02 chapter2 reservoir

ĐẠI HỌC QUỐC GIA THÀNH PHỐ HỒ CHÍ MINH TRƯỜNG ĐẠI HỌC BÁCH KHOA TP.HCM KHOA ĐỊA CHẤT DẦU KHÍ PETROLEUM GEOLOGY THÁI BÁ NGỌC - BMĐCDK ORIGIN & PROPERTIES OF HYDROCARBON CONDITION FOR AN ACCUMULATION OF OIL AND GAS? RESERVOIR IMPERMEABLE SEAL MIGRATION ROUTE MATURE SOURCE ROCK TRAP Petroleum System Elements Petroleum System Elements Anticlinal Trap Top Seal Rock (Impermeable) Reservoir Rock (Porous/Permeable) Potential Migration Route Source Rock (Organic Rich) 24803 CHAPTER 02 RESERVOIR *RESERVOIR 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 * * Figure 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 Figure POROSITY  Porosity is the percentage of volume of voids to the total volume of rock It has the symbol : ≤  ≤ (or 0% ≤  ≤ 100%) Figure Figure 21 a , a series of channels has coalesced Oil entrapment in this case would be stratigraphic and Figure 21b : oil entrapment can only be stratigraphic Fig 21: Different degrees of vertical continuity If the sand body with lateral continuity, shown in Figure 21a , were deformed structurally, oil entrapment would become structural rather than stratigraphic Figure 22 Case History: Intisar Field, Libya Figure 23 is an isopach map of one of the Intisar (formerly Idris) reef fields located in the Sirte basin of Libya This field is a stratigraphic trap contained within a reef or carbonate buildup In the map, notice the simple sub circular geometry of the reservoir The thickness of the reservoir increases from zero to about 1,200 feet in an approximate distance of only 2.5 miles Figure 23 Figure 24: geological cross-section showing the various lithological facies of the reef Figure 25: Petrophysical cross-section showing the distribution of zones of different porosity 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:  Solution gas drive  Gas cap drive  Water drive  Gravity Drainage  Combination drive ° DISSOLVED GAS DRIVE RESERVOIR Characteristics Reservoir pressure Surface gas-oil ratio Water production Well behavior Expected oil recovery Trend Decline rapidly and continuously First low, then rises to maximum and then drops Non Requires pumping at early stage to 30 percent of oil in place GAS CAP DRIVE RESERVOIR Characteristics Trend Reservoir pressure Falls slowly and continuously Surface gas-oil ratio Rises continuously in up structure wells Water production Absent or negligible Well behavior Long flowing life Expected OR 10 to 20-30 percent of OIP WATER DRIVE RESERVOIR Characteristics Trend Reservoir pressure Remains high Surface gas-oil ratio Remains low Water production Starts early and increases appreciable amount Well behavior Flow until water production gets excessive Expected oil recovery 35 to 70 percent GRAVITY DRAINAGE DRIVE RESERVOIR Characteristics Trend Reservoir pressure Remains in medium rates Surface gas-oil ratio Stable Water production Negligible Well behavior Requires pumping at early stage Expected oil recovery 15 to 20 percent ENHANCED OIL RECOVERY (EOR) Enhanced oil recovery methods attempt to improve these efficiency factors by: ° Reducing the mobility ratio by increasing water viscosity; ° Reducing the mobility ratio by decreasing oil viscosity; ° Altering interfacial tension of the water – oil interface; and ° Improving the relative permeability characteristics ENHANCED OIL RECOVERY METHODS Water flooding ° Chemical recovery processes:  Polymer flooding  Surfactant – polymer flooding  Caustic flooding ° Thermal recovery processes:  Steam flooding  In-situ combustion ° Miscible recovery processes ° Exercise