Presentation on oil Reservoir performance relationship

Reservoir engineering

1. Methods Of Calculating Reserves Volumetric Method Reservoir Limit Test Material Balance Method Decline Curve Method

2. Reserves Estimate vs. Property Life Two Factors are Important Implementation of new technology improves reservoir performance Cost containment improves economic limiting rate

3. Volumetric Method Volumetric estimate is the calculation of oil and gas in place by determining the geometric extent of the reservoir. Undersaturated Oil Reservoir OGIP = (OOIP) x R si A B C D E F G  Cut-Off  & SW Cut-Off Comparison of Gross and Net Pay h t = A + B + C + D + E + F + G h o = B + D + G 7758 barrels = 1 acre-ft

4. Volumetric Method Saturated Oil Reservoir OOIP = 7758 A o h o  (1 - S w )/B o OGIP = Solution Gas + Gas-Cap Gas OGIP = (OOIP) x R si + 43,560 A g h g  (1 -S wc )/B gi or OGIP = (OOIP) x R si + m (OOIP)/ B gi Gas Reservoir OGIP = 43,560 A h g  (1 - S wc )/B gi Condensate = (OGIP) x BPMM 43560 ft 2 = 1 acre GAS OIL GAS

5. Volumetric Method for Estimating Reserves Deterministic Approach Pore Volume (A, h & ) RESERVES S wi , B oi Recovery Factor Probabilistic Approach Pore Volume (A, h & ) RESERVES S wi , B oi Recovery Factor Deterministic Model Stochastic Model Most likely Single Value Estimates Most likely Single Value Probability Distribution Probability Distribution of Values

6. Sources of Data Saturation: Log, core analysis, tracer test Porosity: Log, core analysis PVT: Laboratory, correlations Thickness: Geologic maps, core analysis, log Bulk Volume: Planimetering of geologic maps  

7. Calculation Of Bulk Volume

8. Procedure for Using Contour Prepare a contour map showing the subsea depth of the top and bottom of formation.

9. Procedure for Using Contour Cont’d Planimeter the area enclosed by each contour and draw an acre-ft diagram Bottom (Base) Top OWC GOC Area, Acre 9000 9500 8500 8000 Subsea Depth

10. Procedure for Using Contour Cont’d Calculate net oil pay or net gas using any of the following methods: Planimetering Numerical Integration Others Adjust net pay for the presence of shale. For example, if shale fraction is X, calculated net pay must be multiplied by (1-X) to get the precise net pay.

11. Planimetering of Geologic Maps 1. Planimeter the horizon map 2. Make a graph of depth versus area in acres to locate top of sand 3. Use sand thickness encountered by the wells to base of sand. Alternatively base maps can be used if they are available. 4. Locate fluid contacts on the depth-areal graph.   5. Calculate bulk volumes of oil and gas by planimetering depth- areal graph from fluid contact. GOC WOC Area, acres

12. Numerical Integration 1. Simpson’s Rule   2. Trapezoidal Rule   3 . Pyramidal Rule

13. Exercise No. 17 Isopach map; contour interval: 50 feet. The Isopach map shown in the Figure may be assumed to represent an oil field. By planimetering, the following areas are obtained for the contour lines h(ft) Area (acres) 50 100 150 190 140 60 20 Determine the bulk volume of the reservoir .

14. Solution To Exercise No. 17 Simpson’s Rule Gives: Trapezoidal Rule Gives: Pyramidal Rule Gives: Total = 14, 990 acre-ft

15. Reservoir limit test Method Procedure Perform drawdown test until pseudo-steady state is attained. Graph bottom-hole flowing pressure, Pwf vs. time on Cartesian Calculate slope m Calculate volume drained by well from equation: