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The gas reservoir of the second member of the Dengying Formation in Pengtan 1 well area is a typical ultra-deep carbonate bottom water gas reservoir, water invasion is an important issue affecting the effectiveness of gas reservoir development. The gas reservoir is currently in the early stages of evaluation for development, lack of understanding of water invasion mechanisms in gas reservoirs makes it difficult to develop a development strategies. Based on the existing production data and geological data of the gas reservoir, the mechanism model of single wells in different development zones was established by numerical simulation, to predict the way water invasin and to analyze the key factors affecting water invasion. Resalts show that different types of reservoir barrier layer in the Pengtan 1 well area are developed, the phenomenon of water being blocked by the barrier layer is significant, the overall manifestation of water invasion mode is water cone type and water crest type. The production allocation and the height of water avoidance are the main controlling factors affecting the degree of water invasion and the development effect of the two types of development areas. The understanding of water invasion mechanism obtained by thesis analysis provides technical support for the development strategies of Pengtan 1 well area. [ABSTRACT FROM AUTHOR]

Deep tight gas reservoirs are one of the important unconventional gas reservoirs. Deep burial, tight reservoirs have many characteristics, including diverse accumulation patterns, multiple accumulation regulations, low natural energy generation, complex gas–water relationship, and intricate seepage mechanism. These features of gas reservoirs put forward the requirement for new methods for a reasonable production allocation of horizontal wells and optimization of such allocations from the perspective of stress sensitivity. While CO2 huff-and-puff-based models, numerical simulation models, and thermos-hydrodynamic models have been built to solve these issues, there is still a lack of theoretical guidance for reasonable production allocation, especially with the edge-water problem. Here, we present a new one-dimensional mathematical and physical model to capture the stable movement of the gas–water interface in deep tight edge-water gas reservoirs. Our results show that there is a starting pressure in deep tight gas reservoirs. The starting pressure gradient increases with the growth of water saturation, which is far greater than the starting pressure gradient of medium, shallow gas reservoirs under the same water saturation. In addition, by considering the stable movement of the gas–water interface under the starting pressure, we found that the gas well has a larger upper limit of production differential pressure, a smaller seepage velocity, and a lower upper limit of production allocation. Finally, we make a comparison between our model results and production characteristics of real gas wells and find a consistency between the model results with real data. Our model provides a theoretical framework for reasonable production allocation of gas wells in deep tight gas reservoirs with the edge water.

Reasonable production allocation of tight sandstone gas reservoirs is an important basis for efficient development of wells. Combining multiple mathematical models, the modified flowing material balance equation was established considering the variation of viscosity and compressibility, and a reasonable production allocation process was developed. The results show that: ① The flow material balance method ignores the change of compressibility, viscosity and deviation coefficient in the calculation. Compared with the results calculated by the material balance method, the results of the flow material balance method are smaller. ② A modified flowing material balance method is established, verified by the production of 670 wells in the study area during stable period. Compared with the open flow rate method, the error of dynamic reserve allocation method is smaller, with an error of 0.07%. ③ When dynamic reserves are used to allocate production, the initial decline rate of wells is reduced by 74.65% on average, the production on stable period increases by 21.28%, and the time increases by 1.79%. This study provides support for dynamic reserve calculation and reasonable production allocation of gas wells in the study area, and has important guiding significance for the formulation of reasonable development plan and economic and efficient development of tight sandstone gas reservoirs.