Study On Daqing Peripheral Low Permeability Reservoir Classification Method And Development Countermeasures

With the further development of the outskirt area surrounding Daqing oil field, many problems related to production appear gradually.Firstly, the production in the development process of the oil field is becoming less effective, the increase of the water cut and the decline of the production are both much faster than before; Secondly, the less grade of the production formation is, the more difficult in water flooding development technique is. The reservoir is mainly located in the area with much lower abundance and permeability.Thirdly, the develop -pment potential and effective methods decrease gradually, while the cost and the contradiction-n between input and output are increased day by day. In this condition, the requirement of continuous development of the low permeable oil field cannot be satisfied by the original evaluation method, optimum technologies, production modes and methods. According to this condition, the permeable reservoirs are classified by the study of micro characteristics of low permeable reservoirs in this paper. Based on this, production strategies are promoted to improve the effective production and commercial development of the outskirt low permeable and grade reservoirs.In order to study the characteristic of the pore configuration in the low permeable formation, the constant flowing rate mercury-injection and Kim Sang-electron microscope experiments are adopted to study the parameters pattern of the natural cores with different permeabilities such as: permeability, average porous channel radium, average throat channel radium, pore throat ratio, tortuosity, coordinate number, form factor and fractal dimensionality. Some recognition can be obtained by followings: the distribution pattern of the pore channel radium is similar with different low permeable rock; however, the difference in distribution of the throat channel radium is apparent. The correlation between the throat channel radium and permeability is less, on the contrary, there is apparent pattern of the correlation between the throat radium and permeability. In a word, the permeability of low permeable reservoir is controlled by the throat radium. At the condition of the same permeability rock, there is no apparent relationship between the throat channel fractal dimensionality and the pore channel fractal dimensionality which can be concluded that the difference in complexity between throat channel and pore channel is small. The water flooding effect in low permeable reservoirs is not only affected by pore structure but also by the pattern of fluids flowing in porous media in low permeable rock. The mobile fluid saturation analysis is made by the nuclear magnetic resonance method, as the results indicate that: There is a favorable correlation between the mobile fluid saturation and the sweepefficiency,the production potential of the reservoir can be better revealed by the mobile fluidsaturation rather than the parameters of the permeability.Based on the experimental analysis of the actuating pressure test,when the actuatingpressure gradient permeability is less than 1×10^-3μm²,the actuating pressure will increasesharply with the decreased permeability,which indicate that when the permeability is lowerthan 1×10^-3μm²,the other displacing methods should be explored because of the unfavorableuse of water flooding.Based on the comparison between the cure of actuating pressuregradient of water flooding and that of gas flooding,it indicates that the alternation pattern ofactuating pressure gradient is similar between the water flooding and gas flooding. When theactuating pressure of water flooding is higher than that of CO₂ flooding,and the permeabilityis higher than 0.5×10-3μm2,the value of the gas actuating pressure gradient is lower,andthe trend of the decrease in actuating pressure gradient will be flatten out with the increase ofthe permeability.According to the relative permeability curves,there is a more strongcorrelation between the permeability and recovery in the low permeable reservoirs,and thesweep efficiency will decrease with the decrease of the permeability. When the permeability islower than 10×10^-3μm²,the decrease amplitude of the recovery is the most,the lowestvalue can be to 16.5%,which can indicate that when the permeability is lower than10×10^-3μm²,the water flooding effect will be worse; the pore throat ratio has a greatinfluence in the residual oil saturation,with the increase of the pore throat ration,theresidual oil saturation will be increased,if the stretch of two phase flowing fluids is less,the recovery of water flooding will be decreased.Based on the research on the low permeable rock pore structure and the characteristic offluid flowing in porous media,four parameters such as permeability,pore throat ratio,throat channel radium and actuating pressure gradient are adopted. Cluster analysis is adoptedto classify the outskirt reservoir of Daqing oil field into four categories: The characteristics ofoutskirt reservoirs in Daqing oil field are analyzed,following results can be obtained: Thedepth for the whole outskirt areas is lower,and there are 52 reservoirs which is less than1500m,the reserve ratio is 65%. There are 49 reservoirs in outskirt with shallow fracture,micro fracture and apparent fracture,the formation reserve is 78.3%. There are 26 reservoirwithout fractures,the fractures are mainly in east-west direction in Chao Yanggou,YuShulin and Tou Tai oil fields. There are less fractures in other directions. The reservesabundance of developed outskirt reservoirs is 21×10⁴t/km²ï½ž92×10⁴t/km²,and there are 25reservoirs with the reserves abundance less than 50t/km2,which is 44.8% of the geologicreserve. There are 54 reservoirs with the much lower reserves abundance more than 50 t/km2, where the geologic reserve is the 87.7% of the Fu Yang formations, the average reserves abundance is 58.9×10⁴t/km², which belongs to lower reserves abundance.The water cut, injection production ratio, control degree of water flooding and production rate are chosen to classify the developed reservoirs, which provide the foundation for the development strategy.According to the production data of outskirt developed reservoirs in Daqing oil field, the effect of the infill adjustment is studied. The adjustment infill effect of the reservoirs with different permeability in Daqing oil field is analyzed, plans of infill adjustment are determined for different types of reservoirs. The experiments on pressure sensitive effect of low permeable reservoirs are operated. The results indicate that when there is no fracture, the pressure sensitive effect will be apparent with the decrease of the throat radium. The main factors that affect the pressure sensitive effect can be due to the throat radium. When the permeability is the same, the fracture will affect a little on the pressure sensitive , the degree of pressure sensitive effect will be higher with the increase of the fracture density.The research is mainly focused on the theory of advancing water injection and CO2 flooding, the displacement effects of different type reservoirs with advancing water injection and CO2 flooding are provided; The air displacement possibility is studied, when the permeability is higher than 0.2×10-3μm2, the stale burning front can be formed. With the decease of the permeability, the displacing rate of the burning front will decrease, but which is less. At the same position of axial ratio, the increasing rate of temperature will be different with different pore throat ratio. When the pore throat ratio is less, the increase of the temperature will be larger which can indicate that the burning efficiency could be influenced by the pore throat ratio. The effect of horizontal drilling process in radial direction is analyzed, this technique with the characteristic of direction determination and depth determination. It can also improve the less effective layers or wells condition, short the space between the injection and production wells, improve the relationship between the injection and production, which can also adjust the contradiction of the layer space or the plane.Based on the classify of the low permeable reservoirs, combined with the development grading methods, according to the different kinds of reservoirs, the production development strategies are promoted, also, the theoretical foundation of the reasonable development of the outskirt reservoirs in Daqing oil field is provided.