Oil-Based Drilling Fluid Fluid Loss Additive - Oxidized Asphalt Product Introduction

With the development of the petroleum industry, the drilling sector has been expanding, and the application of asphalt-modified products in drilling has increasingly gained attention. Asphalt consists of a small amount of hydrocarbon compounds and a large number of non-hydrocarbon compounds. Asphalt is generally classified into two main categories: petroleum asphalt and natural asphalt. In petroleum drilling, the widely used asphalt-modified products are primarily classified into two categories: modified colloidal asphalt and modified dry powder asphalt. The commonly used asphalt modification products in oilfields, provided by Qingdao Meilian Energy, are primarily modified dry powder asphalts.

These modified products can include natural asphalt or petroleum-based modified asphalts (such as emulsified asphalt, oxidized asphalt, sulfonated asphalt, cationic latex asphalt, etc.). The modification of asphalt allows it to have appropriate solubility and dispersibility in drilling fluids. The soluble portion enhances the lubricity of the drilling fluid, while the dispersible portion effectively forms a sticky layer on the wellbore wall along with other additives in the drilling fluid. This results in the formation of a dense mud cake and oil film on the wellbore wall, which reduces friction between the drill bit and the wellbore, and prevents spalling during collisions between the drill bit and wellbore.

Due to the hydrophobic components of asphalt in the wellbore mud cake and its "peeling" effect, the fluid loss is effectively blocked from permeating into the formation. Moreover, asphalt-based substances can seal microfractures in the formation, preventing the drilling fluid and filtrate from penetrating through them. This mechanism is highly effective in preventing wellbore collapse and protecting the oil reservoir. Therefore, asphalt-based products serve as highly effective wellbore stabilizers and oil reservoir protectants in petroleum drilling operations.

Oil-Based Drilling Fluid Fluid Loss Additive - Oxidized Asphalt for Formation Blocking

The oxidized asphalt used as a fluid loss additive in oil-based drilling fluids plays a unique role through its strong adsorption ability. It adsorbs and "peels" onto the surfaces of clay particles and shale, preventing the hydration and dispersion of the clay particles. This creates a hydrophobic oil film, reducing the contact between the shale and water. As a result, it effectively protects the drilling fluid by stabilizing the colloidal particles, inhibiting the hydration of shale, blocking microfractures in shale, and filling the pores of conglomerates. In turn, this helps to reduce fluid loss and stabilize the wellbore.

The primary components of asphalt-asphaltenes and resins-serve specific functions within the drilling fluid. Asphaltenes help to increase the viscosity of the drilling fluid, while resins act to block the micropores in the mud cake, thereby reducing the fluid loss. Moreover, after dissolution and dispersion of the asphalt, it can effectively synergize with clay or organic soils, maintaining good viscosity and shear force in the drilling fluid. The use of emulsifiers further enhances the performance of the oxidized asphalt.

Because oxidized asphalt contains a high effective asphaltene content (over 60%), it significantly improves the performance of the drilling fluid, ensuring both effective fluid loss control and wellbore stability.

Selection of Asphalt Softening Point Based on Downhole Temperature

The softening point of oxidized asphalt is a critical indicator for determining its suitability for use in drilling applications. Typically, the softening point is selected based on the downhole temperature: higher downhole temperatures require a higher softening point asphalt, while lower temperatures necessitate a lower softening point asphalt. The effectiveness of oxidized asphalt is highly dependent on choosing the correct softening point. If the softening point is improperly selected, such as using a low-softening-point oxidized asphalt in high-temperature wells, the asphalt will fully dissolve in the wellbore, failing to block pores and fractures as intended. Conversely, selecting a high-softening-point asphalt in low-temperature wells will prevent the asphalt from softening in the drilling fluid, causing the particles to remain rigid and ineffective in sealing pores. In some cases, the particles may even be removed during screening, leading to waste.

Drilling fluids apply pressure to the wellbore wall, causing the oxidized asphalt particles to be forced into microfractures, which are typically on a micrometer to nanometer scale. The oxidized asphalt particles, which are generally irregular and diamond-shaped in appearance, are not easily forced into these microfractures unless they soften and deform under pressure. Therefore, the softening point of the oxidized asphalt is crucial to its effectiveness.

As the downhole temperature gradually increases during drilling, it is necessary to choose an asphalt with a softening point that corresponds to the temperature range encountered. The softening point of oxidized asphalt is an average value that changes with temperature. Our oxidized asphalt is a mixture of petroleum asphalt and natural asphalt that has been specially treated by oxidation. Natural asphalt undergoes millions of years of sedimentation and further oxidation, resulting in a relatively consistent carbon chain length within a specific range. As a result, the softening point of the asphalt also falls within a range, which can automatically match the temperature of the formation. At different downhole temperatures, the asphalt may soften or become a colloid with some flowability, which is then forced into fractures under pressure.

For example, if the downhole temperature is 120°C, the design softening point range of the oxidized asphalt would be 60-120°C, allowing it to naturally adjust. Otherwise, various types of asphalt with different softening points would need to be prepared, which requires frequent adjustments and increases the complexity of onsite operations and logistics management.

Thus, we have designed four types of oxidized asphalts with different softening point ranges:

Type 1: 60-120°C

Type 2: 120-150°C

Type 3: 150-180°C

Type 4: Above 180°C

Oxidized asphalt particles smaller than 2 mm can also be used as an oil-based drilling fluid lost circulation additive. A portion of the particles dissolves in the oil, providing both colloidal and particulate properties, thus enhancing the sealing effect. This avoids the use of rigid sealants that could block drilling equipment.

Oil-Based Drilling Fluid Fluid Loss Additive - Oxidized Asphalt Internal Control Specifications

Oxidized Asphalt Testing Items

Reference Standard: Meilian Energy Corporate Standard

Note: The aging temperature should be 15-20°C lower than the product's softening point.

Product Sales and Application:

Since 2015, the company's products have been sold to major clients such as PetroChina, Sinopec's drilling engineering subsidiaries, leading domestic mud service companies, BAKER HUGHES (USA), MI (Middle East), Saudi Aramco, Kuwait Oil Company, and others.

Actual Application Case (Overseas):

In 2015, the Kuwait National Petroleum Company (KNPC) – Raudhatain Oilfield, the oil-based drilling fluid (density: 2.22-2.34) was used to replace the commonly used MI Swarco-produced Versatrol M. The locally produced oxidized asphalt was evaluated and tested within the mud system, and a corresponding evaluation report was produced.

Product Comparison: Meilian Energy Oxidized Asphalt vs. Other Market Oxidized Asphalts

Base Mud Composition:

2% Primary Emulsifier

2% Secondary Emulsifier

1.5% Wetting Agent (Cationic Type)

2% Organic Clay

15% Barite

20% Ammoniated Calcium Water Solution

Oil to Water Ratio: 4:1

Application Case (Domestic)

On-site Evaluation from a Company:

The company replaced the lost-circulation agent in the shale gas well 2.10 g/cm³ white oil-based drilling fluid system and the Tarim Oilfield diesel-based drilling fluid system with the lost-circulation agent produced by Meilian Energy. A comparative evaluation was conducted with the same additive amount. The experimental data is shown in Table 1 and Table 2.

Table 1: Performance Evaluation in Shale Gas Well 2.1 g/cm³ White Oil-Based System

Remarks:

Aging Condition: 120℃ × 16h

Rheology and Demulsification Voltage: Measured at 50℃.

Table 2: Performance Evaluation in Tarim Oilfield Diesel-Based System

Remarks:

Formula 3-4 Aging Condition: 180℃ × 16h

Formula 5-6 Aging Condition: 160℃ × 16h

Rheology and Demulsification Voltage: Measured at 65℃.

Conclusion:

From the experimental data in Table 1 and Table 2, it is evident that after replacing the lost-circulation agent in the shale gas well 2.10 g/cm³ white oil-based system and the Tarim Oilfield diesel-based system with Meilian Energy's lost-circulation agent, there was a significant reduction in high-temperature high-pressure filtrate loss. Meanwhile, the impact on rheology and electrical stability was minimal.

Domestic On-site Application Case Summary

This table summarizes some of the on-site applications in domestic shale gas fields, focusing on wells in Sichuan province during 2019 and 2020.