RESERVOIR (cơ sở KHOA học địa CHẤT dầu KHÍ SLIDE TIẾNG ANH)

CHAPTER 02 RESERVOIR RESERVOIR DEFINITIONS A single continuous deposit of gas and/or oil in the pores of a reservoir rock A reservoir has a single pressure system and don’t communicate with other reservoirs  The portion of the trap that contains petroleum, including the reservoir rock, pores, and fluids  A pond, lake or environment that is used store liquids  RESERVOIR TYPICAL TYPES Main reservoir rock The Reservoir Rock: Sandstone An outcrop of pebbly sandstone (at base of cliff) overlain by red sandstone The Budleigh-Salterton pebble beds, of Triassic age A few kilometres to the east these beds dip into the subsurface, and form part of the oil reservoir at the Wytch Farm Field, which is Britain’s largest onshore oil field The Reservoir Rock: Dolomite • The Cairns Formation, of Devonian age, exposed near Canmore, in the Front ranges of the Rocky Mountains, just east of Banff, Alberta This is one of the more important reservoir units in the subsurface of Alberta The Reservoir Rock: Dolomite This is an example of an important reservoir rock type Fossil stromatoporoids have been hollowed out by the chemical conversion of limestone to dolomite, creating pore spaces so large that they are sometimes called “cavernous porosity” Making reservoirs today: Limestones • An exposure of modern limestone in the Florida Keys This limestone is only a few hundred years old It shows the structure of coral and other organic remains Note the numerous pore spaces • Burial of this limestone would probably lead to reduction in porosity as a result of cementation Good quality reservoir rocks, such as the dolomite shown in another picture, are created by dissolution of some of the rock This usually occurs many millions of years after the initial formation and burial Fundamental physical properties of a reservoir RESERVOIR (cont.) There are two fundamental physical properties that a good reservoir must have: + Porosity: sufficient void space contain significant petroleum + Permeability: the ability of petroleum to flow into, or out of these voids  The common rock types that have favorable combination of porosity and permeability to be reservoirs are sandstones and carbonates  The Bach Ho field of Viet Nam Fig 16: Schema of weathered activities when the structure is uplifted to the surface Fig 17: Paleotecto nic sections along White TigerNorthern Eastern Dragon structures Fig 18: Geological longitudinal section along White Tiger-Northern Eastern Dragon structures Reservoir Continuity • Most oil fields not occur in single sheetshaped reservoirs of great lateral continuity with uniform porosity and permeability distributions • Most oil accumulations occur in heterogeneous reservoirs with permeability barriers because of shale breaks or local cemented zones Figure 22 is the reservoir engineer's dream: a blanket sand of uniform porosity and permeability distribution This occurs with a single oil- water contact In this case for a well drilled at location or through the reservoir of any other location, gross pay equals net pay Figure 23 is somewhat different: the sand is shaling out from right to left across the section, thus for a well drilled at location the net pay of the reservoir is less than the gross pay There is still one oil accumulation, or at least one major one, but there is a small separate accumulation with its own oil: water contact in the lower left-hand part of the figure Figure 24 shows another situation There is a series of separate oil pools with their own oil: water contacts This is not a genuine anticlinal structural trap, but a series of stratigraphic traps which pinch out towards the crest of the structure For each reservoir, net pay equals gross pay Cross-Sectional Continuity Reservoir continuity in cross-section is an important consideration in determining reservoir quality (Harris and Hewitt, 1977) Figure 27 , Figure 27 Figure 28 a: a series of channels has coalesced Oil entrapment in this case would be stratigraphic and Figure 28b: oil entrapment can only be stratigraphic Fig 28: Different degrees of vertical continuity If the sand body with lateral continuity, shown in Figure 28a , were deformed structurally, oil entrapment would become structural rather than stratigraphic Figure 29 RESERVOIR ENERGY SOURCE Gas dissolved in oil  Free gas under pressure  Gas reservoir  Oil reservoir wet/free gas cap  Fluid pressure  Hydrostatic – hydrodynamic  Compressed water, gas, oil  Elastically compressed rock  Gravity  Combination of the above  RESERVOIR DRIVE Reservoir drive is the natural energy in a reservoir that forces the fluids out of the rock and into the well  Every oil field has at least one reservoir drive  Type of reservoir drives in oil field include:  RESERVOIR DRIVE (Cont.) Former:  Solution gas drive  Gas cap drive  Water drive  Gravity Drainage  Combination drive Now: Fluid Extension drive 2.Gas-cap drive 3.Water drive 4.Compaction drive 5.Combination drive .. .RESERVOIR DEFINITIONS A single continuous deposit of gas and/or oil in the pores of a reservoir rock A reservoir has a single pressure system and don’t communicate with other reservoirs... petroleum, including the reservoir rock, pores, and fluids  A pond, lake or environment that is used store liquids  RESERVOIR TYPICAL TYPES Main reservoir rock The Reservoir Rock: Sandstone... Alberta This is one of the more important reservoir units in the subsurface of Alberta The Reservoir Rock: Dolomite This is an example of an important reservoir rock type Fossil stromatoporoids