2. Standing's Method for Present IPR

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1 Koya University College of Engineering School of Chemical and Petroleum Engineering Petroleum Engineering Department Petroleum Production Engineering II Predicting Present and Future IPRs (Standing Method). Standing's Method for Present IPR Farhad Abdulrahman Assistant Lecturer Standing s Method The initial work of Vogel assumed a flow efficiency of 1.00 and did not account for wells that were damaged or improved. Standing (1970) essentially extended the application of Vogel's (Vogel did not consider formation damage) proposed a companion chart to account for conditions where the flow efficiency was not equal to 1.00, as shown in figure 3.0 Figure 3.0: Inflow performance relation, modified by standing. 1/13/016 Figure 3.0 shows IPR curves for flow efficiencies between 0.5 and 1.5. Several things can be obtained from this plot: The maximum rate possible for a well with damage. The maximum rate possible if the damage is removed and FE = 1.0 The rate possible if the well is stimulated and improved. The determination of the flow rate possible for any following pressure for different values of FE. The construction of IPR curves to show rate versus flowing pressure for damaged and improved wells. Standing proposed a companion chart to account for conditions where the flow efficiency is not 1.0, As shown in figure 4.0, the flow efficiency is defined as: Ideal drawdown FE = Actual drawdown = P wf Eq..1 P wf P wf = P wf + P skin Rearranging Eq..1 FE = P wf P skin P wf Eq.. Farhad Khoshanw 1

2 Effect of Altered Permeability For a well draining from a cylindrical reservoir volume at pseudo-steady state condition; ln 0.47 r e r FE = w ln 0.47 r Eq..3 e r + S w Where, S is the dimensionless skin factor As shown in figure 4.0, an undamaged well would flow at rate q for a flowing pressure P wf, while, the damaged well must flow at the lower pressure of Pwf in order to produce the same rate q. The P skin is the difference between P wf and Pwf. Effect of Skin Factor Standing s Method Figure 4.0: Pressure profile of damaged wells produced by solution gas drive. 1/13/016 Figure 5.0 shows the region of damaged wellbore and its resistance to flow near the wellbore. There are many factors which cause or control this situation: Invasion of the zone by mud of kill-fluids Swelling of shale Accumulation of obstacles around the perforation area Figure 5.0: Skin effect 1/13/016 Farhad Khoshanw

3 The determination of P skin is made by first determining S (skin factor) from a standard pressure build up test on a well as shown in figure 6.0 P skin was defined by Van Everding as: P skin = 141. μ o β o S Eq..4 k o h The standard equation for determining skin is: S = P 1 hr P wf m k log μc r Eq..5 w From the S value we can find out that: S = 0 indicate no alteration. S = + ve indicates damaged well S = ve indicates improvement and that values of -3 to -5 are common for fractured reservoir. The value of P skin is then calculated from: P skin = 0.87 S m Eq..6 m in both equations.5 &.6 is the slope, and determined from the pressure build-up test (Horner Plot), as shown in figure 6.0. Or is determined from the following equation: m = 16.6 μ o β o Eq..7 k o h Standing s Method Standing plotted the dimensionless IPR curves for all the reservoir cases as shown in figure 3.0 and arrived at the following relationship between the above dimensionless parameter: max = 1 0. P wf 0.8 P wf Eq..8 Where j = value of FE and P`wf is the ideal flowing pressure. 1/13/016 Figure 6.0: Horner Plot, build-up test From Eq..1 we can write: P wf = FE FE P wf Dividing both sides by : 1 P wf = FE FE ( P wf ) By rearaagning the above equ. and solving for P wf P wf = 1 FE + FE P wf Eq..9 Substituting equation.9 in equation.8; and work for Qo, to get Eq. Qo max.10 or.11 as follow: = FE + FE P max Or max = 1.8 FE 1 wf FE + FE P wf P wf 0.8 FE 1 P wf Eq..11 Farhad Khoshanw 3

4 Standing Procedure Example Using test data (P wf and q o ) and the value of FE existing when the test was conducted, calculate q o max using equation.10 (or by using figure 3.0).. Assume various values of P wf and calculate q o for each P wf from equation Other values of FE may be used to determine the effect of increasing FE by stimulation. Using the following data, construct an IPR for this well at present condition and for a value of FE=1.3. The present conduction data are : = 085 psig, P b = 100 psig and FE = 0.7 From the test for q o = 0 STB day, P wf = 1765 psig. Solution of Example 1.0 Solution of Example 1.0 (contd.) 1. Determine q o(max) by using equation.11. Using the equation.11 and working for q o : Q 0(max) = 1.8 FE 1 P wf P r 0.8 FE (1 P wf P r ) q 0 = FE 1 P wf FE 1 P wf 085 Q 0(max) = = 1100 STB/Day 3. For both FE=0.7 and FE=1.3 assume various P wf, and put in equation of step, from there calculate the corresponding q o. Table of series of P wf versus q 0 at FE=0.7 & FE= Plot the IPR for the Two Flow Efficiencies P wf 1 P wf q o FE = 0.7 FE = FE = 0.7 FE = 1.3 1/13/016 Farhad Khoshanw 4

5 Reservoir Performance Predicting Future IPR 3. Standing's Method for Future IPR Standing Method Standing (1970) essentially extended the application of Vogel s to predict future inflow performance relationship of a well as a function of reservoir pressure. He noted that Vogel s equation. Vogel s Equation can be rearranged as (H.W): ( ) max = 1 P wf P wf Eq. 3.1 The productivity index of a well can be defined by Eq.3.1 Standing introduced the productivity index J into Eq. 3.1 as follow: J = () max P wf Eq. 3. Standing Method (contd.) If we assume fluid saturation to be the same everywhere in the reservoir, which is analogous to ''zero drawdown'' then: J = lim J P wf Standing then defined the present (current) zero drawdown productivity index as: J P = 1.8 () max Eq. 3.3 Where,J P is Standing s zero-drawdown J. The J P is related to the productivity index by: J J P = P wf Eq. 3.4 Standing Method (contd.) J can also be arrived from the following equation: J k o S o, S g h = μ o B o ln r e r 3 w 4 To arrive to the final expression for predicting the desired IPR expression, Standing combines equation 3.3 with equation 3.1 to eliminate ( ) max to give: = J f ( ) f P wf f 0.8 P wf f Where, the subscript f refers to future condition. Eq. 3.5 Standing Method (contd.) Standing suggested that J * f can be estimated from the present value of J * p by the following expression: k ro μ o β o J f = J f P Eq. 3.6 kro μ o β o P where the subscript P refers to the present condition. If the relative permeability data is not available, J * f can be roughly estimated from: J f = J ( ) f P Eq. 3.7 ( ) P Farhad Khoshanw 5

6 Standing's methodology from predicting a future IPR is summarized in the following steps: 1. Using the current time condition and the available flow test data, calculate ( max ) from Vogel s Equation or Equation (3.1). 3. Using fluid property, saturation and relative permeability data, calculate both k ro μ o β o f and k ro μ o β o P 4. Calculate J * f by using equation (3.6). Use equation (3.7) if the oil relative permeability data is not available.. Calculate J * at the present condition, i.e., J * p, by using equation (3.3). 5. Generate the future IPR by applying equation (3.5) - Notice that other combinations of equations (3.1) through (3.4) can be used to estimate J * p. Example (Future IPR) A well is producing from a saturated oil reservoir that exists at its saturation pressure of 4000 psig. The well is flowing at a stabilized rate 600 bbl/day and a P wf = 300 psig. Material balance calculations provide the following current and future predictions for oil saturation and PVT properties. Present Future p r µ o, cp.4. B o, bbl/stb k ro Generate the future IPR for the well at 3000 psig by using Standing's method. Farhad Khoshanw 6