Thus, a cationic surfactant such as n-dodecyltrimethylammonium bromide (DTAB) is proposed as an additive in the bentonite solution to overcome this problem. In this study, laboratory experiments were conducted to determine the most stable modified bentonite solution before being analyzed in a core flooding test. This study showed that the most stable bentonite solution was 20 µm nanoclay with 13.7 x 10-3 mmol/kg DTAB.
Indeed, the modified bentonite solution has the potential to be used as a blocking agent in a permeability modification method. Industrial bentonite mainly contains Ca2+ and Na+ to form Ca-bentonite and Na-bentonite due to the counterbalance of exchangeable cations in the inner layer of bentonite particles (Yunfei et al., 2006, Onal, 2006). There are many applications of bentonite in the oil and gas industry such as in the drilling process and sealing wells.
In the drilling process, bentonite is the main component of the drilling fluid or the so-called water-based mud (Al-Homadhi, 2007). Thus, in this study, a cationic surfactant will be used as a swelling inhibitor for bentonite and its compatibility will be evaluated to obtain an effective permeability modifier in the formation.
Problem Statement
In this study, bentonite is proposed as a permeability reducing agent and will evaluate its performance and effectiveness using laboratory experiments. However, bentonite alone is not compatible to be injected into the reservoir as it can solidify before it can reach the "thief" zones. Finally, the performance of modified bentonite materials will be compared with other conventional blocking agents for permeability modification.
Alternatively, bentonite clay is suggested as a permeability modifier because it can withstand high temperature conditions and high stability. Ideally, bentonite is injected and penetrated into the reservoir and flows to the high permeability zone to block that particular area so that water or gas flooding can flow through the low permeability zone and sweep the oil away. The purpose of this study is to determine the effectiveness of the permeability modifier using bentonite.
However, by merely contacting water with bentonite, it tends to build up and solidify in the wellbore before penetrating through the reservoir. Therefore, cationic surfactant will be used in this study to determine its compatibility with bentonite and act as a blocking agent in the reservoir.
Objectives
Scope of Study
This study is important for students as well as for the oil and gas industry, especially in the EOR method, because the conformity problem in the heterogeneous reservoir reduces the effectiveness of the EOR application due to the observation of an early water breakthrough. Extensive studies have been done to improve the compatibility of the heterogeneous reservoir and many of the studies have used chemical-based materials as the blocking agent. However, there are many limitations when applying chemicals to the tank and this can be met by replacing the chemical based material with bentonite.
The use of bentonite as a blocking agent is feasible for EOR projects where it requires less cost and constraints. On the other hand, this project is feasible to carry out considering the ability of the final year student and the time constraint with the help of a tutor. Analytical assessment can be done by accessing journals, books and other sources.
LITERATURE REVIEW
- Reservoir Conformance
- Conformance Improvement Methods
- Bentonite Applications
- Steric Stabilization
- METHODOLOGY
- Materials
- Sample Preparation
- Stability Determination
- Investigation of Rheological Properties
- Core Flooding Analysis
In Figure 2.1(b) area conformation problem is shown by the existence of a fracture across the reservoir extending from injection well through one of the production wells. The main reason of petroleum reservoir conformation problem is due to the variation of fluid flow capacity in the heterogeneous formation (Robert et al., 2011). In addition, it is important to understand the unique chemical structure of the bentonite to determine the chemical bond when it is in contact with other materials, for example in this study is cationic surfactant.
Only a small amount of cationic surfactant is needed to increase the viscosity of the fluid and thus improve shear resistance. Colloidal system or solution stability determination are dispersed phases finely divided in a dispersion medium. The size of the particles can result in: a) Bentonite flowing into the highly permeable channel and (b).
For example, particle diameters between 1 and 1000 nm may exhibit colloidal character due to the particle surface area available for interaction to occur. The stability of the solution is determined by the behavior of the particles when they interact with each other. The attractive force dominates when the particles will stick to each other and coagulation occurs due to the bridging of the particles.
Cationic surfactant is one of the examples of water-loving particles whose hydrophilic contains positively charged ions. In this study, the stability of the modified bentonite suspension is determined by identifying the optimal amount of bentonite and cationic surfactants to be used to achieve stability. In this section, a PH meter is used to determine the pH value of the samples.
When determining stability, bentonite turbidity is considered to compare the settling rate of bentonite at different pHs, as well as when mixed with different concentrations of cationic surfactant. A turbidimeter will be used to obtain the exact turbidity value of all samples. Then the resistance created on the inner cylinder is transferred to a precision spring that causes the reading on the dial to deform.
In this study, the optimum stabilization-modified bentonite solution is used to determine the rheological properties of the solution. The diameter and length of the core sample are measured before testing with Figure 3.5.
RESULTS AND DISCUSSION
- Bentonite Solution Preparation
- Turbidity Results
- Bentonite solution with varies pH value
- Bentonite solution with varies DTAB concentration
- Sample of 20µm nanoclay with 13.7x10 - 3mmol/kg of DTAB concentration with adjusted pH value
- Turbidity results for Different Agents
- Rheological Properties Results
- CONCLUSION
However, since brine is used in the solution, it will reduce the stability of the solution. Thus, in this study, several samples with different properties are prepared to determine the optimal stability of the solution. The purpose of the different pH values is that each bentonite solution with a different pH results in a different turbidity value that indicates the stability of the solution.
The interaction between bentonite minerals during collision will determine the dispersion stability of the solution. This is to measure the settling speed of the solutions, which also determines the stability of the particles. Therefore, aggregation of particles will occur due to a decrease in the stability of the suspension.
However, in lower concentration which is 11.7x10-3mmol/kg, the stability of the solution is probably the same as 13.7x10-3mmol/kg, but has less value in turbidity. In addition, as referred to Figure 4.6, the trend of the turbidity results of the solutions is most likely the same that they decreased rapidly in the early times. This is by filling every surface area of the bentonite particles with the middle particles and thus dominating the repulsive force.
Therefore, the plastic viscosity of the modified bentonite solution is stated to be 1.5 cP. In this section, the selected solution, which is 20 µm nanoclay with a DTAB concentration of 13.7 x 10-3 mmol/kg, is tested using the Benchtop Permeability System (BPS) to determine the effectiveness of the solution when applied to a core sample. That is, the objective of conducting this experiment is to determine the reduced amount of porosity and permeability of the core sample after treatment with a modified bentonite solution.
Poroperm is used in this study before testing the core with BPS to determine the porosity and permeability data of the original sample. Therefore, in this study, it shows that modified bentonite solution is able to reduce the permeability of the core sample in about 64% of the original permeability. The performance of the selected permeability modifier which is 20µm nanoclay with 13.7x10-3mmol/kg DTAB concentration is determined using Benchtop Permeability System (BPS).
The modified bentonite solution is able to reduce the fluid permeability of the core sample by approx. 64% from the original permeability. In addition, the rheological properties of the modified bentonite solution are determined and the result of plastic viscosity is 1.5 cP and the yield strength is 1 lb/100ft2.
RECOMMENDATIONS
Finally, the selected bentonite solution, which in this case is 20 µm nanoclay with 13.7x10-3 mmol/kg DTAB concentration, can be tested under different temperature conditions. This is to determine the stability of the solution when the temperature changes during core analysis testing. Although bentonite is stable at high temperatures, modified bentonite solution with the presence of DTAB may have different stability conditions.
Core analysis tests with different temperature can be performed using Relative Permeability System (RPS), but due to various factors, Benchtop Permeability System (BPS) was used in these studies using ambient temperature. Physicochemical properties of bentonites an overview. Communication, Faculty of Natural Sciences, University of Ankara Series B Chemistry and Chemical Engineering, pp.007-021. Colloidal stability of bentonite clay considering surface charge properties as a function of Ph and ionic strength'.
Effect of temperature and additives on the critical micelle concentration and thermodynamics of micelle formation of sodium dodecyl benzenesulfonate and dodecyltrimethylammonium bromide in aqueous solution: a conductometric study'. Effect of Ph loading and layers on formation damage in porous media containing swelling clays.
