Duration of Event (hr)

Transcription

1 Homework 5: Analysis and Interpretation of a Pressure Drawdown/Buildup Test Sequence Given: Introduction: READ THIS FIRST! This problem consists of a pressure drawdown/buildup test sequence but one with a very significant twist the drawdown test was conducted early in the life of the well, and the pressure buildup test was conducted approximately 3 years later. You should also note that a major well workover occurred shortly after the initial completion, and the "final" well completion is considerably different. You should expect differences in calculated parameters formation permeability should be unaffected, but parameters related to the well completion may vary for the two cases. Other points: The "first" pressure drawdown test was terminated prematurely due to a miscommunication between field and service personnel (the pressure gauge was removed from the well too soon). As such, this test may present analysis and interpretation challenges as the recovered test data show the significant influence of wellbore storage effects. The workover consisted of changing the packer assembly and performing a small hydraulic fracture treatment to remove near-well skin damage. These data are for a pressure drawdown/buildup test sequence run on a producing oil well in a regular (40 acre) pattern development (assume that the well is centered in a bounded square reservoir). The data plots (Cartesian, semilog, and log-log plots) are attached. Reservoir properties: φ=0.10 r w =0.33 ft c t =15x10-6 psia -1 h=150 ft Oil properties: B o =1.2 RB/STB Production parameters: Event µ o =1.5 cp Duration of Event (hr) Pressure at start of Event (psia) Oil Flowrate (STB/D) 1. First Drawdown Test 44 p i = Well Workover 336 (2 weeks) N/A 0 3. Production Sequence 26,280 (3 years) N/A Final Buildup Test 400 p wf ( t=0)= Note: The solution to this homework is available in file (P324_99A_Exam_1_Prob_5.pdf). You are encouraged to make use of this solution but you remain responsible for all calculations, graphical analysis, etc. Failure to provide all details will result in severe grading penalties.

2 2 Required Results Pressure Drawdown Case Required: Drawdown Case You are to estimate the following: Log-log analysis: a. The wellbore storage coefficient, C s. b. The formation permeability, k. Cartesian analysis of "early" time (wellbore storage distorted) data: a. The pressure at the start of the test, p i. b. The wellbore storage coefficient, C s. Semilog analysis of "middle" time (radial flow) data: a. The formation permeability, k. b. The near well skin factor, s. c. The radius of investigation, r inv, at the end of radial flow. Cartesian analysis of "late" time (boundary-dominated flow) data: a. The reservoir drainage area, A. b. The oil-in-place, N. Material balance equation: a. Estimate the average reservoir pressure, p, at the end of the test (the last point). Results: Drawdown Case Log-log Analysis: Wellbore storage coefficient, C s = RB/psia Formation permeability, k = md Cartesian Analysis: Early Time Data Pressure at start of test, p i = psia Wellbore storage coefficient, C s = RB/psia Semilog Analysis: Formation permeability, k = md Near well skin factor, s = Radius of Investigation, rinv (end of radial flow) = ft Cartesian Analysis: Late Time Data Reservoir drainage area, A = acres The oil-in-place, N = STB Average reservoir pressure, p (material balance Eq.) = psia

3 3 Required Results Pressure Buildup Case Required: Buildup Case You are to estimate the following: Log-log analysis: a. The wellbore storage coefficient, C s. b. The formation permeability, k. Cartesian analysis of "early" time (wellbore storage distorted) data: a. The pressure at the start of the test, p wf ( t=0). b. The wellbore storage coefficient, C s. Semilog analysis of "middle" time (radial flow) data: a. The formation permeability, k. b. The near well skin factor, s. c. The radius of investigation, r inv, at the end of radial flow. d. The extrapolated pressure, p*. e. Average reservoir pressure, p (MBH technique) Cartesian analysis of "late" time (boundary-dominated) data: "Muskat Plot" a. Average reservoir pressure, p. Results: Buildup Case Log-log Analysis: Wellbore storage coefficient, C s = RB/psia Formation permeability, k = md Cartesian Analysis: Early Time Data Pressure at start of test, p wf ( t=0) = psia Wellbore storage coefficient, C s = RB/psia Semilog Analysis: (MDH and Horner analysis) Formation permeability, k = md Near well skin factor, s = Radius of Investigation, r inv (end of radial flow) = ft Extrapolated pressure, p* (from Horner analysis) = psia Average reservoir pressure, p (MBH technique) = psia Cartesian Analysis: Late Time Data ("Muskat Plot") Average reservoir pressure, p = psia

4 4 Drawdown Test Data Data Functions: Pressure Drawdown Case Point t (hr) p wf (psia) p (psi) p' (psi) (dp/dt) (psi/hr)

5 5 Pressure Buildup Test Data Data Functions: Pressure Buildup Case Point t (hr) t e (hr) Horner Time p ws (psia) p (psi) p' (psi) (dp/d t) (psi/hr) E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E

6 Test Summary Plots: Test Summary Plots 6

7 Log-Log Plot (Pressure Drawdown Case) Log-Log Plot: Pressure Drawdown Case Pressure Drop and Pressure Drop Derivative Data 7

8 Early-Time Cartesian Plot: Pressure Drawdown Case Early-Time Cartesian Plot (Pressure Drawdown Case) 8

9 Semilog Plot: Pressure Drawdown Case Semilog Plot (Pressure Drawdown Case) 9

10 Late-Time Cartesian Plot: Pressure Drawdown Case Late-Time Cartesian Plot (Pressure Drawdown Case) 10

11 Log-Log Plot (Pressure Buildup Case No Rate History) Log-Log Plot: Pressure Buildup Case Pressure Drop and Pressure Drop Derivative Data 11

12 Log-Log Plot (Pressure Buildup Case Includes Rate History) Log-Log Plot: Pressure Buildup Case Pressure Drop and Pressure Drop Derivative Data Effective Time Format 12

13 Early-Time Cartesian Plot: Pressure Buildup Case Early-Time Cartesian Plot (Pressure Buildup Case) 13

14 Semilog Plot: Pressure Buildup Case Semilog Plot (Pressure Buildup Case No Rate History) 14

15 Horner Semilog Plot: Pressure Buildup Case Horner Semilog Plot (Pressure Buildup Case Includes Rate History) 15

16 Late-Time Cartesian Plot ("Muskat Plot"): Pressure Buildup Case Late-Time Cartesian Plot ("Muskat Plot") (Pressure Buildup Case) 16