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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? Geomechanical model Geology Mechanical Elastic + Strength Stratigraphy Properties Earth Stress and Pore Pressure Oilfield Review, Summer 2003, Watching Rocks Change: Mechanical Earth Modelling A geomechanical model comprises 1. Mechanical properties (including intact rock, fractures and faults) 2. Stress state, and 3. Pore pressure This 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 www.crusher.mines.edu Jerry Meyer, PhD thesis http://www.chevron.com/fraderesponse/ Permeability Change Orientation + containment Oilfield Review, 4 (4), 4-17 Fracture Tortuosity Seal Breach Frack growth One Model Many Applications Wellbore stability Courtesy of Saudi Aramco Hubbert, and Willis, 1957 Bruno, M., SPE 79519 Wellbore integrity Subsidence and Compaction 1978 1986 Limiting factors for the value of geomechancial models A successful project has many parents Technology Contracts Communication Many factors contribute to a successful project There is a sweet spot, when technology, contracts and communication are ALL executed well And 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 Minimum Mineral elements H2O CO2 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 Minimum principle applied to GM projects Liebig’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 Minimum 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 technology 2. Poor communication 3. Contracting mechanism I will not speak about limits imposed by • Lack of knowledge, training and experience … (baseline competencies), or Technology Communication • Organizational structure Contracts If you ask me, I will offer my opinion 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 reactivation/bedding parallel slip Finite element modelling of shearing of drill-pipe After: http://www.drillingcontractor.org/studytackles-industrys-shearing-capabilities-26402 Applied technology as a limiting factor I Observation by client: • Stuck pipe during drilling • Suspected cause: fault reactivation/bedding parallel slip Geomechanical 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 Geological Society is in Central London Geological Society is on the North Side of Piccadilly Entrance Both images show the location of the Geological Society Both maps are useful, but only one map is useful to find the entrance? A simple explanation for failure on a plane-of-weakness Effective stress change during pressure increase DP 𝜎3′ 𝜎2′ 𝜎3′ 𝜎2′ 𝜎1′ 𝜎1′ 𝜎𝑛′ Solid black lines: Mohr circles pre-drill Stippled black: Mohr circles with increased pore pressure due to high mudweight Complexity arises from determining good estimates/bounds for effective stresses and strength properties 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 injection Avoid creation of hydraulic pathways between reservoirs Injector A Producer A Vertical compaction Vertical dilation Applied technology as a limiting factor II Client issue: Stacked reservoirs produced with water injection Avoid creation of hydraulic pathways between reservoirs Injector A Producer A 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 Vertical compaction Vertical dilation Applied technology as a limiting factor II Client issue: Stacked reservoirs produced with water injection Avoid creation of hydraulic pathways between reservoirs Injector A Producer A Geomechanical model delivered: • 4D numerical model • Lower reservoir only My kids would call this an “epic fail” 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 Technical Contractual • Reasons I have encountered are: o Key person has left the team (without a sufficiently detailed handover) o Asset team too busy Communication o Model delivered to technical services team, without study passed on to asset team (asset team stating “we did not know about the existence of Models that are never used, despite such a model, and we asked for being technically sound and fit for support”) purpose o Change in priority for asset team 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. Technology 2. Communication 3. Contracting process Avoiding these limiting factors takes: 1. Vigilance on behalf of technical experts 2. Honesty about the status quo and 3. Clear thinking by all involved Thank you – Any Questions Jorg Herwanger [email protected] Tel: +44 (0) 208 943 9074 www.ikonscience.com