Abstract:

core samples collected from Yushulin,Chaoyanggou and Toutai oilfields to the east of Daqing placanticline have been tested with the CMS-200 porosity and permeability tester.For the sake of observing the stress sensitivity of low permeability reservoir during the oilfield exploitation, initial pressure (initial formation pressure) and maximum confining pressure (maximum overburden pressure)have been chosen;and the recovery time of simulated pressure have properly been prolonged,due to the consideration of the protracted nature of field's waterflood development and the rheological property of the rocks. Experimental results show that the low-permeability reservoir is relatively sensitive to stress change, i.e. the permeability will have a relatively large decrease with the increase of stress.However, permeability has also recovered to a certain degree with the waterflooding to be prolonged, and the degree of recovery is related to the extent of initial permeability: the degree of recovery is greater with higher initial permeability; vice versa. Especially the low-permeability reservoir with permeability of less than 1.0×10^-3 μm² is very sensitive to stress change,and the resulting solid-liquid coupling effect is also very evident.The permeability of 1.0×10^-3 μm² can then be referred to as the limit of reservoir's stress sensitivity.From the viewpoint of oilfield development, the solid-liquid coupling effect will do more harm than good, so exploitation of low-permeability reservoirs should,as far as possible,be kept at the foramtion pressure to eliminate the influence of solid-liquid coupling. Except the factors of reservoir reformation and advanced development technique,the influence of solid-liquid coupling must also be considered while determining the low limit of productivity. It is suggested that the lower limit of productivity can be set at permeability ≥1.0×10^-3 μm² for reference while making strategic decision.

Key words: low-permeability oilfield, stress sensitivity, solid-liquid coupling effect, rheological property, oilfields to the east of Daqing placanticline