Integrated Approach to Evaluate Unconventional and Tight Reservoirs in Abu Dhabi

Steiner, Stefan H.; Ahsan, Syed Asif; Noufal, Abdelwahab; Franco, Bernardo Jose; Koksalan, Tamer; Amjad, Kashif; Helja, Emina; Alhosani, Sabah; Adesanya, A O

doi:10.2118/177610-ms

Cited by 5 publications

References 4 publications

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Basin Scale Geomechanical Modeling of Tight Carbonate Reservoir in Abu Dhabi: Implications on Pore Pressure Development

Fadipe

Bouhlel

Noufal

2016

Day 1 Mon, November 07, 2016

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The in-situ stress state in a rock mass is widely recognized as being of major importance in unconventional field. The inherent variation of stress distribution associated with geological environments is widely recognized as being a key factor in an unconventional field; hence, the need to understand from the basin-scale phase is critical. The three main ingredients needed to formulate a model for the mechanics of the porous sediments, are the concepts of bulk stress, pore pressure and compaction. Most available rock-stress-based numerical engines uses default laboratory properties for the set of lithology's in their library. However, understanding the mechanical properties of the lithologies and applying such to the model makes the result more representative of the local geology. This paper is an update on the previously published model (Mohamed et al., 2015), exploring the impact of rock stress and external geomechanical boundary (otherwise known as tectonic stress) on pore pressure development and rock failure. Middle Cretaceous formation (layer of interest ~ 150 m) was sub-divided into seven layers based on mechanical log signatures. Athy's law, formulated with effective stress combined with 3-D rock stress based on poro-elasticity, was used in the forward modeling simulator to improve the pore pressure prediction. Depositional events such as erosion and hiatus periods were also taken into account during simulation. The development of porosity, pore pressure, temperature, stress and related rock failure through time were simulated and calibrated to measured data. The main geomechanical properties, such as Young's Modulus, Poisson ratio, cohesion and friction angle depend on lithology and porosity. Appropriate relationship were established and ultimately used to calibrate the first–pass rock properties prediction from the numerical engine. Model porosity is dependent on burial depth, weight of the overburden sediment columns, and lithology properties. The mean stress was ultimately considered in deriving pore pressure results. Results reveal a dynamic representation of the three principal effective and total stresses within the studied formations. The maximum stress shows a NE-SW trend in the synclinal area and N-S trend on the anticlinal structures, the medium stress shows N-S trend on the synclinal structure with an E-W and NW-SE trend on Well A and Pseudo-well A wells respectively. The minimum stress reveals a NW-SE direction on the synclinal area and N-S trend on both flanks. The model also shows an improved pore pressure result ranging from 26.97 – 42.50 MPa (with 28.46 MPa average values within layers of interest) revealing ~ 1450 psi (10 MPa) difference when compared to the previous model where rock stress modeling was not performed.

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Basin Scale Geomechanical Modeling of Tight Carbonate Reservoir in Abu Dhabi: Implications on Pore Pressure Development

Fadipe

Bouhlel

Noufal

2016

Day 1 Mon, November 07, 2016

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An Iterative Response-Surface Methodology by Use of High-Degree-Polynomial Proxy Models for Integrated History Matching and Probabilistic Forecasting Applied to Shale-Gas Reservoirs

Wantawin

Dachanuwattana

et al. 2017

SPE Journal

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Summary Response-surface methodology (RSM) has been widely used in the petroleum industry as an assistive tool for numerical-reservoir-simulation studies. Instead of generating simulation cases exhaustively to solve history-matching (HM) problems, proxy models that are created by RSM provide useful benefits in terms of simplicity and computational efficiency. However, the capability of proxy models to fully capture uncertainty ranges of HM results and production forecasts might be deficient in complex problems if the simplified proxy models only deliver partial solutions. Hence, to decide whether the uncertainty-assessment process by proxy models is complete, the models should deliver as many HM solutions as required to build probability distribution of production forecasts. Therefore, we developed the work flow to combine both processes into an integrated proxy-based approach that searches for the accepted HM solution while probabilistic forecasts are evaluated simultaneously. In addition, the combined work flow is an iterative approach. It gradually modifies the proxy models dependent on the increasing number of completed simulation runs, which continually update the original proxy model into higher degree of polynomial. The use of higher-degree-polynomial equations appears to have the benefit to provide an expanded set of HM solutions inside the uncertain parameter space compared with the commonly used quadratic form. More solutions found from the iterations could eventually approximate wider uncertainty ranges of probabilistic forecasts, which is consistent with the direct Markov-chain Monte Carlo (MCMC) method but with a significant reduction of simulated cases. Finally, this paper applies the proxy-based approach to a reservoir-simulation model containing a horizontal hydraulic-fractured well in the Marcellus Shale formation. This proxy-based approach helps assess the uncertainty of reservoir and fracture properties of unconventional reservoirs. Also, it is useful for evaluating the ranges of ultimate gas recovery.

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Supervised Waveform Analysis to Find Wasia Carbonate Stratigraphic Traps in Rub' Al-Khali Basin, Saudi Arabia

AlQattan

Zhang

2017

Day 1 Mon, November 13, 2017

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The Wasia Formation presents opportunities to explore for stratigraphic traps in the Saudi Arabian Rub’ Al-Khali Basin because it contains numerous interbedded reservoirs, sources, and sealing rocks. The mid-Cretaceous Wasia Formation includes a rudist carbonate platform with five, third-order sequences comprising, from oldest to youngest, Safaniya, Mauddud, Ahmadi, Rumaila, and Mishrif members. These members include proximal shallow-marine, highstand carbonate shoals at the platform margin in close proximity to fine-grained carbonate deposits in the Shilaf Basin. The resulting depositional cycles and stratigraphic architecture position muddy-tight seals, adjacent to porous shallow-marine carbonate-shoal bodies. Two members (Safaniya and lowermost Mishrif) have high organic-matter content situated in the oil window. Core data, well logs, seismic signals, and modern analogs were analyzed to help understand the Wasia deposition. Detailed correlations were made of well logs and neural network training was used to generate electro-facies. Next, supervised waveform analysis was used, correlated to five well log facies, to create five waveform facies including (1) lagoon, (2) back-shoal, (3) shoal, (4) slope, and, (5) basin facies. Sources of potential uncertainties include data processing, seismic to well ties, position of stratigraphic tops and seismic horizon interpretation. To minimize these, care was taken in data processing and a blind test was performed to validate the final interpretation. On the basis of integrating the aforementioned data with our waveform facies, a reference geological model was built demonstrating that potential stratigraphic traps are porous, shallow-marine carbonate shoals intercalated with muddy-tight slope deposits resulting in isolated, porous carbonate reservoir bodies sealed by tight rocks. For example, the Ahmadi Memberseal was deemed to be too thin to seal the oil in the underlying Mauddud. In addition, muddy-tight lowermost Mishrif Member strata are also too thin to seal oil in the underlying Rumaila. In the worst case, laterally extensive upper Mishrif reservoirs are not sealed by interbedded lateral seals even though the Aruma shale seals their tops. The two best trap configurations include (1) the first highstand lower sequence of the Mishrif reservoir sealed by interbedded extensive transgressive muddy Mishrif carbonates and (2) thick Ahmadi and lowermost Mishrif fine-grained carbonates sealing Mauddud and Rumaila highstand system tracts.

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Integrated Approach to Evaluate Unconventional and Tight Reservoirs in Abu Dhabi

Cited by 5 publications

References 4 publications

Basin Scale Geomechanical Modeling of Tight Carbonate Reservoir in Abu Dhabi: Implications on Pore Pressure Development

Basin Scale Geomechanical Modeling of Tight Carbonate Reservoir in Abu Dhabi: Implications on Pore Pressure Development

An Iterative Response-Surface Methodology by Use of High-Degree-Polynomial Proxy Models for Integrated History Matching and Probabilistic Forecasting Applied to Shale-Gas Reservoirs

Supervised Waveform Analysis to Find Wasia Carbonate Stratigraphic Traps in Rub' Al-Khali Basin, Saudi Arabia

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