Challenged by swelling clays and problematic mineralogy

An operator in the Caney Shale region of Oklahoma wanted to optimize production in this organically rich shale-oil reservoir. The technically challenging characteristics in a new development area of the Caney Shale needed an integrated workflow to unlock the reservoir’s commercial oil and gas production potential. The reservoir required extensive fluid and rock interaction testing due to the high percentage of swelling clays that have proven to be problematic in the Caney Shale mineralogy (often >20% smectite and mixed layer clays).

Typically, shale gas reservoirs are hydraulically fractured with slickwater and low sand concentrations, even reservoirs with swelling clays. The base fluid is often treated with additives to try and stabilize those clays, but the combination of clay mineralogy and low fracture conductivities have not proven to be successful in the Caney Shale. This approach had been taken by several operators striving for efficient Caney Shale completions while minimizing costs, but many operators abandoned all Caney Shale activity and moved their focus to other gas and oil plays.

Integrated workflow using Mangrove stimulation design and HiWAY technique

Schlumberger proposed to implement Mangrove stimulation design to construct and design a basic reservoir model in the Petrel E&P software platform. Offset well logs and adjacent vertical well information were used to define the zones during the zoning process and to capture the reservoir characterization. Due to the challenging mineralogy, extensive fluid and rock interaction testing was performed to select the optimum base fluid for clay stabilization.

Once this base fluid was determined, the treatment fluids and proppants were defined based on the desired design parameters

The reservoir quality was defined using the LWD measurements acquired during the drilling of the lateral. The completion quality was based on the measured fracture gradients in the adjacent vertical well, which were then projected along the lateral, while maintaining the relationship to the geologic structure. These same vertical measurements were incorporated to define layering above and below the Caney Shale interval. Integration of the reservoir and completion quality then resulted in the creation of optimal stages and the ability to efficiently place perforation clusters specifically tailored for this completion. Finally, pump schedules were designed and appropriate simulations were performed and validated to confirm the recommendations using Planar3D fracturing design simulator based on a planar 3D model.

Understanding the high potential for proppant embedment due to high clay content and in situ stresses, the HiWAY technique was selected, which places higher fracture conductivities for improved deliverability. The HiWAY technique achieves the overall goal of hydraulic fracturing to improve the connectivity between reservoir and well by creating highly conductive paths with a proppant pack, and removes the dependence of the fracture on proppant characteristics. This is done by creating open channels inside the fracture, which enables substantially higher hydraulic conductivity for reservoir fluids compared to a conventional fracturing treatment. This is done by placing the fracture proppant heterogeneously in the form of proppant “columns” surrounded by open flow channels.

Wells in Caney Shale proven to be economically viable for first time

The integrated workflow resulted in economic production of more than 200 bbl/d, design efficiency and the decision to apply the same workflows in future well designs and field development. Application of the HiWAY technique in the Caney Shale, coupled with reservoir-specific fracturing fluid chemistry, resulted in a dramatic increase in fracture flow capacity, overcoming swelling clays, high overall clay content, and proppant embedment, to provide superior deliverability for formation fluids.

The obstacles that have hindered economic production from the Caney Shale, were overcome by applying the Mangrove stimulation design, HiWAY technique, and fracturing fluid chemistry to address challenging reservoir characteristics. The results of the integrated workflow expanded the potential for economic production from the Caney Shale.