رسائل ماجيستير
English
2015
Identifying Optimum Conditions for Stable Wormholes Created by Chelating Agents
Mohamed A. Mahmoud, أسعد أحمد عبدالله بري
جامعة الملك فهد للبترول والمعادن · السعودية
Acidizing of carbonate formations is a common practice to reduce the formation damage near the wellbore. In fact, acid stimulation removes the damage created by the drilling and completion fluids and also creates channels (wormholes) that can bypass the damaged area. In this process, acidic solution is injected to dissolve part of the rock matrix and creates conductive channels that facilitate the flow of hydrocarbons to the wellbore. Recently, researchers investigated the usefulness of chelating agents as stand-alone stimulation fluids to create wormholes in carbonate reservoirs. They showed that chelating agents can effectively be used as stimulation fluids especially in the cases of high temperature and low injection rate situations.This research targets the use of different types of chelating agents at different formulations as stimulation fluids for carbonate rocks. The optimum pH and concentration values of each solution will be screened to determine the optimum pH and concentration as a base of each solution based on solubility tests. Deionized water and sea water will be used for stimulation fluids preparation. Carbonate rocks will be stimulated using chelating agents such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and hydroxyethylenediaminetriacetic acid (HEDTA) to investigate their performance in creating stable and efficient wormholes. The wormholes will be evaluated after stimulation using CT scan, NMR, and acoustic measurements to assess the rock integrity. This study will provide a detailed description to the performance of these chelating agents in creating stable wormholes. Viscosity of chelates will be measured at different temperatures and different amounts of Calcium ions to establish their relation. At the end, wormhole growth propagation with chelating agents will be modeled by matching the actual pressure drop versus the pore volume injected using the existing models to test their applicability, and apply the necessary modifications to the existing models to obtain the best match.Solubility screening studies showed that DTPA and HEDTA chelating agents were soluble at pH values as low as 2.0 in all chelant concentrations prepared by deionized water and sea water. EDTA was not soluble at pH values less than 5.0 when sea water was used for dilution. None of the studied chelating was found to be suitable as iron control agent to be added to 20% HCl acid when sea water was used for mixing. 5% DTPA and HEDTA chelating agents were found to be good iron control agents for 20% HCl acid. Core flooding studies showed that the optimum injection rate for the chelating agents was in the range of 1.5 – 2.0 cc/m when both minimum chelant volume and minimum experiment time were used in determinations. Studies on the rock elastic properties revealed that chelating agents have negligible effect on relatively strong carbonate rocks such as Indiana Limestone, whereas, less strong rocks such as Austin Chalk can be highly affected by injecting chelating agents.