Geomechanics: A Key Input for Optimizing Drilling and Hydraulic Fracturing in a Depleted Oil and Gas Field in Kazakhstan

摘要

The Akshabulak field in the South Turgayskiy basin is located in a Mesozoic intracontinental rift with an Upper Jurassic to Lower Cretaceous fill.The heterogeneous reservoir hosts significant oil and gas reserves and it has been successfully exploited with the implementation of hydraulic fracturing.After nearly 20 years of production,the reservoirs are significantly depleted and drilling new wells has been challenging.It became clear that an improved understanding of the geomechanical properties is required for delivery of a quality borehole and optimum hydraulic fracture stimulation for achieving long-term sustainable well performance.This paper illustrates the workflow used for building the 1D-Geomechanical model required for optimum well construction and for optimizing the design of multi-stage hydraulic fracturing jobs.The one-dimensional model integrates basic petrophysical logs,dipole acoustic data,regional tectonic history,interpretation of mini-frac data and drilling data for identification of the current stress state.The resulting best-fit 1D-Geomechanical model has been successfully applied on the latest wells drilled in this field.The new understanding of the in-situ stresses along with optimized wellbore stability predictions effectively balanced the risk of mud losses with the risk of borehole shear failures.Recently,a high quality horizontal well was successfully drilled towards the predicted best stress orientation,enabling optimal reservoir development and production.Additionally,having a better understanding of the fracture gradient in the carbonate formation,which serves as a seal isolating the reservoir from the lower water zone,is critical.The new geomechanical model predicted a higher stress gradient as opposed to the established understanding of this formation.The hydraulic fracturing design was optimized by allowing a higher pump pressure during the stimulation treatment,which resulted in higher production without any sign of water breakthrough.Consequently,a robust and effective geomechanical model has proven to be essential for enhancing recovery by improving the effectiveness of hydraulic fracturing,improving borehole quality by applying recommended optimal mud weights,as well as reducing NPT and costs by improving drilling performances.