钻井液与完井液

Abstract:
Accurate prediction of drilling fluid rheological parameters is of great importance to the accurate computation of high temperature high pressure (HTHP) hydraulic parameters and borehole pressure, and to maintain the safety of drilling operation. Based on the database of drilling fluid rheological parameters obtained in laboratory experiments, nine flow models were evaluated for their adaptability to different drilling fluid systems in a wide temperature and pressure range. Among these models, the Herschel-Bulkley model (medium and low temperature, low pressure) and the four-parameter flow model were selected for evaluating their adaptability to oil based drilling fluids, the hyperbolic flow model was selected for evaluating its adaptability in a wide temperature and pressure range to water based drilling fluids. The selected flow models are the bases for accurately predicting the borehole pressures in HTHP wells. Based on the experiment data development and multivariate nonlinear fitting, a new model was established for predicting the rheological parameters of different drilling fluid systems with different flow models in a wide temperature and pressure range. This new model was then verified with borehole pressure data obtained from an HTHP well. The verification results show that the error existed for using the hyperbolic flow model as the basis to calculate the bottom hole pressure is 1.31%, indicating that the new model has satisfied the needs for accurate computation of borehole pressures in deep and ultra-deep HTHP wells.

Preparation and Evaluation of an Organosilicon Water Block Inhibitor for Low Permeability Gas Reservoirs

GUO Xuan, SUN Jinsheng, LYU Kaihe, JIN Jiafeng

2023, 40(2): 156-162. doi: 10.12358/j.issn.1001-5620.2023.02.002

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Abstract:
To solve the waterblocking damage caused by water phase invasion during drilling and completion of the low permeability gas reservoir, a cationic silicone surfactant DAT was synthesized by the hydrosilylation and epoxy ring opening reactidouble-endedle ended hydrogenated silicone oil (DHSO), allyl glycidyl ether (AGE), trimethylamine hydrochloride (TMHC), defoamer, and other additives were used to prepare the anti-waterblocking agent DAH. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance o solve the problem of water block resulted from water invasion in drilling and completion of a low permeability gas reservoir, a cationic organosilicon surfactant DAT was synthesized through hydrosilylation reaction and epoxides ring-opening reaction, and by compounding the DAT with a defoamer, an organosilicon anti-water-block agent DAH was produced. The cationic organosilicon surfactant DAT is synthesized with raw materials such as double-ended hydrogen-containing silicone oil (DHSO), allyl glycidyl ether (AGE) and trimethylamine hydrochloride (TMHC). Characterization of the final product with Fourier infrared spectroscopy and HNMR has proved that the molecular structure of the final product conforms to the expected design. The performance of DAH was evaluated by laboratory tests such as surface tension measurement, contact angle test of cores, self-imbibition test of cores, core displacement test etc. The test results reveal that a 1% DAH solution has a surface tension greatly reduced to 21.28mN/m, the contact angle of the DAH water solution is increased from 20° to 110°, the amount of water imbibed by the core sample tested is reduced by 83.1%, and the percent permeability recovery is increased to 82.68%. These test results have proved that DAH can greatly reduce the surface tension of water, and can form a tight absorptive membrane on the surfaces of a core through electrostatic action, thereby reversing the surface of the core from hydrophilic to hydrophobic, and effectively reducing the invasion of water into the formation during drilling and completion operations. This performance of DAH is also helpful to water flow back, making it an excellent additive for reducing the damage caused by water blocking; this is of great importance to the protection of the productivity of a low permeability reservoir.

Synthesis and Evaluation of Epoxy Resin Self-Degradation Plugging Agent for Fractured Formation

WEI Anchao, LIU Shujie, JIANG Donglei, LIU Peikai, ZENG Chunmin, QIU Zhengsong, LIU Zhengkai

2023, 40(2): 163-168. doi: 10.12358/j.issn.1001-5620.2023.02.003

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Abstract:
In view of the technical difficulties in plugging and protecting fractured reservoirs, based on the analysis of the self-degradation mechanism of epoxy resin materials, this paper developed a new type of epoxy resin self-degradation plugging agent, and experimentally explored the influence of the dosage of curing agent and modifier on the performance of the new type of epoxy resin self-degradation plugging agent. With the help of pressure bearing strength experiment, long fracture plugging simulation experiment device, reservoir protection tester, etc., the compressive strength, fracture plugging and reservoir protection performance were systematically tested. The experimental results show that the newly developed epoxy resin self-degradable plugging agent has good degradation performance. The final degradation rate can reach more than 90% at all temperatures, and the degradation rate is more than 95% at 120 ℃ for 96 h. The environmental temperature and pH can promote its degradation; At the same time, the self-degradable plugging agent has a high elastic modulus and a good compression crushing rate, and the compression crushing rate is only 6.2% under 30 MPa. Combined with the particle size grading optimization, the new epoxy resin self-degradable plugging agent can effectively block the cracks between 0.5-4 mm, and has a good crack pressure bearing sealing effect, the result of reservoir protection experiment shows that after 8 days of degradation of self-degradable plugging agent, the core permeability recovery rate reaches 99.1%, and the reservoir protection effect is good.

Simulation Device and Experimental Study on Leakage and Plugging of Active Water Fracture Hole

LIU Jinhua, LI Daqi, LI Fan, SONG Bitao, YANG Yunlong

2023, 40(2): 169-175. doi: 10.12358/j.issn.1001-5620.2023.02.004

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Abstract:
Research shows that there is no equipment for simulating the mud loss zones in fractures and vugs with active water. Based on the investigation and study on the characteristics of the mud loss zones in fractures and vugs with active water, the functions to be achieved and the corresponding parameters of the simulation apparatus were clearly defined, and the structure and components of the apparatus were determined. The simulation apparatus is composed of five subsystems, which are the fracture and vug simulation subsystem, the formation water simulation subsystem, the lost circulation material slurry injection subsystem, the borehole simulation subsystem and the data acquisition subsystem. This simulation apparatus can be used to simulate a water flowing speed of 10 m/min and has a pressure bearing capacity of 2 MPa, satisfying the needs of controlling mud losses into most fractures and vugs with active water. Using this apparatus, the factors affecting the retention of gel in mud loss channels with active water were evaluated. The test results show that in a mud loss channel with atmospheric pressure, good retention of the lost circulation control gel can be obtained at the following conditions: the injection rate of a lost circulation control gel is greater than 1.2 times of the water flowing rate, the adhesion strength of the gel is greater than 10.1 N/m², and the density of the gel is between 1.1 g/cm³ and 1.2 g/cm³. This study has provided a guideline to the control of mud losses into fractures and vugs with active water.

Study and Application of High-temperature Resistant Non-sulfonated Semi-saturated Salt Water Drilling Fluid

XU Jiang, WU Yu, AN Zhiwei, YOU Fuchang, SHU Man

2023, 40(2): 176-183. doi: 10.12358/j.issn.1001-5620.2023.02.005

Abstract(624) HTML (267) PDF (2199KB)(105)

Abstract:
Aiming at the problems of poor environmental performance of sulfonated water-based drilling fluid and the insufficient temperature resistance of existing non-sulfonated water-based drilling fluid, the non-sulfonated humic acid resin filtration reducer DEM-SEAL was synthesized on the basis of the mixed raw materials of humic acid, lignin and tannin extract, and was modified by silane coupling agent, organic acid and diamine, and it was analyzed and characterized by infrared spectrum, thermogravimetry and gel chromatography. The experimental results show that the temperature resistance of DEM-SEAL was 180 ℃, the LC₅₀-96 h was 101,020 mg/L, the total sulfur content was 0, which is non-toxic and environmentally friendly. When the dosage of DEM-SEAL was 4.0%, the API filtration and HTHP filtration of the base slurry aged at 180 ℃ were only 7.6 mL and 16.8 mL, with a reduction rate of 75.2% and 83.0%, and it was little impact on the viscosity of mud. Combined with the excellent characteristics of DEM-SEAL, a set of high-temperature resistant non-sulfonated semi-saturated salt water drilling fluid system was constructed. The density range was 1.30～1.80 g/cm³, the temperature resistance reached 180 ℃, the API filtration was less than 5.0 mL, the HTHP filtration was less than 15.0 mL, which has good performance of rheological and low filtration. The LC₅₀-96 h was 55,600 mg/L, and the BOD₅/COD_cr was 23.51%, which is non-toxic and biodegradable. The system has been successfully applied in a high temperature and deep well in Xinjiang oilfield. The bottom hole temperature was 179 ℃, the rheological property was stable in the drilling process, the filtration and wall building performance was good, and there were no complex accidents of borehole. Under the premise of safe drilling, the objective of "non-sulfonation" of high-temperature resistant drilling fluid was realized, which provided technical reference for the research and development of high-temperature non-sulfonated drilling fluids in China.

Design and Evaluation of an Integrated Drilling and Completion Fluid

XU Jie, XU Lin, LI Xiwen, KOU Lei, XU Mingbiao

2023, 40(2): 184-192. doi: 10.12358/j.issn.1001-5620.2023.02.006

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Abstract:
The integrated drilling and completion fluid is the development of the traditional drill-in fluid used in offshore open hole drilling. The formulation of this new-generation drill-in fluid is based on the D₉₀ empirical rule and the membrane shielding principle, and the concept of low-shear-rate viscosity is used. The insertion of temporary plugging agent particles and film-forming at the pore entrance of the formation rocks form a unidirectional shielding ring, which not only protects the reservoir from being damaged, but also can be flowed back directly, thereby simplifying the well completion procedure. This paper describes the design of the new-generation drill-in fluid as well as the experiment for examining the micro structure of the key components and the basic performance of the drill-in fluid. Experiments on the reservoir protection performance of the drill-in fluid show that the flexible and the rigid temporary-plugging particles in the drill-in fluid plug the pore entrances in a synergetic way, promoting the formation of the unidirectional shielding ring. Of the temporary-plugging particles, the rigid particles have irregular shapes, with median particle size of 9.5 μm, which is greater than the sizes of the pores; whereas the flexible film-forming particles are in regular spherical shapes with average particle size of 25.4 μm, the narrow size distribution of the flexible particles is beneficial to inter-particle filling and deformation coalescence. The drill-in fluid has good rheology at temperatures between 5 ℃ and 130 ℃, and its average low-shear-rate viscosity is 30,802 ± 1,892 mPa∙s, which satisfy the needs of flowback and block removal. The drill-in fluid has good lubricity, high inhibitive capacity and high resistance to seawater and drilled cuttings contamination. It is a good one-way plugging agent and direct flowback operation produces a high permeability recovery. Field application of this drill-in fluid indicated that the drilling of the reservoir section was smooth and successful, the requirements of direct flowback were satisfied, and the procedure of completing the well was simplified.

Ultra-High Density Drilling Fluid Technology for the Well Hetan-1

WANG Xin, TAN Chun, WANG Zhibin, LUO Yucai, ZHOU Yi, ZHANG Minli, WANG Wei, JIA Dongmin

2023, 40(2): 193-201. doi: 10.12358/j.issn.1001-5620.2023.02.007

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Abstract:
The well Hetan-1 is a key exploratory well drilled by CNPC at the Linhe depression in the Hetao basin in Huabei oilfield. The completion depth of this well is 6,460.44 m and was drilled to explore the reservoir characteristics of the Paleogene and the Neogene systems in the Guangming anticline in the Xinglong tectonic belt. The third interval of this well penetrated formations of four different formation pressure coefficients, and the safe drilling windows of the formations are narrow. Killing the well by raising mud weight, controlling mud losses and drilling with managed pressure were used in drilling this interval. When drilling into the formation with ultra-high pressure fluids, the mud density was increased in one step from 1.80 g/cm³ to 2.55 g/cm³, and the well was successfully completed. The kill mud stored at the rig site had a density of 2.60 g/cm³, a density limit of water based drilling fluids weighted with barite. Several downhole troubles were encountered during drilling, such as borehole collapse, pipe sticking because of creeping tight hole in mudstone formations containing gypsum, high pressure saltwater invasion as well as mud losses. The interval was drilled with a high temperature ultra-high density compound saltwater drilling fluid, and controlling mud losses while drilling technique was used seven times to enhance the pressure bearing capacity of the formations. During drilling, finer screens were used on shale shakers for better solids control, the drilling fluid was continually optimized for its composition, the weighting materials were carefully selected, the content of bentonite in the mud was adjusted to satisfy the needs of stabilizing mud rheology, and the content of the low-gravity solids in the mud was carefully controlled at as low as possible level. With these measures, problems such as narrow drilling windows, difficulties in controlling the rheology of a high temperature high solids content drilling fluid with ultra-high density were successfully solved, ensuring the stability of the properties of the ultra-high density drilling fluid in high temperature drilling and completion operations. The drilling of this well has created six drilling technical indicators in this area at the same period. An industrial oil flow of 302.4 m³ was produced daily, realizing the target of exploring oil and gas in the deepest well in the Bayan oilfield, and of providing technical support to the drilling and completion operations.

Study and Application of a New Environmentally Friendly Drilling Fluid in Through-Casing Sidetrack Drilling

LIU Bo, GAO Long, CHEN Mingyong, SUN Huan, HUANG Xuping, ZHAO Ying

2023, 40(2): 202-208. doi: 10.12358/j.issn.1001-5620.2023.02.008

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Abstract:
Several problems have been encountered in the development of the Sulige gas field, for example, the caving and sloughing of the hard and brittle mudstones of the Shuangshi formation of the Permian system, borehole instability of the black mudstones as well as difficulties in exerting weight to the bit in horizontal slide drilling, to name but three. Environmental protection requirements have limited the use of conventional shale inhibitors. In previous drilling operation, long time reaming, sidetracking after plugging the abandoned hole have been the norm for some time. To deal with these problems, an environmentally friendly cellulose shale inhibitor CQYJZ-3 was developed through chemical modification of a hemicellulose derivative, and an environmentally friendly drilling fluid named HCG-1, which is suitable for through-casing sidetracking of horizontal wells in Sulige gas field, was developed. Laboratory experimental results show that HCG-1 drilling fluid has stable rheology and good properties such as inhibitive capacity, lubricity, contamination resistance and corrosion inhibition. It is a non-toxic easy-to-degrade drilling fluid. This drilling fluid has been successfully used on 10 wells in the Sulige gas field. Field operation showed that HCG-1 had stable properties, good inhibitive capacity and lubricity. Wireline logging was successful at the first try. No downhole troubles were encountered during drilling. The HCG-1 drilling fluid can be also recovered for re-use. Good application achievements were obtained with the use of the HCG-1 in the Sulige gas field.

CEMENTING FLUID

Study and Application of a High Temperature Retarding Agent for Well Cementing

LING Yong, YU Qianqian, MA Ruran, LI Xiaolin, ZHANG Chengxing, ZHENG Qilin, LIN Zhihui

2023, 40(2): 209-215. doi: 10.12358/j.issn.1001-5620.2023.02.009

Abstract(664) HTML (234) PDF (2405KB)(74)

Abstract:
At temperatures between 130 ℃ and 150 ℃, a cement slurry treated with the commonly used retarding agent AMPS/IA has a thickening time that is longer than the thickening time at lower temperatures. This is an abnormal phenomenon that is risky to the well cementing operation and negatively affects the quality of cementing jobs. In laboratory experiment, AMPS and IA were reacted with each other through radical solution copolymerization. During the copolymerization, EDTA-2Na (disodium ethylene-diamine tetra-acetic acid) and CTAC (cetyl trimethyl ammonium chloride) were added to compound with the copolymerization product. The final product of the copolymerization, BH-R103L, is a retarding agent which can be used to prevent the abnormal thickening time. Comprehensive evaluation of the retarding agent BH-R103L revealed that it has reliable high temperature resistance and gel strength adjustment property. A cement slurry treated with BH-R103L has a thickening time that is adjustable between 120 ℃ and 150 ℃. At 150 ℃, a cement slurry treated with 2% (BWOC) BH-R103L has a thickening time longer than 300 min, and the thickening time has a linear relationship with the concentration of BH-R103L in the cement slurry. Using BH-R103L, the abnormal thickening time is eliminated, the cement slurry has a low initial consistency, the temperature and concentration sensitivity become low, and the thickening timeline becomes normal. BH-R103L has good compatibility with high temperature filter loss reducers such as AMPS, and can be used to inhibit “soft core” phenomenon of a cement slurry at elevated temperatures. Cured at 60 ℃, the set cement has a strength that develops very fast, other general properties of the set cement all satisfy the needs of well cementing operation. BH-R103L has been used in the cementing operation on the 203H153 platform in Luzhou block, Sichuan Province, sonic logging results showed that the cementing job quality met the designed requirements.

Study on a Cement Slurry for Cementing Uncemented Shallow Section of Old Casing String by Secondary Displacement

YIN Hui, LIU Huajie, CUI Jie, ZHANG Hongwei, ZHANG Hongxu, BU Yuhuan, CHAI Demin

2023, 40(2): 216-221. doi: 10.12358/j.issn.1001-5620.2023.02.010

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Abstract:
In Shengli Oilfield, after more than 20 years’ development, the production casing strings above the top of the set cement in some early development wells have been seriously damaged by corrosion, and this badly hinders the normal production of the oil and gas wells. To deal with this problem, it was proposed to conduct secondary well cementing to the free section of the production casing string in the shallow formations. This secondary well cementing not only repairs the integrity of the casing string, it also protects the casing string from further corrosion. Several factors were considered in developing the required cement slurry, such as the technical characteristics of cement slurry injection into the annulus, the nature of the shallow formations being soft, and the requirements of the secondary cementing operation outside the free section of the production casing string. A low-density low-viscosity strong-thixotropy long-thickening time cement slurry was formulated with carefully selected gel agent, low-viscosity thixotropic agent, fluid loss additive and retarder. The composition of the cement slurry is as follows: 40% class G oil well cement + 30% fly ash + 30% slag + (20% – 25%) low-viscosity thixotropic agent L-TA + 2.5% polyvinyl alcohol fluid loss additive+ (0.16% – 0.32%) ZnO + 1% dispersant + 0.5% defoamer. Water/solids ratio of this cement slurry is 0.56. This cement slurry has a density that is as low as 1.5 – 1.6 g/cm³, viscosity of less than 50 mPa∙s, thickening time of longer than 15 h, difference of average gel strengths of 17.885 N/m², as well as repeatable thixotropy. Field application proved that this cement slurry satisfied the requirements of the secondary cementing outside the free section of the casing string in the shallow formations in Shengli Oilfield.

Study on the Influence of Elastic Toughness Cement Slurry Performance and Short-term Corrosion Mechanism under HPHTHS Conditions

YU Lin, TAN Huijing, REN Yang, LIU Siyan, YE You

2023, 40(2): 222-232. doi: 10.12358/j.issn.1001-5620.2023.02.011

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Abstract:
To understand the corrosion environment of a set cement at high temperature, high pressure and high H₂S/CO₂ conditions and the complex work condition thus formed, a series of experiments were conducted to study the property change and short-term corrosion mechanisms of elastic tough cement slurries under the “three-high” conditions. A class G cement slurry was treated with three main elastic tough additives commonly used, i.e., rubber powder at 10%, basalt fiber at 0.3% and styrene-butadiene latex at 10%. The cement slurry thus formulated was rendered elasticity to some extent. Using several methods such as mechanical property measurement, XRD, FTIR, MIP and SEM-EDS etc., changes were studied in the mechanical properties, distribution of pore throat sizes, types of hydration products and micro-structures before and after the cement slurry was treated with the three additives and was cured under corrosion conditions. The measurement results show that the addition of the three elastic tough additives is beneficial to the decrease of the brittleness and to the increase of the toughness of the set cement. Among these additives, the basalt fiber is the best additive for controlling the fracture development in the set cement when it fails, and the styrene-butadiene latex is the best additive for reducing the elastic modulus and maintaining a high flexural strength of the set cement. After undergoing a short-term corrosion in liquid environment, the mechanical strengths of the cement samples were all improved, especially the set cement containing basalt fiber and styrene-butadiene latex. Basalt fiber under the corrosion conditions showed stable properties, the dense calcium carbonate crystals produced in the corrosion process were piled in the pores located at the interfaces between the basalt fiber and the cement matrix, leading to a decrease in the total pore volume in the corroded set cement and a substantial increase in the mechanical strength of the set cement. The styrene-butadiene latex can form a polymer membrane inside the set cement, which covers and wraps up the cement matrix, thereby improving the anti-corrosion property of the cement surfaces.

Numerical Simulation Study on Mechanics of High Density Elastic and Tough Cement Slurries

LI Chengsong, LI Shekun, FAN Mingtao, ZHANG Haixiong, YUAN Mingye, LEI Gang

2023, 40(2): 233-240. doi: 10.12358/j.issn.1001-5620.2023.02.012

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Abstract:
Deep shale gas reservoirs are buried in deep formations with high temperatures and high fracture pressures. In fracturing these reservoirs, high flowrate and high pump pressure result in severe problem of sustained annular pressure. Compared with shallow shale gas reservoirs, deep shale gas reservoirs, because of their high formation pressures, have to be cased off with weighted cement slurries. The cement sheath is composed of not only the pure cement, it also contains weighting agents and additives that are used to improve the elasticity of the cement sheath. Based on this idea, a meso-mechanical model for high density elastic cement slurries is established to guide the improvement of the mechanical performance of the cement sheath in deep shale gas reservoirs. The effects of the additives added into a cement slurry on the mechanical performance of the set cement has been preliminarily analyzed. It was found in the study that 1) weighting materials and elasticity additives, because of the difference in their rigidity, can change the macro-mechanical performance of the set cement; 2) the interaction between the physical dimensions of the elasticity additives and the weighting agents must be considered in cement slurry design, and the bonding strength of the elasticity additive with the cement must be strengthened; 3) a cement slurry was designed with a selected weight material, whose particles are in rhombus-like shape, and a hydrophilic elastic agent. The mass ratio of the two additives was determined through experiment. This cement slurry, which has a density of 2.3 g/cm³, has 48 h compressive strength of greater than 20 MPa, and a elastic modulus of less than 7 GPa. With this cement slurry, a cement sheath of low elastic modulus and high strength cement sheath can be obtained in cementing deep shale gas reservoirs. The study achievements are of great guiding importance to the design of cement slurries for use in deep shale gas reservoirs.

Impact Resistance Mechanical Properties and Damage Characteristics of Set Cement Containing Nitril Rubber Powders

SUN Xialan, REN Qiang, WU Ke, HUANG Kun, MEI Kaiyuan, ZHANG Gaoyin, CHENG Xiaowei

2023, 40(2): 241-250, 258. doi: 10.12358/j.issn.1001-5620.2023.02.013

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Abstract:
Oil well cement is a typical brittle material, presently many studies are focused on improving the toughness and reducing the brittleness of the cement sheath, as well as prolonging the service life of an oil/a gas well without impairing the safety of the well. In this study, the microsphere nitrile rubber powder (MRP) and the irregular nitrile rubber powder (NRP) were separately added to cement slurry to investigate the mechanical performance of impact resistance and the damage characteristics of the set cement. Using a split Hopkinson pressure bar (SHPB) with a diameter of 50 mm, the dynamic impact resistance performance of different set cement samples was tested. The dynamic compressive strength, energy evolution and damage characteristics of the set cement samples were discussed using the test results. A set cement sample containing 6% MRP had dynamic compressive strength of 64.02 MPa, and the absorbed energy of the sample was 39.93 J, equivalent to an absorbed energy rate of 49.91%. Another set cement sample containing 6% NRP had dynamic compressive strength of 74.06 MPa, and the absorbed energy of the sample was 46.56 J, equivalent to an absorbed energy rate of 58.20%. It was found from high-speed photographing and micromorphology observation that NRP is more closely bonded with the set cement matrix, and the crack resistance of the set cement was improved through crack deflection mechanism, which is beneficial to prolonging the load bearing time of the sample and increasing the consumption of the load energy.

FRACTURING FLUID & ACIDIZING FLUID

A New Reservoir Wettability Characterization Method for Fracturing Fluid Performance

SUN Chenhao, HUANG Sha, DONG Sailiang, ZOU Jialing

2023, 40(2): 251-258. doi: 10.12358/j.issn.1001-5620.2023.02.014

Abstract(496) HTML (223) PDF (3267KB)(49)

Abstract:
Unconventional reservoirs have characteristics of complex pore geometry, high heterogeneity and low permeability. The wetting behavior between the fluid and solid is the dominant factor that controlling the static and dynamic fluid displacements, which is of great crucial for evaluating the fracturing fluid performance, enhancing the oil recovery during the fracturing fluid imbibition, and optimizing the fracturing fluid formulation. In this paper, we propose a new in-situ wettability characterization method based on the Gauss-Bonnet theorem and 3D micro-computed tomography experiments. In addition, we systematically analyze the effect of complex wetting condition on fracturing fluid performance during the imbibition process of fracturing fluids by applying digital rock technology and lattice-Boltzmann method simulations. It is elucidated that the wettability characterization method by the topological principles is more accurate than in-situ microscopic contact angles, of which accuracy is higher than 95%. It is also capable of characterizing the wettability that is influenced by different wetting characteristics. Simultaneously, the tight oil recovery in the homogeneous water-wet reservoir is 33.8% higher than that of mixed-wet reservoirs, which leads to a better performance of fracturing fluid. The initial condition of reservoir is commonly mixed-wet. Therefore, the formulation of fracturing fluid needs to be optimized to reduce the rock wettability and enhance tight oil recovery.

Evaluation of the Performance of a CO₂ Water Based Compound Fracturing Fluid

WU Jun, LU Junkai, LIU Yi, DU Fanglan, LUO Cheng

2023, 40(2): 259-264. doi: 10.12358/j.issn.1001-5620.2023.02.015

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Abstract:
CO₂ dry fracturing operation has to be performed in a closed environment and the fracturing fluid additives need to be added under pressure. These requirements result in high operation cost, low sand ratio, low operation scale, as well as high operational difficulties. To deal with these problems, ZHENG Yan et al. presented and tried a quasi-dry CO₂ fracturing technology. In the quasi-dry fracturing operation, the accurate control of the parameters of the liquid is key to the success of this technology, and the parameter control needs to be optimized repeatedly. This study was focused on the use of a fracturing fluid mainly formulated with CO₂ (> 70%, a water based CO₂ fracturing fluid) with conventional equipment in atmospheric pressure. Main factors affecting the ratio of the components and the thickening performance of the fracturing fluid were studied. The fluid was formulated with a visual CO₂ sampler, and by observing the settling of the ceramsite the thickening of the liquid CO₂ can be understood. The interaction of the water and the liquid CO₂, the effects of the ratio of the water component and temperature on the thickening of the CO₂ water based fracturing fluid were studied. The results of the study show that 2% AF-2 CO₂ and 2% AF-6 water based thickening agent can be used to thicken the liquid CO₂ and water, rendering them stable sand suspending ability. The two thickening agents can be used together in one fracturing fluid with no negative interactions. A CO₂ water based compound fracturing fluid at 30% or less water content and at temperatures less than 5 ℃ can be thickened fast, and has stable sand suspending ability. The fracturing fluid formulated was used successfully in field operations, with the highest sand content of 35%.

COMPLETION FLUID

Damage Preventative Completion Fluid for Sandstone Geothermal Reservoir

YANG Lili, WANG Shibo, ZHANG Yongwei, DING Jian, JIANG Guancheng

2023, 40(2): 265-271. doi: 10.12358/j.issn.1001-5620.2023.02.016

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Abstract:
The development and utilization of geothermal resources in China is at a rapid stage of development, with the development and utilization of geothermal resources in sandstone thermal reservoirs of medium and low temperatures as the main. However, during the development of geothermal resources, due to the special geological structure of loose sandstone thermal reservoir, during the drilling and completion process, the reservoir sand production is serious, and the drilling and completion fluid is easy to enter the reservoir to cause sensitivity damage, as well as the problem that the solid substances in the drilling and completion fluid block the reservoir and cause the reservoir permeability to drop. In order to solve the above problems, this study introduced the key treatment agents, such as bionic wall fixative, stealth acid PF-HTA and corrosion inhibitor, and optimized the dosage through experiments. Finally, the polymer film stealth acid completion fluid system was formed. Laboratory research shows that the completion fluid system has a large permeability recovery value after polluting the reservoir core, good compatibility with drilling fluid, little damage to the reservoir, and good reservoir protection effect.

The Inhibitive Performance and Mechanisms of a Compound Corrosion Inhibitor in Inhibiting P110 Steel in a High Temperature High Density Inorganic Salt Completion Fluid

ZOU Peng, ZHANG Shilin, HUANG Qi, YANG Jie, WANG Jian, WANG Zhifang, ZHANG Long

2023, 40(2): 272-278. doi: 10.12358/j.issn.1001-5620.2023.02.017

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Abstract:
A high density low-corrosion inorganic completion fluid was developed to try to satisfy the needs of developing petroleum from high temperature deep wells (bottom hole temperature > 160 ℃ and well depth > 5 000 m). These needs include formation pressure balancing, formation damage mitigation and corrosion inhibition. Corrosion of this completion fluid to the P110 steel was evaluated with a high temperature high pressure (HTHP) corrosion tester and weight-loss method at different temperatures (160 – 180 ℃), completion fluid densities (1.80 – 2.30 g/cm³) and corrosion inhibitor concentrations (1% – 5%). The study shows that the average rate of corrosion and the rate of pitting corrosion increase with temperature, and decrease with the concentration of the corrosion inhibitor. The corrosion inhibitor in the completion fluid has good corrosion inhibition effect. The dense film of the corrosion products on the surface of the P110 steel plate tested was observed using SEM. The mechanisms of corrosion inhibition of the corrosion inhibitor in the completion fluid were revealed through X-ray energy spectrometer (EDS) and X-ray photoelectron spectrometer (XPS). It was found that there were Fe₃O₄, Fe₂O₃ and an organic iron complex between the trivalent iron and the organic components of the corrosion inhibitor in the completion fluid formed on the surface of the P110 steel plate. The corrosion inhibitor not only takes part in the formation of the product film, it also accelerates the oxidation passivation of the iron, thereby synergistically achieving the inhibition of the corrosion to the P110 steel by the high density inorganic salt completion fluid at elevated temperatures. This high density low-corrosion inorganic salt completion fluid was tried on a well drilled in Wuwei county, Anhui province. The completion fluid not only balanced the formation pressure, it also mitigated the corrosion of the completion fluid to the completion string. This high density low-corrosion completion fluid has broad application prospect.

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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