Concept to Execution: Successful Proactive Geo-Steered Horizontal Well Case Studies from a Low Permeability Reservoir of Barmer Basin, India
Authors: Pal Arindam , Chowdhury Manabesh , Phinney Eric , Das Amlan , Dwivedi Nikhilesh , Lobo Kenneth 
Published: November 2016

Barmer Hill is a low permeability lacustrine reservoir complex of Paleocene-Eocene age deposited in Barmer Basin, North West India. In Mangala-Aishwariya area, this reservoir consists of laminated, high porosity (25-35%), low permeability (~0.2-4 mD) porcellanites of biogenic origin. Commercial development of analogue low permeability reservoirs are carried out with multi-stage hydraulic fracturing in horizontal wells. This paper outlines the planning to execution of three actively geo-steered complex horizontal wells from an appraisal drilling campaign in Barmer Hill.

Mangala and Aishwariya fields are tilted fault blocks with 3-way fault closure bound by a major down-to-the-west normal fault. The structural complexity is exacerbated by a series of cuspate, low angle listric faults in the Barmer Hill Formation. The gravity faulted area is structurally complex and seismic imaging is challenging. Downdip towards the east, the Barmer Hill Formation is well imaged and the units gently dip (2o −10o) south-east.

Detailed reservoir characterization work is carried out before horizontal well planning in the structurally complex tight reservoirs of Barmer Hill. Transverse and longitudinal horizontal wells are designed along the principal stress directions to prove the toe-down, toe- up and along-strike drilling concepts respectively. Subsurface uncertainties, engineering constraints and completion requirements for hydrofracturing are considered while optimizing the well designs. The associated operational risks are mitigated in real time, with wellsite and logging-while-drilling (LWD) data. Each well is actively geo-steered through reservoirs of low resistivity contrast and placed within respective zones of interest.

Drilling with a three casing policy in Barmer Hill, the 8-1/2" intermediate section of the well is landed right below the top of target reservoir at an optimum inclination. In 6" drainhole section, the inclination is either built-up or dropped to align the trajectory with the formation dip appropriately. The well azimuth is primarily guided by the regional understanding of principal stress directions and collision constraints. The drainhole section is geo-steered through the target reservoir with a state-of-art bed boundary mapping tool. Density Imaging (DI) and Distance to Boundary (DTB) estimation with resistivity inversion modelling resulted in successful operational execution of the extremely challenging drainhole sections. The uncertainty in predicting the structural top and thickness of the reservoir section is narrowed by offset well information and real time interpretation.

In Barmer Hill, Well-1, a transverse toe-down well at 85o inclination, tracked the reservoir boundary till resistivity diminished towards flank. Well-2, a transverse toe-up well penetrated the listric faults at 95o inclination, encountering several reservoir units. Well-3, a longitudinal along-strike horizontal well penetrated the structural crest at inclination of 92o, delivering a drainhole section of 1200m. The integrated approach of proactive geo-steering has resulted in successful execution of some of the longest 6" drainholes drilled in the Indian subcontinent.