Fluid Engineering Solutions for Effective Shale and Pay Zone Damage Control
Ajay Kumar, A. K. Barthwal, Vinod Sharma, and V. K. Jain
Chemistry, IDT,ONGC, Dehradun, India
Significant attention is being given to stabilize troublesome shale as long interval of shale are drilled to reach underlying payzone, which may have claystone/silt. Hydratable Montmorillonite and Non hydratable Kaolinite/ Illite are problematic and may cause packoff or enlarged hole. Reduction in permeability of payzone due to swelling of available clay and fines migration would cause payzone damage. Depleted reservoir has made shale control tricky as increase in mud weight to control shale may cause pay zone damage.
Fluid engineering solution provides much needed relief in controlling shales and minimizing pay zone damage. Significant advancement in drilling fluid engineering based on rock-fluid interaction principles has been made in ONGC from initial Dispersed system (CL-CLS) to Electrolyte-Polymer (KCl-PHPA) system to High performance water base KCl-PHPA-Glycol system. This has resulted into substantial improvement in shale control with comparatively low mud weight. Application of Non damaging drilling fluid, devoid of damaging constituents like bentonite and barites, is being made to drill pay zone which has resulted into improvement in productivity. These fluids are being used in all assets and basins of ONGC. KCl-PHPA polymer system has been found to be a boon for identification of oil water contact and computation of oil saturation in low resistivity low contrast fresh water shaly sands of Tipams of Assam asset. Advanced Non damaging drilling fluid with Formate salts and Second generation high performance water base system with ecofriendly amines for shale control have also been developed which are planned to be field tested in near future.
The twin policy of using High performance water base drilling fluid for shale control and Non-damaging drilling fluid for payzone damage control in development drilling in ONGC is paying good returns.
Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery