One-way pressure sealing agent for well drilling and preparation method thereof

Abstract

The invention discloses a one-way pressure sealing agent for well drilling and a preparation method thereof, and the one-way pressure sealing agent comprises the following components in parts by mass: 100 parts of cellulose, 25-45 parts of calcium carbonate powder, 10-15 parts of floating beads and 3-6 parts of sodium carboxymethyl starch. The floating beads are filled with the sodium carboxymethyl starch, and the polycaprolactone is used for plugging, so that the sodium carboxymethyl starch can be directionally conveyed to a well wall gap for expansion and plugging, and a super-strong plugging and sealing effect is realized.

Description

Technical Field

[0001] This invention relates to the field of drilling fluid technology, and in particular to a one-way pressure sealant for drilling and its preparation method. Background Technology

[0002] During oil drilling, lost circulation (WS) frequently occurs, which is the leakage of drilling fluid from the wellbore into formation pores and fractures. WS poses a significant threat to drilling operations, leading to drilling fluid loss, prolonged drilling cycles, and accidents such as blockage, stuck pipe, and wellbore collapse. To ensure the normal operation of drilling, a certain amount of one-way pressure sealant must be added to the drilling fluid for plugging. One-way pressure sealant is an additive used to prevent formation leakage and control drilling fluid loss. During drilling fluid circulation, it dynamically seals the formation through a one-way pressure difference (blocking under positive pressure and automatically releasing under negative pressure). It is mainly composed of natural cellulose and inorganic salts.

[0003] Patent 202311457703.2 discloses a drilling fluid plugging agent, its preparation method, and its application. The agent is prepared by selecting several materials from sepiolite, apricot shell, coconut fiber, walnut shell, and peanut shell as the main material, and epoxy resin and polyacrylamide as the coating material. The coating material is then sprayed onto the main material. While the main materials used in this plugging agent are all biodegradable and environmentally friendly, and will not pollute the formation, the plugging particles are bonded together by the epoxy resin, making this a permanent chemical sealant, which makes subsequent unblocking relatively troublesome.

[0004] Patent CN200810115975.3 discloses a plugging agent for drilling, which includes nut shell powder, limestone powder, and oil-soluble resin. It achieves a high-efficiency plugging effect by adjusting the gradation of each particle. However, since the nut shell powder used is not processed, the gum and lignin produced by its decomposition at high temperature will generate a large number of bubbles, which can easily cause blowout accidents.

[0005] How to use biodegradable materials to achieve efficient and safe sealing of well leaks is a key research focus for enterprises' green and long-term development. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a one-way pressure sealing agent for drilling and its preparation method, so as to solve the problems of poor physical sealing effect and difficult degradation of raw materials in the prior art.

[0007] The objective of this invention is achieved through the following technical solution: a one-way pressure sealant for drilling, comprising the following components by mass: 100 parts cellulose, 25-45 parts calcium carbonate powder, 10-15 parts cenospheres, and 3-6 parts sodium carboxymethyl starch.

[0008] Preferably, the calcium carbonate powder has a particle size of 300-800 mesh.

[0009] Preferably, the particle size of the cenospheres is 100-400 mesh.

[0010] Preferably, the cenospheres are pretreated by immersing them in an acidic solution and stirring to etch pores for 24-48 hours, and then removing the intact cenospheres that have sunk to the bottom and drying them.

[0011] A method for preparing a one-way pressure sealant for drilling includes the following steps: S1. Put the etched and perforated cenospheres and sodium carboxymethyl starch powder into a vacuum mixer and stir under vacuum for 12-14 hours to fill the cenospheres with powder. S2. Coating the chlorinated beads with an organic coating agent; S3. Mix the weighed cellulose, calcium carbonate powder, and celery beads evenly to obtain the final product.

[0012] Preferably, in step S1, the cenospheres are completely immersed in sodium carboxymethyl starch powder.

[0013] Preferably, in step S1, the vacuum is first drawn to 0.08 MPa, and then the pressure is increased to 0.5 MPa.

[0014] Preferably, the organic coating agent is polycaprolactone, and the molecular weight of the polycaprolactone is greater than 40 kDa.

[0015] Preferably, in step S2, polycaprolactone is dissolved in ethyl acetate solution to prepare a 15% concentration solution. The cenospheres are immersed in the polycaprolactone solution for 10-15 seconds and then quickly pulled out. After repeated immersion, the cenospheres are placed at 40°C and dried in a ventilated environment for 2 hours to evaporate and form a film.

[0016] The present invention has the following advantages: 1. By filling water-soluble sodium carboxymethyl starch into cenospheres and sealing them with polycaprolactone, the sodium carboxymethyl starch is prevented from combining with water before filling the gaps in the well wall, thus reducing its impact on the viscosity of the drilling fluid and preventing water absorption failure during storage. At the same time, after the sodium carboxymethyl starch is filled into the gaps along with the cenospheres, it absorbs water and expands, which can burst the cenospheres. After bursting, the cenospheres change from spherical to irregular sheet-like structures. Combined with cellulose, calcium carbonate and hydrated sodium carboxymethyl starch, it can physically fill and seal the pores, achieving a super strong leak-stopping and sealing effect. 2. Compared with other water-absorbing and swelling agents such as sodium alginate, sodium carboxymethyl starch has a high expansion ratio (200-300 times), which is conducive to the bursting of the cenosphere from the inside. At the same time, its water absorption rate constant is low (only 33), which is beneficial to prevent disintegration before being transported to the well wall gaps in long-distance drilling. 3. Polycaprolactone has a melting temperature of 60℃, which is not only suitable for rapid solidification of cenospheres at low temperatures, but also allows it to melt rapidly at low temperatures after being transported into the well, opening the channels of the cenospheres and causing sodium carboxymethyl starch to absorb water and expand, thus ensuring the sealing effect of sodium carboxymethyl starch and cenospheres. 4. The unidirectional pressure sealing agent is suitable for cellulose, sodium carboxymethyl starch, and polycaprolactone, all of which are biodegradable and environmentally friendly materials. Meanwhile, calcium carbonate powder and cenospheres are acid-soluble materials. When used in conjunction with the wellbore pore sealing, a physical bridging method is adopted, which is conducive to low-cost and rapid unblocking in the later stage. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention.

[0018] A one-way pressure sealant for drilling is prepared according to the following steps. S1. Pre-treatment of cenospheres with opening: Select 100 cenospheres and immerse them in 10% hydrochloric acid solution, stir and etch the opening for 24-48 hours. Filter and take out the cenospheres with intact particles that have settled to the bottom and dry them at 40℃. S2. Add the etched and perforated cenospheres and 20-30 parts of sodium carboxymethyl starch powder into a vacuum mixer, ensuring that the cenospheres are completely submerged in the sodium carboxymethyl starch powder. First, slowly evacuate the vacuum to 0.08 MPa for 3 hours, then gradually increase the pressure to 0.5 MPa for 6-8 hours, and finally reduce the pressure to atmospheric pressure for 3 hours to allow the powder to fill the cenospheres. Filter out the cenospheres. S3. Dissolve polycaprolactone with a molecular weight greater than 40 kDa in ethyl acetate solution to prepare a 15% coating solution. Immerse the cenospheres in the polycaprolactone solution for 10-15 seconds and then quickly pull them out. Repeat the immersion process 3 times and place them in a ventilated place at 40℃ for 2 hours to evaporate and form a film. During the drying process, keep vibrating to reduce cenosphere adhesion. S4. Mix 100 parts of weighed cellulose, 25-45 parts of calcium carbonate powder, and cenospheres evenly to obtain a one-way pressure sealing agent.

[0019] Example 1 A drilling unidirectional pressure sealant comprises 100 parts cellulose, 25 parts 300-mesh calcium carbonate powder, 15 parts 400-mesh cenospheres, and 3 parts sodium carboxymethyl starch filled into the cenospheres.

[0020] Example 2 A drilling unidirectional pressure sealant comprises 100 parts cellulose, 25 parts 800-mesh calcium carbonate powder, 15 parts 400-mesh cenospheres, and 3 parts sodium carboxymethyl starch filled into the cenospheres.

[0021] Example 3 A drilling unidirectional pressure sealant comprises 100 parts cellulose, 20 parts 300-mesh calcium carbonate powder, 25 parts 800-mesh calcium carbonate powder, 15 parts 400-mesh cenospheres, and 3 parts sodium carboxymethyl starch filled into the cenospheres.

[0022] Example 4 A drilling unidirectional pressure sealing agent comprises 100 parts cellulose, 20 parts 300-mesh calcium carbonate powder, 25 parts 800-mesh calcium carbonate powder, 15 parts 100-mesh cenospheres, and 6 parts sodium carboxymethyl starch filled into the cenospheres.

[0023] Example 5 A drilling unidirectional pressure sealing agent comprises 100 parts cellulose, 20 parts 300-mesh calcium carbonate powder, 25 parts 800-mesh calcium carbonate powder, 10 parts 100-mesh cenospheres, and 4 parts sodium carboxymethyl starch filled into the cenospheres.

[0024] Comparative Example 1 A drilling unidirectional pressure sealant is made by uniformly mixing 100 parts of cellulose, 20 parts of 300-mesh calcium carbonate powder, 25 parts of 800-mesh calcium carbonate powder, and 15 parts of 100-mesh unetched pores.

[0025] Comparative Example 2 A drilling unidirectional pressure sealant is made by uniformly mixing 100 parts of cellulose, 20 parts of 300-mesh calcium carbonate powder, 25 parts of 800-mesh calcium carbonate powder, 15 parts of 100-mesh unetched pores of cenospheres, and 3 parts of sodium carboxymethyl starch.

[0026] Comparative Example 3 A drilling unidirectional pressure sealant is made by uniformly mixing 100 parts of cellulose, 20 parts of 300-mesh calcium carbonate powder, 25 parts of 800-mesh calcium carbonate powder, 15 parts of 100-mesh unetched pores of cenospheres, and 3 parts of sodium alginate.

[0027] Performance testing According to the standard Q / SY 1096-2012, the sealing agents prepared in Examples 1-5 and Comparative Examples 1-3 were tested for apparent viscosity change rate and sealing filtration loss at an addition amount of 3%.

[0028] serial number Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Apparent viscosity change rate, % 6.6 6.7 6.7 6.4 6.2 5.8 23.8 16.3 Filtration loss (30 min), ml 18 16 13 9 11 38 29 34 As shown in the table above, the sealing agents prepared in Examples 1-5 all had a sealing filtration loss of less than 40 ml in the drilling fluid, which meets the standard requirements. The sealing filtration loss and apparent viscosity change rate of Examples 1-5 were both less than those of Comparative Examples 1-3. The direct addition of sodium carboxymethyl starch and sodium alginate can improve the sealing ability, but it also has a significant impact on the apparent viscosity of the drilling fluid. The internally filled sodium carboxymethyl starch can cause the floats to disintegrate from the inside and fill the gaps. Compared with direct addition, it not only improves the plugging ability, but also reduces the impact on the apparent viscosity of the drilling fluid.

[0029] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A one-way pressure sealant for drilling, characterized in that: Based on parts by weight, it includes the following components: 100 parts cellulose, 25-45 parts calcium carbonate powder, 10-15 parts cenospheres, and 3-6 parts sodium carboxymethyl starch.

2. The drilling unidirectional pressure sealant according to claim 1, characterized in that: The calcium carbonate powder has a particle size of 300-800 mesh.

3. The drilling unidirectional pressure sealant according to claim 1, characterized in that: The particle size of the cenospheres is 100-400 mesh.

4. The drilling unidirectional pressure sealant according to claim 1, characterized in that: The cenospheres are pretreated by immersing them in an acidic solution and stirring to etch pores for 24-48 hours. The cenospheres that sink to the bottom and remain intact are then dried.

5. A method for preparing a one-way pressure sealant for drilling according to any one of claims 1-4, characterized in that, Includes the following steps, S1. Put the etched and perforated cenospheres and sodium carboxymethyl starch powder into a vacuum mixer and stir under vacuum for 12-14 hours to fill the cenospheres with powder. S2. Coating the chlorinated beads with an organic coating agent; S3. Mix the weighed cellulose, calcium carbonate powder, and celery beads evenly to obtain the final product.

6. The method for preparing a one-way pressure sealant for drilling according to claim 5, characterized in that: In step S1, the cenospheres are completely immersed in sodium carboxymethyl starch powder.

7. The method for preparing a one-way pressure sealant for drilling according to claim 5, characterized in that: In step S1, the vacuum is first drawn to 0.08 MPa, and then the pressure is increased to 0.5 MPa.

8. The method for preparing a one-way pressure sealant for drilling according to claim 5, characterized in that: The organic coating agent is polycaprolactone, and the molecular weight of polycaprolactone is greater than 40 kDa.

9. A method for preparing a one-way pressure sealant for drilling according to claim 8, characterized in that: In step S2, polycaprolactone is dissolved in ethyl acetate solution to prepare a 15% concentration solution. The cenospheres are immersed in the polycaprolactone solution for 10-15 seconds and then quickly pulled out. After repeated immersion, the cenospheres are placed at 40°C and dried in a ventilated environment for 2 hours to evaporate and form a film.