天然气水合物钻采一体化模拟实验系统及降压法开采初步实验

An integrated experimental system for gas hydrate drilling and production and a preliminary experiment of the depressurization method

现有的天然气水合物(以下简称水合物)开采技术实验研究通常在较小尺寸的模拟实验装置中进行,由于反应釜样品尺寸较小,导致明显的边界效应且实验结果难以在现场中得到应用,因而研发大尺寸水合物综合开采实验系统刻不容缓。为此,针对我国南海神狐海域泥质粉砂型水合物储层,基于降压法开采思路和工艺流程,研发了一套水合物钻、采一体化模拟实验系统,主要包括主体高压装置、钻采一体化、气液供给、围压加载、回压控制、气液固分离及在线监测、温度控制、数据测控与后处理等模块;利用该系统进行了冰点附近CO2水合物初步开采模拟实验;基于实验结果建立了数据获取及分析的基本流程,初步获得了在降压法开采CO2水合物过程中储层的温度、压力场变化以及产气、产水规律。实验结果表明:①该实验系统可模拟实际地质条件制备接近海洋水合物储层的样品,通过电阻层析成像技术实时监测水合物成藏与分布情况;②该实验系统还可模拟钻井、降压开采工艺与过程,实时监测出砂与管道流动等过程中产气量、产水量、产砂量、温度、压力等多个物理参数的变化情况,实现试采全过程的实验模拟。结论认为:①在出口压力一定的情况下,CO2水合物的产气、产水速率具有很大的波动性;②CO2水合物分解过程中储层温度分布不均匀,最大的温度降幅为5℃,表明水合物分解呈现出非均一性与随机性。

The current natural gas hydrate extraction experimental research has always been carried out in a small-scale simulation test device, and the resulted boundary effect is so obvious due to the small size of samples in the reaction kettle that the experimental results will be difficult to apply in the field. In view of this, aiming at the clayey-silt gas hydrate reservoir in the Shenhu area, South China Sea, a set of integrated experimental system for the drilling and exploitation of gas hydrate is developed innovatively based on the idea of depressurization method and the technological process. This experimental system consists of high-pressure system, drilling simulation module, liquid supply module, gas supply module, confining pressure loading module, back-pressure control module, output separation module, temperature control module, data acquisition module and operation platform. With this experimental system, the samples similar to marine hydrate formations were prepared from the experimental system with the actual geological surroundings simulated. The electrical resistance tomography was used to real-time monitor the dynamic distribution of gas hydrate in sediments inside the high-pressure vessel (521 L). This experimental system can also simulate the process of wellbore drilling in hydrate reservoirs and depressurization extraction, and realize the real-time monitoring of parameters in the whole trial production process such as gas production, water production, sand production, temperature, pressure, etc. We also carried out a preliminary experiment on the CO2 hydrate extraction via the depressurization method by using this simulation experimental system. On this basis, the fundamental procedures for data access and analysis were thus established and the variation of temperature and pressure fields and gas/water output laws in the reservoirs were both achieved in the process of CO2 hydrate extraction by the depressurization method. The results show that (1) the gas production and water production rate fluctuate greatly even at a constant export pressure;(2) the reservoir temperature distribution is uneven during hydrate decomposition, and the maximum temperature is decreased by 5 ℃, suggesting that the hydrate decomposition is heterogeneous and stochastic. The abundant and credible experimental results based on this system are expected to provide important data support for marine gas hydrate production tests.