Geology

At Rozet Field, the lack of abundant core analyses or modern logs necessitates the adoption of more assumptions than usual in order to estimate OOIP and remaining recoverable reserves. Two different methods for calculating the recovery efficiency of the waterflood were applied withinnine 5-spot patterns resulting in maximum rates of 40% and 30% respectively. Average recovery factors in the combined 5-spot patterns are 27.5% and 24.4% respectively. Both values indicate the waterflood is probably not as effective as it could have been when compared to similar fields producing from the Muddy Formation.

The calculated OOIP for the Muddy Formation at Rozet is about 74.7 million barrels, of which a little over 19 million barrels have been recovered. The recovery factor for the field is then about 25.5%. If a 40% recovery factor is achievable with an efficient waterflood, then the remaining recoverable oil reserves from the Muddy Formation at Rozet Field are approximately 10.8 million barrels. This magnitude of a target should warrant further investment in improved and enhanced recovery methods there.

At nearby Windmill Field, secondary recovery has yet to be implemented in the Muddy reservoir. Wireline log suites containing porosity logs in this field enable more confidence in the geologic mapping and OOIP calculations than at Rozet. Cumulative oil production there is 677,735 barrels, resulting in a recovery factor of about 14.8%. Assuming the clay content does not vary significantly from that observed at the adjacent Rozet Field, a well-designed waterflood should be effective at increasing production in Windmill Field. If a recovery factor of 40% could be achieved by implementing secondary recovery efforts there, it could result in the production of an additional 1,157,465 barrels of oil.

• Nine different reservoirs in seven fields have employed fieldwide CO2 EOR in Wyoming.
• Between 2010 and 2020, incremental oil recovery from the nine CO2 EOR projects accounted for over 10% of Wyoming’s total oil production.
• Wyoming is not constrained by CO2 sources that can be used for EOR projects.
• Wyoming is also not constrained by fields potentially amenable to CO2 EOR.
• Wyoming is not constrained by pipeline capacity for additional CO2 transport, but is hampered by the existing pipeline system not reaching many of the best-potential fields, especially in the Big Horn Basin.
• The most successful CO2 floods resulted from proper reservoir characterization and associated optimized project design. Wyoming has seen incremental oil recovery from individual CO2 EOR projects as high as 18% of OOIP and volumes as high as 30 million barrels.
• Where net CO2 efficiencies could be calculated, CO2 efficiency is as low as 6 Mcf/bbl of incremental oil recovered, which compares very favorably to other successful projects around the world.

Reservoir characterization and predictive modeling has provided options for enhancing production in a recently discovered trend in the Muddy Formation near Hirsch Field, in northeastern Campbell County, Wyoming. This report outlines the procedures followed to develop a detailed 3-D geologic model of the Muddy Formation in the Hirsch area and provides the results of simulations run on 73 different scenarios for developing the reservoir. This study can serve as a template for operators interested in exploring possible ways to improve production in their own fields.

Thermal maturity, the degree to which the total organic carbon in a formation has been transformed from kerogen to producible hydrocarbons due to heat and pressure, is an important measure for not just the quality of a source rock, but also helps for delineating areas more favorable for unconventional drilling. EORI’s report of thermal maturity of the Mowry Shale in the Powder River Basin provides a detailed map based on a large public T_max data set.

Key observations include:

• Nearly all of the Mowry deeper than 8000’ currently generates hydrocarbons
• The basin axis has shifted slightly westward since the Mowry began generating hydrocarbons
• The Mowry 8000’ line plays an important role in demarcating the over-pressured Mowry and related clay diagenesis.
• The maximum maturity levels in the Mowry are in the “wet gas” stage

Wyoming, perhaps more than any other state, is dependent on revenues generated from the development and sales of minerals within its borders and has a vested interest in ensuring that its resources are properly and efficiently exploited. Maximizing the efficiency of oil and gas production in Wyoming is one of the primary goals of the Enhanced Oil Recovery Institute (EORI). Potential methods or practices that can improve or enhance the recovery efficiency of oil and gas production in the state are of paramount interest. Likewise, those policies or practices that hinder such efforts are also important to discuss.

Wyoming has nearly one billion barrels of proved oil reserves, a significant portion of which is still on primary production. Assessing the potential for secondary recovery from current oil fields is always a daunting task and requires evaluations regarding whether any given field will respond favorably to secondary recovery efforts.

This paper makes general assumptions regarding the feasibility of using a water flood to enhance oil recovery in a field based on publicly available data. The conclusions resulting from these assumptions are meant to be a guideline for the potential of future water flooding and are not meant to provide detailed evaluations of any given field’s ultimate recovery.

Ash Minnelusa Unit Conclusions

• Monitor, monitor, monitor. Make changes based upon reservoir response.
• Improved understanding of the problem improves process application and results
• Volumetric sweep (gels) should be applied before mobility control
• Implement gel processes early for maximum benefits
• Incremental oil expected to exceed 400,000 BBLS (18.4%%5 OOIP) for $0.88/BBL
• Field experience is critical with gel processes. Experience at Ash can be applied to other reservoirs

Background and objective

How do the high K strikes in core data possibly impact oil production Ash Creek field in Pilot 3?

Outline:

• Introduction & model settings
• Comparison of the simulation results
• Primary analysis of Ash Creek data
• Conclusions

Conclusions

1. The synthetic models of Pilot 3 area are generated and the simulations are completed.
2. The high values of core permeability do impact the production, injection efficiency, and sweep efficiency.
3. In general, an uniform permeability distribution over the entire field is better for high production, high injection and high sweep efficiency over the entire field.
4. However, in a small local area, cells having high permeability seems better for production. seems better for production.
5. High heterogeneity of the field made a high remaining oil in place and a high homogeneity field will produce a high amount of oil.

Polymer-augmented waterflooding of the Minnelusa in Wyoming has proven to be a successful method for improving production in most cases compared to normal waterfloods. Polymer is a lowcost, low-risk option when considering a method for enhancing production of a particular field. Its primary function is to improve the mobility ratio of the injected water by increasing its viscosity, thereby improving the volumetric sweep and conformance within the reservoir.

Advantages of using polymer include: (1) low cost, (2) preventing early water breakthrough, (3) improving volumetric sweep and conformance, (4) increasing oilwater ratios, (5) mobilizing oil that would likely have been bypassed under normal waterflood conditions, (6) mitigating heterogeneous permeabilities within the reservoir, and (7) other enhanced oil recovery injection technologies can still be applied after the polymer flood. Most, but not all, Minnelusa fields examined exhibited improved recoveries using polymer compared to fields under conventional waterfloods. Uneconomical polymer floods can be caused by a variety of factors, chief of which is the failure to properly understand the internal architecture of the reservoir prior to initiating the flood.

The authors use multivariate statistics to highlight best practices in the drilling of Codell and Niobrara reservoirs of the northern Denver-Julesburg (DJ) Basin in southeastern Wyoming. The conclusions in this paper differ from a 2017 report by the Wyoming State Geological Survey on the same topic and illustrate why simple crossplots are not sufficient to properly analyze plays where a number of variables must be addressed and weighed simultaneously.

For the Codell, this study reveals that the attributes of Proppant Volume, Horizontal Length, Gas-Oil Ratio (GOR), and Treatment Rate have the greatest influence on 6-, 12-, and 18-month cumulative oil production. By examining the individual attribute responses, the current best design in the Codell is a lateral length of at least 9,600 feet (ft), a job size of 12 million (MM) lbs, a treatment rate of at least 40 barrels per minute (bpm), and a GOR of 570 standard cubic feet per barrel (scf/bbl). The type curves from decline curve analysis provided predictive monthly production. The best EURs were obtained with the optimized design and yielded better overall economics when entered into the economic model.

For the Niobrara, a 9MM lb job size with a lateral length of 10,000 ft, a GOR of 900 scf/bbl, and a treatment rate between 40 and 45 bpm is optimal. Due to lack of available pricing data and the inability to generate valid type curves of production, an economic analysis could not be conducted for the Niobrara.