The document summarizes core analysis techniques including coring operations, laboratory analysis, and methods to estimate properties like water saturation and generate relative permeability curves. It discusses coring methods, laboratory experiments for routine and special core analysis, hydraulic unitization to characterize the reservoir based on flow behavior, and techniques to estimate water saturation from capillary pressure data and generate relative permeability curves from the same. The reservoir was characterized into 7 hydraulic units with the gas zone mostly composed of HU 5 and oil zone of HU 3 based on their average porosity and permeability. Issues with estimating water saturation profiles due to heterogeneity were also highlighted.

1. Core Analysis Aman Arora Summer Trainee Reservoir Management Group RIL

2. Coring Operations Laboratory Analysis Hydraulic Unitization Estimation of Water Saturation from Capillary Pressure Generation of Relative Permeability Curve(s) from Capillary Pressure Topics Covered

3. Coring Operations

4. Conventional Coring ( while drilling) Conventional Core No sleeve Aluminum sleeve Rubber/Plastic sleeve Sponge Core Gel Core Pressure core Sidewall Coring ( post-drilling) Percussion Rotary Coring Methods

5. Rig-site Lab Operations

6. Laboratory Core Analysis

7. This includes all the experiments and test procedures on core samples, and the data/results collected. The two major categories of core analysis or experiments are: conventional or routine core analysis, special core analysis. Laboratory Analysis

8. This yields the most basic data about the reservoir. This includes the following: Routine Core Analysis (RCA)

9. These are more complex and the data furnished are of wider diversity. They will require longer core preparation and testing times and more specialized and expensive equipment Some common SCAL experiments and data are listed in the following table. Special Core Analysis (SCAL)

11. Hydraulic Unitization

12. Rock properties vary widely in reservoir depending on sedimentation, diagenesis etc. Such variations affect reservoir storage and flow behavior, and thus its study. Reservoir characterization is a prerequisite for efficient development and management of these reservoirs Reservoir Characterization

13. Reservoir description can be defined as the integration of microscopic, mesoscopic and macroscopic scales of data to compile reservoir zonation that accurately describes reservoir and reservoir dynamics. i.e To discretize the reservoir into subunits such as layers and grid blocks and to assign representative values of all petrophysical parameters to each unit. Reservoir Characterization

14. Ebanks (1987) defined hydraulic flow units as “a mappable portion of the reservoir within which geological and petrophysical properties, controlling the flow of fluids, are consistent and predictably different from the properties of other reservoir rock portion”. Hydraulic unit are defined by: Mineralogy (type, abundance, morphology, and location relative to pore throat) Texture (grain size, grain shape, sorting, packing) What is a Hydraulic Unit?

15. Flow Zone Indicator (FZI) method classifies section based on their pore throat characteristics Process: Calculate Reservoir Quality Index (RQI) Calculate φz (ratio of Pore Volume to Grain Volume) Calculate FZI FZI Method

16. Taking a suitable FZI interval, different HU are decided On the graph of Log RQI Vs Log φz , all samples of one HU lie on a straight line of unit slope. Each HU is allotted a color for easy identification. HU zonation is supported by other evidence like lithology, LPSA etc. FZI Method

20. K Vs PHI

21. Summary

23. 7 Hydraulic Units were formed. Most of the core samples taken from gas zone are of HU 5. (avg. φ=19.8% , avg. k=81.72md) Most of the core samples takes from oil zone are of HU 3. (avg. φ=26% , avg. k=1900.73md) Observations

24. Estimation of Water Saturation using Capillary Pressure

25. Part A: Generation of Global J-function curve Get capillary pressure data from core samples. Convert Pc to J-Function using the formula: Plot all “J(Sw) Vs. Sw” on the same graphs, and find a representative curve for the family. This is called the Global Curve. Procedure

28. Part 2:Calculation of Free Water Level (FWL) Take a number of samples, and calculate their threshold/displacement pressure using empirical formula: Convert Pt into Height The Pt of the most comparable sample to the GOC is considered. Depth of FWL = GOC + H Procedure

30. Procedure Part 3: Calculation of Water Saturation For each sample, calculate Height above Free Water Level (FWL) Convert Height above FWL into capillary pressure in reservoir condition Convert Pc at reservoir conditions to Pc at laboratory conditions Change Pc (lab) to J(Sw) Calculate Sw by correlating from Global J-Function Curve.

35. The saturation profile does not show any predictable behavior, because; The reservoir is highly heterogeneous The petrophysical properties show huge variation The Sw values from Dean Stark are more comparable to values from J-function than log. The log values are initial readings without tuning with electrical properties from SCAL. Observation

36. Generation of Relative Permeability Curve from Capillary Pressure

37. Permeability is defined as the ability of a medium to allow a fluid flow. It is a measure of fluid conductivity of a material. What is Permeabilty?

38. When two or more fluids flow in a reservoir, they impede the flow of one another. Relative permeability is the fluid conductivity of one fluid in the presence of another fluid(s). Relative Permeability is expressed as permeability on one fluid over the absolute permeability. What is Relative Permeabitity?

39. There are two ways to get relative permeability values: Experimental Results Steady State Measurement Unsteady State Measurement Estimation from Capillary Pressure data Measurement of Rel. Permeability

40. Drainage applies to processes where the wetting phase is reducing in concentration. Imbibition applies to process where the wetting phase is increasing in concentration. Drainage or Imbibition?

41. Two Phase Drainage Curves Procedure Get Centrifuge Capillary Pressure Data. Plot Pc Vs. Sw* and calculate the Pore Size Distribution Index, λ. Put the value of λ in the equations of Krw and Krn. Plot the relative permeability curves and average them.

47. Basics of coring operations were covered. Various experiments conducted were studied. The reservoir was characterized based on flow behavior. 7 HU were formed. Due to insufficient data, only ONE J-Function was defined, and using it the saturation distribution was obtained. Relative permeability was also calculated using capillary pressure. Summary

48. The when, why and how of coring and core analysis. The planning and execution of a coring program. The importance and applications of core analysis. Key Learnings

49. Thank You