滇东-黔西煤层气井排采动态影响因素及初始排水速度优化步骤

基于滇东-黔西地区40余口(排采井12口)煤层气井资料,通过单井排采动态典型指标提取和地质、工程因素综合分析,并结合数值模拟,探讨了恩洪、老厂、土城区块煤层气井排采动态影响因素,提出了相应的初始排水速度优化步骤。结果表明,研究区排采动态差异较大,其中,单井动用资源丰度、渗透率作为基础因素,决定了煤层气井产气能力,单井动用资源丰度越高、渗透率越大,产气量越高,同时,I类和II类煤体结构与III类煤体结构相比,煤层气井产气量高。初始排水速度是煤层气井排采动态的关键控制因素,排水速度较大时,即使渗透率较高,单井动用资源丰度较大,产气量仍然较低。控制初始排水速度具有双重意义:一是减缓绝对渗透率(应力敏感)降低速度,二是减缓水相渗透率降低速度。基于前述认识,通过全国煤层气开发区现行排采工作制度调研和研究区排采动态分析,指出研究区应以慢排为原则,把握阶段降压特征,提出了多煤层合采低速-阶梯降压初始排水速度优化步骤,对滇东黔西多煤层合采煤层气井生产具有一定的实际意义。

Influencing factors of drainage dynamics of CBM wells and primary drainage rate optimization in East Yunnan-Western Guizhou area

Based on the data of more than 40 wells(12 drainage wells) in East Yunnan-Western Guizhou area,the influencing factors of drainage dynamic in Enhong,Laochang and Tucheng blocks are discussed through the ex-traction of drainage dynamic typical indexes of CBM wells and the comprehensive analysis of geological and engineering factors,combined with numerical simulation and the primary drainage rate optimization steps are finally put forward.The results show that there is a great difference in the drainage dynamic of CBM wells in the study area.The producing resource abundance and permeability determine the gas production capability of CBM wells as basic factors.The higher the producing resource abundance and the permeability are,the higher gas pro-duction is.Meanwhile,the reservoirs with coal body structure Type I and II have a higher gas production compared to that with coal body structure Type III.The primary drainage rate is the key controlling factor of drainage dynamics of CBM wells.When the primary drainage rate is relatively high,even with the permeability and the producing resource abundance being high,the gas production is still relatively low.Controlling the primary drainage rate has two meanings:one is to slow down the reduction of absolute permeability(stress-sensitive),and the other is to delay the occurrence of two-phase flow,both having objective to extend the depression cone to maximum.Based on the above understanding,it is pointed out that slow drainage should be key in the study area.A low rate-ladder type pressure reduction,during primary drainage,is proposed.This pressure reduction regime has a certain practical significance for co-production from multiple-coalbeds in East Yunnan-Western Guizhou area.