A Novel Equipment-Friendly and Environment-Friendly Well Stimulation Fluid for Carbonate Reservoirs: Better Wormholes and Lower Corrosion at Reservoir Conditions
Authors: Pandey Jyoti Shanker , Nazari Negar , Thomsen Kaj , Barati Reza 
Published: January 2018

Matrix acidizing is a popular technique in Oil and gas industry to enhance the well productivity. For a successful acidizing job, dissolution behavior of formation rock with injected acid needs to be fully understood. At Reservoir conditions, dissolution rates of carbonate rocks in injected acid is one of the control mechanisms of the wormhole formation and propagation. Corrosion is also an important consideration during acidizing at high temperature. The primary objective of the current study is to compare dissolution and corrosion rates of a novel environment-friendly product (FF-01) with 15% Hydrochloric acid (HCl) and 15% HCl containing commercial additives (15% HClA); measured at reservoir conditions using the Rotating Disk apparatus (RDA). The Ultra Series FF-01 is a newly developed organic acid by Earthborn Clean, a division of Earthborn Environment Technologies LP, based in Kansas. USA. Overall Research focus is to develop a novel environment- friendly, equipment- friendly, nonhazardous, low corrosive acidizing fluid (FF-01) as an alternative to conventional acids used for production and injection wells for deep carbonate reservoirs.

FF-01 is a biodegradable, non-toxic, non-flammable, earth-friendly, safe, non-Newtonian acidizing fluid. In order to compare FF-01 with strong conventional acids, experimental data of more than 50 experiments are generated using Indian limestone core samples in RDA under varying reservoir conditions (500-2000 psi, 25°-80 °C). Under mass transfer reaction regime with laminar flow conditions, samples from the setup are collected at predetermined intervals. These effluent samples are further investigated to measure Ca2+ ion concentration using inductively coupled plasma/ Optical Emission Spectrometry (ICP-OES). This setup is further used to compare the corrosiveness of FF-01, 15% HCl and 15% HClA on 13-Cr steel coupons at several pressure and temperatures. Anton Paar Rheometer is used to study the viscosity behavior of FF-01 under reservoir conditions.

Experimental results suggest that FF-01 is comparable with 15% HClA when it comes to dissolution/corrosion rates. Deeper and non-uniform etching patterns are also observed on limestone cores in FF-01 however etching was absent for 15% HCl and 15% HClA due to face dissolution. Increase in temperature and pressure improves the etching channels which suggest better conductivity channel and improved permeability using FF-01. Flow consistency index values lower than 1 at reservoir conditions indicates the shear thinning behavior of FF-01 which means FF-01 shows higher viscosity at lower shear rate which prevents leak-off of FF-01 and allow for branching of the original wormhole. Various studies demonstrate that FF-01 is an environment-friendly and equipment-friendly acid. Application of FF-01 during acidizing will result in additional profits and cost savings by increasing the service life of well tubing, decreasing the need for corrosion inhibitors.