鄂尔多斯盆地东北缘神府区块南部8+9号煤层地应力评价方法与应用

Evaluation method and application for in-situ stress in No. 8+9 coal seam, southern Shenfu block, northeastern margin of Ordos Basin

吴嘉伟 汤韦 祝彦贺 王存武 田永净 訾敬玉 杨江浩 时贤

WU Jiawei TANG Wei ZHU Yanhe WANG Cunwu TIAN Yongjing ZI Jingyu YANG Jianghao SHI Xian

1. 中海油研究总院有限责任公司, 北京 100028; 2. 中海油能源发展股份有限公司 工程技术分公司, 天津 300452; 3. 中国石油大学(华东) 石油工程学院, 山东 青岛 266580

1. CNOOC Research Institute Co., Ltd., Beijing 100028, China; 2. CNOOC EnerTech-Drilling & Production Co., Tianjin 300452, China; 3. School of Petroleum Engineering, China University of Petroleum (East China), Qingdao, Shandong 266580, China

现今地应力方向和大小影响着煤层水力压裂缝的延伸，是煤层气井网部署、压裂设计的重要地质参数。合理评价煤层现今地应力方向和大小，对煤层气勘探开发具有重要意义。以鄂尔多斯盆地东北缘神府区块南部8+9号煤层现今地应力方向和大小为研究内容，基于阵列声波测井、微地震监测和成像测井，评价煤层及顶底板现今最大水平主应力方向；在注入—压降实测地应力参数约束下，确定煤层组合弹簧模型参数，并计算煤层现今地应力大小。结果显示，研究区东部8+9号煤层及顶底板现今最大水平主应力方向整体近NNE向，西部最大水平主应力方向可能受大量的压裂改造和不活动断层周围应力场扰动，发生不同方向偏转；20口井地应力测井计算结果显示，垂深1 902～2 181 m的8+9号煤层垂向主应力范围47～54 MPa，最小水平主应力范围35～44 MPa；最大水平主应力范围42～50 MPa，侧压系数小于1，表现为正断层地应力状态。研究区东部NNE向最大水平主应力方向是经历中新生代印支期SN向挤压、燕山期NNW向挤压和喜马拉雅期NNE向挤压的继承。考虑东部裂缝预测区叠加不同构造阶段平均NNW走向的天然裂缝的分布和NNE最大水平主应力方向正断层地应力状态下NNE向竖直压裂缝的延伸模式，以提高水平井大规模极限体积压裂产量为目标，建议在垂直现今NNE向最大水平主应力方向和垂直NNW向平均天然裂缝走向的水平井方位区间内，综合利用天然裂缝产能和人工压裂缝产能进行水平丛式井布井，并进一步对地应力方向和天然裂缝参数进行精细化表征，以指导施工压裂设计，提高煤层气产量。

The direction and magnitude of the present in-situ stress influence the propagation of hydraulic fractures in coal seams, making it a key geological parameter for coalbed methane (CBM) well network deployment and fracturing design. Accurate evaluation of the present in-situ stress direction and magnitude in coal seams is crucial for CBM exploration and development. This study focused on the direction and magnitude of the current in-situ stress in the No. 8+9 coal seam in the southern Shenfu block, northeastern margin of the Ordos Basin. Array acoustic logging, microseismic monitoring, and imaging logging were used to evaluate the direction of the present maximum horizontal principal stress in the coal seam and its roof and floor. Under constraints of the current in-situ stress magnitude from injection/falloff tests, parameters for the composite spring model were determined, and the current in-situ stress magnitude was further calculated. The results showed that the direction of the present maximum horizontal principal stress for the No. 8+9 coal seam and its roof and floor in the eastern part of the study area was nearly in the NNE orientation. In the western part, the directions of the maximum horizontal principal stress may deviate due to stress field disturbances around inactive faults and hydraulic fracturing activities. In 20 wells, calculations of the in-situ stress showed that the vertical principal stress in the No. 8+9 coal seam with a vertical depth of 1 902-2 181 m was 47-54 MPa. The minimum horizontal principal stress was 35-44 MPa, and the maximum was 42-50 MPa. With a lateral pressure coefficient less than 1, it was in the normal faulting stress state. In the eastern part of the study area, the NNE-oriented maximum horizontal principal stress was sequentially evolved from the SN-oriented compression during the Meso-Cenozoic Indosinian stage, the NNW-oriented compression during the Yanshanian stage, and the NNE-oriented compression during the Himalayan stage. Considering the distribution of natural fractures with an average NNW orientation during different tectonic stages, as well as the propagation pattern of NNE-oriented vertical hydraulic fractures under the normal faulting stress state with NNE-oriented maximum principal horizontal stress in the eastern fracture prediction area, it was recommended to deploy horizontal cluster wells within the azimuthal interval perpendicular to the current NNE-oriented maximum horizontal principal stress direction and the average NNW-oriented natural fracture direction. This approach aims to enhance production through large-scale extreme volume fracturing in horizontal wells by integrating the productivity of natural fractures and induced hydraulic fractures. In addition, the in-situ stress direction and natural fracture parameters should be further characterized in detail to guide fracturing design and improve CBM production.

中国海洋石油有限公司重大项目课题“煤层气地质工程关键参数表征及甜点区评价技术”(KJGG2022-1001)和中海油研究总院自立课题“临兴—神府深层煤储层含气性及主控因素研究”(2023-ZXZL-FCG-02)联合资助。

https://doi.org/10.11781/sysydz2025010027