钻井液与完井液

Abstract:
The technical problems of drilling fluid in ultra-deep, unconventional oil/gas, deep water, hot dry rock, polar, natural gas hydrate and other complex formations are systematically sorted out. The key scientific problems and core engineering problems are discussed. Combined with the research progress of drilling fluid technology in recent years, the development of drilling fluid technology for ultra-deep, unconventional oil/gas, deep water, hot dry rock, polar, natural gas hydrate and other complex oil and gas is provided.The problems in the drilling of complex formations, such as hightemperature, high-pressure and high- salinity, serious shale hydration, wellbore instability, large temperature difference, loss circulation, formation damage, and low degree of automation of drilling fluid maintenance, domestic and foreign researchers have developed key material, systems and equipments such as high-temperature and high-salinity water-based/oil-based drilling fluid, constant rheological drilling fluid, anti-ultra-high temperature foam drilling fluid, environmentally friendly ultra-lowtemperature drilling fluid, intelligent temperature and pressure response plugging material, degradable reservoirprotection material, drilling fluid online monitoring and automatic feeding system. However, with the increasingly complex formationconditions of drilling, there are still deficiencies in drilling fluid materials in terms of ultra-high temperature resistance, ultra-long-term stability, clay swelling inhibition, and environmental protection performance. Severe/total loss circulation, reservoirprotection, and drilling fluid automation control still face severe challenges. In order to meet the performance requirements of drillingfluid in the process of drilling in complex formations, it is necessary to further study the working/failure mechanism of drilling fluidadditives under complex formation conditions, the structure-activity relationship changes and action mechanism of drilling fluidadditives at different scales such as micro-meso-macro scales, establish a safe and efficient multi-functional integrated controlmethod of drilling fluid, construct intelligent drilling fluid theory and technology, and provide technical support for the development of complex underground resources.

DRILLING FLUID

Application of Drilling Fluid Technology in Drilling a Long Horizontal Section Well in Block Fengxi in Qinghai

ZHANG Minli, YUAN Guide, ZHUANG Wei, WANG Wei, LIU Wu, GUO Chao, MING Hongtao, YANG Pengmei

2024, 41(1): 31-38. doi: 10.12358/j.issn.1001-5620.2024.01.002

Abstract(22) HTML (9) PDF (2058KB)(6)

Abstract:
To obtain high production rate with less oil and gas wells, The Qinghai oilfield decided to drill five long open hole horizontal wells in the Fengxi structure which is located in the Dafengshan area in Qaidam Basin. Water-based and oil-based drilling fluids were to be used to drill these wells, and the results be compared to improve and perfect the technical prototype for future drilling and completion of long open hole and long horizontal section horizontal wells in the same area. This paper summarizes the field engineering of a high-quality compound saltwater drilling fluid on the well Fengxi IH1-5 and analyses are briefly conducted on the application, control of the engineering parameters, rheology and sand carrying capacity of the drilling fluid. The well Fengxi IH1-5, which is 5,487 m in depth, has a length of horizontal section of 2,541 m, the longest horizontal section in the Qinghai oilfield. This well has broken several records in this oilfield, such as penetrating the highest percentage of pay zones (100%), the longest footage (1,566 m) drilled in a single bit run, the longest horizontal section (1,000 m) in which short trips were performed, as well as the first application of casing floatation technology in casing running etc. The success of the drilling operation has milestone significance in applying the ultralong horizontal section well drilling technology in the Qinghai oilfield. Compared with the drilling operation of the offset wells drilled with oil-based drilling fluids, the use of this high-quality compound saltwater drilling fluid has gained better results in drilling than the oil-based drilling fluids previously used in other wells. The success gained in applying the water-based drilling fluid has provided a good guidance for optimizing the properties of water-based drilling fluids for horizontal wells with long open hole and long horizontal sections.

Microscopic Behavior Analysis of Core Components of Water-based Drilling Fluid at High Temperature

ZHANG Yuwen, ZHANG Yang, SONG Tao

2024, 41(1): 39-44. doi: 10.12358/j.issn.1001-5620.2024.01.003

Abstract(25) HTML (9) PDF (2786KB)(15)

Abstract:
The key to the stable performance of water-based drilling fluid at high temperature is related to the dispersion state of core colloidal particles, but the influence of the dispersion state of colloidal particles is very complicated. For the core components of water-based drilling fluid, the shear stress-strain temperature curve of bentonite colloid was obtained through high-temperature and high-pressure rheological testing, and the particle size distribution of colloidal particles was tested after different temperature effects. The dispersion, flocculation, and aggregation states and formation mechanisms of clay mineral colloidal particles were analyzed within the temperature range of room temperature to 220 ℃. In addition, the high temperature stability mechanism of porous fibrous clay mineral colloid rich in magnesium was revealed from a microscopic perspective by means of SEM test and clay mineral layer structure analysis. At the same time, based on a comprehensive analysis of the changes in rheological properties and filtration loss before and after high-temperature hot rolling, the interaction mechanism between bentonite/composite clay minerals and polymer based treatment agents at high temperatures is revealed from the perspectives of clay mineral structure characteristics, polymer chain breakage, adsorption characteristics, etc. Combined with experimental results, it is clear that low concentration bentonite/sepiolite composite colloids have significant high-temperature stability advantages, which provides theoretical support for the construction of ultra-high temperature water-based drilling fluid.

Key Technologies for Drilling Horizontal Wells in Thin Interbedded Tight Reservoirs with Complex Pressure Systems

WU Xiaohong, LI Yunfeng, ZHOU Yan, KAN Yanna, LI Ran, LUO Cheng

2024, 41(1): 45-52. doi: 10.12358/j.issn.1001-5620.2024.01.004

Abstract(26) HTML (7) PDF (2562KB)(18)

Abstract:
The Sha-3 member V reservoir in the Gaoliu block, Nanpu sag is a typical interlayered thin sandstone and thin claystone tight reservoir with complex formation pressure systems and densely distributed artificial fractures resulted from many years of fracturing and injection operations. Horizontal drilling in this area is faced with problems such as mud losses, oil and water kicks as well as collapse of borehole walls. This paper describes, based on the formation characteristics of the Gaoliu block, the technical difficulties in horizontal drilling, and points out the causes of mud losses and borehole wall collapse. To solve these problems, an oil based drilling fluid was formulated with a nanometer/micrometer sized emulsified borehole wall collapse preventing agent, graphite microspheres, a micrometer flexible plugging agent and calcium carbonate of ultrafine particles, which render the drilling fluid capacities such as plugging, high pressure bearing and borehole wall stabilizing. The oil based drilling fluid has low filtration rate and has the ability of maintaining the strengths of the claystones that is 5 times higher than other drilling fluids. With this drilling fluid, the pressure bearing capacity of the sandstones of medium and high permeability can be increased to 18 MPa. Bridging and solidification mud loss control techniques were used to control mud losses. Using this drilling fluid, horizontal drilling through the tight reservoirs in the Gaoliu block was safely performed and no borehole wall collapse was encountered during drilling in more than ten wells. In formations where mud losses were encountered, the mud losses were controlled and the pressure bearing capacity of the formation was increased by 5.4 MPa, satisfying the requirement of subsequent drilling.

Ultra-High Temperature Drilling Fluid Technology for Second Sidetracking of the Well Shunbei-16X

YU Deishui, WANG Lu, LIU Shiyin, WU Xiuzhen, WANG Xu

2024, 41(1): 53-59. doi: 10.12358/j.issn.1001-5620.2024.01.005

Abstract(28) HTML (8) PDF (2170KB)(12)

Abstract:
The well Shunbei-16X is a well drilled in the #16 fault zone in Shunbei area by Sinopec Northwest Petroleum Bureau. This is a four-interval deviated exploration well drilled to the Yingshan formation of the Ordovician system. The temperature at 6,680 m was predicted to be 168.9 ℃. After drilling to the designed depth of 6,777 m, decision was made to deepen the well with a high performance drilling fluid ENVIROTHERM NT. The drill pipe got stuck and the well was plugged, then sidetracked with an oil -based drilling fluid. Well test showed no industrial oil production. The well was then re-plugged and sidetracked again with a high temperature drilling fluid. The second sidetracking of the well was done to 7,533 m MD/7,417 m TVD, the bottom hole temperature measured was 209 ℃, and the maximum mud density was 1.75 g/cm³, indicating that the formation at the total depth of the well is an extremely high temperature ultra-high pressure formation. The high performance drilling fluid used to drill the sidetracked section of the well had excellent rheology and settling stability at extremely high formation temperatures as well as excellent resistance to CO₂ and formation water contamination. The second sidetracking was successful, and no downhole troubles were ever encountered.

First Application of the Synthetic-Based Drilling Fluid BIODRILL S in Block Kenli of Bohai Oilfield

PENG Sanbing, LI Bin, HAN Dongdong, XU Lei, CHENG Longsheng, HUANG Xianbin

2024, 41(1): 60-67. doi: 10.12358/j.issn.1001-5620.2024.01.006

Abstract(24) HTML (8) PDF (2177KB)(16)

Abstract:
Drilling operation in the Block Kenli 9-1 of the Bohai Oilfield has long been faced with high risks of borehole wall collapse resulted from complex formation lithologies, fault zones, shales that are easy to hydrate and disperse, as well as sandstones in which tight hole problem is frequently encountered. To deal with the borehole wall collapse problem a BIODRILL S synthetic based drilling fluid has been formulated. The BIODRILL S synthetic based drilling fluid is formulated with a base oil which is synthetic oil of choice, a composite plugging additive PF-MOSHIELD, as well as other drilling fluid additives, taking into account the formation lithology and environmental protection requirement. The BIODRILL S drilling fluid has good rheology , and is resistant to 26% calcium contamination and 15% cuttings contamination. Furthermore, it has excellent plugging capacity, settling stability and lubricity. The HTHP filter loss tested on a sand plate tester is 3.2 mL. The sag index of the mud after standing for 7 d is 0.53, and the extreme coefficient of friction is 0.082. BIODRILL S was first used in the Block Kenli 9-1. The application showed that: 1) the BIODRILLS can be used to solve the shale hydration problem and the tight hole problem in the sandstone formation encountered previously in this block; the drilled cuttings produced in drilling the formations in and above the third section are intact, with sizes distributed between 4 cm and 7 cm. 2) Hole cleaning is well done with the BIODRILL S drilling fluid, the ratio of YP/PV is greater than 0.59 Pa/mPa∙s, the φ₆ and the φ₃ reading are all greater than 9, and the drilling fluid has good shear thinning property. All these properties result in good hole cleaning and the prevention of the occurrence of cuttings bed. 3) The drilling fluid has excellent lubricity, making possible the direct tripping (out of hole) through the high angle (55°, 70° and 67°) well sections.

Research on Cementing and Loss Prevention Drilling Fluid Technology During Drilling in the Sea Basin

HE Yinbo, XU Jie, CUI Guojie, ZHANG Lei, LIN Hai, CHEN Zhuo, JIN Jingyang

2024, 41(1): 68-75. doi: 10.12358/j.issn.1001-5620.2024.01.007

Abstract(31) HTML (7) PDF (3718KB)(4)

Abstract:
This paper analyzes the geological features and drilling fluid loss situations in the China's Sea Basin, identifying the challenges in leak prevention and plugging technology in this area. These include prevalent formation fractures with micro to millimeter-scale multi-scale cracks, and even the coexistence of fractures and cavities, which pose difficulties in choosing appropriate plugging materials and lead to a low success rate for first-time plugging. Moreover, there are extensive sections of weathered crust in the formation, coupled with highly developed fractures and severe fragmentation in some strata, resulting in secondary development of fractures, critical fluid loss or even non-return fluid loss. In response to these challenges, this paper synthesizes a type of gelation plugging agent, BFD-1, using polyvinyl alcohol, polypropylene acid, and organics with hydroquinone structures as raw materials. Experimental results show that the compressive strength of the artificial loose rock core increased by 19.34% after being soaked in 4% BFD-1 aqueous solution. Based on BFD-1, field plugging materials were combined to create drilling fluid systems for leak prevention and plugging for lost channels with different size. The drilling fluid exhibits excellent circulation-lost-control and cementing capabilities, and effectively prevents pressure transmission. The research results provide support for the subsequent lost-circulation control technology in this area.

Mechanisms and Inhibition of Borehole Instability Encountered in Drilling the Shiqianfeng Formation – Shihezi Formation in the East of Yan’an Gas Field

WANG Bo, WU Jinqiao, WANG Mengyu, LI Wei, YANG Chao, MA Zhenfeng, YANG Xianlun, LI Cheng

2024, 41(1): 76-83. doi: 10.12358/j.issn.1001-5620.2024.01.008

Abstract(28) HTML (10) PDF (3845KB)(7)

Abstract:
To find out the inherent causes related to the borehole wall collapse in drilling the Shiqianfeng formation – Shihezi formation in the east of the Yan’an gas field, samples were taken from the rig-sites and were studied for their mineral composition, physical-chemical features and mechanical characteristics. Based on the study a measure dealing with the borehole wall collapse, which is to inhibit the self-imbibition of liquid into the formation rocks, is presented. From the study it was found that the Shiqianfeng formation – Shihezi formation in the east of the Yan’an gas field contain 15.44% – 47.52% clays, and are a formation with weak expandability and moderate dispersibility. The rock samples are developed with micro-fractures and micro-fissures which are the main causes for the invasion of liquids and hence the collapse of borehole walls. The percent cuttings recovery of the samples tested on hot roller tester in distilled water is less than 67.2%, and the linear percent expansion of the cores made of the samples in distilled water is less than 8.14%. The Shihezi formation shows stronger dispersibility and stronger hydrophilicity than those of the Shiqianfeng formation. After soaking in a drilling fluid, the triaxial compressive strength of the Shiqianfeng sample is reduced from 186.04 MPa to 98.13 MPa, and the triaxial compressive strength of the Shihezi sample is reduced from 90.09 MPa to 49.21 MPa, indicating that the invasion of the drilling fluid into the rocks along the micro-fractures and micro-fissures causes the strengths of the formations to reduce. Using 0.3% self-imbibition inhibitor ZXS-1, the degrees of saturation of water phase and oil phase in the rock samples can be reduced from 72.6% and 86.6% to 4.7% and 33.5%, respectively, and the ZXS-1 additive can form a dense layer of adsorption around the surfaces of the rocks, thereby turning the wettability of the rock surfaces from hydrophilicity to hydrophobicity. By inhibiting the water imbibition into the rocks, the micro-fractures and micro-fissures are plugged and the liquid can no longer invade into the rocks, and the borehole walls are thus stabilized.

Development and Performance Evaluation of a High Performance Drilling Fluid Viscosifier

SUN Zhenfeng, YANG Chao, LI Jie, ZHANG Jinghui, ZHAO Kaiqiang, WANG Chen

2024, 41(1): 84-91. doi: 10.12358/j.issn.1001-5620.2024.01.009

Abstract(23) HTML (8) PDF (2992KB)(6)

Abstract:
A high performance viscosifier DV-1 has been developed to solve the problem of degradation and losing effectiveness of drilling fluid viscosifiers in high temperature and high salinity conditions. VD-1 is synthesized through free radical copolymerization with monomers such as MAPS, MAC and NVP. The initiator of the polymerization reaction is AIBA. The optimal reaction condition, determined through orthogonal experiment method, is as this: reaction temperature is 50 ℃, concentration of the monomers is 40%, concentration of initiator is 0.4%, and reaction time is 4 h. The reaction product was characterized using FTIR, ¹H-NMR and TG-DTA, and the viscosifying capacity, high temperature high salinity performance and the ling-term effectiveness of the synthesized product were evaluated. The evaluation experimental results show that 1% water solution of DV-1 has apparent viscosity of 44.7 mPa∙s. After aging at 180 ℃ for 16 h, the viscosity of the water solution is still maintained at 53.2% of its original viscosity. DV-1 is resistant to the contamination of salts. DV-1 also has good long-term effectiveness; after aging at 180 ℃ for 72 h and 120 h, the viscosity of the solution is still maintained at 50.5% and 40.7% of its original viscosity. DV-1 has EC₅₀ of 30 200 mg∙L⁻¹, meeting the standard of discharge in offshore area. The viscosifying mechanisms of DV-1 are studied by observing the spatial 3D morphology and by analyzing the Zeta potential of DV-1 in solution, it is concluded that DV-1 viscosifies in solution because the molecules of DV-1 have stable main chains and rigid side chains, the amphoteric ionic structure inhibits the continual curling of the side chains, thus effectively improving the salt resistant performance of DV-1 as a viscosifier.

CEMENTING FLUID

Ultra-high Temperature Resistant Cement Slurry and Its Application in Hot Dry Rock

XIAO Jingnan, LI Xiaojiang, ZHOU Shiming, WEI Haoguang, YANG Hongqi

2024, 41(1): 92-97. doi: 10.12358/j.issn.1001-5620.2024.01.010

Abstract(16) HTML (9) PDF (3444KB)(6)

Abstract:
It is easy to cause the strength retrogression of cement sheath, especially at the long-term high temperature condition of dry hot rock. At present, the method of adding sand to strengthen cement is widely used in high temperature cementing operations. However, the strength retrogression of cement still exists when the temperature is above 200 ℃, resulting in casing collapse and annular flow, which seriously affects the wellbore safety. To solve the problem of cement strength retrogression at the ultra-high temperature, a new high-temperature stabilizer (SCKL) was developed by optimizing the phase composition of cement based on the enhanced effect of silica aluminum bonding. The effect of SCKL on the inhibition of set cement strength retrogression at high temperatures was evaluated. The results showed that the compressive strength of set cement was 18.2 MPa at 48-hour age for 300 ℃ curing temperature. And the strength reached 23.2 MPa after 30 days, which inhibited the strength retrogression of cement under long-term high temperature conditions. The influence of temperature on the microstructure and hydrates of set cement was revealed based on the XRD and SEM tests. Finally, a new durable heat-resistant cement system was developed. The cement slurry had very good settlement stability and could meet the requirement of safe cementing in DHR wells at a temperature difference of 100 ℃. The durable heat-resistant cement system has been successfully applied in five wells in Gonghe Basin, Qinghai Province. The cementing qualities are very good, which provides a guarantee for the integrity of cement sheath sealing in dry hot rock.

Preparation of A 240 ℃ Cement Slurry Filter Loss Reducer Prepared through Thermal Initiation Polymerization

LIN Xin, LIU Shuoqiong, XIA Xiujian, MENG Renzhou

2024, 41(1): 98-104. doi: 10.12358/j.issn.1001-5620.2024.01.011

Abstract(11) HTML (4) PDF (2755KB)(6)

Abstract:
A terpolymer cement slurry filter loss reducer HTFLA-A is developed to deal with the poor thermal stability of the cement slurry filter loss reducers presently in use. HTFLA-A is designed and synthesized through high temperature thermally induced polymerization instead of the conventional water solution initiation polymerization. HTFLA-A works normally at temperatures up to 240 ℃. The optimal synthesis condition of HTFLA-A is: mass ratio of water to the monomers is 1:1, reaction temperature is 150 ℃, pH of the reaction system is 9, and the reaction time is 32 h. The molecular structure of HTFLA-A is characterized with FT-IR, DSC/TGA and NMR. The results of the study show that the final synthesis product HTFLA-A is the expected product. Weight loss on heating of HTFLA-A at 439 ℃ is only 23.80%. The reason for this low weight loss on heating is because in the high temperature synthesis, the unstable structures in the monomer molecules and the by-products of the synthesis process are all removed from the final product, thus improving the high temperature stability of the target product. Performance evaluation of HTFLA-A shows that at a concentration of 1.2%, HTFLA-A can control the API filtration rate of a cement slurry to below 50 mL at test condition of 180-240 ℃ and 6.9 MPa.

Cement Sheath Integrity and Decay Law of Interface Mechanical Properties Under Ultra-high Temperature Thermal Cycling

CHEN Yi, ZHANG Binqi, LIU Peng, ZHOU Niantao

2024, 41(1): 105-111. doi: 10.12358/j.issn.1001-5620.2024.01.012

Abstract(10) HTML (3) PDF (4281KB)(4)

Abstract:
The failure of cement sheath integrity caused by temperature fluctuations and continuous changes in the wellbore and cyclic loading and unloading in periodic steam stimulation of heavy oil thermal recovery wells will threaten the integrity of the wellbore, lead to frequent safety issues such as wellhead movement. A method for evaluating the bonding strength of cement sheath under high-temperature thermal cycling environment was proposed in this paper to clarify the failure mechanism of cement sheath integrity and the degradation law of interface bonding strength under high-temperature thermal cycling, and to avoid the failure of the interface bonding between the casing and the cement sheath during steam stimulation. A proprietary testing device for the bonding strength of cement sheath that integrates pouring, curing, heating, and testing was independently developed. The interface integrity and mechanical integrity of the "production casing-cement sheath-technical casing" system under thermal cycling were tested and evaluated. Experimental results on the integrity and interfacial bonding performance of cement sheath under thermal cycles at three different temperatures (30 ℃↗150 ℃↘30 ℃, 30 ℃↗200 ℃↘30 ℃, 30 ℃↗250 ℃↘30 ℃) obtained. The research results indicate: the ultra-high temperature thermal cycling has a significant negative impact on the mechanical and interfacial integrity of the cement sheath. With the increase of temperature and thermal cycle times, the shear strength of cement sheath interface decreases sharply, and the integrity failure degree of cement sheath body also increases. The cement sheath interface debonds after 7^th thermal cycle of 150 ℃, 5^th thermal cycle of 200 ℃, 1st thermal cycle of 250 ℃, respectively. The interaction between casing and cement sheath completely disappear (the shearing force, chemical bonding force, friction, shearing strength is all equal to 0) after 13^th thermal cycle of 150 ℃, 9^th thermal cycle of 200 ℃, 7^th thermal cycle of 250 ℃, respectively. The body failure includes radial cracking and circumferential cracking. Radial cracking, circumferential cracking, and interface debond cause the failure of the cement sheath integrity, sealing integrity, and interface integrity. Micro cracks and micro gaps will generate which cause deformation, damage, and leakage of cement sheath. The casing becomes a free section, causing safety issues such as annular pressure and wellhead movement.

Preparation of a High Temperature- and Salt-Resistant Styrene Butadiene Latex under the Action of Composite Emulsifiers and the Performance Evaluation Thereof

WANG Qike, LI Xiaolin, XIAO Yao, SHANG Xiaoyang, LIU Wenming, ZHAO Jiaqi, GUO Jintang

2024, 41(1): 112-118. doi: 10.12358/j.issn.1001-5620.2024.01.013

Abstract(8) HTML (4) PDF (3011KB)(3)

Abstract:
Styrene butadiene latex as a toughening agent in well cement slurries has some deficiencies such as poor thermal stability and salt resistance, and the styrene butadiene latex has to be used together with latex conditioners. To solve these problems, the styrene butadiene latex is modified with other monomers, such as sodium styrenesulfonate and itaconic acid as the functional monomers, and a composite emulsion system containing OP-10 and SDS to produce an SCMBR latex. The effects of different emulsifier formulation on the properties of the latex were investigated. The microstructure of the SCMBR latex was characterized with particle size, Zeta potential and transmission electron microscope. The thermal stability and salt resistance of the SCMBR latex was evaluated. Laboratory experimental results show that the SCMBR latex has good thermal stability, the thermal decomposition temperature is as high as above 400 ℃. The SCMBT latex also shows good salt resistance. TEM image shows that the SCMBT latex is evenly dispersed with no aggregate existed. The SCMBT latex can significantly improve the stability of cement slurries, it reduces the amount of free liquid to less than 1%, and the difference between the density of the top and the density of the bottom can be reduced to 0. The SCMBT latex can also be used to improve the rheology of the cement slurries and the flexural strength of set cement. A set cement modified with the SCMBR latex has 28 d flexural strength 20.5% higher than the flexural strength of the pure set cement. In deep and ultra-deep well cementing the SCMBR latex will have broad application prospect.

A New Nanometer Accelerating Early Strengthen Agent for Oil Well Cement

LU Haichuan, ZHU Haijin, WANG Jiandong, XU Delu, JIN Kai, GAO Jichao, ZHANG Xiangrui, SHI Linglong

2024, 41(1): 119-124. doi: 10.12358/j.issn.1001-5620.2024.01.014

Abstract(17) HTML (7) PDF (2679KB)(4)

Abstract:
Accelerators used in conventional oil well cement cause casing to corrode, viscosify the cement slurry and cause the cement slurry to have weak early strength. To solve these problems, a new nanometer accelerating early strength agent A-1 is developed through solution synthesis. Study on the general properties and working mechanisms of A-1 indicate that A-1 can both improve the rheology of cement slurries and shorten the thickening time of cement slurries at medium and low temperatures, significantly accelerating the development of the strength of the set cement. The thickening time ratio reaches 0.33, the time for strength development can be shortened by 50%, the 6 h compressive strength can be 5 times higher than that of the base slurry, and the later strength improvement rate can still reach 29%. Moreover, this nanometer accelerating early strength agent can significantly shorten the transition time of the gel strength of cement slurries, showing good anti-channeling performance. Microanalysis results show that the nanometer accelerating early strength agent can alter the micromorphology of set cement through nucleation template effect, thereby accelerating the hydration of set cement, making the set cement denser and hence improving the mechanical performance of set cement.

FRACTUREING FLUID & ACIDIZING FLUID

Conductivity Prediction Based on Fracture Closure Theory and 3D Printing

JI Guofa, YU Hao, TIAN Hongzhao

2024, 41(1): 125-132. doi: 10.12358/j.issn.1001-5620.2024.01.015

Abstract(11) HTML (3) PDF (4550KB)(5)

Abstract:
The conductivity of acid-etched fractures is important to the optimization of acid-fracturing program and the production evaluation of a well. In testing the conductivity of acid-etched fractures, the core column under test may break down at high closure pressures and this will cause the test results to become inaccurate. To deal with this problem, the conductivity of acid-etched fractures is studied using the 3D scanning and 3D printing technologies as well as the theory on the closure of fractures under pressure. In the study, the core samples were first acid etched. Using reverse modeling technology, the 3D model of the acid-etched cores was obtained. Using the SLA3D printing technology, a 3D core model with rough walls was prepared. Then seepage experiment was conducted under different confining pressures on the acid-etched cores and the 3D printed cores. Using the discretized data processing method, the deformation of the fractures under the action of the closure stress was presented using numerical simulation in combination with the Hertz contact model and a conductivity prediction interface programed with the N-K model. The study results show that the 3D digital model of the real rocks and the real core samples made with the SLA3D printing technology together can be an effective way of preparing complex fractured core models. The errors of the conductivity test made on the acid-etched cores and the 3D printed cores, the test made on the 3D printed cores as well as the numerical simulation are all less than 7.7%, and the errors between the numerical simulation results and the carbonate core test results are less than 9.6%. The experiment and numerical simulation results obtained under low closure pressures can be used to predict the conductivity of the fractures under high closure pressures. The study method proposed provides a reliable approach for quantitatively characterizing the conductivity of acid-etched fractures.

COMPLETION FLUID

Offshore Gas Hydrate Completion Fluid System Construction and Performance Evaluation

FENG Ming, LIAO Bo, WANG Jintang, ZENG Xianjin

2024, 41(1): 133-140. doi: 10.12358/j.issn.1001-5620.2024.01.016

Abstract(24) HTML (5) PDF (15237KB)(8)

Abstract:
Gravel packing is an effective method for preventing sand production during the exploitation of gas hydrate reservoirs. However, the accompanying completion fluid system faces technical challenges, such as secondary hydrate formation and low gravel packing efficiency. Therefore, this paper combines the experience of conventional oil and gas reservoir development in the South China Sea, considers the particularity of gas hydrate reservoirs, constructs different gas hydrate completion fluid systems, and evaluates the complete performance of these systems based on laboratory experiments and numerical simulation techniques. The research results show that commonly used thermodynamic inhibitors such as ethylene glycol and salts require relatively high addition amounts to achieve good inhibition effects, but the higher completion fluid density cannot meet the on-site construction requirements, so kinetic inhibitors need to be used as substitutes. The experimental tests and numerical simulation results show that the completion fluid system formulated with the self-developed SYZ-2 kinetic inhibitor can meet the requirements of various on-site indicators and achieve good completion effects. After comparative analysis, the optimal completion fluid is brine+2.5%PF-HCS+2.0%PF-CA101HT+6.5%NaCl+ 1.0%SYZ-2.

Competent Authorities：China National Petroleum Corporation Ltd

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

Editor-in-Chief：Shi-chun Chen

Address： Editorial Department 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

CN13-1118/TE

ISSN1001-5620

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2024, Volume 41, Issue 1