Abstract
Deep carbonate reservoirs are rich in oil and gas resources. However, due to poor pore connectivity and low permeability, it is necessary to adopt hydraulic fracturing technology for their development. The mechanism of hydraulic fracturing for fracture initiation and propagation in carbonate rocks remains unclear, especially with regard to selection of the type of fracturing fluid and the fracturing parameters. In this article, an experimental study focusing on the mechanisms of hydraulic fracturing fracture initiation and propagation is discussed. Several factors were studied, including the type of injecting fracturing fluids, pump flow rate, fracturing pressure curve characteristics, and fracture morphology. The results showed the following: (1) The viscosity of fracturing fluid had a significant effect on fracturing breakdown pressure. Under the same pump flow rate, the fracturing breakdown pressure of slick water was the lowest. Fracturing fluids with low viscosity could easily activate weakly natural fractures or filled fractures, leading to open microcracks, and could effectively reduce the fracturing breakdown pressure. (2) The fluctuations in fracturing pump pressure corresponded with the acoustic emission hits and changes in radial strain; for every drop of fracturing pressure, acoustic emission hits and changes in radial strain were mutated. (3) Under the same fracturing fluid, the pump flow rate mainly affected fracturing breakdown pressure and had little effect on fracture morphology. (4) The width of the main fracture was affected by the viscosity and pump flow rate. Maximum changes in radial strain at the fracturing breakdown pressure point occurred when the fracturing fluid was guar gum. (5) With gelled acid and cross-linked acid fracturing, the main fractures were observed on the surface. The extension of the fracturing crack was mainly focused near the crack initiation parts. The crack expanded asymmetrically; the wormhole was dissolved to break through to the surface of the specimen. (6) The dissolution of gelled acid solution could increase the width of the fracturing crack and improve the conductivity of carbonate reservoirs.
Highlights
With the development of economy and society, demand for energy is increasing gradually
(6) The dissolution of gelled acid solution could increase the width of the fracturing crack and improve the conductivity of carbonate reservoirs
We studied the effect of different fracturing breakdown pressures, changes in radial strain, fracture morphology, and acoustic emission (AE) characteristics with different injection fracturing fluids and compared and analyzed the effects of fracturing fluids and pump flow rate on the complex fractures
Summary
With the development of economy and society, demand for energy is increasing gradually. Oil and gas account for 56% of primary energy consumption. Carbonate reservoirs in ultra-deep wells contain abundant oil and gas resources, accounting for 60% of the proven oil and gas reserves in the world. The Ordovician carbonate reservoir in the northern part of Ordovician is the main oil production area in China. Because the Ordovician carbonate reservoir in the Tarim Basin has extremely low permeability, most of the wells need to be stimulated. Hydraulic fracturing is an important technology used to increase production, and it has been successfully applied to reservoirs with low permeability [1]. The hydraulic fracturing behavior of rocks has been studied by a large number of researchers, these have mainly focused on tight sandstone and shale [2]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
