| Based on continuous pig gas-lift with U-shaped double string, a new continuous pig gas-lift with only one string is advised to cancel severe slip loss in continuous gas-lift well with low pressure and efficiency. In this system, the string is installed by casing wall. The pig falls in noncentral annulus. The pig, injection gas and nature gas from gas reservoir are collected by a funnel-shaped pig collector. In lift pipe, a series of steady ideal slug flow is formed. Therefore, flowing bottom-hole pressure (FBHP) decreases and recovery efficiency enhances. What's more, it can assist these wells with high gas/liquid ratio to have the capability of producing without gas injection, which is named pig assisted flowing. But this system is more complex than continuous pig gas-lift with U-shaped double string. For example, how to keep tubing string by casing wall, the pig track in noncntral annulus is unknown, how to unload the liquid in well bore, etc. Aimed at those problems, basal theory and the application of new continuous pig gas-Lift are studied. The main finished work in detail is as following:(1) Based on accurately predicting two-phase pressure drop in gas-lift well, slip loss in 20 gas-lift wells is analyzed by statistics. In continuous pig gas-lift system with one string, the critical mass production and the working submergence/well depth ratio are available. And the demands of casing program are given in detail. Here working submergence refers to the depth from working fluid level to working valve.(2) Based on U-shaped pig gas-lift's experimental facility, a new one is established, which specifications of tubing pipe is 25 m high and 040 mm of diameter and these of casing pipe is 11.3 m high and 0124 mm. The process of pig continuous gas lift with one string and that of pig assisted flowing in producing water & gas well are simulated. Pig track in noncentral annulus, flow regime of three-phase with gas, water, pig in lift pipe, gas channeling and water leaking between the pig and the tubing is observed. And pressure curve and differential pressure curve in measuring nipple of lift pipe is available in steady flow state.(3) Based on the analysis of experiment phenomena, mathematical model is established to calculate the value of liquid leaking when pig density is less than gas density and the experiment is used to get the value of gas channeling when pig density is more than gas density. And the theory and numerical simulation method of 3-phase flow with gas, liquid and pig in the continuous pig gas-lift system with one string are established. The mathematical model considers the instantaneity of the fluid flowing state. The numeric process of the model uses finite difference method of time and length. Thesebasal theories are important for the design of continuous pig gas-lift system with one string.(4) The noncentral annulus is pig's passage, so unloading valve isn't installed to unload the liquid in well bore. A new unloading method without unloading valve is described in detail as follows. Firstly, the gas with high pressure is injected into the tubing and the noncenteral annulus at the same time. The liquid in well hole is injected in the reservoir, and when casing pressure reach release condition, then release in a moment to unload the liquid in well bore by gas lift. After the production is steady, the pig is launched into noncentral annulus to begin continuous pig gas-lift with one string. And relative mathematic model is established to describe this process after release.(5) The reasonable distribution of tubing excentralizer is critical to ensure that the pig falls from noncentral annulus into pig collector at the same time step. Based on conservation of energy, critical equation is established to describe the condition that the equalization of the tubing between the adjacent excentralizer is destroyed. The comprehensive judgment method for determining the position of the centralizer is given. It considers the infection from deviation angle, drift azimuth and inclination, etc. Helical buckling analysis is given.(6) The recommended method of continuous pig gas lift with one string in producing water & gas well is given. Technical requirements and operation procedure are established in detail for pilot test. It has more important direct significance for pilot test.(7) The mathematical model of lift efficiency is established considering pig's mass, pig's frequency and the oil pressure. The lift efficiency is divided into 2 parts and the energy loss is importantly analyzed. These theories provide theoretic gist for quantitatively valuing lift effect of continuous pig gas lift with one string.2 typical producing water & gas wells from ShuNan Plant are taken an example for continuous pig gas lift with one string. Shenl3 well has enough producing energy. After the gas-well deliverability and the slip loss by continuous gas lift are analyzed, pig assisted flowing is recommended and its results is predicted. Continuous pig gas lift with one string is advised in Long32 well. The completion program is given and lifting process is simulated. |
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