2022 Vol. 42 No. 4
Abstract：
Nanwu Sag of the South Yellow Sea Basin is one of the most favorable hydrocarbon accumulation areas in the Mesozoic-Cenozoic Basin in the South Yellow Sea, with good exploration potential. However, due to its complex structural characteristics, no breakthrough has been achieved in oil and gas exploration. Using the latest 3D seismic and drilling data, this paper analyzes the structural characteristics of Nanwu Sag on the basis of fine structural interpretation. It is concluded that Nanwu Sag has experienced two major stages of tectonic evolution, fault depression and depression, with two stages and three groups of normal faults. Under the control of faults, three local structural belts are developed, mainly composed of fault nose and fault block traps. The hydrocarbon accumulation in Nanwu Sag has the characteristics of near-source and near-fault accumulation, and the development of deep and large faults is the key factor for hydrocarbon transport. Through the study, the structural characteristics and key factors of accumulation in Nanwu Sag are summarized, and it is proposed that the northern slope belt has deep and large faults, and good trap conditions, which is a favorable exploration zone.The study has reference significance for the exploration work of Nanwu Sag.
Nanwu Sag of the South Yellow Sea Basin is one of the most favorable hydrocarbon accumulation areas in the Mesozoic-Cenozoic Basin in the South Yellow Sea, with good exploration potential. However, due to its complex structural characteristics, no breakthrough has been achieved in oil and gas exploration. Using the latest 3D seismic and drilling data, this paper analyzes the structural characteristics of Nanwu Sag on the basis of fine structural interpretation. It is concluded that Nanwu Sag has experienced two major stages of tectonic evolution, fault depression and depression, with two stages and three groups of normal faults. Under the control of faults, three local structural belts are developed, mainly composed of fault nose and fault block traps. The hydrocarbon accumulation in Nanwu Sag has the characteristics of near-source and near-fault accumulation, and the development of deep and large faults is the key factor for hydrocarbon transport. Through the study, the structural characteristics and key factors of accumulation in Nanwu Sag are summarized, and it is proposed that the northern slope belt has deep and large faults, and good trap conditions, which is a favorable exploration zone.The study has reference significance for the exploration work of Nanwu Sag.
2022, 42(4): 7-16, 35.
DOI: 10.3969/j.issn.1008-2336.2022.04.007
Abstract：
Drilling reveals that hydrocarbon enrichment in different fault blocks and horizons of Weixi exploration area W structure is obviously different, but the controlling factors are unknown. In order to clarify the controlling factors of the differential enrichment of hydrocarbon in this structure, the key accumulation factors of different fault blocks were studied and compared in detail. On the premise of clarifying the oil source and accumulation period, the control action of migration system and preservation conditions on differential enrichment was studied. The results show that hydrocarbons of W structure have the same source and the same petroleum accumulation period which is after the Middle Miocene. The differential enrichment of hydrocarbon is mainly controlled by oil and gas dredging and fault sealing. W3Ⅱand W3Ⅲ sand groups are the advantage sandstone conductive layers under the regional mudstone cap rock, which is the premise of hydrocarbon enrichment. The relationship between the dominant sandstone carrier layer and the oil source fault and the distribution of the regional cap rock are the main controlling factors of the differential enrichment of oil and gas on the plane. The development degree of the direct cap rock is the main controlling factor of the differential enrichment of oil and gas along the fault in the vertical direction. The research results have reference significance for the next hydrocarbon exploration in W structure of Weixi exploratory area.
Drilling reveals that hydrocarbon enrichment in different fault blocks and horizons of Weixi exploration area W structure is obviously different, but the controlling factors are unknown. In order to clarify the controlling factors of the differential enrichment of hydrocarbon in this structure, the key accumulation factors of different fault blocks were studied and compared in detail. On the premise of clarifying the oil source and accumulation period, the control action of migration system and preservation conditions on differential enrichment was studied. The results show that hydrocarbons of W structure have the same source and the same petroleum accumulation period which is after the Middle Miocene. The differential enrichment of hydrocarbon is mainly controlled by oil and gas dredging and fault sealing. W3Ⅱand W3Ⅲ sand groups are the advantage sandstone conductive layers under the regional mudstone cap rock, which is the premise of hydrocarbon enrichment. The relationship between the dominant sandstone carrier layer and the oil source fault and the distribution of the regional cap rock are the main controlling factors of the differential enrichment of oil and gas on the plane. The development degree of the direct cap rock is the main controlling factor of the differential enrichment of oil and gas along the fault in the vertical direction. The research results have reference significance for the next hydrocarbon exploration in W structure of Weixi exploratory area.
Abstract：
There are huge reserves of low permeability oil and gas resources in the deep strata of East China Sea. Restricted by the physical properties of the reservoir itself and the impact of well drilling and completion, the protection effect of some gas wells is not ideal. Based on the low permeability reservoir core data of a gas well in East China Sea, the laboratory evolution experiments of wettability, nonlinear seepage, nuclear magnetic resonance and drilling fluid damage are carried out, and the basic characteristics and seepage law of low permeability reservoirs are revealed, and the availability of such reservoirs is evaluated. Combined with the drilling and completion of the well, the influencing factors of the low permeability reservoir pollution of the gas well are further analyzed. The study shows that the low permeability reservoir rock of this gas well is hydrophilic and the pore throat is small, so it is not easy to release the water lock after it occurs. The characteristics of nonlinear seepage are obvious under low pressure gradient. The percentage of movable fluid in the reservoir below 10×10−3 μm2 is less than 57.86%, which belongs to the third class of reservoirs, and is hard to mobilize. Compared with the soaking time, the damage of drilling pressure differential is greater. Thus the drilling pressure difference should be controlled within 3.5 MPa as far as possible.
There are huge reserves of low permeability oil and gas resources in the deep strata of East China Sea. Restricted by the physical properties of the reservoir itself and the impact of well drilling and completion, the protection effect of some gas wells is not ideal. Based on the low permeability reservoir core data of a gas well in East China Sea, the laboratory evolution experiments of wettability, nonlinear seepage, nuclear magnetic resonance and drilling fluid damage are carried out, and the basic characteristics and seepage law of low permeability reservoirs are revealed, and the availability of such reservoirs is evaluated. Combined with the drilling and completion of the well, the influencing factors of the low permeability reservoir pollution of the gas well are further analyzed. The study shows that the low permeability reservoir rock of this gas well is hydrophilic and the pore throat is small, so it is not easy to release the water lock after it occurs. The characteristics of nonlinear seepage are obvious under low pressure gradient. The percentage of movable fluid in the reservoir below 10×10−3 μm2 is less than 57.86%, which belongs to the third class of reservoirs, and is hard to mobilize. Compared with the soaking time, the damage of drilling pressure differential is greater. Thus the drilling pressure difference should be controlled within 3.5 MPa as far as possible.
Abstract：
Focusing on the difficult problems of unclear understanding of the mechanism of tapping the potential of remaining oil and the seepage characteristics in the ultra-high water cut stage of the bottom water heavy oil reservoir in Bohai Oilfield, this paper takes the main sand body of typical fluvial facies in Q oilfield as an example to carry out the experimental study on the ultimate water displacement efficiency of different types of reservoir samples under 2 000 PV high-multiple water displacement. The experimental results show that after high multiple water flooding at 2 000 PV, the maximum displacement efficiency of thin oil, common type 1 heavy oil and common type 2 heavy oil is 76.5%, 75.5% and 72.5% respectively. Under the same high-multiple water flooding conditions, the inflection point of the oil displacement efficiency of thin oil samples appeared at 100 PV, the inflection point of the common type 1 heavy oil samples appeared at 300 PV, and the common type 2 heavy oil samples appeared at 1000 PV. The greater the viscosity of formation crude oil, the later the inflection point appears, and the later the abandonment time of water flooding to the residual oil state. In the high multiple displacement process of 100～1000 PV, the oil displacement efficiency per PV of the common type 2 heavy oil samples, is higher than that of thin oil samples and the common type 1 heavy oil samples. Under the high multiple water displacement condition of 2 000 PV, the oil displacement efficiency can finally reach up to 72.5%. The experimental results can provide mechanism support for large liquid extraction and tapping potential of heavy oil with bottom water in the ultra-high water cut stage.
Focusing on the difficult problems of unclear understanding of the mechanism of tapping the potential of remaining oil and the seepage characteristics in the ultra-high water cut stage of the bottom water heavy oil reservoir in Bohai Oilfield, this paper takes the main sand body of typical fluvial facies in Q oilfield as an example to carry out the experimental study on the ultimate water displacement efficiency of different types of reservoir samples under 2 000 PV high-multiple water displacement. The experimental results show that after high multiple water flooding at 2 000 PV, the maximum displacement efficiency of thin oil, common type 1 heavy oil and common type 2 heavy oil is 76.5%, 75.5% and 72.5% respectively. Under the same high-multiple water flooding conditions, the inflection point of the oil displacement efficiency of thin oil samples appeared at 100 PV, the inflection point of the common type 1 heavy oil samples appeared at 300 PV, and the common type 2 heavy oil samples appeared at 1000 PV. The greater the viscosity of formation crude oil, the later the inflection point appears, and the later the abandonment time of water flooding to the residual oil state. In the high multiple displacement process of 100～1000 PV, the oil displacement efficiency per PV of the common type 2 heavy oil samples, is higher than that of thin oil samples and the common type 1 heavy oil samples. Under the high multiple water displacement condition of 2 000 PV, the oil displacement efficiency can finally reach up to 72.5%. The experimental results can provide mechanism support for large liquid extraction and tapping potential of heavy oil with bottom water in the ultra-high water cut stage.
2022, 42(4): 31-35.
DOI: 10.3969/j.issn.1008-2336.2022.04.031
Abstract：
Sand production prediction is an important link in formulating oil and gas field development plans. Scientific sand production prediction can provide decision-making basis for the selection of oil and gas field completion methods. In this paper, considering various sand production prediction methods, which are commonly used in oil and gas fields at home and abroad, such as acoustic travel time method, combined modulus method and sand production index method, as well as the influence of water content, crude oil viscosity and other factors on sand production, a sand production risk assessment method is established by scoring method. The method is applied to the case analysis, and the results show that it is highly consistent with the actual development of oil and gas fields. The factors considered by this method are more comprehensive and reasonable, which has certain popularization and application value in sand production prediction and analysis.
Sand production prediction is an important link in formulating oil and gas field development plans. Scientific sand production prediction can provide decision-making basis for the selection of oil and gas field completion methods. In this paper, considering various sand production prediction methods, which are commonly used in oil and gas fields at home and abroad, such as acoustic travel time method, combined modulus method and sand production index method, as well as the influence of water content, crude oil viscosity and other factors on sand production, a sand production risk assessment method is established by scoring method. The method is applied to the case analysis, and the results show that it is highly consistent with the actual development of oil and gas fields. The factors considered by this method are more comprehensive and reasonable, which has certain popularization and application value in sand production prediction and analysis.
Abstract：
In order to accurately calculate the deviation coefficient of natural gas in a high-CO2 gas field in East China Sea, and further to improve the reliability of gas reservoir engineering, gas production engineering and surface engineering design, 192 groups of the high-CO2 content gas deviation factor experiments were carried out with the Canadian DBR-PVT instrument. Then 192 sets of corresponding simulation calculations were carried out using 12 state equations such as BWRS, PR and SRK in ASPEN HYSYS software. The main influencing factors of the deviation factor were discussed, and the accuracy of calculating deviation coefficient by software state equations was evaluated. The results show that within the experimental range, pressure and CO2 content have great influence on the deviation factor, while temperature has little influence on it. The deviation coefficient first decreases and then increases as the pressure rises. The PR and Sour PR state equations have the highest accuracy in calculating the high-CO2 content gas deviation factor, with the average relative error of 1.09% and the maximum relative error of 5.74%. Therefore, when the CO2 content of natural gas is high, it is recommended to use the PR and Sour PR state equations to calculate the deviation factor.
In order to accurately calculate the deviation coefficient of natural gas in a high-CO2 gas field in East China Sea, and further to improve the reliability of gas reservoir engineering, gas production engineering and surface engineering design, 192 groups of the high-CO2 content gas deviation factor experiments were carried out with the Canadian DBR-PVT instrument. Then 192 sets of corresponding simulation calculations were carried out using 12 state equations such as BWRS, PR and SRK in ASPEN HYSYS software. The main influencing factors of the deviation factor were discussed, and the accuracy of calculating deviation coefficient by software state equations was evaluated. The results show that within the experimental range, pressure and CO2 content have great influence on the deviation factor, while temperature has little influence on it. The deviation coefficient first decreases and then increases as the pressure rises. The PR and Sour PR state equations have the highest accuracy in calculating the high-CO2 content gas deviation factor, with the average relative error of 1.09% and the maximum relative error of 5.74%. Therefore, when the CO2 content of natural gas is high, it is recommended to use the PR and Sour PR state equations to calculate the deviation factor.
Abstract：
Some water injection wells of Bohai Sea L Oilfield show that injection pressure increases rapidly and injection is difficult, and the amount of water injection can not meet the reservoir injection allocation. Therefore, the under-injection causes of injection wells in L Oilfield are analyzed. The reservoir rock sensitivity, drilling and completion fluids damage and injection water damage to reservoir are evaluated by core displacement experiments. The compatibility between injection water and formation water is evaluated by static compatibility test. The results show that the reservoir has strong velocity sensitivity damage and the water injection rate of some wells at initial stage is far more than critical injection rate of velocity sensitivity damage, resulting in irreversible particle migration damage. The core permeability damage rate of drilling and completion sequence operating fluids is between 35.5% to 48.2%, and that of single injection water is between 31% and 35.2%. The reservoir damage caused by solids invasion in drilling fluids and injection water quality exceeding the standard for a long time is the key reason for the generally poor injection capacity of injection wells in L Oilfield. It is suggested that new wells begin injecting after flowback or acidification should be carried out at initial stage to reduce the damage of drilling fluids. The initial injection rate should be controlled below the critical injection rate of velocity sensitivity, and the injection rate should be increased step by step to avoid the damage of particle migration. Meanwhile the control of key indexes such as suspended solids content, oil content and sulfate reducing bacteria in injection water should be strengthened.
Some water injection wells of Bohai Sea L Oilfield show that injection pressure increases rapidly and injection is difficult, and the amount of water injection can not meet the reservoir injection allocation. Therefore, the under-injection causes of injection wells in L Oilfield are analyzed. The reservoir rock sensitivity, drilling and completion fluids damage and injection water damage to reservoir are evaluated by core displacement experiments. The compatibility between injection water and formation water is evaluated by static compatibility test. The results show that the reservoir has strong velocity sensitivity damage and the water injection rate of some wells at initial stage is far more than critical injection rate of velocity sensitivity damage, resulting in irreversible particle migration damage. The core permeability damage rate of drilling and completion sequence operating fluids is between 35.5% to 48.2%, and that of single injection water is between 31% and 35.2%. The reservoir damage caused by solids invasion in drilling fluids and injection water quality exceeding the standard for a long time is the key reason for the generally poor injection capacity of injection wells in L Oilfield. It is suggested that new wells begin injecting after flowback or acidification should be carried out at initial stage to reduce the damage of drilling fluids. The initial injection rate should be controlled below the critical injection rate of velocity sensitivity, and the injection rate should be increased step by step to avoid the damage of particle migration. Meanwhile the control of key indexes such as suspended solids content, oil content and sulfate reducing bacteria in injection water should be strengthened.
2022, 42(4): 48-51, 56.
DOI: 10.3969/j.issn.1008-2336.2022.04.048
Abstract：
With the development of Bohai Oilfield, the incompatibility between injected water and reservoir water cause corrosion and scaling of downhole string, resulting in reservoir pollution, plugging and water injection pressure increasing. Conventional single pressurize and acidizing methods can not solve the secondary precipitation problem of scaling ions. Consequently, period of validity is short and multiple plug removal is needed, which causes high expense. In order to reduce the pressure and increase the injection of water injection wells, referring to the principle of oil well fracturing stimulation, this paper tries to form micro-fractures near the reservoir by water micro pressure cracking plugging without adding sand, then compound boiling acidification technology to improve the sweep efficiency and fingering of acid solution, and prevent the secondary precipitation of scaling ions. The application in Bohai water injection well shows that the water injection pressure has decreased obviously, and the daily water injection volume and apparent water absorption index have increased greatly. After 7 months of production, the daily water injection is still stable without obvious fluctuation, which indicates that the micro fracturing and acidizing technology is capable of improving reservoir permeability, reducing injection pressure, increasing water injection, and long action cycle. It has a good prospect of popularization and application.
With the development of Bohai Oilfield, the incompatibility between injected water and reservoir water cause corrosion and scaling of downhole string, resulting in reservoir pollution, plugging and water injection pressure increasing. Conventional single pressurize and acidizing methods can not solve the secondary precipitation problem of scaling ions. Consequently, period of validity is short and multiple plug removal is needed, which causes high expense. In order to reduce the pressure and increase the injection of water injection wells, referring to the principle of oil well fracturing stimulation, this paper tries to form micro-fractures near the reservoir by water micro pressure cracking plugging without adding sand, then compound boiling acidification technology to improve the sweep efficiency and fingering of acid solution, and prevent the secondary precipitation of scaling ions. The application in Bohai water injection well shows that the water injection pressure has decreased obviously, and the daily water injection volume and apparent water absorption index have increased greatly. After 7 months of production, the daily water injection is still stable without obvious fluctuation, which indicates that the micro fracturing and acidizing technology is capable of improving reservoir permeability, reducing injection pressure, increasing water injection, and long action cycle. It has a good prospect of popularization and application.
2022, 42(4): 52-56.
DOI: 10.3969/j.issn.1008-2336.2022.04.052
Abstract：
Large amount and wide distribution of wells containing hydrogen sulfide make it difficult to conduct sulfide treatment in Gudao. The high hydrogen sulfide wells mainly distribute in the steam flooding block. Single well wellhead casings were mainly used for the treatment of desulfurization agent and turned out it worked well. In recent years, with the development of extended oilfields, non-thermal production wells in some blocks of Kenxi Oilfield have also produced high-content hydrogen sulfide gas, which is widely distributed, using a large amount of chemicals, and causing the high cost of comprehensive treatment. At the same time, the mineralization of the produced fluid in the extended oilfields is high, and the compatibility of conventional desulfurizers is poor, which promotes scaling and affects production. Non-thermal production wells are not in a stable high temperature and high pressure environment, the cause of hydrogen sulfide generation is still unclear, and there is no good targeted treatment measures. Therefore, for the peripheral oilfield blocks of Gudao, in this paper, the mechanism of hydrogen sulfide generation in non-thermal production wells and the research on biological desulfurization technology in non-thermal production wells have been camied out, which obtained obvious application result and effectively solved the safety and environmental problems in the production site, it has good promotion prospects.
Large amount and wide distribution of wells containing hydrogen sulfide make it difficult to conduct sulfide treatment in Gudao. The high hydrogen sulfide wells mainly distribute in the steam flooding block. Single well wellhead casings were mainly used for the treatment of desulfurization agent and turned out it worked well. In recent years, with the development of extended oilfields, non-thermal production wells in some blocks of Kenxi Oilfield have also produced high-content hydrogen sulfide gas, which is widely distributed, using a large amount of chemicals, and causing the high cost of comprehensive treatment. At the same time, the mineralization of the produced fluid in the extended oilfields is high, and the compatibility of conventional desulfurizers is poor, which promotes scaling and affects production. Non-thermal production wells are not in a stable high temperature and high pressure environment, the cause of hydrogen sulfide generation is still unclear, and there is no good targeted treatment measures. Therefore, for the peripheral oilfield blocks of Gudao, in this paper, the mechanism of hydrogen sulfide generation in non-thermal production wells and the research on biological desulfurization technology in non-thermal production wells have been camied out, which obtained obvious application result and effectively solved the safety and environmental problems in the production site, it has good promotion prospects.
Abstract：
The reservoirs of the Z oilfield in the western South China Sea generally have complex conditions such as poor physical properties, low structural accuracy, and sand body pinching out. Boundary detection while drilling was introduced to effectively improve Drilling Ratio and Reserve Utilization. This technology can measure three-layer model formation resistivity, distance from drill bit to upper/lower surrounding rock and reservoir boundary. It can also perform boundary strata characterization and provide Geosteering services. Boundary detection while drilling has been widely used in complex offshore oil and gas fields development, ecpecially in fields with conditions of low proven structure, strong reservoir heterogeneity, and edge/bottom water reservoirs. This paper briefly describes the development of Geosteering technology, sorting out the principle and technical characteristics of boundary detection while drilling, and demonstrates the methods to adjust the wellbore trajectory through identified reservoir boundary and reservoir change results. Boundary detection technology increases the travel distance of the trajectory of the horizontal section of Well H in the "sweet spot" reservoir, achieving a good steering application effect. The actual production exceeds the pre-drilling allocation by about 60 m3/d. At the same time, it avoids geological and engineering risks and can be used as guidance for subsequent drilling of horizontal wells in similar oil and gas reservoirs.
The reservoirs of the Z oilfield in the western South China Sea generally have complex conditions such as poor physical properties, low structural accuracy, and sand body pinching out. Boundary detection while drilling was introduced to effectively improve Drilling Ratio and Reserve Utilization. This technology can measure three-layer model formation resistivity, distance from drill bit to upper/lower surrounding rock and reservoir boundary. It can also perform boundary strata characterization and provide Geosteering services. Boundary detection while drilling has been widely used in complex offshore oil and gas fields development, ecpecially in fields with conditions of low proven structure, strong reservoir heterogeneity, and edge/bottom water reservoirs. This paper briefly describes the development of Geosteering technology, sorting out the principle and technical characteristics of boundary detection while drilling, and demonstrates the methods to adjust the wellbore trajectory through identified reservoir boundary and reservoir change results. Boundary detection technology increases the travel distance of the trajectory of the horizontal section of Well H in the "sweet spot" reservoir, achieving a good steering application effect. The actual production exceeds the pre-drilling allocation by about 60 m3/d. At the same time, it avoids geological and engineering risks and can be used as guidance for subsequent drilling of horizontal wells in similar oil and gas reservoirs.
Abstract：
Reservior fluids properties identification plays an important role in production, especially for offshore oil fields which usually are lack of well logging data. The difference between water saturation and the irreducible water saturation calculated by logging data is generally used to identify reservoir fluids properties. In fact, whether the reservoir produces water or not depends not only on the water saturation and the irreducible water saturation, but also on the relative permeability and viscosity of fluid in reservoirs. In this paper, the method of using water content calculated by logging data and petrophysics to evaluate the output ratio of oil and water of the reservoir is proved to be effective. This method has a great significance to identify the fluid property of the reservoir and can lay a solid foundation for oilfield completion and production.
Reservior fluids properties identification plays an important role in production, especially for offshore oil fields which usually are lack of well logging data. The difference between water saturation and the irreducible water saturation calculated by logging data is generally used to identify reservoir fluids properties. In fact, whether the reservoir produces water or not depends not only on the water saturation and the irreducible water saturation, but also on the relative permeability and viscosity of fluid in reservoirs. In this paper, the method of using water content calculated by logging data and petrophysics to evaluate the output ratio of oil and water of the reservoir is proved to be effective. This method has a great significance to identify the fluid property of the reservoir and can lay a solid foundation for oilfield completion and production.
2022, 42(4): 67-70.
DOI: 10.3969/j.issn.1008-2336.2022.04.067
Abstract：
Wireline formation test is difficult to implement and has high risk because it is easily affected by well trajectory and well conditions in directional well operation. As result, it has a great impact on reservoir evaluation. The FASTrak HD of Baker Hughes company is not limited by well trajectory and has low operation risk. It not only retains all functions of Testrak, but also adds fluid analysis module, pressure drop pump and sample barrel module. Moreover it is capable of sampling so that the problem of pressure measurement and sampling of directional wells is solved. This tool has been successfully applied for the first time in Bohai Oilfield and provides a new operation mode for pressure measurement and sampling of subsequent directional wells.
Wireline formation test is difficult to implement and has high risk because it is easily affected by well trajectory and well conditions in directional well operation. As result, it has a great impact on reservoir evaluation. The FASTrak HD of Baker Hughes company is not limited by well trajectory and has low operation risk. It not only retains all functions of Testrak, but also adds fluid analysis module, pressure drop pump and sample barrel module. Moreover it is capable of sampling so that the problem of pressure measurement and sampling of directional wells is solved. This tool has been successfully applied for the first time in Bohai Oilfield and provides a new operation mode for pressure measurement and sampling of subsequent directional wells.
2022, 42(4): 71-75.
DOI: 10.3969/j.issn.1008-2336.2022.04.071
Abstract：
LS 17-2 gas field group is the first self-developed deep-water high production gas field in the western South China Sea, with an average water depth of 1500 m. Deep-water oil and gas development not only needs to overcome harsh offshore environmental conditions, but also faces many challenges such as poor diagenesis of shallow stratum, complicated mechanical behaviors of riser and drill string, high well control requirements. So elaborate drilling technical measures have been taken including drilling rig capability evaluation, high precision underwater position system, safe avoidance distance design and directional well trajectory design, etc. Meanwhile, methods such as stability analysis of riser and subsea wellhead, checking the depth of the surface conductor into the mud, conductor installation through jetting drilling are being used as key technologies in order to complete the drilling operation safely and effciently. The successful development of LS 17-2 project further solidifies the safe and efficient operation mode of offshore deep-water drilling, and provides reference for the subsequent exploration and development of deep-water oil and gas fields.
LS 17-2 gas field group is the first self-developed deep-water high production gas field in the western South China Sea, with an average water depth of 1500 m. Deep-water oil and gas development not only needs to overcome harsh offshore environmental conditions, but also faces many challenges such as poor diagenesis of shallow stratum, complicated mechanical behaviors of riser and drill string, high well control requirements. So elaborate drilling technical measures have been taken including drilling rig capability evaluation, high precision underwater position system, safe avoidance distance design and directional well trajectory design, etc. Meanwhile, methods such as stability analysis of riser and subsea wellhead, checking the depth of the surface conductor into the mud, conductor installation through jetting drilling are being used as key technologies in order to complete the drilling operation safely and effciently. The successful development of LS 17-2 project further solidifies the safe and efficient operation mode of offshore deep-water drilling, and provides reference for the subsequent exploration and development of deep-water oil and gas fields.
Abstract：
During the drilling process, when drilling with different boreholes unlocks the formation, the cracks, joints and other flaws exposed on the borehole wall are different. Experiment shows that generally the smaller the borehole, the more stable the borehole wall is. However, this intuitive understanding is lacking of theoretical support. Since the flaws of the wall such as cracks and joints cannot be accurately described, the influence of wellbore size on well stability is rarely used in the calculation of collapse pressure. To solve this problem, a brittle formation borehole stability model based on Weibull's statistical strength-size-effect theory was established, and the main influencing factors such as inhomogeneity and borehole size were discussed. The results showed that with the uniformity of the surrounding rock increased, the impact of borehole size on the stability of the borehole wall is reduced; compared to the reference 6˝ borehole, in which the collapse pressure increases with the borehole size increases. For the actual construction, while meeting the requirements of other projects, use small boreholes as much as possible for the formation that is easy to collapse.
During the drilling process, when drilling with different boreholes unlocks the formation, the cracks, joints and other flaws exposed on the borehole wall are different. Experiment shows that generally the smaller the borehole, the more stable the borehole wall is. However, this intuitive understanding is lacking of theoretical support. Since the flaws of the wall such as cracks and joints cannot be accurately described, the influence of wellbore size on well stability is rarely used in the calculation of collapse pressure. To solve this problem, a brittle formation borehole stability model based on Weibull's statistical strength-size-effect theory was established, and the main influencing factors such as inhomogeneity and borehole size were discussed. The results showed that with the uniformity of the surrounding rock increased, the impact of borehole size on the stability of the borehole wall is reduced; compared to the reference 6˝ borehole, in which the collapse pressure increases with the borehole size increases. For the actual construction, while meeting the requirements of other projects, use small boreholes as much as possible for the formation that is easy to collapse.
Abstract：
CNOOC uses e-Drilling software to perform real-time simulation of wellbore cleaning, and the calculation results of this software have low accuracy. In order to improve the accuracy of borehole cleaning calculation, a new method for borehole cleaning calculation has been explored. By calculating the critical flow rate required for the suspension of cuttings in the annulus and the flow rate of the drilling fluid in the annulus, the critical flow rate and the flow rate of the drilling fluid are compared to determine the thickness of the cuttings bed, and then calculate the concentration of cuttings in the annulus and the wellbore ECD (equivalent circulating density). The new method has been used to calculate two extended reach wells in Area A. Compared with calculated results of the e-Drilling software and measured ECD values, the results show that the accuracy of calculation with the new method is improved obviously. The practice shows that this method has higher technical value.
CNOOC uses e-Drilling software to perform real-time simulation of wellbore cleaning, and the calculation results of this software have low accuracy. In order to improve the accuracy of borehole cleaning calculation, a new method for borehole cleaning calculation has been explored. By calculating the critical flow rate required for the suspension of cuttings in the annulus and the flow rate of the drilling fluid in the annulus, the critical flow rate and the flow rate of the drilling fluid are compared to determine the thickness of the cuttings bed, and then calculate the concentration of cuttings in the annulus and the wellbore ECD (equivalent circulating density). The new method has been used to calculate two extended reach wells in Area A. Compared with calculated results of the e-Drilling software and measured ECD values, the results show that the accuracy of calculation with the new method is improved obviously. The practice shows that this method has higher technical value.
2022, 42(4): 85-90.
DOI: 10.3969/j.issn.1008-2336.2022.04.085
Abstract：
The extensive application of modern machinery has put forward higher requirements for the safety and reliability of the power system of drilling rigs. In order to ensure the smooth application of electronic equipment on the complex and severe environment of drilling rigs, besides improving the reliability and electromagnetic compatibility of the equipment itself, it is necessary to increase the redundancy and improve the quality of power supply. This paper mainly analyzes the power supply redundancy and UPS power supply. Combined with the actual application of offshore drilling rigs, a feasible scheme has been put forward and has been applied. The application has achieved good practical results in practice, which provides a useful reference for the design and optimization of the power supply reliability of drilling rig power systems.
The extensive application of modern machinery has put forward higher requirements for the safety and reliability of the power system of drilling rigs. In order to ensure the smooth application of electronic equipment on the complex and severe environment of drilling rigs, besides improving the reliability and electromagnetic compatibility of the equipment itself, it is necessary to increase the redundancy and improve the quality of power supply. This paper mainly analyzes the power supply redundancy and UPS power supply. Combined with the actual application of offshore drilling rigs, a feasible scheme has been put forward and has been applied. The application has achieved good practical results in practice, which provides a useful reference for the design and optimization of the power supply reliability of drilling rig power systems.
2022, 42(4): 91-94.
DOI: 10.3969/j.issn.1008-2336.2022.04.091
Abstract：
The operation of offshore ultra-high temperature and pressure wells is difficult due to the characteristics of ultra-high formation temperature, ultra-high formation pressure and the extremely narrow pressure window. Coring in ultra-high temperature and pressure well sections involves high risks such as well control and lost circulation, so it is a very difficult operation. This paper analyzes the technical difficulties of coring in the ultra-high temperature and high pressure well section, so as to study the coring barrel, drilling tool assembly, drilling parameter optimization, well control measures and leakage prevention measures, and puts forward the improvement plan of the coring barrel, recommended drilling tool assembly and drilling parameters, well control measures and leakage prevention measures, which have been applied in the practice of Well LD13 with the ultra-high temperature and high pressure for the first time. The reconstructed coring barrel was used in the construction, which controlled the well control risk, avoided lost circulation, and finally achieved 100% coring recovery. The coring operation in the offshore ultra-high temperature and high pressure well section of South China Sea was successfully completed. The application effect is obvious, which can provide effective reference for coring in the offshore ultra-high temperature and high pressure well section.
The operation of offshore ultra-high temperature and pressure wells is difficult due to the characteristics of ultra-high formation temperature, ultra-high formation pressure and the extremely narrow pressure window. Coring in ultra-high temperature and pressure well sections involves high risks such as well control and lost circulation, so it is a very difficult operation. This paper analyzes the technical difficulties of coring in the ultra-high temperature and high pressure well section, so as to study the coring barrel, drilling tool assembly, drilling parameter optimization, well control measures and leakage prevention measures, and puts forward the improvement plan of the coring barrel, recommended drilling tool assembly and drilling parameters, well control measures and leakage prevention measures, which have been applied in the practice of Well LD13 with the ultra-high temperature and high pressure for the first time. The reconstructed coring barrel was used in the construction, which controlled the well control risk, avoided lost circulation, and finally achieved 100% coring recovery. The coring operation in the offshore ultra-high temperature and high pressure well section of South China Sea was successfully completed. The application effect is obvious, which can provide effective reference for coring in the offshore ultra-high temperature and high pressure well section.
2022, 42(4): 95-100.
DOI: 10.3969/j.issn.1008-2336.2022.04.095
Abstract：
The long transmission shaft of anchor winch on a marine semi-submersible rig has many corroded pits after years of use.Since the anchor winch is an imported equipment and has no relevant technical parameters, the paper describes the measurement and analysis process of the technical parameters of the long transmission shaft and the bearing of windlass, and determines the technical parameters such as tolerances and dimensions of the long transmission shaft according to the technical standards. It is considered that the interference fit between the long transmission shaft and the rolling bearing is adopted, and the tolerance zone of the long transmission shaft is r6. The long transmission shaft and the sliding bearing adopt a clearance fit.The corroded pits of the shaft were repaired by laser welding, and the repaired shaft was ground on a grinder. The corroded parts of the shaft were repaired by iron plating. After the iron plating, the shaft was ground on a grinder, and the repaired shaft surface Ra=0.8 µm after processing was repaired. After assembly and trial operation, the anchor winch works normally.The research result fills the technical gap of the overhaul of long transmission shaft of anchor winch on marine semi-submersible rig, and has the corresponding reference significance for the overhaul of long transmission shaft of anchor winch on marine.
The long transmission shaft of anchor winch on a marine semi-submersible rig has many corroded pits after years of use.Since the anchor winch is an imported equipment and has no relevant technical parameters, the paper describes the measurement and analysis process of the technical parameters of the long transmission shaft and the bearing of windlass, and determines the technical parameters such as tolerances and dimensions of the long transmission shaft according to the technical standards. It is considered that the interference fit between the long transmission shaft and the rolling bearing is adopted, and the tolerance zone of the long transmission shaft is r6. The long transmission shaft and the sliding bearing adopt a clearance fit.The corroded pits of the shaft were repaired by laser welding, and the repaired shaft was ground on a grinder. The corroded parts of the shaft were repaired by iron plating. After the iron plating, the shaft was ground on a grinder, and the repaired shaft surface Ra=0.8 µm after processing was repaired. After assembly and trial operation, the anchor winch works normally.The research result fills the technical gap of the overhaul of long transmission shaft of anchor winch on marine semi-submersible rig, and has the corresponding reference significance for the overhaul of long transmission shaft of anchor winch on marine.
2022, 42(4): 101-106.
DOI: 10.3969/j.issn.1008-2336.2022.04.101
Abstract：
In the bay of Bengal, there are 4 nearly paralleled subsea oil pipelines to go across 2 paralleled channels with the breadth approximate to 1.2 km. By using the method of pipeline laying and post-trenching, trenching is carried out for an average of 20 times, and 4 submarine oil pipelines are buried below the elevation required by waterway dredging, where the maximum trenching depth could achieve 11.9 m. With respect to difficulties in the plan process and challenges in each stage, by various of technical evaluation, narrow deep trenching machine with air lift eduction is utilized, combined use of SBP and 3D Sonar Survey during trenching operation, pipeline safety and integrity is analyzed after trenching. The final investigation and evaluation results show that the post-trenching operation meets the design requirements and ensures the integrity of the pipeline. Practice has proved that water jetting trencher can be utilized for post-deep trenching combined with comprehensive technical measures.
In the bay of Bengal, there are 4 nearly paralleled subsea oil pipelines to go across 2 paralleled channels with the breadth approximate to 1.2 km. By using the method of pipeline laying and post-trenching, trenching is carried out for an average of 20 times, and 4 submarine oil pipelines are buried below the elevation required by waterway dredging, where the maximum trenching depth could achieve 11.9 m. With respect to difficulties in the plan process and challenges in each stage, by various of technical evaluation, narrow deep trenching machine with air lift eduction is utilized, combined use of SBP and 3D Sonar Survey during trenching operation, pipeline safety and integrity is analyzed after trenching. The final investigation and evaluation results show that the post-trenching operation meets the design requirements and ensures the integrity of the pipeline. Practice has proved that water jetting trencher can be utilized for post-deep trenching combined with comprehensive technical measures.
2022, 42(4): 107-110.
DOI: 10.3969/j.issn.1008-2336.2022.04.107
Abstract：
Through automatic control, FPSO mild steel arm mooring lubrication control system can realize the forced injection of grease to each lubrication point of mooring system for lubrication, which plays a decisive role in maintaining the integrity of single point equipment, process stability and personnel safety. The FPSO mild steel arm mooring lubrication system in Bohai has been running for nearly ten years. Due to the lack of functions and poor stability of the original equipment, many problems need to be solved. In order to improve the stability of equipment and process, the lubrication control system was studied and a scheme of upgrading the lubrication control system was put forward. After the lubrication system was upgraded and put into use, the existing equipment safety hazards, production process hazards and personnel safety hazards were solved. This paper mainly introduces the idea of mooring system lubrication system upgrade, hardware selection and related software configuration, which can be used for reference by other similar systems and equipment.
Through automatic control, FPSO mild steel arm mooring lubrication control system can realize the forced injection of grease to each lubrication point of mooring system for lubrication, which plays a decisive role in maintaining the integrity of single point equipment, process stability and personnel safety. The FPSO mild steel arm mooring lubrication system in Bohai has been running for nearly ten years. Due to the lack of functions and poor stability of the original equipment, many problems need to be solved. In order to improve the stability of equipment and process, the lubrication control system was studied and a scheme of upgrading the lubrication control system was put forward. After the lubrication system was upgraded and put into use, the existing equipment safety hazards, production process hazards and personnel safety hazards were solved. This paper mainly introduces the idea of mooring system lubrication system upgrade, hardware selection and related software configuration, which can be used for reference by other similar systems and equipment.
