Graduation Project 2: A Conventional Reservoir Engineering Study of Gas Field

1. Graduation Project 2:  A Conventional Reservoir Engineering Study of Gas Field Advisors: Prof. Jamal Abo Kasem & Dr. Hazim Al Attar Done by Ahmed Al Janahi 200440231 Hosam Zablawe 200337528 Mohamed Yehia 200440262

3. Introduction: Project Description Study the performance of a gas reservoir associated with water aquifer.

4. Introduction: Importance of the study This project is one of the assignments new engineers are expected to perform in the industry after graduation. The results of such study is crucial for the development of any gas reservoir subjected to partial or full water influx. Prediction of reservoir performance under existing production scheme and under proposed production scenarios. Enable us to apply software package called OilWat/GasWat developed by IHS Energy Group-based in Houston, to run material balance calculations.

5. Background Theory: Material Balance Equation (M.B.E) Definition

6. Background Theory: Material Balance Equation (M.B.E) Definition

7. Background Theory: M.B.E Assumptions Zero Dimensional. Single homogenous unit. Time independent. The equation is not evaluated in a step-wise pressure. Pressure appears explicitly and implicitly in M.B.E.

8. Background Theory: Appropriateness of M.B.E for gas When material balance is applied to hydrocarbon accumulation, it depends on: How rapidly the pressure waves reach the boundary of the reservoir (pressure is equilibrated). So that it may be treated as zero dimensional reservoir. This, in turn, is dependent on the magnitude of the hydraulic diffusivity constant K/fµC.

9. Background Theory: Appropriateness of M.B.E for gas The larger the value of this parametric group, the more rapidly is pressure equilibrium achieved. The diffusivity constant will be several times larger if it contains gas rather than oil.

10. Methods & Techniques: Material Balance Methods P/Z- interpretation technique

11. Methods & Techniques: Material Balance Methods Havlena-Odeh interpretation

12. Methods & Techniques: Material Balance Methods Van Everdingen- Hurst: The two dimensionless parameters tD and rD are given by:

13. Methods & Techniques: Material Balance Methods

15. Methods & Techniques: Future Performance Method

16. Methods & Techniques: Future Performance Method

17. The Software: OilWat/GasWat This program can perform the following tasks: Predict the original hydrocarbon-in-place in a reservoir, with or without water influx. Generate a reservoir pressure profile versus time, given original hydrocarbon-in-place.

18. Solved Examples Example 1: A volumetric Gas Reservoir:

19. Example 1: A volumetric Gas Reservoir: Solved Examples

20. Example 1: A volumetric Gas Reservoir: Solved Examples

21. Example 2: A gas reservoir with a linear aquifer: Solved Examples

22. Example 3: Pressure prediction for Example 2: Solved Examples

23. Field Data Calculations: Reservoir Information Consists of six layers Mainly composed of oolitic grainstones with some thin interbeds of anhydrite No apparent structural trap growth during the deposition

24. Field Data Calculations: Reservoir & Aquifer Parameters

25. Field Data Calculations: Reservoir Production

26. Field Data Calculations: Average Pressure Method

27. Field Data Calculations: Average Pressure Method

28. Field Data Calculations: Average Pressure Method

29. Extrapolating the first part of the p/Z trend to the x-axis (p/Z=0) should give us an estimate to the OGIP. Field Data Calculations: P/Z Method

30. Field Data Calculations: Havlena-Odeh Method

31. Field Data Calculations: Linear Aquifer Model

32. OGIP = 4.8E+11 scf Type of aquifer = Radial Aquifer Rd =8 Td = 0.02 Field Data Calculations: Radial Aquifer Model (The best Fit)

33. Field Data Calculations: Radial Aquifer Model (The best Fit)

34. Prediction of the reservoir performance was done at two different offtake rates for 24 years after 35.5 years of production. 20 MMSCF which is less than the current operating rate (30 MMSCF). 40 MMSCF and it is higher than the operating rate. Field Data Calculations: Future Performance

35. Field Data Calculations: Future Performance

36. We have to compromise between maintaining the reservoir at high pressure while production or depleting it to a very low pressure. Cost Estimation

37. When H2S is present, gas productions should comply with safety measures set by API under code no. RP 55. Flaring of gas should be kept at minimum level. Safety and Environmental Considerations

38. Conclusions We are the first group of students to implement OilWat/GasWat software in graduation projects. This software is similar to the ones which are used by operating companies. It seems that in most cases we may need to adjust some of the aquifer parameters to best fit the short hand form of MBE. Material balance can be applied to determine OGIP and to identify the drive mechanisms in a selected gas field.

39. Conclusions Van Everdingen-Hurst has been found adequate to identify the reservoir derive mechanism (moderate water drive) and to characterize the aquifer model (rd =8). Future performance plan depends on the maximum recovery factor that could be reached in a specific field with respect to the depletion pressure. It is always recommended to produce the gas at a high offtake rate provided that there is a market for the produced gas.

40. Recommendations It is recommended to produce the gas as fast as possible, provided that there is a market for the gas. The surface production facilities must have the capability to handle such large gas volume produced. It is recommended to drill a couple of wells in the water aquifer. This practice would ascertain the collection of more accurate information about the aquifer.

41. Another scenario for predicting the performance of the reservoir is the gas injection. Water influx is detrimental to gas production. Subsequently, it is recommended to produce the gas as fast as possible, provided that there is a market for the gas. Recommendations

42. Gant Chart