高煤阶煤层气井单相流段流压精细控制方法——以沁水盆地樊庄—郑庄区块为例

目前已有的煤层气井排采控制技术未考虑煤层供水量变化的影响,抽油机冲次调节有效性差,调节频繁且容易造成流压波动,使储层受到伤害。为此,针对沁水盆地樊庄—郑庄区块下二叠统山西组3号煤层,基于煤层产水规律的井底流压控制方法理论推导,通过研究煤层气井处于单相流段时煤层的产水规律,以及煤层气井抽油机系统的排水规律,确定了井底流压的精细控制方法,并进行了现场试验。结果表明:(1)煤层气井在单相流段,随着井底流压的降低,日产水量呈线性增加,其斜率由于储层物性存在差异而有所不同;(2)研究区新投产井抽油机系统理论排水量与实际排水量呈线性关系,排量系数为0.888,单相流段煤层气井日产水量与抽油机冲次呈正比;(3)通过现场试验确定合理的日降压幅度下抽油机冲次与累积生产时间趋势线的斜率和截距,在气井排采时只要确保抽油机冲次随着累积生产时间的增加严格按该斜率线性增加,就可以保证实际日降压幅度等于合理的日降压幅度。结论认为,该方法实现了煤层气井处于单相流段时对井底流压的精细控制,对于煤层气井实现高产具有指导作用。

A fine control method of flowing pressure in single-phase flow section of high-rank CBM gas development wells: A case study from the Fanzhuang–Zhengzhuang Block in the Qinshui Basin

The existing CBM well production control technologies don't take into consideration the effect of the variation of water supply amount of coal seams, so the frequency regulation of pumping unit is less effective and so often to result in the fluctuation of flowing pressure, and consequently reservoirs are damaged. In this paper, No.3 coal seam of Shanxi Fm, Lower Permian in the Fanzhuang–Zhengzhuang Block of the Qinshui Basin, was taken as the study object. After the water production laws of coal seams when a CBM well is in the stage of single-phase flow and the drainage laws of pumping unit system in a CBM well were investigated, a fine control method was determined for bottom hole flowing pressure by theoretically deriving the bottom hole flowing pressure control method based on water production laws of coal seams. Then it was tested on site. And the following research results were obtained. First, when a CBM well is in the stage of single-phase flow, daily water production increases linearly with the decrease of the bottom hole flowing pressure, and the slope is different due to the differences of reservoir physical properties. Second, it is the linear relationship between the theoretical displacement and the actual value of the pumping unit system in the new production wells, and the displacement coefficient is about 0.888. The daily water production of a CBM well in the stage of single-phase flow is proportional to the frequency of pumping unit. Third, the slope and intercept of the frequency-cumulative production time trend line of pumping unit under the reasonable daily pressure decline amplitude are determined by conducting field tests. During the production of gas wells, the actual daily pressure decline amplitude can be guaranteed to be equal to the reasonable value so long as the frequency of pumping unit strictly increases linearly with the increase of cumulative production time according to the reasonable slope. In conclusion, the bottom hole flowing pressure of the CBM wells in the stage of single-phase flow can be controlled precisely by virtue of this method, which plays an active role in promoting the high yield of CBM wells.