Impact of Natural Fractures in Reservoir Modelling and Characterization. Case Study in UAE

Mandl, Johannes; Mills, Carey; Obaidli, Eissa Al; Basioni, Mahmoud; Ali, Khalfan Al; Blooshi, Ahmed Al; Belova, Natela; Arroyo, Elkin R.

doi:10.2118/193316-ms

Day 4 Thu, November 15, 2018 2018

DOI: 10.2118/193316-ms

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Impact of Natural Fractures in Reservoir Modelling and Characterization. Case Study in UAE

Johannes Mandl

Carey Mills

Eissa Al Obaidli

et al.

Abstract: The offshore Field-A Gas Development Project is an integral part of the Abu Dhabi Deep Gas Project targeting untapped hydrocarbon reserves with priority given to gas reservoirs to satisfy an increasing gas demand and sustain economic growth of Abu Dhabi Emirate. Well test data from Field-A Khuff Formation cannot be modeled solely using a matrix based porosity system and requires the presence of fracture network to give a "mixed" porosity system to explain the observed flow test results. To asses… Show more

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Cited by 2 publications

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Enabling Production Logging in Commingled Flow During HPHT DSTs Allows Critical Dynamic Data Integration for the Khuff Formation in the UAE

Sookram

Steiner

Basioni

et al. 2019

Day 2 Tue, November 12, 2019

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The United Arab Emirates’ strategy to increase gas production, reduce dependence on pipeline imports and become a net exporter of this commodity has led to various important reserve discoveries. Appraisal wells drilled in gas formations such as the Khuff require both static characterization as well as dynamic data integration to improve the overall reservoir modelling in these complex tight reservoirs. Drill Stem Tests (DST) performed on Khuff appraisal wells provide important dynamic data, however in commingled flow tests more detailed information than that obtained from downhole pressure measurements and surface flow rates is required for a representative dynamic downhole characterization. Production logs (PLTs) can provide the required downhole fluid and flow profiles to differentiate inflow from different reservoirs or individual perforation zones. Such operations can become more complicated in the deep and high temperature Khuff reservoirs, especially when running through the small internal diameters in the DST bottom hole assemblies. The importance of PLT flow profile data for Khuff appraisal wells was recognized early on as a means to help investigate the formation heterogeneity, and the possible influence of natural fracture networks on reservoir productivity. PLTs were included in the DST programs for the appraisal wells, with the next step being preparing logging procedures and equipment to undertake operations as efficiently as possible. This preparation resulted in multiple production logs being successfully acquired in both vertical and deviated wells, along with logs prior to and after acid stimulation, providing invaluable and often surprising insight into the reservoir behavior and feedback for the static reservoir characterization. Along the way various important lessons were learnt that required modifications in some procedures to increase efficiency or reduce operational risks in the difficult downhole conditions. This paper will review some of the production log results and discuss the lessons learnt with the objective of making this type of dynamic data acquisition more visible as a very feasible activity to help improve reservoir characterization even under difficult conditions of logging through drill stem test strings into deep, high temperature reservoirs.

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Enabling Production Logging in Commingled Flow During HPHT DSTs Allows Critical Dynamic Data Integration for the Khuff Formation in the UAE

Sookram

Steiner

Basioni

et al. 2019

Day 2 Tue, November 12, 2019

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Lessons Learned from Extensive Well Testing Operations in Khuff Formations Offshore Abu Dhabi

Hollaender

Basioni

Blooshi

et al. 2020

Day 2 Tue, November 10, 2020

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Sanctioning the development of complex carbonate reservoirs and selecting an adequate development plan is not a trivial matter. Understanding formation heterogeneities such as layering, lateral continuity, natural fracture networks, or the impact of faulting are crucial to identify the optimal development strategy. Furthermore, completions strategies can have an outsized impact on the viability of such projects. Those challenges are particularly acute in the Khuff formations offshore Abu Dhabi and detailed formation evaluation is required. An extensive appraisal campaign was performed in Khuff reservoirs, with multiple appraisal wells drilled in different fields. Those wells were evaluated using detailed logging campaigns and then subjected to well tests, usually through drillstem testing (DST) for targeted intervals. Depending on the openhole logs, one to four tests were performed on each well. Multiple objective had to be met: assess formation potential, tie petrophysical properties to inflow sources observed from production logs, perform descriptive pressure transient analysis to understand formation structure away from the wellbore, and assess the optimal completion and stimulation strategy. The interpretation of well tests, combined with advanced petrophysical analysis, formation test data, and production logs, provided a unique insight into the nature of the Khuff reservoirs. A wide range of responses was observed, from tight to highly productive, but not necessarily with clear prior indications of deliverability or inflow intervals. Clear evidence of natural fracture networks or thin highly productive zones were observed, not necessarily correlated to standard logging results. By contrast, other tests yielded more of a matrix-driven flow, even though marked by significant vertical variations. Lateral continuity was also shown to be a possible development challenge, with behavior changing significantly between wells in relative vicinity of each other. This paper will present the observations but also offer some explanations and highlight remaining questions stemming from the analysis of the data acquired. Critically, this will show how the near-wellbore formation characteristics cannot readily yield a clear picture of larger-scale formation behavior and that only actual well testing combined with an appropriate stimulation strategy can unlock formation potential. Observations from the appraisal data over the wide number of wells considered in this study brought a unique insight into the characteristics of the Khuff reservoirs, offshore Abu Dhabi. We highlight their complexity and identify challenges in reliably characterizing them to enable optimal development. This study also shows how well test results can uniquely provide answers not obtainable through other means.

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Impact of Natural Fractures in Reservoir Modelling and Characterization. Case Study in UAE

Cited by 2 publications

References 3 publications

Enabling Production Logging in Commingled Flow During HPHT DSTs Allows Critical Dynamic Data Integration for the Khuff Formation in the UAE

Enabling Production Logging in Commingled Flow During HPHT DSTs Allows Critical Dynamic Data Integration for the Khuff Formation in the UAE

Lessons Learned from Extensive Well Testing Operations in Khuff Formations Offshore Abu Dhabi

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