Novel Water-Based Mud for Low-Permeable Reservoir in South China Sea
1
School of Petroleum Engineering, China University of Petroleum, Beijing 102249, China
2
CNOOC China Limited, Zhanjiang Branch, Zhanjiang 524057, China
3
Oil Production Research Institute of Huanqing Oil Production Plant of PetroChina Yumen Oilfield Company, Qingyang 745700, China
*
Author to whom correspondence should be addressed.
Energies 2023, 16(4), 1738; https://doi.org/10.3390/en16041738
Submission received: 1 January 2023
/
Revised: 26 January 2023
/
Accepted: 2 February 2023
/
Published: 9 February 2023
(This article belongs to the Special Issue Current Technical Problems of Conventional and Unconventional Oil and Gas Recovery)
Abstract
:Conventional reservoir drill-in fluids used for drilling reservoirs in Weizhou Oilfield encounter rheological problems that result in technical problems such as hole-cleaning in openhole horizontal intervals. Hence, novel drill-in fluid was developed by optimizing the additive quantity and particle size distribution. Lab tests showed that novel drill-in fluids boast high low shearing rate viscosity, and provide promising cutting, carrying, and suspension capabilities. Furthermore, the novel drill-in fluids performed well in reservoir protection, with a permeability recovery rate of more than 90%. The novel drill-in fluids also have high inhibition capabilities with a linear expansion rate of mud shale as low as 10%, with a rolling recovery rate of up to 96.48%. Field application results showed no pipe-stuck was encountered during tripping in the horizontal interval when using the novel drill-in fluid. Moreover, by using the novel drill-in fluids, skin factor was reduced from 20.0 to −3.0, and daily oil production was double what was expected. It was concluded that novel drill-in fluids meets the demand of horizontal drilling intervals in Weizhou Oilfield and improves hole-cleaning and reservoir protection in the horizontal well.
1. Introduction
Weizhou Oilfield is located in the central and western part of geological depression of Weizhou, a depression in the northern Beibu Gulf Basin of the South China Sea, as is shown in Figure 1. It has successively experienced three developmental stages of rifting, fault depression, and depression, and is controlled by normal faults. Its target layer is the Weizhou Formation Section 3 and Section 4. Section 3 is interbedded with medium and fine sandstone and clay of unequal thickness, and siltstone is mixed with colored clay; Section 4 is interbedded with medium and fine sandstone and clay with unequal thickness, and the upper clay is variegated and the lower part is gray clay. Drilling long horizontal wells in the reservoir of the marginal oilfield in Weizhou Oilfield could encounter downhole problems such as caving and the sloughing of the mudstone rocks. For example, in an exploration well K-1, polymer drilling fluid containing 2%KCL cannot inhibit the hydration and swelling of the mudstone formation and the sloughing of brittle mudstone. Tight hole, sloughing, and pipe-stuck were frequently encountered. The horizontal section of the horizontal well drilled in this oilfield is relatively long (800–1000 m), making it difficult to clean the wellbore, and the reservoir section has strong heterogeneity, making it difficult to protect the reservoir. The oilfield uses solid-free organic salt drilling fluid to drill the horizontal section, and its formula is 0.3% caustic soda + 2.0% PF-FLOTROL (fluidity modifier) + 2.0% PF-GBL (white asphalt) + 1.5% PF-LPFH (loss-circulation material) + 3.0% CaCO3 (loss-circulation material) + PF-CONA (Weighting material) + PF-HCOOK (inhibitor). This drilling fluid is a novel type of fast weak gel drilling fluid. The synergistic effect between additives forms a gel without the addition of a cross-linking material. It has low requirements for gel formation temperature and gel formation time, low apparent viscosity, low shear resistance, and a strong adaptability to the environment. However, the dynamic-plastic ratio of drilling fluid is low, and the viscosity at a low shear rate cannot meet the cutting-carrying requirements of a long open-hole horizontal section, which may easily lead to complex downhole situations such as tight-spot during tripping, and back reaming with a pump pressure spike. Moreover, the optimization of the particle size distribution of temporary plugging materials has not been made in accordance with a strong heterogeneous reservoir, resulting in poor reservoir protection [1,2,3,4,5], resulting in an oil well skin factor that often goes above 20, and the actual oil production is lower than expected. Therefore, the author improved the rheological properties and reservoir protection properties of the solid-free organic salt drilling fluid by optimizing the amount of viscosifier and optimizing the particle size distribution of temporary loss-circulation material, and formed a solid-free drilling fluid suitable for the long open-hole horizontal section of this oilfield. In terms of phase organic salt drilling fluid, the field application shows that this drilling fluid can meet the requirements of wellbore cleaning and reservoir protection in a long open-hole horizontal section of Weizhou Oilfield.
2. Materials and Methods
Aiming at the characteristics of reservoirs in the Weizhou Oilfield, the drilling fluids to meet the requirement of drilling engineering and reservoir protection are developed for horizontal drilling. The drilling fluids have no solid phase and the features of fast weak gel. Moreover, the formation was unconsolidated, diagenesis was poor, it was collapsed easily with borehole hydration. In order to solve technical problems, the rheological properties, the inhibition, and the lubrication ability of novel drilling fluid were carefully studied. In view of the poor effect of wellbore cleaning and reservoir protection of the currently used solid-free organic salt drilling fluid in Weizhou Oilfield, the rheology of the drilling fluid is improved by optimizing the amount of viscosifier, and optimizing the particle size of the temporary loss-circulation material to improve the drilling fluid’s rheology. Reservoir protection performance was assessed, so that it can meet the drilling requirements.
2.1. Rheological Optimization
Low shear rate viscosity is an important parameter to measure the rock-carrying capability of drilling fluids. The rock-carrying capability of drilling fluids can be improved by increasing low shear rate, and the addition of viscosifiers is positively correlated with low shear rate. The viscosity enhancer PF-VIS is of low cost and strong adaptability, and is a commonly used viscosity enhancer for drilling fluids. Therefore, based on the current solid-free organic salt drilling fluid in Weizhou Oilfield, the author tested the viscosity of drilling fluid at low shear rate under different amounts of PF-VIS to determine the viscosity of PF-VIS. The test results are shown in Table 1.
It can be seen from Table 1 that with the increase in the amount of viscosifier PF-VIS, the apparent viscosity, plastic viscosity, and shear force of the drilling fluid all increase, especially the viscosity at low shear rate which increases significantly. When the additional amount of PF-VIS reaches 0.7%, its low shear rate viscosity exceeds 30,000 mPa·s, indicating that its rock-carrying ability meets the requirements of drilling horizontal section, and then 2.0% PF-GJC (inhibitor) is added, the lubrication coefficient dropped to 0.11, the low shear rate viscosity exceeded 40,000 mPa·s, and the rheology is further improved. Therefore, it was determined that the viscosity enhancer PF-VIS was added by 0.7%, and then 2.0% PF-GJC (inhibitor) was added.
2.2. Rheological Optimization
2.2.1. Optimization of Particle Size of Temporary Loss-Circulation Material Principle
The key to reservoir protection is to prevent the intrusion of filtrate and solid phase particles. According to the D90 rule, when the D90 of the particle size cumulative distribution curve of the temporary plugging agent particles is equal to the maximum pore throat diameter of the reservoir, the solid phase particles of this size in drilling fluid will be formed by bridge plugging on the borehole. The mud cake with extremely low permeability can achieve ideal temporary plugging effect [6,7,8]. Therefore, the particle size distribution of the temporary plugging agent was optimized according to the D90 rule.
2.2.2. Optimization of Particle Size Distribution of Temporary Plugging Agent
To optimize the particle size distribution of temporary plugging agent, the maximum pore diameter of the pore throat of the reservoir must be obtained first. The author selected cores from Section 3 of Well WZX-1 and Section 4 of Well WZX-2 to manufacture thin artificial cores, and analyze the particle size distribution of pore throats. The results are shown in Table 2. It can be seen from Table 2 that average maximum pore diameter of reservoir pore throat is 121.63 μm.
The acid-soluble temporary plugging agent ultrafine calcium carbonate has a wide particle size distribution, is cheap, easy to acidify and remove plugging, and has good compatibility with reservoirs [9,10,11,12]. Therefore, calcium carbonate was selected as the temporary plugging agent. According to the average value of the maximum pore throat diameter of the reservoir cores in the Section 3 and Section 4, the particle size distribution of the temporary plugging agent calcium carbonate was systematically optimized by applying the complex structure well reservoir damage evaluation and protection technology. When the mass ratio of 800-mesh calcium carbonate to 400-mesh calcium carbonate is 4.01:1, its D90 is equal to the average value of the maximum pore diameter of the pore throat of the layer core. Therefore, it was determined that the mass ratio of 800 mesh calcium carbonate to 400 mesh calcium carbonate is 4.01:1.
By optimizing the rheological properties and reservoir protection properties of the currently used solid-free organic salt drilling fluid, a novel solid-free organic salt drilling fluid formula was formed, which is 3.0% caustic soda + 2.0% PF-FLOTROL (fluidity conditioner) + 20.0% PF-GBL (white asphalt) + 1.5% PF-LPFH (loss-circulation material) + PF-CONA (weighting material) + PF-HCOOK (inhibitor) + 0.7% PF-VIS + 2.0% PF-GJC (Polymer alcohol) + 3.0% CaCO3, CaCO3 is mixed with CaCO3 with a particle size of 800 mesh and 400 mesh, and its mass ratio is 4.01:1.
3. Performance Evaluations
3.1. Inhibition
The mud shale linear expansion rate test and the cuttings recovery rate test were used to evaluate the inhibition of drilling fluids [13,14,15,16,17,18,19,20,21,22,23,24,25]. Shale from Well WZX-1 and Well WZX-2 were selected for a linear expansion test, and the results are shown in Table 3. It can be seen from Table 3 that the linear expansion rate of shale in Well WZX-1 in solid-free organic salt drilling fluid (before and after optimization) is about 10%, indicating that the inhibition of solid-free organic salt drilling fluid after optimization is significant.
The cuttings recovery test is selected from different depths of Well WZX-1 and Well WZX-2, and the results are shown in Table 4. As can be seen from Table 4, the cutting rate in the solid-free organic salt drilling fluid after optimization is about 95%, indicating that the inhibition of clay dispersion of solid-free organic salt drilling fluid after optimization is conspicuous.
3.2. Anti-Pollution
Weizhou Oilfield requires drilling fluid to have the properties of anti-drilling cuttings pollution, anti-seawater pollution, and anti-sodium chloride pollution, so it is necessary to evaluate the optimization of solid-free organic salt drilling fluid.
3.2.1. Anti-Pollution of Cuttings
The performance of optimized solid-free organic salt drilling fluid before and after adding 100 mesh Section 3 drill cuttings was tested. The results are shown in Table 5. It can be seen from Table 5 that with the increase in the amount of drill cuttings, the viscosity of the optimized solid-free organic salt drilling fluid slightly increases, the API filtration decreases, and its performance is relatively stable, indicating that it has a very good resistance to cuttings.
3.2.2. Anti-Fouling Performance of Seawater
The performance of optimized solid-free organic salt drilling fluid before and after seawater pollution was tested. The results are shown in Table 6. It can be seen from Table 6 that with the increase in seawater pollution, the apparent viscosity and plastic viscosity of optimized solid-free organic salt drilling fluid gradually decreased, and the fluid loss increased, but the change was not obvious, and it still met the drilling requirements, indicating that the optimized solid-free organic salt drilling fluid has better performance of anti- seawater pollution.
3.2.3. Anti-Sodium Chloride Contamination
The performance of optimized solid-free organic salt drilling fluid before and after adding sodium chloride was tested. The results are shown in Table 7. It can be seen from Table 7 that with the increase in sodium chloride addition, the apparent viscosity and plastic viscosity of the optimized solid-phase organic salt-free drilling fluid slightly increased, and the filtration loss increased, but the change was not obvious. It can still meet the drilling requirements, indicating that the optimized solid-free organic salt drilling fluid has a fine resistance to sodium chloride pollution.
3.3. Reservoir Protection Performance
Shale cores from a vertical depth of 2660.00 m in Well WZX-1 of Weizhou Oilfield were selected, and the ZDY50-180ZDY50-180 core dynamic damage apparatus was used to evaluate the reservoir protection performance of solid-free organic salt drilling fluid (before and after optimization). Firstly, test the oil phase permeability of the cores saturated with formation water, then contaminate the cores with solid-free organic salt drilling fluid (before/after optimization) at 120 °C, 3.5 MPa for 2 h, then take out the cores, and use gel breaking fluid at 120 °C, 0.7 MPa. Break the gel for 2 h, then replace the gel-breaking fluid with completion fluid, and finally test the oil phase permeability of the core, and then calculate the permeability recovery rate according to the results of the two core permeability tests. The results are shown in the Table 8.
It can be seen from Table 8 that the permeability recovery rate of cores contaminated with solid-free organic salt drilling fluid before optimization is about 85%, and the permeability recovery rate after optimization is more than 90%, indicating that the reservoir protection performance of solid-free organic salt drilling fluid has been greatly improved.
3.4. Blocking Performance
The core with a gas permeability of 14.5 mD was selected, and the plugging ability of the drilling fluid with a density of 1.4 kg/L solid-free organic salt drilling fluid before and after optimization was evaluated by using a JLX-2 dynamic loss-circulation plugging tester. The thickness of the mud cake formed on the core before and after the optimization of the solid-free organic salt drilling fluid was 3 and 1 mm, respectively, and the depth of intrusion into the core was 4.1 and 1.5 cm, respectively. At 120 °C and a differential pressure of 13 MPa, the filtration loss of optimized solid-free organic salt drilling fluid was only 4.2 mL, which indicates that the optimized solid-free organic salt drilling fluid has a strong plugging performance and can meet the drilling requirements.
4. Field Application
In Weizhou Oilfield, when drilling in Section 4 of a reservoir in the early stage, the hole-cleaning problem is significant and the actual drilling period exceeds the design period by 3–4 days; at the same time, due to the lack of particle size matching of temporary loss-circulation material, the skin factor is high, and usually reaches more than 20; therefore, the reservoir protection effect is not ideal. This time, four wells in a Weizhou block used an optimized solid-free organic salt drilling fluid, and the horizontal sections of the target layers were all in Section 4. The optimized solid-free drilling fluid technology solves the problem of a long horizontal section. The improvement of hole-cleaning in the horizontal section of the open-hole is that there is no tight-spot in the whole process of tripping, and no back-reaming is required for tripping. The design drilling period was 20 days, the actual drilling period was 12 days, and the efficiency was increased by 40%; the average skin coefficient was −3, and the production was two times higher than expected, indicating good reservoir protection. Taking the horizontal well operation of Well Weizhou H1 as an example, the field application of optimized solid-free organic salt drilling fluid is analyzed below. Weizhou H1 drilled the φ311.1 mm hole by side-tracking in the φ339.7 mm casing of the original well at the first spudding, and drilled the Wanglougang, Dengloujiao, Jiaowei, Xiayang, and Weizhou Section 1 formation, respectively, and ran φ244.5 mm casing to the clay of Weizhou Section 1 formation, providing a high upper casing shoe bearing pressure for the oil-based mud operation in the second spudding; the second spudding φ215.9 mm hole in the Weizhou Section 4 formation lands on the target sand. Then, φ177.8 mm casing was run to cement gray clay which was easily collapsed in the Weizhou Section 2 and Section 3 formation; the horizontal section with a hole size of φ151.8 mm was drilled to open the Weizhou Section 4 reservoir, and finally completion perforated pipe was run to support the borehole. In order to ensure hole-cleaning and reservoir protection goals in the long open-hole section, corresponding measures were taken in the field operation:
- (1)
- In total, 200 mesh shale-shaker screen was used in the whole well section, and solid control equipment was used to control the solid phase content of the drilling fluid, so that the solid phase content of the drilling fluid in the system was as low as possible, so as to achieve the purpose of optimal and fast drilling and wellbore cleaning;
- (2)
- PF-FLO (starch) was used to improve rheology of drilling fluid and strictly control the filtration loss of the drilling fluid within 4 mL to form mud cake with a thickness of 1.5 mm on the borehole;
- (3)
- In order to prevent clay in Weizhou Section 4 from collapsing, the density and viscosity of the drilling fluid should be appropriately increased, and PF-VIS (viscosifier) was used to increase viscosity of the drilling fluid at a low shear rate, thereby improving the hole-cleaning effect of the drilling fluid. Fine application results have been achieved, as follows:
- (4)
- The phase of cuttings return from the shale-shaker was clear, indicating that the cuttings in the long horizontal open-hole section were well delivered. Tripping was smooth, and there was no need to back-ream to pass a tight spot;
- (5)
- The drilling encounter of the sandstone reservoir section exceeded 92%, the production of the reservoir exceeded that expected by two times, and the footage in the horizontal section reached 1000 m, setting two records of the longest horizontal well section in the Beibu Gulf and the highest reservoir encounter, as shown in Table 9. As shown in the table, compared with a comprehensive skin factor of more than 20 adjacent wells, the overall skin factor of this operation was −3 on average, and the reservoir protection effect was prominent.
- (6)
- In the case of drilling clay, fine borehole stability allowed the perforated pipe to run smoothly, the operation efficiency was significantly improved, and considerable operating costs were saved;
- (7)
- In the case of relatively high annular cuttings concentrations caused by a limited pump rate and a long horizontal open-hole section, the rheological changes of solid-free organic salt drilling fluid used in adjacent wells before optimization were high, as shown in Table 10. The rheology of the optimized solid-free organic salt drilling fluid in the second operation had little change, and the filtration loss was greatly reduced, as shown in Table 11, indicating that the optimized system had a fine anti-pollution capability.
Table 9.
Comparison of skin factor.
| Well Name | Skin Factor | |
|---|---|---|
| Before optimization | WZ-X1 | 20 |
| WZ-X2 | 22 | |
| After optimization | WZ-H1 | −3 |
| WZ-H2 | −3 |
Table 10.
Comparison of drilling fluid rheology at different depth.
| Well Depth(m) | Density (kg·L−1) | Apparent Viscosity (mPa·s) | Plastic Viscosity (mPa·s) | Yield Point Pa | Gel Strength Pa | API Filtration mL |
|---|---|---|---|---|---|---|
| 3300 | 1.41 | 50.0 | 30.0 | 20.0 | 6/7 | 9.1 |
| 3400 | 1.42 | 56.0 | 33.0 | 22.0 | 7/9 | 9.5 |
| 3500 | 1.42 | 60.0 | 37.0 | 24.0 | 10/8 | 10.2 |
| 3600 | 1.43 | 62.0 | 40.0 | 24.0 | 11/9 | 11.0 |
Table 11.
Comparison of drilling fluid rheology at different depth.
| Well Depth (m) | Density (kg·L−1) | Viscosity (mPa·s) | Plastic Viscosity (mPa·s) | Yield Point Pa | Gel Strength Pa | API Filtration mL |
|---|---|---|---|---|---|---|
| 3300 | 1.40 | 44.0 | 24.0 | 21.0 | 5/6 | 3.8 |
| 3400 | 1.40 | 45.0 | 24.0 | 21.0 | 4/6 | 3.8 |
| 3500 | 1.40 | 45.0 | 25.0 | 22.0 | 4/6 | 3.9 |
| 3600 | 1.40 | 46.0 | 25.0 | 22.0 | 5/6 | 3.8 |
The novel drilling fluid was optimized by a high temperature filtration loss reducer, high temperature viscosifier, high temperature drilling starch, water block prevent agent, ultrafine carbonate, polyamine, and high temperature stabilizer. The mud cake formed on cores was easy to remove. The selected water block preventer, when added at a concentration of 2%, reduced the tension of the oil–liquid interface of the mud of filtration, indicating a fine water block preventer for reservoir protection. This novel formulation is suitable for low permeable reservoir horizontal drilling.
5. Conclusions and Recommendations
- (1)
- The formulation of a conventional solid-free organic salt drilling fluid system was optimized. The indoor evaluation of its inhibition, anti-caving, and anti-pollution capabilities showed that the optimized system is capable of carrying and suspending drilling cuttings, and the permeability recovery rate of reservoir core exceeded 90%, the expansion rate of clay was only 10%, and the hot-rolling recovery rate of clay was as high as 96.48%. This drilling fluid system can solve the problems of sand carrying and reservoir protection in long open-hole horizontal well sections of a reservoir.
- (2)
- The drilling fluid performance of this system is easy to maintain and the reservoir protection effect is fine. In the later stage, it is recommended to use a higher level of 1600 mesh loss-circulation material calcium carbonate for particle size distribution to further improve the reservoir protection capacity of drilling fluid system.
- (3)
- Field application results show that the optimized drill-in drilling fluid system can successfully solve the problem of mud boulder, wellbore cleaning, lubrication, and pipe-stuck which has existed for a long time. The perforated pipes were run through the hole smoothly. The application of novel solid-free organic salt drilling fluid in the reservoir section of Weizhou Oilfield has achieved excellent drilling operations and accomplished the geological reservoir development plan, which can provide reference for operations in blocks with similar stratigraphic characteristics.
Author Contributions
Conceptualization, S.L. and Y.L.; methodology, S.L.; validation, P.H.; formal analysis, W.L.; investigation, Z.L.; resources, Y.L.; writing—original draft preparation, S.L.; writing—review and editing, S.L.; supervision, Y.L. All authors have read and agreed to the published version of the manuscript.
Funding
This work is supported by National Science and Technology Major Project (Project No. 2022ZX05028001-009).
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
Not applicable.
Conflicts of Interest
The authors declare no conflict of interest.
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Figure 1.
Weizhou Oilfield.
Table 1.
The effect of viscosity increasing material to solid-free organic salt drilling fluid.
| PF-VIS Add Amount,% | /Condition | Density (kg·L−1) | Apparent Viscosity (mPa·s) | Plastic Viscosity (mPa·s) | Yield Point Pa | Gel Strength Pa | API Filtration mL | Low Shear Rate Viscosity (mP·s) | Lubrication Factor |
|---|---|---|---|---|---|---|---|---|---|
| Before aging | 1.4 | 30 | 21 | 8 | 2/3 | ||||
| After aging | 37 | 27 | 9 | 4/5 | 2.2 | 25,007 | 0.17 | ||
| 0.7% | Before aging | 1.4 | 36 | 20 | 16 | 3/4 | |||
| After aging | 35 | 21 | 14 | 3/5 | 2.0 | 32,846 | 0.15 | ||
| 0.7% * | Before aging | 1.4 | 44 | 24 | 20 | 4/5 | |||
| After aging | 45 | 25 | 20 | 4/6 | 2.4 | 41,987 | 0.11 |
Note: * added 2.0% PF-GJC (inhibitor). Aging conditions are at 120 °C hot-rolling for 16 h, the same below.
Table 2.
Analysis of pore throat size distribution.
| Core No. | Well Name | Well Depth/m | Section | Average Pore Diameter Ratio | Average Pore Diameter/μm | Maximum Pore Diameter/μm | Minimum Pore Diameter/μm |
|---|---|---|---|---|---|---|---|
| 27 | WZX-1 | 2479.50 | Section 3 | 6.01 | 24.85 | 124.36 | 1.54 |
| 16 | WZX-1 | 2685.90 | Section 3 | 4.98 | 22.35 | 125.47 | 1.99 |
| 23 | WZX-2 | 3175.00 | Section 4 | 6.09 | 19.3 | 115.36 | 2.12 |
| 32 | WZX-2 | 3299.80 | Section 4 | 5.67 | 20.89 | 121.32 | 1.23 |
Table 3.
Comparison of shale swelling rate between before/after optimization of solid-free organic salt drilling fluid.
Table 3.
Comparison of shale swelling rate between before/after optimization of solid-free organic salt drilling fluid.
| Well Name | Well Depth/m | Condition | Shale Swelling Rate % |
|---|---|---|---|
| WZX-1 | 2686.00 | Before optimization | 10.2 |
| After optimization | 11.8 | ||
| WZX-2 | 2436.00 | Before optimization | 9.50 |
| After optimization | 9.11 |
Table 4.
Comparison of shale recovery rate between before/after optimization of solid-free organic salt drilling fluid.
Table 4.
Comparison of shale recovery rate between before/after optimization of solid-free organic salt drilling fluid.
| Well No. | Well Depth/m | Condition | Shale Recovery Rate/% |
|---|---|---|---|
| WZX-1 | 2436.00 | Before optimization | 95.11 |
| After optimization | 96.48 | ||
| WZX-2 | 3175.10 | Before optimization | 91.25 |
| After optimization | 92.27 | ||
| 3266.40 | Before optimization | 93.91 | |
| After optimization | 94.66 |
Table 5.
Evaluation of Anti-pollution capability of cuttings between before/after optimization of solid-free organic salt drilling fluid.
Table 5.
Evaluation of Anti-pollution capability of cuttings between before/after optimization of solid-free organic salt drilling fluid.
| Add Amount of Cuttings,% | Condition | Density (kg·L−1) | Apparent Viscosity (mPa·s) | Plastic Viscosity (mPa·s) | Yield Point Pa | Gel Strength Pa | Filtration Loss mL |
|---|---|---|---|---|---|---|---|
| 0 | Before aging | 1.40 | 44.0 | 24 | 20.0 | 2/3 | |
| After aging | 45.0 | 25 | 20.0 | 4/5 | 2.4 | ||
| 5 | Before aging | 1.40 | 39.0 | 18 | 21.0 | 3/4 | |
| After aging | 48.0 | 27 | 21.0 | 3/5 | 3.1 | ||
| 10 | Before aging | 1.40 | 39.0 | 18 | 21.0 | 4/5 | |
| After aging | 46.0 | 26 | 20.0 | 4/6 | 2.8 | ||
| 15 | Before aging | 1.41 | 43.5 | 22 | 21.5 | 4/5 | |
| After aging | 49.0 | 27 | 22.0 | 4/6 | 2.9 |
Table 6.
Evaluation of anti-seawater pollution capability between before/after optimization of solid-free organic salt drilling fluid.
Table 6.
Evaluation of anti-seawater pollution capability between before/after optimization of solid-free organic salt drilling fluid.
| Seawater Invasion Amount/% | Condition | Density (kg·L−1) | Apparent Viscosity (mPa·s) | Plastic Viscosity (mPa·s) | Yield Point Pa | Gel Strength Pa | API Filtration mL |
|---|---|---|---|---|---|---|---|
| 0 | Before aging | 1.4 | 44.0 | 24 | 20.0 | 2/3 | / |
| After aging | 45.0 | 25 | 20.0 | 4/5 | 2.4 | ||
| 5 | Before aging | 1.4 | 35.0 | 18 | 17.0 | 3/4 | |
| After aging | 39.0 | 19 | 20.0 | 3/5 | 3.8 | ||
| 10 | Before aging | 1.4 | 34.0 | 18 | 16.0 | 4/5 | |
| After aging | 38.0 | 21 | 17.0 | 4/6 | 3.9 | ||
| 15 | Before aging | 1.4 | 32.5 | 16 | 16.5 | 4/5 | |
| After aging | 39.0 | 21 | 18.0 | 4/6 | 4.0 |
Table 7.
Evaluation of Anti-sodium chloride pollution capability between before/after optimization of solid-free organic salt drilling fluid.
Table 7.
Evaluation of Anti-sodium chloride pollution capability between before/after optimization of solid-free organic salt drilling fluid.
| Add Amount of NACL, % | Condition | Density (kg·L−1) | Apparent Viscosity (mPa·s) | Plastic Viscosity (mPa·s) | Yield Point Pa | Gel Strength Pa | API Filtration mL |
|---|---|---|---|---|---|---|---|
| 0 | Before aging | 1.4 | 44.0 | 24 | 20.0 | 2/3 | |
| After aging | 45.0 | 25 | 20.0 | 4/5 | 2.4 | ||
| 5 | Before aging | 1.4 | 45.0 | 20 | 25.0 | 3/4 | |
| After aging | 45.0 | 25 | 20.0 | 3/5 | 3.6 | ||
| 10 | Before aging | 1.4 | 45.0 | 21 | 24.0 | 4/5 | |
| After aging | 49.0 | 25 | 24.0 | 4/6 | 3.5 | ||
| 15 | Before aging | 1.4 | 45.5 | 22 | 23.5 | 4/5 | |
| After aging | 55.0 | 27 | 28.0 | 4/6 | 3.8 |
Table 8.
Evaluation of plugging material particle matching between before/after optimization of solid-free organic salt drilling fluid.
Table 8.
Evaluation of plugging material particle matching between before/after optimization of solid-free organic salt drilling fluid.
| Core No. | Drilling Fluid | Gas Permeability Rate/mD | Oil Phase Permeability/mD | Permeability Recovery Rate/% | |
|---|---|---|---|---|---|
| Before Pollution | After Pollution | ||||
| 21 | Before optimization | 1.44 | 0.594 | 0.512 | 86.12 |
| 22 | 2.40 | 1.002 | 0.833 | 83.13 | |
| 1 | After optimization | 8.99 | 1.447 | 1.345 | 92.97 |
| 12 | 3.69 | 0.733 | 0.669 | 91.30 | |
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Lin, S.; Lu, Y.; Liu, Z.; Lu, W.; Hu, P. Novel Water-Based Mud for Low-Permeable Reservoir in South China Sea. Energies 2023, 16, 1738. https://doi.org/10.3390/en16041738
AMA Style
Lin S, Lu Y, Liu Z, Lu W, Hu P. Novel Water-Based Mud for Low-Permeable Reservoir in South China Sea. Energies. 2023; 16(4):1738. https://doi.org/10.3390/en16041738
Chicago/Turabian StyleLin, Siyuan, Yunhu Lu, Zhiqin Liu, Wei Lu, and Po Hu. 2023. "Novel Water-Based Mud for Low-Permeable Reservoir in South China Sea" Energies 16, no. 4: 1738. https://doi.org/10.3390/en16041738
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