Effect of fiber on the rheological properties of gelled acid

Bo Gou,Xiao Li,Kunjie Wang,Mingyong Zeng,Jianchun Guo

doi:10.1007/s13202-021-01123-3

Abstract

Degradable fiber is widely used to assist gelled acid diversion and reduce acid leak-off in the acid stimulation of carbonate hydrocarbon reservoirs in Sichuan Basin of China. The rheological properties of an acid system will affect the geometry of the acid-etching fracture. However, the effect of fiber on the rheological properties of gelled acid is not yet clear. This paper investigates the rheological properties of gelled acid with various fiber concentrations at different temperatures. The results show that when the temperature is less than the degradable temperature of the fiber, the apparent viscosity of gelled acid rises gradually with an increase in fiber concentration, while the fiber has no significant effect on the viscosity of gelled acid at the degradable temperature. The dissolution process of fiber in gelled acid experiences none-dissolution, surface dissolution, dissolution and fining, and a complete dissolution stage from low to high temperatures, which all have different effects on gelled acid viscosity. The fiber links more gelling agent molecules of gelled acid together to form a quasi-network structure between the fiber and fiber and the fiber and polymer, which results in a rise in the viscosity of gelled acid. The acid system also shows a strong shear thinning property under different temperatures and fiber concentrations. However, the power-law index n of this acid system always maintains a steady average value of about 0.181, while the change pattern of consistency index K is similar to the change in viscosity with varying fiber concentrations and temperatures. The research results are useful for acid fracturing treatment design in carbonate reservoir.

Highlights

Marine carbonate hydrocarbon reservoirs are an important hydrocarbon resource
The fiber concentration ranging from 0.1 to 0.5 wt% may be enough for controlling acid leak-off and reducing acid-rock reaction rate, but insufficient for creating new fracture, so the effect of extend fiber concentration should be discussed in the future
Compared with no fiber gelled acid, the apparent viscosity of the gelled acid within 0.5 wt% fiber was increased by 34.9%, 28.9%, and 24.7% at temperatures of 60 °C, 80 °C, and 100 °C, Analysis of the micro-morphology of fiber in gelled acid at different temperatures with fixed concentration 0.5 wt% in Fig. 6, shows that the gelled acid had a strong corrosion effect on fiber, which became more obvious under increasing temperatures

Summary

Introduction

Marine carbonate hydrocarbon reservoirs are an important hydrocarbon resource. Recently, many deep and ultra-deep naturally fractured carbonated gas reservoirs have been found in Sichuan and China’s Tarim Basin (He et al 2019). Keywords Carbonate reservoir · Acid fracturing · Degradable fiber · Gelled acid · Rheological property · Apparent viscosity Guo et al (2015b) showed that the apparent viscosity of fiber-assisted hydroxypropyl guar fracturing fluid was affected by shear rate, fiber concentration, and temperature.

Results

Conclusion