钻井液与完井液

Abstract:
In ultra-deep water drilling, the formation of natural gas hydrates aways endanger the safety of drilling and production. The development of excellent kinetic hydrate inhibitors (KHI) which are compounded with thermodynamic is of great importance to the effective inhibition of gas hydrates in ultra-deep water drilling. Using 4-acryloyl morpholine and N-vinylpyrrolidone to copolymerize in different molar ratios to produce kinetic gas hydrate inhibitor ACNs. The reaction conditions are optimized through single-factor method, the reaction products are analyzed by IR, SEM and gel permeation chromatograph, and the properties of the products are evaluated by methane-hydrate simulation (MHS) test and tetrahydrofuran (THF) inhibition performance test. Through the evaluation and test, the best ACN is selected, and is compared with other KHIs. The best ACN is then compounded with thermodynamic gas hydrate inhibitors to produce a gas hydrate inhibitor for use in drilling fluids for drilling in areas with water depth of more than 2,000 m and with narrow safe drilling windows. XXXX found in studies that the best ACN can be obtained when AIBN is used as the reaction initiator and let the monomers react under 65 ℃ for 6 h, and 2% ACN (4∶6) has the optimum inhibition. The formulation of the gas hydrate inhibitor is 2%ACN + 1%KHI-1 + 35%glycol + 5%NaCl. The density of the gas hydrate inhibitor is 1.078 g/cm³, and the initial crystallization time of the gas hydrate inhibitor measured at −25 ℃with THF method is 32 min. The drilling fluid tested has a density of 1.150 g/cm³, a high temperature high pressure filtration rate of less than 17 mL, and a percent shale cuttings recovery in hot rolling test of greater than 82%, satisfying the relevant requirements for the drilling fluid.

Mechanisms of Borehole Wall Instability of Deep Coal Seam in Ordos Basin and Drilling Fluid Countermeasures

LYU Kunhong, ZHANG Hui, TIAN Deliang, YANG Boyuan, LI Jun, OUYANG Yong, AN Jintao, QIN Cheng

2024, 41(5): 564-573. doi: 10.12358/j.issn.1001-5620.2024.05.001

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Abstract:
In response to the problem of wellbore instability in deep coal seams in the Ordos Basin, the mechanism of wellbore instability in the 8^# coal reservoir of the Benxi Formation in the Nalin 1 block was revealed from the perspectives of mineral analysis, microstructure analysis, physical-chemical properties and mechanical properties. Combined with the multiple synergy wellbore stability theory, a three-effect synergistic anti-sloughing drilling fluid technology strategy of plugging performance-inhibitive capacity-lubricity was proposed. By optimizing the key inhibitor, plugging agent and lubricant, an anti-sloughing drilling fluid system suitable for Benxi Formation in Nalin 1 block was formed. A comprehensive evaluation was conducted from the perspectives of basic performance, plugging property, inhibitory property, and pressure transmission ability. The laboratory test results show that the anti-sloughing drilling fluid formulation system had good rheological properties. The drilling fluid had API filtration rate of 2.4 mL, HTHP filtration rate of 7.5 mL, strong inhibitory ability. The percent recovery of shale cuttings was greater than 90%, 16 h linear swelling rate was less than 5%. The drilling fluid had excellent sealing performance. Plugging of 400 μm fractures with the drilling fluid renders the formation in which these fractures exist a pressure bearing capacity of 5 MPa. Field application has shown that the newly developed anti-collapse drilling fluid can effectively suppress the collapse of deep coal seams in the Nalin 1 well area, reduce the diameter expansion rate, increase the mechanical drilling rate, and prevent complex downhole accidents. It can meet the needs of coal and rock gas drilling on site and has good prospects for promotion and application.

Synthesis and Evaluation of Modified Sulfomethylated Phenolic Resin MSP-1

ZHANG Gaobo, YANG Shuangquan, LI Peihai

2024, 41(5): 574-581. doi: 10.12358/j.issn.1001-5620.2024.05.003

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Abstract:
This paper analyzes the status quo of the application and deficiency of the original sulfomethylated phenolic resin as a filtration reducer in water based drilling fluids. Based on the analysis, a new modified sulfomethylated phenolic resin, MSP-1, has been developed through molecular design to replace the old sulfomethylated phenolic resin. In the molecules of MSP-1 adsorption groups are introduced to render MSP-1 special functions to overcome the problems encountered in field use. Laboratory evaluation results show that in 15% brine drilling fluids, the performance of MSP-1 is comparable to the old sulfomethylated phenolic resin SMP-1, while in 30% brine drilling fluids, MSP-1 performs better than SMP-1. Without the use of the thinner SMK (a sulfomethylated tannin extract), MSP-1 alone can reduce the high temperature high pressure filtration rate of a 30% brine drilling fluid to only 17 mL after aging at 180 ℃. Since there are strong adsorption groups in the molecules of MSP-1, the amount of MSP-1 adsorbed onto the surfaces of clay particles is increased, almost eliminating the foaming effect of SMP-1 in 15% brine drilling fluids and greatly reducing the viscosity effect of MSP-1 in drilling fluids. These advantages of MSP-1 have rendered it good prospects for promotion and application.

Study on Temperature-Controlled Liquid-Solid Phase Change Mud Loss Control System and Mud Loss Control with In-situ Self-Generated Bridging Particles

WANG Jiaqin, YANG Yanjie, ZHAO Cheng, LIU Shanghao, BAO Dan, ZHANG Peng

2024, 41(5): 582-588. doi: 10.12358/j.issn.1001-5620.2024.05.004

Abstract(119) HTML (45) PDF (3396KB)(43)

Abstract:
Mud losses into fractures are a technical difficulty frequently encountered in drilling operation. The technical bottleneck is the poor matching between the traditional bridging lost circulation materials and the sizes of the channels through which the mud is lost, and this generally leads to repeated mud losses at the same depth. To deal with this problem, a temperature controlled liquid-solid phase change lost circulation control system is developed based on the principles of thermosetting resin emulsification and high-temperature crosslinking polymerization. This system can adaptively enter fractures of different openings, and form in-situ inside the fractures high-strength particles with a wide size distribution to control the mud losses under the action of the high temperatures in the mud loss zones. In laboratory studies, the structures of the bridging particles generated in-situ inside the fractures are characterized, the mechanical properties and performance of the bridging particles to plug the fractures are tested. The results of the studies show that in the temperature-controlled liquid-solid phase change lost circulation control system, the contents of the high molecular weight resin, the emulsifier, the dispersant, the crosslinking agent and the distilled water are 37%, 5.2%, 0.07%, 25.9% and 31.83%, respectively. This system can in-situ generate particles with sizes distributed between 0.1 mm and 5 mm at temperatures between 50 ℃ and 90 ℃ inside the mud loss zones. After being aged at 120 ℃, the D₉₀ degrading rate of the bridging particles under 60 MPa is only 0.4%, indicating that the system has high compressive strength. Using one temperature-controlled liquid-solid phase change lost circulation control system, fractures with openings between 1 mm and 5 mm can all be plugged, and the plugged fractures can bear pressures up to10 MPa. This system can be used to realize adaptive plugging, and is expected to solve the difficulties in controlling mud losses into fractures of unknown openings.

A Temporary Plugging Drill-in Fluid with Highly Soluble Multilevel Bridging Particles for Carbonate Reservoir

GAO Wei, FAN Sheng, QI Biao, DAI Changlou, JIA Hu, NIU Chengcheng

2024, 41(5): 589-602. doi: 10.12358/j.issn.1001-5620.2024.05.005

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Abstract:
The sensitivity of the carbonate reservoir in the second block of the Shunbei oilfield is evaluated through rock fracture stability correction method. In the evaluation drilling fluid samples taken from operational field were used and the results of the evaluation show that the main factors causing reservoir damage are stress sensitivity and solids invasion; the damage to the reservoir caused by these two factors totals 78.07%. In laboratory study, the idea of “temporarily plugging the reservoir during drilling and the plugging agents can be removed in well completion” was adopted in drilling fluid design, and the microfractures in the reservoir rocks are intentionally protected with the plugging agents. According to the theory of bridging and plugging the microfractures, plugging agents that are highly acid soluble and fibers that are degradable are selected as the key additives working together to plugging the microfractures. Using these plugging agents, a drill-in fluid capable of plugging the microfractures in the reservoir through multiple bridging is formulated. The performance of the drill-in fluid in resisting high temperatures and salt and calcium contamination as well as the settling stability, compatibility and reservoir protection property are evaluated. The results show that the drill-in fluid works normally at temperatures up to 180 ℃, the pressure bearing capacity of the layers formed by the solids of this drill-in fluid exceeds 10 MPa, the permeability recovery after acid job is 96.86%, an increase by 16.23% over conventional drill-in fluids containing no acid soluble temporary plugging agents. This drill-in fluid has strong plugging capacity the high rate of flow-back characteristics, and is expected to alleviate the formation damage in the second block in Shunbei oilfield.

Synthesis and Application of a Self-Degradable Polymeric Lost Circulation Material

ZHENG Wenwu, LIU Fu, ZHANG Junyi, HAN Jing, CAO Qichao, WANG Xiong, WANG Song

2024, 41(5): 603-608. doi: 10.12358/j.issn.1001-5620.2024.05.006

Abstract(111) HTML (31) PDF (2289KB)(34)

Abstract:
Oil and gas well drilling have long been faced with a technical difficulty-mud loss, and this problem still remains unresolved. Polymer gel lost circulation material (LCM), a kind of LCM commonly used today, has several deficiencies such as low pressure bearing capacity, small expansion after water absorption, poor high temperature and salt resistance as well as inability to self-degrade etc. To deal with these problems, a self-degradable polymer LCM was synthesized with carefully selected monomers at optimum conditions determined by orthogonal experiment. This degradable LCM, when first in contact with water, has low rate of expansion, and is thus easy to enter quickly into the fractures where a plugging layer is formed. The LCM forming the plugging layer continuously swells with time and forms in the fractures an embedded plugging layer, thereby increasing the retention ability of the LCM in the loss zones and the shear strength of the plugging layer. Experimental results show that the saturated water adsorption capacity of this LCM can be as high as 156.9 g/g, and the degradation rate of the LCM after 21 d exceeds 90%. In laboratory experiment, polymer sulfonate drilling fluid samples were treated with 5% of this LCM and several other LCMs presently in use and were then tested on a 3-5 mm wedge-shaped fracture tester, the drilling fluid treated with the new degradable LCM has a pressure bearing capacity of 17.5 MPa, significantly higher than those of the other LCMs. In dynamic damage experiment conducted at simulated formation conditions, rock cores with 3 mm fractures were used to evaluate the ability of the self-degradable LCM to resist formation damage. The experimental results show that the permeability recovery of the cores flooded with the new self-degradable LCM treated drilling fluid was 90%, indicating that the new self-degradable LCM causes very slight formation damage. In field application, the polymer sulfonate drilling fluid treated with the self-degradable LCM is able to successfully plug the fractures through which the mud is lost, proving that the LCM has good application prospects.

Lost Circulation Materials for Controlling Mud Losses while Drilling with RSS

JIA Yonghong, GUO You, ZHANG Wei, YE Anchen, GUO Chunping, HE Yinbo

2024, 41(5): 609-616. doi: 10.12358/j.issn.1001-5620.2024.05.007

Abstract(107) HTML (35) PDF (3601KB)(42)

Abstract:
In drilling operation the rotary steering system (RSS) is easy to be blocked by the lost circulation materials (LCMs), causing problems such as interruption of downhole instrument signal transmission, deviation of wellbore trajectory as well as blocking of mud circulation. Moreover, addition of conventional LCMs into a mud is easy to cause the mud viscosity to increase remarkably, which in turn results in problems such as high pressure loss along the flow line and thick mud cakes etc. It is thus required that the LCMs shall have the properties of “being able to pass through the RSS”, “high plugging capacity” and “low impact on mud viscosity”. To achieve this object, a lost circulation control fiber named Fiber-1-1 has been developed with a thermally stable plant fiber, a raw material which is shredded, screeded and hydrophobically modified to produce the final product. The performance of the Fiber-1-1 was evaluated in accordance with the relevant industrial standard, and a method of evaluating its ability to pass through the RSS during drilling was established. The evaluation results show that the performance of the Fiber-1-1 has reached the requirements of the industrial standard; it causes the apparent viscosity of a drilling fluid to increase by 10%, a lost circulation slurry containing Fiber-1-1 has filtration rate of 26 mL; after circulating for 30 min, a drilling fluid treated with the Fiber-1-1 causes pump pressure to increase by less than 5%, indicating that the Fiber-1-1 can smoothly pass through RSS. An oil-based drilling fluid and a water-based drilling fluid, each of which is treated with 3% Fiber-1-1, can plug the sand beds of 20-40 meshes under experiment conditions of 150 ℃ and 5 MPa, with accumulated mud losses of 4 mL and 8 mL, respectively. And in the final part of the paper, how the Fiber-1-1 passes through RSS and how it cures mud losses are analyzed with Zeta-potential measurement and through micromorphology observation.

Controlling Lost Circulation by Stagewise Strengthening Formation with Cementable Lost Circulation Material in Well Cha-302 Cementable

WANG Lifeng

2024, 41(5): 617-621. doi: 10.12358/j.issn.1001-5620.2024.05.008

Abstract(85) HTML (36) PDF (2065KB)(27)

Abstract:
Well Cha-302 is a key appraisal well located in a gentle slope belt structure in the south of the Songliao Basin. This well penetrated in the third interval the Yingcheng formation which is developed with tuff into which mud is easy to lose. During drilling, lost circulation was encountered several times at depths 3,686 m, 3,726 m and 3,955 m. When drilling into the deeper Huoshiling formation, higher formation pressure required that the upper section be strengthened to increase the pressure bearing capacity to an equivalent density of more than 1.38 g/cm³. Since the tuff formation drilled has low formation pressure, the mud is easy to lose into this formation, and when mud losses happen, the conventional lost circulation control methods are unable to effectively control the mud losses. To overcome these difficulties, a low density cementable lost circulation slurry was adopted. Based on the severity of mud losses in different spots, the total concentration of the bridging agents, the ratio of the different particles and the cement strength of the lost circulation slurries were accordingly adjusted. For the three main points of mud losses, the formation strengths were gradually increased by a certain increment. The results of the field operation show that during formation strengthening, the pressure decreased twice significantly and then increased slowly, and finally the pump pressure reached 16.2 MPa. After drilling out the cement plug, the equivalent circulation density at the bottom was 1.38 g/cm³, and the lower Huoshiling formation was successfully drilled. This technique of controlling lost circulation is first used in the Chaganhua block in the south of the Songliao Basin, it effectively strengthens the tuff formation and provides a new technical clue for controlling mud losses.

CEMENTING FLUID

Extra-High Temperature High Density Cement Slurry for Cementing Liners through Salt Formation in Well Qieshen-1

XU Dawei, WANG Xiaojing, XU Chunhu, WEI Haoguang, CHANG Lianyu

2024, 41(5): 622-629. doi: 10.12358/j.issn.1001-5620.2024.05.009

Abstract(87) HTML (25) PDF (3167KB)(22)

Abstract:
The well Qieshen-1 is an exploration well deployed by Sinopec in block Tazhong in Tarim Basin. The well was drilled to a depth of 8,745.00 m in four intervals, with static bottom hole temperature being 196 ℃. Technical difficulties such as high temperature, high pressure, salt formation, narrow clearance between the wall of the hole and the casing string as well as difficulties in displacing the whole-oil based drilling fluid were encountered in cementing the casing string in the fourth interval. To deal with these difficulties, studies were conducted on the strength decay of the set cement and the settling stability, rheology and thickening time of the cement slurry. A saltwater resistant high density (Max. density 2.3 g/cm³) cement slurry that is stable at 230 ℃ was developed as a result of the study. Using aluminum-rich materials in the cement slurry, the decay of the strength of the set cement is inhibited. The settling stability of the cement slurry is improved by selecting weighting materials of different particle sizes, and silica fume. Other additives, such as high temperature filter loss reducers, compounded retarders and polyether-carboxylic acid dispersants were used to adjust the properties of the cement slurry to the required levels. Laboratory experiments show that the API filtration rate of the cement slurry is 44 mL, the flow index n is greater than 0.7, the thickening time is linearly adjustable, the high temperature settling stability is 0.01 g/cm³, and the 1 d and 28 d compressive strengths of the set cement are 192. MPa and 27.1 MPa respectively, with no signs of strength decay observed. With the use of oil displacing weighted prepad fluid and the adoption of other well cementing techniques, the well Queshen-1 was successfully cemented.

Development and Evaluation of a Temperature-Sensitive Deformable Fibrous Capsule Lost Circulation Material

TIAN Hui, BU Yuhuan, HU Miaomiao, SHEN Shengda, CAO Chengzhang

2024, 41(5): 630-639. doi: 10.12358/j.issn.1001-5620.2024.05.010

Abstract(87) HTML (30) PDF (4757KB)(31)

Abstract:
A temperature-sensitive deformable fibrous capsule with shape memory has been developed to address the difficulties in mixing cement slurries and the slurry thickening problem caused by the oversize and excessive dosage of the fibrous materials presently in use, such as glass fiber, polypropylene fiber, sisal fiber and ceramic fiber etc. When the ambient temperature is lower than the deformation-response temperature, the particle sizes of the fibrous capsules are relatively small, therefore it is easy for the capsule particles to form high density particle packing in passages through which cement slurries are lost. When the ambient temperature reaches the deformation-response temperature, the fibrous capsules are activated and begin to expand, causing the particles packed in high densities to squeeze each other and to form high strength bridging inside the passages. The losses of the cement slurries are thus effectively brought under control. The process with which the fibrous capsules are produced can encapsulate 6 mm fibers into a 3 mm capsule, thereby increasing the effective concentrations and sizes of the fibers in loss-control cement slurries, improving the plugging performance of the cement slurries, minimizing the risks of fluid losses and ensuring the job quality of well cementing. The average fluidity of a cement slurry treated with the temperature-sensitive deformable fibrous capsules is 22 cm, and the initial consistency of the cement slurry is 25 Bc, comparable to the consistency of the pure cement slurry. Compared with cement slurries directly treated with fibrous materials, the cement slurry treated with the temperature-sensitive deformable fibrous capsules has rheology and pumpability that are significantly improved and the compressive strength of the set cement is greatly increased. The 7 d compressive strength of a set cement containing 5% temperature-sensitive deformable fibrous capsules reaches 50 MPa. The development and application of the temperature-sensitive deformable fibrous capsules help solve the difficulties encountered in cement slurry mixing and the slurry thickening problem, and are of significance to the success of high-quality well cementing operation.

Carboxyl Functionalized Carbon Nanotube and Its Effects on Set Cement

JIA Hui, JIN Xin, WEI Haoguang, LI Xiaojiang

2024, 41(5): 640-645. doi: 10.12358/j.issn.1001-5620.2024.05.011

Abstract(52) HTML (20) PDF (2460KB)(20)

Abstract:
With the continual development of unconventional oil and gas, complex downhole conditions have presented higher requirements on the various mechanical properties of set cement for well integrity, and these requirements have urged the development of high performance nanomaterials for improving the performance of the set cement. In this study, a carboxyl functionalized carbon nanotube dispersion was developed through dilute-acid acidization process. The dispersibility of the dispersion was measured by means of contact-angle measurement, UV-visible absorption spectroscopy as well as settling stability measurement etc., and the effect of the carboxyl functionalized carbon nanotube on improving the mechanical properties of set cement was verified. The study shows that carboxyl functionalization reduces the diameters of the carbon nanotube particles by 89.71%, and can convert a hydrophobic material to hydrophilic one. Carboxyl functionalization also improves the dispersion stability of the carbon nanotube by 100%. A cement slurry treated with 0.005% carboxyl functionalized carbon nanotube has the compressive strength of the set cement increased by 16.05%, the flexural strength by 25.82%, and the tensile strength by 18.07%.

Study on Corrosion Rate of Cement Monomineralic C₂S in CO₂ Geological Sequestration Environment

WANG Xiying

2024, 41(5): 646-653. doi: 10.12358/j.issn.1001-5620.2024.05.012

Abstract(61) HTML (27) PDF (2757KB)(20)

Abstract:
In geological sequestration and application of CO₂, the cement used in well cementing is easy to react with CO₂, an acidic gas produced downhole, causing the set cement for well cementing to be corroded and the mechanical properties of the set cement decline remarkably. Presently, the corrosion rate of the set cement monomineralic C₂S in CO₂ geological sequestration and application environment is still not clearly understood. In this study, several measuring methods, such as SEM, XRD and TG etc., are used to quantitatively analyze the changes of the corrosion products of C₂S. The yield coefficient α of the corrosion product CaCO₃ can be obtained by fitting the molar yield rate of the corrosion product CaCO₃ with the non-steady state diffusion permeation model. The SEM experimental results show that after the corrosion reaction, the surfaces of the C₂S cement monomineralic particles have undergone great changes, producing part of the corrosion product CaCO₃; The XRD experimental results show that crystal forms of the corrosion product CaCO₃ of the monomineralic C₂S are mainly calcite and aragonite. The TG experimental results show that the amount of the corrosion products increases with the corrosion time of the C₂S cement monomineral. The fitting results indicate that the yield rate of the corrosion products of C₂S increases with temperature, at 90 ℃ the yield rate of the corrosion product CaCO₃ has a maximum yield coefficient α of 54.90.

High Temperature Hydration of Low Density Cement Slurries Weighted with Hollow Microspheres

ZHAO Hu, MA Chunxu, SONG Weikai, TIAN Ye, ZOU Yiwei, SUN Chao

2024, 41(5): 654-660. doi: 10.12358/j.issn.1001-5620.2024.05.013

Abstract(57) HTML (20) PDF (3040KB)(26)

Abstract:
Hollow microspheres are made of borosilicate glass and contain in their molecules abundant SiO₂. In laboratory experiment, several pieces of set cement of low density cement slurries containing hollow microspheres are tested at 120 ℃ and 150 ℃ respectively for their properties such as compressive strength, permeability, microstructure and adjustability of thickening process, confirming the effects of hollow microspheres on the high temperature hydration characteristics of cement slurries. Laboratory study shows that at both 120 ℃ and 150 ℃, the siliceous components of the hollow microspheres participate in the hydration process of the cement, thereby inhibiting or compensatory inhibiting the strength of the set cement. At 120 ℃ only 16% hollow microspheres can in 28 d inhibit the decay of the compressive strength. At 150 ℃, silica fume and hollow microspheres have to be used together, with both amounted in the cement to at least 40%, to inhibit the decay of the compressive strength of the set cement. At elevated temperatures, hollow microspheres’ reaction with other components in the cement slurry results in the formation of significant pore contours on the surfaces of the hollow microspheres. With the extension of aging time, the total porosity of the set cement increases. The pores increased in the set cement from the cement slurry without silica fume are mainly capillary pores with diameters in the range of 50-100 nm, the permeability of the set cement increases significantly with aging time from the initial 0.003 mD to 0.011 mD, while the net increment of the permeability is not relatively small. On the other hand, the pores increased in the set cement from the cement slurry treated with silica fume are mainly gel pores with diameters less than 50 nm, and the permeability of the set cement basically does not change greatly with aging time. In the set cement without the treatment of silica fume, the Ca(OH)₂ diminishes in 14 d, reacting with the glass microspheres to produce C–S–H gels. In the hydration products of the cement slurry treated with silica fume, no Ca(OH)₂ is found and the reaction proceeds swiftly to form tobermorite phase with good ability to resist strength decay. The thickening time of the hollow microsphere weighted low density cement slurries is adjustable, and the silica fume and the hollow microsphere do not negatively affect the early-stage hydration process of the cement slurries at high temperatures.

Technology for Cementing High Pressure Narrow Density Window Gas Zones in Well Dongqiu-X

ZHAO Lingxiao, WANG Chuncai, YE Sutao, ZOU Shuang, WANG Jiandong, WANG Biao

2024, 41(5): 661-667. doi: 10.12358/j.issn.1001-5620.2024.05.014

Abstract(56) HTML (15) PDF (3417KB)(23)

Abstract:
The well Dongqiu-X is an exploration well drilled in the Qiulitage tectonic zone of the Kuche sag in the Tarim Basin. The fifth interval of the well was drilled to a depth of 6,130 m with Φ215.9 mm bits and a drilling fluid of 2.17 g/cm³, and was prematurely completed at that depth. During drilling mud losses occurred several times and oil and gas shows in the open hole section were encountered at different depths. Oil/gas kick and mud losses coexist in the same interval, with safe drilling window of only 0.06 g/cm³, meaning that severe losses of cement slurries during well cementing are prone to happen, and the losses of cement slurries may induce well blowout. To deal with this problem, precise pressure control while drilling was adopted to safely control the wellbore pressure, and a tough self-healing cement slurry was used to ensure the long-time integrity of the wellbore. The well Dongqiu-X was successfully cemented using the self-healing cement slurry combined with the use of liner hanger with top packer for auxiliary sealing. CBL/VDL logging results showed that the percent qualified cementing job was 94.3%. When the sixth interval was drilled with a mud of lower density, the drilling operation and the well completion operation were all successfully conducted , and no pressure trap in the annular space was found. The use of the well cementing technology has successfully solved the difficulties encountered in drilling high pressure gas well.

FRACTUREING FLUID & ACIDIZING FLUID

A Multifunctional Sand-carrying and Oil-displacement Fracturing Fluid System Based on Physical Cross-linking

LI Jianshen, HUANG Qiushi, YAN Songbing, LIU Qing, WANG Maogong, DONG Jingfeng, ZHENG Miao

2024, 41(5): 668-676. doi: 10.12358/j.issn.1001-5620.2024.05.015

Abstract(55) HTML (17) PDF (2573KB)(17)

Abstract:
It is difficult to avoid the contradiction between the high sand-carrying capacity of fracturing fluids, the flowback and formation damage of gel breaking fluid during the shale oil extraction process. A new multifunctional sand-carrying and oil-displacement fracturing fluid system (PN-PPS), with high sand-carrying capacity, low damage and high oil displacement, it was developed by synergizing surfactant (PN) and polymers (PPS) and relying on the physical cross-linking to enhance the network structure. PN-PPS has excellent sand-carrying capacity and temperature and salt resistant performance by relying on the dense network structure. The sand-carrying time of ceramic in PN-PPS solution is as high as 510 min, profit from the network structure of the system strengthened by physical cross-linking. The gel breaking of PN-PPS quickly and thoroughly, the residue content of the gel breaking fluid is less than 34.5 mg/L and core damage is less than 18%. Further, PN-PPS shows excellent oil displacement performance, with oil washing efficiency higher than 99% at 90 ℃, and the oil imbibition recovery rate of 20.46%, compare with water displacement, the oil displacement rate of oil-displacing agent increased by 12.54%. Therefore, the application of PN-PPS can ensure efficient sand carrying fracturing and realize in-situ oil displacement without flowback, through combining the fracturing and oil repulsion processes. the application of PN-PPS provides an innovative solution for shale oil extraction, which is of great significance for the development of the integrated technology of fracturing and displacement.

Preparation of Corrosion Inhibitor for Self-Diverting Acid and Mechanisms of Corrosion Inhibition

CUI Bo, CHEN Jun, AI Junzhe, FENG Puyong, RONG Xinming, WANG Shun

2024, 41(5): 677-685. doi: 10.12358/j.issn.1001-5620.2024.05.016

Abstract(58) HTML (23) PDF (3883KB)(19)

Abstract:
Self-diverting acids are widely used in the acidification and fracturing of carbonate reservoirs. Corrosion inhibitors, because of the special molecular structures of the viscoelastic surfactants, have poor compatibility with other additives and corrosion control efficiency that is quite low. In this study, two pyridine quaternary ammonium salt corrosion inhibitors, SI-1 and SI-2, are synthesized with 1-chloromethylnaphthalene, 4-ethylpyridine, benzyl chloride and 2,3-cyclopentenopyridine. The corrosion control performance and the effects on the viscosity of self-diverting acids of SI-1 and SI-2 were investigated using corrosion tester and rheometer. The morphology and chemical components of steel plates before and after corrosion by acids were analyzed from the microscopic perspective by means of SEM, EDS, atomic force microscope and X-ray photoelectron spectroscopy. The corrosion mechanisms of the two corrosion inhibitors were studied using molecular dynamics simulation. The results of researches show that SI-1 and SI-2 have good corrosion control performance in self-diverting acids, minor effects on the viscosity of the self-diverting acids and wide applicability, and is cost-efficient. Compared with SI-1, SI-2 has better performance. A self-diverting acid treated with 1% SI-2 has corrosion rate at 90 ℃ of 1.04 g/(m²∙h), corrosion rate at 120 ℃ of 7.43 g/(m²∙h), final viscosity of the VES residual acid stabilized at 190 mPa∙s or higher. The cost of treatment can be reduced by 20% with SI-2. After adding 1% corrosion inhibitor in the acid, the surfaces of the steel plates show no obvious corrosion, the Fe content increases greatly, and the surface roughness decreases significantly. With SI-2, the Fe content increases from 86% to 94%, and R_a decreases from 137 nm to 84 nm. In both cases C—N and organic C=O bonds are detected on the surfaces of the steel plates, indicating the existence of the adsorption membranes of the corrosion inhibitors. Molecular dynamics simulation shows the mechanisms of corrosion inhibition are as follows: SI-2 has small energy gaps and high adsorption energy. After being adsorbed on the surfaces of the steel plates, a dense adsorption membrane is produced, isolating the corrosion media and the surfaces of the steel plates, thereby remarkably inhibiting the corrosion process of the steel plates. SI-2 has been used in the Bohai Oilfield and the Missan Oilfield (Iraq) with excellent operation achievement.

Study on Temporary Plugging Diverted Acidification in Strong Heterogeneous Sandstone：A Case Study of the Silurian in Tazhong

WANG Qing, ZHOU Fujian, YANG Dandan, TAN Yanxin, YU Sen, YAO Erdong, LI Fuyuan

2024, 41(5): 686-694. doi: 10.12358/j.issn.1001-5620.2024.05.017

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Abstract:
Acidizing constitutes a pivotal enhancement strategy for the effective exploitation of low-permeability sandstone oil reservoirs. The Silurian reservoirs in the Tarim Basin, characterized by numerous thin layers and pronounced heterogeneity, present challenges in acid treatment; specifically, acid fluids preferentially enter high-permeability layers, resulting in inadequate stimulation of low-permeability strata. Current techniques for sandstone reservoir acid diversion remain insufficient. This study introduces a fully water-soluble and degradable clean temporary plugging powder, combined with chelating acid, to address the uniform acidizing challenge in heterogeneous sandstone reservoirs. The research employs a parallel core acidizing flow instrument to investigate the blocking characteristics of the clean temporary plugging powder and its acid diversion capabilities under various differential pressures. Laboratory experiments demonstrate that the degradation of this powder is predominantly temperature-controlled, with complete degradation occurring above 90 ℃, resulting in a clear, acidic solution and effectively enhancing core permeability by 20%. A 0.1% concentration of the plugging powder, when injected with chelating acid into the rock, forms an internal and external barrier layer, increasing the temporary plugging skin factor. The maximum sealing pressure differential achieved is 1.87 MPa, 6.7 times that of chelating acid alone. Parallel core acidizing experiments reveal that 100-mesh clean temporary plugging powder at a 0.1% concentration is suitable for reservoirs with a permeability gradient less than 15, effectively reducing the heterogeneity in permeability and improving the transformation of low-permeability cores. Moreover, in the acidizing operation of well 11-9 in the Tarim Basin, the temporary plugging and diversion technique showed a notable increase in pressure and a substantial enhancement in production post-acidizing. Field trials and applications confirm that the temporary plugging and diversion acidizing technique achieves commendable production enhancement and transformation in Silurian reservoirs, offering significant insights for the uniform acidizing of long sections in heterogeneous sandstone reservoirs.

Governed by：
China National Petroleum Corporation Ltd

Sponsored by：
CNPC Bohai Drilling Engineering Co. LtdPetroChina Huabei Oilfield Company

Editor-in-Chief：Shi-chun Chen

Address：
Editorial Office of Drilling Fluid and Completion Fluid, Bohai Drilling Engineering Institute, Yanshan South Road, Renqiu City, Hebei Province

Postcode： 062552

Tel：（0317）2725487　2722354

E-mail： zjyywjy@126.com

CN 13-1118/TE

ISSN 1001-5620

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