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Summary of the 2016 EAGE/SPE Geomechanics Workshop

  

Prepared by Thomas Finkbeiner and Glen Burridge

Middle East October 2016 Abu Dhabi saw the second instalment of the EAGE/SPE Geomechanics Workshop. Chaired by Thomas Finkbeiner (KAUST) and Nick Koutsabeloulis (Schlumberger) the topic of this year’s workshop was ‘Integrated Geomechanics in E&P, Manage and Improve Asset Performance using Geomechanics. Over the course of three days a series of technical presentations, lively discussion sessions, and a survey lead by Glen Burridge of Glen Burridge & Associates (GB&A) attempted to address where geomechanics currently plays a role in asset development and how this may change in the future.

The first day of the workshop dealt with two topics, the application of geomechanics in reservoir characterisation and the use in asset management. To start the workshop off Glen Burridge (GB&A) presented the progress of a survey entitled “Geomechanics – Quo Vadis“ he has been conducting in upstream oil & gas to gauge the opinion on the establishment and value of geomechanics in field development. To date the survey results reflected a European focus not yet covering opinion form the Middle East. The key outcomes from the survey so far identified the two greatest selling points for geomechanics were summarised as drillability (getting to the reservoir) and deliverability (extracting the greatest value from it). Notable geomechanics was identified as increasingly seen as de rigueur for well planning in the form of WBS studies; and full potential may come with use of predictive analytics and longer term vision by drillers. The greatest immediate unrealized potential may exist in conventional Exploration & Appraisal, assuming it provides insight and suitable data is acquired early enough. Benefits for reservoir management were seen as less obvious and require greater buy-in from reservoir engineers in particular. Geomodellers were seen as less phased by geomechanics and ready to see it as an extended static model. The survey was distributed amongst the workshop attendees and would be used to drive discussion throughout the workshop, especially on the final day.

The session on applying geomechanics in reservoir characterization was opened with presentation by Wolfgang Hohl (University of Leoben) who conducted rock mechanics tests on shale samples to investigate the impact on rock mechanical properties resulting from ageing. For this purpose he and his team retrieved shallow core drilled from an outcrop location and exposed it under controlled conditions at various periods of time before sampling and testing. A surprising – but apparently not uncommon – outcome of the study is that compressive strength increases with ageing (as also reflected by ultrasonic velocities). As part of the same project Epslog’s presentation (Christophe Germay) complemented the study with scratch test measurements conducted on similarly aged shale core. The results confirmed that uniaxial compressive strength increases with ageing. Christophe also showed that in contrast, ageing does not appear to impact internal friction as well as ultrasonic velocities. Important recommendations from the test sequence were that core needs to be tested as quickly as possible after coming to surface. Important to include as part of the testing campaign is the immediate acquisition of high resolution data (e.g., scratch strength, Vp, Vs, CT scans, core GR etc.) accompanying the rock mechanics and scratch tests. This increases the amount of available data and allows for multi-variate and multi-parameter regression analyses.

Anna Coradi (ENI E&P) demonstrated with an example from a wellbore stability study that an integrated analysis of petrophysical and image log interpretations with geomechanics to greatly improves predictability and reliability. She contrasted a previous study that resulted in inconsistent results with a new, more advanced, and integrated approach, which greatly enhanced data quality and lead to consistent findings that could be utilized for well planning. Jan ter Heege (TNO) highlighted with an advanced, numerical workflow how production can be optimized in a faulted and fractured reservoir. A key aspect of this multistep approach includes a 3D bulk permeability tensor. This is integrated with 3D full field geomechanical models to obtain a more realistic dynamic reservoir response. Saner Osinga (also from TNO) followed up by demonstrating how the behaviour of fractured shales, carbonates and other fractured rock types is best realized when using implicit modelling. Similar to Jan ter Heege’s paper, permeability anisotropy due to the presence of fractures is a key aspect in this approach as is the incorporation of their shear stiffness. Schlumberger’s Karsten Fisher presented a modelling exercise which demonstrated the impact of rock fabric on hydraulic stimulation results in particular when pore pressure changes occur. This showed how compaction effects in depleted reservoirs and extension in undepleted reservoirs should guide well spacing for infill wells and refracturing. The session concluded with E-Tech’s paper presented by Hamza Shaikh. This highlighted the importance of inclined velocity measurements to determine orientation dependent Biot’s poroelasticity parameters. The paper showed how the commonly assumed constant Biot values between 0.8 and 1.0 do not provide reliable rock characterizations and modelling results.

The afternoon session of the first day concentrated on the use of geomechanics in asset management. The first presentation from Jun Kato (Rockfield) discussed parameter sensitivities affecting an FEM based geomechanical model. This outlined an approach that applied global sensitivity analysis to identify primary and secondary inputs of importance. The aim was to minimise computational cost and identifying which disciplines are critical to engage with. In the example discussed, pore pressure and permeability were identified as primary influencers on model outputs, underlining the importance of fluid flow in the overburden. David Press (Schlumberger) presented a workflow to construct a 3D coupled (flow and mechanical) numerical model in order to consider depletion related compaction and subsidence.  The model clearly showed the impact of coupling fluid flow with mechanical compaction with a 3.5m difference in vertical compaction. The results of the model were used to influence subsea layout and perform wellbore stability analysis. The final presentation of the day was from Sietse de Vries (PDO). This took a broader look at geomechanical risk assessment, which PDO includes at an early stage when planning asset development.  Additionally, the type of geomechanical model that is utilised within the development life cycle reflects the associated risks. These risks are identified and treated separately at field and well scale and may vary depending upon the drive mechanism of the field.

Risk and uncertainty were recurring themes throughout the session and the following discussion. Additionally these themes recurred over the course of the workshop with particular focus on if, how, and when it is addressed by different (sized) companies and at what stage during the asset lifecycle. General consensus agreed that smaller companies without internal geomechanical expertise or experience struggle to understand the value proposition and that broader education and understanding is required.

The second day of the workshop started with a keynote from Tony Addis (Rockfield). The presentation discussed the use of geomechanics to identify opportunites and mitigate risks. Through a number of case studies he focused on the growth of the discipline and how historically it has been used only reactively. The first session of the day addressed the topic of enhanced oil recovery using geomechanics. The two presentations described methods for assessing and overcoming challenges related to permeability damage and low permeability in real cases and using innovative techniques. Jun Kato (Rockfield) addressed the challenge of well injectivity decline. This focused on the numerical modelling of coupled single phased fluid flow mass transport and mechanical field analysis. Thomas Finkbeiner (KAUST) followed with a discussion on the management of a low permeability offshore reservoir, where a watered out horizontal producer was converted into an injection well. A critical aspect in this study was to quantify the risks of early water breakthrough at the adjacent producer when injecting under fracturing conditions.

The geomechanics for drilling and completion session at the previous workshop provided a source of very lively discussion. This year was no different. Four speakers presented case studies demonstrating the use of geomechanical models for addressing wellbore related instability caused by variable mechanical stratigraphy, planes of weakness and soft sediment high pore pressure environment.  All presentations were united with common objectives to reduce risk and non-productive time and each demonstrated the value impact that these analyses can have.  Hemant Singh (Baker Hughes) showed a neat case study of an analytical model looking at reversing the wellbore instability trend from an offshore carbonate field in the UAE. This was followed by Karsten Fischer (Schlumberger) who used a numerical model to consider reactivation of pre-existing planes of weakness during stimulation. In particular this model captured the creation of T-shape fractures at boundaries defined by contrasting properties highlighting the usefulness of computationally prototyping more complex wellbore related problems. E. Sitinjak (Baker Hughes) and Vincenzo De Gennaro (Schlumberger) also showed examples using analytical models to address a case study of wellbore stability in a soft sediment and overpressured environment (E. Sitinjak) and the de-risking of drilling plans through modelling at well and reservoir scale (V. De Gennaro). Further technical discussion topics were prompted by the session chairs. Much interesting conversation was stimulated around the question whether geomechanics has a PR problem, which became a recurring theme of the workshop discussion.

The final day of the conference started with a keynote from Stan Sterns and S. Quinn (Al Hosn Gas). This concentrated on giving an operators view of the use of geomechanics, giving three examples of where they have used it and the apparent shortcomings of the analyses. The day continued with a second presentation from Glen Burridge (GB&A) following on from the opening days presentation on the quo vadis geomechanics questionnaire. The presentation was followed up with a summary and discussion around the results of the quo vadis questionnaire provided by the workshop attendees that had been collated by member of the technical committee. Results collated showed a wide range of opinion related to the objectives, benefits, key actors and assurance targets of geomechanics. Suggestion was that this is best addressed by greater integration and awareness-raising across subsurface. Intervention of the discipline is mostly seen as being reactive rather than proactive. The greatest unrealised potential was judged to be in field development planning how this eventually translates to value creation (productivity, de-risking, HSE). Comparing with the result presented on the first day opinion from the workshop attendees. More emphasis in Abu Dhabi seems to be on applications of geomechanics in tight/unconventional reservoirs and on fracture modelling. More comfort was identified from the attendees with 3D geomechanical modelling and on implications of lab work (reflected by the range of presentations). The key surprise were the answers given to the question ‘who are the key actors (stakeholders)?’. These read like a ‘who’s who’ of Subsurface and included regulators and government bodies. This was a much broader group than the results from the original survey identified which focused around champions/SMEs/technical leads. The survey results prompted more lively discussion on how and where geomechanics needs to move towards in the future in order to have an effective input in asset management.

The final session of the workshop approached the role of geomechanics in tight and unconventional reservoirs. Ashok Sinde (Baker Hughes) considered drilling and completions in a tight reservoir in the Cambay Basin-India. A 1D geomechanical study was used in order to design good horizontal wells and hydraulic fracturing. Kevin Shaw (SIGMA3) discussed drilling and stimulation of a tight gas sandstone reservoir with low porosity in the North Sea. A 1D model was extended to 2D through spectral decomposition of the seismic data, along with a neural network that was used to populate model properties away from the well based on seismic attributes. James Verdon (University of Bristol) presented a novel approach to simulating microseismicity from geomechanical models. This simulation is necessary both to calibrate geomechanical models, to forecast induced seismicity, and to better interpret microseismic observations. Mohammed Benaafi (King Fahd University) showed a geomechanical assessment of the Wajid sandstone, Saudi Arabia. Sandeep Mahajan (PDO) summarised microseismic observations made at a large, mature field in Oman, seeking to link the observations with geomechanical models of the field. Compaction due to depletion was the main issue faced on this field. Tony Addis (Rockfield) provided a walk-through of the evolution of hydraulic fracturing models over the past 15 or so years. The state-of-the-art has moved from simple, 2D elliptical fracture models, to complex, 3D models that include non-planar fractures, interactions with natural fractures, and multiple failure modes. Hamza Shaikh (E-Tech Services) gave the final presentation of the workshop. This showed the use of a hydraulic fracture model to simulate re-fracturing in the Bakken Shale, North Dakota.

The technical committee would finally like to thank the presenters and participants of the workshop for their thought provoking presentations and lively discussion that help to make the workshop a resounding success. The next even is already in the planning for 2018.

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