Quality check and validation of multiwell ELAN results for three wells.

CASE STUDY

Modeling

Multiwell ELAN Processing Reveals Untapped Reserves for ONGCBaramura field re-evaluated using GeoFrame ELANPlus module

”The field assessments using the ELANPlus module uncovered untapped and unknown Baramura reserves and shaped our new development strategy. The new workflow has ensured that we can process several wells concurrently and accurately. Productivity has been improved to drive future project efficiencies.”

Mr. Asim Samanta Head, CEWELL

ONGC

Challenge ■ Efficiently re-examine and update

30-year-old Baramura subsurface maps ■ Address low-contrast resistivity

in gas-bearing sand and shale ■ Update and accelerate interpretation

methodology and technology ■ Develop uniform petrophysical

model for entire field

Solution ■ Use the GeoFrame* ELANPlus module

to undertake multiwell, multimineral modeling interpretation

■ Compute probable formation mineralogy and pore fluid volumes using multilog, least-squares inversion techniques

■ Develop a workflow to process multiple wells simultaneously, and generate a multimineral field model

■ Use isolith maps to provide sand geometry patterns

Results ■ Additional hydrocarbon-bearing

sections revealed ■ Crossfault responsible for reservoir

compartmentalization identified ■ Field-development planning improved ■ Petrophysical reservoir parameters

standardized for improved reserve volumes calculation

■ New field-assessment workflow established

■ Southern culmination much higher than previously perceived

As part of a strategic field re-evaluation, ONGC—the national oil company of India—needed to re-examine the 30-year-old subsurface maps used to interpret the Baramura gas field. These maps were prepared during 1980s for the Baramura’s Miocene Bhuban reservoir sands, to support detailed geological and geophysical investigations of the subsurface formation and structure.

During the initial phase of reserve estimation, ONGC processed and interpreted the field’s 24 wells using its in-house software, based on deterministic interpretation techniques in which each well was analyzed separately—this proved time consuming and inaccurate. ONGC needed a way to process the wells simultaneously, to generate a more realistic and consistent multimineral model in economically viable timescales.

After meeting with Schlumberger to discuss potential solutions, it became clear that the GeoFrame ELANPlus module would allow ONGC to undertake multiwell, multimineral modeling to meet their technical and business objectives.

ELANPlus single well modeling.

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CASE STUDY: Baramura field in India re-evaluated using GeoFrame ELANPlus module

Isolith map depicting Miocene Bhuban sands’ depositional features.

The ELANPlus module provides advanced multimineral log analysis capabilities. It computes the most probable formation mineralogy and pore fluid volumes using a multilog, least-squares inversion technique. It is particularly valuable in areas of mixed lithologies and mineralogies, and dual-porosity systems.

Simultaneous well processingIt was agreed that Schlumberger and ONGC would develop a comprehensive workflow to process multiple wells simultaneously, and generate a multimineral model of the Baramura field that could be used to overcome previous interpretation problems.

The team used the ELANPlus module to apply the multiwell elemental analysis technique. ELAN processing was first undertaken for key wells, with the results and logic applied later to the remaining wells as these are statistically normalized with the key wells. The team knew lithologic and petrophysical parametric behaviors were mostly uniform throughout the field, so the output was then compared with previously interpreted results and tested for validation. Net-to-gross analysis was then carried out simultaneously for all wells, generating high-quality output to help explain lateral field geologic variation, with precision and in a much shorter timeframe than before.

This processed output was then used to generate sand isolith maps, providing sand geometries to highlight the depositional features of Miocene Bhuban sands. Formation-top relief maps and structural maps for Middle Bhuban formation were used to interpret the structural framework of the entire Baramura field, revealing that the southern culmination was much higher than previously interpreted. Earlier interpretations had concentrated around the central culmination only.

Untapped potential With meticulous log correlation, the team was able to reveal additional hydrocarbon zones. When integrated with the multiwell ELAN processing results and sand dynamic properties, a normal crossfault was also identified—responsible for reservoir compartmentalization.

As well as immediately uncovering new reserve volumes, these findings proved critical for ONGC’s continued exploitation of the Baramura field and related development planning. The multiwell ELAN processing information allowed petrophysical reservoir properties to be standardized for improved volumetric reserve calculation. A powerful new field assessment workflow was also established as part of ONGC’s processes.

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