Oil Rim De-Risking and Appraisal Value of Information in a Gas Reservoir

David, Olayinka; Laoye, Abiodun; Odegbesan, Seyi; Isimbabi, Onoze; Obeahon, P. P.

doi:10.2118/184343-ms

Cited by 4 publications

(1 citation statement)

References 6 publications

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“…This approach couples the uncertainty reduction with VOI techniques. Very recently, David et al (2016) have carried out a case study using multiple subsurface scenarios for production forecast and VOI approach to support a key decision whether or not to drill an appraisal well to test for fluid contact and possible presence of an oil rim in a gas reservoir with Lowest Known Gas (LKG) prior to initial gas development. This analysis indicated that the range of oil rim thickness proved to be noncommercial and the VOI analysis showed that drilling of an appraisal well will result in negative value giving the VOI and cost of drilling an appraisal well.…”

Section: Introductionmentioning

confidence: 99%

Optimal Subsurface Appraisal: A Key Link to the Success of Development Projects-Few Examples

Singh¹,

Yemez²,

Izaguirre³

et al. 2017

American Journal of Applied Sciences

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During exploration and production phases, the life of a hydrocarbon field can be distinguished by five main stages: Exploration, appraisal, development, production and abandonment. Of particular interest is the appraisal stage, where billions of dollars are spent across the oil and gas industry on data gathering activities with a view to reducing subsurface uncertainties towards optimizing reservoir development and management. However, very limited attention is often paid to assessing the Value of Information (VOI) during data acquisition requirement planning, before requesting for such information. Appraisal, when conducted optimally, leads to informed sequential decisions resulting in a development plan that optimizes cost, hydrocarbon recovery and attempts to maximize Net Present Value (NPV). On the contrary, suboptimal appraisal, either in the form of under, or over appraisal, impacts project economics. Individual oil and gas companies use their own strategies, procedures and metrics to optimize subsurface appraisals and safeguard profitability and hence there are no industry standards. The capital intensiveness of the industry and emerging low oil price regime has necessitated scrutiny on every dollar spent on data gathering in the current business terrain. Appraisal should be optimized by way of case specific activity of data acquisition to ensure project deliverability under maximum residual uncertainties achieved by minimum appraisal cost. To ensure that the appraisal strategy is value driven, an effort has been made to briefly recapitulate the different components of appraisal strategy necessary for appraisal framing and evaluation workflow. The appraisal locations selection and their sequencing combines uncertainty reduction, probability of success with VOI technique to determine the number of appraisal wells, their sequence of drilling and their justification that is based on economic merit. The effectiveness of this systematic approach has been illustrated through some real field examples. This workflow along with periodic look-back analysis, during appraisal to development phases, has proven to be highly useful for (1) improving the understanding of geological model; (2) assess VOI from appraisal; (3) reduce subsurface uncertainties and (4) improve decision quality and whole cycle project economics.

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Section: Introductionmentioning

confidence: 99%

Optimal Subsurface Appraisal: A Key Link to the Success of Development Projects-Few Examples

Singh¹,

Yemez²,

Izaguirre³

et al. 2017

American Journal of Applied Sciences

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Estimation of Oil-Rim Thickness with Analogue Data in the Absence of Definite Fluid Contacts: A Case study from Onshore Niger Delta

Fouzdar

Kilic²,

Das³

2017

Day 2 Tue, August 01, 2017

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One of the major challenges in field development is to estimate the possible oil-rim thickness, when only known contact is Gas-Down-To (GDT) or Oil-Down-To (ODT), and where seismic analysis cannot resolve the uncertainty. A reliable, repeatable, and practical technique to estimate the ranges of possible oil-rim thickness with the regional analogue would allow for making development decisions, as well as meeting the local regulatory requirements. An analog database with numerous proven hydrocarbon (gas and oil) column heights provides a trend for "gas-to-oil column ratio" by depth, which can be used for predicting possible oil-rim thickness at specific reservoirs with the contact uncertainty. For all the analog reservoirs, fluid thicknesses have been tabulated and a "gas-to-oil column ratio" has been calculated. A simple plot between the "gas- to-oil column ratio" and reservoir depth reveals a certain trend of increasing "gas- to-oil column ratio" by depth. In addition, database also provides a cumulative distribution of regional column heights, which could be used to constrain the maximum estimated hydrocarbon column thicknesses. The trend of increasing "gas-to-oil column ratio" by depth indicates that gas-columns gets much bigger compare to oil-columns as the reservoir depth increasing. With given depth information and estimated "gas-to-oil column ratio" from the database, it is possible to estimate possible range of oil-rim thickness. By investigating the scatter in the trend, it is also possible to estimate a range of "gas- to-oil column ratios". With the help of this methodology, in absence of any definite fluid contact, it is possible to estimate a range of oil-rim thicknesses, which has an impact on field development scenarios; i.e. "gas-only", "oil-then-gas", or "concurrent oil-and-gas" development options. In addition, it could also help field development plan to meet the regulatory requirements; i.e. providing a strong case not to develop or appraise the oil rim.

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Using Compositional-Grading Simulations to Assess Gas-Oil Contacts: Practical Cases from the Niger Delta

Eyitayo

Lawal

Ukaonu

et al. 2017

Day 3 Wed, August 02, 2017

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Encountering a reservoir in either a gas-down-to (GDT) or an oil-up-to (OUT) situation poses a challenge to development planning and reservoir management. The resulting uncertainties in the distribution, in-place and recoverable volumes of oil and gas may jeopardize expeditious execution of the field development project. To confirm the presence or absence of either oil or gas and establish a possible gas-oil-contact (GOC), in some cases the drilling of an appraisal wells(s) may be required. This paper describes a method that does not depend on dedicated appraisal wells to reduce GOC uncertainties and proves to be a valuable method to de-risk planned reservoir developments. Where credible pressure-volume-temperature (PVT) data are available from the subject reservoir, compositional-grading simulations (CGS) can be employed to evaluate the presence (or otherwise) of a GOC within a vertically continuous reservoir column. From a thermodynamic standpoint, the GOC is that depth at which the reservoir fluid transits from being gas-like to oil-like, and vice-versa. Considering some saturated and undersaturated oil reservoirs in the Niger Delta as case studies, this paper demonstrates the applicability of a combination of PVT and CGS to de-risk the presence of GOC without resorting to either a new well or a pilot hole. In the cases where well logs have established GOC, blind tests show excellent agreement between CGS results and well logs. Similarly, CGS accurately suggests the absence of gas-like fluids within the proven undersaturated oil reservoirs examined. Finally, the results of this study will document that CGS is reliable and cost-effective for reducing GOC uncertainties and de-risking field development projects. Consequently, this method is recommended whenever credible PVT data are available.

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Oil Rim De-Risking and Appraisal Value of Information in a Gas Reservoir

Cited by 4 publications

References 6 publications

Optimal Subsurface Appraisal: A Key Link to the Success of Development Projects-Few Examples

Optimal Subsurface Appraisal: A Key Link to the Success of Development Projects-Few Examples

Estimation of Oil-Rim Thickness with Analogue Data in the Absence of Definite Fluid Contacts: A Case study from Onshore Niger Delta

Using Compositional-Grading Simulations to Assess Gas-Oil Contacts: Practical Cases from the Niger Delta

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