1. Dev Dutt Sharma IUGF, 18 Jan 2013, Mumbai
Hydrocarbon Occurrence in Unconventional Shale Reservoirs of Cambay Basin and their Exploitation technologies
Dev Dutt Sharma
IUGF, 18 Jan 2013, Mumbai

2. Presentation Outline Introduction
Hydrocarbon Occurrence in Shale Reservoirs of Cambay Basin
Mechanism of production from Cambay Shale tight reservoirs
Evaluation & Development technologies applied for unconventional shale reservoirs in past
New technologies of formation evaluation, drilling and production
Application of similar new technologies in other basins of India

3. Hydrocarbon Resource Pyramid

4. Introduction
Cambay Petroliferous Basin is on mature stage of exploration in view of 55 years of development and production history with primary focus on known conventional Middle Eocene reservoirs
Basin offers further scopes for exploration and production from deeper tighter unconventional reservoirs of Cambay Shale & Olpad formations, including fractured Deccan Trap, which constitute 2/3 of sedimentary thickness
Recent development of new technologies of formation evaluation, horizontal drilling and multistage hydrofracturing especially in US and Canada have made low productive unconventional Shale Gas, Tight Gas Sands and CBM as attractive resources for production.

5. Location of Cambay Basin

6. Hydrocarbon Occurrence in Shale Reservoirs of Cambay Basin
Cambay Shale known for its major hydrocarbon source also acts as reservoir in Cambay Basin
Occurrence of hydrocarbons in unconventional reservoir of Cambay Shale is known since the first discovery oil at Cambay during 1958
Deeper wells like Cambay-40 & 45 drilled during 1963 & encountered oil & gas while drilling under high heat flow and over pressure conditions
Thereafter, oil & gas production was obtained from so called “fractured shale reservoir” of Cambay Shale in fields like Indrora, Sanand, Jhalora, Kalol, Wadu & Nandej etc
Interestingly, Indrora-1 which was drilled in 1971 is still producing oil on self from high pressured Cambay Shale Reservoir “Indrora Shale Pay”, though in small quantity
Similarly, some wells in Kalol Field like K-165 produced oil from Younger Cambay Shale for long (over 30 years), though at low rate

7. Generalised Stratigraphy of Cambay Basin

8. Characteristics of Unconventional Shale Reservoirs
Unconventional hydrocarbon reservoirs act as source as well as reservoir itself
Relatively thicker ( m) and laterally continuous
Low permeability Tight Gas Sands fall in this category.
Shales are most prominent among them, next CBM.
Low permeability shaly sandstone and siltstone have stratigraphic deposition with migrated and/or insitu hydrocarbon accumulation
Have no free water or oil/gas-water contact being dominantly argillaceous with more of bound water than free water in micropores and fractures.

9. Mechanism of production from Cambay Shale
Geologically, prodelta shale facies equivalent to Chhatral, Mehsana and Mandhali members of arenaceous Kadi Formation form the shale reservoir in Younger Cambay Shale.
Shales associated with thin silts, silt streaks or silt laminations and microfractures act as reservoir in Cambay Shale
Pure shales may offer additional potential for “Shale Gas” due to adsorptions of natural gas on shale surface which can be assessed based on organic maturity.
Dual porosity and dual permeability mechanism is responsible for oil & gas production from low permeability “tight” reservoir in Cambay Shale
Triple porosity and dual permeability model is applicable for “Shale Gas” production from Cambay Shale

10. Prodelta Shale Facies- Chhatral Member

11. Prodelta Shale Facies- Mandhali Member

12. Evaluation technologies applied for Shale reservoirs in the past
Formation evaluation:
It was difficult to identify HC bearing zones by conventional logs due to their low resistivity and high water saturation, interesting sections were picked up based on resistivity build up or kinks.
Overlay of density-neutron porosity on resistivity log was used when available in new wells.
New concept of “Shale Resistivity Ratio” was applied based on analogy with US Gulf of Mexico as applicable to high pressure shales.
Intervals having SRR of considered as “commercial”, as “Small occurrence” and more than 3.5 “Non-commercial” hydrocarbon bearing zones
The concept was applied in newly drilled wells of Sanand, Jhalora, Wadu, Kalol, Indrora, Nandej fields for
perforation testing and identification of bypassed pays in old wells in Cambay Shale section, which proved very effective.
Conventional Sw calculation indicated very high water saturation (70-90%) to which 20-40% shale correction was applied for testing in shale reservoir because of their clayey nature having more of bound water than free water.
As thumb rule 1/6th of perforation interval in shale was considered as pay for estimation of reserves

13. Typical Shale Resistivity Ratio Profile

14. Log correlation of producing Younger Cambay Shale section in Sanand wells

15. Shale Resistivity Ratio Profile Sanand wells
Sanand-A
Sanand-B

16. Log correlation of producing Younger Cambay Shale section in Wadu wells

17. Shale Resistivity Ratio Profile Wadu wells
Wadu-A
Wadu-B

18. Technologies applied for shale reservoirs in past- contd..
Drilling and production:
Oil production from Cambay Shale reservoir which was 50m3/d declined fast to 3-5m3/d within 2-5 years.
Wells required repeated HF for sustained production.
Wells when ceased production or became uneconomical, transferred to higher conventional sandstone/siltstone reservoirs.
Vertical drilling and basic hydro-fracturing (30-40 tons) applied at that time could not enhance productivity for long.
Options were either to drill a vertical well and frac or drill directional for enhanced production from shaly sand, tight silt or shale reservoirs.
Directional drilling and MWD logging techniques were first time applied in Wadu wells, which produced about 40-50m3/d oil and 25, ,000m3/d gas on self flow.
There was no technology to fracture a deep well, greater than 2000m earlier due to which wells like Jabera-1, which gave gas about 5000m3/d from Tight Vindhyan Sandstone at m depth had to be abandoned.

19. New technologies for Tight Reservoir Development applied in Cambay field
Formation evaluation
Horizontal drilling
Multistage fracturing
Microseismic monitoring
Extended production testing

20. Cambay PSC area showing Cambay-76H well
Drilled in NW direction normal to Shmax

21. “Tight” Pay zones occurrence in Cambay Field
m gross interval 3 large pay zones (X, Y and Z) Further possible tight pay zones below Z zone
CAMBAY 76H
Well Path

22. Formation Evaluation of a Type Cambay Well
Sophisticated proprietary log interpretation technology
Curves generated include:
Shale Permeability *
Porosity
TOC *
Variable Density
Lithologies
Free Gas * Sw
Bulk Volume Irreducible *
Free Water *
Effective Porosity
Free Fluid Volume
Volume of Hydrocarbons
Results identified three high potential zones in the Eocene section
EP-III
(X-zone)
EP-IV A
(Y-zone)
EP-IVB
(Y-zone)
YCS
(Z-zone)

23. Drilling & Completion of Cambay-76H
“Proof of Concept” well Camaby-76H was drilled to 2740m (TVD 1762m) with horizontal section of 634m in low permeability Tight Siltstone Reservoir of Eocene in Cambay Field
Completed with 9-5/8”x5-1/2” liner hanger packer with 5-1/2” tubing in 8-1/2” open hole using sliding sleeves and swellable packers
Undergone multistage fracturing (8 stages) by pumping about 1200 tons of per stage against normal ton/job
Fracturing was monitored by microseismic survey to define fracture geometry and permeability trend in the reservoir for further development and production enhancement.
Expected to produce 300, ,000 m3/d of gas against the normal production of 30,000-50,000m3/d with conventional technology.

24. Cambay-76H Well Profile NW SE Cambay-76H OSII X Top Y Top 610m
76H Heel
76H Toe
Y Top
X Top
OSII
Casing Point
Cambay-76H NW SE
610m

25. C-76H well Drilling & Completion Schematic

26. Multistage Fracturing Cambay-76H
8 stage fracture stimulation (16 frac ports) in 7 days
Good fracture connectivity, frac height about 70m
tonnes /stage, total about 1200tons
4,400bbl water per stage @60 bbl/min
Comparable to US frac jobs e.g. Haynesville
C76H well bore

27. Microseismic Monitoring
Microseismic Operations
8 Frac treatments at the Well Cambay-76H monitored over a period of 8 days
Used Passive Seismic Emission Tomography (PSET®) technology to image the microseismic activity resulting from the fracture treatment
Indian-based seismic company recorded hours of data, processed hours
Event signal strength generally weak, noise levels high due to cultural activity
Velocity model initially calibrated by a perforation shot in an offset well.
Mechanical ball drop events during fracturing provided additional calibration
Extracted 617 microseismic events, 229 mechanical events
Location errors less than +/-15m in horizontal and vertical directions

28. Microseismic Acquisition
991 stations in array represented by red lines.
Station spacing is 20 m
Array consists of 10 lines radiating out from the well head
High fold, wide azimuth & large aperture coverage of sq. km.
Cambay 76H well path shown by yellow dashed line
Data acquired using Aram Aries-II recording system at 2ms sampling rate provided by IOT.

29. Microseismic Interpretation

30. Extended Production Testing
Extended production testing includes:
Post frac well cleanup
Long term flow rate testing through different beans
Installation of EPS
Medium term reservoir performance
PLT logging
PVT sampling , fluid composition (gas, oil/ condensate, water) and pressure information

31. Field Development Strategy

32. Application of similar New Technologies for Tight Reservoirs in other basins of India
The applied new technologies for production enhancement from tight hydrocarbon reservoirs in Cambay Basin can be suitably applied in other basins of India having similar reservoirs like KG, Cauvery, Assam-Arakan, Rajasthan, Vindhyan and Gondwana
Advantage with Indian basins is large multiple pay thickness ( m), moderate depths ( m), better porosity and permeability with evidence of hydrocarbons while drilling
Application of new technologies will help in making deeper, thicker and tighter hydrocarbon reservoirs commercially producer, thus contributing to the growing demand significantly in the country

33. Multistage Fracturing Animation

34. Thank you