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Plano, TX, United States

Wang J.,Denbury Resources | Liu Y.,Texas A&M University
SPE Production and Operations Symposium, Proceedings | Year: 2011

Horizontal well completion and stimulation technologies are the keys to successfully develop shale gas reservoirs. The impacts of hydraulic fracture parameters, hydraulic fracture induced complex natural fracture system, and rock characteristics to well performance need to be clearly understood. Numerical simulation based methods provided a better way over other conventional methods for modeling well performance in shale gas reservoirs. However, current numerical simulation methods, dual porosity modeling and discrete modeling, have following limitations: 1) time-consuming in setting up hydraulic and natural fracture systems; 2) large computation time required. We developed a new methodology to simplify hydraulic and natural fracture systems. Since large variations in natural fracture distribution and reservoir characteristics may result in unpredictable complex fracture network that cannot be accurately represented by discrete modeling, the hydraulic fracture and hydraulic fracture induced complex natural fracture system are treated as one enhanced zone. The simplified coarse dual porosity, dual permeability simulation model enables us to evaluate the effectiveness of stimulation treatment and understand shale gas production mechanism in a short time. To validate the new methodology, simulation results of a fine-grid reference model were compared with the simplified model. The simplified model greatly decreases simulation time and provides accurate results. We applied this methodology to Haynesville shale gas wells. Historical gas production and flowing BHPs were matched. Reservoir and enhanced zone parameters were obtained after history matching, including porosity and permeability of the matrix and natural fracture system, half length, width, and permeability of the enhanced zone, as well as EUR. Simulation results indicate that if conductivities of enhanced zones are in same order shorter enhanced zone is corresponding to sharp production decline, while long enhanced zone is corresponding to relatively slower production decline. Conductivity of enhanced zone is the controlling factor for early time production performance and behaviors of flowing BHPs, while Matrix permeability and SRV half-length are the controlling factors for late time production performance. Sensitivity analyses then were conducted to quantify the impact of the reservoir characteristics and enhanced zone parameters. The simulation results provided insights into effective stimulation designs and flow mechanism for shale gas reservoirs. Copyright 2011, Society of Petroleum Engineers. Source

Palisch T.T.,Carbo Ceramics | Handren R.J.,Denbury Resources
SPE Production and Operations | Year: 2010

The evolution of fracturing technology has provided the industry with numerous advances, ranging from sophisticated fluid systems to tip-screenout designs to propagation modeling. Interestingly, these advances typically have focused on conventional designs that use a crosslinked-fluid system. However, as the development of unconventional (e.g., tight gas, shales, coalbed methane) or underpressured reservoirs has increased, so has the demand for innovative hydraulic-fracture designs. The most recent of these design changes has been the popular method of placing proppant with slickwater, linear gel, or hybrid treatments. Although our industry has significant expertise in fracture design, most of our experience has been in conventional crosslinked-fluid systems. However, there are many aspects of crosslinked-fluid design that either do not apply to slickwater treatments or, in some cases, are contrary to the requirements of slickwater treatments. This paper will begin by reviewing the motivation, benefits, and concerns with slickwater fracturing and discuss why this seemingly old method has regained popularity over conventional crosslinked designs in many reservoirs. In addition, the authors will detail some of the important theories related to slickwater fracturing, including fracture width and complexity, proppant transport and settling, and conductivity requirements. In each scenario, emphasis will be placed on the different strategy employed compared to crosslinked-fluid designs, and the mistakes or misunderstandings that are frequently made will be highlighted. Where appropriate, laboratory testing, field measurements, reference material, and other resources are presented to support the observations made by the authors. This paper will serve as a resource to any engineer or technician who is designing/pumping slickwater fracs, or who is considering this technology for potential application. By applying the concepts presented in this paper, engineers will be able to appropriately evaluate the potential benefits of using this technique in their completions, as well as draw on the experiences of others to take full advantage of this technology. Copyright © 2010 Society of Petroleum Engineers. Source

Seale S.R.,Weatherford | Cousins B.,Weatherford | Hanna R.,Denbury Resources
Society of Petroleum Engineers - SPE Intelligent Energy International 2014 | Year: 2014

As companies working in the oil and gas industry move into the Digital Energy age, they often have to deal with legacy SCADA platforms that fail to meet the challenges of supporting their growing enterprise. Intelligent asset management across a company's entire network of pipelines, plants, and producing fields requires the acquisition, management, and manipulation of large volumes of data. Without the proper enterprise strategy in place, a company often finds itself with fragmented data and applications all across the enterprise and unusable or unmanageable IT systems. These fragmented solutions often become a liability when trying to manage an asset's technology, equipment, and people. A short list of the Technical and People Challenges include: • Addressing SCADA systems that historically were managed by I&E field personnel • Multiple SCADA vendors, solutions, and versions deployed • Challenges associated with the IT responsibilities being outsourced to multiple integrators • A multiple integrator and system approach, creating installations that are unique and independent from each other • Addressing a network infrastructure that allows for enterprise visibility • Historical data warehousing that was never in scope with future needs This paper discusses an enterprise approach to SCADA that supports distributed assets across multiple vertical sectors (plants, pipelines, producing facilities). The approach has been implemented in several CO2 enhanced oil recovery (EOR) projects by Denbury Resources, as it solves the requirements for support of the process and business network,data replication, system failover, redundant control centers, and data historization and management across the enterprise. Denbury is deploying the enterprise SCADA system in a growing number of its CO2 EOR assets, which includes both projects that are being converted and new assets being added through the acquisition of properties. Copyright 2014, Society of Petroleum Engineers. Source

Dahan M.W.,Denbury Resources
73rd European Association of Geoscientists and Engineers Conference and Exhibition 2011: Unconventional Resources and the Role of Technology. Incorporating SPE EUROPEC 2011 | Year: 2011

Well Ba-E-1 was drilled in the Tompa prospect (now the Ba-IX Mining Plot) in Hungary targeting the Miocene and Cretaceous formations between 2600 and 3500 mTVD. These are tight sandstones and the expected permeabilities were in the range of 0.001 to 0.5 mD. Two hydraulic fracture treatments were performed. The first fracture treatment was in the lower part and the second treatment was in the upper part of the deepest interval. With no previous propped fracturing experience in this field, the first treatment was designed as a conventional crosslinked gel treatment to minimize the risk of a premature screenout. Following the analysis of the data from the first zone, it became clear that the average permeability was closer to the minimum expectation of 0.001 mD. Due to lower than expected stimulation effectiveness of the first fracture, and the confirmation of the low permeability, the 2nd fracture treatment was changed to a waterfrac design. This formation clearly falls into the category 'unconventional', and consequently was a good candidate for a waterfrac. This paper describes the pre-frac diagnostics, fracture execution and post-frac production evaluation of this unconventional gas well. Special emphasis is placed on the use of small volume injection tests (DFIT) to obtain an estimate of the in-situ kh, since it is impossible to perform pre-fracture welltests in such a formation. The result of the DFIT analysis is then used to constrain the post-fracture welltest analysis in a numerical simulation model that includes fracture filtrate cleanup modeling. Post-frac analysis showed that the initial proppant pack damage is high and effective fracture length is much smaller than the created length, especially with crosslinked gel. The crosslinked gel treatment was not able to cleanup effectively, and therefore showed limited stimulation effectiveness. The first ever waterfrac in a gas reservoir performed in Europe showed a more significant production improvement during the short post-frac test. The results from this well suggest that, as in North America, waterfracs appear to have better initial production than crosslinked gel fracs due to better fracture cleanup in European reservoirs with micro Darcy permeability. Copyright 2011, Society of Petroleum Engineers. Source

An apparatus is provided for maintaining a steady flow rate and pressure of a carbon dioxide stream at high pressure when a low-pressure source of the carbon dioxide varies with time. Liquid level in an accumulator that is sized to accommodate variations in supply rate is controlled by sub-cooling of liquid entering the accumulator and heating in the accumulator, the sub-cooling and heating being controlled by a pressure controller operable in the accumulator.

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