Fracturing measures are common practice for horizontal wells of tight oil reservoirs. Thus, production estimation is a significant problem that should be solved. However, previous models for the production of fractured horizontal wells of tight oil reservoirs have some problems. In this paper, we present a semi-analytical model based on the volumetric source method to simulate production from nonplanar fracture geometry in a tight oil reservoir. First, we developed an analytical model based on the volumetric source method in nonplanar fracture geometry with varying widths. Second, the model was coupled with fracture flow and solved by the Gauss–Seidel iteration. Third, the semi-analytical model was verified by a numerical reservoir simulator. Finally, sensitivity analysis was conducted for several critical parameters. Results of validations showed good agreement between this paper’s model and the numerical reservoir simulator. The results from the sensitivity analysis showed that (1) production increases with an increased number of fracture segments; (2) production drops more quickly with a smaller fracture half-length in the first stage, and it drops slowly with a smaller fracture half-length in the second stage; (3) cumulative production increases more quickly with a bigger fracture conductivity; and (4) cumulative oil production from a fracture with a constant width and without stress sensitivity coefficient is smaller than that from a fracture with varying widths and with stress sensitivity coefficient. This research provides a basis and reference for production estimation in tight oil reservoirs.

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.

In order to improve the recovery rate, fractured horizontal wells are widely used in tight reservoirs. In general, a complex fracture system is generated in tight reservoirs to improve oil production. Based on the fractal theory, a semianalytical model is presented to simulate a complex fracture system by using the volumetric source method and superposition principle, and the solutions are determined iteratively. The reliability of this model is validated through numerical simulation (Eclipse 2011); it shows that the result from this method is identical with that from the numerical simulation. The study on influence factors of this model was focused on matrix permeability, fractal dimension, and half-length of main fracture. The results show that (1) the production increases with the increase of half-length of main fracture and matrix permeability during the initial production stage, but the production difference becomes smaller in different half-length of main fractures and matrix permeability in middle and later stages and (2) the cumulative production increases with the increase of fractal dimension, and the increments of cumulative production in different fractal dimensions gradually increase during the initial production stage, but the increments tend to be stable in middle and later stages. This study can be used for forecasting the oil production from bottom water tight oil reservoirs with complex hydraulic fractures. It can also guide in optimization of horizontal well fracturing design to improve oil production and oil recovery in bottom water tight oil reservoirs.