Multi-thermal Fluid Research Articles

Phased optimization of multi-thermal fluid flooding for enhanced oil recovery

Multi-thermal fluid flooding has become a critical technique in heavy oil reservoirs and is widely applied in China. Owing to the complexity of the displacement process and the involvement of multiple injection media, conventional optimization methods are unable to achieve economic and efficient development of heavy oil. In this study, an efficient phased parametric optimization method for multi-thermal fluid flooding was developed using horizontal wells in heavy oil reservoirs. This method utilizes particle swarm optimization (PSO), which targets the net present value for the phased optimization of multi-thermal fluid flooding. A comparison between the phased optimization and non-phased optimization shows that the cumulative oil production increased by 16.74% and the net present value increased by 39.66% with phased optimization. The effectiveness of the phased optimization method was verified using a field model. Optimal injection parameter charts were developed for each phase of the multi-thermal fluid flooding under different reservoir parameter conditions. The charts illustrate that the optimal gas injection rate and chemical mass concentration tend towards zero during the steam flooding initiation phase under varying reservoir parameter conditions. Conversely, all the media injection rates increased during the thermal fluid control and steam breakthrough phases. Additionally, with an increase in the crude oil viscosity, effective formation thickness, and original oil saturation, the optimal injection rate of the various media increases. However, with an increase in the permeability and reservoir depth, the optimal injection rate of the various media decreases.

Mathematical modeling for the production performance of cyclic multi-thermal fluid stimulation process in layered heavy oil reservoirs

Multi-thermal fluid (MTF), with a unique thermophysical characteristics, has been widely applied in the enhanced heavy oil recovery processes. Especially for the layered heavy oil reservoirs, MTF shows more attractive than the conventional saturated steam. In this study, we propose an improved mathematical model for the production performance of cyclic MTF stimulation process in layered heavy oil reservoirs. In this model, based on a three-zone assumption, we first derive a productivity model for the thermal-fluids huff-n-puff process in layered heavy oil reservoirs. Thereafter, considering the typical EOR mechanisms of non-condensable gases in MTF, the viscosity reduction effect caused by CO2 dissolution and the effect of formation energy supplement caused by N2 are mathematically described. Simultaneously, because of the nonlinear temperature spreading behavior in the formation, an MTFs flooding experiment is also performed to characterize the effect. Meanwhile, a heating radius model with the consideration of steam overlap effect is also involved in our model. Then, the calculation results are compared against the results of a commercial simulator to confirm the accuracy, while a sensitivity analysis on the reservoir and operation parameters is performed. This paper provides a quick estimation approach for the productivity of cyclic MTF stimulation process in layered heavy oil reservoirs.

A Novel Prediction Model for Steam Temperature Field of Downhole Multi-Thermal Fluid Generator

Aiming at the low efficiency of heavy-oil thermal recovery, a downhole multi-thermal fluid generator (DMTFG) can improve the viscosity reduction effect by reducing the heat loss of multi-thermal fluid in the process of wellbore transportation. The steam generated by the MDTFG causes damage to the packer and casing, owing to the return upwards along the annular space passage of the oil casing. To mitigate this damage, a heat transfer model for multi-channel coiled tubing wells and a prediction model for the upward return of the steam temperature field in the annulus were established with the basic laws of thermodynamics. Models were further verified by ANSYS. The results indicate the following four conclusions. First of all, when the surface pressure is constant, the deeper the located DMTFG, the shorter the distance for the steam to return would be. It is easier to liquefy the steam. Second, the higher the temperature of the steam produced by the downhole polythermal fluid generator, the larger the upward distance of the steam would be. Third, the higher the steam pressure at the outlet of the downhole polythermal fluid generator, the smaller the distance of steam upward return would be. Finally, the larger the diameter of the multi-channel conversion piping, the greater the distance of the steam return would be. It is meaningful to provide valuable theoretical guidance for packer position designing in the field. Meanwhile, the study also provides a modeling basis for the subsequent study of artificial intelligence in the downhole temperature field.

Diffusion and Dissolution Behaviors of CO2, CH4, and N2 in Heavy Oil under High-Temperature and -Pressure Conditions: Insights into Heavy Oil Production via Multithermal Fluid Stimulation

Diffusion and Dissolution Behaviors of CO₂, CH₄, and N₂ in Heavy Oil under High-Temperature and -Pressure Conditions: Insights into Heavy Oil Production via Multithermal Fluid Stimulation

Experimental investigation on supercritical multi-thermal fluid flooding using a novel 2-dimensional model

Supercritical multi-thermal fluid (SCMTF) is a promising alternative to traditional thermal agents for deep heavy oil recovery. However, no 2-dimensional experimental investigation on SCMTF flooding has been conducted due to the limitations of existing apparatuses. Therefore, the primary objective of this study is to develop a novel assembly for investigating the performance of SCMTF flooding. Subsequently, the SCMTF chamber evolution is characterized using newly developed equipment, and enhanced oil recovery (EOR) mechanisms are proposed. Finally, the effects of the injection temperature, injection pressure, scN2/scCO2 mixture, and heavy oil viscosity on SCMTF are comprehensively studied. The results show that the SCMTF chamber displays an inverted trapezoidal shape with a uniform front. SCMTF flooding can enhance heavy oil recovery by 13.36% relative to steam flooding by sweep area expansion, oil mobility improvement, and miscible flooding. Increasing the injection temperature, injection pressure or scN2/scCO2 mixture to SCW molar ratio can facilitate the production of heavy oil, while using SCMTF in an extra-heavy oil cannot maximize the EOR effect of SCMTF. Notably, the high yield of coke produced at elevated temperatures may lead to potential formation damage.

Cyclic Supercritical Multi-Thermal Fluid Stimulation Process: A Novel Improved-Oil-Recovery Technique for Offshore Heavy Oil Reservoir

Cyclic supercritical multi-thermal fluid stimulation (CSMTFS) is a novel technology that can efficiently recover heavy oil, while the heating effect, production and heat loss characteristics of CSMTFS have not been discussed. In this study, a physical simulation experiment of CSMTFS is conducted with a three-dimensional experimental system. The results of the study indicate that the whole process of CSMTFS can be divided into four stages, namely, the preheating stage, production increase stage, production stable stage and production decline stage, of which the production stable stage is the main oil production stage, and the production decline stage is the secondary oil production stage. In the first two stages of the CSMTFS process, there is no supercritical multi-thermal fluid chamber, and only a relatively small supercritical multi-thermal fluid chamber is formed in the last stage of the CSMTFS process. Out of the supercritical multi-thermal fluid chamber, supercritical water in the thermal fluids condensates to hot water and flows downward to heat the subjacent oil layer. At the same time, the non-condensate gas in the thermal fluids accumulates to the upper part of the oil layer and reduces heat loss. The analysis of heat loss shows that the heat loss rate gradually increases at first and then tends to be stable. Compared with conventional thermal fluid, the CSMTFS can more effectively reduce heat loss. The enthalpy value of supercritical multi-thermal fluid is significantly increased compared with that of multi-thermal fluid, which effectively solves the problem of insufficient heat carrying capacity of multi-thermal fluid. Overall, cyclic supercritical multi-thermal fluid stimulation can effectively solve the problems of conventional heavy oil thermal recovery technology in offshore heavy oil recovery; it is indeed a new improved-oil-recovery technique for offshore heavy oil. The findings of this study can help in better understanding the cyclic supercritical multi-thermal fluid stimulation process. This study is significant and helpful for application of CSMTFS technology in heavy oil recovery.

A Study on Generation and Feasibility of Supercritical Multi-Thermal Fluid

Supercritical multi-thermal fluid is an emerging and efficient heat carrier for thermal recovery of heavy oil, but the generation of supercritical multi-thermal fluid and its feasibility in thermal recovery are rarely discussed. In this paper, generation and flooding experiments of supercritical multi-thermal fluid were carried out, respectively, for the generation and feasibility of supercritical multi-thermal fluid. During the experiment, the temperature and pressure in the reactor and sand-pack were monitored and recorded, the fluid generated by the reaction was analyzed by chromatography, and enthalpy of the reaction product and displacement efficiency were calculated, respectively. The experimental results showed that the change in temperature and pressure in the reactor could be roughly divided into three stages in the generation process of supercritical multi-thermal fluid. The higher the proportion of oil in the reactant, the higher the maximum temperature in the reactor. When the proportion of oil and water in the reactant was constant, the temperature rise in the reactor was basically the same under different initial temperature and pressure conditions. Compared with the initial temperature and pressure, the oil–water ratio of the reactants had a significant effect on the generated supercritical multi-thermal fluid. The higher the proportion of oil, the more gas that was generated in the supercritical multi-thermal fluid, and the lower the specific enthalpy of the thermal fluid. Under the same proportion of oil and water, the gas–water mass ratio of the supercritical multi-thermal fluid generated by the reaction of crude oil was lower, and the specific enthalpy was higher. Through this study, it was found that supercritical multi-thermal fluid with a low gas–water mass ratio had higher oil displacement efficiency, higher early oil recovery rate, a larger supercritical area formed in the oil layer, and later channeling. The results of this study show that the optimal gas–water mass ratio of supercritical multi-thermal fluid was about 1, under which the oil displacement efficiency and supercritical area in the oil layer reached the maximum. Correspondingly, the optimal proportion of oil in the reactant when generating supercritical multi-component thermal fluid was about 10%. In oilfield applications, because the gas–water ratio in supercritical multi-component thermal fluid has a significant impact on oil displacement efficiency, the optimization of supercritical multi-thermal fluid should not only consider the generation process but also consider the oil displacement effect of the thermal fluid. The findings of this study could improve our understanding of the characteristics of generating supercritical multi-thermal fluid and the feasibility of supercritical multi-thermal fluid generated under different conditions in the oil displacement process. This research is of great significance for field applications of supercritical multi-thermal fluid.

The Supercritical Multithermal Fluid Flooding Investigation: Experiments and Numerical Simulation for Deep Offshore Heavy Oil Reservoirs

The supercritical multithermal fluids (SCMTF) were developed for deep offshore heavy oil reservoirs. However, its EOR mechanisms are still unclear, and its numerical simulation method is deficient. In this study, a series of sandpack flooding experiments were first performed to investigate the viability of SCMTF flooding. Then, a novel numerical model for SCMTF flooding was developed based on the experimental results to characterize the flooding processes and to study the effects of injection parameters on oil recovery on a lab scale. Finally, the performance of SCMTF flooding in a practical deep offshore oil field was evaluated through simulation. The experiment results show that the SCMTF flooding gave the highest oil recovery of 80.89%, which was 29.60% higher than that of the steam flooding and 11.09% higher than that of SCW flooding. The history matching process illustrated that the average errors of 3.24% in oil recovery and of 4.33% in pressure difference confirm that the developed numerical model can precisely simulate the dynamic of SCMTF flooding. Increases in temperature, pressure, and the mole ratio of scN2 and scCO2 mixture to SCW benefit the heavy oil production. However, too much increase in temperature resulted in formation damage. In addition, an excess of scN2 and scCO2 contributed to an early SCMTF breakthrough. The field-scale simulation indicated that compared to steam flooding, the SCMTF flooding increased cumulative oil production by 27122 m3 due to higher reservoir temperature, expanded heating area, and lower oil viscosity, suggesting that the SCMTF flooding is feasible in enhancing offshore heavy oil recovery.

Cooperative Mechanism and Technology Parameters Optimization of Multi-thermal Fluid Huff & Puff Development in Heavy Oil Reservoir

The extra-heavy oil reservoirs in Central Asia have the characteristics of shallow burial, high crude oil viscosity, and strong reservoir heterogeneity. Conventional steam huff&puff have good initial development effects, but because energy cannot be replenished in time, steam huff&puff in the later stages huff&puff production declined fast and the effective production time is short. According to the current situation of oil reservoir development, a development technology combining multi-thermal fluid huff&puff and steam huff&puff is proposed. At the initial stage of production, steam is used to reduce viscosity, and in the later stage, N₂ in the multi-thermal fluid is used to pressurize, expand the steam chamber volume, and dissolved CO₂ to reduce viscosity. For single wells of different modes, using numerical simulation to design reasonable combined development modes and injection parameters, the research shows that multi-thermal fluid huff&puff after 5 cycles of steam huff&puff can achieve the best oil increase effect, and the best steam injection intensity 10t/m, gas injection intensity of 1500m3/m, 29 wells have been implemented in M heavy oil field in Central Asia. after use the multi-thermal fluid and superheated steam huff&puff coordinated development methods, the average well daily oil increment reached 0.6-4t/d, the water cut is reduced by 10-21%, the oil-steam ratio is increased by 0.4-0.6, realizing the efficient development of shallow buried extra-heavy oil reservoirs.

Experimental investigation of a novel method for heavy oil recovery using supercritical multithermal fluid flooding

The objective of this study was primarily directed to the development of experimental setups to investigate the potential of supercritical multithermal fluid (SCMTF) flooding processes. Then, the recovery mechanisms of SCMTF flooding were proposed for the first time. Finally, the impact of the injection temperature, injection pressure, injection rate, and supercritical nitrogen (scN2) and supercritical carbon dioxide (scCO2) mixture amount on the SCMTF flooding performance were systematically studied in this research. The results show that SCMTF flooding is a technically and economically viable recovery process for deep heavy oil reservoirs. Supercritical water (SCW) has a greater role than the scN2 + scCO2 mixture in SCMTF flooding. The most-efficient SCMTF flooding recovered an additional 32.24% of the original oil in place (OOIP) compared to steam flooding. The injection of SCMTF at a high temperature or pressure is beneficial for the production of heavy oil. However, the high yield of coke produced at a high temperature may lead to potential formation damage. Thus, using an intermediate amount of the scN2 + scCO2 mixture in SCMTF may lead to more efficient and economical performance.

Corrosion behavior of Cr-bearing steels in CO2-O2-H2O multi-thermal-fluid environment

Multi-thermal fluid is used to enhance heavy oil recovery, but it also causes severe corrosion failure of metallic tubing and its mechanism is still open to debate. In the present work, the corrosion behavior of commercial steels with different Cr content (3 wt%, 9 wt%, and 25 wt%) in simulated CO2-O2-H2O multi-thermal fluid environments were studied by immersion corrosion test and microstructural characterization. The results exhibit that the Cr content of steel determines the type of corrosion products. The less protective corrosion scale is mainly composed of FeCO3, (Fe, Cr)3O4, and Fe2O3, which is formed on the surface of 3Cr and 9Cr steels. The protective corrosion scale is mainly Cr2O3, which is formed on the surface of 25Cr steel. Only when the Cr content in steel is sufficient (i.e. 25 wt%) to repair the serious depletion of Cr in the metal near the scale/metal interface in time, can protection of the corrosion scale be sustained, to improve its ability to resist the corrosion of multi-thermal fluids.

Pyrolysis of heavy oil in supercritical multi-thermal fluid: An effective recovery agent for heavy oils

As a novel thermal agent, supercritical multi-thermal fluid (SCMTF) has great potential to be used for heavy oil reservoirs. However, its viability and enhanced oil recovery (EOR) mechanisms have not been investigated. Therefore, a series of tests were conducted in a newly designed autoclave to compare crude oil pyrolysis in steam, supercritical water (SCW), SCW + supercritical nitrogen (scN2), SCW + supercritical carbon dioxide (scCO2) and SCMTF, and the viability of SCMTF was evaluated. Then, the possible mechanisms of pyrolysis in SCMTF were proposed. Finally, the effects of temperature, pressure, and the amount of SCMTF on pyrolysis in SCMTF were investigated. The results show that the SCMTF treatment of raw crude oil at 653 K and 23 MPa resulted in molecular weight, density and C15+ content reduction rates of 44.67%, 6.45% and 12.06%, respectively, and gave a gas yield of 7.91 wt % and an increase in the light oil fraction of 10.17 wt %. SCMTF is more effective than steam, SCW and SCW + scN2 for upgrading heavy oil. In detail, SCW dominates the pyrolysis processes; scCO2 accelerates dealkylation, and increases oil mobility by dissolution and light hydrocarbons extraction; and scN2 can maintain reservoir pressure and form a gas-cap, which reduces heat loss. Increases in scCO2 fraction, temperature, pressure and the amount of SCMTF can enhance the heavy oil upgrading. However, pyrolysis at a high temperature is adverse to light oil production (the oil product yield was merely 67.10% at 683 K) due to undesirably high gas and coke yields of 13.32% and 19.58%, respectively.

Analysis on PVT test and empirical formula of Bohai heavy oil with different types of dissolved gases

Accurate prediction of PVT properties of heavy oil system is of great significance to the design of injection–production parameters and dynamic analysis of multi-thermal fluid stimulation in heavy oil reservoir. The saturation pressure and viscosity of Bohai heavy oil system at different temperature and different gas oil ratio conditions were tested and analyzed. The functional relations of regression equations for saturation pressure and viscosity are constructed based on classical PVT correlations, but the parameters in the equations different from classical correlations are obtained from present experiment test data with multiple regression method. The empirical formula analysis results indicate that the 2-parameter equation can almost completely fit the experimental data, but its application scope is narrow. Although the 4-parameter equation has an extensive adaptability, its fitting accuracy is very low. The 3-parameter equation can not only better fit the saturation pressure and viscosity of heavy oil for the same gas under different dissolved gas oil ratios and different temperatures, but also has a wide application range. It is recommended to use the 3-parameter equation for physical property analysis and calculation of heavy oil. The research results provide a basis for the accurate prediction of heavy oil PVT parameters.

Experimental study on horizontal-well multi-thermal fluid stimulation process in offshore heavy oil reservoirs

The development of offshore heavy oil is sensitive and complex, which is limited by factors such as platform space, economy, pollution and security, so conventional thermal recovery techniques such as cyclic steam stimulation and steam flooding have difficulty in achieving favorable development effect for offshore heavy oil reservoirs. Horizontal-well multi-thermal fluid stimulation (HW-MTFS) process is a relatively new thermal recovery technique, which combines the multiple advantages of gas injection, horizontal well and thermal recovery process. In this paper, the HW-MTFS physical model was firstly designed. Thereafter, the influences of different factors on steam absorption along horizontal wellbore were studied by sand-packed model experiments. Finally, the development performance of horizontal-well cyclic steam stimulation (HW-CSS) process and horizontal-well multi-thermal fluid stimulation process was compared by two groups of physical experiments. The results indicate that different injection factors significantly influenced the steam absorption along horizontal wellbore. Compared with steam injection, the multi-thermal fluid injection could effectively improve the steam absorption along horizontal wellbore. The HW-MTFS process had a higher oil rate and production, and the recovery of HW-MTFS process was 42% higher than that of HW-CSS in three cycles.

Corrosion mechanism of electroless Ni–Sn–P coating in multi thermal fluid

Multi thermal fluid generated by burning of fuel and oxygen-containing gas has been applied to enhance the production of heavy oil. While the thermal fluid containing carbon dioxide, nitrogen gas, oxygen and steam has caused serious corrosion damage of metallic tubing. Electroless Ni-P coatings show excellent corrosion resistance in many environments and Sn seems to have the potential to improve coating toughness and corrosion resistance. In the present work, Ni–Sn–P coating was prepared on N80 tubing substrate by electroless method, and its corrosion performance in multi thermal fluid was investigated. The results revealed that electroless Ni–Sn–P coating containing ∼2 wt% Sn was dense, defect-free and uniform, and possessed amorphous structure. After 240 h exposure, the bare N80 tubing suffered from severe corrosion and formed a thick, complex, and porous corrosion scale mainly composed of iron oxides. In contrast, N80 tubing substrate with Ni–Sn–P coating showed much more excellent corrosion resistance by forming an extremely thin NiO/Ni(OH)2/SnO2 corrosion layer and maintaining the amorphous structure.

Roles of Flue Gas in Promoting Steam Flow and Heat Transfer in Multithermal Fluid Flooding

Multithermal fluid technology is becoming an important method in the field of heavy oil development. However, because of insufficient investigation on the heat transfer for the multithermal fluid, some development phenomena and characteristics still cannot be well explained. In order to determine the effect of flue gas on the thermal swept scope, multithermal fluid flooding experiments were carried out through 1D sandpack. The temperatures along the sandpack were measured. On this basis, steam heat transfer simulation experiments were conducted and the heat transfer coefficients were calculated. The mechanism of flue gas on steam heat transfer was analyzed. The results show that at the same heat injection conditions, the thermal swept scope for the multithermal fluid flooding was larger than that for the steam flooding. With the increase of flue gas proportion in the multithermal fluid, the heat transfer coefficient decreased and the condensation pattern was transformed from drop condensation to film condensation gradually. The flue gas can form gas film on the surface of the cold body and inhibit the heat transfer between steam and the cold body. Because of the inhibiting effect of flue gas on steam heat transfer, flue gas can reduce the heat transferred to the rock matrix in flooding and thus promote steam to carry more heat further. Meanwhile, flue gas can accelerate the flow of steam in porous media, which also leads to the expansion of the thermal swept scope for the multithermal fluid flooding.

Experimental study on the mechanism of enhanced oil recovery by multi-thermal fluid in offshore heavy oil

The multi-thermal fluid process is a new technology that was generated for the development of offshore heavy oil. It has achieved remarkable results in the development of Bohai Oilfield. However, the mechanism of enhanced oil recovery still requires further discussion. Based on the physical similarity criterion, a physical simulation experimental device was independently designed to execute laboratory experiments on different thermal recovery methods (hot water, steam, and multi-thermal fluid), after which the contents of the four components of developed heavy oil were measured and analyzed. The results of the physical simulation experiments indicated that: (1) Thermal viscosity reduction and thermal expansion are the principle mechanisms of hot water flooding; (2) Thermal viscosity reduction and steam distillation are the principle mechanisms of steam flooding, which are accompanied by a certain degree of aquathermal cracking reaction between heavy oil and steam; and (3) thermal viscosity reduction and aquathermal cracking reaction are the principle mechanisms of multi-thermal fluid flooding. Due to the synergistic effect of nitrogen and carbon dioxide, the effect of viscosity reduction by the dissolution effect and gas-water hybrid drive must also be considered. The analysis results of the four components of developed heavy oil by the different thermal recovery methods indicated that the multi-thermal fluid changed the balance of the aromatics-asphaltene-resin regime and strengthened the development degree of the asphaltene component in heavy oil, thereby improving oil recovery through the thermal/physical/chemical mechanism.

Production prediction of cyclic multi-thermal fluid stimulation in a horizontal well

Cyclic multi-thermal fluid stimulation (i.e., huff and puff) in a horizontal well is an effective way to recover offshore heavy oil reservoirs. To rapidly predict reservoir production performance, an analytical model for predicting the productivity of a cyclic multi-thermal fluid stimulation in a horizontal well was developed in this study. The underlying assumption in this study is that multi-thermal fluids spread around the horizontal well cylindrically at the beginning of injection and then along the top or bottom as the fluids contact those regions; this creates a composite reservoir with hot and cold zones. First, a production formula for a horizontal well in the composite reservoir described was derived using the equivalent flow resistance method from the water electric analogy principle. A heat diffusion model of multi-thermal fluids was then used to describe how the fluids spread out in the reservoir. Then, an evolution model of the physical fields was built by considering the enhanced oil recovery mechanism of multi-thermal fluids, which describes the evolution of temperature, pressure, oil viscosity, relative permeability curves, etc. during the huff-and-puff process. A new formula was used to determine the reduction in viscosity caused by carbon dioxide present in the fluid. The desired production prediction model was then established by coupling the developed production formula, heat diffusion model and evolution model. The analytical model was verified by numerical simulations and application to an offshore oil field. This study described an effective and quick method for productivity prediction, reservoir dynamic analysis and injection optimization.

Multi-thermal fluid assisted gravity drainage process: A new improved-oil-recovery technique for thick heavy oil reservoir

Abstract Multi-thermal fluid is a new heat-carrier proposed in decades. This paper introduces multi-thermal fluid into the thermal recovery process of thick heavy oil reservoir (THOR). First, using the method of physical simulation, the superiority of multi-thermal fluid is investigated from the Pressure–Volume–Temperature (PVT) performance and displacing characteristics. Thereafter, based on multi-thermal fluid injection technology and steam-assisted-gravity-drainage (SAGD) theory, a new Improved-Oil-Recovery technique for THORs, Multi-thermal Fluid Assisted Gravity Drainage (MFAGD) technique is proposed in this paper. Applying the dimensionless scaling criterion of gravity-drainage process, two 3D gravity-drainage experiments (SAGD, SAGD-to-MFAGD) are conducted. Thus, the enhanced-oil-recovery (EOR) mechanisms of multi-thermal fluid in heavy oil reservoirs are analyzed, and the thermal recovery performance of MFAGD process is discussed. Results indicate that compared with SAGD process, MFAGD process has a higher recovery rate, and it could further improve the gravity-drainage effect in THOR. Besides the conventional operation of SAGD, the EOR mechanisms of MFAGD technique also include heat insulation, energy recovery, gas dissolution and auxiliary cleanup of non-condensable gas. This method technologically supports the effective and efficient development of THORs.

The flow and heat transfer characteristics of multi-thermal fluid in horizontal wellbore coupled with flow in heavy oil reservoirs

Abstract As a new improved oil-recovery technique, multi-thermal fluid injection technology through a horizontal well has been widely used in the development process of heavy oil reservoirs. The flow and heat transfer characteristic of multi-thermal fluid in horizontal wellbore is significantly important for the productivity evaluation and parameters design of the horizontal well. Considering the specific physical properties of multi-thermal fluid, fluid absorption in perforation holes and pressure drop characteristics along the horizontal wellbore, this paper developed the flow and heat transfer model of multi-thermal fluid in perforated horizontal wellbore. In order to evaluate the heating effect of the multi-thermal fluid, a concept of effective heating length of a horizontal well is proposed. Then, a sensitivity analysis process is performed to study the influence of reservoir/fluid parameters and operating parameters on the flowing process of multi-thermal fluid in horizontal wellbore. Simultaneously, using the method of orthogonal numerical test, differential analysis and variance analysis are also conducted. Results show that the flowing process of multi-thermal fluid in horizontal wellbore includes a single-phase flowing process and a gas–liquid two-phase flowing process. The influence of oil viscosity on the flow and heat transfer characteristics of multi-thermal fluid in horizontal wellbore is most significant. Thereafter, the solution of our semi-analytical model is compared against the test results of an actual horizontal well from an oilfield in China. It is shown that the model results are in good agreement with the real test results. This model could be used to calculate and predict the flow and heat transfer characteristics of multi-thermal fluid (or saturated steam) in a perforated horizontal wellbore.