Multifunctional polymer drilling fluid cake modifier, preparation method and application thereof

Abstract

The present application belongs to the field of oilfield drilling fluid, and discloses a multifunctional polymer drilling fluid mud cake modifier, a preparation method and application thereof, wherein the mud cake modifier comprises, by mass fraction, 5-95% of acicular wollastonite powder, 1-20% of sodium gluconate and 1-10% of instant sodium carbonate; the mud cake modifier is directly added into drilling fluid during use, and the addition amount is 0.5-1.5% by mass fraction. The mud cake modifier can improve the hardness, compactness and toughness of the mud cake, and improve the properties of the mud cake on the well wall; the mud cake modifier can form a thin, hard, tough and compact mud cake on the well wall, reduce the filtration loss of the drilling fluid, improve the rheological property of the drilling fluid, has no obvious influence on the density and viscosity of the drilling fluid, and has the dual functions of enhancing the affinity between the cement sheath and the mud cake and stabilizing the well wall.

Description

Technical Field

[0001] This invention relates to the field of oilfield drilling fluids, specifically to a multifunctional polymer drilling fluid mud cake modifier, its preparation method, and its application. More specifically, it relates to a modifier for improving the performance of polymer drilling fluid mud cake in oil and gas wells, its preparation method, and its application. Background Technology

[0002] As exploration and development deepen, unconventional tight oil reservoirs have gradually become a hotspot for development. The typical completion process for these reservoirs involves horizontal well cementing followed by perforation and large-scale fracturing. Cementing quality is a crucial factor, directly affecting the effectiveness of subsequent fracturing. Currently, the cementing quality of horizontal wells is generally low, mainly due to two factors: Firstly, the horizontal casing deflects downwards towards the wellbore under gravity, forming a narrow annulus. This results in uneven thickness of the cement sheath after cementing, or water separation in the cement slurry, with the separated water accumulating on the upper side of the wellbore, causing channeling. Secondly, the narrow annulus on the lower wellbore also leads to low displacement efficiency of mud cake and drilling fluid on the lower side of the wellbore during cement slurry injection, easily forming channeling and further affecting cementing quality. These adhered mud slurries and the resulting mud cake have a distinct layered structure, failing to bond well with the cement slurry, exhibiting poor solidification and forming a weak interface in the cementing process—a loosely structured, porous, and permeable annular cement transition zone. In the presence of underground oil, gas, and water, these weak interfaces form channels for oil, gas, and water flow. Over time, the bonding at these interfaces deteriorates significantly, severely impacting cementing quality evaluation. While mud cake formed on the wellbore is detrimental to cementing, a sufficiently thick and dense mud cake is beneficial for drilling and completion processes, reducing drilling fluid loss and formation damage. Therefore, considering the needs of drilling, completion, and cementing processes, forming a thin, hard, tough, and dense mud cake on the wellbore not only helps reduce drilling fluid filtrate intrusion and contamination of the wellbore but also improves the bonding effect at the cementing interface.

[0003] To achieve the above objectives, many technologies have emerged, such as MTC technology, MTA technology, and multifunctional drilling fluid technology. Interface reinforcing agents (CN201410315515.0, CN201710395746.0, CN201810900364.3) that can improve the interfacial bonding strength have also been developed. MTC and MTA technologies suffer from complex processes, high construction difficulty, and high costs. Furthermore, the effectiveness of MTC technology at the casing location in oil formations remains unclear. Multifunctional drilling fluid technology has drawbacks such as formation contamination. Interface enhancers have complex compositions, and their high-temperature resistance needs further clarification. They are added to the drilling fluid after drilling is completed and the well is circulated. The principle of interface enhancement is that after mud cake forms on the wellbore, drilling fluid containing interface enhancers is circulated downhole for a certain period. A layer of mud cake containing interface enhancers adheres to the outside of the original mud cake on the wellbore. This layer has high hardness and good affinity with the cement sheath and the original mud cake, thereby improving the cementing interface bonding strength and cementing quality. However, this method does not completely change the properties of the mud cake formed on the wellbore during drilling. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a simple, low-cost, and high-temperature resistant modifier for improving the performance of polymer drilling fluid mud cake in oil and gas wells. This mud cake modifier is added to the drilling fluid during the drilling process. It can improve the hardness, density, and toughness of the mud cake, and improve the properties of the mud cake on the wellbore. It can achieve the formation of a thin, hard, tough, and dense mud cake on the wellbore, while reducing the filtration loss of the drilling fluid and improving the rheological properties of the drilling fluid, without significantly affecting the density and viscosity of the drilling fluid. It has the dual function of enhancing the affinity between the cement sheath and the mud cake and stabilizing the wellbore.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A multifunctional polymer drilling fluid mud cake modifier is a mixed solid powder composed of needle-shaped wollastonite powder, sodium gluconate, and fast-dissolving sodium silicate.

[0007] Furthermore, the needle-shaped wollastonite powder provided by the present invention is an ultrafine powder with a particle size of 2000-2500 mesh, a SiO2 content of more than 49%, and a CaO content of more than 43%.

[0008] Furthermore, the instant sodium silicate modulus provided by the present invention is 1-3, preferably 1.5-2.5.

[0009] Furthermore, the contents of the three components of the mud cake modifier, by mass fraction, are as follows: 5%-95% acicular wollastonite powder, 1%-20% sodium gluconate, and 1%-10% instant sodium silicate.

[0010] A method for preparing a multifunctional polymer drilling fluid mud cake modifier involves mixing the three reagents in a mixer according to their respective content ratio requirements, with no particular order of addition.

[0011] An application of a multifunctional polymer drilling fluid mud cake modifier is described, wherein the above-mentioned mud cake modifier is directly added to the drilling fluid, and the amount added is 0.5%-1.5% by mass fraction.

[0012] Specifically, drilling fluid with added mud cake modifier forms mud cake on the well wall through a filtration process under the action of hydrostatic pressure difference. As the formation depth increases, the formation pore pressure and temperature gradually increase, and the filtration pressure on the well wall is also different at different well depths.

[0013] The mechanism of action of the polymer drilling fluid mud cake modifier provided by this invention is as follows: Needle-shaped ultrafine wollastonite powder reacts with the water filtrate to generate hydrated calcium silicate with a certain strength inside the mud cake. Furthermore, its needle-like structure acts as a skeletal support within the mud cake, and the formation of the skeletal structure and hardening centers increases the strength of the mud cake. Sodium gluconate, through electrostatic repulsion and steric hindrance, improves the dispersibility and flowability of solid particles in the drilling fluid, reduces the viscosity of the drilling fluid, and thins the mud cake. On the other hand, it can also complex metal cations in the cement filtrate, generating macromolecular complexes inside the mud cake and at its interface with the cement ring, increasing the amount of network support material inside the mud cake, improving its density, and transforming the simple physical contact between the mud cake and the cement ring into chemical affinity, enhancing their mutual interaction. Sodium silicate, through adsorption and thickening of the diffusion double layer, makes the mud cake more porous, thus making it easier to be flushed away, thereby reducing the thickness of the mud cake. Simultaneously, the SiO3 in sodium silicate... 2- It can also induce Ca in cement filtrate 2+ Mg 2+ The reaction occurs and further hydration forms silicate hydrate gels. These gel-like substances serve as a provider of hardening agents, increasing the strength of the mud cake, while also acting as a binder and sealant, reducing the permeability of the mud cake.

[0014] The polymer drilling fluid mud cake modifier provided by this invention is a white solid mixture that can be added directly to water-based drilling fluid in appropriate amounts according to drilling requirements. It has good solubility and is easy to apply. The price is 4,000-6,000 yuan per ton, making it low-cost.

[0015] The polymer drilling fluid cake modifier provided by this invention has certain viscosity-reducing and water-loss-reducing effects, but has almost no effect on the density of the drilling fluid.

[0016] The beneficial effects of this invention compared to the prior art are:

[0017] (1) The present invention provides a polymer drilling fluid cake modifier that can improve the hardness, density and toughness of the cake, improve the properties of the cake on the well wall, and reduce the filtration loss of the drilling fluid, while having no significant effect on the density and viscosity of the drilling fluid.

[0018] (2) The present invention provides a polymer drilling fluid mud cake modifier, which improves the cementing interface bonding strength by improving the mud cake performance and enhancing the affinity between cement sheath and mud cake. Attached Figure Description

[0019] Figure 1 These are macroscopic morphological photos of the mud cake before and after adding the mud cake modifier in Example 1. (a) indicates no mud cake modifier was added; (b) indicates the addition of the mud cake modifier.

[0020] Figure 2 These are macroscopic morphological photos of the mud cake before and after adding the mud cake modifier in Example 2. (a) indicates no mud cake modifier was added; (b) indicates the addition of the mud cake modifier. Detailed Implementation

[0021] The present invention is described in detail below through specific embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained commercially.

[0022] Example 1

[0023] There are two standard methods for preparing drilling mud cakes indoors: one is the API condition, which involves static filtration for 30 minutes at 0.69 MPa in an API medium-pressure filtration meter at room temperature; the other is high-temperature and high-pressure filtration, i.e., static filtration for 30-30 minutes at 3.5 MPa, with the temperature set according to the formation temperature. The choice of method depends on the actual well depth. Generally, for shallow to medium-depth wells, API medium-pressure filtration is used to prepare mud cakes, while for deep and ultra-deep wells, high-temperature and high-pressure filtration is preferred. In this example, the experimental well is a deep well, so the filtration temperature was designed to be 100℃, and the pressure was set to the standard pressure of 3.5 MPa. Under natural conditions, drilling fluid forms mud cakes on the wellbore through the filtration process under the action of hydrostatic pressure differential. As the formation depth increases, the formation pore pressure and temperature gradually increase, and the filtration pressure on the wellbore varies at different depths. However, due to limited indoor conditions, it is impossible to provide all downhole pressure and temperature conditions; therefore, the mud cake preparation must be set according to the standard pressure.

[0024] This embodiment uses the following formula:

[0025] The polymer drilling fluid cake modifier is composed of 97% acicular wollastonite powder, 1% sodium gluconate, and 2% sodium silicate. The above three agents are mixed evenly to obtain the drilling fluid cake modifier, which is added to the polymer drilling fluid at a rate of 1%. In this example, the test well is a deep well; therefore, a high-temperature, high-pressure static filtration method is used to prepare the cake. First, a filtration test is conducted using a high-temperature, high-pressure filtration instrument at 3.5 MPa and 100℃ to prepare the cake. Then, the prepared cake is placed in cement filtrate and cured at 100℃ for 7 days. The performance of the cake and the main performance parameters of the drilling fluid are measured, and the results are shown in Tables 1 and 2.

[0026] Table 1. Effect of the drilling fluid mud cake modifier of the present invention on mud cake performance.

[0027]

[0028] Table 2. Effects of the drilling fluid mud cake modifier of the present invention on the main properties of drilling fluid.

[0029]

[0030] The appearance of the mud cake before and after adding the modifier, after curing with cement filtrate, is as follows: Figure 1 As shown, by Figure 1 It is evident that the mud cake without the addition of the mud cake modifier is particularly thick, while the thickness is significantly reduced after the addition of the mud cake modifier, and the surface of the mud cake is uniform and smooth, with a significant improvement in appearance.

[0031] Example 2

[0032] Prepare the ingredients according to the following formula:

[0033] The polymer drilling fluid cake modifier is composed of 95% acicular wollastonite powder, 2% sodium gluconate, and 3% sodium silicate. The above three agents are mixed evenly to obtain the drilling fluid cake modifier, which is added to the polymer drilling fluid at a rate of 0.5%-1.0%. In this example, the test well is a shallow to medium-depth well, therefore the API method was used to prepare the cake. First, a filtration loss test was conducted using a medium-pressure filtration tester at room temperature and 0.69 MPa to prepare the cake. Then, the cake was placed in cement filtrate and cured at 45°C for 7 days. The performance of the cake and the main performance parameters of the drilling fluid were measured, and the results are shown in Tables 3 and 4.

[0034] Table 3. Effect of the drilling fluid mud cake modifier of the present invention on mud cake performance.

[0035]

[0036] Table 4. Effects of the drilling fluid mud cake modifier of the present invention on the main properties of drilling fluid.

[0037]

[0038] The appearance of the mud cake before and after adding the modifier, after curing with cement filtrate, is as follows: Figure 2 As shown, by Figure 2 It is evident that the surface of the mud cake without the addition of the mud cake modifier is rough, with a few cracks and a relatively large thickness, while the surface of the mud cake with the addition of the mud cake modifier is uniform and smooth, and the thickness is significantly reduced, resulting in a significant improvement in appearance.

[0039] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A multifunctional polymer drilling fluid mud cake modifier, characterized in that, It is a mixed solid powder composed of acicular wollastonite powder, sodium gluconate, and instantaneous sodium silicate. The contents of the three components, by mass fraction, are as follows: acicular wollastonite powder 5%-95%, sodium gluconate 1%-20%, and instantaneous sodium silicate 1%-10%. The acicular wollastonite powder is an ultrafine powder with a particle size of 2000-2500 mesh, a SiO2 content of over 49%, and a CaO content of over 43%.

2. The multifunctional polymer drilling fluid cake modifier of claim 1, wherein, The modulus of the instant sodium silicate is 1-3.

3. The multifunctional polymer drilling fluid cake modifier of claim 1, wherein, The modulus of the instant sodium silicate is 1.5-2.

5.

4. A method for preparing a multifunctional polymer drilling fluid mud cake modifier, characterized in that, The needle-shaped wollastonite powder, sodium gluconate, and instant sodium silicate as described in any one of claims 1-3 are stirred and mixed evenly in a mixer. The three reagents are added in no particular order.

5. Use of a multifunctional polymeric drilling fluid mud cake modifier, characterized in that, The mud cake modifier described in any one of claims 1-3 is directly added to the drilling fluid, and the amount added is 0.5%-1.5% by mass fraction.

6. The use of a multifunctional polymer drilling fluid mud cake modifier according to claim 5, wherein, The mud cake modifier is added to the drilling fluid and forms a mud cake on the well wall through a filtration process.

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