Research On Cooling Gathering & Transportation And Comprehensive Optimization Design Technology Of Daqing Peripheral Oilfields

With the development of Daqing peripheral oilfields entering the middle and high water-cut stages, the surface oil gathering and transportation system widely experienced a series of inconsistent situations, such as the drop in load rate, decline of operation efficiency and rise of energy consumption, which leads to the increase in production cost of crude oil. Therefore, the implementation of energy-saving and consumption-reducing measures, deep optimization research and technology simplification for the gathering and transportation system have fallen within the key projects in the overall surface plan of oilfield. For the gathering and transportation process adopted in the low-permeability peripheral oilfields of Daqing, we carried out such researches on the technical limits of cooling gathering & transportation and the design optimization of pipe network in order to enhance the economic benefit of oilfield development and construction and to reduce the investment in surface construction and energy consumption of productive operation. The main research results are given as bellow:(1) Develop the test device to fully simulate the influence of physical property of oil, temperature of soil environment, specification of oil-gathering pipe, flow rate and other working conditions on the parameters of water-mixing gathering and transportation process, and to determine the technical limits of cold transportation based on the comprehensive results of analysis on temperature drop of gathering & transportation pipes, change in pressure drop, oil-water flow pattern and deposit on pipe wall;(2) According to the test, the increase in water content of oil return system and reasonable improvement of flow rate can help to reduce the pressure loss during the low-temperature flow and ensure the implementation of low-temperature gathering & transportation process; the oil return temperature in the high water-cut stages can be reduced to 3~5℃bellow the solidification point of crude oil; the crude oil's water-content rate and flow rate in the gathering and transportation system serve as the main factors to affect the oil-water flow pattern, and the mixing flow pattern of"water-in-oil-in water (W/O&W)"is the typical flow pattern of two phase flow in the cold transportation pipeline.(3) The deposits on the wall of cold transportation pipeline is a mixture featuring loose structure, with the holes fully filled with crude oil, gelatine, asphaltene, water and other mechanical admixture; the deposition in the pipeline follows such four mechanisms as molecular diffusion, Brownian movement, shear dispersion and gravity settlement.(4) The field cooling gathering & transportation test for the low-permeability peripheral oilfields of Daqing shows that in order to realize the most economical operation (namely lowest heat and power expenses) given the oil return temperature of 32℃, it is suggested that the water injection temperature in summer shall be 50~56℃, with average water injection amount of single well being 0.58 m3/h, the water injection temperature in winter shall be 57~63℃, with average water injection amount of single well being 0.67m3/h.(5) For the star-like and looped oil/gas gathering and transportation pipe networks widely adopted by the low-permeability oilfields, we study and establish a mathematical model for the location-allocation optimization of pipe network, analyze the structure features and computational complexity of model, and give the corresponding solution strategies of hybrid genetic-simulated annealing algorithm, with a purpose to reduce the investment in the construction of network.(6) Respectively study and establish the secondary hybrid planning mathematical model and the corresponding solving method for the location-allocation optimization of star-like and looped oil/gas gathering and transportation pipe network which has obstructions in the distribution area.(7) Study and establish a mathematical model for the multi-objective optimization design of single-pile looped oil gathering pipe network featuring water injection in order to minimize the investment in pipe network construction and the power and heat consumption. In accordance with the actual development situation of oilfields and the intents of designer, adopt the evaluation function method to give the alternative model of multi-objective optimization problem, and work it out through the hybrid genetic algorithm.