The Study Of Mechanism,Method,Application Of Natural Gas Huff And Puff In Deep Heavy Oil Reservoirs

Effective development in deep heavy oil reservoir is a worldwide problem.Conventional thermal recovery technology does not fit because of heat loss problems for buried deep,thin oil layer,poor physical properties of the heavy oil reservoir.It is a creative new technology for enhancing deep heavy oil recovery by natural gas huff and puff in deep heavy oil reservoir.The crude oil is extracted by using oil-dissolved gas drive and volume expansion of compressed gas-driven energy to drive to the bottom,in which gas is injected at high pressure to be fully dissolved and highly compressed in the formation.Its main role is to reduce viscosity of crude oil to enhance oil flow in the formation and recovery,to reduce the interfacial tension,to reduce driving resistance;to improve the expansion ratio and reservoir pressure of crude oil by injecting natural gas into crude oil.The some results is initially achieved in using gas injection at domestic and abroad(carbon dioxide,nitrogen,air,flue gases,natural gas,etc).Through physical experiment and numerical simulation,the study on mechanism of flooding in heavy oil reservoir has been carried.But from the current research of hydrocarbon injection mechanism and pilot tests,it was showed that there are many urgent problems in the theoretical study and practical application.these issues is the bottleneck for efficient development by gas injection theory,hampering development and application of reservoir gas injection method.The indoor laboratory physical simulation mechanism is evaluated using experimental methods on natural gas first.The important mechanisms of gas huff and puff is indicating that reducing crude oil viscosity and interfacial tension,improving expansion ratio,transfering composition and mass,dispersizing viscosity because of the micro-bubbles.The analysis on Lukeqing deep heavy oil indicates that the oil viscosity is obviously reduced through injecting hydrocarbon gas,droping sticky ranges reached 90%above.With the increasesing dissolved gas volume,pressure is increased and volume coefficient is increased,at inflection points of right volume coefficient reduces with the increasing pressure.The interface tension of crude oil is reduced 85%above than degassed crude.Through the component mass transfer effect of injected gas,light components reduces,heavy components increases,component changes significantly.The dissolution characteristics of hydrocarbon gas in the oil system is displayed in porous and non-porous medium,there are the best relationship between dissolution time,dissolved gas-oil ratio and depth.One of the important mechanism of natural gas huff and puff is bubble oil drive.The high pressure injected gas is separated from the crude oil in bubble form in the production process.Dissolved gas supersaturation causes the imbalance between free gas and solution gas,in which the such imbalances resulted from the effect of bubble nucleation kinetics and diffusion coefficient.Below the bubble point pressure,there is a "quasi-bubble point pressure",that is,the pressure is as the bubble size to grow out of viscous crude oil bound,started when escaping from the crude oil,depending on the depletion rate.The summary of bubble oil phenomenon in non-balance state on Lukeqing heavy oil is that viscosity distribution law features of oil sample indicates that the dissolved rate and proliferation rate is slow,only near the oil and gas two-phase contact surface the higher of dissolved gas oil is obtained,the more deep away from two-phase contact surface,the more large viscosity and the lower dissolved gas oil,the lower volume coefficient.By analyzing the gas simulation test results,flow physical model of four areas,namely:distance from the bottom strata of injection wells,it is divided into the super-saturated,pseudo-saturated,saturated and undersaturated area.The area characteristics is not obvious early restricted by affected radius.Due to the saturated zone of the previous high pressure gas injection,buck will gradually become saturated zone and in the process to be pseudo-saturated zone.If the pressure drop is too large and it may even have been formed in the super-saturated zone.In oil-gas two-phase flow region,oil relative permeability increases and gas relative permeability decreases with the lager capillary number.The reason is that,as the pressure difference increases,the relative capillary resistance,viscous force becomes large,oil flow in the bubble interference due to smaller.Then according to the indoor experimental research results,displacement mechanism of gas huff and puff is mproved that the non-equilibrium quasi saturation state formation of foam oil is the important one of the mechanism of oil displacement.The natural gas non equilibrium quasi saturated zone seepage physical model is put forward,and establishment of reflecting natural gas in the process of quasi saturated foam oil flow mathematical model of seepage flow of non equilibrium.It designs the disperse phase and continuous phase in the model.SBubble and Bubble is in the dispersed phase,Heavy oil,NG,Free Gas is in continuous phase.SBubble in the oil phase,has the general gas phase character of a dispersion components,BBubble is gas phase in a dispersion component;Heavy oil is representative of the ground degassed oil,belongs to the continuous phase,NG is representative of natural gas,belongs to the continuous phase,Free Gas is representative of natural gas dissolved in oil,belongs to the continuous gas phase undergoing the series reaction of NG?SBubble?BBubble?Free Gas.Using reservoir numerical simulation model considering the foamy oil flow,matching the indoor one-dimensional drive of Lukeqing heavy oil,the foam oil percolation characteristics in the reservoir is visual represented,and impact factors of foam oil were analyzed by means of numerical simulation.With the characterization of the small bubbles of foam oil(SBubble),the mole fraction in the oil phase increases,the viscosity of the oil phase is reduced.Conversely,with the small bubbles reduced mole percentage in the oil phase,the increase in the viscosity of the oil phase.When the increase in the content of the small bubbles,the oil phase density decreases,i.e.its compression is increased.When the content of the small bubbles is gradually reduced,the oil phase density increases,its compression resistance decreases.Small bubbles lower the viscosity,the lower the viscosity of the entire oil phase,the oil production,the higher the stage tired.the higher the compression factor of small bubbles,the lower the density of the oil phase,and the greater the elastic energy,the more accumulated stages oil production.Based on the consideration foamy oil flow mathematical model,using the three-dimensional three-phase compositional simulation method considering the physical diffusion,it is discussed that foam oil impaction is on the recovery process of the natural gas throughput in heterogeneous reservoir.Using vertical profile model,the average permeability of the true reservoir of heavy oil reservoir Lukeqin 90 × 10-3?m2,considering the permeability distribution coefficients of variation for the weak degree of heterogeneity 0.2,strong degree of heterogeneous 0.8,respectively,the parameters is studied on multiphase flow in foamy oil that is simulation grid size,the degree of heterogeneity,injected gas reaction rate,the injected gas molar density.The research results show that the nonequilibrium feature large mesh model(ie,large grid needs more time to reach equilibrium),diffusion,dispersion the PVT unbalanced characteristics are interrelated.Therefore,in the design of the simulation must establish the appropriate grid model to reflect the true injection movement.At smaller heterogeneous formation the exploitation of the natural gas throughput is little restricted when the lower level of the gas diffusion,and almost non-existent.Higher diffusion level the heterogeneity effect appeared gases priority affect crude oil production,resulting in homogeneous reservoirs using huff and puff but showed low crude oil production from the reservoir breakthrough.The speed of injected gas reaction rate affects the presence of the micro-bubble of the oil phase,and when the reaction rate is low,the micro-bubble,affecting the mobility of heavy oil,the decrease in the amount of cumulative oil recovery.With the increase of cyclic rounds,increasing higher NG molar component of the producing gas outputs;the higher injected gas molar density,the higher the value of output vapor NG The NG component producer wells oil phase showed decreased and then increased with the reservoir formation pressure drops,but when pressure drops to a certain extent,that is intended to bubble point pressure of the oil phase,showing NG the upward trend,because in this period there have been a large number of NG presence of crude oil due to the form of micro-bubbles.Using the combination of the related technology of fluid flow in porous media,numerical computation and numerical simulation,the foam deliverability equation and the effect of the one-dimensional non-equilibrium non-lag mathematical model based on the speed and pressure of the relaxation effects in the heavy oil,further study of the deep heavy gas throughput of important guiding significance and academic value,it has important implications for economic and efficient development of deep heavy oil reservoir.Conventional heavy oil deliverability equation assumes the instantaneous balance relationship between the flow velocity and pressure gradient and is based on the generalized darcy solving.Referenced in the foamy oil physical parameters of the mathematical characterization method proposed by predecessors,the finite difference method is used to obtain the production capacity of the two-dimensional model foam oil heavy oil system considering speed lag effect of production equation.The calculation results show that the initial capacity is not the biggest bubble oil production capacity,which producing for some time.Considering the speed relaxation time,with the extension of the relaxation time,the level of capacity is lower,the maximum capacity corresponding appears earlier.Relaxation characteristics of the heavy oil rheology flow in porous media have a significant impact,it can determine the the imbalance of seepage linear.When the natural gas throughput in the solution gas drive stage exhibits extremely complex flow characteristics of the foamy oil flow,the heavy oil relaxation effect is more prominent on the imbalance in the flow in porous media.Foamy oil characteristics two dual media assuming that the fluid is heavy oil component 1 and the microbubbles component 2,considering the micro-bubble pressure changes lagged effect,the one-dimensional bounded unstable linear seepage problem is established and the numerical solution is by using the matlab software.The results show that,when considering the pressure imbalance lag effect of heavy oil in porous media,imbalance effects are caused by the formation pressure decreased slowly regardless of the flow time early or late.There is an optimum value at the injection time and the effective radius of gas injection.Finally considering the numerical simulation of the foamy oil flow,the typical geological model is established for the Lukeqin deep heavy oil reservoirs to discuss natural gas throughput of gas injection parameters on the effects of producing.Using the experimental orthogonal optimization design technology,the speed of the gas injection,gas injection pressure gas injection time,soak time,the amount of fluid production,minimum oil production boundaries,the production cycle,the seven parameters are calculated.This study conducted a total of 108 programs run to exclude completely and efficiently inferior portfolio in each combination of parameters.Using the optimized parameters frequency histogram,the analysis of various parameters on the influencing factors of the natural gas throughput is carried and the optimal gas injection parameters are obtained.Optimal injection and production parameters,gas injection rate in more than 20000 m3/d,injection gas pressure more than 42MPa,the gas injection time in 20 days,soak time in more than 10 days,the amount of fluid production 16m3/d or more days,the effective production cycle of the 300 day.The summary and effect evaluation is carried on heavy oil reservoir Lukeqin 2005-2012 round batchs.Influenced of reservoir properties,the formation energy,breathing capacity,gas injection parameters,the single well stimulation effect is different.The former three measures yield gold stage,the formation energy well maintained has the throughput effect long valid.Follow-up rounds need to increase the size of the gas injection as well as the complement formation energy to guarantee throughput.Statistics of 19 oil wells show that,gas injection strength greater than 1000(square/meters/day),day yield of 2 tons/d,throughput effect better.The greater the intensity of the gas injection,the quality of the injected fluid in the same time,the larger the radius viscous reducing,the more soluble natural gas in crude oil,the higher the bubble point pressure,the more prone to foam oil.Soak time of 10-15 days,the development of effective,extended soak time to promote oil and gas miscible with little effect.Electrical measuring acoustic travel time is greater than 260,greater than 18%porosity,permeability greater 10×10-3?m2,relatively good physical properties,throughput wells increasing oil is greater than 2t/d to good effect.Deep heavy oil reservoir Lukeqin experienced laboratory evaluation stage,the conceptual model design,feasibility study and design of the development plan stages,nearly seven years of the pilot test stage,the effect of evaluation analysis showed that the natural gas throughput exploitation of heavy oil reservoirs has been achieved fruitful results.This paper summarizes the field results obtained on the basis of deeply analysis of the foamy oil characteristics of multiphase percolation characteristics,more realistic characterization of heavy oil with relaxation effects using the mathematical characterization in the process of natural gas throughput speed and pressure hysteresis effect on production.Advanced discussion of the new technology and new topics is to broaden the application prospects of the producing method.