Gas production from each perforation cluster has an obvious difference along with the horizontal wellbore in shale gas reservoirs. Some special perforation clusters evenly do not produce any gas, which means that those perforation clusters are not fractured. In shale gas reservoirs, only when the shale gas section was fractured with equal volumes of fracturing fluids, gas can be produced evenly. In this study, a stress theory around the perforation tunnel considering the stress around the wellbore and an induced stress by leaking of the fluid and the tunnel is presented. The results show that (1) fractures will quickly be created at two of the three perforation clusters and then the fracture of the cluster initiates. (2) The rate through each cluster is different, and the fracture volume created will have a big difference. (3) The fracture distribution between three perforation clusters are different, thus shale gas production also will be different. The theory and the method presented in this paper, can be used for different reservoirs besides shale gas reservoirs, thus it can be applied and referred widely.

A semianalytical coupled reservoir/wellbore model based on the volumetric source for horizontal wells of sulfur gas reservoirs is presented, which considers sulfur deposition and permeability heterogeneity. Compared to the results without considering the sulfur deposition effect, the results of this paper model is better fitted to field production data and average relative errors of two simulated results are 8.37% (considering sulfur deposition) and 23.38% (not considering sulfur deposition). Based on the model, we perform sensitivity in terms of various sulfur depositions, producing pressure drop, and permeability contrast. Results show that the production decreases with increased sulfur deposition, and the flow rate along the wellbore in the horizontal well decreases because of sulfur deposition. The production without and with sulfur deposition increases with increased producing pressure drop, while the production without sulfur deposition is higher. Also, higher producing pressure drop causes a higher nonuniform inflow profile along the horizontal well. Sulfur deposition can reduce a nonuniform biased inflow profile along the horizontal well in heterogeneous sulfur gas reservoirs, but the horizontal well production is reduced. Therefore, sulfur deposition is crucial for the production prediction and inflow profile along the horizontal well in heterogeneous sulfur gas reservoirs.

Sour gas reservoirs are an important part of unconventional gas reservoirs, which are widely distributed in the world. However, elemental sulfur deposition, channel plugging, and productivity reduction consequentially occur in the development of high sour gas fields as pressure drops. The accurate prediction of sulfur deposition is a very important work for sour gas reservoirs. In this paper, a fractal model is presented for predicting elemental sulfur saturation in the presence of natural fracture. The model takes into consideration the effects of non-Darcy flow. In addition, the influence parameters such as fractal dimension, fractal index, and non-Darcy flow are studied. The results showed the following: (1) sulfur deposition was overestimated by Hu’s model, and this paper model is more accurate for prediction of sulfur deposition; (2) elemental sulfur deposition decreases with the increase of the fractal dimension, while elemental sulfur deposition increases with the decrease of the fractal index; and (3) non-Darcy flow should be considered because it causes a faster rate of sulfur deposition. This research will provide a basis and reference for predicting elemental sulfur saturation in the presence of natural fracture for sour gas reservoirs.

Detailed information is provided for the design and construction of nitrogen drilling in a coal seam. Two prototype wells are considered. The Guo model is used to calculate the required minimum gas injection rate, while the Finnie, Sommerfeld, and Tulsa models are exploited to estimate the ensuing erosion occurring in pipe strings. The calculated minimum gas injection rates are 67.4 m 3 /min (with water) and 49.4 m 3 /min (without water), and the actual field of use is 90-120 m 3 /min. The difference between the calculated injection pressure and the field value is 6.5%-15.2% (formation with water) and 0.65%-7.32% (formation without water). The results show that the Guo model can more precisely represent the situation of the no water formation in the nitrogen drilling of a coal seam. The Finnie, Sommerfeld, and Tulsa models have different sensitivities to cutting densities, particle size, impact velocity and angle, and pipe string hardness.

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