Application of Horizontal Well Cementing Slurry Technology in Western Sichuan

1. Characteristics of Horizontal Wells in Western Sichuan
Since the beginning of this year, a large number of horizontal wells have been launched in western Sichuan. The main characteristics of horizontal wells in western Sichuan are:
1. The inclination depth of the well is generally about 2500-3500m, and some of the individual wells reach or exceed 4000m.
2. The vertical depth of the well is about 2500-2700m.
3. The slope making point is mostly about 1000-1400m, and the length of the slope making section is generally about 400-500m, so the slope making rate is relatively high and the full angle change rate is relatively large. The full angle change rate (/30m) of some wells reaches more than 10.
4. The horizontal well section length is generally about 900-1000m.
5. The well bore structure is mostly three-opening structure, and some wells are two-opening structure:
6. The production casing is mostly 139.7mm casing, and the clearance for cementing construction in 215.9 wells is relatively large.
7. The formation is prone to hydration, expansion and collapse, and oil-like mud is commonly used in horizontal well sections.
8. The bearing capacity of Penglaizhen Formation and Shaximiao Formation in the target stratum is relatively high, and the bearing equivalent of some wells reaches 2.0g/cm3.
9. During electrical logging of well completion, some wells may not be able to measure the well diameter of horizontal well section.
Technical difficulties in 2. horizontal well cementing in western Sichuan
1. The horizontal section is also the gas zone section, so the cement slurry is required to have zero water separation and good stability and anti-gas channeling performance.
2. The mud generally contains oil (3%-5%), and the oil will adhere to the casing and the well wall to affect the interface cementation quality, requiring the front-end liquid system to have strong oil displacement ability.
3. The mud has poor performance, high viscosity and high static shear force. According to the displacement theory model, the cement slurry is required to have high dynamic shear force to improve the displacement efficiency.
4. During the injection and replacement process, the annular return velocity is relatively low, generally less than 1 m/s, the flow pattern of cement slurry is difficult to achieve turbulent flow, the replacement efficiency is difficult to guarantee, and the cement slurry is also required to have relatively high dynamic shear force.
5. The well pad in western Sichuan is located in the agricultural plain area, and the environmental protection requirements are strict, so the cement slurry preparation and construction process are required to avoid pollution.
6, the western Sichuan region drilling production progress is fast, requiring cement slurry waiting time is short, cement stone strength development fast.
7. Although the horizontal section casing is equipped with centralizer, the tendency of casing to lean against the well wall always exists, and there is still the problem of small clearance between casing and well wall.
8. The cuttings bed in the horizontal section is difficult to clean, which affects the cementing quality of the lower shaft wall.
Main Measures for 3. Cementing Slurry Technology in Horizontal Wells
1, adjust the cement paste zero water. The settlement stability of cement slurry is ≤ 0.02.
2, the use of retarder BS200R-2 and expansion agent BS500, to achieve the right angle of cement slurry thickening and lattice expansion to achieve a better anti-gas channeling effect.
3. Improve the quality of interface cementation
The main factors affecting the quality of interface cementation are: false mud cake, oil film, sand and micro-gap.
For the fake mud cake, the washing liquid with strong penetration ability and the isolation liquid with strong washing and suspension ability are used. The washing liquid destroys the structure of the fake mud cake and takes away part of the solid phase, and the isolation liquid strips off the fake mud cake and takes it away.
For the oil film, use the flushing fluid with strong oil displacement ability. The surface active material in the flushing fluid has strong phase conversion ability and can fully wet the interface to improve the coupling force between the cement stone and the two interfaces, and the alkaline material and the surfactant have a synergistic effect to further improve the oil displacement effect.
For sand deposition, in addition to the use of isolation fluid with strong suspension capacity, well cleaning should be done in terms of process.
For the micro-gap, the micro-expansion cement slurry system is used to avoid volume shrinkage, and at the same time, the cement stone and the interface produce stress, and improve the quality of the bonding surface.
4. Improve displacement efficiency
Turbulent displacement is the best flow pattern to improve displacement efficiency. The critical conditions for 139.7mm casing to reach turbulence in the annulus are: displacement ≥ 5 m3/min (cement slurry density 1.90g/cm3, apparent viscosity 200mPa.s), or cement slurry apparent viscosity ≤ 45mPa.s (cement slurry density 1.90g/cm3, displacement displacement 1.5 m3/min). However, neither of these two can be achieved.
Under the existing conditions, according to the displacement theory, the high dynamic shear force cement slurry system can be used to achieve better displacement efficiency, and the high dynamic shear force cement slurry system also has a higher viscosity, so the viscosity advantage can also be used to improve the displacement efficiency.
Density advantages can also improve displacement efficiency, but are limited by wellbore conditions and cost.
Under the premise of meeting the ground construction, the cement slurry system and spacer fluid system have the following properties to improve the displacement efficiency:
Under ground and circulating temperature conditions: cement slurry viscosity> spacer fluid viscosity> slurry viscosity; dynamic shear force of cement slurry ≥ 40Pa.
5. All cement slurry materials are dry mixed, and clean water is directly used for construction to reduce environmental risks.
6. Retarder is the main factor affecting the development of cement stone strength. The BS200R-2 wide retarder currently selected has little sensitivity to temperature, which can make the top strength of cement slurry develop rapidly when the thickening time meets the design requirements: 12-hour compressive strength is 7.5MPa, and 24-hour compressive strength is 10MPa. BS200R, the aqua product of the retarder, has been widely used in northeast Sichuan and achieved good results.
7. In view of the small gap between casing and the lower well wall, the casing "floating" process can be adopted.
8, the use of plastic cement slurry system, cement stone mechanical properties, can greatly reduce the damage to the cement ring of the plug sweeping operation, is conducive to maintaining the quality of cementing.
Key Points of Process Control in 4. Construction
1. The admixture shall be sampled strictly to ensure the stable performance of the admixture.
2. Assign special personnel to monitor the links that are not directly involved (ash mixing, ash loading and ash unloading).
3. Each tank of ash must be sampled and tested on site.
4. The spacer fluid, pilot slurry and mud used in the compatibility test must be the large samples prepared on site and ready to be put into the well.
5. Adjust the thickening time to a longer interval during the small sample experiment. In order to avoid the problem of short local thickening time caused by uneven mixing of retarder (based on BS200R-2-type wide retarder, which is less sensitive to temperature and can make the top strength of cement slurry develop rapidly when the thickening time meets the design requirements).
6. During the construction, a spare cement truck is equipped. The displacement of the cement truck is as large as possible, preferably about 1.8 m3/min, so as to realize the annular return speed of 1 m/s.
7, due to the slurry thick construction pump pressure may be higher, according to the high pressure construction requirements for preparation.
5. implementation effect
1. Cementing quality evaluation of Well Shifang 109-1H:
Cementing quality evaluation: the sound amplitude curve quality is excellent, and the cementing quality is excellent according to statistics. Cementing quality of main oil and gas intervals: the cementing quality of the horizontal section reservoir is excellent, and the sealing quality of the upper and lower 30m of the gas layer is excellent.
Analysis of factors affecting cementing quality:
Unfavorable factors: the unmeasured cement slurry volume of horizontal section cannot be accurately determined, the slurry viscosity is relatively high (55s), the static shear force is relatively high (6pa/18pa), and the dynamic shear force is relatively high (15pa);
Favorable factors: the advantage of density difference is prominent (mud density 1.45g/cm3, cement slurry density 1.92g/cm3), cement slurry thick dynamic shear force is high, cement slurry volume is sufficient (circulating effluent slurry 10m3); Strong flushing fluid and isolation fluid with strong flushing and suspension capacity are used; Swirl drag reduction rigid centralizer is used in high slope section and horizontal section.
2. Cementing quality evaluation of Well Shifang 3-1H:
Cementing quality evaluation: the quality of sound amplitude curve is excellent. According to statistics, the cementing quality of the third opening is excellent. Good interpretation of the reservoir cementing quality, good surrounding rock isolation.
Analysis of factors affecting cementing quality:
Unfavorable factors: the amount of cement slurry in horizontal section cannot be determined accurately, the slurry viscosity is relatively high (64s), and the dynamic shear force of cement slurry is relatively low (11pa);
Favorable factors: the advantage of density difference is prominent (mud density 1.48g/cm3, cement slurry density 1.89g/cm3), mud static shear force is low (3pa/10pa), and injection displacement is high (1.8 m3/min); Strong flushing fluid and isolation fluid with strong flushing and suspension capacity are used. Rigid centralizers with swirl flow reduction and drag reduction are used in large slope sections and horizontal sections.
3. Cementing Quality Evaluation of Well Lopeng 2-1H
Cementing quality evaluation: the quality of sound amplitude curve is excellent. According to statistics, the cementing quality is high. The sealing quality of the measured oil and gas interval sealed in this layer is mainly excellent, and the sealing quality of the gas layer 30 meters above and below is excellent.
Analysis of factors affecting cementing quality:
Unfavorable factors: the amount of unmeasured cement slurry in horizontal section cannot be determined accurately, and the density of spacer fluid 1.26g/cm3 is only 0.01g/cm3 higher than that of well slurry;
Favorable factors: the advantage of density difference is prominent (mud density 1.25g/cm3, cement slurry density 1.59g/cm3), mud static shear force is low (2pa/8pa), cement slurry dynamic shear force is high (62pa); Strong flushing fluid and isolation fluid with strong flushing and suspension capacity are used; rigid centralizer is used in high slope section, and spiral flow reducing centralizer is used in horizontal section.
4. Well Cementing Quality Evaluation of Well Shifang 3-3HF
Cementing quality evaluation: the quality of sound amplitude curve is excellent. The cementing quality is high. The sealing quality of the measured oil and gas interval sealed in this layer is excellent, and the sealing quality of the gas layer 30 meters above and below is excellent.
Analysis of factors affecting cementing quality:
Unfavorable factors: the amount of unmeasured cement slurry in horizontal section cannot be accurately determined, the slurry viscosity is relatively high (65s), and the dynamic shear force is relatively high (21pa);
Favorable factors: the advantage of density difference is prominent (mud density 1.48g/cm3, cement slurry density 1.87g/cm3), cement slurry dynamic shear force is high (51.5pa), mud static shear force is low (1/5pa), construction displacement is high (1.8 m3/min); Strong flushing fluid and isolation fluid with strong flushing and suspension capacity are used; swirl drag-reducing rigid centralizers are used in high-angle and horizontal sections.
5. Cementing quality evaluation of well Xinfan 1-1H
Cementing quality evaluation: the quality of sound amplitude curve is excellent (high quality rate: 98.5%; good rate: 1.5%).
Analysis of factors affecting cementing quality:
Unfavorable factors: the amount of cement slurry in horizontal section cannot be determined accurately, and the slurry viscosity is relatively high (68s);
Favorable factors: the advantage of density difference is prominent (mud density 1.38g/cm3, cement slurry density 1.90g/cm3), cement slurry dynamic cutting force is high (56pa), and construction displacement is high (1.8 m3/min); Strong flushing fluid and isolation fluid with strong flushing and suspension capacity are used. Swirl drag-reducing rigid straighteners are used in high inclination and horizontal sections.
6. Quality Evaluation of Mapeng 25-1HF Cementing
Cementing quality evaluation: the quality of sound amplitude curve is excellent. The pressure test of casing string is qualified.
Analysis of factors affecting cementing quality:
Unfavorable factors: the amount of unmeasured cement slurry in horizontal section cannot be accurately determined, the slurry viscosity is relatively high (58s), and the shear force is high (7.5/17.5pa);
Favorable factors: the advantage of density difference is prominent (mud density 1.58g/cm3, cement slurry density 1.87g/cm3), cement slurry dynamic cutting force is high (47pa), and construction displacement is high (1.8 m3/min); Strong flushing fluid and isolation fluid with strong flushing and suspension capacity are used. Swirl drag reducing rigid centralizer is used in large slope section and horizontal section.
7. Well Cementing Quality Evaluation of Well Majing 18
Cementing quality evaluation: the quality of sound amplitude curve is excellent. Analysis of factors affecting cementing quality:
Unfavorable factors: high mud density (1.90g/cm3) and cement slurry density of 2.04g/cm3 have no obvious advantage of density difference;
Favorable factors: mud dynamic shear force 12 pa cement slurry dynamic shear force 117pa has obvious dynamic shear force difference advantage and high construction displacement (1.7 m3/min); Strong flushing fluid and spacer fluid with strong flushing and suspension capacity are used. The average borehole diameter is 242.77mm (expansion rate is 12.45), and centralizers are used in both vertical and inclined borehole sections.
8. Well Cementing Quality Evaluation of Well Shifang 17-1HF
Cementing quality evaluation: the quality of the sound amplitude curve is excellent, the quality of the variable density curve is excellent, the cementing quality evaluation of the main reservoir is excellent, and the surrounding rock isolation is good. The pressure test of casing string is qualified.
Analysis of factors affecting cementing quality:
Adverse factors: the amount of cement slurry with unmeasured borehole diameter in horizontal section cannot be accurately determined, and the slurry performance is poor: high viscosity (75s) and high shear force (static shear force 5/17pa, dynamic shear force 18.5pa);
Favorable factors: the advantage of density difference is prominent (mud density is 1.44g/cm3, cement slurry density is 1.90g/cm3), the dynamic cutting force of cement slurry is high (52pa), and the construction displacement is large (1.8 m3/min); Strong flushing fluid and isolation fluid with strong flushing and suspension capacity are used; Swirling and drag reducing rigid centralizers are used in highly deviated and horizontal sections.
　　　
6. awareness and views
Through practice, we can draw the following preliminary understanding and views:
1. High mud static shear force and high dynamic shear force are not conducive to ensuring cementing quality.
2. The cement slurry has outstanding advantages over the slurry density difference, which is conducive to ensuring the cementing quality.
3, large displacement construction is conducive to ensure the quality of cementing.
4. High dynamic shear force of cement slurry is beneficial to improve cementing quality.
5, the use of flushing fluid, spacer fluid, cement slurry system and other horizontal well slurry technology in the imitation of oil-based mud horizontal well cementing saw a certain effect.
6. The use of swirl drag reduction rigid centralizer in horizontal well section is beneficial to casing centering and overcoming the problem of thin cement ring or even no cement ring in the lower well wall, and is also beneficial to the improvement of displacement efficiency in horizontal well section.
7. It is difficult for horizontal wells with target B higher than target A to ensure cementing quality.
8, horizontal well cementing is mostly high pump pressure construction.
9. Cementing is a systematic project and must be understood and supported by drilling engineering.