The success of an unconventional hydrocarbon development depends on effective stimulation of reservoir rocks maintaining well integrity during stimulation and production especially for the Vaca Muerta. While key decisions such as well spacing and completion intensity greatly impact the economics of the asset development, well integrity remains as the key risk that must be mitigated to warrant effective stimulation of the formation. In cooperation with SHELL [Bai 2016, Yeh 2018] we have developed a coupled geomechanical and reservoir modeling workflow that can address the interplay of well spacing and completion intensity, while mitigating the risk of casing deformation.
Integrated geomechanical and reservoir modeling incorporates a range of multi-disciplinary inputs such as the layered geologic model, well drilling and landing zone, completion design, operational management strategies, and production performance. In a first step the hydraulic fracturing model is calibrated to best available field data. After sufficient calibration quality is reached the forecast quality at neighboring wells is verified. Then the model is used in the forecast mode to optimize well spacing for single or multi-layered field development, including optimal well landing zone identification and completion design that attempts to maximize Net Profite Value (NPV) and Estimated Ultimate Recovery (EUR), while also predicting the potential magnitude and location of bedding plane shear induced casing deformation events.
The results provide critical inputs for decisions on well spacing, well landing and completion designs with reduced number of field trials for achieving optimal operational conditions. In addition, the workflow provides valuable insights for critical data acquisition to evaluate and forecast field performance.
To address the industry-wide challenge to increase predictability and confidence in numerical models an appropriate characterization of rock heterogeneity and handling of uncertainties of subsurface parameters is crucial. These two critical functionalities are addressed with the developed technology. Firstly, we capture the subsurface layering heterogeneity, i.e. thickness and spatial frequency of shale, carbonate and ash layer occurrence, along with natural fractures or planes of weakness with a truly 3D anisotropic modeling approach. Secondly, we balance the estimation of uncertainty ranges in model input parameters with the ability to converge to a calibrated geomechanical model with sufficient forecast quality for the evolution of the fracture network and resulting hydrocarbon production. After the successful calibration,this technology has shown to be appropriate for the accuracy of prediction of well EUR outside the calibrated conditions and is today standard approach for hydraulic fracture modeling in SHELL [Bai 2016].
A case study with TOTAL [Pourpak 2019] is presented in this paper to demonstrate the effective way of incorporating subsurface heterogeneity and variability into hydraulic fracture models to achieve a calibrated reservoir model and to use that model in the forecast mode to predict EUR along with all costs and NPV for a large window of variability of operational parameter.
In addition, the risk of shear deformation along bedding planes, which is believed to be one of the main mechanisms for casing deformations and well integrity issues, is investigated and measured These quantifications of casing deformation risk are used today as constraint in the optimization process to achieve profitable production and minimization of casing deformation at the same time.