Phase inversion spacer fluid for well cementation

Abstract

The invention discloses a phase inversion spacer fluid for well cementation. The phase inversion spacer fluid is prepared from the following components in parts by weight: 0.3 to 0.7 part of defoaming agent PC-X62L, 2 to 4 parts of separant PC-S32S, 10 to 20 parts of phase inversion agent WS-W31L, 80 to 100 parts of weighting agent barite powder and 95 to 105 parts of water. When the phase inversion spacer fluid is added into cement paste and oil-based mud, an original oil phase system can be converted into a water phase system, the subsequent cleaning effect is guaranteed, and the cement paste can be better attached to a well wall and a casing pipe. And meanwhile, the cement paste strength can be controlled, the thickening safety window is prolonged, the rheological property is enhanced, and the cement paste has a wide application prospect in oil and gas well cementation.

Description

Technical Field

[0001] This invention relates to the technical field of oilfield drilling and cementing, and more specifically, to a reverse-rotation separator fluid for cementing. Background Technology

[0002] During oilfield drilling, oil-based drilling fluids (i.e., oil-based mud) are typically used to stabilize the wellbore, cool the drill bit, and carry cuttings. While this fluid performs well, it presents a problem during cementing: it makes the wellbore and casing surfaces oleophilic, meaning an oil film adheres to them, preventing cement slurry from adhering properly.

[0003] If the cement slurry does not adhere firmly to the wellbore and casing, gas or liquid leaks may occur, affecting the safety and lifespan of the oil and gas well. To address this issue, a common method is to use a separator fluid to clean the wellbore. The separator fluid primarily functions to separate the drilling fluid from the cement slurry, preventing the drilling fluid from contaminating the cement slurry used for cementing.

[0004] Currently, conventional isolation fluids are mainly composed of isolation agents, water loss reducing agents, and water. They have the following disadvantages: (1) Weak cake cleaning ability: The formula contains only a small amount of anionic surfactant (generally 0.3% to 0.5%), HLB value <10, penetration depth of the cake is less than 0.5 mm, and it cannot reduce the cohesion of the cake; lacking the peeling-dispersion synergistic component, it can only wash the surface of the "cake + rock debris" composite filter cake with a thickness of 1 to 3 mm, and more than 70% of it remains in place. The cementation surface is actually still "mud-mud" butt joint. (2) Lack of wetting reversal function: It does not contain hydrophilic reversal agent, and the surface tension is maintained at 45 to 55 mN m -1 The casing / wellbore contact angle is maintained at 95–110° in an oil-wet state. After the cement slurry comes into contact with the oil-wet surface, the growth of hydration crystals is hindered, and the bonding strength at the first interface generally decreases by 30%–50%. At the second interface, due to the obstruction of mud cake, the effective contact area between the cement stone and the formation is less than 60%, resulting in micro-annular gaps and a high risk of interlayer sealing failure. Incomplete cleaning coupled with failure to reverse wetting will lead to a simultaneous decline in the bonding strength at both interfaces, resulting in a cementing quality rating that is only at the edge of acceptable, making it difficult to meet the long-term sealing requirements of zero channeling in shale gas and high-pressure gas wells.

[0005] In addition, the cement slurry thickening time is a core parameter determining the success or failure of the construction and the quality of cementing. It refers to the time from when the cement slurry is mixed until it loses its fluidity and reaches the specified consistency. It must be matched with the total construction time of pumping, displacement, etc. In the current complex well conditions such as deep and ultra-deep formations, the problem of excessively short thickening time occurs frequently, which can easily lead to safety accidents such as pump stalling and stuck drill bits, resulting in construction interruption. It is also difficult to ensure that the drilling fluid is fully displaced, and the residue will form a weak cement band, creating a risk of crossflow. Moreover, conventional isolation fluids have poor compatibility with cement slurry and drilling fluid, which can easily lead to a sudden reduction in the slurry thickening time, exacerbating the risks.

[0006] Therefore, it is crucial to develop a separating fluid that can quickly achieve reverse rotation in actual cementing, truly changing the well wall from "oil-loving" to "water-loving," thereby improving the water wetting ability between the well wall and the casing wall and extending the thickening time of the cement slurry. This fluid is of great significance in improving the cement sheath bonding quality, ensuring smooth construction, and ensuring the long-term safety of oil and gas wells. Summary of the Invention

[0007] To overcome the aforementioned defects and shortcomings in the existing technology, the present invention provides a reverse-rotation isolation fluid for cementing.

[0008] The first objective of this invention is to provide the application of the anti-conversion agent WS-W31L in cementing of oil and gas wells.

[0009] A second objective of this invention is to provide a reverse-inversion isolation fluid.

[0010] A third objective of this invention is to provide the application of the aforementioned reverse-rotation isolation fluid in cementing oil and gas wells.

[0011] The fourth objective of this invention is to provide a method for cementing oil and gas wells.

[0012] This invention claims protection for the following: The application of the reverse conversion agent WS-W31L in cementing of oil and gas wells, wherein the reverse conversion agent WS-W31L is obtained by fully mixing PC-W31L flushing fluid and micro silica powder.

[0013] Preferably, the ratio of the PC-W31L rinsing solution to the silica powder is 100 mL: (2-3) mg.

[0014] More preferably, the ratio of the PC-W31L rinsing solution to the silica powder is 100 mL: 2.5 mg.

[0015] Preferably, the thorough mixing is achieved by stirring at 800–1200 rpm / min for 4–6 min.

[0016] More preferably, the thorough mixing is achieved by stirring at 1000 rpm / min for 5 min.

[0017] Preferably, the density of the PC-W31L rinsing solution is 1.1 to 1.3 kg / L.

[0018] More preferably, the density of the PC-W31L rinsing solution is 1.2 kg / L.

[0019] An inversion and isolation liquid, by weight, comprises 0.3-0.7 parts of defoamer, 2-4 parts of isolation agent, 10-20 parts of inversion agent, 80-100 parts of weighting agent and 95-105 parts of water; The phase inversion agent is WS-W31L, which is obtained by thoroughly mixing PC-W31L rinsing solution and microsilica powder.

[0020] Preferably, the ratio of the PC-W31L rinsing solution to the silica powder is 100 mL: (2-3) mg.

[0021] More preferably, the ratio of the PC-W31L rinsing solution to the silica powder is 100 mL: 2.5 mg.

[0022] Preferably, the thorough mixing is achieved by stirring at 800–1200 rpm / min for 4–6 min.

[0023] More preferably, the thorough mixing is achieved by stirring at 1000 rpm / min for 5 min.

[0024] Preferably, the density of the PC-W31L rinsing solution is 1.1 to 1.3 kg / L.

[0025] More preferably, the density of the PC-W31L rinsing solution is 1.2 kg / L.

[0026] Preferably, the defoamer is PC-X62L.

[0027] Preferably, the release agent is PC-S32S.

[0028] Preferably, the weighting agent is barite powder.

[0029] Preferably, by weight, it comprises 0.5 parts of defoamer, 2 parts of release agent, 10 parts of phase inversion agent, 85.5 parts of weighting agent and 100 parts of water.

[0030] The application of the aforementioned reverse-rotation isolation fluid in oil and gas well cementing.

[0031] A method for cementing oil and gas wells, using a reverse-rotation separator fluid to clean the wellbore; By weight, the phase-inverting isolation liquid contains 0.3 to 0.7 parts of defoamer, 2 to 4 parts of isolation agent, 10 to 20 parts of phase-inverting agent, 80 to 100 parts of weighting agent and 95 to 105 parts of water; The phase inversion agent is WS-W31L, which is obtained by thoroughly mixing PC-W31L rinsing solution and microsilica powder.

[0032] Preferably, the ratio of the PC-W31L rinsing solution to the silica powder is 100 mL: (2-3) mg.

[0033] More preferably, the ratio of the PC-W31L rinsing solution to the silica powder is 100 mL: 2.5 mg.

[0034] Preferably, the thorough mixing is achieved by stirring at 800–1200 rpm / min for 4–6 min.

[0035] More preferably, the thorough mixing is achieved by stirring at 1000 rpm / min for 5 min.

[0036] Preferably, the density of the PC-W31L rinsing solution is 1.1 to 1.3 kg / L.

[0037] More preferably, the density of the PC-W31L rinsing solution is 1.2 kg / L.

[0038] Based on a simplified five-element formula of "water + defoamer + separator + reverse agent + weighting agent", the defoamer first eliminates gas disturbance in water, then the separator establishes a suspended skeleton, then the reverse agent completes the "oil-in-water → water-in-oil" switching and strips the oil film, and finally the weighting agent adjusts the density online. The five components work together to achieve the integrated goal of cementing cleaning and isolation with "one agent replacement, ten-second reversal, and full density coverage".

[0039] Preferably, the defoamer is PC-X62L.

[0040] Preferably, the release agent is PC-S32S.

[0041] Preferably, the weighting agent is barite powder.

[0042] Preferably, by weight, the phase inversion isolation liquid contains 0.5 parts of defoamer, 2 parts of isolation agent, 10 parts of phase inversion agent, 85.5 parts of weighting agent, and 100 parts of water.

[0043] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a phase-reversing separator fluid for cementing. Adding this phase-reversing separator fluid to cement slurry and oil-based mud can transform the original oil-phase system into a water-phase system, ensuring subsequent cleaning effectiveness and allowing the cement slurry to better adhere to the wellbore and casing. Simultaneously, it enables controllable cement slurry strength, extends the thickening safety window, and enhances rheological properties, showing broad application prospects in oil and gas well cementing. Detailed Implementation

[0044] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0045] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0046] Microsilica powder: purchased from Sichuan iwindsi New Material Co., Ltd. (https: / / www.iwindsi.com / product / 16.html), 92% fully encrypted, gray-black.

[0047] Example 1: A reverse-rotation separator fluid for cementing This embodiment provides a reverse-rotation separator fluid for cementing, comprising the following components by weight: 100 parts water, 0.5 parts defoamer PC-X62L, 2 parts release agent PC-S32S, 10 parts phase inversion agent WS-W31L, and 85.5 parts weighting agent barite powder; The preparation method of the phase inversion agent WS-W31L is as follows: At room temperature, 0.5 mL of 0.5% silica fume solution (w / v) was added to 100 mL of PC-W31L rinsing solution (density: 1.20 kg / L), and the mixture was stirred at 1000 rpm / min for 5 min to prepare the phase inversion agent WS-W31L.

[0048] Example 2: A reverse-rotation separator fluid for cementing This embodiment provides a reverse-rotation separator fluid for cementing, comprising the following components in parts by weight: 100 parts water, 0.5 parts defoamer PC-X62L, 4 parts release agent PC-S32S, 20 parts phase inversion agent WS-W31L, and 100 parts weighting agent barite powder; The phase inversion agent WS-W31L was prepared according to Example 1.

[0049] Example 3: A reverse-rotation separator fluid for cementing This embodiment provides a reverse-rotation isolation fluid for cementing, comprising the following components in parts by weight: 100 parts water, 0.5 parts defoamer PC-X62L, 4 parts release agent PC-S32S, 20 parts phase inversion agent WS-W31L, and 80 parts weighting agent barite powder; The phase inversion agent WS-W31L was prepared according to Example 1.

[0050] Comparative Example 1: A reverse-rotation separator fluid for cementing This comparative example provides a reverse-rotation separator fluid for cementing, comprising the following components in parts by weight: 100 parts water, 0.5 parts defoamer PC-X62L, 2 parts release agent PC-S32S, 5 parts phase inversion agent WS-W31L, and 85.5 parts weighting agent barite powder; The phase inversion agent WS-W31L was prepared according to Example 1.

[0051] Comparative Example 2: A reverse-rotation separator fluid for cementing This comparative example provides a reverse-rotation separator fluid for cementing, comprising the following components in parts by weight: 100 parts water, 0.5 parts defoamer PC-X62L, 2 parts release agent PC-S32S, 25 parts phase inversion agent WS-W31L, and 85.5 parts weighting agent barite powder; The phase inversion agent WS-W31L was prepared according to Example 1.

[0052] Example 4: Rheological properties and demulsification voltage of the pre-flush fluid obtained by mixing cementing reverse-rotation separator fluid with oil-based mud. I. Experimental Methods The cementing reverse-rotation isolation fluids prepared in Example 1 and Comparative Example 1 were mixed with oil-based mud at volume ratios of 100:0, 95:5, 75:25, 50:50, 25:75, 5:95, and 0:100, respectively, to obtain pre-filled fluid 1 (with the cementing reverse-rotation isolation fluid prepared in Example 1) and pre-filled fluid 2 (with the cementing reverse-rotation isolation fluid prepared in Comparative Example 1). The rheological properties and demulsification voltage values ​​of pre-filled fluid 1 and pre-filled fluid 2 were then tested.

[0053] Rheological property testing: Pretreatment solution 1 and pretreatment solution 2 were placed in an 85℃ atmospheric pressure thickener and cured for 20 min, and then their rheological properties were tested by a six-speed viscometer (speeds of 3, 6, 100, 200, 300 and 600 rpm respectively).

[0054] Demulsification voltage test: Under room temperature conditions, place the electrode probe of the demulsification voltage tester into beakers containing pre-solution 1 and pre-solution 2 respectively, stir slowly, and measure the value twice.

[0055] II. Experimental Results The rheological properties of pre-fluid 1 and pre-fluid 2 are shown in Table 1. As can be seen from Table 1, after adding the cementing reverse-rotation separator fluid of Example 1, the viscosity of pre-fluid 1 decreases and its fluidity increases. While the viscosity of pre-fluid 2 also decreases after adding the cementing reverse-rotation separator fluid of Comparative Example 1, its viscosity is still higher than that of pre-fluid 1 with the same added volume. These results indicate that the cementing reverse-rotation separator fluid of Example 1, when mixed with oil-based mud, not only does not thicken but also enhances fluidity, while the fluidity-enhancing effect of the cementing reverse-rotation separator fluid of Comparative Example 1 is not as good as that of the cementing reverse-rotation separator fluid of Example 1.

[0056] Table 1. Rheological properties of pre-fluid 1 and pre-fluid 2

[0057] The demulsification voltage values ​​of pre-fluid 1 and pre-fluid 2 are shown in Table 2. When the cementing phase-reversing isolator fluid and oil-based mud of Example 1 are mixed at a volume ratio of 5:95, pre-fluid 1 is close to conductive, which is close to the oil-in-water state. As the volume of cementing phase-reversing isolator fluid increases, the demulsification voltage value gradually decreases, indicating that the oil phase in pre-fluid 1 continuously transitions to the water phase.

[0058] In Comparative Example 1, when the cementing reverse-rotating separator fluid and oil-based mud were mixed at a volume ratio of 5:95, the pre-fluid 2 remained in an oil-in-water state. Only when mixed at a volume ratio of 25:75 did pre-fluid 2 approach conductivity, meaning it approached a water-in-oil state (but the demulsification voltage was too high, failing to meet requirements). This is because in cementing reverse-rotating separator fluids, an excessively low reverse-rotating agent level prevents the fluid from converting the oil phase from oil-wet to water-wet, maintaining a continuous oil phase in the system, resulting in an unstable interface between the cementing reverse-rotating separator fluid and the mud.

[0059] The above results indicate that adding the phase-inversion separator fluid prepared in Example 1 can transform oil-based mud from the oil phase to the water phase, and the phase transformation effect is significantly better than that of the phase-inversion separator fluid in Comparative Example 1.

[0060] Table 2 Demulsification voltage values ​​of pre-fluid 1 and pre-fluid 2

[0061] In Examples 2 and 3, the cementing reverse-rotation isolation fluid and oil-based mud were mixed at volume ratios of 100:0, 95:5, 75:25, 50:50, 25:75, 5:95, and 0:100. The rheological properties and demulsification voltage of the resulting pre-fluid were tested using the same method, and the results were similar to those of Example 1.

[0062] Example 5: Rheological properties, thickening time, and demulsification voltage of the pre-flush fluid obtained by mixing the back-rotating separator fluid and cement slurry for cementing. I. Experimental Methods The cementing back-rotating isolation fluid prepared in Example 1 was mixed with cement slurry at volume ratios of 100:0, 95:5, 75:25, 50:50, 25:75, 5:95, and 0:100 to obtain pre-fluid 3, and then the rheological properties of pre-fluid 3 were tested.

[0063] Rheological property testing: The mixture was cured in an 85℃ atmospheric pressure thickener for 20 min, and then its rheological properties were tested using a six-speed viscometer (speeds of 3, 6, 100, 200, 300, and 600 rpm).

[0064] The cementing reverse-rotation isolation fluid prepared in Example 1 and Comparative Example 2 was mixed with cement slurry at volume ratios of 0:100, 5:95 and 25:75, respectively, to obtain pre-filled fluid 4 (with added cementing reverse-rotation isolation fluid prepared in Example 1) and pre-filled fluid 5 (with added cementing reverse-rotation isolation fluid prepared in Comparative Example 2). Then, the thickening time and compressive strength of pre-filled fluid 4 and pre-filled fluid 5 were tested.

[0065] Thickening time test: Pre-solvent 4 and pre-solvent 5 were placed in a pressurized thickener and their thickening time was tested at 85℃ and 40 MPa.

[0066] Compressive strength test: Place pre-treatment liquid 4 and pre-treatment liquid 5 into the mold respectively, then place the mold into the pressure curing kettle, and cure for 24 h at 85℃ and 21 MPa. After curing, remove the mold, demold the sample, and test its strength using a compressive strength testing machine.

[0067] II. Experimental Results The rheological properties of the pre-filled fluid 3 are shown in Table 3. As can be seen from Table 3, after adding the cementing reverse isolation fluid of Example 1, the viscosity of the pre-filled fluid 3 decreases and the fluidity increases. This indicates that the cementing reverse isolation fluid of Example 1, when mixed with cement slurry, not only does not thicken but also enhances the fluidity.

[0068] In Examples 2 and 3, the cementing reverse-rotation isolation fluid and cement slurry were mixed at volume ratios of 100:0, 95:5, 75:25, 50:50, 25:75, 5:95, and 0:100. The rheological properties of the resulting pre-fluid were then tested using the same method, and the results were similar to those of Example 1.

[0069] Table 3 Rheological properties of pre-fluid 3

[0070] The thickening times of pre-fluid 4 and pre-fluid 5 are shown in Table 4. As can be seen from the results in Table 4, the mixing of the cementing reverse-rotation separator fluid and cement slurry in Example 1 at volume ratios of 5:95 and 25:75, respectively, effectively offsets the risk of premature setting caused by uneven mixing on-site. Compared to the pre-fluid after mixing the cementing reverse-rotation separator fluid and cement slurry at a volume ratio of 5:95, the thickening time of pure cement slurry without the addition of cementing reverse-rotation separator fluid was shortened by 41 minutes, posing a potential risk of pump blockage.

[0071] The results above indicate that the back-rotating separator fluid for cementing in Example 1 can effectively extend the thickening time and provide an additional construction time window.

[0072] Table 4 Thickening times of pre-fluid 4 and pre-fluid 5

[0073] The compressive strengths of pre-flush fluid 4 and pre-flush fluid 5 are shown in Table 5. As can be seen from Table 5, under normal pressure curing at 85℃, the compressive strength of pure cement slurry is 27.1 MPa. After mixing the cementing reverse-rotation isolation fluid and cement slurry of Example 1 at volume ratios of 5:95 and 25:75 respectively, the compressive strengths of the resulting pre-flush fluids decreased to 19.5 MPa and 14.3 MPa, respectively, with compressive strength retention rates of 72.0% and 52.8%, respectively, exhibiting a linearly adjustable "addition-strength" relationship.

[0074] In Example 1, after the cementing reverse isolation fluid and cement slurry were mixed at a volume ratio of 25:75, the compressive strength of the pre-flush fluid 4 decreased by 47.2%, which is lower than the limit of 70% of the standard of CNOOC Oilfield Services. The compressive strength of the pre-flush fluid 5 directly decreased to close to zero, which does not meet the standard requirements.

[0075] Table 5 Compressive strength of pre-fluid 4 and pre-fluid 5

[0076] In Examples 2 and 3, the cementing reverse separation fluid and oil-based mud were mixed at volume ratios of 0:100, 5:95 and 25:75. The thickening time and compressive strength of the resulting pre-fluid were tested using the same method, and the results were similar to those of Example 1.

[0077] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. The application of the reverse conversion agent WS-W31L in cementing of oil and gas wells, characterized in that, The inverse conversion agent WS-W31L is obtained by thoroughly mixing PC-W31L rinsing solution and microsilica powder.

2. The application according to claim 1, characterized in that, The ratio of PC-W31L rinsing solution to microsilica powder is 100 mL: (2-3) mg.

3. The application according to claim 1, characterized in that, The density of the PC-W31L rinsing fluid is 1.1 to 1.3 kg / L.

4. A phase-reversal isolating fluid, characterized in that, By weight, it contains 0.3 to 0.7 parts of defoamer, 2 to 4 parts of release agent, 10 to 20 parts of phase inversion agent, 80 to 100 parts of weighting agent and 95 to 105 parts of water; The phase inversion agent is WS-W31L, which is obtained by thoroughly mixing PC-W31L rinsing solution and microsilica powder.

5. The phase-reversal isolating fluid according to claim 4, characterized in that, The defoamer is PC-X62L.

6. The phase-reversal isolating fluid according to claim 4, characterized in that, The release agent is PC-S32S.

7. The phase-reversal isolating fluid according to claim 4, characterized in that, The weighting agent is barite powder.

8. The phase-reversal isolating fluid according to claim 4, characterized in that, By weight, it contains 0.5 parts defoamer, 2 parts release agent, 10 parts phase inverting agent, 85.5 parts weighting agent and 100 parts water.

9. The application of the reverse-rotation isolation fluid according to any one of claims 4 to 8 in cementing oil and gas wells.

10. A method for cementing oil and gas wells, characterized in that, Clean the wellbore with a reverse-rotation isolation fluid; By weight, the phase-inverting isolation liquid contains 0.3 to 0.7 parts of defoamer, 2 to 4 parts of isolation agent, 10 to 20 parts of phase-inverting agent, 80 to 100 parts of weighting agent and 95 to 105 parts of water; The phase inversion agent is WS-W31L, which is obtained by thoroughly mixing PC-W31L rinsing solution and microsilica powder.

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