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Agenda Geomechanical models all have the same building blocks …but they are not identical Limiting factors for the value of geomechanical models Applied technology Communication Contracts The way forward?
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Reasons why some geomechanical models turn out “unfit for purpose”Jorg Herwanger
Geomechanics: Quo Vadis?SPE London October Meeting Geological Society, London-Tue. 27th October 2015
Agenda
1. Geomechanical models all have the same building blocks …but they are not identical
2. Limiting factors for the value of geomechanical models – Applied technology– Communication– Contracts
3. The way forward?
Geomechanical models all have the same building blocks …… but they are not identical
What is a geomechanical model?
Oilfield Review, Summer 2003, Watching Rocks Change: Mechanical Earth Modelling
Geology MechanicalStratigraphy
Elastic + StrengthProperties
Earth Stress andPore Pressure
Geomechanical model
A geomechanical model comprises1. Mechanical properties (including intact rock, fractures and faults)2. Stress state, and3. Pore pressureThis can be in 1D (e.g. along a wellbore), in 3D (the full field), and 4D (including production)Based on the model, useful predictions for reservoir development and management are made
Geomechanical models have many applications
19861978
Subsidence and Compaction
One ModelMany Applications
Fracture Tortuosity
Jerr
y M
eyer
, PhD
thes
is
Wellbore integrity
Bru
no, M
., S
PE
795
19
Permeability Change
ww
w.c
rush
er.m
ines
.edu
Frack growth
Hub
bert,
and
Will
is, 1
957
Seal Breach
http://www.chevron.com/fraderesponse/
Orientation + containment
Oilf
ield
Rev
iew
, 4 (4
), 4-
17
Wellbore stability
Courtesy of Saudi Aramco
Limiting factors for the value of geomechancial models
A successful project has many parents
Technology Contracts
Communication
Many factors contribute to a successful projectThere is a sweet spot, when technology, contracts and communication are ALL executed wellAnd conversely …
The Liebig minimum principle Justus von Liebig’s minimum principle states:• The yield in agricultural production is
proportional to the amount of the most limiting nutrient
• For example, a plant needs (i) mineral elements (Phosphorus + Nitrates from the soil), (ii) CO2 (from the air) and (iii) water to grow
• Each of the three can become the most limiting nutrient, or “bottleneck” in the growth of plants
The “Liebig barrel” is used to demonstrate the principle:• The shortest slat becomes the limiting factor
for filling the barrel, and the volume of liquid in the barrel is proportional to the shortest slat
H2OMineral
elements
Minimum
CO2
Minimum principle applied to GM projectsLiebig’s minimum principle re-stated:• The value in a geomechanics project is directly
related to the most limiting factor in the bidding and execution of projects
In this talk, I will share experiences of geomechanics projects, where the value of a project was decreased, due to a limit imposed by:1. Applied technology2. Poor communication3. Contracting mechanism
I will not speak about limits imposed by • Lack of knowledge, training and experience
(baseline competencies), or• Organizational structureIf you ask me, I will offer my opinion
ContractsTechnology Communication
Minimum
…
Limiting factors: Applied technology I
The pesky matter of scale
Applied technology as a limiting factor I
Observation by client:• Stuck pipe during drilling• Suspected cause: fault re-
activation/bedding parallel slip
Finite element modelling of shearing of drill-pipe After: http://www.drillingcontractor.org/study-tackles-industrys-shearing-capabilities-26402
Applied technology as a limiting factor I
Observation by client:• Stuck pipe during drilling• Suspected cause: fault re-
activation/bedding parallel slipGeomechanical model delivered:• 3D numerical model (cell size 100m
x 100m x 10m in region of interest)• Looked for cells with “high plastic
strain” in region of interest• No analysis of effect of increase in
Pp as an effect of overbalanced drilling
• No inclusion of “planes of weakness” such as faults/bedding planes or attempt at failure analysis
Both images show the location of the Geological SocietyBoth maps are useful, but only one map is useful to find the entrance?
Geological Society is in Central London
Geological Society is on the North Side of Piccadilly
Entrance
𝜎 𝑛′
A simple explanation for failure on a plane-of-weakness
𝜎 1′𝜎 3
′ 𝜎 2′𝜎 1
′𝜎 3′ 𝜎 2
′
Effective stress change during pressure increase
DP
Solid black lines: Mohr circles pre-drillStippled black: Mohr circles with increased pore pressure due to high mudweightComplexity arises from determining good estimates/bounds for effective stresses and strength properties
Failure line in
tact rock
Failure line plane of w
eakness
Limiting factors: Applied technology II
The pesky matter of building the wrong model
Applied technology as a limiting factor II
Client issue:Stacked reservoirs produced with water injectionAvoid creation of hydraulic pathways between reservoirs
AAInjector Producer
Vertical compaction
Vertical dilation
Applied technology as a limiting factor II
Client issue:Stacked reservoirs produced with water injectionAvoid creation of hydraulic pathways between reservoirs
It seems pretty clear what elements need to be included into a model
Or may be not. Let’s look at the model delivered to client
A AInjector Producer
Vertical compaction
Vertical dilation
Applied technology as a limiting factor II
Client issue:Stacked reservoirs produced with water injectionAvoid creation of hydraulic pathways between reservoirs
Geomechanical model delivered:• 4D numerical model• Lower reservoir only
My kids would call this an “epic fail”
A AInjector Producer
Vertical compaction
Vertical dilation
Limiting factors: Communication
Communication as a limiting factor
The sad story of “stacked models”
• “Stacked models”, are models that have never been looked at
• Reasons I have encountered are:o Key person has left the team
(without a sufficiently detailed handover)
o Asset team too busyo Model delivered to technical services
team, without study passed on to asset team (asset team stating “we did not know about the existence of such a model, and we asked for support”)
o Change in priority for asset team
Technical Contractual
Communication
Models that are never used, despite being technically sound and fit for purpose
Limiting factors: Contracts
Contracts as a limiting factor
A typical contracting mechanism for NOC’s
1. Expression of Interest (EOI) and technical pre-qualification
2. Companies above technical threshold are invited to bid
– Pre-qualification run by technical team, now contracting department takes over
3. Closed bid– Cheapest bidder wins– No technical qualification of bids– No assurance that the winning bid will solve
the problem, as de-coupled from statement of technical competencies in 1 + 2
Good, fast, cheap – choose two
Contracts as a limiting factor
“Enterprise Solutions” and “Global Service Contracts”• May work well for rental cars and
standardized manufacturing• May work less well for bespoke
consulting
This is not to say that partnerships are discouraged. On the contrary, having worked together before (service company + oil company; or internal services + asset team) can markedly improve quality of service
My bespoke model: “But look it has a different license plate / contract number”
Conclusions
Factors limiting the value of geomechanical models
I presented three factors that can limit or destroy the value of a geomechanical model:1. Technology2. Communication3. Contracting process
Avoiding these limiting factors takes:4. Vigilance on behalf of technical experts5. Honesty about the status quo and6. Clear thinking by all involved
