organic base to maintain very low pH as a vehicle for aggressiveness, along with the creation of buffers and surface tension relievers. 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 FF-01 product for stimulation and matrix treatment of carbonate 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 atomic emission spectroscopy (ICP-AES), that FF-01 dissolves limestone rock samples with smaller reaction constants compared to HCl. However, it will dissolve the same mass of rock if enough time is given, and it lasts longer during the course of reaction while leaving fewer residues. Core floods using HCl and FF-01 were performed at temperatures of 25 °C and 40 °C. Wormhole paths were observed using CT scan imaging. The results showed that core surface was strongly dissolved for the HCl treated cores, but wormholes were not deeply extended into the core. On the other hand, core surface was mildly dissolved for the FF-01 treated cores, but wormholes were deeply extended into the core. HCl performs better in cleaning the near wellbore rock while FF-01 performs better in generating long wormholes and higher effective permeability compared to the cores that were treated using HCl. FF-01 was able to increase permeability in limestone core samples by up to 795 times.
