​ANPERC Senior Research Scientist Dr. Thomas Finkbeiner will attend the SPE/EAGE Workshop: The Future of Geomechanics in Brown Fields and Unconventionals from May 2-3 2018 in Abu Dhabi. Finkbeiner, who is also a member of the organizing committee, will be the Chairperson of the first session, Data Accuracy, Reliability and Model Robustness, at the Workshop.

Abstract: Building geomechanical models requires the definition of detailed material models, knowledge of associated hydro-thermo-mechanical (HTM) parameters and an understanding of in-situ stress and pore pressure conditions. In particular, with the advent of complex 3D geomechanics modelling, the capability to reliably predict risks associated with drilling, completion and production remains controversial. There can be many uncertainties, either natural or man-made, that surround the underlying parameters and scaling techniques, and quite often there is simply a lack of data.

This session aims at investigating state of the art approaches to deal with:

Abstract:

OMV has developed an integrated workflow, involving geomechanics and reservoir engineering, to evaluate injectivity, fracturing and caprock stability. It determines operating envelopes for water injection programmes in brown fields.

Questions addressed include:

(1) What is the operating envelope for injection of water?

(2) Are fractures going to be generated in the reservoir sands and, if yes, how long will the fractures grow?

(3) In which direction are the fractures going to grow with respect to the horizontal wellbore (e.g. could they reach an adjacent producer)?

(4) Is there a risk of propagation of fractures into the overburden? How does that depend on the injection rates, pressures and injectivity?

(5) Would horizontal wells or injection into the lower layers of the formation improve injectivity?

(6) What are the key subsurface uncertainties for injectivity decline?

(7) How can the surface facilities be optimized to improve injectivity?

(8) How will injectivity of the long horizontal injector develop over time?

To answer these questions, a geomechanical model is constructed and is combined with flow and fracture data. Then, two-dimensional and three-dimensional simulations are performed using models able to simulate fluid-flow, reservoir plugging, thermal and geomechanical effects.

The geomechanical model is constructed based on the available logging data of offset wells. Data including uncertainty ranges for Young's modulus, Poisson's ratio and minimum stress are derived for all layers of the reservoir and overburden. These data, in addition to water quality (e.g. solids, size of solids), oil and water properties, reservoir properties and temperatures are applied in two-dimensional and three-dimensional simulations to investigate the injectivity performance. In a first step, the injectivity is simulated for a base case scenario for a range of parameters. Then, the surface facility conditions are optimized to improve injectivity. After the optimisation, subsurface uncertainties are introduced to evaluate the injectivity decline for a variety of conditions.

Results include calculated pressure drops from the wellbore sand face into the reservoir, location of the different fronts (thermal, water), and propagation of the induced fractures along with plugging of the fracture faces. Other results are the injectivity decline in the reservoir and the safe operating envelope for water injection (e.g. pressures at sand face) to avoid caprock breach. Forward simulations can show that fractures are generated dependent on the injection rates, water quality, injection temperature and the minimum principal stress.

To optimize field management and to avoid the generation of extensive induced fractures, maximum water injection rates together with optimal injection water temperatures and qualities (in terms of solid and oil content) are recommended. This approach improves the operating envelope and reduces the risk of injectivity decline, to avoid out-of-zone injections caused by pressure build up above the minimal horizontal stress of the cap rock.