煤层气井开发效率及排采制度的研究

DEVELOPING EFFICIENCY AND THE WORKING SYSTEM OF WELLS DURING THE DE-WATERING GAS PRODUCTION PROCESS IN COALBED METHANE RESERVOIRS

分析我国煤层气井排水采气过程中井筒附近应力的变化,认为由于井筒液面下降太快,导致井筒附近渗透率降低,煤层气井无法获得长期持续的较高产量,从而使得开发效率低下。为此,从煤层气井排采工作制度方面探讨了我国低渗煤层气藏的增产问题,针对煤层低渗和压缩性大的特点,运用地下渗流力学理论,建立了煤层气井排水采气数学模型,给出了同时间条件下煤层气井排采制度的定量解,以数值模拟的方法优化了煤层气井排采的工作制度,得出逐级降压的工作制度能扩大气井压降漏斗的体积,使煤层气解析范围增大,从而增加了煤层气井的累积采气量。该数学模型及其定解为我国煤层气井在开发过程中井底压力如何降低以及降低幅度、速度控制在何种程度,给出了量的参数,为低渗煤层气井合理开采提供了一个新的途径。

After analyzing stress changes near the wellbore during the de-watering gas production process in coalbed methane reservoir, this study thought that the permeability decrease caused by falling of the liquid surface in the wellbore impaired the sustaining high production rate of the well. Therefore, this study focused on how to enhance the recovery of coalbed methane reservoirs in China from the aspects of the working system of de-watering gas production process. A mathematical model was built incorporating the low permeability and high compressibility of coalbed methane reservoir and hydromechanical theories. By this model, the well working system of de-watering gas production in coalbed methane reservoir was solved quantitatively, inferring that gradual pressure drawdown could extend the volume of the pressure drop funnel and in consequent increased the cumulative gas production from the well. In general, this model provides quantitative parameters, such as timing and range of drawdown, for the working system of wells in dewatering gas production process, and also presents a new way to reasonably exploit coalbed methane reservoir.