Hydraulic Proppant Fracturing of Carbonaceous Shale Source Rock: A Case Study in North Kuwait Jurassic Gas Asset
Authors: Fidan E. , Al-Mefleh K. , Abdul-Samad Z. , Alaabdin Z. , Naqi Y. , Al-Salali Y. , Ajayi A. , Wu L. Pei , Salem A. 
Published: September 2023

A strategic expansion road map is developed by the North Kuwait Jurassic Gas asset (NKJG) in order to increase the non-associated Jurassic Gas (JG) production by 60-70% in the next 2-3 years to meet the growing domestic demand. The Middle Marrat accounts for the majority of gas production, yet depletion has become a main concern in reaching asset's production targets and to sustain a high production plateau. This fact has necessitated the formulation and execution of a robust appraisal and development strategy of the unconventional resources across the Organic Carbonaceous Shale (OCS), which is the primary source rock of the NKJG reservoirs.

Stimulation technique is the key to achieving the production forecast for each well located in the OCS since several challenges due to unique formation properties pose complicated issues to be carefully considered in stimulation design, execution and post-stim testing. Lithological characteristics of the OCS are different from the North American shales in general, as the organic-rich clay with limestone intercalations make this reservoir sensitive to inorganic acids with high potential of in-situ sludge formation. Additionally, structural plastic deformation of the formation can lead to "dirty inflow", leading to formation and/or sludge flowing and causing wellbore fill. Due to this behavior in the presence of HCl, hydraulic proppant fracturing is identified as an enabler for productivity enhancement. Proppants pose several challenges such as the potentially high breakdown pressures due to high leak off and near wellbore stresses in the naturally fractured limestone intercalations. In addition, the presence of mobile water and clay-bound water is an added complexity in establishing commercial production from the OCS.

To overcome this plethora of challenges and to develop the concept of hydraulic proppant fracturing as a strategic enabler for production, a study was initiated to determine the optimum fluid system and proppant type(s) for fracturing the OCS. Proppant selection process involved laboratory tests such as scratch tests, thick wall cylinder (TWC), fracture toughness, embedment tests and particle size distribution. These laboratory tests were needed to synthetize the ability to prop-open the induced fractures and stabilize the pack after closure. Regarding choosing the fracture fluid, fluid efficacy/leak-off tests using a core plug, retained permeability tests and fluid compatibility tests were done. Furthermore, the completion type with perforation were modelled and optimized to reduce NWB friction.

This paper will summarize and share the workflow, the attained best practices and the learnings while discussing the immediate and future plans of the NKJG asset in developing the OCS reservoir with regards to the completion and stimulation type selection, and the implementation phases of the critical activities to ensure commercial and clean inflow are established in post-stim flowback tests and production.