| In order to solve the problems encountered during the exploitation process in the gas field of Xushen 1 block, on the basis of the geological characteristics of gas field and the conditions of gas well in various development phase, the optimization of reservoir stimulation and the key technology study were carried out in depth, which is significant both in the theory and practice to develop the gas field of Xushen bolock-1.1 It is ascertained that the main reservoir damage problems in the operation in Xushen bolock-1 are: (1) water sensitivity, salinity-sensitivity and water-lock damage occurred when the reservoir's water saturation is under the irreducible water saturation; (2) alkali sensitivity, velocity sensitivity, pressure sensitivity and water invasion damage under the irreducible water saturation; (3) the blockage of fracture by solid phase in the working fluid; (4) inorganic precipitate damage caused by the high pH solutions of high valence metal ions such as calcium, magnesium,etc. Hereby, nine practical measures to protect the reservoir in Xushen 1 block were brought forward, providing the basis to optimize the stimulation measures and rational development technologies.2 Perforation completion was chosen to complete the gas wells in Xushen 1 block. The sizes of tubing and casing were decided. The perforation parameters, procedure and the height of slurry back flowing in production casing were suggested.3 The formula of fracturing fluid system adequate for the fracturing operation in Xushen 1 block was given out and its properties were evaluated. It was appointed out that the modified guar gum should be used as the thichening agent for the high temperature fracturing fluid to be used in the gas well in Xushen 1 block. According to the requirements of operation in the deep gas formation, hydroxypropyl modified guar gum should be used. Compound crosslinking agent should be used in the fracturing fluid system. The crosslinking control agent of CNN-01, CNN-02 should be used, so as to endow the fracturing fluid with good performance of slow crosslinking.4 Through the contrastive analysis on the fracturing data of volcanic formation in 2002~2005 and the actual effect, the characteristic parameters to diagnose the fracturing in volcanic rock was suggested, and the operation parameters for the volcanic formation fracturing was optimized. On the basis of analyzing the data of flowing back after fracturing obtained previously in Daqing and other oilfields, three methods for flowing back and finding production volume after fracturing were introduced, which were proved to be helpful by the application in Weishen-5 well and Zhaoshen-11 well. It is suggested that during the fracturing process, the procedures of gel breaker supplement and quick back flow by compulsive closure should be applied. The integration pipe string for fracturing - fluid flowing back - gas testing and the separate layer fracturing string for deep gas formation should be used.5 Actual measurement on Xushen 6#, Xushen1-1# wells and the history matching showed the formation thermal conductivity (K) is 61.1923 kJ/( h.m.K) in Xushen 1 block. On the basis of this value, the methods to compute the pressure, temperature at wellhead under the condition of proration gas production were optimized. The wellhead pressure and temperature for 20 years from now were forecasted. The influencing factors of wellhead pressure and temperature were studied.6 The gas well flow-stop pressure computing method was optimized. The computing and forecasting on the gas well flow-stop pressure for wells in Xushen 1 block showed:(1) As the WGR increases, the borehole pressure loss in gas well increases;(2) If chose to use the big size tubing, the borehole pressure loss will decline, but the carrying capacity will increase greatly, for the low productivity gas well, choice of big tubing will cause the flow-stop of gas well prematurely;(3) As the wellhead back pressure increases, the flow-stop pressure will increase;(4)At the condition of water breakthrough, the flow-stop pressure will increase sharply;(5) The bigger the size of tubing, the higher the flow-stop pressure.The technologies were given out which could make full use of the formation energy, reduce the gas well flow-stop pressure, prolong the flowing period. The gas well abandonment pressure was computed. It is decided that the factors influencing the abandonment pressure are mainly the buried depth of gas reservoir, productivity, water cut, minimal wellhead back pressure, size of the gas production tubing and the technical level of the gas recovery by water drainage, and so on.7 The applicable conditions of Turner critical flow velocity and critical production formula were analyzed. The computing methods for continuous fluid drainage of gas well in Daqing gas field were optimized. For Xushen 1 block gas wells, when it is produced by pressurizing, the WGR is 0~7m3/10~4m~3, the tubing of 23/8" can meet the requirement of borehole fluid carrying for single well with production of 1.31~1.53×10~4m~3/d; when it is produced without pressurizing, the WGR is 0~7m3/10~4m~3, the tubing of 23/8" can meet the requirement of borehole fluid carrying for single well with production of 3.08~3.50×10~4m~3/d. the high strength small size tubing can meet the requirements of gas production by water drainage in Xushen 1 block.8 The problem of change from flowing to artificial lift water drainage to produce gas was studied. the technologies for gas production by water drainage were compared, the characteristics and applicability of various technologies were appointed out, and it is suggested that the technology of gas recovery by foam drainage and relative supporting measures can be applied in Xushen 1 block.9 The forming condition and influencing factors of natural hydrate were studied. Computation and analysis on the data from Xushen 1 block showed:(1)If the formation pressure and the borehole pressure are high, the possibility of hydrate forming is big;(2)The possibility of hydrate forming is small if the formation temperature and the borehole pressure are high;(3)If the production increases, the wellhead pressure declines, the wellhead temperature is high and the possibility of hydrate forming is small;(4)For a certain gas production, there exists a optimal tubing size, here, the hydrate forming possibility is small;(5)The deeper the well, the bigger the temperature drop scope, the bigger the possibility of hydrate forming near the wellhead.Through computing and forecasting on wellhead temperature after throttling, it is appointed out that four procedures should be carried out to prevent the forming of hydrate before throttling for Xushen-1 block.10 The procedures of preventing borehole hydrate forming were optimized. The design plan of chemical agent inhibitor preventing borehole hydrate forming was introduced. The measures of preventing wellhead hydrate forming were put forward. For different gas well conditions, various chemical species, the chemical adding amount was given out.The achievements obtained in this dissertation have reference values for the gas recovery by water drainage in the similar gas fields. |
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