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DRIVE MECHANISM
Dr. Ir. Rachmat Sudibjo 1
TEKNIK RESERVOIR LANJUTTeknik Perminyakan - TrisaktiINTEGRATED PETROPHYSICS
Integrating geoscience disciplines to achieve dynamic reservoir description
Integrated Petrophysics
RESERVOIR DESCRIPTION
CORING
CONVENTIONAL CORE
PETROGRAPHIC ANALYSIS Thin Section Petrography
microphotographs illustrates the typical components of a sandstone reservoir
Poorly sorted sandstone
Oolitic limestone
Scanning Electron Microscopy Analysis
Useful Porosity
Some micro porosity may not be observed in conventional core analysis. Most porosity indicating logs see unconnected porosity, but the sonic log may not see any or all of the microporosity.
FLUID SATURATION
CAPILLARY PRESSURE
RELATIVE PERMEABILITY
LOGGING UNIT
DRILLING FLUID INVASION
Resistivity Response versus Depth of Investigation
THE PETROPHYSICAL MODEL
General Rules For Picking Log Values
In thick beds, pick average values(heavy black vertical lines) ===>Old style induction log, layer roughly15 feet (5 meters), pick peaks and valleys;other logs, pick averages ===>
FORMATION VOLUME FACTOR Bo = 1 1.4 Bw = 1 1.1Bg = 0.005- 0.007Volume @ kondisi reservoir / volume @ kondisi permukaan (standar)
Sangat praktis untuk konversivolume dari kondisi reservoirke permukaan dan sebaliknya
Juga dapat digunakan untuk mengkonversi unit volumedari bbl > scf etc27teknik reservoir lanjut - RS -teknik perminyakan - trisakti
MONETIZATION (VOL. STANDARD)
material balance: diperlukan konversi dari volume reservoir ke volume permukaan (standard)
28teknik reservoir lanjut - RS -teknik perminyakan - trisakti$$$$$$Basic Conceptsteknik reservoir lanjut - RS -teknik perminyakan - trisakti29Pressure gradientteknik reservoir lanjut - RS -teknik perminyakan - trisakti30
During a period of sedimentation, grains of sediment are continuously building up, in a water environment, the pore spaces between the grains were, therefore, filled with water. If the pore throats through the sediment are interconnecting all the way to surface, the pressure of the fluid at any depth in the sediment will be same, i.e. formation pressure. This pressure depends only on the density of the fluid in the pore space and the depth (hydrostatic pressure), independent of the pore size or pore throat geometry. hydrostatic pressure. Formation gradient pressure is generally equal to 0.433 psi/ft for freshwater. Deviations from this gradient and its associated pressure at a given depth are considered abnormal pressure.
Formation Pressure Definition Normal Hydrostatic PressureThe vertical pressure at any point in the earth is known as the overburden pressure or geostatic pressure. The overburden pressure at any point is a function of the mass of rock and fluid above the point of interest. In order to calculate the overburden pressure at any point, the average density of the material (rock and fluids) above the point of interest must be determined. The average density of the rock and fluid in the pore space is known as the bulk density of the rockOverburden Pressure Lithostatic PressureOverburden Pressure
Normal pressure gradientP grad water = 0.433 psi/ftP grad oil = 0.35 psi/ftP grad gas = 0.08 psi/ft
teknik reservoir lanjut - RS -teknik perminyakan - trisakti34
teknik reservoir lanjut - RS -teknik perminyakan - trisakti35
Fluid contactstekres lanjut teknik perminyakan - trisakti36
Pressure gradient in Reservoirteknik reservoir lanjut - RS -teknik perminyakan - trisakti37
Penentuan fluids contacts tekres lanjut teknik perminyakan - trisakti38
teknik reservoir lanjut - RS -teknik perminyakan - trisakti39OWCPEAK STRUCTUREGOCWater GradientOil GradientGas GradientCwCoCgPo = PwPo = PgDepthPressureDifferential Density EffectsThis effect is encountered when a gas reservoir with a significant dip is drilled. Because of a failure to recognize this potential hazard, blowouts may occur.
teknik reservoir lanjut - RS -teknik perminyakan - trisakti41OWCPEAK STRUCTUREGWCWater GradientOil GradientGas GradientPo = PwPg = Pw.Well TestDepthPressure Reserve Estimation Methods
1. Volumetric Method
Early stage of reservoir development Geology, Geophysics, Rock and Fluid properties Recovery Factor (RF) assigned arbitrarily No time dependency, No Production data Reservoir limits for reserve classification
Structure on top of production well
BHP vs Depth
BHP vs depth (upper & lower bonds of prediction confidence at @ 80%
the shift across the boundary between good and poor quality sand (Capillary chart)
Structure map on top of porosity
Minimum cut off:permeability = 1 mdPorosity = 2-4% (carbonate) = 7-10%(sandstone)
Isopach map of total net sand
Net oil isopach above HKW
Isopach of total net oil sand
Perhitungan Kandungan Minyak (OOIP) Secara Volumetric
52 Reserve Estimation Methods
2.Material Balance
Later stage of development Geological data, Rock and Fluid properties, Production data RF is calculated Time dependantDRIVE MECHANISMSOLUTION GAS DRIVE: RF= 10-15%GAS CAP GAS DRIVE RF = 15 25%WATER DRIVE RF = 20 40%GRAVITY DRAINAGE RF = 15 30%
54teknik reservoir lanjut - RS -teknik perminyakan - trisakti
SOLUTION GAS DRIVE
Solution Gas DriveCrude oil under high pressure may contain large amounts of dissolved gas. When the reservoir pressure is reduced as fluids are withdrawn, gas comes out of the solution and displaces oil from the reservoir to the producing wells. The efficiency of solution gas drive depends on the amount of gas in solution, the rock and fluid properties and the geological structure of the reservoir.
Recoveries are low, on the order of 10-15 % of the original oil in place (OOIP). Recovery is low, because the gas phase is more mobile than the oil phase in the reservoir.
Solution gas drive reservoirs are usually good candidates for water-floodingGAS CAP DRIVE
Gas Cap DriveThe initial reservoir pressure is below the bubble point, so there is more free gas in the reservoir than the oil can retain in solution.This free gas, because of density difference, accumulates at the top of the reservoir and forms a cap. In gas cap drive reservoirs, wells are drilled and completed in the oil producing layer of the formation. As oil production causes a reduction in pressure, the gas in gas cap expands and pushes oil into the well bores. WATER DRIVE
Water DriveMost oil or gas reservoirs have water aquifers. When this water aquifer is continuously fed by incoming water, then this bottom water will expand as pressure of the oil/gas zone is reduced because of production.
The expanding water also moves and displaces oil or gas in an upward direction from lower parts of the reservoir, so the pore spaces vacated by oil or gas produced are filled by water.
The oil and gas are progressively pushed by water towards the well bore. Recovery factor may reach 50% of the original oil in place (OOIP)GRAVITY DRAINAGE
Gravity Drainage
Gravity drainage may be a primary producing mechanism in thick reservoirs that have a good vertical communication or in steeply dipping reservoirs. Gravity drainage is a slow process because gas must migrate up structure or to the top of the formation to fill the space formerly occupied by oil. Gas migration is fast relative to oil drainage so those oil rates are controlled by the rate of oil drainage.COMBINATION DRIVE
Material Balance MethodUnderground withdrawal (oil + gas + water) = Expansion of oil+ dissolved gas (A)+ Expansion f gas-cap gas (B)+ Reduction in HCPV (C)+ water influx (D)
Material Balance Method - Basic Principle A = Increase in HCPV due to the expansion of the oil phase (oil +dissolved gas). B = Increase in HCPV due to the expansion of the gas phase (free gasin the gas cap). C = decrease in HCPV due to the combined effects of the expansion of the connate water and the reduction in reservoir pore volume. D = decrease in HCPV due to water encroachment (from aquifer)
MATERIAL BALANCEN =
N=vol. minyak @ standarG=vol. gas @ standarW=vol. air @ reservoirm=vol.gas/vol.minyak@reservoirNp=prod.minyak@standarGp=prod. gas@ standarWp=prod. air @ standarWe=intrusi air @ reservoirBo, Bg, Bw= unit vol. menyesuaikan65teknik reservoir lanjut - RS -teknik perminyakan - trisaktiMATERIAL BALANCEsimultaneous drivesN =
66teknik reservoir lanjut - RS -teknik perminyakan - trisaktiMATERIAL BALANCEsimultaneous drivesN =
DDI = Depletion Drive IndexSDI = Segregation Drive IndexWDI = Water Drive Index DDI+SDI+WDI = 1
67teknik reservoir lanjut - RS -teknik perminyakan - trisaktiStraight Line MBEMBE can be modified as equations of straight lines, which can be applied to different types of reservoirs (Havlena Odeh).
F= N (Eo + m Eg + Ef,w) + We Bw
F = summation of production terms: Np [Bo + (Rp Rs) Bg] + Wp Bw (rb)Eo = Oil and Dissolved gas expansion terms [ (Bo Boi) + (Rsi Rs) BgEg = Gas cap expansion term Boi (Bg / Bgi 1)Ef,w = rock and water compression/expansion terms (1+m) NBoi --------------- (cw Swc + cf) p + We Bw (1 Swc)
MBE- Definitions of VariablesProduction dataNp = Cumulative oil produced (stb)Gp = cumulative gas produced (scf)Wp = Cumulative water produced (stb)Rp = Gp/Np = Cumulative produced gas-oil ratio (scf/stb)Reservoir Datapi = Initial mean pressure in the reservoir (psi)p = current mean pressure in the reservoir, (psi)Swc = connate water saturation, (fraction)cf = Compressibility of formation (psi-1)Fluid PVT DataBgi = Initial gas volume factor at pi (ft3/scf)Bg = Gas volume factor at current pressure p (ft3/scf)Boi = Initial oil volume factor at pi (rb/stb)Bo = Oil volume factor at current pressure p (rb/stb)cw = Compressibility of water (psi-1)Bw = Formation volume factor of water at current pressure p (rb/stb)Rsi = solution gas-oil ratio at initial pressure pi (scf/stb)Rs = solution gas-oil ratio at current pressure p (scf/stb)No gas cap, no water drive70
No gas cap71
No water drive72
No gas cap73
No water drive74
WATER INFLUX
DDI = Depletion Drive IndexSDI = Segregation Drive IndexWDI = Water Drive Index DDI+SDI+WDI = 1
75teknik reservoir lanjut - RS -teknik perminyakan - trisaktiWATER INFLUX
STEADY STATE : SCHILTHUIS
MODIFIED STEADY STATE : HURST
UNSTEADY STATE : VAN EVERDINGEN & HURST 76teknik reservoir lanjut - RS -teknik perminyakan - trisaktiWATER INFLUX
77teknik reservoir lanjut - RS -teknik perminyakan - trisaktiWATER INFLUX
k= konstanta water influx [bbl/day/psi] dp= (pi-p) di batas reservoir / aquifer [psi]
c= konstanta water influx [bbl/day/psi dp= (pi-p) di batas reservoir- aquifer [psi] a = konstanta konversi waktu [f. unit waktu] B= konstanta water influx [bbl/day/psi] dp= penurunan tekanan [psi] Q(t)=dimensionless water influx78teknik reservoir lanjut - RS -teknik perminyakan - trisaktiWater InfluxVan Everdingen (re/rw = 2 4)teknik reservoir lanjut - RS -teknik perminyakan - trisakti79
Van Everdingen (re/rw = 2 4)teknik reservoir lanjut - RS -teknik perminyakan - trisakti80
Van Everdingen (re/rw = 5 10)
Reserve Estimation Methods
3.Decline Curve Analysis Later stage of development, production rate undergoes natural decline Mostly Production data, no Pressure data RF is calculated Time dependant
Decline curve of an oil well
Advantage of Decline CurvesDecline curves are the most common means of forecasting production. Theyhave many advantages:Data is easy to obtain,They are easy to plot,They yield results on a time basis, andThey are easy to analyze.Exponential DeclineIf the conditions affecting the rate of production of the well are not changed byoutside influences, the curve will be fairly regular, and, if projected, will furnishuseful knowledge as to the future production of the well.
in the exponential decline, the wells production data plots as a straight line on a semilog paper. The equation of the straight line on the semilog paper is given by:
q = qi .eDt
Where:q = wells production rate at time t, STB/dayqi = wells production rate at time 0, STB/dayD = nominal exponential decline rate, 1/dayt = time, day
Hyperbolic Decline
If the wells production data plotted on a semilog paper concaves upward, then it is modeled with a hyperbolic decline. The equation of the hyperbolic decline is given by:
q=qi(1+bDi.t)-1/b
Where:
q = wells production rate at time t, STB/dayqi = wells production rate at time 0, STB/dayDi = initial nominal exponential decline rate (t = 0), 1/dayb = hyperbolic exponentt = time, day
Harmonic Decline
A special case of the hyperbolic decline is known as harmonic decline, where b is taken to be equal to 1. The following table summarizes the equations used in harmonic decline:
q=qi/(1+bDi.t)
Where:
q = wells production rate at time t, STB/dayqi = wells production rate at time 0, STB/dayDi = initial nominal exponential decline rate (t = 0), 1/dayb = hyperbolic exponent = 1t = time, day
Reserve Estimation Methods
4.Reservoir Simulation applied at any stage, more reliable for matured reservoirs Geological, Rock and Fluid properties, Production data More useful as reservoir management tool
FRACT. FLOW & ITS DERIVATIVEteknik reservoir lanjut - RS -teknik perminyakan - trisakti88
FRACTIONAL FLOW EQUATIONteknik reservoir lanjut - RS -teknik perminyakan - trisakti89
WATER FRACTIONAL FLOWteknik reservoir lanjut - RS -teknik perminyakan - trisakti90
FRONT & AVERAGE WATER SATURATIONSteknik reservoir lanjut - RS -teknik perminyakan - trisakti91
TRANSITION ZONEteknik reservoir lanjut - RS -teknik perminyakan - trisakti92
2D FLUID FLOWteknik reservoir lanjut - RS -teknik perminyakan - trisakti93
teknik reservoir lanjut - RS -teknik perminyakan - trisakti94
Microscopic displacementteknik reservoir lanjut - RS -teknik perminyakan - trisakti96
Vertical sweep efficiencyteknik reservoir lanjut - RS -teknik perminyakan - trisakti97
teknik reservoir lanjut - RS -teknik perminyakan - trisakti98
Sweep effeciency
Sweep effeciencyteknik reservoir lanjut - RS -teknik perminyakan - trisakti100
Areal & vertical sweep eff.teknik reservoir lanjut - RS -teknik perminyakan - trisakti101
Displacement efficiencyteknik reservoir lanjut - RS -teknik perminyakan - trisakti102
where S oi = initial oil saturation at start of floodB oi = oil FVF at start of flood, bbl/STB = average oil saturation in the flood pattern at a particular point during the flood
DYKSTRA PARSONS coefficient of K variation (V)teknik reservoir lanjut - RS -teknik perminyakan - trisakti104
V =k50 = median permeability value, mDk84.1 =permeability at 84.1% probabilityPlot of permeability data on log normal paperteknik reservoir lanjut - RS -teknik perminyakan - trisakti105K, mDPercent of sample with higher Permeability5099.990.01
V =
Dykstra Parson, WOR = 1
vMDykstra Parson, WOR = 5
VMDykstra Parson, WOR = 25
VMDykstra Parson, WOR = 100
VM
Water ConingP > 0,433(w -o)hc
teknik reservoir lanjut - RS -teknik perminyakan - trisakti115
Water Coning In A Vertical Oil Well
For an reservoir with an underlying water-zone, and the perforated interval at the top of the oil-zone, a number of researchers have proposed methods for determining the Critical oil flow rate (Qoc).teknik reservoir lanjut - RS -teknik perminyakan - trisakti116The commonly-used methods are: - Meyer-Garders Method- Chaperon's Method- Schol's Method- Hoyland-Papatzacos-Skjaeveland's Method - Sobosinski - Cornelius
All these methods apply to the isotropic reservoir case where horizontal permeability equals vertical permeability, except for Chaperon's more general anisotropic case.Water Coningteknik reservoir lanjut - RS -teknik perminyakan - trisakti117
Water coning & fingeringteknik reservoir lanjut - RS -teknik perminyakan - trisakti118
Water coning in horizontal wellteknik reservoir lanjut - RS -teknik perminyakan - trisakti119
Critical Pressure Drawdown & Production Rateteknik reservoir lanjut - RS -teknik perminyakan - trisakti120P > 0,433(w -o)hc
P = pressure draw down at the well = water specific gravity = oil specific gravityhc = vertical distance from the bottom of well completion to OWCMeyer-Garders Methodteknik reservoir lanjut - RS -teknik perminyakan - trisakti121
0.001535Chaperon's Methodteknik reservoir lanjut - RS -teknik perminyakan - trisakti122
Schol's Methodteknik reservoir lanjut - RS -teknik perminyakan - trisakti123
Hoyland-Papatzacos-Skjaeveland's Methodteknik reservoir lanjut - RS -teknik perminyakan - trisakti124
Metode BOURNAZEL dan JEANSON
teknik reservoir lanjut - RS -teknik perminyakan - trisakti125
0.00137Sobocinski dan Cornelius M < 1, =0.5 M> 1, = 0.6Z : dimensionless cone heighttd : dimensionless time, t: daysteknik reservoir lanjut - RS -teknik perminyakan - trisakti
Contoh perhitunganteknik reservoir lanjut - RS -teknik perminyakan - trisakti127
nomenclatureteknik reservoir lanjut - RS -teknik perminyakan - trisakti128Where: Qoc = critical oil well rate, STB/day h = oil column thickness, ft hp= perforated interval, ft kh= horizontal permeability, md kv= vertical permeability, md ko= effective oil permeability, md (ko= rock permeability x oil relative permeability)re = drainage radius of well, ftrw = wellbore radius, ftBo = formation volume factor of oil o = oil viscosity, cp o = oil density, lb/ft3 w = water density, lb/ft3Note that the critical rate is the oil rate below which water breakthrough will never occur; this rate may be too low for practical and economic reasons.Water coning Input dataOil column thicknessftPerforated intervalftWellbore radiusftDrainage radiusftPermeabilitymDOil relative permeabilityOil densitylb/ft3Water densitylb/ft3Formation volume factorOil Viscosityteknik reservoir lanjut - RS -teknik perminyakan - trisakti129OUTPUT VARIABLES Critical Oil Flow RateSTB/day Meyer-Garder's Method Chaperon's Method Schol's Method Hoyland-Papatzacos-Skjaevelandteknik reservoir lanjut - RS -teknik perminyakan - trisakti130Critical Oil Flow Rate (Anisotropic)STB/day Chaperon's Method