煤层气L型水平井防窜气排采控制方法研究

Anti-channeling methods for coalbed methane production using L-type horizontal wells

煤层气采用L型水平井开发,可使单井稳产气量达到8000m^(3)/d以上,但由于L型水平井无沉砂口袋,无法靠重力实现气、水自然分离,易发生油管窜气,导致泵效大幅下降,制约进一步排水降压。前期通过优化排采举升工艺,油管窜气现象得到了一定缓解,但对低流压产气井和高流压产气井的治理效果仍然不理想。以沁水盆地樊庄-郑庄区块L型水平井为例,通过研究分析56口发生油管窜气井的气、水变化规律,建立了窜气严重程度评价指标,利用灰色关联度法找出影响油管窜气的主控因素,明确产生油管窜气的原因,并在优化排采制度方面提出了2种防治油管窜气的方法。结果表明:井筒环空的液柱高度是引发油管窜气的先决条件,油管窜气随液柱高度降低突然发生,当液柱高度大于75m时,出水口不窜气或以轻、中度窜气为主;当液柱高度小于75m时,以重度窜气为主,且发生窜气后其窜气程度随液柱高度的降低呈指数增大。气液比是影响窜气程度大小的关键因素,且窜气程度随气液比的增大呈对数增大,当气液比小于30时,以轻度和中度窜气为主,当气液比大于30时,以重度窜气为主。通过控制恒定高套压,采取“控压排水”法,可有效提高泵吸入口附近两相流的持液率;通过控制日产气量,采取“控产排水”法,将泵吸入口附近的气液比降低至30以下,可有效降低油管窜气程度。在此基础上,结合防窜气排采举升工艺,最终实现油管窜气的标本兼治。

Coalbed methane(CBM)production using L-type horizontal wells can yield stable single-well production of up to above 8000 m^(3)/d.However,due to the lack of sand settling pockets,L-type horizontal wells fail to achieve gas-water separation under the action of gravity.Consequently,gas channeling from tubing is prone to occur,significantly decreasing pumping efficiency and restricting further drainage and pressure reduction.By optimizing the lifting process for production in the early stage,the gas channeling from tubing has been somewhat alleviated.However,the anti-chan-neling effects remain unsatisfactory in low-fluid-pressure and high-yield gas wells.This study examined L-type hori-zontal wells in the Fanzhuang-Zhengzhuang block within the Qinshui Basin.Based on the changing patterns of gas and water in 56 wells subjected to gas channeling from tubing,this study established evaluation indicators for gas channel-ing severity.Using grey relational analysis,this study identified dominant factors influencing gas channeling from tubing,determining the causes.Furthermore,this study proposed two methods for preventing and controlling gas chan-neling from tubing to optimize the production system.Key findings are as follows:(1)The annular liquid column height in the wellbore is proved to be the prerequisite for gas channeling from tubing.Gas channeling from tubing can occur suddenly with a decrease in the liquid column height.Liquid column heights above 75 m suggest the absence of gas channeling or the occurrence of mild/moderate gas channeling primarily at the outlet,while those below 75 m are pre-dominantly associated with severe gas channeling.Moreover,gas channeling severity increases exponentially with a de-crease in the liquid column height.(2)The gas-liquid ratio is identified as a critical factor affecting gas channeling sever-ity,which increases logarithmically with the former.Gas-liquid ratios below 30 suggest mild/moderate gas channeling primarily,whereas those above 30 are principally associated with severe gas channeling.(3)The pressure-controlled drainage method,by remaining constant high casing pressure,can effectively enhance the liquid holdup of the two-phase flow near the pump inlet.The production-controlled drainage method,by controlling the daily gas production,can re-duce the gas-liquid ratio near the pump inlet to below 30.Both methods,which can effectively alleviate the gas channel-ing from tubing,combined with the anti-channeling lifting process for production,can jointly eliminate gas channeling from tubing.