深部煤层气井合理排采制度优化设计研究——以鄂尔多斯盆地东缘神府区块为例

Optimal Design of Rational Drainage Schedule for Deep Coalbed Methane Wells:Taking the Shenfu Block in Eastern Ordos Basin as An Example

近几年,我国深部煤层气开发取得重大突破,初期产量平均可达万方每天,但产量递减较快,排采制度有待优化。为保障深部煤层气长期稳定生产,提高最终可采储量,亟需开展合理排采制度优化设计研究。本研究以鄂尔多斯盆地东缘神府区块深部煤层气藏为例,根据区块19口井的历史拟合与预测结果,确定了深部煤层气井产能评价指标,分析各参数与产能评价指标之间的相关性,给出产能高、中、低三类井的识别图版;提出多目标排采制度优化设计方法,制定神府区块高、中、低产井的合理排采制度模板,并将三类井排采制度模板应用于新井。研究表明:第二年平均日产气量包含了气井短期和较长一段时间内产能的变化,可作为深部煤层气井产能评价指标。煤储层厚度、煤储层温度、原始煤储层压力、临界解吸压力、Langmuir压力、煤储层渗透率、供给半径、裂缝半长、煤粉伤害临界流速9个参数与第二年平均日产气量呈正相关关系,而孔隙压缩系数、裂缝应力敏感系数和煤粉渗透率伤害率3个参数与第二年平均日产气量呈负相关关系。根据临界解吸压力与渗透率参数交汇图可有效判别高、中、低产井;高、中、低产井分别具有各自的最优排采制度,排采速度不是越快越好,尤其低产井受煤粉影响十分显著,建议缓慢排采。研究成果可为神府区块深部煤层气新井井位优选、排采制度制定提供依据,为深部煤层气长期稳定高效开发奠定基础。

In recent years,the development of deep coalbed methane has achieved significant breakthrough in China.The initial production of deep coalbed methane can reach up to 10,000 m3 per day,but the production decreased rapidly.It is therefore urgent to optimize the design of a reasonable drainage schedule in order to ensure long-term stable production of deep coalbed methane and increase the ultimate recoverable reserves.Taking the deep coalbed methane reservoir in the Shenfu Block on the eastern edge of the Ordos Basin as an example,this work determined the productivity evaluation indicators for deep coalbed methane wells based on the history matching and prediction results of 19 wells in the block.The relationship between various parameters and productivity evaluation indicator was analyzed,and identification charts for high,medium,and low productivity wells were provided.A multi-objective optimization design method for drainage schedule was proposed,and reasonable drainage schedule templates for high,medium,and low productivity wells in the Shenfu Block were developed.The drainage schedule templates for three types of wells were applied to new wells.Results show that the second year's average daily gas production,which can indicate the short-term and long-term productivity changes of gas wells,can be used as an evaluation index for the productivity of deep coalbed methane wells.There is a positive relationship between the average daily gas production in the second year and nine parameters,including coal reservoir thickness,coal reservoir temperature,original coal reservoir pressure,critical desorption pressure,Langmuir pressure,coal reservoir permeability,supply radius,half-length of fracture,and critical flow rate of pulverized coal damage.The pore compressibility,fracture stress sensitivity coefficient,and permeability damage rate resulted from pulverized coal are negatively correlated with the average daily gas production in the second year.The intersection diagram of critical desorption pressure and permeability can effectively distinguish high,medium,and low productivity wells.High,medium,and low production wells have their own optimal drainage schedules,and faster drainage speed cannot yield better development effect.Especially,low productivity wells are significantly affected by pulverized coal,so it is recommended to drainage slowly.This research can provide a basis for the optimization of new well locations and the formulation of drainage schedule for deep coalbed methane wells in the Shenfu Block,which will lay a foundation for the long�term stable and efficient development of deep coalbed methane.