| Under the background of energy conservation and green development for energy,natural gas is still the realistic source which optimizes domestic energy structure and improves the atmospheric environment.Xushen gas field in Songliao Basin has been an important part of natural gas produced areas in China since the exploitation in 2004,especially in “using gas to supply oil output” strategy in Daqing Oilfield.However,the difficulties and benefits of development in the field are challenged by the high-cold climate,poor reservoir property and amounts of CO2 in natural gas.Reducing investment and controlling cost are the key to realize continuous effective development of the gas field.As the supporting technology for gas field development,surface gathering and transportation is the assurance of gas field which is safety,smooth and efficient.So simplification,optimization and standardization of the gathering and transportation process are the significant supporting of effective development of the Xushen gas field in extremely cold areas.Carrying out the topological layout optimization design of gas gathering and transmission pipelines network can obtain significant economic benefits.According to the characteristics of impenetrable obstacles such as villages and marshes in Xushen gas field,the representation method of obstacle polygon and the optimization model and solution method of pipeline route around obstacles are established.Considering the influence of obstacles on the topological layout of gas gathering and transmission pipeline network,the mathematical model of topological layout optimization with obstacles is established under the the optimization objective of minimum construction cost for the whold pipeline network.In the the model,the structural characteristics of pipeline network,the feasibility of station and pipeline layout,and the treatment gas volume of station are set as the constraints.Aiming at the hierarchical structure and solving difficulties of the model,the advantages of the hybrid leapfrog algorithm and the fireworks algorithm are combined.The improved explosion operator,the improved mutation operator and the mirrored search operator are proposed respectively to optimize the hybrid algorithm,and a new hybrid leapfrog fireworks intelligent optimization algorithm(SFL-FW)is constructed.According to the convergence theorem,it is proved that SFL-FW algorithm can converge to the global optimal solution with probability 1,and the numerical comparison experiment shows that SFL-FW algorithm has better and more comprehensive optimization performance than the other intelligent optimization algorithms.The application example of a block in Xushen gas field shows that the total investment of pipeline network after optimization is reduced by 3208100 yuan,and the investment saving ratio is 14.17%,which verifies the effectiveness of the optimization model and the algorithm.Based on the practice that the type-selection of pipelines is larger and the power of electric tracing is higher,the multi-objective parameters optimization mathematical model of gas gathering and transmission pipeline network is established.In the model,the objectives of minimum total construction investment and the minimum running cost of pipelines heat tracing are concerned,and the constraints of operation process,flow safety,value range are modeld as the constraints.Considering the difficulties of multi-objective,multi-constraints,multi decision variables and complex non-linear of the model,combining the Max Min strategy,crowding distance strategy and constraint feasibility criterion,a hybrid diversity ranking strategy is proposed,and a multi-objective hybrid leapfrog fireworks intelligent optimization algorithm(MSFL-FW)is constructed,which can save 6.4344 million yuan when applied to the optimization of Xushen gas gathering and transportation pipelines,and the capital ratio is 20.3%.The good optimization performance has proved the effectiveness of the proposed optimization model and algorithm.According to anti-freezing and operation system of the gas gathering pipe,the paper studies on hydrate formation and methanol injection effects on hydrate decomposition with considering gas mass,temperature,pressure and liquid producing,and contrasts advantage and potential of electric-heat tracing and anti-freezing by injecting methanol for granting smooth and efficient operation of the gas gathering pipe in extremely cold areas,which synthesizes single well investment and energy consumption.The result shows that hydrate formation temperature gradient decreases with pressure rising after the temperature is higher than 17℃.Hydrate formation time,which is mainly in 80～100 minutes,grows linearly as the formation increases when temperature and pressure are specified,and formation conditions are related to natural gas composition.It means that formation pressure decreases when gas density and content of propane and isobutene increase at the same temperature.Single well investment and cost of the anti-freezing by injecting methanol which is the replacing technology of electric-heat tracing are reduced by 65.56% and 16.45% respectively,and it is be suitable for the gas wells with pipe length larger and water content smaller.The gas gathering simplification technique,which is made of multiple well combine and separation,rotation measurement and multi-well vacuum heat transfer,determined a set of rotation measurement process that well amounts are no more than 10,gas amount ratio is less than 1:10,and single well measure time is in 8～24 hours.At the same time,this paper reveals the corrosion behavior and causes.It is considered that 2205 duplex stainless steel is the best pipeline material resistant to CO2 corrosion and chloride ion stress corrosion.Although 316 L stainless steel has strong CO2 corrosion resistance,it is very sensitive to chloride ion medium stress corrosion.The application of anticorrosion technology in Xushen gas field effectively reduces the potential corrosion hazard and eliminates the occurrence of corrosion perforation leakage.Based on operation optimization of the gathering and transportation process above,the process is set up to be supported with electricity,automation,civil construction,anti-corrosion and other auxiliary profession,which is combined with technological process optimization,well station layout and tube valve fittings.Typical conditions are divided in accordance with the thought that season module plan confirmed in advance in extremely cold areas,construction standards unification and basic condition seriation are completed.A series of standardized design documents are determined on basis of the thought that the process is supplied and improved continually.Traditional pattern of construction planning,design and execution is broken through.Standardization model of surface gathering and transportation process of the deep gas field is structured and applied in the Xushen-3 block.This shorten the design period and construction period more than 20% and 10% respectively.The study shows that standardization technology research,which is combined with anti-freezing of the gas field,measurement and separation,well station layout,and corrosion prevention to optimize gathering process,is confirmed considering a fact that construction period is limited in extremely cold areas.It is important meaning for playing a role on integration of ground and underground to maximize benefit of the gas field development. |
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