![]() The decrease in the matrix pore pressure results in the matrix medium compaction, thereby affecting the ultimate cumulative production of shale gas wells. The third stage is that the gas in the matrix flows into natural fractures or artificial fractures under the pressure difference between the matrix system and the fracture system. The secondary fracture network is more sensitive than hydraulic fractures thus, the porosity and permeability parameters are easier to decrease under the increasing effective stress conditions. ![]() The second period is the mass-transfer process of free gas in the secondary unpropped fracture network to the hydraulic fracture. In the initial production stage, free gas in propped hydraulic fractures is transferred to the wellbore under the pressure drop near the wellbore, which can lead to a high initial fracturing fluid flowback rate and early gas breakthrough. (20) The geo-mechanical properties also exist in the multiscale gas mass-transfer process, as shown in Figure 1. The diversity of pore structure scales in shale reservoirs makes the flow mechanism of shale gas complicated, covering from the molecular scale to the macro scale. The controlled pressure mechanism can essentially be explained by the geological reservoir stress. (15,16) In the later period, production reversal may occur, and the stable production period of gas wells can be prolonged. Shale gas flow is generally restricted by setting different sizes of nozzles at the wellhead, (14) which decreases the decline rate of wellhead pressure and sacrifices the initial high production to achieve long-term stable production. (13) Pressure drop management has attracted a lot of attention in recent years. (12) Improper adjustment of the flowback rate can cause proppant backflow, reduce fracture conductivity, and even lead to reservoir damage. Among them, depressurization production means that there is no flow restriction at the wellhead, and the bottom hole flow pressure in the initial production stage is rapidly reduced to the constant pressure of the gas well. (11) According to the bottom hole flow pressure drawdown management approaches, the production behavior of shale gas wells can be divided into depressurization production and controlled pressure production. The outlet flow through nozzles is mainly adjusted to control the production pressure difference and alleviate the stress sensitivity damage to reservoirs. ![]() On the other hand, the advancement of theoretical models presents an opportunity for better representation of the managed pressure drop production process.ĭuring the production practice for shale gas formations, selecting a suitable production strategy is conducive to the production decline rate reduction and the optimal cumulative production of shale gas reservoirs. There have thus been works to improve and enhance it for use in theoretical models for shale formations. The influence of water–rock interaction on the managed pressure drawdown mechanism cannot be ignored. As observed from the current review, an accurate description of the pressure drop management mechanism is crucial for the theoretical model of the pressure control production process for shale gas wells. The key influence of managed pressured production for single wells in shale reservoirs is elaborated as well. An optimized theoretical model is therefore essential because it can lead to a precise estimation of the ultimate long-term production and capture instantaneously the actual shale gas reservoir depletion phenomenon with various production systems compared to other available methods. Among them, numerical simulations are commonly seen in cognizance of characterizing the managed pressure drawdown production period but are found to be relatively time-consuming and also computationally expensive. Each approach has its own merits and demerits. Moreover, different classifications of the managed production simulation research approaches are discussed in detail. However, clarifying the water–shale interaction physical chemistry process and developing a mathematical model that accurately describes the water–shale interaction mechanism remain a challenge. This work presents a review of the pressure drawdown management mechanisms for shale gas formations. ![]() Thereby, an adequate production system, namely, the managed pressure drop method, has been widely introduced to the industrial practice application by decelerating the wellbore pressure drop rate and ultimately improving the long-term production process. The flow capacity of shale gas reservoirs is easily impaired during the depletion process due to strong stress sensitivity.
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