Permeability Enhancement Mechanism of Acidizing in Steam-Assisted Gravity Flooding Wells

Round 1

Reviewer 1 Report

Thanks for submitting to MDPI. 

Title: Semms to be quite long can we make more smart? Kindly review. 

Line 16  steam huff and huff -----pls correct

Line 22 taken as the examples ----pls list down

Line 28 which can increase the permeability of natural core by--- what about other two wells>---pls provide typical data for them also.

Keywords : Pls use few from the list given in

Enhanced Oil Recovery Technologies, 2nd Volume (mdpi.com)

Figures 1 & 2 pls label completely

Figures 1 & 2 pls provide reference 

Line 112 construction pressure ==== boring / drilling pls revisit

Line 114  acid ===== which acid pls?

Line 117 enhancing permeability ---- Reference

Line 194 ----  Nevertheless, there has been currently no economical and effective 194 means to break through the low permeability interlayers.-----pls revisit

Line 200 different well types------pls quantify

Figure 3 pls label type of material/formation with (a), (b), (c) and (d)

Line 212 vThe main components of the reservoir sandstone are volcanic rock debris (42.1%), 212 quartz (15.3%) and feldspar (13.5%) The complex matrix mainly includes argillaceous 213 (8.4%) and kaolinite (2.2%).---- how was determined / determined yourself in study or through some reference?

TABLE 1 If parameters determined in study of taken from reference pls clarify. Further if self determined in study pls mention the test methods?

Line 233  the three main acids to prepare 232 the mixed acid should include hydrochloric acid, hydrofluoric acid and fluoborate acid.---- what was rational behind the selection?

Line 227 experimental methods ------- Do we have some Chinese/European/American standards? if so pls specify?

Line 238  Under the premise of achieving the dissolution effect, the economic cost was saved as far as possible------ How pls elaborate?

Line 242 Out of 100% pls respecify the composition ----------36% hydrochloric acid, 40% hydrofluoric acid and 40% fluoroboric acid were used to 242 prepare the acidizing fluid.-------Any reference?

Line 244 The natural cores were 244 taken from the inspection well in Shu Yi District. The crude oil and formation water were 245 provided by Shuyi District of Liaohe Oilfield  ----- Its one source / project above you have mentioned three kindly review

Line 248 large piece of core   -- -   pls specify length?

Line 256 The mixture of acid and core sample was put into the oven at a temperature 45℃.-------- why 45?

Equations 1 and 2 ------ Reference pls

Pls label S equation no. 

Pls label Figures 4 and 5?

Figure 6 can you physically show the experimental setup in a photograph?

TABLE 2 If parameters determined in study of taken from reference pls clarify. Further if self determined in study pls mention the test methods?

TABLE 3 If parameters determined in study of taken from reference pls clarify. Further if self determined in study pls mention the test methods?

TABLE 4 If parameters determined in study of taken from reference pls clarify. Further if self determined in study pls mention the test methods?

Pls label Figure 7

Line 320 cores typo

On what basis the concentration of acids were selected. How much time was given ??? (Figure 8)?

Line 334  compound ---- pls use different word

Line 337 was set as 2% 337 tentatively ---Have you made some trial mixes? what was rational in using the %ages?

Line 334 to 354 --   Pls improve the rational in present form its quite orthodox approach (Figure 9).

Lines 357 to 387 Pls improve the rational in present form its quite orthodox approach (Figure 10 & 11).

Line 390 core slice dissolution experiments (test method???)

Table 5 Formular typo

Table 5 what was rational not clear?

Figure 12 how image analysis was carried out for permeability determination?

Figure 13 - Permeability type i.e. three dimensional, two dimensional or one dimensional. If one dimensional than along which plane?

Figure 14 where is similar figures for other two locations claimed above?

Figure 14 need correction and need to be verified/compared through some authenticated results in literature? In present form it is very difficult to evaluate?

Conclusions should be derived from the objectives of the study? In present form they are mixed up and confusing. Try to make it smart and short after necessary tailoring. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Few tenses and grammar modifications are required. 

Author Response

 

Author reply: ß We thank the reviewer for the positive comments and helpful suggestions.

1. Title: Semms to be quite long can we make more smart? Kindly review.

Author reply: ß We thank the reviewer for the helpful suggestions. We have changed the title of the paper to Permeability Enhancement Mechanism of Acidizing in  Steam-assisted Gravity Flooding Wells。

2. Line 16 steam huff and huff -----pls correct

Author reply: ß We thank the reviewer for the helpful suggestions. The expression has been corrected as ‘steam huff and puff’. We have carefully addressed all the issues mentioned by the reviewers. The following text has been updated on Page 1, Line 16 of the revised Main Manuscript.

“Steam-assisted gravity oil drainage (SAGD flooding) is a cutting-edge technology for the development of heavy oils, which is gradually replacing steam huff and puff and has been used more and more widely.”

3. Line 22 taken as the examples ----pls list down

Line 28 which can increase the permeability of natural core by--- what about other two wells>---pls provide typical data for them also.

Author reply: ß We thank the reviewer for the suggestions. The research in this manuscript only focused on the Shuyi District of Liaohe Oilfield. Based on the study of reservoir sensitivity characteristics of this block, a working fluid system for acidizing fracturing suitable for this well was determined. The following text has been updated on Page 1, Lines 21- 25 of the revised Main Manuscript.

“A typical kind of well with SAGD flooding actually applied in China, Shuyi District of Liaohe Oilfield, was taken as the example to study the optimization of crack parameters. Based on the study of reservoir sensitivity characteristics in this well, the formulations of working fluids for targeted acidizing fracturing were developed by optimizing the weight percentages of main acid solution and additives.”

4. Keywords : Pls use few from the list given in Enhanced Oil Recovery Technologies, 2nd Volume (mdpi.com)

Author reply: ßWe have supplemented and changed some keywords based on the reviewer's suggestions：Steam assisted gravity drive, enhanced oil recovery, acidification, low permeability intervals, increased permeability.

5. Figures 1 & 2 pls label completely

Figures 1 & 2 pls provide reference

Author reply: ß We thank the reviewer for the helpful suggestions. A large amount of research and on-site experience have shown that there will be pieces of remaining oil above the intervals when the intervals with low physical properties exist above the steam injection well are continuously difficult to be broken through, as demonstrated in Fig. 1. A large amount of research and on-site experience have shown that there will be pieces of remaining oil above the intervals when the intervals with low physical properties exist above the steam injection well are continuously difficult to be broken through, as demonstrated in Figure 1 of this main manuscript. When the intervals with low physical properties exists between the steam injection well and the production well, as shown in Figure 2, it may severely limit the recovery rate by blocking the flow of crude oil whose viscosity is reduced by heat towards the production well. The following references have been updated on Page 16, Lines 487– 495 of the revised Main Manuscript.

“[19] Zhao Haifeng ,Xiong Yuangui ,Zhen Huaibin ,Liu Changsong ,Li Xuejiao. Experimental investigation on the fracture propagation of three-stage acid fracturing of tight sandstone gas reservoir[J]. Journal of Petroleum Science and Engineering ,2022 ,211.

[20] Mehrjoo Hossein ,Norouzi-Apourvari Saeid ,Jalalifar Hossein ,Shajari Mostafa. Experimental study and modeling of final fracture conductivity during acid fracturing[J]. Journal of Petroleum Science and Engineering ,2022 ,208.

[21] Dou Haoran, Xie Jingna, Xie Jun, Sun Gongshuai, Li Zhao, Wang Zhenyang, Miao Yanan. Study on the mechanism of the influence of HNO₃ and HF acid treatment on the CO₂ adsorption and desorption characteristics of coal[J]. Fuel, 2022, 309.

[22] Yan Fuli, Shi Yongmin, Tian Yu. Synthesis and Characterization of Surfactant for Retarding Acid–Rock Reaction Rate in Acid Fracturing[J]. Frontiers in Chemistry, 2021, 9.”

 

6. Line 112 construction pressure ==== boring / drilling pls revisit

Author reply: ß We thank the reviewer for the comments. The construction pressure refers to the pressure in which the acid pressure working fluid is injected into the formation by the fracturing truck on the well through the special acid pressure pipe column arranged in the wellbore. The following text has been updated on Page 3, Lines 110– 112 of the revised Main Manuscript.

“Acidizing fracturing, refers to the injection of acid into the formation under conditions where the acid injection pressure at the bottom of the well is greater than the fracturing pressure of the formation rock, is a commonly used stimulation method in oil fields.”

7. Line 114  acid ===== which acid pls?

Author reply: ß We thank the excellent comments from the reviewer. Acid corrosion conductivity is a general term, which represented that the flow conductivity of cracks after acid solution is injected. Injection of any acid suitable for acidizing can result in an increase in the permeability of the matrix around the fracture after acidizing.

8. Line 117 enhancing permeability ---- Reference

Author reply: ß We thank the reviewer for the excellent comments. According to the reviewer’s suggestion, we have cited the reference on enhancing permeability. The 23rd references have been updated on Page 16, Lines 496– 497 of the revised Main Manuscript.

“[23] Xu Haoran, Cheng Jingru, Zhao Zhihong, Lin Tianyi, Liu Guihong, Chen Sicong. Coupled thermo-hydro-mechanical-chemical modeling on acid fracturing in carbonatite geothermal reservoirs containing a heterogeneous fracture[J]. Renewable Energy, 2021, 172.”

9. Line 194 ----  Nevertheless, there has been currently no economical and effective 194 means to break through the low permeability interlayers.-----pls revisit

Author reply: ß We thank the reviewer for the constructive comments. The following text has been updated on Page 5, Lines 193– 195 of the revised Main Manuscript.

“There has been currently some means to break through low permeability interlayers. Nevertheless, these means cannot meet the dual needs of economic benefits and development effects at the same time.”

10. Line 200 different well types------pls quantify

Author reply: ß We thank the reviewer for the excellent comments. The following text has been updated on Page 5, Lines 200– 201 of the revised Main Manuscript.

“In this paper, based on the actual situation of different well types in China (including vertical wells, horizontal wells, multistage fracturing wells and so on), the application of acidizing fracturing assisted SAGD development were studied especially.”

11. Figure 3 pls label type of material/formation with (a), (b), (c) and (d)

Author reply: ß We thank the reviewer for the excellent comments. The 4 pictures in Figure 3 are 4 cores used to carry out the acidizing for permeability enhancement experiment of rocks in intervals with low physical properties. The Figure 3 has been updated on Page 6, Lines 216– 217 of the revised Main Manuscript.

(a) experimental core 1	(b) experimental core 2	(c) experimental core 3	(d) experimental core 4

Figure 3. Natural core samples.

12. Line 212 The main components of the reservoir sandstone are volcanic rock debris (42.1%), 212 quartz (15.3%) and feldspar (13.5%) The complex matrix mainly includes argillaceous 213 (8.4%) and kaolinite (2.2%).---- how was determined / determined yourself in study or through some reference?

Author reply: ß We appreciate the insightful comments from the reviewer. The X-ray powder diffraction (XRD) technology can be used to analyze the components of the sandstones. The following text has been updated on Page 5, Lines 200– 201 of the revised Main Manuscript and the corresponding 36^th reference has been added on Page 17.

“The main components of the reservoir sandstones measured by the X-ray powder diffraction (XRD) technology are volcanic rock debris (42.1%), quartz (15.3%) and feldspar (13.5%) [36].

[36] Li, Changming, Song Lisha, Cao Yali, Zhao Shunbo,Liu Hui,Yang Chen,Cheng Haifeng,Jia Dongyang. Investigating the Mechanical Property and Enhanced Mechanism of Modified Pisha Sandstone Geopolymer via Ion Exchange Solidification [J]. Gels, 2022, 8(5).”

13. TABLE 1 If parameters determined in study of taken from reference pls clarify. Further if self determined in study pls mention the test methods?

Author reply: ß We thank the reviewer for the comments. The parameters shown in Table 1 were determined according to the porosity and permeability measurement of core in net confining stress, from Energy Sector Standard of the People's Republic of China (standard number SY/T 6385-2019).  

14. Line 233  the three main acids to prepare 232 the mixed acid should include hydrochloric acid, hydrofluoric acid and fluoborate acid.---- what was rational behind the selection?

Author reply: ß We thank the reviewer for the comments. The content of carbonate rock in the core is small, and the dissolution effect of single hydrochloric acid will not be obvious. The acid sensitivity index of this section was large, indicating that fluoroborate or hydrofluoric acid had better acidizing effect. However, the acid content should not be too high, excessive acidizing might lead to collapse of the formation. As a result, the acidizing fluid system is composed of these three types of acid.

15. Line 227 experimental methods ------- Do we have some Chinese/European/American standards? if so pls specify?

Author reply: ß We thank the reviewer for the helpful comments. The acid solution dissolution experiments were carried out according to the test method for macrostructure and defect of steel by etching, from Standard issued by General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China (standard number GB/T 226-2015). This method has been proven in many literatures and the corresponding 37^th and 38^th references have been added on Page 17 of the revised Main Manuscript.

“[37] Ryu Miyoung,Kim Hwan, Lim Mihee,You Kwangsuk,Ahn Jiwhan. Comparison of Dissolution and Surface Reactions Between Calcite and Aragonite in L-Glutamic and L-Aspartic Acid Solutions[J]. Molecules,2010,15(1).

[38] Shan G,Igarashi K and Ooshima H. Dissolution kinetics of crystals in suspension and its application to L-aspartic acid crystals[J]. Chemical engineering journal,2002,88 (3).”

16. Line 238  Under the premise of achieving the dissolution effect, the economic cost was saved as far as possible------ How pls elaborate?

Author reply: ß We thank the reviewer for the comments. The three main acids to prepare the mixed acid include hydrochloric acid, hydrofluoric acid and fluoborate acid. Hydrochloric acid costs less, however, the dissolution effect of single hydrochloric acid is not good. The high-cost fluoroborate or hydrofluoric acid has better acidizing effect due to the large acid sensitivity index of this targeted section. Therefore, when compounding these three types of acid, increasing the amount of fluoroborate and hydrofluoric acid can achieve better acidizing and dissolution effects, while increasing the proportion of hydrochloric acid in the whole system as much as possible under the condition of ensuring the effect is beneficial to save cost.

17. Line 242 Out of 100% pls respecify the composition ----------36% hydrochloric acid, 40% hydrofluoric acid and 40% fluoroboric acid were used to 242 prepare the acidizing fluid.-------Any reference?

Author reply: ß We thank the reviewer for the comments. This formula is obtained by experiments based on the acid working fluid formula currently used in the ShuYiblock of LiaoHe Oilfiled.

18. Line 244 The natural cores were 244 taken from the inspection well in Shu Yi District. The crude oil and formation water were 245 provided by Shuyi District of Liaohe Oilfield  ----- Its one source / project above you have mentioned three kindly review

Author reply: ß We thank the excellent comments from the reviewer. These three sources (including natural cores, the crude oil and formation water) were all provided by Shuyi District of Liaohe Oilfield. The cores were taken from the inspection well in Shu Yi District of Liaohe Oilfield, while the crude oil and formation water were taken from the formation the crude oil and formation water.

19. Line 248 large piece of core   -- -   pls specify length?

Author reply: ß We thank the reviewer for the excellent comments. Large pieces of cores used to conduct experiment was the 4 cores shown in Figure 3 and Table 1. The specify lengths of these 4 cores were 7.82 cm, 5.10 cm, 8.44 cm and 5.41 cm, respectively. The following text has been updated on Page 6, Lines 250– 251 of the revised Main Manuscript.

“The oil of large pieces of cores mentioned in Table 1 was absorbed and these cores were dried, then the cores were crushed and sifted.”

20. Line 256 The mixture of acid and core sample was put into the oven at a temperature 45℃.-------- why 45?

Author reply: ß We thank the reviewer for the constructive comments. The temperature of the reservoir studied in this manuscript is 45 ℃. The oven was set as  45 ℃ to simulate the actual temperature of the formation of Liaohe Oilfield ShuYi District. The following text has been updated on Page 6, Lines 258– 259 of the revised Main Manuscript.

“The mixture of acid and core sample was put into the oven at a temperature of 45℃, which simulated the actual temperature of the formation of Liaohe Oilfield ShuYi District.”

21. Equations 1 and 2 ------ Reference pls

Author reply: ß We thank the reviewer for the comments. The reference for equations 2-1 and 2-2 has been updated on Page 7, Line 267 and Page 17, Line 533 of the revised Main Manuscript.

“The total mass of filter paper and the residual sample was weighed and recorded as m₂, then the dissolution rate was calculated with the following equation [39].

[39] Ling Daosheng, Zhu Song, Zheng Jianjing, Xu Zijun, Zhao Yunsong, Chen Liuping, Shi Xilin, Li Jinlong. A simulation method for the dissolution construction of salt cavern energy storage with the interface angle considered [J]. Energy, 2023,263, doi: 10.1016/j.energy.2022.125792.”

22. Pls label S equation no.  Pls label Figures 4 and 5?

Author reply: ß We thank the reviewer for the comments. The equation on Page 8, Lines 292 of the revised Main Manuscript has been labeled as 2-3. The following text and Figures have been updated on Page 7, Lines 275– 278 of the revised Main Manuscript.

“

 

Figure 4. Core powder dissolution experiment.

(a) experimental core 1

(b) experimental core 2

(c) experimental core 3

(d) experimental core 4

 

Figure 5. Residue filtration.

(a) experimental core 1

(b) experimental core 2

(c) experimental core 3

(d) experimental core 4”

23. Figure 6 can you physically show the experimental setup in a photograph?

Author reply: ß We thank the reviewer for the helpful suggestions.

 

1 - liquid bottle; 2 - constant speed pump; 3 - intermediate container; 4 - filter; 5-6 way valve；6 -- core gripper; 7 - regulating valve; 8 - pressure gauge; 9 - measuring cylinder; 10 - manual pressure pump

Figure 6. Schematic diagram of the acidizing displacement experimental setup.

24. TABLE 2 If parameters determined in study of taken from reference pls clarify. Further if self determined in study pls mention the test methods?

Author reply: ß We thank the reviewer for the comments. The parameters shown in Table 2 were determined according to the porosity and permeability measurement of core in net confining stress, from Energy Sector Standard of the People's Republic of China (standard number SY/T 6385-2019).  

25. TABLE 3 If parameters determined in study of taken from reference pls clarify. Further if self determined in study pls mention the test methods?

Author reply: ß We thank the reviewer for the helpful comments. The experimental results shown in Table 3 were obtained by the Standard issued in formation damage evaluation of the People's Republic of China (standard number SY/T 5358-2010). This method has been proven in many literatures and the corresponding references have been added on Page 17, Lines 536 -539 of the revised Main Manuscript.

“[40] Zhixuan, Li Lin, Liu Jiawei, Chen Jia., Xu Zhongzheng, Wu Yining, Dai Caili. Probing the effect of Young's modulus on the plugging performance of micro-nano-scale dispersed particle gels[J]. Petroleum Science, 2022, 2: 688-696.

[41] Grattoni Carlos Atilio, AL-Sharji Hamed H., Yang Canghu, Muggeridge Ann H., Zimmerman Robert W. Rheology and Permeability of Crosslinked Polyacrylamide Gel[J]. Journal of Colloid & Interface Science, 2001, 240: 601-607.”

26. TABLE 4 If parameters determined in study of taken from reference pls clarify. Further if self determined in study pls mention the test methods?

Author reply: ß We appreciate the insightful comments from the reviewer. The X-ray powder diffraction (XRD) technology can be used to analyze the components of the sandstones. Also, the mineral composition of rocks shown in Table 4 were measured by the XRD technology. The following text has been updated on Page 5, Lines 200– 201 of the revised Main Manuscript and the corresponding 36^th reference has been added on Page 17.

“The main components of the reservoir sandstones measured by the X-ray powder diffraction (XRD) technology are volcanic rock debris (42.1%), quartz (15.3%) and feldspar (13.5%) [36].

[36] Li, Changming, Song Lisha, Cao Yali, Zhao Shunbo,Liu Hui,Yang Chen,Cheng Haifeng,Jia Dongyang. Investigating the Mechanical Property and Enhanced Mechanism of Modified Pisha Sandstone Geopolymer via Ion Exchange Solidification [J]. Gels, 2022, 8(5).”

24. Pls label Figure 7

Author reply: ß We thank the reviewer for the comments. The Figure 7 has been labeled and the following text has been updated on Page 7, Lines 275– 278 of the revised Main Manuscript.

“(a) experimental core 1	(b) experimental core 2
(c) experimental core 3	(d) experimental core 4

Figure 7. Electron microscope images of the core before acidizing.”

25. Line 320 cores typo

Author reply: ß We thank the reviewer for the excellent comments. These cores are the samples used to conduct experiment, the specific parameters of these 4 cores have been shown in Table 1.

Table 1. Base data of cores used in acid sensitivity experiment.

Core number	Length (cm)	Diameter (cm)	dry weight (g)	wet weight (g)	pore volume (cm3)	permeability (10-3μm2)
1	7.82	2.512	86.485	92.772	6.292	18.64
2	5.104	2.518	44.33	50.22	5.89	274.12
3	8.44	2.508	93.275	100.21	6.935	17.28
4	5.41	2.49	73.641	79.96	6.319	14.32

26. On what basis the concentration of acids were selected. How much time was given ??? (Figure 8)?

Author reply: ß We thank the reviewer for the excellent comments. The concentration of single acid was selected based on the Field experience with acid injection of Liaohe oilfield Shuyi district. The reaction time of single was 4 hours. The following text has been updated on Page 9, Lines 326– 329 of the revised Main Manuscript.

“The single hydrochloric acid with the concentration of 5%-13%, single hydrofluoric acid with the concentration of 1%-5% and single fluoboric acid with the concentration of 1%-7% were prepared according to the field experience in Liaohe oilfield Shuyi district. The dissolution effects of them within 4 hours were tested respectively.”

27. Line 334  compound ---- pls use different word

Author reply: ß We thank the reviewer for the excellent comments. Different word has been used to replace the expression of ‘compound’. The following text has been updated on Page 10, Lines 337– 339 of the revised Main Manuscript.

“Then these three acids were mixed to prepare the acidizing formula system, during this period, it was necessary to ensure that the various components in the core were fully dissolved.”

28. Line 337 was set as 2% 337 tentatively ---Have you made some trial mixes? what was rational in using the %ages?

Author reply: ß We thank the reviewer for the helpful comments. When mixing hydrochloric acid, fluoboric acid and hydrofluoric acid to prepare the acidizing formula system, it was necessary to ensure that the various components in the core were fully dissolved. Provided that the concentration of hydrofluoric acid was lower than 2%, the dissolution effect cannot meet the requirement.

29. Line 334 to 354 --   Pls improve the rational in present form its quite orthodox approach (Figure 9).

Lines 357 to 387 Pls improve the rational in present form its quite orthodox approach (Figure 10 & 11).

Author reply: ß We thank the reviewer for the helpful comments. When the concentration of hydrofluoric acid was set as 7% and the concentration of hydrofluoric acid was 2%, the dissolution rate was still slightly higher than expected due to the high concentration of hydrofluoric acid. As a result, the concentrations of hydrofluoric acid were set as 1.5% and 1% to save cost (Figure 9). The best dissolution effect could be achieved when the concentration of fluoboric acid was 3%. Due to the high cost of using fluoboric acid, the concentration of fluoboric acid was set at 3% for economic consideration. When the concentration of fluoboric acid was 3% and the concentration of hydrofluoric acid was 1%, good dissolution effect could be obtained at 7% concentration of hydrochloric acid. The concentration of hydrochloric acid was determined to be 7%. The following text and Figure 10 have been updated on Page 10, Lines 355– 357 and Page 11, Lines 376– 378 of the revised Main Manuscript.

“Afterwards, the concentration of hydrochloric acid was set as 5% and the concentration of hydrofluoric acid was 1%, so that the concentration of fluoboric acid was further optimized.

 

Figure 10. Effect of concentration of hydrochloric acid on dissolution rate.”

30. Line 390 core slice dissolution experiments (test method???)

Author reply: ß We thank the reviewer for the helpful comments. The core slice dissolution experiments were carried out according to the test method for macrostructure and defect of steel by etching, from Standard issued by General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China (standard number GB/T 226-2015). This method has been proven in many literatures and the corresponding 37^th and 38^th references have been added on Page 17 of the revised Main Manuscript.

“[37] Ryu Miyoung,Kim Hwan, Lim Mihee,You Kwangsuk,Ahn Jiwhan. Comparison of Dissolution and Surface Reactions Between Calcite and Aragonite in L-Glutamic and L-Aspartic Acid Solutions[J]. Molecules,2010,15(1).

[38] Shan G,Igarashi K and Ooshima H. Dissolution kinetics of crystals in suspension and its application to L-aspartic acid crystals[J]. Chemical engineering journal,2002,88 (3).”

32. Table 5 Formular typo

Table 5 what was rational not clear?

Author reply: ß Here, we conducted experiments based on the commonly used types and concentrations of acid fluids in oilfield field applications, as follows.

Table 5 Solution combinations used in core slice dissolution experiments

Number	Fomular
1	Formation water + 2% ethanol
2	Distilled water + 2% ethanol
3	10% hydrochloric acid + 2% ethanol
4	5% hydrofluoric acid + 2% ethanol
5	5% fluoroboric acid + 2% ethanol
6	5% polyphosphate + 2% ethanol
7	3% polyphosphate + 2% fluoroboric acid
8	4% hydrochloric acid + 2% polyphosphate + 5% fluoroboric acid + 4% acetic acid + 2% ethanol

 

33. Figure 12 how image analysis was carried out for permeability determination?

Author reply: ß We thank the reviewer for the comments. The specific permeability value could not be determined from Figure 12, while the blockage of the pores after acidizing dissolution could be observed. For example, by comparing Figure 12 a1 and Figure 12 b1, it was seen that the pores after dissolution were likely to be blocked by small particles. The injection of the acid solutions could effectively address the problem of particle migration, thereby improving the permeability enhancement ability.

34. Figure 13 - Permeability type i.e. three dimensional, two dimensional or one dimensional. If one dimensional than along which plane?

Author reply: ß We appreciate the insightful comments from the reviewer. The permeability mentioned in Figure 13 refers to the one dimensional permeability, it migrates along the oil flow direction.

35. Figure 14 where is similar figures for other two locations claimed above?

Figure 14 need correction and need to be verified/compared through some authenticated results in literature? In present form it is very difficult to evaluate?

Author reply: ß We thank the reviewer for the suggestions. The research in this manuscript only focused on the Shuyi District of Liaohe Oilfield. Based on the study of reservoir sensitivity characteristics of this block, a working fluid system for acidizing fracturing suitable for this well was determined. The production after acidizing and SAGD of using this formular in Liaohe oilfield Shuyi district was shown in Figure 14.

36. Conclusions should be derived from the objectives of the study? In present form they are mixed up and confusing. Try to make it smart and short after necessary tailoring.

Author reply: ß We thank the editor for the constructive suggestions. Main research findings have been quantified in the conclusions part to fit the objectives of the study. The following text has been updated on Page 15, Lines 433– 452 of the revised Main Manuscript.

“Combining targeted acidizing fracturing and SAGD flooding is an effective method to break through the low permeability interlayers, so that enabling the steam chamber to break through the interlayers smoothly and quickly. In this paper, the acid fracturing working fluid suitable for Liaohe oilfield Shuyi district was determined. based on the reservoir sensitivity characteristics. The results of core dissolution experiments showed that hydrochloric acid and polyphosphate had poor dissolution effects on the formation. Although hydrofluoric acid and fluoroboric acid, especially fluoroboric acid, had good dissolution effects, they were prone to form small particles that plugging pores after dissolution. The combination of the above multiple acid solutions can effectively address the problem of particle migration, thereby improving the permeability enhancement ability. The actual permeability enhancing capacity of the acid fracturing working fluid formula ‘4% hydrochloric acid + 2% polyphosphate + 5% fluoroboric acid + 4% acetic acid + 2% ethanol’ was verified with the natural core of the corresponding block. Acidizing measures implemented on-site led to the beginning of reduction in water cut and increase in the oil production, indicating that applying acidizing to could enhance permeability. The range of enhancement permeability of the acidizing system in intervals with low physical properties of the reservoir developed by SAGD flooding was 35.48%~57.06%. The studies in this paper provided guidance for targeted acidizing fracturing and promote the application of SAGD flooding from the perspective of breaking through intervals with low physical properties, so that effectively improving oil recovery.”

Reviewer 2 Report

The topic is currently of interest as it aims to optimize the SAGD method, reducing energy consumption and consequently emissions. However, the use of reagents and their direct injection into the subsurface should be carefully evaluated, especially regarding soil and groundwater pollution. This aspect is missing in the presented paper, which would be useful to know and would be consistent with the attention given to the environment through emission reductions in steam production.

Additionally, some points need attention:

• Line 27: Specify whether the percentages of acid are in weight or volume.
• Introduction: It appears unbalanced as it is too extensive compared to other parts of the paper; it should be reduced.
• Lines 212-215: It's advisable to cite the sources from which the compositional information of the studied reservoirs is derived.
• Paragraphs 2.2.2-2.2.3: The description of the analytical methods used and the instruments used is missing. This information needs to be integrated.
• Paragraph 3.1, Table 4: How was the mineralogical composition determined?
• Bibliography: Standardize it according to the journal's standards.

Author Response

Comments to the author This topic is currently of great interest as it aims to optimize the SAGD method, reduce energy consumption and thus reduce emissions. However, the use of agents and their direct injection into the ground should be carefully evaluated, particularly with regard to soil and groundwater contamination. This aspect is missing from the submission, which is useful to know and is consistent with the concern for the environment by reducing emissions in steam production.

Author reply: ß We thank the reviewers for their positive comments and all their very useful suggestions.

In addition, there are a few points to note:

1. Line 27: Specifies whether the acid percentage is by weight or volume. Author response: ß We thank the reviewers for their suggestions. Percentage of acid is by weight The following text has been updated on page 1 of the revised main manuscript, lines 23-25. "Based on the study of the reservoir sensitivity characteristics of this well, a targeted acidizing fracturing working fluid formula was developed by optimizing the weight percentage of the main acid solution and additives."
2. Introduction: Compared to the rest of the paper, it seems unbalanced because it is too broad; it should be reduced.
   Author reply: ß We appreciate the review's excellent review. We have simplified the presentation of the work introduction. Experiments related to acid fracturing and SAGD flooding have been rewritten in the introduction. For example, the revised main manuscript has the following text updated on page 2, lines 48-54, lines 75-80, and page 4, lines 152-156.
   "In 1981, Butler [6] hypothesized that the oil leakage process was extended from the original theoretical two-dimensional direction to a three-dimensional direction. The oil leakage rate in the new hypothesis was treated as an important variable to derive an equation expressing the relationship. In 1986, The Alberta Oil Sands Technology and Research Authority used the SAGD equation proposed by Butler to launch the world's first SAGD pilot experimental project, the Underground Test Facility (UFT) project [7]. The UFT project achieved great success in trial production , proving that SAGD technology is suitable for heavy oil recovery.
   In 2010, Sharma [14] derived a new model for gravity drainage of super-heavy oil flowing at the edge of the steam chamber. Where the maximum oil velocity occurs depends on the relative permeability curve of oil to water and the oil viscosity. In the verification of actual field conditions, it was shown that the relevant penetration effect is an integral part when calculating actual oil production rate [15,16].
   In 2012, S.M. Fatemi [29] conducted numerical simulations to study the impact of different geometric properties of shale interlayers on SAGD flooding production and steam chamber development. The longer the length of the continuous shale interlayer, the higher the density, and the worse the SAGD effect. The smaller the vertical distance between the continuous shale interlayer and the steam injection well, the lower the recovery factor.
3. Lines 212-215: It is recommended to cite sources of information on the composition of the reservoir under study. Author response: ß We thank the reviewers for their insightful comments. X-ray powder diffraction (XRD) technology can be used to analyze the composition of sandstone. The following text has been updated in lines 200-201 on page 5 of the revised main manuscript and the corresponding reference to item 17 has been added on page 36. “The main components of the reservoir sandstone measured by X-ray powder diffraction (XRD) technology are volcanic rock fragments (42.1%), quartz (15.3%) and feldspar (13.5%) [36]. [36] Li Changming, Song Lisa, Cao Yali, Zhao Shunbo, Liu Hui, Yang Chen, Cheng Haifeng, Jia Dongyang. Research on the mechanical properties and enhancement mechanism of ion exchange solidification modified skin sandstone geopolymer [J]. Gers, 2022, 8(5).
4. Paragraph 2.2.2-2.2.3: lack of description of the analytical methods used and the instruments used. This information needs to be integrated. Author response: ß We thank the reviewers for their helpful comments. The analysis method can be found in the acid solution dissolution experiment based on the macrostructure and defect testing method of etched steel in the standards promulgated by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China (Standard No. GB/T 226-2015). This approach has been confirmed in many documents and the corresponding references to items 37 and 38 have been added to page 17 of the revised main manuscript. The description of the instruments used has been updated on page 6 of the revised main manuscript, lines 237-238. “Use a universal crusher, sample sieve, thermostat, and extraction oil washer to conduct experiments. [37] Liu Miying, Jin Huan, Lin Mixi, You Guangshu, An Zhihan. Comparison of dissolution and surface reaction of calcite and aragonite in L-glutamic acid and L-aspartic acid solutions [J]. Molecules, 2010,15(1). [38] Shan G, Igarashi K and Ooshima H. Dissolution kinetics of crystals in suspension and its application in L-aspartic acid crystals [J]. Transactions of the Chinese Society of Chemical Engineering, 2002, 88 (3). "
5. Paragraph 3.1, Table 4: How is mineral composition determined?
   Author's reply: ß Thanks to the reviewer for his excellent comments. X-ray powder diffraction (XRD) technology can be used to analyze the composition of sandstone. In addition, the mineral composition of the rocks shown in Table 4 was measured by XRD technique.
6. Bibliography: Standardized according to journal standards.
   Author response: ß We thank the reviewers for their helpful suggestions. We carefully checked the entire manuscript to correct bibliographic errors and formatting issues. We carefully processed all references to standardize them according to the journal's standards.

Author Response File: Author Response.pdf

Reviewer 3 Report

Manuscript "Permeability Enhancement Mechanism of Acidizing Fracturing in Intervals with Poor Physical Properties of Wells developed by Steam-assisted Gravity Flooding" by Ming Yu, Chao Xu, Yujie Bai, Che Zou, Weibo Liu, Guangsheng Cao , Xi Yi and Jing Zhang has been submitted for review. 

The manuscript has a number of deficiencies that need to be corrected. Correction of the following deficiencies is necessary to improve the quality of the manuscript, enhance the ease of comprehension of the presented material, and increase the reader's interest.

1) The introduction is very long. The authors provide a lot of theoretical information, which overloads the text, and often your statements are not accompanied by evidence. In the introduction you should analyze your previous work and note what has been done, what are the shortcomings, what was done incorrectly.  

2) Figure 3 - add the designation Natural core samples.

3) There is no mention of Figure 4 and Figure 5 - add designations.

4) Figure 6 is not readable, needs to be redone. 

5) Figure 7 - add designations.

6) Table 5 does not follow the journal design rules.

7) Add Discussion section

Moderate editing of English language required

Author Response

Comments to the Author

The manuscript has a number of deficiencies that need to be corrected.
Correction of the following deficiencies is necessary to improve the quality of the manuscript, enhance the ease of comprehension of the presented material, and increase the reader's interest.

1) The introduction is very long. The authors provide a lot of theoretical
information, which overloads the text, and often your statements are not accompanied by evidence. In the introduction you should analyze your previous work and note what has been done, what are the shortcomings, what was done incorrectly.
Author reply:  We thank the review for the excellent comments. We have
simplified the expressions of the introduction of the work. The experiments related to acidizing fracturing and SAGD flooding have been rewritten in the introduction section. For example, the following text has been updated on Page 2, Lines 48– 54, Lines 75- 80 and Page 4, Lines 152– 156 of the revised Main Manuscript.

In 1981, Butler [6] has assumed that the oil leakage process expands from the original theoretical two-dimensional direction to a three-dimensional direction. The oil leakage rate in the new hypothesis is taken as an important variable to derive an equation where the relationship is expressed. In 1986, the Alberta Oil Sands Technology and Research Authority has used the SAGD equation proposed by Butler to launch the world’s first SAGD pilot experimental project, namely the Underground Test Facilities (UFT) project [7]. The UFT project has achieved great success in pilot production, proving that the SAGD technology is suitable for heavy oil recovery.
In 2010, Sharma [14] has deduced a new model for gravity drainage of super heavy oil flowing at the edge of steam chamber. The location where the maximum oil velocity occurs depends on the curvature of oil relative permeability curve to water and the oil viscosity. In the verification with the actual situation on site, it is shown that the rela-tive permeability effect is an indispensable part when calculating the
actual oil pro-duction rate [15,16].

In 2012, S.M. Fatemi [29] has conducted numerical simulations to study the effects of different geometric properties of shale interlayers on the production of SAGD flooding and the development degree of steam chamber. The longer the length and higher the density of continuous shale interlayers, the worse the SAGD effect. The smaller the vertical distance between the continuous shale interlayer and the steam injection well, the lower the recovery rate.”

2) Figure 3 - add the designation Natural core samples.
Author reply: We thank the reviewer for the excellent comments. The 4
pictures in Figure 3 are 4 cores used to carry out the acidizing for permeability enhancement experiment of rocks in intervals with low physical properties. The Figure 3 has been updated on Page 6, Lines 216– 217 of the revised Main Manuscript.

3) There is no mention of Figure 4 and Figure 5 - add designations.
Author reply:  We thank the reviewer for the comments. The following text and Figures have been updated on Page 7, Lines 275– 278 of the revised Main Manuscript.

4) Figure 6 is not readable, needs to be redone.
Author reply:  We have supplemented relevant textual explanations and physical images based on the reviewer's suggestions, so that readers can better understand our research method.

5) Figure 7 - add designations.
Author reply:  We thank the reviewer for the comments. The Figure 7 has been labeled and the following text has been updated on Page 7, Lines 275– 278 of the revised Main Manuscript.

6) Table 5 does not follow the journal design rules.
Author reply: We thank the reviewer for the useful comments. We have carefully addressed Table 5, and the following text has been updated on Page 12, Lines 393– 394 of the revised Main Manuscript.

7) Add Discussion section
Author reply: We thank the review for the helpful comments. We have improved the expression of the discussion part. The following text has been updated on Page 10, Lines 329– 338 of the revised Main Manuscript.
“The three main acids to prepare the mixed acid include hydrochloric acid, hydrofluoric acid and fluoborate acid. Hydrochloric acid costs less, however, the dissolution effect of single hydrochloric acid is not good. The high-cost fluoroborate or hydrofluoric acid has better acidizing effect due to the large acid sensitivity index of this targeted section. Therefore, when compounding these three types of acid, increasing the amount of fluoroborate and hydrofluoric acid can achieve better acidizing and dissolution effects, while increasing the proportion of hydrochloric acid in the whole system as much as possible under the condition of ensuring the effect is beneficial to save cost. Then these three acids were mixed to prepare the acidizing formula system, during this period, it was necessary to ensure that the various components in the core were fully dissolved.”

After reading the paper, I think it would benefit from pre-review editing. I couldn't understand the significant differences (3 orders of magnitude) between permeabilities reported in Table 1 and Table 3. Moreover, terms used in Table aren't properly defined, which makes it impossible to understand. Equation should be numbered; the  methodology part must clearly explain the differences between rock
samples with different numbers (is there any significance to numbers, are there any mineralogical/structural/hydrodynamic differences between the samples, why were some experiments conducted with one type of sample and other experiments with another?).
I would like to remind the authors, that the level of detail in a paper should be sufficient for other researcher to reproduce the experiment and results.
Author reply: We thank the review for the useful comments.
(1) The significant differences (3 orders of magnitude) between permeabilities reported in Table 1 and Table 3 was caused by the migration of particles in reservoir. The injected acid reacts with the reservoir minerals to precipitate or release particles, resulting in a significant decrease in reservoir rock permeability.
(2) The equation on Page 8, Lines 292 of the revised Main Manuscript has been labeled as 2-3.
(3) The core samples used to carry out the experiment are the same ones. The misuse of core number resulted in this problem. The rock numbers in Table 1, 2, 3 and Table 4 have been changed to the same in the revised revised Main Manuscript.

(4) The details of this study could be proved by many standards issued by People's Republic of China. For example, the acid solution dissolution experiments were carried out according to the test method for macrostructure and defect of steel by etching, from Standard issued by General Administration of Quality Supervision, Inspection and  Quarantine of the People's Republic of China (standard number GB/T
226-2015). This method has been proven in many literatures and the corresponding 37th and 38th references have been added on Page 17 of the revised Main Manuscript.
“[37] Ryu Miyoung,Kim Hwan, Lim Mihee,You Kwangsuk,Ahn Jiwhan.
Comparison of Dissolution and Surface Reactions Between Calcite and Aragonite in L-Glutamic and L-Aspartic Acid Solutions[J]. Molecules,2010,15(1).
[38] Shan G,Igarashi K and Ooshima H. Dissolution kinetics of crystals in suspension and its application to L-aspartic acid crystals[J]. Chemical engineering journal,2002,88 (3).”

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thanks for submission of revised version. 

Line 27: The studies on targeted acidizing fracturing are beneficial to enhance the oil recovery heavy oil reservoirs------The word heavy oil reservoirs - Kindly revisit?

Introduction: For references kindly follow the MDPI format

Not all reviewers comments as summarized in the modified paper? Kindly revisit the main manuscript 

Figure 1 if the direction of the acid fracture is vertical in interlayer? Kindly re- examine?

Line 191 actual situation of different well types in China------Can we classify based on materials in place of country/location? Kindly reexamine

Figure 3 & Table 1 copyright citation permission pls verify?

Figure 4 and 5 references were used by Authors data usage statement?

Figure 6 kindly label original experimental setup figure also?

Figure 7 kindly label?

Figure 12 pls label?

How Figure 14 was drawn ? Not clear yet Pls elaborate discussion

Conclusions were not derived from objectives? - Pls revisit

 

Thanks

 

 

 

 

 

Few grammar and tense corrections are requested as pointed out. 

Author Response

Dear Professor：

we are very grateful to you and the referees for the valuable comments and constructive suggestions/feedback. We have improved the manuscript accordingly and carefully addressed all the comments.We describe the detailed changes we have made to the manuscript following the comments from the referees. All changes made are also highlighted in yellow in the revised manuscript, and their locations are referred to in our responses.

1. Line 27: The studies on targeted acidizing fracturing are beneficial to enhance the oil recovery heavy oil reservoirs------The word heavy oil reservoirs - Kindly revisit?

Author reply: ßWe have removed all text related to heavy oil as suggested by the reviewer.

2. Introduction: For references kindly follow the MDPI format

Author reply: ßWe have made changes to the reference format in the paper based on the suggestions of the reviewers.

3. Not all reviewers comments as summarized in the modified paper? Kindly revisit the main manuscript.

Author reply: ßWe have carefully reviewed the revised manuscript of the paper, and all previous review comments and content have been revised and replied to.

4. Figure 1 if the direction of the acid fracture is vertical in interlayer? Kindly re- examine?

Author reply: ßOur research mainly aims to dissolve acid gas into the upper part of acid etched fractures, so the acid etched fractures themselves are perpendicular to the formation. This part of the content has been supplemented and described in the paper.

Due to the shallow depth of the actual formation in Liaohe Oilfield, the fracture morphology is mainly horizontal fractures. Therefore, acid gas can be used to dissolve the upper part of the acid corroded fractures. Therefore, the acid corroded fractures are perpendicular to the formation and can dissolve upwards or downwards, communicating different layers[19-21]

5. Line 191 actual situation of different well types in China------Can we classify based on materials in place of country/location? Kindly reexamine

Author reply: ßThis article focuses on the dissolution experiment of gas acid on rocks and optimizes the acid solution formula, mainly applied to steam assisted gravity drive oil wells. Other types of oil wells have not yet started to be applied, and we have removed the impact of well type in the revised manuscript.

6. Figure 3 & Table 1 copyright citation permission pls verify?

Author reply: ßFigure 3 shows the natural rock cores selected in our experiment, and Table 1 shows the mineral composition of the rocks measured through X-ray diffraction experiments. In order to help readers better understand the relationship between acid etching effect and acid solution formula, the relevant pictures and tables are the samples we actually obtained.

7. Figure 4 and 5 references were used by Authors data usage statement?

Author reply: ßFigures 4 and 5 show the experimental phenomena during our experiment, which have been marked in the paper. These images are original and do not require any other references.

8. Figure 6 kindly label original experimental setup figure also?

Author reply: ßWe have marked the physical image in Figure 6 based on the reviewer's suggestion.

9. Figure 7 kindly label?

Author reply: ßThe specific numbers in Figure 7 correspond to the experimental core numbers in Table 4. Figure 7 shows the electron microscope photos of cores 1-4, which have been marked accordingly

10.  Figure 12 pls label?

Author reply: ßWe have marked the experimental core category in the figure based on the reviewer's suggestion.

11.  How Figure 14 was drawn ? Not clear yet Pls elaborate discussion

Author reply: ßFigure 14 shows the application effect in the oilfield field, and the changes in oil well production before and after acidification have been modified in the paper based on the reviewer's suggestions.

1According to the optimized acid fluid formula system in Figure 13, on-site experiments were conducted on acid fracturing. The experimental block is the oil well of SAGD in Shuguang Oil Production Plant of Liaohe Oilfield. As shown in Figure 14, the initial daily increase of oil production was 1.6 t. So far, a cumulative oil production increase of 1002 t has been achieved in this district.

12. Conclusions were not derived from objectives? - Pls revisit

Author reply: ßWe have made changes to the conclusion section of the paper based on the suggestions of the reviewers, as follows

• The results of core dissolution experiments showed that hydrochloric acid and polyphosphate had poor dissolution effects on the formation. Although hydrofluoric acid and fluoroboric acid, especially fluoroboric acid, had good dissolution effects, they were prone to form small particles that plugging pores after dissolution.
• The combination of multiple acid can effectively address the problem of particle migration, thereby improving the permeability enhancement ability. The actual permeability enhancing capacity of the acid fracturing working fluid formula ‘4% hydrochloric acid + 2% polyphosphate + 5% fluoroboric acid + 4% acetic acid + 2% ethanol’ was verified with the natural core of the corresponding block.
• Acidizing measures implemented on-site led to the beginning of reduction in water cut and increase in the oil production, indicating that applying acidizing to could enhance permeability. The range of enhancement permeability of the acidizing system in intervals with low physical properties of the reservoir developed by SAGD flooding was 35.48%~57.06%.

Author Response File: Author Response.pdf