原始地层条件下深部煤层气钻前节理煤岩破碎可靠性预测及分级标准研究

Accurately predicting joint coal crushing degree under the condition of original formation will greatly reduce the risk of deep coal formation drilling. At present, very little research is carried out for this problem, mainly due to the randomness of coal crushing caused by the uncertainty of the coal crushing influence factors. For this reason, the deep joint coal crushing criterion is firstly determined by granular flow true triaxial numerical experiments and laboratory experiments under the condition of original formation. Then, on the basis of obtaining distribution functions of joint coal crushing influence factors, the reliability method is introduced to establish prediction model of coal single point crushing, and the corresponding classification standard is proposed based on dimensionless crushing coefficient of given reliability index. Again, the mapping relation between coal crushing influence factors and logging information to be drilling is established, and the joint coal crushing reliability prediction method is proposed along the direction of horizontal well trajectory. Finally, on the basis of obtaining the stress field of deep coal formation using fine inversion method, the coal crushing reliability prediction method of deep reservoir plane is proposed. Through the above research, combined with the field tests, a set reliability analysis method to predict deep joint coal crushing degree is established. It has a scientific significance to reduce risk of China's deep coal formation drilling, maintain wellbore stability, optimize the location of drilling well and design orbit position of multi-branch horizontal wells.

准确预测原始地层条件下节理煤岩破碎程度将极大降低深部煤层气钻井风险。目前针对这一问题的研究非常少，主要原因在于煤岩破碎影响因素的随机性引起了节理煤岩破碎的不确定性。基于此，拟首先利用细观离散元的颗粒流真三轴数值试验和室内实验确定原始地层条件下深部节理煤岩破碎准则；然后，在获取节理煤岩破碎影响因素分布函数的基础上，引入可靠性方法提出节理煤岩单点破碎预测模型，并建立基于给定可靠度指标下无量纲破碎系数的分级标准；再次，通过建立节理煤岩破碎因素与待钻井测井信息间的映射关系，提出水平井井眼轨迹方向节理煤岩破碎可靠性预测方法；最后，以精细反演获取的深部煤层地应力场为基础，提出煤储层平面破碎分级可靠性预测方法。通过以上研究，并结合现场应用建立一套满足现场要求的节理煤岩破碎预测方法。该研究对降低我国深部煤层气钻井风险、保持井壁稳定、优化钻井井位及设计水平井多分支轨道方位具有重要科学意义。

准确预测原始地层条件下节理煤岩破碎程度将极大降低深部煤层气钻井风险。目前针对这一问题的研究非常少，主要原因在于煤岩破碎影响因素的随机性引起了节理煤岩破碎的不确定性。基于此，本项目首先利用室内实验确定原始地层条件下深部节理煤岩破碎准则；然后，在获取节理煤岩破碎影响因素分布函数的基础上，引入可靠性方法提出节理煤岩单点破碎预测模型，并建立基于给定可靠度指标下无量纲破碎系数的分级标准；再次，通过建立节理煤岩破碎因素与待钻井测井信息间的映射关系，提出水平井井眼轨迹方向节理煤岩破碎可靠性预测方法；最后，以精细反演获取的深部煤层地应力场为基础，提出煤储层平面破碎分级可靠性预测方法。本项目研究成果在ZP-05二开以下层段进行了预测，预测结果表明：（1）易破碎煤层段为784-785m，破碎系数为0.8-1.0，钻进时应尽量避开，以免发生煤层破碎、井眼垮塌现象。（2）稳定煤层主要分布在781-784m煤层段，破碎系数为05-0.7（C级较弱破碎），钻进时宜在此段穿行。另外，煤储层平面破碎分级预测模型在晋城区块得到具体应用，预测结果表明：晋城地区破碎系数在0.2-1.32之间；晋城地区的破碎系数由西北到东南增大，高值区集中分布在断裂构造带附近；晋城地区的西北部区域煤岩破碎系数较小。