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With the success of hydraulic fracturing in the US shale-gas plays, why are more operating companies not using energized fluids to minimize the use of water, decrease the amount of proppant required, and (theoretically) enhance long-term productivity? It appears that Canadians have been somewhat more receptive to the idea and are more willing to use energized fluids, with apparently positive results. Perhaps it is too early in the game to convince operators in the US to take another look at this technology with an open mind. Allow me to start a dialogue in this area. The perception that using energized fluids is more expensive to achieve the same goal could be one hurdle keeping operators from using them.
Summary This paper describes ways to optimize vertical and lateral spacing of horizontal wells in a stacked bench development up-front and, if necessary, adjust the development spacing based on early time Gas-Oil-Ratio (GOR) behavior, other diagnostic methods, and/or seismic inversion. In recent years, the Permian Basin has become the leading unconventional resource play due to, among other things, the high quality of the resource and stacked-bench horizontal well developments. Maximizing recovery and profitability in a stacked-bench unconventional play is challenging because operators must optimize both the inter-bench vertical well spacing and the intra-bench lateral well spacing. Generally, well interference can be detected by comparing well productivities, initial reservoir pressures, Stimulated Rock Volumes, and Expected Ultimate Recoveries against forecasted well performance. However, such analyses do not directly reveal whether any observed interference is due to inter-bench or intra-bench interactions. Without the ability to distinguish inter-bench interference from intra-bench interference in advance, vertical and lateral spacing optimization might be achieved only at the risk of over-capitalizing a development. This paper presents a case study in which an analysis of GOR behavior was coupled with other analyses to determine the source of interference. Stand-alone (i.e., widely-spaced) wells in each bench were found to display unique GOR characteristics. When horizontal wells in different benches interfered with one another, however, the GOR trends observed in the wells were synchronized. Wells with synchronized GORs exhibited substantial departure (better or worse) from expected performance, thereby confirming the hypothesis that they were interfering. Among wells that had synchronized GORs, in some cases, production from one well appeared to have been captured by another well, whereas in other cases, productivity of both wells were affected. It was found that the contrast in the elastic properties of the stacked benches, which was discerned from the inversion of seismic data, played a key role in the vertical interference between wells. When stacked benches have similar elastic properties, much stronger interference was observed than when the elastic properties were dissimilar. As demonstrated by previous laboratory experiments (Thiercelen et al., 1987), mineback studies (Warpinski et al., 1981; Warpinski et al., 1987), and modeling (Thiercelen et al., 1987; Barree et al.; 1998; Smith et al., 2001; Zhang et al., 2007), a large contrast in the elastic properties between benches appears to create flow barriers at the interface.
Abstract Multi-stage acid fracturing in a tight carbonate formation can be an alternative to propped fracturing as a relatively cost-effective completion treatment. However the success of the treatment depends on many factors as to whether enough conductivity by acid etching has been created, and weather the selected chemical treatment has worked well in-situ under the specific geologic environment. Thus, observation and evaluation of past practice is important to develop further optimal stimulation procedures. In this paper, an integrated methodology to conduct performance evaluation of multi-stage acid fracturing treatment in a horizontal well is presented. The method is applied to a field case in Tarim Basin in China. The integrated procedure starts with obtaining closure pressure and the formation breakdown pressure. Bottomhole treating pressure is then estimated from surface treating pressure in cases if it is not measured directly. A treatment pressure history match is then conducted to estimate the fracture geometry using commercial software. A 3-D acid fracture conductivity profile is generated using the in-house acid fracture simulator. Then using the reservoir face pressure and the acid fracture conductivity profile obtained by the acid fracture simulator, the cross-sectional flowing area created by acid fracturing fluid is estimated using pressure transient analysis. Evolution of fracture extension and acid etching during the stimulation is calculated assuming a bilinear flow regime. After production starts, a linear flow diagnostic approach provides the cross-sectional area flowing that has the flow from the matrix. This enables us to compare flowing cross-sectional area with induced area by the stimulation, which is defined as treatment efficiency. A field application based on the proposed procedure shows the effectiveness of the approach. The integrated approach provides engineers with additional information as to whether the designed acid fracturing has been performed appropriately under high closure stress field. It is eventually helpful to discuss past practice and improve candidate selectivity in a company decision making process.
Abstract The topic of inter-well communication in unconventional reservoirs has received significant attention as it has direct implications to well spacing considerations. However, it has been the observation of the authors that interference is often inferred without direct evidence of its occurrence, or without an understanding of the various mechanisms of interference. This paper presents a rigorous procedure for correctly identifying interference during a well's production cycle. First, the various mechanisms of interference are defined. Next, analytical simulations are run to reveal the expected behavior for interference through fractures and reservoir matrix. Data validation is performed, followed by a procedure for identifying interference. Finally, the data is history matched with numerical models based on the learning from the previous step. The approach is applied to an eight well pad in the Horn River Basin. Two wells were found to be in communication. From this procedure, it was possible to determine that these wells are in communication through fractures or high permeability channels. The procedure in this paper is designed to help production analysts diagnose interference and avoid common pitfalls. The workflow is generalized and can be applied to other multi-well pad completions.