Geomechanics for Unconventional Reservoirs

Geomechanical analysis of unconventional reservoirs

Operators are now developing more complex and costly oil and gas plays. Understanding the geomechanical behavior of such systems throughout the production lifetime is becoming increasingly important. Geomechanical analysis of the evolving stress state in the reservoir and the surrounding formations, in conjunction with understanding the migration and maturation of the hydrocarbons they contain, leads to improved understanding of how to place and design wells for maximum efficiency and stability. This is particularly true when exploiting unconventional reservoirs.

Shale gas

To unlock shale gas it is important to maximize the well contact area to ensure the highest production rates. This is often achieved by hydraulic fracturing, contact-staggered fracturing technology, and horizontal drilling. In designing the development plan it is also important to consider the location and behavior of natural fractures, as well as anisotropy and heterogeneity in the shales. These factors have a huge influence on the success of hydraulic fracturing and resulting production.

Planning successful completions and production requires a detailed knowledge of the shale’s heterogeneity and anisotropy. Our shale gas geomechanics services help to understand these effects by measuring and modeling the horizontal and vertical variations in mineralogical and mechanical properties, as well as the distribution and characterization of faults and natural fractures that influence hydraulic fracturing and production rates. Rigorous 3D stress modeling is provided by the Petrel Geomechanics system and hydraulic fracture modeling by using a well-centric model.

For ideal well placement and the selection of fracturing points in multi-stage simulation operations it is crucial to fully understand the prevailing stress state. Conventional isotropic stress modeling in shales is not able to identify the stress contrasts that point to the sweet spots, or the stress barriers that provide containment and ensure the maximum drainage area is opened. Schlumberger’s geomechanics experts provide the advanced anisotropic stress modeling necessary to make these completion decisions and plan successful hydraulic fracturing.

Our advanced field scale geomechanical modeling also allows the operator to make hydraulic fracturing decisions in the context of the entire reservoir so that well drainage can be optimized through a complete knowledge of the stress changes across the field.

Coalbed methane

Coalbed methane reservoirs are different from conventional reservoirs in a number of ways, but the primary differences are water production and gas-storage mechanism. Hydrocarbon-storage capacity in most oil and gas reservoirs is related to porosity because gas is trapped and stored in the pore systems of the matrix. Coals have moderate intrinsic porosity, yet they can store up to six times more gas than an equivalent volume of sandstone at a similar pressure. Challenges include multiple thin zones, poor quality coals, and seemingly endless volumes of formation water. Earth modeling programs, such as the Schlumberger Petrel and ECLIPSE software packages, include modules specifically developed to evaluate CBM reservoirs

Modeling for optimal formation contact and effective forecasts

This is done by starting with a Petrel Geomechanics model that links the geomechanical characterization of the reservoir and the completion design. A near-wellbore analysis is carried out using the reservoir permeabilities and properties taken from well log information. A well-centric MEM is then constructed which incorporates the well trajectory and the well completion design.

The well-centric MEM is used for hydraulic fracture design, based on 3D fracture geometry and permeability. Dynamic modeling simulates the fracture-reservoir interaction, investigating the complex interaction between any pre-existing fracture networks and hydraulically induced fractures. Fracture direction is governed by the direction of the principal stresses in the earth that have been evaluated using shear sonic data from the SonicScanner tool. The updated reservoir model can then be used for production forecast runs.

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