Dynamic Modeling Workflow for an Unconventional Biogenic Gas Reservoir with Multistage Hydraulic Fracture. A Case Study of Miocene Gachsaran Formation, Abu Dhabi, United Arab Emirates
Authors: Gueddoud Abdelghani , Al Hanaee Ahmed , Khan Riaz , Abdelaal Atef , Kurniawan Redy , Al Ameri Abdulla 
Published: December 2021

The Miocene Gachsaran Formation across Onshore Abu Dhabi and Dubai possesses high potential of generating shallow biogenic gas. A dynamic model and field development plan generated based on a detail G&G analysis to understand and evaluate its capability as promising gas resources. Specific approaches and workflow generated for volumetric and dynamic reservoir model capable of defining the most viable development strategy of the field from both an economic and technical standpoint. The proposed workflow adapts also the development plan from single pad-scale to full field development plan. A fine-grid field-scale with more than hundreds of Pads covering the sweet spot area of three thousands of square kilometers including structure, reservoir properties built based on existing vertical wells, newly drilled horizontal wells and seismic interpretation.

In this paper, a robust workflow for big and complex unconventional biogenic gas reservoir modeling and simulation technique have been developed with hydraulic fracture and stimulated area created through LGR. Independent workflows generated for the adsorbed gas in place calculation, desorption flow mechanism, and Pads field development plan. An accuracy on in place calculation, desorption flow mechanism and Pseudo steady state flow through direct and indirect total gas concentration measured using (1) Pressurize core and sorption isotherm capacity experiment, (2) Langmuir /BET function and Vmax scaling curves for each grid cells, and (3) Gas concentration versus TOC relationship. Field development plan for unconventional shallow biogenic gas reservoirs is possible only if a communication network created through hydraulic fractures connects a huge reservoir area to the wellbore effectively.

A complete workflow presented for modeling and simulation of unconventional reservoirs, which in-corporates the characterization of hydraulic fracture and their interaction with reservoir matrix. Dual porosity model has been constructed with accurate in place calculation through scaling the Langmuir function and calculation Vmax for each grid cell of the full field model, The single Pad design approach in the development plan has exhibited great advantages in terms of improvement in the quality and flexibility of the model, reduction of working time with the same Pad model design which is adapted for the full field development plan.

The proposed unconventional modeling and field development plan workflow provides an efficient and useful unconventional dynamic model construction and full field development planning under uncertainty analysis. Minimizing the uncertainty in place calculation and production forecasting for unconventional reservoirs necessitates an accurate direct and indirect data measurement of gas concentration and flow mechanism through the laboratory measurement. Field development plan for unconventional reservoirs is possible only if fracture network can be created through hydraulic fractures that connects a huge reservoir area to the wellbore effectively through pad completion.