Feasibility Analysis Of Periodic Water Injection In River Sand Reservoir Of Tahe Oilfield

The formation energy of channel sand reservoirs in Tahe oilfield has been declining rapidly. Currently, the formation pressure is maintained at 55-72% with a downward trend in formation energy. Because of the poor reservoir development by water injection, the uncertain factor of water injection and the lacking of efficient technology of reservoir development, this research is meaningful and valuable for effect evaluation by cyclic water injection in channel sand reservoir Tahe oilfield.Based on the geologic characteristics of channel sand reservoir and development characteristics by water injection in Tahe oilfield, this research using the method of geological research and reservoir numerical simulation to analyze the distribution of remaining oil, improved the plan of reservoir development by water injection, evaluated the effect of application which has been highly improved. Also, this research developed a popular and practical reservoir development technology by water injection for channel sand reservoir. There are five research results are as follow:(1) According to understanding of the geological of the channel sand reservoirs in Tahe oilfield, the No.l interbeds of TK1115 well area is continuously distributed. Because of redrawing the up-structure of TK7226 well area, channel area is reduced by 0.02km~2, the effective thickness is thinned by 0.16m; and compared to plan without water injection, the geological reserves are decreased by 12×10~4t from 63×10~4t.(2) The development effect and main controlling factor of channel sand reservoirs for TK1115, AT9 and TK7226 well areas were analyzed. The three sand channels were edge water reservoir with weak formation energy and the structure were E-W-trending, and the increase of water cut is the main controlling factor. The formation energy was still in a lower state (48%) in AT9 well area; however, the energy was supplemented by water injection. The formation energy maintenance was 70.8% and 76.7% in TK1115 and TK7226 well area.(3) Based on the geologic reservoir recognition and fine reservoir description, the model of inter-well high-permeability belt in channel sand was established, and the distribution of remaining oil was studied by numerical simulation.(4) The injection-production parameter has been optimized, such as the optimal injection-production method, injection-production ratio, appropriate fluid production per well, injection-production period and reasonable water injection rate. For TK1115 well area, those optimized injection-production parameter was cyclic injection-production method,1:1 for injection-production ratio,20m~3 for appropriate fluid production per well, nine months for injection-production period and large water injection rate with short injection time.(5) After the optimal cyclic water injection plan was tested in in field application in TK1115 well area, the pilot test by water injection achieved a remarkable effect; and then the water injection plan was popularized to ten injection-production well groups with channel sand reservoir. Compared to plan without water injection, the cumulative oil production increased by 11906t and daily average oil production increased by 60t. Thus, the effect of oil production by water injection is significant.