Volume 28,Issue 6,2021 Table of Contents
2021, 28(6):1-11.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.001
Abstract:
After nearly 40 years of development and practice，a relatively complete series of development technologies with Shengli characteristics has taken shape during the heavy oil reservoirs development and a significant development effect has been achieved in Shengli Oilfield. In October 2020，the cumulative production of heavy oil in Shengli Oilfield exceeded 100 million tons. Since“The Twelfth Five-Year Plan Period in 2011-2015”，multiple technologies have been developed to address severe situations such as low oil prices and high steam injection costs，including the HDNS（horizontal well+dissolver+nitrogen gas+steam injection）technology for super heavy oil in shallow and thin reservoirs，the chemical steam flooding technology for deep heavy oil reservoirs，the quality and efficiency enhancement technologies for heavy oil reservoirs，and the viscosity reduction cold recovery technology. These technologies supported the stability of heavy oil production and the improvement of benefits and promoted the progress of development theories and technologies for heavy oil reservoirs. At present，the heavy oil reservoirs development in Shengli Oilfield is facing several problems and challenges such as poor quality of un-producing reserves，low recoveries in mature reservoirs，and large thermal recovery emissions. Technical strategies and research directions are put forward from the aspects of producing rate enhancement in new reservoirs，recovery improvement in mature reservoirs，and green and low-carbon development to provide technical support for the benefit development and green development of the heavy oil reservoirs in the Shengli Oilfield.
After nearly 40 years of development and practice，a relatively complete series of development technologies with Shengli characteristics has taken shape during the heavy oil reservoirs development and a significant development effect has been achieved in Shengli Oilfield. In October 2020，the cumulative production of heavy oil in Shengli Oilfield exceeded 100 million tons. Since“The Twelfth Five-Year Plan Period in 2011-2015”，multiple technologies have been developed to address severe situations such as low oil prices and high steam injection costs，including the HDNS（horizontal well+dissolver+nitrogen gas+steam injection）technology for super heavy oil in shallow and thin reservoirs，the chemical steam flooding technology for deep heavy oil reservoirs，the quality and efficiency enhancement technologies for heavy oil reservoirs，and the viscosity reduction cold recovery technology. These technologies supported the stability of heavy oil production and the improvement of benefits and promoted the progress of development theories and technologies for heavy oil reservoirs. At present，the heavy oil reservoirs development in Shengli Oilfield is facing several problems and challenges such as poor quality of un-producing reserves，low recoveries in mature reservoirs，and large thermal recovery emissions. Technical strategies and research directions are put forward from the aspects of producing rate enhancement in new reservoirs，recovery improvement in mature reservoirs，and green and low-carbon development to provide technical support for the benefit development and green development of the heavy oil reservoirs in the Shengli Oilfield.
SHU Qinglin
,
ZHENG Wangang
,
ZHANG Zhongping
,
YANG Xiaomin
,
WU Wei
,
WU Guanghuan
,
ZHAO Hongyu
,
ZHENG Xin
2021, 28(6):12-21.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.002
Abstract:
The development of heavy oil reservoirs in Shengli Oilfield is dominated by thermal huff and puff and water flooding. The oil-to-steam ratio decreases by rounds and the remaining oil between wells is difficult to produce effectively in thermal recovery heavy reservoirs；it is not economical to drill new wells. The oil-to-water mobility ratio is high and the operating cost per ton of oil increases in water flooding heavy oil reservoirs，worsening the economic benefit and leading to a recovery factor of less than 20%. Since“The thirteenth Five-Year Plan Period in 2016-2020”，the technical idea of additive，synergistic，and balanced displacement was devised to improve the development effect of low-efficiency heavy oil reservoirs and enhance mobility and oil recovery through multi-stage profile control and chemical viscosity reduction. According to the study of viscosity mechanism of heavy oil，the research on depolymerization and emulsification mechanisms of viscosity reducer was deepened，and the compound mechanisms with chemical viscosity reduction were investigated，such as multi-stage profile control and flooding，anti-swelling，and gas solubilization. Key chemical agents such as oligomeric viscosity reducer and viscoelastic emulsification profile control and flooding agents and dual-function foaming agents were developed，and the decision-making and control technology for scheme optimization was improved，thus forming the compound flooding technology of heavy-oil chemical viscosity reduction with“strong profile control and flooding，viscosity reduction，anti-swelling，activity，and solubilization”as the core. Different from the“binary”and the“ternary”polymer flooding of conventional thin oil and the chemical flooding of common heavy oil，this technology has been successfully promoted and applied to various types of heavy oil reservoirs，such as those after multi-round huff and puff，sensitive，and high-temperature high-salinity water-drive ones，covering a geological reserve of 15 million tons. It is expected to increase the recovery factor by more than 8%，which effectively supports the transformational and beneficial development of low-efficiency heavy oil reservoirs.
The development of heavy oil reservoirs in Shengli Oilfield is dominated by thermal huff and puff and water flooding. The oil-to-steam ratio decreases by rounds and the remaining oil between wells is difficult to produce effectively in thermal recovery heavy reservoirs；it is not economical to drill new wells. The oil-to-water mobility ratio is high and the operating cost per ton of oil increases in water flooding heavy oil reservoirs，worsening the economic benefit and leading to a recovery factor of less than 20%. Since“The thirteenth Five-Year Plan Period in 2016-2020”，the technical idea of additive，synergistic，and balanced displacement was devised to improve the development effect of low-efficiency heavy oil reservoirs and enhance mobility and oil recovery through multi-stage profile control and chemical viscosity reduction. According to the study of viscosity mechanism of heavy oil，the research on depolymerization and emulsification mechanisms of viscosity reducer was deepened，and the compound mechanisms with chemical viscosity reduction were investigated，such as multi-stage profile control and flooding，anti-swelling，and gas solubilization. Key chemical agents such as oligomeric viscosity reducer and viscoelastic emulsification profile control and flooding agents and dual-function foaming agents were developed，and the decision-making and control technology for scheme optimization was improved，thus forming the compound flooding technology of heavy-oil chemical viscosity reduction with“strong profile control and flooding，viscosity reduction，anti-swelling，activity，and solubilization”as the core. Different from the“binary”and the“ternary”polymer flooding of conventional thin oil and the chemical flooding of common heavy oil，this technology has been successfully promoted and applied to various types of heavy oil reservoirs，such as those after multi-round huff and puff，sensitive，and high-temperature high-salinity water-drive ones，covering a geological reserve of 15 million tons. It is expected to increase the recovery factor by more than 8%，which effectively supports the transformational and beneficial development of low-efficiency heavy oil reservoirs.
2021, 28(6):22-29.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.003
Abstract:
According to the production characteristics of steam huff and puff in heavy oil wells，this paper establishes a predictive model for the steam injection cycle of heavy oil with the neural network method and the historical production and management data of heavy oil wells in the 4th Member of Eocene Shahejie Formation（Es4）of Block Cao4 in Shengke oil production management area of Shengli Oilfield. The production and full cost of wells for steam injection cyclic of heavy oil are predicted with the proposed model and compared with their historical data of short-and long-term production and full cost.Further，the model is optimized，which enables the multi-dimensional intelligent prediction of steam injection cycle of heavy oil. Moreover，it improves the production prediction accuracy of heavy oil wells，the prediction accuracy of the best time of steam injection cycle of heavy oil，and the preparation efficiency of the best measure scheme for steam injection cycle of heavy oil and enhances the intelligent decision-making，analysis，and management ability of heavy oil wells and the benefit and development level of oil production management areas. Since the technology was popularized and applied in the heavy oil block of Shengke oil production management area in 2021，effective steam injection cycle of heavy oil has been performed for 165 well times in the oil production management area. The cumulative oil increment is 7×104 t in wells for steam injection cyclic of heavy oil. The oil increment is increased by 1×104 t，and the effective oil increase rate is about 17%，compared with those in the same period in 2020.
According to the production characteristics of steam huff and puff in heavy oil wells，this paper establishes a predictive model for the steam injection cycle of heavy oil with the neural network method and the historical production and management data of heavy oil wells in the 4th Member of Eocene Shahejie Formation（Es4）of Block Cao4 in Shengke oil production management area of Shengli Oilfield. The production and full cost of wells for steam injection cyclic of heavy oil are predicted with the proposed model and compared with their historical data of short-and long-term production and full cost.Further，the model is optimized，which enables the multi-dimensional intelligent prediction of steam injection cycle of heavy oil. Moreover，it improves the production prediction accuracy of heavy oil wells，the prediction accuracy of the best time of steam injection cycle of heavy oil，and the preparation efficiency of the best measure scheme for steam injection cycle of heavy oil and enhances the intelligent decision-making，analysis，and management ability of heavy oil wells and the benefit and development level of oil production management areas. Since the technology was popularized and applied in the heavy oil block of Shengke oil production management area in 2021，effective steam injection cycle of heavy oil has been performed for 165 well times in the oil production management area. The cumulative oil increment is 7×104 t in wells for steam injection cyclic of heavy oil. The oil increment is increased by 1×104 t，and the effective oil increase rate is about 17%，compared with those in the same period in 2020.
2021, 28(6):30-37.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.004
Abstract:
Steam-assisted gravity drainage（SAGD）is a thermal recovery technology for the efficient development of heavy oil reservoirs. The Long Lake Oilfield in Canada is faced with problems such as high viscosity of crude oil，low permeability and large thickness of the sand-mud interbed，and difficult crude oil production above the interbed. In response，laboratory experiments on the start-up pressure gradient of heavy oil at different permeability and temperature were carried out. The feasibility of crude oil passing through the interbed under gravity was analyzed. On this basis，three sets of two-dimensional SAGD physical simulation experiments were carried out to study the influence of the thickness of the sand-mud interbed on the expansion of the SAGD steam chamber and the production effect of SAGD and obtain the expansion thickness limit of the SAGD steam chamber under the condition of the sand-mud interbed. The results show that the flow of heavy oil in the interbed has a start-up pressure gradient in the process of oil sand exploitation. The crude oil above the interbed will start the flow merely by gravity only when the temperature in the formation above the interbed reaches 200 ℃ or more and the viscosity of the crude oil decreases to below 8.966 mPa·s. The steam chamber shows a trend of the vertical expansion weakening，the horizontal expansion increasing，and the ability of the steam to break through the interbed declining as the thickness of the sand-mud interbeds in the formations increases. The steam can break through the interbed and the crude oil above the interbed can be produced to a certain extent when the permeability of the sand-mud interbed is 50 mD and its thickness is less than 6 cm.
Steam-assisted gravity drainage（SAGD）is a thermal recovery technology for the efficient development of heavy oil reservoirs. The Long Lake Oilfield in Canada is faced with problems such as high viscosity of crude oil，low permeability and large thickness of the sand-mud interbed，and difficult crude oil production above the interbed. In response，laboratory experiments on the start-up pressure gradient of heavy oil at different permeability and temperature were carried out. The feasibility of crude oil passing through the interbed under gravity was analyzed. On this basis，three sets of two-dimensional SAGD physical simulation experiments were carried out to study the influence of the thickness of the sand-mud interbed on the expansion of the SAGD steam chamber and the production effect of SAGD and obtain the expansion thickness limit of the SAGD steam chamber under the condition of the sand-mud interbed. The results show that the flow of heavy oil in the interbed has a start-up pressure gradient in the process of oil sand exploitation. The crude oil above the interbed will start the flow merely by gravity only when the temperature in the formation above the interbed reaches 200 ℃ or more and the viscosity of the crude oil decreases to below 8.966 mPa·s. The steam chamber shows a trend of the vertical expansion weakening，the horizontal expansion increasing，and the ability of the steam to break through the interbed declining as the thickness of the sand-mud interbeds in the formations increases. The steam can break through the interbed and the crude oil above the interbed can be produced to a certain extent when the permeability of the sand-mud interbed is 50 mD and its thickness is less than 6 cm.
2021, 28(6):38-45.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.005
Abstract:
The ultra-heavy oil reservoirs of Fengcheng Oilfield in Xinjiang are continental braided fluvial facies with strong heterogeneity. The permeability variation coefficient is 0.7-0.9，and the distribution density of muddy interlayers is 2.4 strips/m. As a result，SAGD well groups have some prominent problems，such as low producing degree of the horizontal section and uneven expansion of steam chambers. In virtue of the mechanical properties and the dilation mechanism of reservoir rocks，this paper studies the controllable upgraded dilation technology by using large-scale physical simulation and coupled numerical simulation of rock mechanics under the true triaxial in-situ stress，and specifies the optimal dilation methods and parameters for breaking the interlayers between injection and production horizontal wells，breaking the interlayers above steam injection horizontal wells，and producing multilateral well sections of SAGD reservoir. According to the results，the oil sands of Well Block A of Fengcheng Oilfield has a strong dilation effect under low confining pressures. A complex dilation area can be formed under the effect of both constant pressure and stepwise raised pressure，and the maximum dilation volume is as high as 7%. Under the condition of reasonable dilation parameters，the dilation radius of ultraheavy oil reservoirs of Fengcheng Oilfield can reach 10-15 m. Compared with the traditional fast and uniform start-up technology，the technology for the upgraded dilation of SAGD reservoirs with strong heterogeneity and ultra-heavy oil can realize better reservoir adaptability and significantly increase oil production.
The ultra-heavy oil reservoirs of Fengcheng Oilfield in Xinjiang are continental braided fluvial facies with strong heterogeneity. The permeability variation coefficient is 0.7-0.9，and the distribution density of muddy interlayers is 2.4 strips/m. As a result，SAGD well groups have some prominent problems，such as low producing degree of the horizontal section and uneven expansion of steam chambers. In virtue of the mechanical properties and the dilation mechanism of reservoir rocks，this paper studies the controllable upgraded dilation technology by using large-scale physical simulation and coupled numerical simulation of rock mechanics under the true triaxial in-situ stress，and specifies the optimal dilation methods and parameters for breaking the interlayers between injection and production horizontal wells，breaking the interlayers above steam injection horizontal wells，and producing multilateral well sections of SAGD reservoir. According to the results，the oil sands of Well Block A of Fengcheng Oilfield has a strong dilation effect under low confining pressures. A complex dilation area can be formed under the effect of both constant pressure and stepwise raised pressure，and the maximum dilation volume is as high as 7%. Under the condition of reasonable dilation parameters，the dilation radius of ultraheavy oil reservoirs of Fengcheng Oilfield can reach 10-15 m. Compared with the traditional fast and uniform start-up technology，the technology for the upgraded dilation of SAGD reservoirs with strong heterogeneity and ultra-heavy oil can realize better reservoir adaptability and significantly increase oil production.
2021, 28(6):46-53.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.006
Abstract:
The comprehensive water cut of heavy oil reservoirs with edge water in Gudong Oilfield does not increase but decreases after significant liquid-producing capacity enhancement. With regard to this problem，a study was carried out on the liquid-producing capacity of the middle-high permeability heavy oil reservoirs with the edge water in the late stage of reservoir development. In light of the mechanics of fluid flow through a porous medium，a flow tube method and a material balance method were used to derive the deliverability equation of oil-water two-phase flow in the heavy oil reservoirs with the edge water，and the main factors affecting the development results were analyzed. At the same time，a conceptual model was constructed on the basis of the geological conditions of Kendong Block 18-32，and numerical simulation was employed to study the adaptive conditions and reasonable working system for liquid-producing capacity in the late stage of reservoir development. As a result，a set of evaluation methods suitable for the liquid-producing capacity of heavy oil reservoirs with the edge water were formed. The results demonstrate that reservoir thickness，the distance from the liquid-producing capacity enhancement well to the oil-water boundary，well spacing，and liquid-producing capacity enhancement parameters are the key factors affecting liquid-producing capacity. Field application indicates that the total oil production of 11 wells in the objective block increases by 2.47×104 t；and the average water cut grows by 0.2%；further the output-to-input ratio reaches 3.5∶1.
The comprehensive water cut of heavy oil reservoirs with edge water in Gudong Oilfield does not increase but decreases after significant liquid-producing capacity enhancement. With regard to this problem，a study was carried out on the liquid-producing capacity of the middle-high permeability heavy oil reservoirs with the edge water in the late stage of reservoir development. In light of the mechanics of fluid flow through a porous medium，a flow tube method and a material balance method were used to derive the deliverability equation of oil-water two-phase flow in the heavy oil reservoirs with the edge water，and the main factors affecting the development results were analyzed. At the same time，a conceptual model was constructed on the basis of the geological conditions of Kendong Block 18-32，and numerical simulation was employed to study the adaptive conditions and reasonable working system for liquid-producing capacity in the late stage of reservoir development. As a result，a set of evaluation methods suitable for the liquid-producing capacity of heavy oil reservoirs with the edge water were formed. The results demonstrate that reservoir thickness，the distance from the liquid-producing capacity enhancement well to the oil-water boundary，well spacing，and liquid-producing capacity enhancement parameters are the key factors affecting liquid-producing capacity. Field application indicates that the total oil production of 11 wells in the objective block increases by 2.47×104 t；and the average water cut grows by 0.2%；further the output-to-input ratio reaches 3.5∶1.
2021, 28(6):54-62.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.007
Abstract:
Due to high viscosity，heavy oil shows the non-Darcy flow in porous media. The numerical simulation software based on the Darcy model fails to fully consider the influence of variable starting pressure gradients and pressure sensitive effect on oilfield production indicators. In light of the heterogeneity of actual reservoirs and pressure sensitive effect，the starting pressure gradient was converted into a variable related to fluidity and its directionality was taken into account. Then a mathematical model of variable starting pressure gradients was constructed for heavy oil reservoirs，which was discretized and linearized to solve pressure and saturation in a fully implicit manner. The pre-processing and post-processing modules of the simulator were connected to ECLIPSE for the numerical simulation of typical heavy oil blocks，and the simulator was applied to a field model to characterize seepage field distribution. The results demonstrate that the starting pressure gradient will reduce the water flooding swept area，aggravate the non-piston phenomenon and the inter-layer contradiction，and the pressure sensitive effect will impair oil displacement efficiency.
Due to high viscosity，heavy oil shows the non-Darcy flow in porous media. The numerical simulation software based on the Darcy model fails to fully consider the influence of variable starting pressure gradients and pressure sensitive effect on oilfield production indicators. In light of the heterogeneity of actual reservoirs and pressure sensitive effect，the starting pressure gradient was converted into a variable related to fluidity and its directionality was taken into account. Then a mathematical model of variable starting pressure gradients was constructed for heavy oil reservoirs，which was discretized and linearized to solve pressure and saturation in a fully implicit manner. The pre-processing and post-processing modules of the simulator were connected to ECLIPSE for the numerical simulation of typical heavy oil blocks，and the simulator was applied to a field model to characterize seepage field distribution. The results demonstrate that the starting pressure gradient will reduce the water flooding swept area，aggravate the non-piston phenomenon and the inter-layer contradiction，and the pressure sensitive effect will impair oil displacement efficiency.
8 Feasibility study of geothermal energy assisted recovery for offshore shallow heavy oil reservoirs
2021, 28(6):63-70.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.008
Abstract:
The thermal recovery technology is the main method for heavy oil reservoirs in Bohai Oilfield，but it is usually accompanied with high-energy consumption and large capital expenses，restricting the exploitation of offshore heavy oil reservoir. With regard to Bohai Oilfield A with abundant geothermal resources，we proposed a deep geothermal energy assisted recovery method for shallow heavy oil reservoirs and systematically introduced its technological design. In light of the actual geological background of Bohai Oilfield A，a numerical model of geothermal energy assisted recovery for heavy oil reservoirs was built，which was combined with the heat transfer theory and oil-gas flow laws. In addition，the feasibility of this method was verified by economic evaluation，and sensitive factors were analyzed. The simulation results show that the injected water，heated by the geothermal reservoir，has a temperature above 80 ℃ when it returns to the heavy oil reservoir. The water can effectively heat the heavy oil reservoir to dramatically reduce the viscosity of heavy oil. The cumulative oil production reaches 3.0×106 m3，which is twice the cumulative oil production by conventional seawater injection. Moreover，the net present value over 20 years of production is CNY21.8×108，proving the good economic feasibility of geothermal energy assisted recovery，and the payback period is 2 years. Sensitivity analysis finds that recovery results are satisfactory at the water injection temperature of 50-60 ℃；the long horizontal well section reveals a better utilization of geothermal energy and a higher recovery factor of heavy oil；the water injection rate has multiple influences on geothermal energy assisted recovery.
The thermal recovery technology is the main method for heavy oil reservoirs in Bohai Oilfield，but it is usually accompanied with high-energy consumption and large capital expenses，restricting the exploitation of offshore heavy oil reservoir. With regard to Bohai Oilfield A with abundant geothermal resources，we proposed a deep geothermal energy assisted recovery method for shallow heavy oil reservoirs and systematically introduced its technological design. In light of the actual geological background of Bohai Oilfield A，a numerical model of geothermal energy assisted recovery for heavy oil reservoirs was built，which was combined with the heat transfer theory and oil-gas flow laws. In addition，the feasibility of this method was verified by economic evaluation，and sensitive factors were analyzed. The simulation results show that the injected water，heated by the geothermal reservoir，has a temperature above 80 ℃ when it returns to the heavy oil reservoir. The water can effectively heat the heavy oil reservoir to dramatically reduce the viscosity of heavy oil. The cumulative oil production reaches 3.0×106 m3，which is twice the cumulative oil production by conventional seawater injection. Moreover，the net present value over 20 years of production is CNY21.8×108，proving the good economic feasibility of geothermal energy assisted recovery，and the payback period is 2 years. Sensitivity analysis finds that recovery results are satisfactory at the water injection temperature of 50-60 ℃；the long horizontal well section reveals a better utilization of geothermal energy and a higher recovery factor of heavy oil；the water injection rate has multiple influences on geothermal energy assisted recovery.
2021, 28(6):71-78.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.009
Abstract:
As an alternative for steam stimulation in heavy oil reservoirs，in-situ combustion often faces many problems in thick heavy oil reservoirs，such as low vertical sweep efficiency and channeling combustion. In view of the characteristics and development history of this type of reservoirs，the existing development well pattern based on steam stimulation was used to sidetrack the horizontal section of the vertical oil production wells，and the plane fire flooding was changed to gravity fire flooding. Considering the geological and engineering conditions in the reservoirs，the influence of different factors on the development effect of gravity fire flooding with vertical well sidetracking was analyzed. In addition，the internal stimulation mechanism of this method was studied，and the evaluation model between the recovery factor and the main controlling factors was built with the multiple linear regression equation. The results show that the gravity fire flooding with vertical well sidetracking improves the recovery factor of thick heavy oil reservoirs by 42%. When the sidetracking length of the vertical well is about 1/2 of the well spacing，efficient production can be obtained. Moreover，the evaluation model of recovery factors agrees with the numerical simulation result by more than 85%，guiding the timing of converting production modes and medium-and long-term planning for the field.
As an alternative for steam stimulation in heavy oil reservoirs，in-situ combustion often faces many problems in thick heavy oil reservoirs，such as low vertical sweep efficiency and channeling combustion. In view of the characteristics and development history of this type of reservoirs，the existing development well pattern based on steam stimulation was used to sidetrack the horizontal section of the vertical oil production wells，and the plane fire flooding was changed to gravity fire flooding. Considering the geological and engineering conditions in the reservoirs，the influence of different factors on the development effect of gravity fire flooding with vertical well sidetracking was analyzed. In addition，the internal stimulation mechanism of this method was studied，and the evaluation model between the recovery factor and the main controlling factors was built with the multiple linear regression equation. The results show that the gravity fire flooding with vertical well sidetracking improves the recovery factor of thick heavy oil reservoirs by 42%. When the sidetracking length of the vertical well is about 1/2 of the well spacing，efficient production can be obtained. Moreover，the evaluation model of recovery factors agrees with the numerical simulation result by more than 85%，guiding the timing of converting production modes and medium-and long-term planning for the field.
LI Qiu
,
HE Houfeng
,
GUAN Wenlong
,
JIANG Youwei
,
TANG Junshi
,
XI Changfeng
,
ZHENG Haoran
,
WANG Xiaochun
2021, 28(6):79-86.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.010
Abstract:
Characteristics of fire flooding are the joint result of complex physicochemical processes of fire flooding and geological conditions of reservoirs，which serve as an important basis for plan design and tracking control of fire flooding. With the help of a one-dimensional combustion tube apparatus for heat tracking compensation，we comparatively analyzed the displacement characteristics of linear fire flooding of heavy oil reservoirs with different properties and compared them with those of flue gas flooding. The results show that the viscosity of crude oil significantly affects the liquid production rate by fire flooding. For the low viscosity crude oil，most of the crude oil with the high initial liquid production rate at the stage is exploited in the early and middle stages of fire flooding. While for the high viscosity crude oil，most of the crude oil with the low，or even no initial liquid production rate is exploited in the middle and late stages of fire flooding. The water cut during fire flooding mainly depends on the initial water saturation of the formation（water saturation before fire flooding）. When the initial water saturation of the formation is higher than the irreducible water saturation，the water cut is high at the beginning of fire flooding，then gradually decreases and levels off. The production performance at the initial stage of fire flooding（gas injection volume is less than one time of pore volume）is similar to that of flue gas flooding. In the continuous development，the fire flooding still maintains a stable oil recovery rate，while the recovery increment by the flue gas flooding gradually declines. The recovery by fire flooding has an approximately linear relationship with cumulative gas injection volume，which indicates that gas injection volume is crucial to the effect of fire flooding.
Characteristics of fire flooding are the joint result of complex physicochemical processes of fire flooding and geological conditions of reservoirs，which serve as an important basis for plan design and tracking control of fire flooding. With the help of a one-dimensional combustion tube apparatus for heat tracking compensation，we comparatively analyzed the displacement characteristics of linear fire flooding of heavy oil reservoirs with different properties and compared them with those of flue gas flooding. The results show that the viscosity of crude oil significantly affects the liquid production rate by fire flooding. For the low viscosity crude oil，most of the crude oil with the high initial liquid production rate at the stage is exploited in the early and middle stages of fire flooding. While for the high viscosity crude oil，most of the crude oil with the low，or even no initial liquid production rate is exploited in the middle and late stages of fire flooding. The water cut during fire flooding mainly depends on the initial water saturation of the formation（water saturation before fire flooding）. When the initial water saturation of the formation is higher than the irreducible water saturation，the water cut is high at the beginning of fire flooding，then gradually decreases and levels off. The production performance at the initial stage of fire flooding（gas injection volume is less than one time of pore volume）is similar to that of flue gas flooding. In the continuous development，the fire flooding still maintains a stable oil recovery rate，while the recovery increment by the flue gas flooding gradually declines. The recovery by fire flooding has an approximately linear relationship with cumulative gas injection volume，which indicates that gas injection volume is crucial to the effect of fire flooding.
2021, 28(6):87-93.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.011
Abstract:
To understand the underground combustion state during the fire flooding development of Du66 Block，we worked out a new method to identify the combustion state during fire flooding. Three production wells were selected to carry out the follow-up monitoring of crude oil and tail gas for five years. The gas chromatographic fingerprint technique of crude oil and the multi-dimensional gas chromatographic technique of tail gas were used to study the fingerprint characteristics and parameters of crude oil and tail gas of high-temperature oxidation during fire flooding in the production field. The results show that the chromatographic fingerprint of n-alkanes of crude oil is featured by forward main peak carbon，higher lighttoheavy ratio，increased content of light hydrocarbons，isoparaffins，and n-alkanes after high-temperature oxidation in the fire flooding production site. The chromatographic fingerprint of isoprenoid hydrocarbons shows reduced Ph/nC17 and Pr/nC18；the content of iC21 is nearly the same as or less than that of nC19. Oxygen conversion，apparent hydrogen-to-carbon atomic ratio，and carbon-dioxide content in tail gas are effective parameters for the high-temperature oxidation of fire flooding.In addition，cracked components such as olefins and hydrogen appear in the multi-dimensional chromatographic fingerprint of tail gas.
To understand the underground combustion state during the fire flooding development of Du66 Block，we worked out a new method to identify the combustion state during fire flooding. Three production wells were selected to carry out the follow-up monitoring of crude oil and tail gas for five years. The gas chromatographic fingerprint technique of crude oil and the multi-dimensional gas chromatographic technique of tail gas were used to study the fingerprint characteristics and parameters of crude oil and tail gas of high-temperature oxidation during fire flooding in the production field. The results show that the chromatographic fingerprint of n-alkanes of crude oil is featured by forward main peak carbon，higher lighttoheavy ratio，increased content of light hydrocarbons，isoparaffins，and n-alkanes after high-temperature oxidation in the fire flooding production site. The chromatographic fingerprint of isoprenoid hydrocarbons shows reduced Ph/nC17 and Pr/nC18；the content of iC21 is nearly the same as or less than that of nC19. Oxygen conversion，apparent hydrogen-to-carbon atomic ratio，and carbon-dioxide content in tail gas are effective parameters for the high-temperature oxidation of fire flooding.In addition，cracked components such as olefins and hydrogen appear in the multi-dimensional chromatographic fingerprint of tail gas.
2021, 28(6):94-100.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.012
Abstract:
In light of the characteristics and development status of heavy oil reservoirs，three surfactants with different properties were compounded based on the evaluation of static foam properties and oil displacement performance. The oil displacement efficiency of CO2 flooding assisted by different surfactants was studied，and the dominating performance of the surfactants was clarified. The experimental results show that the recovery factor of the heterogeneous core with a permeability ratio of 3.0 grows by 19.7%，13.2%，and 15.2%，respectively after CO2 flooding assisted by surfactants S1，S2，and S3，which is superior to the oil displacement by direct CO2 injection. This demonstrates that the surfactants can improve the CO2 flooding of heavy oil reservoirs in the high water-cut stage. The mechanism of enhanced oil recovery（EOR）is mainly manifested as the oil displacement contributed by surfactants and the foam induced by the surfactants with subsequent CO2.When the emulsifying capability of a surfactant is stronger，the emulsification will be more evident，and the increase in oil displacement efficiency will be larger；stronger static foaming ability makes it easier to foam with CO2 in the core；the foam formed by CO2 with the surfactant of strong foaming ability but weak stability is more favorable for deep profile control. As the permeability ratio of the heterogeneous core increases from 3.0 to 9.0，the oil displacement efficiency of CO2 flooding assisted by the three surfactants declines to varying degrees. The increase in the recovery factor of S1-assisted CO2 flooding reduces to 12.6%，and compared with S2 and S3，S1 is more adaptable to the heterogeneous changes in the core. Therefore，for the target reservoir，the compound surfactant S1 with strong emulsification，strong foaming ability，but weak stability performs best in assisting CO2 flooding for EOR.
In light of the characteristics and development status of heavy oil reservoirs，three surfactants with different properties were compounded based on the evaluation of static foam properties and oil displacement performance. The oil displacement efficiency of CO2 flooding assisted by different surfactants was studied，and the dominating performance of the surfactants was clarified. The experimental results show that the recovery factor of the heterogeneous core with a permeability ratio of 3.0 grows by 19.7%，13.2%，and 15.2%，respectively after CO2 flooding assisted by surfactants S1，S2，and S3，which is superior to the oil displacement by direct CO2 injection. This demonstrates that the surfactants can improve the CO2 flooding of heavy oil reservoirs in the high water-cut stage. The mechanism of enhanced oil recovery（EOR）is mainly manifested as the oil displacement contributed by surfactants and the foam induced by the surfactants with subsequent CO2.When the emulsifying capability of a surfactant is stronger，the emulsification will be more evident，and the increase in oil displacement efficiency will be larger；stronger static foaming ability makes it easier to foam with CO2 in the core；the foam formed by CO2 with the surfactant of strong foaming ability but weak stability is more favorable for deep profile control. As the permeability ratio of the heterogeneous core increases from 3.0 to 9.0，the oil displacement efficiency of CO2 flooding assisted by the three surfactants declines to varying degrees. The increase in the recovery factor of S1-assisted CO2 flooding reduces to 12.6%，and compared with S2 and S3，S1 is more adaptable to the heterogeneous changes in the core. Therefore，for the target reservoir，the compound surfactant S1 with strong emulsification，strong foaming ability，but weak stability performs best in assisting CO2 flooding for EOR.
2021, 28(6):101-106.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.013
Abstract:
The water-flooding development in ordinary heavy oil reservoirs faces the problem of low oil recovery due to high crude oil viscosity and serious fingering. It is urgent to change the development method to further enhance oil recovery. Taking the ordinary heavy oil reservoirs in Block B21，Gudao Oilfield as the target area，through numerical simulation，we established the boundary chart of the reasonable viscosity ratios between the displacing phase and crude oil for polymer flooding in reservoirs with different crude oil viscosity. Through indoor viscosity-increasing experiments，we determined the polymer concentration limit applicable to the target area. Then numerical simulation was conducted to optimize and determine the best polymer injection concentration. Combining physical simulation experiments，we optimized the alternate in? jection method of high and low concentrations，thereby greatly improving oil recovery under the same polymer usage. Considering development effect and economic efficiency，the usage chart of economic limits under different crude oil and polymer prices was formulated，which can significantly guide the economic and efficient development of polymer flooding in ordinary heavy oil reservoirs. Field application results showed that as of July 2021，the daily oil production has witnessed a maximal increase of 156 t/d from 285 t/d to 441 t/d，and the composite water cut has seen the largest decrease of 12.9% from 89.1% to 76.2%. The cumulative oil increment was 61.4×104 t，and the oil recovery has improved by 7.0%，achieving an obvious effect of oil production increase and water cut decrease.
The water-flooding development in ordinary heavy oil reservoirs faces the problem of low oil recovery due to high crude oil viscosity and serious fingering. It is urgent to change the development method to further enhance oil recovery. Taking the ordinary heavy oil reservoirs in Block B21，Gudao Oilfield as the target area，through numerical simulation，we established the boundary chart of the reasonable viscosity ratios between the displacing phase and crude oil for polymer flooding in reservoirs with different crude oil viscosity. Through indoor viscosity-increasing experiments，we determined the polymer concentration limit applicable to the target area. Then numerical simulation was conducted to optimize and determine the best polymer injection concentration. Combining physical simulation experiments，we optimized the alternate in? jection method of high and low concentrations，thereby greatly improving oil recovery under the same polymer usage. Considering development effect and economic efficiency，the usage chart of economic limits under different crude oil and polymer prices was formulated，which can significantly guide the economic and efficient development of polymer flooding in ordinary heavy oil reservoirs. Field application results showed that as of July 2021，the daily oil production has witnessed a maximal increase of 156 t/d from 285 t/d to 441 t/d，and the composite water cut has seen the largest decrease of 12.9% from 89.1% to 76.2%. The cumulative oil increment was 61.4×104 t，and the oil recovery has improved by 7.0%，achieving an obvious effect of oil production increase and water cut decrease.
2021, 28(6):107-113.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.014
Abstract:
Polymer viscosity reducer shows a good application prospect in the recovery of conventional heavy oil reservoirs.The basic properties and emulsifying viscosity reduction properties of partially hydrolyzed polyacrylamide（HPAM）and two polymer viscosity reducers（P-OVR-1 and P-OVR-3）were compared in this paper. The contributions of their apparent viscosity and activity to enhanced oil recovery during the displacement were studied in depth. The results show that P-OVR-1 and P-OVR-3 have good emulsifying viscosity reduction properties for heavy oil，mainly through emulsifying and dispersing the crude oil. The smaller the particle size of the emulsion comes with a better viscosity reduction effect. Under the effects of increasing water-phase viscosity and reduced oil-phase emulsifying viscosity of P-OVR-1 and P-OVR-3，the oil recovery in large pores and small pores was increased in varying degrees. The enhanced oil recoveries of large and small pores after P-OVR-3 flooding were 8.48% and 9.59% respectively. The residual oil in small pores was mainly obtained by the viscoelasticity of polymer viscosity reducers. In large pores，the efficient displacement of columnar residual oil and oil film was realized mainly depending on the high surface activity of polymer viscosity reducer to reduce the capillary force，adhesion and cohesion.
Polymer viscosity reducer shows a good application prospect in the recovery of conventional heavy oil reservoirs.The basic properties and emulsifying viscosity reduction properties of partially hydrolyzed polyacrylamide（HPAM）and two polymer viscosity reducers（P-OVR-1 and P-OVR-3）were compared in this paper. The contributions of their apparent viscosity and activity to enhanced oil recovery during the displacement were studied in depth. The results show that P-OVR-1 and P-OVR-3 have good emulsifying viscosity reduction properties for heavy oil，mainly through emulsifying and dispersing the crude oil. The smaller the particle size of the emulsion comes with a better viscosity reduction effect. Under the effects of increasing water-phase viscosity and reduced oil-phase emulsifying viscosity of P-OVR-1 and P-OVR-3，the oil recovery in large pores and small pores was increased in varying degrees. The enhanced oil recoveries of large and small pores after P-OVR-3 flooding were 8.48% and 9.59% respectively. The residual oil in small pores was mainly obtained by the viscoelasticity of polymer viscosity reducers. In large pores，the efficient displacement of columnar residual oil and oil film was realized mainly depending on the high surface activity of polymer viscosity reducer to reduce the capillary force，adhesion and cohesion.
CHEN Guihua
,
WU Guanghuan
,
QUAN Hong
,
ZHAO Hongyu
,
DENG Hongwei
,
WEI Tao
,
ZHANG Wei
,
KANG Yuanyong
2021, 28(6):114-121.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.015
Abstract:
In order to effectively produce deep，low-permeability and sensitive heavy oil reservoirs which is extremely difficult to develop，this paper takes Block Wang152 of Wangjiagang Oilfield in Shengli Oil Province as an example to conduct in-depth analysis of development difficulties and flow mechanism，and on this basis，puts forward an innovative technology of viscosity reduction induced flooding. Besides，in virtue of the single-tube sand-filling flooding model experiments，reservoir engineering methods and numerical simulation methods，the paper studies the development technology limits of deep，low-permeability and sensitive heavy oil reservoirs. According to the proposed technology，viscosity reduction is implemented in producing wells for them to enhance huff-and-puff recovery；early continuous flooding with variable concentrations and later viscosity reduction and flooding with variable concentrations and slugs are implemented in injection wells. The results show that the technology helps increase the recovery of deep，low-permeability and sensitive heavy oil reservoirs by 14.3%. The key parameters of the development technology such as the flooding mode，the effective cycle，the concentration of viscosity reducers，and the injection volume are also optimized and determined. The pilot test results of Wang152-X6 well group in Block Wang152 show that，by September 2020，the peak daily oil production of the well group was 11.5 t/d，which was 5.4 times higher than that before the test. After 157 days of flooding with a cumulative injection of 6 534 m3，the viscosity reduction induced flooding proved effective in all production wells，and the cumulative oil production of the well group reached 856 t. Due to the significantly improved development，the oil recovery was predicted to increase by 11.0%，which has realized the transition from un-producing to effective producing of deep，low-permeability and sensitive heavy oil reservoirs.
In order to effectively produce deep，low-permeability and sensitive heavy oil reservoirs which is extremely difficult to develop，this paper takes Block Wang152 of Wangjiagang Oilfield in Shengli Oil Province as an example to conduct in-depth analysis of development difficulties and flow mechanism，and on this basis，puts forward an innovative technology of viscosity reduction induced flooding. Besides，in virtue of the single-tube sand-filling flooding model experiments，reservoir engineering methods and numerical simulation methods，the paper studies the development technology limits of deep，low-permeability and sensitive heavy oil reservoirs. According to the proposed technology，viscosity reduction is implemented in producing wells for them to enhance huff-and-puff recovery；early continuous flooding with variable concentrations and later viscosity reduction and flooding with variable concentrations and slugs are implemented in injection wells. The results show that the technology helps increase the recovery of deep，low-permeability and sensitive heavy oil reservoirs by 14.3%. The key parameters of the development technology such as the flooding mode，the effective cycle，the concentration of viscosity reducers，and the injection volume are also optimized and determined. The pilot test results of Wang152-X6 well group in Block Wang152 show that，by September 2020，the peak daily oil production of the well group was 11.5 t/d，which was 5.4 times higher than that before the test. After 157 days of flooding with a cumulative injection of 6 534 m3，the viscosity reduction induced flooding proved effective in all production wells，and the cumulative oil production of the well group reached 856 t. Due to the significantly improved development，the oil recovery was predicted to increase by 11.0%，which has realized the transition from un-producing to effective producing of deep，low-permeability and sensitive heavy oil reservoirs.
2021, 28(6):122-128.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.016
Abstract:
After multi-cycle cyclic steam stimulation（CSS），heat interconnections and high heat-consuming channels form between oil wells in heavy oil reservoirs，which results in low thermal efficiency and poor development effect. Since the combined viscosity reduction flooding for chemical water shutoff and profile control is considered as a green and low-carbon replaced method for effective recovery，studying its mechanisms is crucial to guiding on-site projects. Considering the characteristics of the experimental oil reservoir，this paper selects chemical agents to build the combined viscosity reduction flooding system for chemical water shutoff and profile control，and studies the oil displacement mechanism of the system by laboratory experiments. The results show that water shutoff and profile control agents with high viscosity can reduce the oil-water mobility ratio，enhance the production of residual oil in small pores，effectively inhibit viscous fingering，improve the mobility，and adjust the flow field. Absorbed on the surface of crude oil，viscosity reducers can improve the oil phase flow ability and enhance the oil flooding efficiency. Meanwhile，by blocking throats of corresponding size，emulsion droplets help increase the flow resistance of the channeling-path and expand the swept ranges，which can realize viscosity reduction and profile control. There is synergistic effect between water shutoff and profile control agents and viscosity reducers. Water shutoff and profile control agents improve the emulsifying capacity of viscosity reducers and facilitate them to enter the low-permeability area，which improve the production overall reservoirs. Since the remaining oil at the edges and the residual oil could be produced by using water shutoff and profile control agents and viscosity reducers respectively，the remaining oil saturation is significantly reduced.
After multi-cycle cyclic steam stimulation（CSS），heat interconnections and high heat-consuming channels form between oil wells in heavy oil reservoirs，which results in low thermal efficiency and poor development effect. Since the combined viscosity reduction flooding for chemical water shutoff and profile control is considered as a green and low-carbon replaced method for effective recovery，studying its mechanisms is crucial to guiding on-site projects. Considering the characteristics of the experimental oil reservoir，this paper selects chemical agents to build the combined viscosity reduction flooding system for chemical water shutoff and profile control，and studies the oil displacement mechanism of the system by laboratory experiments. The results show that water shutoff and profile control agents with high viscosity can reduce the oil-water mobility ratio，enhance the production of residual oil in small pores，effectively inhibit viscous fingering，improve the mobility，and adjust the flow field. Absorbed on the surface of crude oil，viscosity reducers can improve the oil phase flow ability and enhance the oil flooding efficiency. Meanwhile，by blocking throats of corresponding size，emulsion droplets help increase the flow resistance of the channeling-path and expand the swept ranges，which can realize viscosity reduction and profile control. There is synergistic effect between water shutoff and profile control agents and viscosity reducers. Water shutoff and profile control agents improve the emulsifying capacity of viscosity reducers and facilitate them to enter the low-permeability area，which improve the production overall reservoirs. Since the remaining oil at the edges and the residual oil could be produced by using water shutoff and profile control agents and viscosity reducers respectively，the remaining oil saturation is significantly reduced.
2021, 28(6):129-134.
DOI: 10.13673/j.cnki.cn37-1359/te.2021.06.017
Abstract:
Permeable viscosity reducing displacement agent is a polymer viscosity reducing agent，which has excellent effects of water-phase viscosity increasing and oil-phase viscosity reducing. It can inhibit water channeling and effectively improve the recovery of heavy oil by water flooding. From the mesoscopic and microscopic levels，the mechanism of enhanced oil recovery by permeable viscosity reducing displacement agent had been analyzed and explored. CT scanning oil displacement experimental study shows that in the process of simulating heterogeneous reservoir flooding，2 peaks of pure oil phase and emulsion phase appear，and the equilibrium utilization of high and low permeability layers is realized. The results of micro displacement model displacement experiments show that permeable viscosity reducing displacement agent can form many kinds of fluid forms with heavy oil during the displacement process and play different roles in the process of reservoir flooding：the formation of oil-in-water（W/O）emulsion at the initial stage of displacement will enlarge the swept volume. Continue to inject the agent，W/O emulsion can be converted into water-in-oil-in-water（W/O/W）emulsion to improve flow capacity. The formation of micro emulsion can improve the stripping efficiency of oil phase on rocks. The distribution characteristics of remaining oil after displacement by permeable viscosity reducing displacement agent show that the relative content of cluster flow and drop flow is significantly reduced，indicating that it has excellent sweep expansion and oil washing effect，which has important reference significance for remarkable improving the recovery of low efficiency water flooding heavy oil reservoirs.
Permeable viscosity reducing displacement agent is a polymer viscosity reducing agent，which has excellent effects of water-phase viscosity increasing and oil-phase viscosity reducing. It can inhibit water channeling and effectively improve the recovery of heavy oil by water flooding. From the mesoscopic and microscopic levels，the mechanism of enhanced oil recovery by permeable viscosity reducing displacement agent had been analyzed and explored. CT scanning oil displacement experimental study shows that in the process of simulating heterogeneous reservoir flooding，2 peaks of pure oil phase and emulsion phase appear，and the equilibrium utilization of high and low permeability layers is realized. The results of micro displacement model displacement experiments show that permeable viscosity reducing displacement agent can form many kinds of fluid forms with heavy oil during the displacement process and play different roles in the process of reservoir flooding：the formation of oil-in-water（W/O）emulsion at the initial stage of displacement will enlarge the swept volume. Continue to inject the agent，W/O emulsion can be converted into water-in-oil-in-water（W/O/W）emulsion to improve flow capacity. The formation of micro emulsion can improve the stripping efficiency of oil phase on rocks. The distribution characteristics of remaining oil after displacement by permeable viscosity reducing displacement agent show that the relative content of cluster flow and drop flow is significantly reduced，indicating that it has excellent sweep expansion and oil washing effect，which has important reference significance for remarkable improving the recovery of low efficiency water flooding heavy oil reservoirs.
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