Critical Parameters in Static and Dynamic Modeling of Tight Fluvial Sandstones
- Clark Huffman (Montana Tech.) | Osman Gonul Apaydin (Schlumberger) | Yuan Z. Ma (Exxon Corp.) | Dean P. Dubois (EnCana Oil & Gas (USA) Inc.) | Fabian Oritsebemigho Iwere (Schlumberger) | Barbara A. Luneau (Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 9-12 October, Dallas, Texas
- Publication Date
- Document Type
- Conference Paper
- 2005. Society of Petroleum Engineers
- 5.1.1 Exploration, Development, Structural Geology, 4.1.5 Processing Equipment, 5.5 Reservoir Simulation, 1.6 Drilling Operations, 5.5.7 Streamline Simulation, 1.7.5 Well Control, 5.5.3 Scaling Methods, 5.1.5 Geologic Modeling, 4.1.2 Separation and Treating, 2.4.3 Sand/Solids Control, 2.5.4 Multistage Fracturing, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.1 Reservoir Characterisation, 5.2.1 Phase Behavior and PVT Measurements, 5.8.1 Tight Gas
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This paper presents an integrated static and dynamic evaluation for selecting an appropriate geostatistical modeling method that best represents the production from a tight, stacked fluvial sandstone reservoir.The critical parameters investigated include sand body geometry, water saturation permeability, and hydraulic fracture properties.This effort involves the construction of several static and dynamic models within a one-square mile section of the field.
The study area contains about twenty-four wells with varying productivity or EUR, indicative of the reservoir heterogeneity.Several geological scenarios were developed to characterize facies/sand bodies, and multiple realizations of each scenario were investigated.Reservoir properties including porosity, water saturation and permeability were populated for each realization using sequential Gaussian simulation.
The geological scenarios incorporated variations of three widely used facies modeling algorithms: fluvial object, defined object, and sequential indicator simulation.These algorithms have their pros and cons in representing the distribution of reservoir facies.The model constraints, including facies at wellbores, global facies proportion, vertical facies probability, and areal facies probability constructed from well data were held constant between the scenarios, and infill well locations were used to evaluate the static facies prediction.
Reservoir dynamic models were used to rank individual scenario performance.The static and dynamic models share the same grid dimensions and no upscaling of reservoir properties was performed.The grid system and the recurrent data (completion, production and pressure histories) for the wells were consolidated in schedule files for input into a reservoir simulator.While there were no attempts to match the historical performance of the wells, boundary conditions and/or constraints derived from field operation were determined and used as production controls for the wells.Average hydraulic fracture properties were assigned to the fracture cells of each well, and gas production under depletion drive was simulated with the flow models thus built.The results were evaluated qualitatively and quantitatively to select the appropriate modeling workflow for constructing the static and dynamic models of the field.
The Jonah field covers an area of approximately 23,000 acres located in the northwestern Green River Basin in Sublette County, Wyoming.It produces gas from stacked fluvial channel sandstones of the Upper Cretaceous Mesaverde and Lance and Unnamed Tertiary formations at drilling depths ranging from 7200ft to 12,500ft.The reservoirs are overpressured with the top of the overpressure zone corresponding approximately with the Cretaceous-Tertiary boundary.
The field has been developed on 80-ac spacing with 2 wells per spacing unit. Several pilot drilling projects have established areas with 20- and 10-ac well spacing.To attain economical gas production rates, the wells are stimulated with multiple hydraulic fractures.Three to six individual sands were completed per stage with 4-6 stages per well.The number of stages has increased over the years and 9-12 stages are now common.
The producing section consists of approximately 2200 to 3000 feet of stacked lenticular sandstones and siltstones interbedded with floodplain shales, and minor coals that were deposited in a low-energy fluvial system over a rapidly subsiding alluvial plain. Channel-fill deposits were deposited by meandering to anastomosing rivers resulting in single and stacked, multichannel systems1. The thickness of individual sandstone units ranges from 5ft to 150ft. Heterogeneity in sandbody geometry is one of the greatest uncertainties in the reservoir.
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