Matrix Acidizing

Learning Objectives

After completing this topic “Matrix Acidizing“, you will be able answer to:

• What is acidizing process?
• What is acidizing in drilling?
• What is matrix stimulation?
• What is the difference between hydraulic fracturing and acidizing?
• What are the differences between matrix acidizing and fracture acidizing?
• Which acid is used in acidizing process?
• What is iron control agent?
• How is HCl used in fracking?
• What is SandStone acidizing?
• What is in hydrochloric acid?
• What is stimulation in oil and gas?
• What is acid job in oil industry?
• How do you make hydrofluoric acid?
• What are the objectives of matrix stimulation?
• What is the purpose of using additives in acidizing process for oil well?
• What are acid additives?

By completing this topic and then applying the learnings in your job, you will be able to attain Basic Application Competence Level in Acidizing and Other Chemical Treatments.

Introduction Matrix Acidizing

Welcome to our comprehensive guide on matrix acidizing, a powerful technique used in the oil and gas industry to enhance the productivity of hydrocarbon reservoirs. In this article, we will delve into the intricacies of matrix acidizing and provide you with valuable insights to help you to understanding and implementing this technique.

Understanding Matrix Acidizing

Matrix acidizing is a well stimulation technique that tries to increase the flow of oil or gas from reservoir rocks by dissolving the formation matrix and establishing new channels. It involves the injection of acid, typically hydrochloric acid, into the reservoir formation at high pressure. The acid reacts with the rock, primarily carbonate formations, and dissolves the minerals, thereby creating wormholes or channels that connect the wellbore to the reservoir. This process effectively increases the permeability of the reservoir and enhances production rates.

The Matrix Acidizing Process

1. Formation Evaluation: Before conducting matrix acidizing, a thorough evaluation of the reservoir formation is essential. This evaluation includes analyzing well logs, core samples, and production data to determine the rock type, mineral composition, and permeability of the formation. Understanding these parameters helps in designing an effective acidizing treatment.
2. Acid Selection: The selection of the acid type and concentration is crucial for successful matrix acidizing. Different reservoir formations require specific acid types, such as hydrochloric acid (HCl) or organic acids. The acid concentration is tailored to the reservoir characteristics to achieve optimal dissolution and stimulation.
3. Pre-flush and Acid Injection: Prior to injecting the acid, a pre-flush fluid is often used to remove any solid debris or damaging particles near the wellbore. Once the pre-flush is complete, the acid is injected into the reservoir through the wellbore using specialized equipment. The acid is pumped at high pressure to penetrate the formation and initiate the dissolution process.
4. Reaction and Dissolution: As the acid contacts the rock formation, a chemical reaction occurs, dissolving the carbonate minerals present in the reservoir matrix. This reaction creates channels and enlarges existing pore spaces, enabling improved fluid flow. The acid also helps remove any formation damage caused by drilling or completion processes, further enhancing productivity.
5. Post-treatment Evaluation: After the acidizing treatment, an evaluation of the well’s performance is conducted to assess the effectiveness of the stimulation. Well testing, production logging, and pressure analysis are performed to measure the increase in flow rates and the overall success of the matrix acidizing operation.

This type of acidizing treatment is designed to remove skin damage that extends beyond the immediate surface of the perforations or the face of the producing zone. Acid enters the pore space of the formation below fracturing pressure and dissolves both the surface of the rock and the flow restricting contaminants within the matrix.

A matrix acidizing treatment may be effective penetrating into the formation only a few inches or up to several feet from the wellbore, depending on formation permeability. In wells that have suffered from skin damage, production can increase many-fold. However, if a well had little or no skin damage, an acidizing treatment stimulates natural production little more than one to two times, depending on its design. Figure 1 (stimulation of natural production) illustrates this phenomenon.

Matrix acidizing regains permeability by removing formation damage from the perforation tunnels and existing flow channels around the wellbore to a depth of only a few inches. The amount of lost production is directly related to the extend and depth of formation damage, as shown in Figure 2 (effect of damage on well productivity).

The greatest productivity loss occurs in wells with severely damaged permeability within the first few inches from the wellbore. According to Schecter (1992), three of the primary mechanisms that contribute to an acidized well’s productivity include “erosion of the pore structure as the acid flows through these pores, consumption of the acid and, selective dissolution of certain minerals. Erosion of the pore structure leads to both increase porosity and permeability…

Surface Equipment Matrix Acidizing

Execution and Wellsite Operations

The execution of matrix acidizing plays a pivotal role in the overall success of the operation. Proper planning, equipment selection, and adherence to safety protocols are crucial during the wellsites operations. Let’s delve into the key aspects of executing matrix acidizing and the essential steps involved.

1. Pre-Job Planning: Thorough pre-job planning is essential to ensure a well-executed matrix acidizing operation. This includes a comprehensive evaluation of the reservoir characteristics, well history, and production data. The planning phase also involves determining the optimal acid volume, concentration, and injection rate based on the reservoir conditions and the desired results.
2. Equipment Selection: Choosing the right equipment for matrix acidizing is crucial for a smooth operation. Acid storage tanks, pumps, and blending units should be selected based on the acid volume and concentration requirements. The equipment must be compatible with the chosen acid and capable of delivering it to the wellbore at the desired rates.
3. Well Preparation: Prior to acid injection, the wellbore needs to be prepared to ensure efficient acid placement. This may involve cleaning the wellbore, removing any obstructions or debris, and isolating specific zones for acid treatment using packers or plugs.
4. Acid Injection: The actual acid injection process begins with carefully controlled pumping of the acid into the wellbore. The injection rate and pressure are closely monitored to ensure effective acid placement and prevent any formation damage. Injection profiles may be adjusted during the operation based on real-time data and observations.
5. Soaking Period: After the acid has been injected into the formation, a soaking period follows. This allows the acid to react with the matrix minerals and dissolve them, creating pathways for improved fluid flow. The soaking period duration is determined based on the reservoir characteristics, acid type, and desired reaction rates.
6. Flowback and Cleanup: Once the soaking period is complete, flowback operations commence to remove the spent acid and other byproducts from the wellbore. This is done using specialized flowback equipment and techniques to ensure efficient cleanup while minimizing the risk of formation damage.
7. Post-Treatment Evaluation: After the flowback and cleanup, a thorough post-treatment evaluation is conducted to assess the effectiveness of the matrix acidizing operation. This may involve well testing, pressure monitoring, and production analysis to measure the increase in reservoir productivity and validate the success of the stimulation.
8. Monitoring and Surveillance: Continuous monitoring and surveillance of the well following matrix acidizing are crucial to track its long-term performance. Regular well inspections, production monitoring, and periodic testing help identify any changes or issues that may require remedial action or further optimization.

Throughout the execution of matrix acidizing, strict adherence to safety protocols is of utmost importance. Proper handling, storage, and disposal of acids, as well as the use of personal protective equipment, ensure the well-being of the personnel involved and mitigate environmental risks.

The successful execution of matrix acidizing requires meticulous planning, appropriate equipment selection, and strict adherence to safety guidelines. By following the essential steps and monitoring the operation closely, engineers can maximize the effectiveness of matrix acidizing, unlocking the full potential of the reservoir and enhancing overall productivity.