Analysis of Critical Parameters Affecting the Formation of Wormholes in Acid Stimulation of Carbonate Formations

Open Access
Almarri, Hamad
Graduate Program:
Energy and Mineral Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 20, 2015
Committee Members:
  • Yilin Wang, Thesis Advisor
  • Stimulation
  • Acid
  • Wormhole
  • Carbonate
Well stimulation has been the norm in the petroleum industry for decades to increase well productivity or injectivity. The increase in the productivity or the injectivity index of a certain well comes from smaller drawdown pressure and less formation damage. Formation damage around the wellbore can be caused by several factors such as completion, perforation, drilling fluids, chemical precipitations, fine migration, and EOR fluids. In order to overcome this formation damage which restricts the flow of fluids between the wellbore and the rock matrix, acids are pumped through the wellbore and into the rock formation. As a result of a reaction triggered by the acid, highly conductive channels form which connect the wellbore to the undamaged rock matrix, thus bypassing the damaged zone. These highly conductive channels are known as wormholes. Wormholes as the name implies are tube-like, highly branched conduits. The degree of branching as well as the size of the wormhole dictates how effective these wormholes are. Therefore, an optimum type of wormholes with the right amount of branching and the right size is always desirable. The objective of this study is to understand how different dissolution patterns which form during a typical acid treatment affect the overall effectiveness of an acidizing treatment. Using a 3-D core scale model, the theory of an optimum wormhole condition is tested and the effect of several other parameters on the resulting dissolution pattern are examined. The parameters which are examined include injection rate, acid concentration, permeability-porosity relations, heterogeneity magnitude, reservoir pressure, reaction rate, mineral solubility, and acid diffusivity. After simulating the effect of each one of these parameters on the wormhole, the resulting trends are compared to preexisting trends in the literature. Moreover, a scale up method is adopted in this study to examine how the effect of these parameters translates on the field scale. Finally, a post acid treatment flow chart, based on observations from all the simulation runs, is developed to suggest a method to utilize the results from a single acid job and apply it to future treatments.