IDEAZ

New Trends in Earth Sciences - Exploration of Energy Resources

Akhil Prabhakar (Int. Mtech 4th yr GPT)Swapnil Pal (Int. Mtech 4th yr GT)Ojaswita Singh (Mtech 1st yr GPT)

IIT Roorkee

STRATEGIES IN GEOPHYSICS FOR ESTIMATION OF CONVENTIONAL AND

UNCONVENTIONAL RESOURCES.

Why this topic?

With every passing day, energy security and availability is becoming the most important concern for people. In this day and age, can we imagine a dignified life and growth without access to energy?We are fully aware of the facts that…• Fossil fuels reserves are depleting fast. (Are they?)• Renewables are intermittent and still expensive.• Nuclear future seems uncertain. • Any other breakthrough technologies don’t seem to be on the horizon yet.

Demand for energy Source of energy ?

Nimboo PaniHotel A Hotel B

Assumptions:

3 fresh lemons and few immature lemons

a. 1 fresh lemon = 1 glass of juiceb. Uncertainty in immature lemons

Hotel B

Hotel A

Either let the tourist go to the other hotel as they do not have that sophisticated technique to exploit those immature lemons and thus become bankrupt

Innovate in their existing techniques to exploit those immature lemons and meet the present demand, thus securing their jobs and sustaining their business.

The choice made by chef will decide the future of Hotel A…

Analogy between Energy Industry and this “Nimboo Pani” story.

Hotel A

TouristGeneral Population

Oil and Gas Industry

Geoscientist Chef

Fresh lemons

Conventional hydrocarbon

Analogy between Energy Industry and this “Nimboo Pani” story.

Immature lemons

Unconventional hydrocarbon

Energy Juice

Hotel BRenewable Energy

Innovate in their existing techniques to exploit those unconventional hydrocarbons and meet the present demand, thus securing our jobs and credibility of being a geoscientist.

Either let the policy makers go to the renewable energy as we do not have that sophisticated technique to exploit those unconventional hydrocarbons and thus become bankrupt

Therefore the choice made by a geoscientist will be decisive to decide the future of Oil and Gas Industry.

PART I

The role of geophysics in petroleum resources estimation and classification. — New industry guidance and best practices

Published in “The Leading Edge, November 2012” issue.

Geophysical Technologies

PRMS

Integration of various data sets

Key areas where seismic technologies impact “modern” resource estimation:-

• Faulted Reservoirs

• Prediction of rock and fluid properties.

• Reservoir surveillance

EASY OIL is an OLD STORY… !

For faulted reservoirs

Seismic attributes: Used as part of integrated analysis to assess the likelihood of economically producible reservoir in an undrilled fault block.

Seismic amplitude anomalies may be used to support reservoir and fluid continuity across faulted reservoir provided that the following conditions are met:

• Within the drilled fault block, well logs, pressure, fluid data and test data demonstrate a strong tie between the hydrocarbon-bearing reservoir and the seismic anomaly.

• Fault throw is less than reservoir thickness over (part of ) the hydrocarbon bearing section across the fault and the fault is NOT considered to be a major, potentially sealing, fault.

• The seismic flat-spot or the seismic anomaly is spatially continuous and at the same depth across the fault.

Faulted hydrocarbon-bearing reservoir

Well logs, pressure, fluid data

Integration of data sets

Faulted Reservoirs…

Faulted Reservoirs…A seismic amplitude anomaly has been calibrated to a hydrocarbon-bearing reservoir by well D. The drilled area is separated by faults from three other fault blocks to be targeted by development wells A, B, and C.

Type of resources associated with undrilled blocks

Hydraulic communication across the fault

Inte

grat

ed

anal

ysis

If Complex Geology…??

• Increased level of uncertainty inherent in the data

• Appropriately classify the volumes BASED ON the uncertainty components.

• The levels of risk and uncertainty should be commensurate the quality of the data,

velocity uncertainty, repeatability, and quality of supporting data.

Faulted Reservoirs… Before any seismic attribute analysis, mapping the faults in 3D is a must.

This impacts the likelihood assessment of economically producible reservoir in undrilled fault block, and hence the resource classification.

The detailed mapping of the faults PROVIDES evidence for reservoir continuity across the fault relay-ramp,

Fluid Properties

• Seismic technology can be used to predict the rock and pore-fluid properties of the reservoir and sometimes its pressure regime.

• In PRMS-AG section 3.2.2, the following guidance is given:

“The reservoir properties that 3D seismic can potentially predict under suitable conditions are porosity, lithology, presence of gas/oil saturation as well as pressure.”

An overview on seismic data quality & requirements for such an analysis

The oil accumulation is trapped against a fault to the northeast dipping to an oil-water contact (OWC) to the southwest. The seismic amplitude maps are from a near-offset (left) and far-offset (right) volume. The oil-water contact appears as an amplitude increase on the near offsets and an amplitude decrease on the far offsets. Both run along a structural contour. The seismic amplitude response is consistent with the trap geometry, the depositional model, and the seismic rock properties from the well data.

• In this example, the key uncertainty for estimation of in-place volumes is the distribution of net sand thickness. The low, mid, and high net sand maps are the output of a probabilistic seismic inversion. Each map fits the well data used to constrain the model. The three net sand maps reflect the uncertainty in the net sand distribution and can be used to constrain three different “oil-in-place” scenarios in low, mid and high case static models that can be carried through to reservoir simulation and are thus key input to the resource volume assessment and classification.

Fluid Properties…

Reservoir Surveillance

• Time-lapse seismology (4D seismic) impacts estimation of resources and reserves in various ways

• Bypassed oil reserves can be spotted on time-lapse seismic when a compartment fault block or other discrete component of the trap) is identified by time-lapse seismic as an isolated pool that previously was believed to be part of the field’s connected pool or pools.

New discoveries

Fluid contact surveillance

Development of Oil Recovery Techniques

Reservoir Surveillance

Better (& time updated) resource estimation

…Updated reservoir estimates• Time-lapse seismic results revealed an area in the west of the F block without 4D sweep that

differed from what was expected. • Spectrally boosted 3D seismic evidence for a (newly mapped) normal fault cutting the F

block into two separate blocks.• The new fault was incorporated in the model update, allowing an improved history match by

adjusting the fault seal properties. • Now, the initially bypassed volumes block F will have to be reclassified from “developed

reserves” to “contingent resources”.

BUT…Until further development activities mature!

…Updated reservoir estimates• Changes of saturation in the interval swept by the water can noticeably alter the

acoustic/elastic impedance of the reservoir. This impedance change can be detected by time-lapse seismic comparisons.

• These OWC changes, as derived from time-lapse seismic results, can subsequently be mapped out laterally and be used to UPDATE the static and dynamic reservoir models hat underpin the resources and reserves volumes estimate.

…Updated reservoir estimates• Steam-assisted gravity drainage (SAGD) (in-situ thermal recovery method) is being used to

develop some 20 billion barrels of bitumen below the surface.• The acoustic properties of bitumen sands strong response to temperature changes.

a significant velocity decrease through zones in the reservoir which have been thermally altered by the SAGD process.

monitoring of the thermal evolution over time.

Uncertainty in seismic predictions Predictions from 3D seismic data aimed at defining

Inherent Uncertainty

Fluid flow

Rock/Fluid

properties

Trap geometr

y

The accuracy of a given seismic based prediction is dependent on:

1. The quality of the seismic data (bandwidth, frequency content, signal-to-noise ratio, acquisition and processing parameters, overburden effects, etc.).

2. The uncertainty in the rock and fluid properties and the quality of the reservoir model used to tie subsurface control to the 3D seismic volume.

ANSWER lies in Integration

of data…

• It is important to realize that this uncertainty assessment will need to be kept evergreen and needs to be revisited when new data become available.

This integrated work flow is the key to:•Near future exploration works in complex geologies.

•Efficient extraction of hydrocarbons from wells.

• Exploration of unconventional resources.

Unconventional resourcesConventional resources Conventional resources exist in discrete petroleum accumulations related to a localized geological structural feature and/or stratigraphic condition (typically with each accumulation bounded by a down-dip contact with an aquifer) that is significantly affected by hydrodynamic influences such as the buoyancy of petroleum in water.

Unconventional resourcesUnconventional resources exist in hydrocarbon accumulations that are pervasive throughout a large area and that are generally not significantly affected by hydrodynamic influences (also called “continuous-type deposits”).

PART IITransition from Conventional to Unconventional

Strategies in geophysics for estimation of unconventional resources.

Published in “The Leading Edge, November 2012” issue.

Overview • The rise of unconventional resource plays to prominence in the oil and gas industry

has presented geophysics with a set of unprecedented challenges, chief among which is problem of resources and reserve estimation.

Traditional concern

Unconventional resource

Parameters for reserve estimation

Conventional Petroleum System

Chance Factors Critical Chance

Source

Charge

Trap

Reservoir

Containment

Unconventional Petroleum System

Important areas which need to be addressed

The quantification of “deliverability system” is the principal area which

geophysical methods must address.

Reliance on seismic inversion, attributes such

as curvature and coherence, and micro-

seismic data.

The low porosity of many unconventional reservoir demands greater trace to

trace fidelity and low noise in the geophysical

data.

Premium acquisition program are needed,

together with strict quality assurance standards.

Geophysical workflow

Defining the container

Establish reservoir continuity

Predict reservoir properties

Integrate with other data analyses

Defining the container

Reservoir estimation begins by defining the boundaries of the reservoir unit.

Non-interpretable coal beds are marked using isopachs and isochrons from usable horizons.

Shale gas reservoir can exhibit subtle reflection character and may not be map able for traditional horizon picking. In such cases, inversion volumes must be used to define reservoir boundaries.

It is already known where the hc’s are!

Additional Geological constraints are the key!

Establish reservoir continuity

Unconventional reservoirs can be surprisingly heterogeneous.

Oil sands reservoirs often contain channel system whose fill can now be non-reservoir. Gas shales can contain non-reservoir facies that also act as frac barriers.

These volume cannot contribute to estimates of original gas in place (OGIP) or oil in place (OOIP), also they can render reservoir zones inaccessible to drainage.

All these reservoir must be identified and mapped and their volumes subtracted from the gross reservoir volume before a development plan with project economics can be prepared.

Source: The leading edge, the strategies in geophysics for estimation of unconventional resources.

Subtle nature of features being mapped makes consistent interpretation difficult!

Establish reservoir continuity

The problem arises in connection with the often low contrast nature of these features in unconventional reservoirs and with the subtle character expression of lithology and mechanical stratigraphy. Statistical approaches can be of value.

What are the tools of geophysics which can be used? Inversion products such as Poisson’s ratio and young’s modulus may be needed to characterise geobodies; coherence volume, character-based facies classification, and such proprietary techniques as Ant tracking are useful, but they require regional calibration.

Source: The leading edge, the strategies in geophysics for estimation of unconventional resources.

Predict reservoir properties

The resource play geophysics differs the most from conventional-play-geophysics. In shale gas projects, geophysics is called upon to characterize reservoir properties before and after the frac program.

The engineers want to know the in-place resource, the fracability, faults to avoid, variations in principal stress direction, the location and orientation of natural fracture systems and the location of barriers. After the frac program, the engineers want to know the SRV, the overlap between fracture patterns, and the location or distribution of proppant emplacement, all which are critical input for geophysical recovery factor calculation.

Source: The leading edge, the strategies in geophysics for estimation of unconventional resources.

Principal stress directions and pore pressures are same…

Resource-play unconventional resource geophysics has 2 principal tasks:

Characterise the state of

the reservoir before

complete simulation

Evaluate the modification of reservoir into a state that permits economic

production.

Resource play

unconventional resource geophysics

Resource-play unconventional resource geophysics has 2 principal tasks:

To characterize the state of the reservoir before completion simulation.

• In both shale and tight oil projects, hydrocarbon recovery is dependent on the existence and connectivity of natural fractures. Often the fairway of interest for the exploitation of such resources is found by mapping these natural fracture systems. In addition to define fracture related producibility are velocity and amplitude anisotropy combined with shear wave birefringence.

To evaluate the modification reservoir into a state that permits economic production.

• This requires us to monitor the stimulated rock, identify bypassed resource pay, verify the resource confinement after stimulation, and predict or forecast the hydrocarbon delivery success from stimulation-induced changes in observed geophysical characteristics. In oil sands work, SAGD projects require geophysics to track the growth of steam chambers with 4D seismic surveys.

Integrate with other data analyses

• This stage in the workflow is critical for unconventional resource geophysics. • Coherence techniques, curvature, horizontal anisotropy, and edge-detection

algorithms can predict fracture zones, but they must be compared with core and image-log data from horizontal wells to calibrate them.

• In unconventional plays, the geophysicists at present is perceived more as a supporting player than in traditional exploration and development, and geophysical interpretation products and predictions sometimes encounter scepticism.

• The standards for reliability, repeatability, and accuracy are high.

• This should clearly be the future direction of R&D efforts in order for geophysics to contribute seriously to resource and reserve estimation.

Data requirements, processing and analysis standards, and emerging technologies

3D seismic acquisition, processing, and elastic inversion

Joint P- and S-wave 3D surveys can offer advantages

VSP surveys for unconventional reservoirs

Micro seismic data for unconventional resource estimation

Here, theANSWER lies in…!

Innovate in their existing techniques to exploit those unconventional hydrocarbons and meet the present demand, thus securing our jobs and credibility of being a geoscientist.

Either let the policy makers go to the renewable energy as we do not have that sophisticated technique to exploit those unconventional hydrocarbons and thus become bankrupt

“The MORE we get to know, andthe MORE we try to quantify (nature’s complexities),the MORE we realize,We know Less!”

THANK YOU

QUESTIONS…??