A Greater Dolphin Area Case Study Part 1: Defining Geological Uncertainty

Taylor, Katy; Kalita, Nik; Dowlath, Joel Frank; Jegede, Olamide Michael; Ameerali, Ronnie Arun

doi:10.2118/158545-ms

Cited by 4 publications

References 2 publications

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Outcrop analogues for hydrocarbon reservoirs in the Columbus Basin, offshore east Trinidad

Bowman¹

2016

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The Mayaro Formation, which is exposed in SE Trinidad, is the key outcrop analogue for prolific hydrocarbon reservoirs in the Columbus Basin, offshore east Trinidad, because it was deposited in the same basin setting by the same depositional system (the palaeo-Orinoco) as the offshore reservoirs. Sequence and parasequence stacking patterns affect the distribution of different types of reservoir sand bodies and heterogeneities, with the potential to influence fluid flow in subsurface hydrocarbon reservoirs. Spectacular outcrops of successions of storm-wave-influenced sand bodies, tens to hundreds of metres thick, deposited in axial and medial delta-lobe settings are characterized by high sand–shale ratios (0.7–>0.95), and are analogues for many producing reservoirs in the basin. Fluvial- and tide-influenced sand bodies deposited in distal distributary settings are also recognized in the outcrops, but may be difficult to distinguish from medial delta-lobe deposits in subsurface data. More complex, thinly bedded distal delta-lobe deposits, with subsurface reservoir potential, exhibit lower sand–shale ratios (0.3–0.6). Complex depositional architectures, with a high proportion of thinly bedded sandstones, also occur in association with delta-front deposits. The distal delta-lobe and delta-front deposits are analogous to some of the most challenging to develop reservoirs in the Columbus Basin.

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Outcrop analogues for hydrocarbon reservoirs in the Columbus Basin, offshore east Trinidad

Bowman¹

2016

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Integrated Dynamic Modelling of Unconsolidated Thin Bedded Reservoirs: The Greater Dolphin Area, Trinidad and Tobago

Nurafza

Urun

Ryan

2017

SPE Latin America and Caribbean Petroleum Engineering Conference

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Over the last 20 years of Dolphin field gas production, it has always been a challenge to estimate inplace volumes, history match pressure and water productions, and generate a reasonable range of production forecasts. Given the unconsolidated nature of the Greater Dolphin Area (GDA) reservoirs, it has not been possible to acquire representative cores and perform successful core plug tests. As a result, estimates of not only static parameters like porosity and saturation, but also dynamic parameters such as compressibility and permeability have been challenging. Historically this led to smaller static volume estimates than dynamic volume estimates from material balance. A new set of static and dynamic GDA reservoir models have been built that integrates and incorporates reservoir engineering techniques and revised petrophysical/geological properties to resolve the mismatch between static and dynamic volumes. Key inputs of this new model are in-depth reviews of dynamic datasets ranging from compressibility, Production Logging Analysis (PLA) results, and both core and well test derived permeability. Revised interpretation of these datasets, along with an iterative approach between static and dynamic QC has resulted in a range of deterministic and probabilistic history matched reservoir models that are used for forecasting and project planning decisions. The main approach was initially focused on reviewing the material balance studies and evaluating the effect of compaction in these unconsolidated sands. This highlighted the impact of compressibility in partially inflating the historical estimates of dynamic volumes. Additionally the study was focused on de-convolving field-wide material balance of comingled production from multiple reservoirs with heterolithic formations and a varied range of static properties and pressure depletion trends. Later the level of communications amongst various compartments and with nearby fields were investigated and taken into account. This assisted with an improved understanding of volume distributions amongst different reservoirs/compartments and helped to constrain the connected volumes, while building the dynamic models. In addition, a new methodology was developed to model permeability based on the kh derived from pressure transient analysis and the layer contributions observed in initial PLA results. This novel permeability modelling technique also helped to match PLA results in wells and individual reservoir layers gas contributions and water productions. These new approaches along with an alternative petrophysical methodology to better estimate water saturation within thin bedded intervals have been incorporated into an integrated workflow to account for both static and dynamic uncertainties. This set of probabilistic simulation models achieved a range of history matched results with a better understanding of dynamic reservoir behavior and also helped to overcome the historical shortage of static volumes required to match observed pressure data. This in itself brought more confidence towards generated production forecasts and future project's decision making processes.

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Re-Evaluating Contributions from Thin Bedded Reservoirs: Integrated Reservoir Modelling of the Greater Dolphin Area

Ryan

Crooks-Smith

Nurafza

et al. 2018

Day 3 Wed, June 27, 2018

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The Dolphin Field has been producing gas since 1996, however predicting in place volumes, reserves and forecasting production has been a challenge since field inception. The fact that in place estimates have increased significantly since development sanction highlights that a range of geophysical, geological and petrophysical uncertainties are associated with the field. Historically, static volumes have been smaller than dynamic volumes estimated from material balance. The explanation of this difference traditionally related to uncertainty in contact depth (given the minimal data on contacts), that adversely caused poor predictions of water production in the historical models. Many of the reservoir units within the Greater Dolphin Area (GDA) are characterised by a heterolithic deltaic succession of centimeter scale very-fine sandstone, siltstone and mudstone. Given the thin-bedded nature of the reservoir, conventional wireline-logging tools lack the resolution to accurately resolve many of the static parameters including water saturation. However, based on the available PLT data, it is believed that these thin-bedded intervals generally contribute to the production from the wells and hence to the fluid flow in the reservoir. A new static and dynamic reservoir model of the GDA has been built that integrates and incorporates new seismic interpretation, petrophysical recharacterization, revised geological and reservoir engineering concepts, and eventually history matching to production data. A key component of this new model build has been integrated modelling iterations amongst different disciplines from new petrophysical interpretations through to dynamic simulation. Initial iterations used a conventional formation evaluation method and resulted in simulations that showed accelerated pressure drops (compared to production data) as a result of failure to capture flow from thin-beded intervals. An alternative petrophysical methodology that aims to better estimate water saturation within thin bedded intervals has been incorporated into a new workflow to account for the thin bed volumes. The new thin bed simulation model results in greater gas contributions from the thin-bedded intervals and helps overcome the historical shortage of static volumes required to achieve a pressure match.

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A Greater Dolphin Area Case Study Part 1: Defining Geological Uncertainty

Cited by 4 publications

References 2 publications

Outcrop analogues for hydrocarbon reservoirs in the Columbus Basin, offshore east Trinidad

Outcrop analogues for hydrocarbon reservoirs in the Columbus Basin, offshore east Trinidad

Integrated Dynamic Modelling of Unconsolidated Thin Bedded Reservoirs: The Greater Dolphin Area, Trinidad and Tobago

Re-Evaluating Contributions from Thin Bedded Reservoirs: Integrated Reservoir Modelling of the Greater Dolphin Area

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