2022 Vol. 39, No. 5

Optimization of Hydrate Inhibition Performance of Deep Water Shallow Drilling Fluid
REN Guanlong, MENG Wenbo, HE Yufa, HUANG Liang, WANG Jintang
2022, 39(5): 529-537. doi: 10.12358/j.issn.1001-5620.2022.05.001
Abstract(663) HTML (258) PDF (3280KB)(84)
The deep water and shallow geological conditions are complex, the soil is loose, the operating pressure window is narrow, the submarine mud line temperature is low, and hydrates are easy to form in the well bore. The drilling fluid is faced with problems such as well bore stability, difficulty in regulating low-temperature rheology, environmental pollution and so on, so the drilling safety operation risk is high. Therefore, taking the shallow drilling of a deep water well in the South China Sea as the research object, the application status of deep-water shallow drilling fluid are summarized and analyzed, the ECD calculation model and well bore temperature field calculation model is established, and the well bore temperature field distribution and hydrate formation risk during deep-water shallow drilling is analyzed. The hydrate inhibition performance of shallow drilling fluid system is optimized in combination with numerical simulation and indoor experiments. The following research results are obtained. First, compared with the measured data, the average error of ECD calculation model and well bore temperature field calculation model for deep-water shallow drilling is less than 8%; Second, it is calculated that the range of hydrate formation area in the well bore gradually decreases with the increase of drilling depth, but there is still a risk of hydrate formation in the well bore during drilling preparation and early drilling; Third, the conventional semi preventive drilling fluid system is optimized as HEM+14%NaCl+6%KCl, which can meet the operation requirements during normal drilling. It is concluded that through the optimization of deep water shallow drilling fluid system, the addition of hydrate inhibitor can be reduced, the drilling fluid formula can be simplified, the drilling cost can be reduced, and the operation efficiency can be improved, which can provide guidance for the drilling fluid design of deep water oil and gas drilling.
Development and Performance Evaluation of High Temperature Salt Resistant Drilling Lubricant
WANG Zonglun, SUN Jinsheng, LIU Jingping, LYU Kaihe, SHAO Zihua, ZHANG Xianfa
2022, 39(5): 538-544. doi: 10.12358/j.issn.1001-5620.2022.05.002
Abstract(714) HTML (257) PDF (2741KB)(121)
Using boric acid, polyols and long-chain fatty acids, a high temperature salt resistant drilling lubricant SOB has been developed to deal with high torque high friction encountered in deep and ultra-deep well drilling. SOB has good lubricity at high temperatures and high salinities. A 5% base mud treated with 1% SOB has its friction coefficient reduced by 92.7%, and the adhesion coefficient of the mud cake produced by that mud is reduced to 0.0405, meaning that SOB has a sustainable lubricity under extreme pressure condition. Percent reduction of friction coefficient at 210 ℃ is generally 90.2%, percent reduction of friction coefficient of a mud containing 35%NaCl at 210 ℃ is generally 81.3%. At high temperature and high salinity conditions, SOB has good compatibility with other components of a high density drilling fluid. After aging at 200 ℃, the rheology of the drilling fluid was not affected, the mud filtration rate can be reduced, and the coefficient of friction of the mud was reduced by 45.09%, meaning that SOB has better lubricity than conventional drilling lubricants. The reason for this phenomenon is that SOB can be effectively adsorbed on the surfaces of the drill strings, forming a layer of film with strong hydrophobicity. The existence of this film changes the direct contact between the drill strings and the borehole wall to a contact between two films of the lubricant, thereby effectively reducing the friction therebetween.
Characteristic Study of Thermosensitive Shape Memory Lost Circulation Materials
FENG Jie, ZANG Xiaoyu, QIU Zhengsong, BAO Dan, ZHENG Lihui
2022, 39(5): 545-549. doi: 10.12358/j.issn.1001-5620.2022.05.003
Abstract(598) HTML (218) PDF (2294KB)(88)
In order to improve the self-adaptability and plugging efficiency of bridging materials and increase the success rate of plugging fractured formation, this paper develops a kind of thermosensitive shape memory lost circulation materials. By crushing and granulating, shape memory particles with different sizes were obtained. Evaluation experiments show that the mechanical properties and shape memory performance of thermosensitive shape memory lost circulation materials are preferable, and the particle size growth rate under high temperature activation is more than 55%. The simulation experiments of fracture plugging show that the temperature has a significant influence on the plugging effect, and the plugging effect of thermosensitive shape memory lost circulation materials is better than that of traditional bridging materials under high temperature. Building a set of formula of plugging fluid with strong self-adaptability, it can successfully plug 3-5 mm coexisting fractures, achieving adaptive and high-efficiency plugging.
Development of Paraffin Microemulsion and Its Application in Water-Based Drilling Fluids
SONG Hanxuan, YE Yan, ZHOU Zhishi, ZHANG Hanyu, ZHANG Qingwen, ZHOU Fujian, GUO Jixiang
2022, 39(5): 550-557. doi: 10.12358/j.issn.1001-5620.2022.05.004
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Analyses of seepage losses through micron and nanometer fractures and pores encountered in ultra-deep drilling in the southwest Tarim Basin show that the plugging agents in the potassium based polymer sulfonate drilling fluid are unable to effectively plug these fractures and pores. To improve the particle sizing for better plugging, a paraffin microemulsion was developed in laboratory. The optimum conditions for the development of the microemulsion was determined through particle size comparison method. It was found through experiment that the optimum quantity ratio of “S+A” : paraffin is 9:1, the optimum agitation speed is 1400 r/min, and the optimum reaction temperature is 120 ℃. The microemulsion thus prepared has D50 particle size of about 2.9 μm, monodisperse particle sizes between 200 nm and 300 nm, surface tension between 45.0 mN/m and 47.5 mN/m, and stable time up to 30 d. The potassium based polymer sulfonate drilling fluid was then optimized with the microemulsion, and good compatibility between them was seen after mixing. The optimized drilling fluid has its apparent viscosity reduced by 3.5 mPa·s, filtration rate reduced by 3.5 mL, thickness of mud cake reduced by 1 mm, and the filtration and wall building performance of the drilling fluid was enhanced. Evaluation of the plugging capacity of the paraffin microemulsion by pressure transmission methos shows that the paraffin microemulsion can be used to improve the pressure bearing capacity of the formation; test of the paraffin microemulsion on plugging the Keziluoyi dense sandstone shows that 58.4% of the microfractures and pores were plugged, indicating that the paraffin microemulsion has good plugging capacity
A Synthetic Based Drilling Fluid with Strong Plugging Capacity for Block Wushi17-2
MA Lei, YUAN Xueqiang, ZHANG Wandong, CAO Feng, DENG Wenbiao, ZHANG Xuefei, YANG Lili
2022, 39(5): 558-564. doi: 10.12358/j.issn.1001-5620.2022.05.005
Abstract(569) HTML (232) PDF (2635KB)(69)
The block Wushi17-2 is an important part of the Nanhai West Oilfield and has significant exploration and development prospects. However, there are severe potential downhole problems encountered during drilling operations, such as borehole wall instability, mud losses and formation damage, has imposed serious challenges to the properties of drilling fluids. Since this block is located nearby a national nature reserve, the environmental friendly performance of drilling fluids remains a great challenging. To deal with these problems, this study proposes the research idea of formulating high performance synthetic based drilling fluid with gas-to-liquid (GTL), followed by optimizing with a primary emulsifier, a secondary emulsifier and a high efficiency plugging agent OSD-2, eventually formulating a synthetic based drilling fluid with a density of 1.5 g/cm3, a temperature resistance of 150 ℃, a high temperature high pressure filtration rate of less than 5 mL and an electric stability of greater than 400 V. The synthetic based drilling fluid has excellent rheology, lubricity, inhibitive capacity and resistance to clay contamination (resistant to contamination of 10% poor-quality clay). The synthetic based drilling fluid satisfied the demands of field operation and helped to solve drilling fluid-related problems during drilling process.
Development and Application of a Protective Agent for Tight Oil and Gas Reservoirs
LI Xintong, ZHENG Wenwu, LIU Fu, SUN Zhongwei, WANG Song
2022, 39(5): 565-572. doi: 10.12358/j.issn.1001-5620.2022.05.006
Abstract(558) HTML (216) PDF (2689KB)(60)
In developing the Benbutu oilfield in Xinjiang, hole size irregularities were often encountered in the water- and hydrocarbon-containing sections, and these greatly affect the quality of the cementing job and damage the reservoirs. To protect the oil and gas reservoirs in the Benbutu oilfield, an elastic polymer microsphere NWL was developed through soap-free emulsion polymerization and was characterized. A reservoir protective agent CBJ was formulated with NWL, a selected anti water-block agent, a kind of rigid acid soluble nanometer particles (CaCO3) and a petroleum resin in a certain quantity ratio. Laboratory experiment was conducted to evaluate CBL in the aspects such as: the compatibility of CBL with the sizes of formation fractures, the acid solubility and oil solubility of CBL, the compatibility of CBL with the drilling fluids presently used, and the reservoir protection performance of CBL. CBL was also tested in field operations. CBL has the particle size distribution that is suitable for plugging formation fractures, good acid solubility and oil solubility. Drilling fluids treated with CBL have filtration rate reduced by about 20%, and percent permeability recovery by more than 80%. Field application and laboratory study show that CBL has good reservoir protection effect, it can be used to protect the reservoirs of Benbutu oilfield in accordance with the local conditions and maximize the production of oil wells.
Borehole Wall Strengthening with Micron and Nano Materials in “Dabadong” Area of Changning
SHE Chaoyi, LI Bo, DAI Feng, XIAO Xinyu, WEN Qianbin
2022, 39(5): 573-578. doi: 10.12358/j.issn.1001-5620.2022.05.007
Abstract(510) HTML (232) PDF (2582KB)(62)
The Longmaxi formation in Changning is highly developed with microfractures because of the tectonic action in the “Dabadong” area and the formation rock components. The sizes of the primary pores are distributed in a range of 0.05-2 μm. The formation stability is very poor and overpull and resistance have been frequently encountered during drilling. Increase in mud weight only cannot control wellbore instability. The drilling fluids presently in use only contain micron-sized plugging agents and are unable to effectively plug the nanometer pores. The lack of nanometer plugging agents cannot help form low permeability plugging layers to hinder the transmission of borehole pressure into the formations. By introducing a nanometer graphene plugging agent, the drilling fluid has both micron-sized and nano-sized plugging agents. Furthermore, the mud weight was determined through geomechanics model. With all these technologies and mud property control, the borehole wall was strengthened. Application of the borehole wall strengthening technology in the well Ning-209H69 showed that the properties of the drilling fluid were stable, no downhole troubles were encountered in the whole drilling process, the average percent hole enlargement was less than 8%, and the borehole wall collapse was effectively eliminated.
Study on Mechanisms of a Highly Adsorptive Polyol Ester Bonded Lubricant for Water Based Drilling Fluids
TAO Huaizhi, MING Xiansen, MA Guangchang, YANG Xukun, JIANG Guancheng
2022, 39(5): 579-586. doi: 10.12358/j.issn.1001-5620.2022.05.008
Abstract(594) HTML (246) PDF (5292KB)(71)
Common lubricants used in water based drilling fluids have weak adsorption on the friction interfaces of metals, and therefore are difficult to form dense and shear-resistant lubricating films thereon, which leads to high friction and torque during drilling. High friction and torque generally result in pipe sticking and high overpull or resistance during tripping of drill string. To improve the adsorption of drilling fluid lubricants on the surfaces of drilling tools, a polyol ester bonded lubricant was developed with a polyol and a long-chain fatty acid through dehydration condensation reaction. This new lubricant worked better in extreme pressure friction test, filter cake adhesion test and “point-to-point” friction test than similar products both from China and abroad. It can be used at temperatures up to 150 ℃. The working mechanisms of the lubricant were studied through four-ball friction test, SEM observation and X-ray photoelectron spectroscopy etc. It was concluded that the polyhydroxy structure of the lubricant can form bonded adsorption on the surface of Fe, which is stronger than the general physical adsorption, it thus can form a dense and shear-resistant lubricating film, having a thickness of about 45 nm, on the surfaces of drilling tools. The lubricant can also be adsorbed onto the surfaces of barite particles, thereby reducing the internal friction of a drilling fluid.
The Synthesis and Evaluation of a Pentaerythritol-Based Hyperbranched Polymer Filter Loss Reducer
SONG Yongtao, ZHOU Feng, YU Weichu, ZHANG Ying, SHU Wenming
2022, 39(5): 587-595. doi: 10.12358/j.issn.1001-5620.2022.05.009
Abstract(580) HTML (230) PDF (2926KB)(77)
Filter loss reducers presently in use have some deficiencies such as great negative impact on mud rheology, poor high temperature resistance and poor salt contamination resistance etc. To overcome these deficiencies, a pentaerythritol-based hyperbranched polymer filter loss reducer PPAAN-1 was developed through radical polymerization with tetraallyl ether (PPTE, a polyene monomer with pentaerythritol as its core molecular structure), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), N-vinyl pyrrolidone (NVP) and acrylamide (AM) as raw material. Based on orthogonal experiment results, the effects of the concentration of the tetraallyl ether on the apparent viscosity of the filter loss reducer PPAAN-1 was also studied. The optimum synthesis condition of PPAAN-1 was finally determined as follows: concentration of PPTE = 17%, AMPS∶AM∶NVP = 2 ∶6∶1, reaction temperature=55 ℃, initiator (AIBN) concentration = 0.2%. In laboratory evaluation, the properties of PPAAN-1 were compared with Driscal and DrisTemp. PPAAN-1 has little effect on mud rheology, good thermal stability and good filtration control capacity. The thermal decomposition temperature of PPAAN-1 is 302.29 ℃. A 30% NaCl drilling fluid treated with 1% PPAAN-1 had API filtration rate (220 ℃) of 9.8 mL and HTHP (150 ℃) filtration rate of 18.5 mL. In high temperature high salinity conditions, PPAAN-1 can form a network structure and adsorb on the surfaces of the clay particles, thereby widening the range of the particle size distribution of clays in a drilling fluid, helping the drilling fluid form dense mud cakes, and reducing the filtration rate of the drilling fluid.
Friction reduction of oleamide lubricants on iron surface
ZHANG Shuncong, DAI Yao, XU Hao, WANG Jiqian, LU Fuwei, LIU Guiying
2022, 39(5): 596-600. doi: 10.12358/j.issn.1001-5620.2022.05.010
Abstract(614) HTML (238) PDF (4773KB)(62)
The adsorption and lubrication properties of four surfactants on the iron surface based on molecular simulation was investigated. Surfactants include oleamide, oleic acid diethylenetriamine, oleic acid triethylenetetramine, and oleic acid tetraethylenepentamine. Results of adsorption simulation showed that the adsorption energies enlarged with the increase of nitrogen atom content. The adsorption energy of oleic acid tetraethylenetetetramine molecule on the iron surface was −1512.4679 KJ·mol−1, which was higher than other three amides. Results of shear dynamics simulation showed that the nitrogen atoms of four surfactants were concentrated on the iron surface. With higher nitrogen content, oleic acid tetraethylenepentamine adsorbed on the shear surface preferentially. On this surface, the nitrogen atom was about 1.6 times the density of the fixed surface. Results of four-ball friction experiment showed that the friction coefficient and the wear scar radius decreased as the nitrogen atom content increased. The friction coefficient of oleic acid tetraethylenepentamine was 0.004,36, which was 1/2 of oleamide. The wear scar radius of oleic acid tetraethylenepentamine was 241.7 μm, which was smaller than other three amides. Results of molecule simulation and experimental showed that the oleamide surfactant has better lubrication effect on the iron surface as the atom content of nitrogen in the molecule increase.
High Temperature High Density Cement Slurry with Corrosion Inhibition Property
CHEN Rongyao, SONG Jianjian, WU Zhongtao, SHI Ligang, ZHAO Jun, WANG Xuechun, LIU Shikang
2022, 39(5): 601-607. doi: 10.12358/j.issn.1001-5620.2022.05.011
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CO2 gas in the deeper part of a high temperature high pressure well generally causes corrosion to the set cement and damages the sealing integrity of the cement sheath. To develop a high temperature high density cement slurry with high corrosion inhibitive capacity, studies were conducted on the key cement materials, and a high temperature high density cement slurry with high corrosion inhibitive capacity was formulated. Analyses of the performance and micro morphology of the cement slurry show that manganese ore powder weighting material can remarkably increase the density of a cement slurry, and the cement slurry also has good corrosion inhibition property at high temperature. In formulating the cement slurry, a filter loss reducer JS18L was used to control high temperature filtration rate, and a cement retarder H16L was used to control thickening time. The corrosion inhibitive capacity of the cement slurry was improved with the use of an inorganic corrosion inhibitor NAM-H and an organic corrosion inhibitor SZ-M2. Using these materials, a high temperature high density (1.90-2.20 g/cm3) cement slurry was formulated. The new cement slurry has good rheology, good stability, low filter loss of less than 50 mL and thickening time adjustable between 3 h and 5 h. The high density set cement at high temperatures has stable mechanical properties and good corrosion inhibitive capacity. The deterioration rate of the 30 d compressive strength of the set cement is less than 25%, and the depth of corrosion is less than 1.5 mm. The results of the study provide technical support to the cementing of high temperature high pressure wells with acid gases and CO2 geological sequestration wells.
Well Cementing with Low Friction Pressure Resistant Leaking Preventive Low Density Cement Slurry
WANG Ding, WAN Xiangchen, YANG Chen
2022, 39(5): 608-614. doi: 10.12358/j.issn.1001-5620.2022.05.012
Abstract(505) HTML (216) PDF (2249KB)(51)
In the Sulige gas field in Changqing Oilfield, the Liujiagou formation is a low pressure formation, the low density cement slurries presently used in this area have poor pressure resistance; the cement slurries under high pressures will have their density increased and rheology deteriorated. In field operations with these cement slurries, the operation pressures were high, generally causing the cement slurries to be lost into the formations, and the cementing quality is poor because of less cement slurries in the annulus. To solve this problem, a new cement slurry with low friction low density was formulated. This new cement slurry is pressure resistant and has the property of preventing itself from being lost into formations. Using the close packing theory, particles of 4 sizes were selected. A light material with excellent pressure resistance and other appropriate additives were selected to formulate the target cement slurry. The density of the new cement slurry is adjustable between 1.25 g/cm3 and 1.35 g/cm3, the Fanning friction coefficient was reduced by about 50%. The new cement slurry has good pressure resistance and leaking preventive property. Study on the agitation and mixing techniques shows that mechanical agitation and mixing can be used, 99% of the properties of the bulk sample and those of the small sample coincide with each other, ensuring the qualification and efficiency of the cement mixing. In field operations in the Sulige gas field, four wells were cemented with success, no loss of cement slurry has ever happened, and the cementing job was qualified. During the cementing, the operational pressure was significantly reduced, and the job quality was obviously improved. This laboratory study and the field application provide a strong technical support to cementing wells penetrating low pressure formations into which cement slurries are easily lost.
Development of New Oil Well Cement Retarder
LIU Jian, ZHANG Zeyu, WEI Haoguang, WANG Mu, ZHOU Shiming
2022, 39(5): 615-621. doi: 10.12358/j.issn.1001-5620.2022.05.013
Abstract(537) HTML (205) PDF (2781KB)(47)
In cementing a long open section well with big temperature differences, overtreatment or inadequate treatment of the cement slurry with retarders at high temperature high pressure will cause the thickening time of the cement slurry to shorten or change irregularly. After the cementing job, the retarding of the top of a long cementing section will cause gas channeling and failure of the sealing integrity of the cement sheath. Through optimized orthogonal experiment, a high temperature organic retarder was developed. By hybridizing an organic material and an inorganic material, and designing a layered structure, the organic material can be intercalated into or bonded with the surfaces of the inorganic material. The cement slurry in the cementing operation will experience a low temperature – high temperature – low temperature process, during which the spacing between the layers of the inorganic material will change with the process. At low temperatures, the inorganic material will dominate the strengthening action, while at high temperatures, the organic material dominates the retarding action. Two inorganic strengthening materials, one is a layered graphene, and the other a double electron layered hydrotalcite, were selected for developing two kinds of new oil well cement retarders. The graphene retarder has good adaptability, it is stable at 150 ℃, and its 72 h strength at 110 ℃ temperature difference is greater than 7 MPa. The double electron layered hydrotalcite is also stable at 150 ℃. Cement slurries treated with the hydrotalcite retarder have rheology that is easy to adjust, and the initial strength develops fast, but the late strength development is not as good as that of the graphene retarder. These retarders can be produced with simple techniques, the raw materials are easy to obtain, and therefore, will have broad promotion and application prospects.
A Medium-Low Temperature Epoxy Based Workover Fluid
LING Yong, MA Ruran, LYU Ze, LIU Shi, LIU Wenming, YU Jingyu, GUO Jintang
2022, 39(5): 622-628. doi: 10.12358/j.issn.1001-5620.2022.05.014
Abstract(542) HTML (217) PDF (2719KB)(45)
Presently the consumption of oil and natural gas has increased sharply, while the development of conventional oil and gas is reducing, this makes the development of unconventional oil and gas, such as oil and gas from deep wells, offshore wells and shale gas wells more and more imminent. In the development of unconventional oil and gas, the sealing integrity of cement sheath may probably be damaged, leading to oil and gas channeling in the annulus which imposes great hindrances and risks to oil and gas production and causes great economic losses. Epoxy based workover fluid can be used to replace cement slurry in workover job to solve the problem of inability of cement slurries to penetrate micro pores. Epoxy based workover fluids have many compositions and poor adaptability. To simultaneously satisfy the needs of workover operation in different formations with different temperatures, facilitate the transportation, storage and deployment of field operation, and improve the economy of workover and promote the industrialization process, a workover fluid was developed with liquid aromatic amine (LAA) as the main curing agent. The performance of the workover fluid was evaluated, the thickening performance and the kinetics of the workover fluid, and the compressive strength and micromorphology of the set product were characterized. The results show that the LAA system has initial consistency of less than 30 Bc, thickening time that is adjustable between 2 h and 5 h, compressive strength that is greater than 20 MPa at various temperatures, and it is able to satisfy the needs of workover operation at temperatures between 30 ℃ and 90 ℃.
Proppant Migration in Fracture Fractured with Supercritical CO2 Fracturing Fluid
GUO Xing, SUN Xiao, MU Jingfu, QIAO Hongjun, LUO Pan, LI Heng
2022, 39(5): 629-637. doi: 10.12358/j.issn.1001-5620.2022.05.015
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In order to optimize the supercritical CO2 fracturing technology and construction parameters, considering the interaction between proppant particles in supercritical CO2 Fracturing Fluid, the multiphase particle grid method in Euler Lagrange method is used to establish the mathematical model of CO2 fracturing proppant migration. The accuracy of the model is verified by indoor hydraulic fracturing proppant migration model experiment, and the supercritical CO2 fracturing proppant migration law is calculated and analyzed. Research shows: Due to the low viscosity of non tackifying CO2, the sand carrying effect is very poor, and the optimization of other parameters has little effect on the sand carrying effect; When the viscosity of CO2 increases to 2.5 mPa·s, the sand carrying effect can be effectively improved. The combination of ultra-light proppant and fine particles has little difference between the sand carrying effect and the viscosity increasing to 10 mPa·s; Optimizing the density ratio of proppant to size can improve the sand carrying effect more obviously; Increasing the displacement can improve the sand carrying effect, but if the displacement continues to increase, the sand carrying effect changes little; Fluid filtration has little effect on CO2 sand-carrying effect. This study provides technical support for solving the problem of poor sand carrying performance of CO2, and has important guiding significance for supercritical CO2 fracturing design optimization and field construction.
Study on Viscoelastic Sand-carrying Mechanism and Imbibition Performance of Nano Variable-viscosity Slickwater
LIU Hanbin, BAI Hao, TANG Meirong, LYU Baoqiang, HAN Chuanghui, WANG Wenzhong, ZHOU Fujian, YAO Erdong
2022, 39(5): 638-645. doi: 10.12358/j.issn.1001-5620.2022.05.016
Abstract(483) HTML (233) PDF (2754KB)(48)
As a new fracturing fluid system with good sand-carrying performance and imbibition displacement, nano variable-viscosity slickwater has been successfully applied to shale oil volume fracturing in Changqing Oilfield. The field test results show that it has good sand-carrying performance and stimulation effect. Under the condition of 40 % sand ratio, the pressure of sand adding process is stable, and the daily oil production of a single well can reach 11.31 tons after fracturing construction, but its sand-carrying mechanism and imbibition performance are not clear. In this paper, the laboratory experimental study on the field concentration of nano variable-viscosity slickwater and the conventional EM30S crosslinkable slickwater system is carried out. Through the experimental methods of dynamic sand-carrying migration, transmission electron microscope (TEM), rheological property evaluation, and pressurized imbibition under the condition of reservoir temperature and pressure, the sand-carrying mechanism of nano variable-viscosity slickwater is revealed and its imbibition performance is evaluated. The experimental results show that the intersection value of elastic modulus and viscous modulus of slickwater reflects the sand-carrying capacity of slickwater solution. The smaller the intersection value is, the stronger the elastic sand-carrying capacity is; Under the same viscosity, the intersection value of viscoelastic modulus of nano variable-viscosity slickwater CNI system is only 0.0741 Hz, which is far lower than 0.181 Hz of field slickwater EM30S, resulting in its static and dynamic elastic sand-carrying performance much higher than EM30S; TEM results show that the strengthening association structure between nano emulsion and variable-viscosity slickwater is the main reason for the enhancement of elastic sand-carrying performance of slickwater. In addition, the results of pressure imbibition experiment show that the nano variable-viscosity slickwater has good imbibition displacement performance, and can replace the crude oil in the nano pores of shale, and the overall recovery can reach 36%. Among them, the order of recovery efficiency of different pore types is: mesopore > micropore > macropore.
Method of Predicting Flow Conductivity of Long-Term Acid-Etched Fractures in Carbonate Reservoirs in Shunbei Oilfield
LI Chunyue, LI Qin, LI Deming, WU Xia
2022, 39(5): 646-653. doi: 10.12358/j.issn.1001-5620.2022.05.017
Abstract(961) HTML (218) PDF (3198KB)(27)
Acid fracturing has been performed with difficulties in the high temperature high pressure carbonate rock hydrocarbon reservoirs in the Shunbei block. The main problem is the dramatic reduction of the effect of acid fracturing resulted from the losses of the flow conductivity of the acid-etched fractures under the long-term action of the closure stresses. In laboratory experiment, the flow conductivity of acid-etched fractures is evaluated to study the changing patterns of the flow conductivity of the acid-etched fractures under different mass fractions of acid, temperatures and closure time. Based on the equations of the flow conductivity of acid-etched fractures under various conditions, a method for predicting the conductivity of long-term acid-etched fractures in Shunbei carbonate reservoir is established and verified. Use this method, the changing pattern of the flow conductivity of the acid-etched fractures at different lengths of time and flow rates is simulated. The simulation results show that at low closure stresses, the reaction rate of the acid is the dominant factor affecting the flow conductivity of the acid-etched fractures. At high closure stresses, however, the dominant factors affecting the flow conductivity of the acid-etched fractures include closure stress, rock characteristics and the nonuniformity of the rock surfaces. The closure stress, on the other hand, is the dominant factor controlling the deformation of the surfaces of the rocks and is also the decisive factor affecting the flow conductivity of the long-term acid-etched fractures. Under long-term action of closure stress, the flow conductivity of a fracture at the deep part of the fracture is decreased in an amplitude larger than the decrease in the flow conductivity of the fracture at its mouth. The distribution of the flow conductivity of artificial fractures produced under mid-term and long-term acid-etching is controlled by the rate of reaction between the acid and the rock.
Study on Workover Fluid Suitable for High Temperature, High Pressure and Low Permeability Reservoirs in Offshore Gas Field
LIANG Yukai, LUO Gang, ZHOU Yuxia, SONG Jifeng, ZHENG Huaan, REN Kunfeng, LIN Kexiong
2022, 39(5): 654-660. doi: 10.12358/j.issn.1001-5620.2022.05.018
Abstract(422) HTML (216) PDF (2327KB)(36)
In view of the problems that workover fluid is easy to cause pollution damage to reservoir and serious corrosion to downhole pipe string during workover operation in a high-temperature, high-pressure and low-permeability gas field on the sea, the laboratory is based on soluble composite salt weighting material HGBZ, combined with high-temperature corrosion inhibitor HSJ-S, temperature and salt resistant waterproof agent HAD-2 and high-temperature bonding agent HJH-2, A set of dual maintenance high temperature and high density workover fluid system suitable for offshore high temperature, high pressure and low permeability gas fields is developed, and its comprehensive performance is evaluated. The results show that the basic performance of the workover fluid system is good, and the density is adjustable between 1.03-1.80 g/cm3; Workover fluid has good anti-corrosion effect, and the corrosion rate of downhole equipment steel is less than 0.076 mm/a; The workover fluid has a good anti swelling effect on clay minerals in the reservoir section of the target gas field, and the anti-swelling rate can reach more than 95%; Workover fluid has good compatibility with formation water in reservoir section and will not produce crystallization precipitation, etc; Workover fluid system can effectively reduce the self-absorption water of natural core, and the permeability recovery value of natural core polluted by workover fluid can reach more than 90% under high temperature for a long time, which has good reservoir protection effect. Well X uses the dual protection high temperature and high density workover fluid system, the workover process is smooth, there is no downhole complex accident, and the productivity recovery rate is high after workover, indicating that the dual protection high temperature and high density workover fluid system studied can meet the workover requirements of offshore high temperature, high pressure and low permeability gas fields.