Blueprint Established for Dynamic Reservoir Assessment in CCUS Projects

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 230941, “Establishing a Blueprint for Dynamic Reservoir Assessment in CCUS Projects,” by Mahmut Sarili, SPE, and Adam Donald, SLB, and Aurifullah Vantala, ADNOC, et al. The paper has not been peer-reviewed.

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The effectiveness of carbon capture, utilization, and storage (CCUS) operations relies on precise in‑situ rock and stress characterization for secure and efficient CO2 storage. Identifying, characterizing, and selecting suitable sites for CO2 geological storage necessitates comprehensive evaluation techniques to determine optimal locations for safe and long‑term carbon containment. By integrating petrophysics, geology, geomechanics, and reservoir engineering, precise in‑situ stress measurements were acquired for two of the operator’s wells, successfully characterizing caprock integrity and reservoir injectivity and creating a blueprint for future CCUS evaluations.

Background

The operator has drilled and evaluated two separate CCUS wells as part of the UAE’s strategic aim of having net‑zero emissions by 2050. These wells seek to describe the in‑situ geomechanical, petrophysical, and hydrodynamic features of potential storage deposits. In this study, the stress behavior and sealing efficiency of target formations were assessed through downhole testing integrated with formation pressure and fluid sampling. The resulting data set enabled robust calibration of a mechanical Earth model (MEM) and supported the development of operational frameworks for future CO2‑injection initiatives.

The testing highlighted in this paper, which the authors refer to as MicroFrac, is a refined technique that induces and monitors local fractures within the subsurface, facilitating direct measurement of minimum in‑situ stress. It can be performed using wireline or pipe‑ conveyed modular formation dynamics testers (MDT), offering safe, quick, and cost‑effective acquisition of stress data at different depths. The MDT‑based MicroFrac platform provides real‑time monitoring of fracture events through comprehensive pressure diagnostics, maintains accurate pressure management using high‑ pressure pump modules, and isolates formation intervals using a dual‑packer system.

The first well’s testing operations focused on the anhydrite caprock to assess its capacity for fracture initiation and sealing performance. The campaign involved two runs, one for formation‑fluid sampling and pressure measurement, and another dedicated to the featured testing. A total of three test sets were conducted wherein fracture initiation and closure were monitored; breakdown pressure data were recorded at two stations, while packer differential‑ pressure threshold was reached on one station without fracture occurrence. For closure‑pressure evaluation, a controlled forced‑closure‑flowback approach was used. Multiple injection and falloff cycles were conducted at each station. Formation microimager (FMI) logs were captured pre‑ and post‑test to validate induced fractures.

In the second well, the scope was broadened to deliver a full mechanical profile across both 8.5‑ and 6‑in. borehole sections. Four MDT runs were completed in the 8.5‑in. section, including fluid sampling with an in‑situ fluid analyzer (IFA) for real‑time fluid analysis. The testing program encompassed 16 test stations, 10 in the 8.5‑in. and six in the 6‑in. section distributed over a several‑thousand‑foot vertical interval. This comprehensive spatial coverage enabled assessment of stress variation and lithological influence essential for future injection design and MEM refinement.

The testing process for the 8.5‑in. section involved several injection/falloff cycles, combining natural and forced closures, and a step‑rate test that was performed to confirm stress parameters. Closure pressures obtained by G‑function and square‑root‑of‑time (SQRT) analyses showed good correlation across methods. Pre‑ and post‑test FMI imagery affirmed the creation of induced fractures, confirming method effectiveness.