SUMMARY: This paper will provide an overview about the use of geomechanics in improving heavy-oil production. If high recovery factors are sought, production of heavy-oil reservoirs requires stimulation to reduce oil viscosity. Intelligent use of geomechanics can create additional porosity and permeability by managing rock dilation and fracturing behavior. As a result, new areas are created for injected stimulants to contact the heavy oil, speeding up viscosity reduction and improving oil production. Additionally, the same mechanism can break down the permeability barriers in the reservoir for the injected stimulants to travel through, ultimately improving the reservoir recovery factor.
Using field examples, this paper illustrates theoretical mechanisms and field results. It will hopefully provide a new paradigm for operators when planning their heavy-oil production, because geomechanics is both a necessity and a means to value creation.
Becoming an increasingly important component of global energy supply, development of heavy-oil resources has attracted world attention. Heavy-oil development in Canada and Venezuela, as well as in other countries such as China, the former Soviet Union, Indonesia, Oman, Russia, and the U.S., are some well-known examples, although the list is definitely not exhaustive. In the recent years, Kuwait, a traditionally conventional oil producer, has embarked on an ambitious mission to develop its heavy-oil resources. Therefore, it is timely to have the worldwide geomechanics community turn their attention toward heavy-oil development and how geomechanics can proactively help improve production rates, increase reservoir recovery, and minimize its environmental footprint (on air, land and water).
SUMMARY: In general, geomechanical works compare evolving in-situ stress conditions with rock’s mechanical strength. Therefore, a basic geomechanical work program consists of defining the original in-situ stress condition, characterizing the rock structure and deformation/strength properties and finally, simulating the dynamical stress conditions after an engineering disturbance is introduced to rock formations which has otherwise reached equilibrium in the geological history.
In many situations, heavy oil production takes place in relatively shallow, weakly- or un-consolidated and/or geologically young rock formations. In-situ stress measurements in the field and laboratory tests on the core samples in these unique situations require special attention to principles and details. Moreover, heavy oil production often requires stimulation by injecting stimulating materials which may be at high pressures and/or high temperatures. Nonlinear coupling between the thermo-hydro-mechanical (THM) mechanisms become significant and must be adequately accounted for. All these unique challenges demand special QC/QA measures in carrying out the geomechanical works. This is the focus of the present paper. These measures are derived from experience in over 1,000 projects/tests and also after a peer review of relevant published works in the industry. Details to be covered include: use of multiple interpretation methods, real-time analysis and openhole in a mini-frac test; use of whole cores, drained condition, slow strain rates and/or heating rates in laboratory tests. It is hoped that this paper will provide a common guidance for the service providers in carrying out their geomechanical works or for the operators in managing similar projects.
Geomechanics has become increasingly important in heavy oil development. It is both a necessity to protect reservoir containment integrity and an opportunity to enhance reservoir production. Heavy oil development requires stimulation in order to achieve a high reservoir recovery factor. The stimulation is carried out by injecting steam and other stimulating materials into the reservoir. The pressure and/or temperature disturbance to the reservoir causes its deformation and impacts the caprock above the reservoir.
SUMMARY: Geomechanical simulations are a powerful tool to forecast caprock deformation and failure behaviour. However, a number of drawbacks associated with simulation are often cited in dissuading their use as a major tool for caprock integrity assessment. This paper will explain that these drawbacks are not inherent in simulation itself. If vigorous efforts are exercised, there are means to overcome these drawbacks. Three approaches are presented: deterministic, probabilistic, and joint inversion. Theoretical principles as well as case histories are given to support observations: (1) forward deterministic simulations are still valid in yielding accurate results that compare well with field observations; (2) probabilistic simulation is a powerful tool to quantify the impact of uncertain material properties and their spatial variability; and (3) the data-intensive nature of a thermal project is an important asset that can be used by a joint mathematical inversion system to make inferences about evolving subsurface processes.
Whether or not it contains resources of economic value, every interval of subsurface rock formation is invaluable and their integrity must be safeguarded. If containment integrity of the caprock above a petroleum reservoir is damaged, reservoir fluid can escape into undesirable locations. This is particularly essential for heavy-oil development because it requires reservoir stimulation through injection of steam, solvent, and other chemicals to reduce the oil viscosity. For example, cumulative energy injected into a reservoir and thus stored at the subsurface during a thermal project is too significant to ignore the caprock integrity issues. If not managed properly, this energy source can harm us socially, environmentally, and economically.
Several incidences of steam release, drilling blowout, reservoir fluid escaping into shallow depths including into groundwater aquifers, or reservoir fluid escaping to the ground surface have been reported publically (Smith et al. 2004; ERCB 2010; AER 2013). More common is the significant casing deformation during thermal operation. Moreover, concerns are raised about the significant uneven surface heave that may alter facilities, roads, landscape, and surface/subsurface hydrogeological conditions.
Caprock integrity eventually becomes a geomechanical issue, even though it is first a concern of hydraulic integrity (i.e., no reservoir fluid should escape through the caprock into more shallow areas). Naturally, such hydraulic integrity is already inherently placed in-situ in the geological history because the caprock has prevented any further upward movement of hydrocarbon migration.