Browsing by Subject "Carbonate Acidizing"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item A New Organic Acid to Stimulate Deep Wells in Carbonate Reservoirs(2014-05-28) Al-Douri, Ahmad FCarbonate acidizing has been carried out using HCl-based stimulation fluids for decades. However, at high temperatures, HCl does not produce acceptable results because of its fast reaction, acid penetration, and hence surface dissolution, and its high corrosion rate. As a result, alternatives to HCl have been investigated including organic acids. In this work, the reaction of a new organic acid with calcite was investigated using the rotating disk apparatus and coreflood setup. The organic acid was obtained using both a phosphorous-based and iron-based catalyst. The rate of reaction of a 10 wt% solution of the new organic acid was measured using the rotating disk apparatus at temperatures up to 250?F. Low-permeability Indiana limestone (1-5 md) samples of 1.5 in. diameter and 0.75 in. length were used. The effect of disk rotational speed (100-1,500 rpm) was investigated. Samples of the reacted fluid were collected periodically and calcium and iron concentrations were measured using Inductively-Coupled Plasma, and used to determine the acid-rock reaction rate and to study the possibility of precipitation. Also, coreflood experiments at different injection rates and a temperature of 300?F were performed to study the effect of the acid on wormhole propagation in calcite. Low-permeability Indiana limestone (1-10 md) cores used in these experiments have a diameter of 1.5-in. and a length of 6 in. For the phosphorus-based acid, experimental results showed that the rate of calcite dissolution at 205?F was controlled only by the rate of mass transfer of the acid to the surface. However, at 250?F, the reaction was controlled by both mass transfer and by the kinetics of the surface reaction. At 205?F, the reaction rate varied from 7.79E-07 to 4.47E-06 gmol/cm^(2).s, while at 250?F, the range was between 5.82E-07 and 2.72E-06 gmol/cm^(2).s. In coreflood experiments, the phosphorus-based acid caused calcium phosphate precipitation at 300?F, while the iron-based acid achieved breakthrough. Also, the optimum injection rate of the iron-based acid was determined to be 2.0 cm^(3)/min. This study summarizes the results obtained and recommends the use of the new organic acid for field applications in calcite reservoirs.Item PREDICTING TEMPERATURE BEHAVIOR IN CARBONATE ACIDIZING TREATMENTS(2010-01-16) Tan, XuehaoTo increase the successful rate of acid stimulation, a method is required to diagnose the effectiveness of stimulation which will help us to improve stimulation design and decide whether future action, such as diversion, is needed. For this purpose, it is important to know how much acid enters each layer in a multilayer carbonate formation and if the low-permeability layer is treated well. This work develops a numerical model to determine the temperature behavior for both injection and flow-back situations. An important phenomenon in this process is the heat generated by reaction, affecting the temperature behavior significantly. The result of the thermal model showed significant temperature effects caused by reaction, providing a mechanism to quantitatively determine the acid flow profile. Based on this mechanism, a further inverse model can be developed to determine the acid distribution in each layer.Item Study of Acid Response of Qatar Carbonate Rocks(2012-02-14) Wang, ZhaohongThe Middle East has 62% of the world?s proved conventional oil reserves; more than 70% of these reserves are in carbonate reservoirs. It also has 40% of the world?s proved conventional gas reserves; 90% of these reserves are hold in carbonate reservoirs. Recently papers published from industry discussed the techniques, planning, and optimization of acid stimulation for Qatar carbonate. To the best of author?s knowledge, no study has focused on the acid reaction to Qatar carbonates. The lack of understanding of Qatar carbonate especially Middle East carbonates and the abundance of Middle East carbonate reservoirs is the main motivation behind this study. This work is an experimental study to understand the acid response to Qatar rocks in rocks with two types: homogenous carbonate and heterogeneous carbonate. A large portion of this research is to further investigate the impact of centimeter scale heterogeneity on the acid stimulation using Qatar rocks. Qatar carbonates have multi-scale heterogeneities which may cause the impact of the injected acids to differ from homogenous case. Recent published field data indicate a much smaller number of pore volume to breakthrough compared with experimental measurement with homogeneous carbonate and heterogeneity is believed to be one of the contributors of causing the low field measurements. In this case, acid linear core-flood experiments were conducted with carbonate core samples of different petrophysical properties to study the impact of both separated and connected vugs and channels on pore volume to breakthrough. Computerized tomography was used in characterization of the heterogeneities. One experiment simulated the response of acid to heterogeneous carbonate in downhole condition with drill-in fluid damage. Homogeneous rock was cored from a well in Qatar. The optimal injection rate was pursued through acid core flood experiments for acid stimulation design and for further reference. It is been discovered that the optimum injection rate for heterogeneous carbonate exists. For the similar acid flux, the corresponding PVBT for buggy limestone correlates inversely with the fraction of total porosity comprised by vugs. For vuggy carbonates with connected vugs and channels, whether or not formation damage exists, the acid tends to create new pore space nearby to the existing vugs and channels. Different strategies need to be made regarding acid stimulation design with homogeneous carbonate, heterogeneous carbonate with separated vugs and channels and heterogeneous carbonate with connected vugs and channels.