古地貌对渤海湾盆地B区块太古宇暴露型潜山变质岩风化带储层裂缝发育的影响

The effects of paleogeomorphology on the development of fractures in reservoirs of weathering metamorphic zone in an exposed Archean burial hill， Block B， Bohai Bay Basin

廖新武 谢润成 周文 汪跃 刘文超 刘卫林 程奇 熊晓军 罗紫薇

Xinwu LIAO Runcheng XIE Wen ZHOU Yue WANG Wenchao LIU Weilin LIU Qi CHENG Xiaojun XIONG Ziwei Luo

古潜山是中国渤海湾盆地油气勘探开发的重要领域，渤中凹陷B区块是近年来中国东部发现的规模最大的凝析气田，该区块为太古宇暴露型潜山，古地貌在储层形成及发育过程中具有重要作用。受古地貌控制，变质岩潜山遭受风化作用时间及强度存在差异，进而影响了风化带储层的发育，尤其是影响了潜山风化带裂缝的形成。在岩心描述、成像测井裂缝解释结果、潜山古地貌恢复及古地貌划分基础上，详细讨论了古地貌对潜山风化带储层裂缝发育的影响。结果表明：①古地貌相对高部位风化淋滤作用较强，裂缝密度较大，古地貌直接影响了风化带裂缝的发育，削弱了内幕带储层的岩石力学性质，在一定程度上间接地控制了内幕带裂缝的发育；②古地貌对潜山风化带的影响深度存在差异，控制了潜山不同深度带的裂缝形成，B区块古地貌呈现明显的东、西区差异，西区风化裂缝带厚度（平均为277 m）明显大于东区（平均为193 m），西区古地貌影响的风化裂缝带深度也大于东区；③古地貌与各组系（期次）的裂缝密度呈明显相关性，即风化带的裂缝发育不仅受古地貌控制，还与各期的构造活动有关，特别是早期的构造活动（印支期）与古地貌共同控制了风化带早期裂缝的形成；④B区块发育3大高幅隆脊残丘区，残丘区裂缝最发育，地貌幅度控制着风化带裂缝的发育，对北西-南东向印支期裂缝的控制作用较强，残丘缓翼水-岩反应更充分，风化淋滤作用强，岩石力学强度降低，更易在各种应力下产生裂缝，并发生规模溶蚀，利于风化带优质储层的形成。

Burial hill is one of the important targets for oil and gas exploration and development in the Bohai Bay Basin where Block B in an exposed Archean burial hill is recently found to be hosting the largest gas condensate field in eastern China. The paleo-geomorphology is suggested to have played an important role in the formation and development of reservoirs in the field that caused differences in duration and intensity of weathering upon the burial hill of metamorphic rocks and thus shaped the development of reservoirs and even the formation of fractures in the weathering zone of the burial hill. Based on core description and image logging interpretation of fractures as well as the restoration and division of the ancient landform of the burial hill， the control of paleogeomorphology on the formation of fractures in the reservoirs of burial hill is discussed in detail. The following results are obtained： ① The weathering and leaching effect is relatively stronger at the higher parts of the paleogeomorphology， resulting in denser fractures. The paleogeomorphology directly affects the development of fractures in the weathering zone， weakens the rock properties of the reservoir in the inner zone， and indirectly controls the development of fractures in the inner zone to a certain extent. ② The depth ranges of effects of paleogeomorphology on weathering zone of buried hill are different in different areas， which controlled the formation of fractures in different depth of the burial hill. The paleogeomorphology in the east part of Block B is very different from that in the west part， with the thickness of the weathering fracture zone in the west part （277 m） significantly larger than that in the eastern part （193 m）. The depth of the weathering fracture zone affected by the paleogeomorphology in the west part is also greater than that in the east part. ③ There is a clear correlation between paleogeomorphology and the fracture density of each fracture group/system （stage）， i.e.， the fracture development in the weathering zone is not only controlled by paleogeomorphology， but also related to the tectonic activities of each period， especially the early tectonic activities （Indosinian period） which controls jointly with paleogeomorphology the formation of early fractures in the weathering zone. ④ Block B contains 3 large high-pitched ridge remnant mound areas with well-developed fractures. Fractures， especially the NW-SE-trending fractures of Indosinian period in the weathering zone are controlled by geomorphologic amplitude. More complete water-rocks reaction occurs in the gentle flanks of the remnant mounds， where the weathering and leaching effect is strong enough to reduce the mechanical properties of the rocks and facilitate the formation of fractures under various stresses and large-scale dissolution， all providing favorable conditions for the formation of high-quality weathering zone reservoirs.

10.11743/ogg20230212