Abstract
Multistage horizontal fracturing is the key technique in developing shale gas reservoirs. In each stage, several perforation clusters will be placed to create complex fractures, and the parameters of perforation clusters are almost the same, so the production from each perforation cluster should be similar. However, in fact, production from each perforation cluster is different vastly. If the characteristics of the shale gas reservoir where the horizontal wellbore oriented through are similar, the cause that resulted in production difference may be uneven proppant distribution among perforation clusters. In order to investigate proppant distribution through perforation clusters, the theory about proppant settling along horizontal lateral is analyzed, which can provide a proper pumping rate for future experiments. Then, an experimental model to simulate horizontal lateral and perforated clusters is designed. Fresh water was pumped to transport proppant flowing into different clusters, the volume of water and proppant through each cluster was qualified. Some parameters, such as proppant concentration, sizes, flow rate, and perforation parameters, are changed in lab tests; the simulation results will be helpful in understanding the phenomenon of uneven proppant distribution in perforation clusters. There are some conclusions from the experimental results. First, proppant settling at different positions along horizontal lateral is different when the slurry is mixed by proppant and water is pumped at different rates. Meanwhile, proppants concentration also has an influence on proppants settling. The settling of proppants will impact proppants distribution among perforation clusters. Second, at a low pumping rate, uneven proppants distribution was observed mostly. When the pumping rate was increased, the phenomenon of uneven proppants distribution was decreasing. Thus, the pumping rate is the main influential factor. Third, uneven proppants distribution can be improved or even avoided by adjusting perforation parameters, such as perforation numbers and diameter.
Highlights
Multistage fracturing of horizontal wells has become the major method to produce oil and gas from low permeability reservoirs, especially from shale gas reservoirs [1,2,3,4,5]
The results showed that the flowing rate influences sand distribution highly, as shown in Figures 3 and 4
In the same pumping rate, the difference of proppant distribution along 3 perforation clusters is small at lower sand concentration, and the difference will be great at higher sand concentration
Summary
Multistage fracturing of horizontal wells has become the major method to produce oil and gas from low permeability reservoirs, especially from shale gas reservoirs [1,2,3,4,5]. E stages and perforation clusters are placed evenly in a horizontal wellbore, but, the rate of gas produced from each stage is different significantly, and recent studies have demonstrated that one in four perforation clusters is not producing and this is almost a common phenomenon in shale gas plays [6,7,8,9,10,11]. A study taken by Warpinski proved that fracture area with low proppants concentration has a negative impact on gas production, and proppant distribution in shale. When proppants carried by fracturing fluid at a high velocity are forced to change flow directions, the difference in specific gravity between proppant and fluid caused most proppant to concentrate near the lowermost perforated interval (toward toe), while the upper intervals receive mostly clean fluid without proppants [14]
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