四川盆地中北部二叠系茅口组复杂滩相白云岩储层地震预测——以角探1井区为例

Seismic prediction technology for complex beach facies dolomite reservoirs of Maokou Formation in central and northern Sichuan Basin:a case study of Jiaotan1 well area

四川盆地中北部(川中北)地区下二叠统茅口组广泛发育高能颗粒滩相白云岩储层,区域内角探1井茅口组的气测产量达112.8×10^(4)m^(3)/d,展现出较大的油气勘探潜力。以川中北地区具有代表性的角探1井区为例,基于茅口组储层的地质特征、测井响应和地震反射分析认为,储层预测存在2大难点:滩相白云岩沉积的非均质性强,沉积边界难以预测;储层与围岩物性差异小,导致储层响应特征不明显且受茅口组顶界地震反射影响。提出了一套适用于川中北地区茅口组复杂滩相白云岩储层的地震预测技术:首先进行古地貌恢复,确定滩相沉积相带;然后在有利相带内,基于正演模拟明确滩相白云岩地震响应,并结合去强轴方法进行地震波形、振幅属性分析,确定滩相白云岩发育区;再以白云岩发育区作为相控条件,进行叠前反演,刻画储层平面分布;最后结合茅口组断裂发育特征,进行储层综合评价。该技术包含3项主要的方法和认识:①采用基于频谱分解的相位重构方法来准确识别茅口组内的弱反射岩性界面,以提高古地貌恢复精度;②提出了波形结构可以反映茅口组滩相白云岩发育情况的认识,采用波谷数属性表征其平面分布;③采用优化的匹配追踪去强轴方法,准确去除茅口组顶界地震波强轴对储层响应的屏蔽作用。基于该技术研究成果部署的2口井的测试产气量均大于100×10^(4)m^(3)/d,且预测储层厚度与测井解释误差小于5 m,有效解决了川中北地区茅口组复杂滩相白云岩储层地震预测的难点。

The high-energy granular beach facies dolomite reservoirs are widely developed in Lower Permian Maokou Formation in central and northern Sichuan Basin.In this region,the gas production detected in Maokou Formation of Well Jiaotan1 can reach 112.8×10^(4)m^(3)/d,demonstrating significant potential for oil-gas exploration.This paper is a case study of the representative Jiaotan1 well area in central and northern Sichuan Basin.Based on the geological characteristics,well log response,and seismic reflection analysis of Maokou Formation reservoir,it is believed that there are 2 major difficulties in reservoir prediction.Firstly,the heterogeneity of beach facies dolomite sedimentation is strong,and it is difficult to predict the sedimentary boundaries;secondly,there is small difference in physical properties between the reservoirs and wall rocks,as a result of which the response characteristics of the reservoir are not obvious and it is still influenced by the seismic reflection of Maokou Formation top interface.Therefore,the paper proposes a set of seismic prediction techniques suitable for complex beach facies dolomite reservoirs of Maokou Formation in central and northern Sichuan Basin.Initially,efforts are made to restore the ancient landforms and determine the sedimentary zones of beach facies.Then,within the favorable facies zone,the seismic response of beach facies dolomite is clarified based on forward simulation,and further the seismic waveform and amplitude attributes are analyzed using the strong seismic event removal methods,thus determining the development area of beach facies dolomite.Additionally,using the development zone of dolomite as the facies control condition,prestack inversion is carried out to characterize the planar distribution of the reservoir.Finally,based on the development characteristics of faults in Maokou Formation,a comprehensive evaluation is performed on the reservoir.This technology includes 3 main methods and relevant understandings as below.(1)A phase reconstruction method based on spectral decomposition is adopted to accurately identify the weak reflection lithological interfaces in Maokou Formation and improve the accuracy of paleogeomorphic restoration.(2)The recognition that waveform structure can reflect the development of beach facies dolomite in Maokou Formation is proposed,and its planar distribution is characterized using the attributes of wave trough number.(3)An optimized matching tracking method will be used to accurately remove the shielding effect of strong seismic event at Maokou Formation top interface on reservoir response.Based on the research results of this technology,the tested gas production of two wells is greater than 100×104m3/d,and the predicted reservoir thickness and logging interpretation error are less than 5 m,effectively solving the difficulty of predicting complex beach facies dolomite reservoirs of Maokou Formation in central and northern Sichuan Basin.