SBIR-STTR Award

This project's objectives are to develop a new andquantitative model of valley-fill reservoirs and reservoirheterogeneities and to verify the model with reservoir computersimulation. Quantitative models have not yet been developed forvalley-fill reservoir oil fields because only in recent years have they been identified as having significant production. More than20 valley-fill fields now produce. Valley-fill reservoirs areformed during periods of rising sea level when riverine, marine, ormixed marine/riverine sandstones are deposited in a valleypreviously cut during lowered sea level. Abrupt lateral andvertical changes occur both within and at the margins ofvalley-fill reservoirs. Geological interpretation of flow units,pore WM, and pore distribution will be compared to reservoirparameters, including permeability and porosity distributions, in10-12 cotes from two valley-fill oil fields. Isopach ntaps andselected cross sections, faed to geologic analysis of cores, willbe constructed to show field scale heterogeneities. MiCrDheterogeneities will be analyzed using thin section analysis, x-raydiffraction mineralogy, and scanning electron analysis. Outcropsnear one of the valley-fill reservoirs will be interpreted inpreparation for a mini ter survey. Phase II will rely onthe findings of Phase I to determine which portion of the fieldsare most suitable for reservoir simulation. Simulation on themost important scales will be carried out and techniques for scale-up of geological variables will be developed and implemented mtoone or more valley-fill reservoir models.Anticipated Results/Potential Commercial Applications as described by the awardee:This project will have immediate application forindependent operators who have no research staff but who developand produce much of the oil from typical valley-fill reservoirs(2-10 million barrel size). Results of the project will beapplicable immediately to reservoir management of oil fieldsidentified as valley-fill reservoirs. Also, economic and technicalplanning for the various production stages involved in reservoirmanagement will be enhanced by delineation of types of flow unitboundaries and by determining the @ and distribution of valley-fillreservoir heterogeneities.

This project will continue to develop two new, quantitative models of valley-fill oil reservoirs with included heterogeneities and verify them with reservoir simulations. Quantitative models integrating geologic and engineering data have not yet been developed for valley-fill reservoirs to a point where they can be simulated. Only recently has the potential impact of valley_fill reservoirs been realized; more than 40 oil fields are now known to produce from valley-fill reservoirs. Three types of simulation will be employed: (1) historical reservoir simulation, (2) conditional simulation, and (3) finite element simulation of analogous outcrops. Results of simulations generated by Sim Best II (Scientific Software Intercomp) or VIP Encore (J. S. Nolan and Associates) will be compared with results of BOAST, a public domain black oil reservoir simulation mode. Geologic, production, pressure, and other data will be integrated prior to simulation. Emphasis will be on comparing flow units within the reservoirs with geologic facies and reservoir heterogeneities, which will be scaled to allow compatibility with the simulators. Phase I analysis yielded two preliminary valley-fill models: one, a predominantly river-deposited Morrow Sandstone "Stateline Trend," SW Stockholm Field, Kansas; the other, Muddy Sandstone, Thunder Creek Field, Wyoming, was deposited primarily by shoreline processes in a valley. Isopach and production maps of the reservoirs indicate great variability in thicknesses and cumulative production. Shale barriers to fiow on varying scales were found to be common. Similar vertical and lateral variability was also noted in detailed Muddy outcrop measured sections, near Thunder Creek Field. In Phase II two fields will be analyzed and simulated: a river deposited field (Sun Ranch Field, Wyoming, Muddy Sandstone) and a mixed shoreline/river deposited field ("Stateline Trend," Kansas). Detailed log analysis and petrophysical analysis will be done on all field wells that are simulated. Detailed minipermeability analysis will be carried out on a 3-D exposure of Muddy Sandstone valley-fills in Wyoming, and finite element simulation will be done to characterize heterogeneities on a scale that examines variability over less than between-well distances. Simulation runs will continue until the quantitative models are verified. The benefits derived from each of the three types of simulation will be compared and recommendations for specific applications will be made.Anticipated Results/Potential Commercial Applications as described by the awardee:The results of this project will have immediate application for independent operators who do not have access to quantitative production tools for valley-fill reservoirs. Comparison of commercial historical reservoir simulations with those generated by BOAST will provide a basis for evaluation of this widely available tool in very heterogeneous reservoirs. Results of the project will be immediately applicable to reservoir management of oil fields identified as valley_fill reservoirs. The scaling and computer techniques developed during the project for handling geologic and flow unit heterogeneities in the various types of simulations will be useful in simulating many types of complex reservoirs.