How Reliable Is Fluid Gradient in Gas/Condensate Reservoirs?

Kabir, C.S.; Pop, Julian

doi:10.2118/99386-ms

Cited by 16 publications

(5 citation statements)

References 25 publications

(8 reference statements)

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“…For formation fluids of low densities, like gases and gas condensates, the limitations of the sensor technology may become an issue. Kabir and Pop (2007) discuss this subject and present case studies and outline methods to quantify the accuracy of the pressure survey. Hashem et al (2004) present further techniques to improve the data quality of formation testing.…”

Section: Static Formation Pressure Surveys and Downhole Fluid Analysismentioning

confidence: 99%

Fluid Composition Equilibrium; a Proxy for Reservoir Connectivity

et al. 2011

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Assessing reservoir connectivity during the earliest stages of reservoir evaluation is highly desirable for successful field development. Nevertheless, it has long been problematic to assess reservoir connectivity prior to production. Recently, downhole fluid analysis has enabled facile assessment of fluid compositional gradients vertically and latterally. Using equations of state, the extent of fluid compositional equilibrium can be established. Only a process that stretches across the entire age of the reservoir is likely to capture geologic events that cause compartmentalization. Fluid composition equilibration requires mixing of the entire content of the reservoir which occurs only on the geologic time scale. Restrictive flow barriers are not compatible with thorough mixing of fluids throughout the reservoir. Fluid composition equilibration provides a tight constraint to test connectivity. In this paper, the time constants for fluid composition equilibration are evaluated in numerical simulations. Equilibration processes are simulated in a simplified model over geologic timescales at isothermal conditions where diffusion and gravity are the active mechanisms. A variety of initial conditions and reservoir fluid types are considered. The effect of barriers on the equilibration time is investigated for single and multiple barriers. The results are compared with analytical calculations. Longer equilibration times correspond to tighter constraints on connectivity. This work shows the progression of compositional gradients over geologic time until all components have reached zero mass flux. It investigates the foundation of connectivity studies that rely on fluid composition. Determination of fluid equilibrium should become part of the standard procedure for reservoir connectivity evaluation.

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Section: Static Formation Pressure Surveys and Downhole Fluid Analysismentioning

confidence: 99%

Fluid Composition Equilibrium; a Proxy for Reservoir Connectivity

et al. 2011

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“…The second one is the evaluation of compositional changes into the reservoir due to gravitational and temperature gradients (effects analyzed in several studies: Zuo et al (2009);Kabir et al (2007); Hoier and Curtis (2000); Fujisawa et al (2008); and it is possible to simulate with commercial software) which will be able to compared with reservoir fluid analysis done in the same field or fields with similar characteristics. The first one is the interval selection far away from gas-water contact to assure a clean reservoir fluid sampl and to avoid rock-fluid properties changes because of water breakthrough.…”

Section: Interval Selectionmentioning

confidence: 99%

Analysis of Operative Variables for Establishing a Procedure to Obtain Representative Fluid Samples in Gas/Condensate Fields

Torres

2010

All Days

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During the exploratory phase, reservoir fluid analysis is an important tool for obtaining the hydrocarbon volume In-Situ, for understanding the behavior of fluids based on the field pressure changes, for defining a fluids production strategy, and as an input for production facilities design, among others. Due to the importance of this information, sampling procedures must guarantee that collected fluids are representative of reservoir ones to allow for reliable results which will be obtained during the PVT laboratory studies.In the ABC Fieldcase, located in Cusco Peru, a Gas-Condensate reservoir with a dew point close to the initial reservoir pressure, it was necessary to develop a detailed operative design in order to guarantee that fluid samples would be representative. This study allowed us to define some steps which must be present in the operative procedure in order to achieve an optimum sampling process.Additionally, it was possible to see the effects in the representativeness of the samples due to pressure depletion, condensate banking, and its compositional analysis. The behavior of the Gas-Condensate ratio, the turbulent flow effects in the formation face, permeabilities, the optimum time for sampling, and flow rates.Finally, it was possible to evaluate the sampling procedure effects and its influence in the representativeness of fluid. An equation of state tuning was carried out for two fluids which were sampled in the same well. In this case, the effects of the different sampling procedures and their repercussions in liquid recovery are analyzed.With the information contained in this study, we can identify the importance of selecting an exclusive sampling period outside of the normal transient pressure testing period and the effects of the main system variables. Keeping in mind the importance of this information and the costs associated with the project, failure is not an option.

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“…Separately, as detailed in reference [6], it is possible to compute and compare theoretical and statistical gradient errors. The theoretical error is computed on the basis of user specified depth and pressure repeatability errors (frequently taken respectively as 1 ft and 0.3 psi, as observed from numerous existing datasets).…”

Section: Model Validationmentioning

confidence: 99%

“…The theoretical error is computed on the basis of user specified depth and pressure repeatability errors (frequently taken respectively as 1 ft and 0.3 psi, as observed from numerous existing datasets). In reference [6] the standard error in the gradients is derived under the assumption that the data is uniformly distributed over a tested interval h, and that on this interval no fluid compositional variation exists. It is function of the number of data points K and can be calculated by (4) σp and σz being respectively the pressure and depth repeatability.…”

Section: Model Validationmentioning

confidence: 99%

“…Recently published paper from Kabir & Pop [6] show a similar approach in the validation that is made of fluid models from 3 different sources of information: pressure gradients, EOS based fluid gradients and wellbore static gradient from dynamically calibrated DST. The wireline formation testing data for the large North Sea offshore well under study is given in Fig.3 [1] Because the compositional gradient was seen in real time during acquisition, several DFA stations were run in the oil zone to scan the fluid.…”

Section: Model Validationmentioning

confidence: 99%

See 1 more Smart Citation

Integration of In-Situ Fluid Measurements for Pressure Gradients Calculations

Dubost¹,

Carnegie²,

Mullins³

et al. 2007

Proceedings of International Oil Conference and Exhibition in Mexico

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fax 01-972-952-9435. AbstractReservoir fluids often show complex compositional behaviors in single columns in equilibrium due to combinations of gravity, capillary and chemical forces. Frequently non equilibrium or non stationary state conditions are also encountered, for instance due to thermal forces acting. Recognizing these behaviors downhole is a complex process that requires a greater number of data points, fluid samples and associated laboratory analysis.The method is illustrated with a published case study [1] from a North Sea appraisal well, where a large compositional gradient has been observed with in-situ fluid measurements. An equation of state is elaborated from a sample and its PVT experimental results, and a compositional gradient is parametized using the DFA observations at the different depths. A polynomial fit is then given to the distributed pressure measurements and the obtained fluid density variations are compared to the fluid model ones.

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How Reliable Is Fluid Gradient in Gas/Condensate Reservoirs?

Cited by 16 publications

References 25 publications

Fluid Composition Equilibrium; a Proxy for Reservoir Connectivity

Fluid Composition Equilibrium; a Proxy for Reservoir Connectivity

Analysis of Operative Variables for Establishing a Procedure to Obtain Representative Fluid Samples in Gas/Condensate Fields

Integration of In-Situ Fluid Measurements for Pressure Gradients Calculations

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