TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Orocual field is located in northern Monagas State of Venezuela and is owned and operated by Petroleos de Venezuela, S.A. (PDVSA), the national oil company of Venezuela. This paper presents the results of the geological and geostatistical modeling aspects of an integrated study for the San Juan Reservoir in Orocual Field, Eastern Venezuela. The objective of this work was to establish a static model to be used in dynamic modeling to determine development potential, risk, and hydrocarbon reserves. Special interest exists in untested but highly prospective areas.A recently acquired 3-D seismic volume was integrated with a detailed core based sedimentology study used to define the depositional environment and facies connectivity. Based on this description, the San Juan Formation is subdivided into 3 major sedimentological units: Lower, Middle and Upper. A stochastic method was used to quantify model uncertainty.The fine grid geostatistical model was up-scaled to provide facies consistency for reservoir modeling. The prediction of heterogeneous fractured reservoir was added to the complexity. Numerical simulation was performed and will be discussed.
The Orocual field is located in the northern Monagas state of Venezuela and is owned and operated by Petroleos de Venezuela S.A. (PDVSA), the national oil company of Venezuela.Reservoir compartmentalization adds complexity to the field, and structurally equivalent, noncommunicating fluid regions exist. An equation of state (EOS) is needed for reservoir modeling, requiring a review of available data and area fluid distributions.A seven-pseudocomponent EOS with a single characterization defining the compositional gradient of the hydrocarbon column from gas to black oil is defined. The method demonstrates that composition relative to depth can be predicted in those parts of the reservoir in which samples do not exist but in which production and test data must be matched, and thus where a gas-to-oil transition occurs.This paper demonstrates a technique to identify representative samples for use in developing an EOS and for initializing fluids in place. A method is presented to adjust the component composition vs. depth, providing consistent vertical composition distribution and compositional-model stability. This method meets the objectives of matching field production observations. A method is presented to quickly initialize a full-field model using a 1D compositional simulator to give full-field-model stability using the local high-temperature gradient.Results of compositional simulation show a single EOS, and vertical compositional and thermal variation reproduce the complex character of the field hydrocarbon column, matching fieldmeasured observations of saturation pressure (p s ), gas/oil ratio (GOR), and fluid densities.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractDiligent management of a high-pressure gas injection program in a field with a complex column of hydrocarbon fluids requires reservoir modeling. It is important and necessary to perform a detailed study of the PVT samples including the evaluation of the fluid distributions and to define an equationof-state (EOS) to be used in a reservoir model.The Orocual field is located in the northern Monagas state of Venezuela and is owned and operated by Petroleos de Venezuela, S.A. (PDVSA), the national oil company of Venezuela. The field is characterized as a complex structure having more than 3000 feet of vertical hydrocarbon column. Fluids change from light gas in the top of the structure to condensate gas, to a near-critical transition fluid and volatile oil, to under-saturated oil at the bottom of the column.Reservoir compartmentalization adds complexity to the field and structurally equivalent, non-communicating fluid regions exist. The dispersion of some sample characteristics versus depth was thought to be the result of non-representative samples. The ability to integrate the PVT data into the geological model adds another dimension in defining the structural complexities.The paper demonstrates a technique to identify representative samples for use in developing an EOS, and for initializing fluids in place. A method is presented to adjust the component composition versus depth, providing consistent vertical composition distribution and compositional model stability. This method meets the objectives of matching field production observations. Also, a method is presented to quickly initialize a full field model using a 1-D compositional simulator to give full field model stability in an environment of high temperature gradient.The final result is a 7 pseudo-component EOS with a single characterization defining the compositional gradient of the hydrocarbon column from gas to black oil. The method demonstrates that composition relative to depth can be predicted in those parts of the reservoir where samples do not exist, but where production and test data must be matched.Other areas in northern Monagas state have similarly complex systems 1 . Many areas are only partially developed and can benefit by applying techniques presented in this paper to describe the fluids and to estimate gas-oil contacts.Results of compositional simulation show a single EOS and vertical compositional variation reproduce the complex character of the field hydrocarbon column, matching field measured observations of saturation pressure (p s ), gas-oil-ratio (GOR) and fluid densities.
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.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Orocual field is located in northern Monagas State of Venezuela and is owned and operated by Petroleos de Venezuela, S.A. (PDVSA), the national oil company of Venezuela. This paper presents the results of the geological and geostatistical modeling aspects of an integrated study for the San Juan Reservoir in Orocual Field, Eastern Venezuela. The objective of this work was to establish a static model to be used in dynamic modeling to determine development potential, risk, and hydrocarbon reserves. Special interest exists in untested but highly prospective areas.A recently acquired 3-D seismic volume was integrated with a detailed core based sedimentology study used to define the depositional environment and facies connectivity. Based on this description, the San Juan Formation is subdivided into 3 major sedimentological units: Lower, Middle and Upper. A stochastic method was used to quantify model uncertainty.The fine grid geostatistical model was up-scaled to provide facies consistency for reservoir modeling. The prediction of heterogeneous fractured reservoir was added to the complexity. Numerical simulation was performed and will be discussed.
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