Equation of State of a Complex Fluid Column and Prediction of Contacts in Orocual Field, Venezuela

Smith, Richard; Bard, Wade; Lugo, Claudia; Yemez, I.; Guerini, Agostino; Whitson, Curtis Hays; Fevang, Øivind

doi:10.2118/63088-ms

Cited by 3 publications

(1 citation statement)

References 7 publications

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“…As discussed, depth-dependent fluid property variation has been shown to occur by discerning PVT properties (Hanafy and Mahgoub 2005;Smith et al 2004;Montel et al 2003). However, direct comparison of independent measurements contributing to fluid gradients has been rare.…”

Section: Introductionmentioning

confidence: 99%

How Reliable Is Fluid Gradient in Gas/Condensate Reservoirs?

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractCollection and analysis of gas/condensate fluid samples present considerable challenges. That is because downhole sampling of a gas/condensate fluid, unlike its oil counterpart, does not guarantee retrieval of single-phase fluid. The same is true for surface sampling because of incomplete surface and/or downhole separation. Given this reality, the PVT analysis of any fluid sample with an equation-of-state (EOS) model demands that the results are verified with independent measurements.Our analyses of many samples show that a good correspondence exists between the PVT-derived gradient and that obtained from wellbore-flow modeling of production-test data. Older generation formation testers, those prior to 1990, although yielding comparable results, had larger error bars owing to system limitations in repeatability of both pressure and depth measurements.We developed a yield-temperature correlation to fill in the information void for reservoirs that fall within the bounds of measured data over a large geographic area. Correlating CO 2 with formation temperature was a stepping stone to the yield/temperature relationship. This approach is applicable for the analysis of both single-reservoir and multi-reservoir samples, which is particularly useful when rapid assessment is needed over large regions.

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Section: Introductionmentioning

confidence: 99%

How Reliable Is Fluid Gradient in Gas/Condensate Reservoirs?

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2006

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Field Development Extensions of Orocual Field and Prediction of Expected Performance in a Fractured Reservoir

Guerini

Lugo

Vargas

et al. 2001

SPE Latin American and Caribbean Petroleum Engineering Conference

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Orocual Field is made up of four structurally compartmentalized fault blocks. The upper two, San Juan 3 (SJ3) and San Juan 6 (SJ6) are more developed. The lower block structures, San Juan 7 (SJ7) and San Juan 9 (SJ9), are more than 1500 feet deeper and are separated by a major thrust fault. These reservoirs primarily consist of light condensate. Recent development suggests that significant potential exists in the SJ6 and SJ7 areas. The difficulty in defining the hydrocarbon column associated with each block, because of limited development, shows significant sensitivity in calculating oil reserves. The San Juan formation is a naturally fractured sandstone reservoir, and has historically produced low sustained rates of less than 1000 BOPD. New techniques in the area have been studied to increase sustained rates to at least 3000 BOPD.This project was designed to develop a method to analyze the probable results of a development program. A reservoir simulation model was constructed as part of an integrated study focused on geostatistics modeling of tight matrix and fracture systems to predict production by extending the proven area of the field. The producing areas have limited data, and previous studies did not consider the fractured nature of the reservoir. The application of geostatistical methods for reservoir characterization, and the use of simulation to assess the static model heterogeneity were identified objectives. The complex structure and fluid columns add to the uncertainty. Various sensitivities were run by applying different constraints to the permeability model, variance in fluid definitions, and well design.The reservoir simulation model shows sensitivity to matrix characterization and less to fracture characterization. This sensitivity is related to well productivity as a function of matrix permeability. The matrix is so tight that a multiple increase of permeability has little effect on well productivity. The permeability appears to be predominately from fractures. Fracture density or fracture permeability shows less effect to change well productivity than matrix permeability. Over 100 simulations were run to predict well and reservoir behavior. Results allow realistic assessment of risk in both reserves and production and to rank alternatives.

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Miscible Gas Injection in Undersaturated Gas-Oil Systems

Høier

Cheng²,

Whitson³

2004

SPE Annual Technical Conference and Exhibition

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Summary This paper discusses miscible gas injection in reservoir fluid systems exhibiting compositional variation with depth characterized by an undersaturated "critical" transition from gas to oil, where all fluid properties exhibit a continuous variation with depth. In an undersaturated gas-oil fluid system all fluids throughout the reservoir are initially first-contact miscible with their neighboring fluids. This implies that full-pressure maintenance, gravity-stable updip gas injection will lead to miscible displacement throughout the reservoir, even for down-dip fluids which are not miscible with the injection gas. The pressure maintenance required is to avoid depletion below initial saturation pressure throughout the reservoir, i.e. maintaining a single-phase fluid system. Compositional reservoir simulation studies have been used to verify this behavior for one-dimensional (1D) flow. Similar results were originally suggested by Hoier and Whitson1. In this paper we study the same mechanism for nonideal reservoir systems characterized by (1) partial pressure maintenance where reservoir pressures locally drop below initial saturation pressure and two phases form prior to injection gas arrival; and (2) two-dimensional (2D) flow in reservoirs with heterogeneities and strong layer-property contrasts. Both situations may have a negative impact on oil recovery compared with full-pressure maintenance and gravity-stable miscible displacement with expected near-100% recovery. 1D and 2D compositional simulations are used based on the reservoir characteristics of a field with an undersaturated gas-oil fluid system - Smorbukk South Field, located in the Norwegian Sea. This field produces rich gas condensate and volatile oil through an undersaturated gas-oil transition from two main geological layers. We present five years of production history with pressure maintenance by gas injection. Introduction A number of fields have been reported where the fluid column grades from gas to oil, but where a saturated gas-oil contact (GOC) does not exist. The transition from gas to oil occurs in a smooth and continuous manner, with the mixture at the gasoil contact being neither gas nor oil, but a critical mixture. The saturation pressure of the GOC mixture is a critical pressure at the reservoir temperature. This critical pressure is the maximum saturation pressure in the entire fluid column. Reservoir pressure is greater than saturation pressure at all depths, so formally the reservoir is undersaturated. We therefore refer to this system as an undersaturated gas-oil system, with an undersaturated gas-oil contact. As pointed out by Schulte2, one characteristic of an undersaturated gas-oil system is that each fluid is first-contact miscible (FCM) with its neighboring fluids when reservoir pressure is maintained above the GOC saturation pressure. This paper looks at the possibility of developing a fullymiscible gravity-stable displacement at pressures lower than the GOC saturation pressure, and in particular when a condensing/vaporizing (C/V) miscible process develops within the gas cap. We begin with a brief list of some published fields with a reported undersaturated gas-oil system.Brent field2–4, UK, Statfjord formation. Mainly oil.Smorbukk field5, Norway, several formations. Mainly gas condensate.Smorbukk South field, Norway. Mainly oil.Birba field6, Oman. Mainly oil.Cusiana field7, Colombia. Mainly oil.Anschutz field8, Overthrust belt, USA. Mainly rich condensate with possible transition into oil.Bunduq field9, UAE. Mainly oil.Orocual field10, Venezuela. Mainly condensate. We are aware of a number of other such fields which have not been reported in the literature, including fields in Norway, Gulf of Mexico, Iran, Algeria, and Libyia. The list is probably much longer than indicated here. Miscibility in Compositionally-Grading Reservoirs In this section we give a short description of concepts, as well as 1D miscibility mechanisms and determination techniques, connected to this specific class of compositional grading reservoirs.

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Equation of State of a Complex Fluid Column and Prediction of Contacts in Orocual Field, Venezuela

Cited by 3 publications

References 7 publications

How Reliable Is Fluid Gradient in Gas/Condensate Reservoirs?

How Reliable Is Fluid Gradient in Gas/Condensate Reservoirs?

Field Development Extensions of Orocual Field and Prediction of Expected Performance in a Fractured Reservoir

Miscible Gas Injection in Undersaturated Gas-Oil Systems

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