Research On Exploration And Estimation Technologies For Subtle Reservoir In Slope Of Qikou Sag

Based on the systemic collection and analysis of the previous definition and classification of subtle reservoir and the current domestic and international researches and development trend of subtle reservoir, this thesis summarized the reservoir-forming condition, type and hydrocarbon distribution of the subtle reservoir in Qikou sag, and systemically studied and proposed the exploration methods and technologies for subtle reservoir in slope of Qikou sag for the first time. These results may guide the exploration of subtle reservoir in the region. Practically, some favorable traps had been found in slope of Qinan and Qibei, which have made great achievements and marked new breakthrough in exploration of subtle reservoir in Dagang prospect.By studying exploration and estimation technologies for subtle reservoir in slope of Qikou sag, major fruits are achieved as follows:1. It is defined that the evolution of Qikou sag is the key attribution for forming the subtle reservoir;the half graben structure is the major factor to decide the type and distribution of subtle reservoir;and major types of subtle reservoir in Qikou slope are stratigraphic unconformity, lithologic updip pinchout, sandstone lens, stratigraphic overlap, diagenetic trap and lithology of structural settings.2. By using 3D seismic data, logging data, core data and cuttings data, sequence stratigraphy study was made for Tertiary in Qikou sag. Through identification, classification and correlation of the sequence, stratigraphic framework of Tertiary sequence was established. Meanwhile, internal sandbody in Sha-3 Member and limestone sublayer in Sha-1 Lower Member was finely classified and correlated under the stratigraphic framework. Biogenic limestone in Sha-1 Lower Member and 3 sets of sand beds in Sha-3 Member were defined as major studied units.3. Through the observation and analysis of core and electrofacies, 7 types of sedimentation were identified in Eogene in Qikou sag, i.e. fan delta, coastal subsea apron, lake-delta, longshore bar, gravity flow, lake and carbonate tableland. Fan delta and coastal subsea apron were widely developed in Sha-3 Member and a few in Sha-1 Member;during the period of sedimentation of Dongying Formation, lake-delta was mainly developed. Through the correlation between seismic facies and sedimentary facies, distribution features of sedimentary system of major target formation in the studied area were identified, providing effective guidance for the subtle reservoir estimation in the region.4. On the basis of comprehensive geologic, logging and drilling data, by using advanced special seismic processing and new interpretation technologies(including high precision horizon calibration, 3D visible interpretation, seismic coherence analysis, attribute analysis, logging constrained inversion, Spec Decomp and seismic forward modeling), the target subtle reservoir was identified, interpreted and its forming mechanism was studied. After finding a batch of favorable lithosome in slope of Qikou sag, wells were deployed. After exploration drilling, industrial hydrocarbon flows were acquired in these wells, which marked outstanding effects and new breakthrough in exploration of subtle reservoir in Qikou slope, promoting the exploration of subtle reservoir in Dagang prospect.5. Considering low degree of exploration and hard estimation of reservoir in Qikou slope, the accuracy to estimate reservoir was greatly improved, through finely studying the macroscopic and microscopic features of reservoir and by using various estimation technologies, under the guidance of reservoir-forming model and the concept of mutual verification. As a result, the distribution features of the target reservoir were well estimated. Besides, a set of systemic technologies for the exploration of subtle reservoir were formed, namely:①high resolution processing of secondary 3D seismic acquisition and seismic data connected processing technology;②technology of high solution sequence stratigraphic classification and correlation;③local structural analysis and fine structural interpretation technology;④technology of integrated analysis of core facies, electrofacies and seismic facies to identify macro-sedimentary system;⑤fine reservoir estimation technologies, typically including forward modeling, constrained inversion of well, optimization of seismic attribute, Spec Decomp, coherence analysis and 3D visualization.