The total energy can be also expressed in the form of pressure Pr p+pg In the formula above: P is the reduced pressure at point M, it stands for the total energy of fluid point M, and p stands for the magnitude of pressure energy Betore oil and gas reservoir development. the pressure that is reduced to the initial oil-water interface of each well should be equal. Then the fluid llows from the place with high reduced pressure to the place with lower reduced pressure after oil and gas reservoir development. Because the reservoir uplift is always much lower than its lateral extension, therefore for the sake of convenience for lly simplitied to the planar seepage flow, hence the cepl of reduced pressure must be used days to come when studying the seepage flow of whole reservoir, all the pressures are reduced pressures if there is no added illustrations Example I-I The mid -depth of formation at a given well is -940m above sea-level, its oil water interface altitude is -1200m. the formation crude oil density is 800kg/m. The reservoir middle pressure actually mcasured is 12. 5MPa, and then what is the reduced pressure on the oil Solution the elevation of middle reservoir of this well is Z=1200-940=260(m) Pr=p+pg 12.5+800×9.8l×260×10 4.54(NPa) In the course of well performance analysis, the formation pressure of cach well need to be compared, and at this moment only use reduced pressure can we get right conclusions 1. 2 The driving fo driving mechanism in reservoir hen the bottom hole pressure of a well in reservior decreases, the oil or gas will flow to the bottom of well. What is the energy driving the oil in reservoir? Some kind of cncrgy is summarized as follows 1.2. 1 Hydrostatic pressure hen there is th area which is connected with oil and gas reservoir the hydrostatic pressure of water supply area is the driving force. The fluid will flow as long as the bottom hole pressure is lower than the pressure of supply area, When the water supply is ample. the pressure on the oil-water interface can be considered unchanged. If the depth of oil-water ressure on oil-water intertace interface is H( Figure 1-4). then the hydrostatic