A Brief Review on Acid Fracturing and its Application in Iran Carbonate Reservoirs with Introducing an EFG Chemical Model

Acid fracturing is a relatively new technique proposed for increasing the reservoir permeability of the conventional as well as unconventional (very low permeability) reservoirs. Acid fracturing increases the permeability and facilitates oil recovery by both creating new cracks in the reservoir and also etching the crack faces. Acidizing the crack faces (usually by ۱۵% HCL) increases roughness of the surfaces leading to crack stability under in-situ closing stresses that eliminates the need for employing propping agents such as sand. Acid fracturing mechanism involve injecting of the acid in a pre-existing (or a prefabricated) crack under high pressure, crack propagation due to highly pressurized injected acid, diffusion of acid into crack faces, chemical reaction of acid with the formation rock, acid leak-off to the matrix, and finally long-term crack closure under in-situ closing stresses. SW Iran and the adjacent offshore areas are rich hydrocarbon-producing regions containing ۹۷% of oil and gas fields of Iran. Almost ۸۰% of Iran oil is extracted from carbonate Asmari and Bangestan group formations. High applicability of acid fracturing in these carbonate formations (because of high reaction rate between carbonate and HCL) and also its applicability in some relatively low permeability (less than ۲ md) oil reservoirs like Ilam and Dariyan, have encouraged the authors to investigate the application of acid fracturing in Iran carbonate oil fields. This paper after explaining the main mechanisms and the related governing equations in brief, reviews the existing numerical methods that can simulate acid fracturing. After that, applicability of this technique in Iran is investigated and some recommendations are made. Finally, an in-house developed chemical numerical code based on Fortran language was verified against an analytical single-species transport problem and numerical result shows good agreements with analytical one.

کلیدواژه ها:

Acid Fracturing ، Numerical Modeling ، Iran Carbonate Reservoirs