## 1 Introduction  
The production of water from gas producing wells is a common occurrence in gas fields. It is attributed to one or more of several reasons such as normal rise of gas-water contact, water coning or water fingering [1; 2; 3; 4]. Water coning occurs in gas reservoirs with the edge-and-bottom aquifer drive, and water will flow into the wellbore from below and above of the perforations and consequently interfere with gas production [5]. Water coning is a common problem which increases the cost of producing operations and raises some environmental problems related to water disposal, and reduces the efficiency of the depletion mechanism and the overall recovery [6]. Thus, understanding the questions such as water invasion in gas reservoirs and its effects on recovery factor is significant for predicting gas productivity and optimizing extraction conditions. Water invasion is a complex phenomenon observed in oil and gas reservoirs, which will occur due to pressure gradients close to the production well and the imbalance between the viscous and gravity forces around the completion interval [7; 8]. There are three essential forces controlling the mechanism, which includes the capillary, viscous and gravity forces [6]. With the change of pressure drawdown, the viscous force pushes the gas phase into the production well, and the lift up of the gas-water interface will be caused by the dynamic pressure distribution near the production well [6; 9; 10; 11]. In contrast, the gravity force will cause water to remain in the gas saturated resign of the reservoirs. When the dynamic force at the wellbore exceeds the gravity force, the pressure gradient will cause the local gas-water contact to rise upward, which will contribute to water invasion and interfere with gas production. Some studies on water invasion in gas reservoirs and its impact on gas productivity have been considered in the past. [PERSON] and [PERSON] [12] studied the water coning phenomenon and demonstrated clearly that water coning would occur at high pressure drop. [PERSON] [13] pointed out that the gravity force was dominant at initial reservoir conditions, and the viscous force would arise to part of the controlling mechanism when the pressure drawdown increased. [PERSON] et al. [14] and [PERSON] et al. [15] analyzed the problem of water coning in naturally fractured reservoirs using experimental work and field data, respectively. [PERSON] et al. [16] and [PERSON] et al. [4] performed the effects of the reservoir properties on water coning with the numerical simulation. [PERSON] et al. [17] and [PERSON] et al. [18] established a mathematical model to predict water properties and the performance of water invasion with the data of gas and water production. [PERSON] et al. [19] used a coning radial model to evaluate the occurrence of coning in naturally fractured reservoirs. [PERSON] et al. [20] and [PERSON] et al. [21] used reservoir cores to analyze the effects of different aquifers on water invasion. [PERSON] [7] proposed a fully coupled poroelastic multiphase fluidflow numerical model to understand the water coning phenomenon in naturally fractured reservoir under the effects of various rock and fluid properties. So far there has been a lot of research work carried out on the performance of water invasion in gas reservoirs. However, water invasion of gas reservoirs is not fully understood and many uncertainties still exist in the process. Hence, there is a necessity to understand water invasion and the effects of these reservoir and production parameters on the problem so as to optimize gas productivity in gas reservoirs. In this study, the experimental system of water invasion in gas reservoirs with the edge-and-bottom aquifer was established, and the elastic expansion of water and gas was considered. Seven full diameter core samples with dissolved pores and fractures were designed and the physical simulations of water invasion in carbonate gas reservoirs were conducted.