2018 Vol. 35, No. 3

Display Method:
2018, 35(3)
Status Quo of the Development of Deep Water Drilling Fluids Worldwide
LUO Jiansheng, LI Zili, LUO Man, LI Huaike, LIU Gang, ZHAO Chunhua
2018, 35(3): 1-7. doi: 10.3969/j.issn.1001-5620.2018.03.001
In this paper the formation characteristics of the deep water areas in GOM, Brazil and West Africa are analyzed. Characteristics of the salt formation and technical challenges encountered in drilling operations are introduced with emphasis. Requirements on drilling fluid design for use in drilling the deep water salt formation and active mudstone are presented. The status quo of the development of deep water drilling fluids is summarized by introducing the deep water high performance water base drilling fluids and deep water synthetic base drilling fluids with constant rheological profile developed by different companies.
Progress in the Study of Environmentally Friendly Drilling Fluid Filtration Reducer
WU Xinlei, YAN Lili, WANG Lihui, WANG Fayun
2018, 35(3): 8-16. doi: 10.3969/j.issn.1001-5620.2018.03.002
The development of environmentally friendly high temperature drilling fluid filtration reducer is an important subject at present, because it plays a key role in dissolving environment pollution. This paper summarizes the progress made at home and abroad in the study of environmentally friendly drilling fluid filtration reducer, and introduces the raw materials used for the development of environmentally friendly drilling fluid filtration reducer and the properties of product, as well as the progress made at home in the modification of natural polymer filtration reducers such as starch, cellulose and lignin. Starch, cellulose and lignin, through chemical modification, have their thermal stability and salt tolerance enhanced, and are able to be used in high temperature well drilling. Presently in China, environmentally friendly filtration reducers have been used in well drilling at 150℃. Some environmentally friendly filtration reducers that work properly at temperatures up to 180℃, are still left unused. Monomers with molecular structures and functional groups (such as sulfonic acid group and lactam group) that can enhance the thermal stability of drilling fluid filtration reducers are sought through study on filtration reducers now available and analyses of the working mechanisms of these high temperature filtration reducers. This paper is expected to be of guidance and reference in the development of environmentally friendly filtration reducers, and to be helpful in accelerating the pace of the development.
Application of Ultra Fine Ilmenite Powder as Drilling Fluid Weighting Agent
WANG Qian, MA Zhaohua, YUAN Xuefang, XU Tongtai, ZHANG Hui, ZHANG Ruifang
2018, 35(3): 17-24. doi: 10.3969/j.issn.1001-5620.2018.03.003
Deep water well, extended reach well, HTHP well and well with narrow safe drilling window are imposing higher and more rigorous requirements on the performance of drilling fluids, especially those requirements such as the rheology, wall building property, settling stability and reservoir protection ability of high density and ultra-high density drilling fluids, which cannot be gained from conventional API barite. New weighting agents have to be found to satisfy the increasing needs of drilling wells with special challenges. Ultra-fine barite, fine manganese minerals and ultra-fine ilmenite are in recent years finding wider application in drilling fluids and have gained good reputation in field application. Relative literatures from both China and abroad have been studied to understand the characteristics of the ultra-fine ilmenite, the effects of ultra-fine ilmenite on the rheology, filtration property and settling stability of water base drilling fluid and oil base drilling fluid, as well as the use of ultra-fine ilmenite in high density and ultra-high density water base and oil base drilling fluids. It is concluded that the rheology of the water base and oil base drilling fluids is improved if ultra-fine ilmenite is used alone or with API barite as the weighting agent. Ultra-fine ilmenite has good acid solubility, and mud cakes of drilling fluids treated with ultra-fine ilmenite are much easier to remove. Ultra-fine ilmenite has better settling stability and poses low damage to reservoir rock permeability. By removing the hematite from ultra-fine ilmenite, the magnetism of ultra-fine ilmenite can be minimized. Although the hardness of ultra-fine ilmenite is higher than that of barite, the D90 of ilmenite is approximately 15 μm, meaning that ultra-fine ilmenite has abradability that is lower than that of API barite. Since ultra-fine ilmenite has narrow particle size distribution (D50≈5 μm), in drilling fluids of the same density, drilling fluid weighted with ultra-fine ilmenite has higher HTHP filtration rate. This can be resolved by adding acid soluble bridging particles with wide particle size distribution. Ultra-fine ilmenite as a whole is a prospective new drilling fluid weighting agent. Ultra-fine ilmenite has been used as weighting agent with great success in Arab Gulf and United Arab Emirates.
Development of and Study on a High Performance Synthetic Base Drilling Fluid
ZHAO Chunhua, LUO Jiansheng, XIA Xiaochun, SUN Qiang, GENG Tie, LIU Gang
2018, 35(3): 25-31. doi: 10.3969/j.issn.1001-5620.2018.03.004
A high performance synthetic drilling fluid has been developed to deal with narrow safe drilling window associated with high temperature high pressure wells. The synthetic base drilling fluid was formulated with three main additives:a new high temperature emulsifier which is resistant to high temperatures to 232℃, a high temperature filter loss reducer and a high temperature lipophilic clay, which were developed through molecular structure design and synthesis. Laboratory experimental results showed that the emulsifying capacity of the emulsifier was as high as 95%, and the emulsion formed with the emulsifier had droplets of evenly distributed sizes. The synergistic action among the filter loss reducer, the emulsifier and the lipophilic clay further improved the emulsion stability, HTHP rheology and filtration control property of the drilling fluid. Compared with conventional synthetic drilling fluids, this drilling fluid has those advantages such as low viscosity, low gel strength, good suspending capacity, superior high temperature stability and low HTHP filter loss. These advantages are helpful to resolving drilling problems associated with high structural strength of drilling fluid such as overpressure of pump during pumping and at startup, severe fluctuation of equivalent circulation density (ECD) resulting in lost circulation and wellbore collapse. The use of the new synthetic base drilling fluid has provided technical support for the safe operation of HTHP wells in petroleum exploration and development.
High Performance Water Base Drilling Fluid CQH-M2 and Its Application on Well Wei204H11-4
LIU Zheng, LI Juncai, LI Xuan, LI Maosen, HU Jing, FAN Jin
2018, 35(3): 32-36. doi: 10.3969/j.issn.1001-5620.2018.03.005
The Longmaxi shale in Chuanyu area is brittle, and is full of micro-fractures and vugs. Challenges encountered during drilling operations are borehole instability and pipe sticking resulted from borehole sloughing. In this paper, the technical difficulties in using the high performance water base drilling fluid CQH-M2 is analyzed and measures dealing with the difficulties are presented based on the geological characteristics of the Longmaxi shale. Additives, such as shale inhibitors, filter loss reducers, lubricants and plugging agents for CQH-M2 have been optimized through laboratory experiments. Laboratory experiments on the evaluation of these additives showed that the inhibitive capacity of CQH-M2 is better than that of another high performance drilling fluid CQH-M1, almost equivalent to oil base drilling fluid in inhibiting the hydration and dispersion of shale. CQH-M2 has good instant and long lasting plugging effect. Mud cakes of CQH-M2 are thin and tough, sealing off porous formations in a satisfactory manner. CQH-M2 is also resistant to the contamination caused by 9% cuttings. In field application, CQH-M2 high performance drilling fluid has satisfied the technical requirements for drilling the well Wei204H11-4. The drilling fluid performed very well during drilling and no downhole troubles have ever been encountered.
Enhancing Pressure Bearing Capacity of Formation to Control Mud Losses in Deep Shale Gas Drilling With Oil Base Drilling Fluids
2018, 35(3): 37-41. doi: 10.3969/j.issn.1001-5620.2018.03.006
With the advancement of shale gas drilling to deeper reservoirs, the density of drilling fluid has approached 1.75 g/cm3, and the density of cement slurry approached 1.85-1.89 g/cm3. To improve the quality of well cementing and prevent the losses of cement slurry, the pressure bearing capacity of the open hole to oil base drilling fluids should be improved. The application of an imported new lost circulation material (LCM) for use in oil base mud on the deep shale gas well Jiaoye-XX (a well drilled in the second phase of shale gas development in Fuling, Sichuan) showed that the oil base mud LCM is able to plug lost circulation zones while drilling, and imposes no negative effect on the rheology of the drilling fluid. The pressure bearing capacity of part of the lost circulation zones was enhanced, from pressure bearing capacity of 1.75 g/cm3 to 1.80 g/cm3. Finally, all the lost circulation zones had their pressure bearing capacity enhanced. Using the imported LCM and an oil base mud LCM T150 of independent intellectual property rights, the pressure bearing capacity of the formations prone to lost circulation was enhanced to 1.85 g/cm3. Study results showed that control of oil base mud losses with the two strongly LCMs is widely applicable and easy to operate. The two strongly lipophilic LCMs are a worth popularizing in controlling oil base mud losses.
Technology of Preventing and Controlling Mud Losses into the Permian Igneous Rocks in Shunbei Oilfield
PAN Jun, LI Daqi
2018, 35(3): 42-47. doi: 10.3969/j.issn.1001-5620.2018.03.007
Lost circulation is one of the main technical roadblocks to safe, fast and efficient drilling in Shunbei oilfield. Analysis of the field operation data concerning lost circulation showed that the Permian system in Shunbei oilfield is highly heterogeneous and full of fractures of different sizes and that are easy to propagate. Generally speaking, lost circulation in the north of the field is not as serious as that in the south of the oilfield. The mechanisms of the lost circulation are mainly caused by pressure differential in the Permian system. Fracture propagation, on the other hand, is a minor cause of lost circulation. A highly efficient plugging agent, SMGF-1, an LCM used while drilling is going on, was selected and added into the drilling fluid by 3%. Laboratory test with this LCM drilling fluid sample showed that the pressure bearing capacity of a sand-bed with 0.45-0.90 mm artificial fractures was 8.5 MPa, indicating that SMGF-1 is effective in controlling mud losses. Another high efficiency lost circulation material, SMKZD-1, an LCM used for controlling mud losses under pressure, was tested on a sand-bed with fractures of 1-3 mm, and the pressure bearing capacity was greater than 5 MPa, indicating that SMKZD-1 is a broad-spectrum high performance LCM. Field operations showed that the use of the two lost circulation materials improves the job quality of preventing and controlling mud losses into the Permian igneous rocks.
Study and Application of Supramolecule Chemical LCM Technology
WANG Yong, JIANG Guancheng, DU Qingfu, XUE Minsheng, YANG Ping, LIU Jianquan, LIU Yongfeng, LI Yingjin
2018, 35(3): 48-53. doi: 10.3969/j.issn.1001-5620.2018.03.008
A supramolecular chemical lost circulation material (LCM) has been prepared based on the supramolecular chemistry theory recently developed. This LCM can be used to control mud losses at different depths. It forms gels of different strengths and elasticity at different temperatures. Lost circulation control techniques have been developed for different rates of mud losses through laboratory experiments. Various problems have been encountered in mud loss control practices, for example, the LCM is unable to stay in mud loss zones, the LCM is easy to mix with water and is therefore diluted, it is difficult for the LCM to be retained and accumulate at the entrance of mud loss channels, and the mud loss channel is difficult to be blocked off, etc. LCM slurries formulated with the supramolecular chemical LCM form gel particles (particle sizes between 100 μm and 2,000 μm) of certain strengths in controllable time span. These elastic deformable gel particles are able to go into and plug formation fractures of 0.15 mm-1.5 mm in size. Fractured formations plugged with the supramolecular chemical LCM have pressure bearing capacity of at least 7.5 MPa. This LCM has been used on three wells (such as the well Ke-205) in Block Zhundong. Field practice showed that a combination of the supramolecular chemical LCM and conventional LCM can be used to control mud losses of different rates during drilling operations. No mud losses have been encountered again in mud loss zones plugged with the supramolecular chemical LCM slurry, indicating that the mud loss control performed was successful. The use of this supramolecular chemical LCM is helpful in reducing the overall drilling cost.
Study and Application of a Drilling Fluid Microemulsion Lubricant NE
DONG Bingqiang, QIU Zhengsong, DENG Zhi, ZHANG Hualian, KANG Yuanbo
2018, 35(3): 54-59. doi: 10.3969/j.issn.1001-5620.2018.03.009
Deficiencies have been found of the drilling fluid lubricants used presently, such as poor high temperature stability, complex preparation process, severe foaming and high level of fluorescence etc. These deficiencies have hindered drilling horizontal wells with longer horizontal displacement, and decreased drilling efficiency. A new micro emulsion lubricant, NE, has been developed with liquid paraffin, Span80 and Tween80 etc. based on the basic principle of colloid and interface chemistry. Laboratory study on the performance of NE showed that the nanophase liquid drops formed by the dispersed NE are positively charged, and the average diameter of the drops is between 187 nm and 258 nm. A bentonite slurry treated with 2.0% NE has its coefficient of friction reduced by 83.8%, and sticking coefficient of mud cake reduced by 74.2%. NE has good high temperature stability; it performs effectively at 160℃. NE has fluorescence level of 2 and is resistant to foaming. NE is compatible very well with drilling fluids. NE can firmly adsorb on the surfaces of minerals and metallic drilling tools through nano effect, thereby greatly enhance the lubricating efficiency of the drilling fluid. Field application has demonstrated that NE greatly reduced torque and friction of drilling tools and minimized the occurrence of pipe sticking, satisfying the lubricity requirement imposed on drilling fluid in horizontal drilling.
Study on Rheology of Consistent Rheology Water Base Drilling Fluid for Deep Water Drilling
GAO Han, XU Lin, XU Mingbiao, YOU Fuchang, LIU Weihong
2018, 35(3): 60-67. doi: 10.3969/j.issn.1001-5620.2018.03.010
Consistent rheology water base drilling fluid, rarely reported presently, is a new working fluid used for deep water drilling. The rheological behavior and the consistent rheology mechanisms were studied by measuring the properties and analyzing the rheological model of the consistent rheology drilling fluid under certain temperature and pressure. It is demonstrated that in pressure range between 0.1 MPa and 35.4 MPa, when temperature was raised from 4℃ to 65℃, the φ6, φ3 readings, yield point and plastic viscosity changed only slightly, which were 10-13, 9-12, 13-18 Pa and 15-22 mPa·s, respectively, and the φ6 and φ3 readings showed "U" type pattern with temperature. At changing temperature/pressure combination, the correlation coefficients of the fitted empirical rheological equations are:Bingham model ≈ Casson model ≈ Herschel-Bulkley model ≈ Robertson-Stiff model, of which the bi-parametric Casson model has the highest correlation coefficient and simple expression and is therefore suitable for use in describing the consistent rheological properties of water base drilling fluid. Introduction of parameters into the Casson's model gave birth to a kinetic rheological equation f(T, P, γ) with high precision of prediction; the average relative error is 7.19% ±4.07%, and the maximum deviation appears at 100 (r/min)/65℃. In this paper, the molecular conformation, molecular structure and association with clay platelets of the key additives are analyzed, and the qualitative structure-activity relationship assumption based on molecular conformation is presented to reveal the essence of the consistent rheology of water base drilling fluids.
Drilling Fluid Technology for Preventing Collapse of Carbargilite Formation in Changqing Gas Field
ZHANG Jianbin, JIA Jun, LIU Zhaoli
2018, 35(3): 68-73. doi: 10.3969/j.issn.1001-5620.2018.03.011
Wellbore collapse in the carbargilite section in Changqing gas field has resulted in frequent occurrence of downhole troubles and sidetracking. To resolve these problems, rock samples taken from the carbargilite formation were studied for the microstructure, cation exchange capacity, mineral composition and physiochemical property. The effect of drilling fluid on the mechanical characteristics and collapse pressure of the rock samples was tested, and the mechanisms in which the carbargilite formation collapses and ideas on which the drilling fluid technology for preventing carbargilite formation collapse was studied were determined. A high performance drilling fluid having strong plugging capacity and high inhibitive capacity was formulated through laboratory experiment. Plugging agents of different hardness and shale inhibitors selected, and nano-emulsion were used to render the drilling fluid properties required. The HTHP filter loss and API filter loss are ≤ 6 mL and ≤ 2 mL, respectively. Rate of sandstone (Shihezi formation) plugged by the drilling fluid is ≥ 85%. Rate of linear swelling of artificial rock cores is reduced by at least 60%. Field application of the drilling fluid on 18 wells in Changqing gas field showed that the percentage of sidetracking when drilling the carbargilite formation was reduced to 16.7%. Average drilling time was reduced by 30 d. The use of this drilling fluid has achieved the desired effect, and satisfied the needs of safely drilling the carbargilite formation in Changqing gas field.
Performance Optimization of a Water Base Drilling Fluid for Continental Shale Gas Drilling in Block Yanchang
WANG Bo, LI Wei, ZHANG Wenzhe, LI Hongmei, WANG Tao
2018, 35(3): 74-78. doi: 10.3969/j.issn.1001-5620.2018.03.012
Abundant shale gas resource has been found in Yanchang, and the exploration and development of the resource is in research stage. The geology of the shale gas reservoirs is complex, and borehole collapse in horizontal drilling has always been a problem. The use of oil base mud to control borehole wall collapse has resulted in environment protection and high cost issues. To address these problems, a water base drilling fluid, PSW-1, was developed for shale gas drilling. The PSW-1 drilling fluid was treated with 0.2% BOP (a polymer), 2.0% gelling agent TQ-1, and 2.0% lubricant ORH-1 to improve its carrying capacity and lubricity. The properties of the PSW-1 are:YP=10 Pa, Gel strengths=4.5 Pa/10 Pa, and friction coefficient=0.07. Field test of PSW-1 on 4 wells demonstrates that it was able to effectively suspend and carry drilled solids, and showed excellent lubricity. The filter loss of the drilling fluid was 2.0-2.8 mL. Percent hole enlargement was only 6.34%. Borehole wall collapse was avoided, and downhole safety was ensured. The successful use of PSW-1 has provided technical support to the development of continental shale gas in block Yanchang.
Drilling Fluid Technology for “Integrated” Wells in North Troyes Oilfield in Kazakhstan
JIAO Xiaoguang
2018, 35(3): 79-83. doi: 10.3969/j.issn.1001-5620.2018.03.013
The north Troyes oilfield (Kazakhstan) in recent years has been carrying out the "integrated" drilling mode which imposes new challenges to drilling fluid. To deal with the challenges, a saturated polymer sulfonate drilling fluid was formulated based on the analyses of geology of the formations and technical problems associated with drilling fluid operations in the north Troyes oilfield. The saturated drilling fluid was treated with two temporary plugging agents, ZD-1 and EP-1. ZD-1 is an acid soluble rigid particle, while EP-1 is an oil soluble deformable particle. The particle size distribution of ZD-1 and EP-1 is compatible with the sizes of pore throat in the reservoir. Test of the drilling fluid treated with 2% EP-1 and 3%ZD-1 on core samples showed that the permeability recovery of the cores was 89%, exceeding the predetermined target of 85% and satisfying the needs of drilling operations. This drilling fluid formulation was used on the first "integrated" well H817 in Kazakhstan, and the well was drilled to the designed depth successfully. Average percent hole enlargement of the well is less than 8% and the ROP is increased by 15.2%. The temporary plugging agents used are able to protect porous carbonate reservoir and reservoirs with micro-fractures from being damaged. Daily oil production rate of the well H817 is 110 t, which is 26.4% higher than the daily production rate of adjacent wells.
Analyses of the Cause of Casing Sticking in Well ZX105 and the Techniques of Freeing the Sticking
2018, 35(3): 84-88. doi: 10.3969/j.issn.1001-5620.2018.03.014
Well ZX105 is the first exploratory horizontal well drilled in Zhixinchang structure in western Sichuan. This well, targeted the lower Shaximiao formation, was designed to drill to measured depth of 3,726 m (TVD 2,506 m). The designed length of the horizontal section was 1,001 m. The casing for the second interval was run and got stuck at 2,847 m when running lift sub and casing hanger to move the casing string. It was believed, through analyses, that it was a pressure differential sticking, and deficiencies of the casing program was the main cause of the sticking. It was also believed that the depth at which the casing for the first interval was run was not enough, and the point at which the casing got stuck is 214 m into the horizontal section, the weight of the casing string in the upper section is not enough to push the casing inside the horizontal section to move forward. The high positive differential pressure at the bottom of the hole thus caused the casing string to get stuck. Based on the analyses, it was decided to lower the mud weight, soak the stuck point with pipe freeing solution, and pressurize the annular space. The stuck casing string finally got free with these measures. This is the first time the stuck pipe gets free in horizontal drilling in the west of Sichuan, and the practice has provided valuable experiences for the development of the target zone, the Lower Shaximiao formation in Zhongjian area, western Sichuan.
Study on Improving the Performance of Cement Slurry with Spherical Ultra-fine Mineral and the Application Thereof
ZHAO Qiyang, YAN Haibing, LI Meiping
2018, 35(3): 89-93,99. doi: 10.3969/j.issn.1001-5620.2018.03.015
Conventional ultra-fine minerals are used to improve the degree of density of cement powders. The use of these ultra-fine minerals, however, leads to increase in the amount of water required, and the results in enhancing the degree of density and compressive strength of the set cement are not as good as expected. To resolve these problems, a new spherical ultra-fine mineral was prepared using special ball milling technique. Improvement made to the packing of cement powders, rheology of cement slurry and compressive strength of set cement with the use of the spherical ultra-fine mineral was studied. It was found that use this new spherical ultra-fine mineral, close packing of cement powders can be realized, and the amount of water used to mix cement slurry remained almost unchanged. The mobility of the cement slurry reached 21 cm. The compressive strength of the set cement was increased by at least 15%. The percentage of poor volume in the set cement was less than 4%. These data show that the spherical ultra-fine mineral filled the pores in the set cement very well, and improved the pore structure of the set cement, remarkably enhancing the degree of density of the set cement. The cement slurry has density that is adjustable between 1.89 g/cm3 and 2.35 g/cm3, and has anti-channeling ability, low filtration rate and stable rheology. Good and obvious effects have been gained in using the spherical ultra-fine mineral on ultra-deep wells drilled in Chuanyu area.
Laboratory Study on a New Low Heat Cement
XING Xijin, WU Zhiqiang, GENG Ya'nan, HE Song
2018, 35(3): 94-99. doi: 10.3969/j.issn.1001-5620.2018.03.016
Shallow hydrate zones are often encountered in offshore deep drilling. Conventional low temperature cement releases quite large amount of heat which, during well cementing, will negatively affect the quality of well cementing because the heat released causes the hydrate zones to destabilize. A special low heat aluminophosphate cement has been prepared in laboratory, and is compounded with high belite sulphoaluminate cement and slug cement to form a new low heat cement-the APE cement. A low heat cement slurry suitable for cementing deep water wells with shallow hydrate zones is prepared by mixing the APE cement and cement additives of independent intellectual property, such as low temperature filter loss reducer, early strength agent and dispersant. The heat of hydration of this cement slurry at density between 1.40 g/cm3 and 1.60 g/cm3 is less than 200 J/g. Set cement aged at 10℃ for 24 h has compressive strength of 3.5 MPa. Filtration control of the cement slurry is less than 50 mL, better than that of the conventional cement slurries. φ300 reading of the cement slurry is less than 300. The new cement slurry has 3 d heat of hydration that is 58 J/g less than that of the conventional low heat cement slurries, and thickening time that is adjustable. Laboratory experiment shows that the new low heat cement slurry has, at low temperatures, low heat of hydration, high early strength, low filtration rate and good thickening property, and is able to satisfy the requirements for cementing deep water wells penetrating hydrate zones.
Evaluation and Application of a Pollution Resistant Spacer Fluid GLJ Converted from Active Mud
ZHOU Daisheng, LI Qian, ZHANG Qigen, WANG Wei, XIE Xiantiao
2018, 35(3): 100-104. doi: 10.3969/j.issn.1001-5620.2018.03.017
With the advance of high temperature deep well and ultra-deep well development in Sichuan and Chongqing, the compatibility of cement slurry for well cementing with drilling fluid, which is probable to cause cement slurry to become thickened and agglomerate, is becoming more and more protruding. A pollution resistant spacer, GLJ, is developed from active mud based on the work done on the analyses of and study on the contamination factors existed in the process of cement slurry-mud contact. Laboratory evaluation and field operations show that GLJ is easy to and convenient to formulate by just adding spacer agents into active mud, thereby reducing the amount of new liquid and weighting materials required and reducing the burden of field stocks. GLJ has good rheology and suspension stability; the rheological properties of GLJ can be adjusted based on the requirements of field operations. Good thermal stability of GLJ makes it possible for GLJ to stay a long time in the borehole without barite settlement. GLJ has excellent compatibility with cement slurry; mixed fluids with different ratios of components of the fluids have consistence that is less than 40 Bc after 240 min of HTHP thickening test. The spacer GLJ has minor effect on the properties of drilling fluids. The remained GLJ in mud tanks and the GLJ returned from the borehole can all be mixed with active mud for reuse, thereby minimizing the effort required for the discharge and treatment of waste fluids, which is of good economic benefits and social benefits.
Effect of Fracturing Fluid on the Migration of Methane in Shale with Nano-sized Fractures
WANG Haiyan, GUO Limei, XU Yun, LIU Ping, GUAN Baoshan, WU Jiaquan, XUE Yanping
2018, 35(3): 105-109. doi: 10.3969/j.issn.1001-5620.2018.03.018
Spatial fracture-network generated fracturing and the characteristics of shale itself produce large amount of nano-sized fractures in the shale. The effect of water retained in shale on desorption and migration of methane was studied through simulation, experiment and data from filed operations. Calculation with empirical equations showed that in nano-sized environment, methane fills the nano-sized fractures and is dissolved into water to form a water dissolved gas. Simulation with molecular dynamics showed that in nano-sized environment the degree of order of water molecules is increased, the hydrogen bond force between molecular chains is decreased. Low flow resistance in the nano-sized environment led to a coefficient of diffusion that was two orders of magnitude greater than that of the macro environment. When methane was dissolved in the water existed in nano-sized channels, the coefficient of diffusion of water molecules was two orders of magnitude greater than that of the water with no dissolved methane in nano-sized environment, and the hydrogen bond force was much lower. In this condition there is almost no flow resistance. Capillary penetration take place in shale formation drives water into nano-sized fractures, and is therefore adsorbed onto the surfaces of shale. The adsorption of water makes it difficult for the water to flow back, resulting in very low flowback efficiency. Water entering into shale competes with methane for adsorption onto the surfaces of shale and displaces methane, reducing the adsorption quantity of methane and is hence beneficial to increasing production rate. On the other hand, at low water saturation, some small amount of methane dissolved permanently in water. Data from adsorption-desorption experiment with active carbon with pre-absorbed water showed that, when the volume of water is equivalent to the pore adsorption quantity of methane on the surface of dry active carbon, and the amount of residue methane that is unable to desorb because of dissolution in water is 13.5% at most. In this condition there is almost no water flowback. All factors considered, the existence of water is beneficial to hydrocarbon production.
Study on Distribution of Low Density Proppants in Hydraulic Fracturing Operations and the Application Thereof
2018, 35(3): 110-113. doi: 10.3969/j.issn.1001-5620.2018.03.019
In hydraulic fracturing operations, the distribution of proppants in the fractures play an important role to the results of the stimulation job. Laboratory experiments have been conducted to study the distribution of settled sand bank of low density proppants in fresh water, in 0.08% HPG solution and 0.3% HPG solution, three solutions with different viscosity, at different flowrates (1, 2, 4 and 6 m3/h, respectively) and different sand/liquid ratios (5%, 10%, 15% and 20%, respectively). Calculating of the experimental data with linear fitting showed that the horizontal migration velocity of the proppants increases with flowrate of the liquid, contrary to the vertical migration speed of the proppants. A "fluctuation" phenomenon was observed during the settling of proppant. At low flowrate (less than or equal to 0.5 m/s) of the liquid at the opening of a fracture, the horizontal migration velocity of proppants is increasing fast. At high flowrate (greater than 0.5 m/s) of the liquid at the opening of a fracture, the increase of horizontal migration velocity of proppants is slow down. Field test have been done on three wells using low density proppants, the average open-flow capacity was 28.015×104 m3/d, 1.91 times of the flowrate of offset wells. The test results provide good guidance to hydraulic fracturing operations.
Lanthanide Series Metal Tracers: Development and Application in Sulige Area
CHANG Qing, LI Qingyi, ZHAO Peng, CAI Jingchao, CAO Susu, LI Shuang, ZHOU Xun, SHAO Shuai
2018, 35(3): 114-118,123. doi: 10.3969/j.issn.1001-5620.2018.03.020
16 tracers have been developed using lanthanide series metals, EDTA·2Na, DTPA and NaOH etc. The tracers were tested with ICP-AES for the detection limit of each element and the interference among the elements. It was concluded that the detection limits of the 16 tracers are between 10 mg/m3 and 80 mg/m3, and no interference was found among these elements. The tracers have been successfully used in the analysis of horizontal well fracturing in Sulige. The analysis was done by examining the relationship between the time required for the tracers to flow back and the concentration of the tracers, by introducing correction factor and by semiquantitatively calculating the volume of flowback fluid from each zone. It was found in the analysis that the seventh segment of the pay zone had the highest rate of flowback. The total amount of tracers flowed back from this segment, by data fitting, was about 49.875 g, and the volume of the flowback fluid was 145.16 m3.
The Detection of Bromide Tracer in Hydraulic Fracturing Flowback
LIU Guoliang, SU Huimin, LU Yongjun, ZHANG Fusheng
2018, 35(3): 119-123. doi: 10.3969/j.issn.1001-5620.2018.03.021
With increasing scale in reservoir fracturing, more rigorous requirement has been placed on chemical tracers and their detection whose sensitivity and accuracy are both affected by the addition of fracturing fluid additives. In laboratory studies, two simulated fracturing fluid samples formulated with HPGG and HPAM respectively, were detected for the bromide ions using phenol red spectrophotometry method, and the factors affecting the detection were also studied. Key factors affecting the detection, such as amount of phenol red and chloramine T, and time for the oxidation reaction were optimized based on the analysis of the measurement principles of the phenol red spectrophotometry. It is pointed out in the paper that for the bromide ions to be detected, it is critical that at pH between 4.7-5.7 (acidic), the equivalent number of phenol red should be greater than that of chloramine T, whose equivalent number should in turn be greater than that of the bromide ions. Working curves were calculated for the detection of bromide ions in two hydraulic fracturing flowback fluids with the phenol red spectrophotometry. Using the two working curves, concentrations of bromides up to 2-20 mg/L can be detected with linearly dependent coefficient not less than 99%. When detecting the bromide ions, the fracturing flowback fluids should first be filtered, ensuring that the operational conditions for the standard working curve of bromide ions are in agreement with the operational conditions under which the samples are detected, thereby to eliminate the effects of other complex components that may exist in the fracturing flowback fluids. This detection method is instructive in promoting the use of bromide tracers in fracturing fluids.
Study and Application of Well Test Fluid for HTHP Wells in Ying-Qiong Basin in South China Sea
YANG Yong, LUO Ming, WEI Anchao, HAN Cheng, LI Zhujun
2018, 35(3): 124-128. doi: 10.3969/j.issn.1001-5620.2018.03.022
Drilling fluids with good thermal stability, settling stability, CO2 contamination resistance and reservoir protection are required to drill wells in the Ying-Qiong Basin in South China Sea where high temperature, high pressure, CO2, and low porosity/low permeability prevail. Downhole troubles have been frequently encountered because of lack of special high temperature high pressure (HTHP) test fluid previously. In many years of study and field practices a set of HTHP test fluid technology has been developed by introducing a high temperature filter loss reducer Calovis into drill-in fluids used, increasing the pH value of the test fluid appropriately, controlling the MBT of the test fluids in a reasonable range, weighting the test fluids with ultra-fine barite, and enhancing the flowback properties of the test fluids. The test fluids have been successfully used on 2 HTHP exploratory wells in the Ying-Qiong Basin. One of the well had CO2 content of 23%, bottom hole temperature over 200℃, and the density of the test fluid used was 2.33 g/cm3. Perforation pressure and annular pressure were transmitted normally. After standing for 7 days, the packer was retrieved successfully, and the properties of the test fluid were not deteriorating. The tested production rate was higher than the expected production rate. All test tasks have been satisfactorily completed.