Langgu sag is one of the hydrocarbon rich sags in Jizhong Depression, with high exploration degree. “Secondary exploration” was carried out in high-exploration-degree area and remarkable results were achieved in structural exploration. It is thought that lithostratigraphic exploration is a feasible way to f ind next target for fi nding large-scale reserves, based on 3D data sets, standing on abundant residual oil and gas resources and developing integrated geologic study. Tectonic inversion occurred during the depositional period of the f irst member of Shahejie Formation-Dongying Formation in Langgu sag, and sand bodies of early-deposition downdip pinchout were converted to updip pinchout, providing structural setting for forming lithostratigraphic traps. Eastern, northern and western provenances developed; sedimentary sand bodies of delta front, fan delta front and nearshore subaqueous fan grew well. Hydrocarbon translocation system of fracture surface, unconformity interface and sand bodies existed in this area. Multiple lithostratigraphic traps grew on steep slope zone, trough zone and gentle slope zone, having favorable reservoir forming conditions. Multiple favorable targets were conf irmed in the fl ank around Tongnan trough of fewer faults and simple tectonic setting, Daxing conglomerate bodies and western Hexiwu, which are the focus of further exploration.

Oil and gas resources are rich in the middle of Raoyang sag, faults and anticlines developed around main oil generating troughs, and Dongying Formation-upper submember of the fi rst member of Shahejie Formation is the major oil-bearing series in this area. Channel sandbodies deposited by meandering river mainly developed in the Formation. Reservoir forming features are expressed by oil-source faults controlling oil and gas distribution, channel sandbodies controlling traps formation and petroleum enrichment. Structural and lithologic reservoirs co-existed and mutual-complemented. The high location of faults and anticlines is mainly structural reservoir, while the wings are lithologic reservoir with low exploration degree and great potential. Analyzing the confi guration of faults and channel sandbodies, there are three main reservoir forming models in the area, i.e. channel sandbody lapout, fault negative landform channel sandbody updip pinchout, and lenticular isolated sandbody of low-amplitude anticlines. Through fi ne research on structure, deposit and reservoir in recent years, channel sandbody distribution was described, therefore, a series of lithologic traps were conf irmed at the wings of Dawangzhuang-Suning structure, and Well Rao10x and Well Ning75 were drilled successfully. Remarkable exploration achievements were made, which showed a good trend of oil jointing in the middle of Raoyang sag.

Aer sag is a small oil-bearing sag newly discovered in Erlian Basin in recent years, of which reservoir-forming conditions are relatively complex. Reservoir assessment was conducted early under the premise of only four exploration wells, based on scientifically demonstrating the rapid assessment applicability of the sag. Analysis shows that there are many factors restricting reservoir assessment including less geologic data, great lateral change in reservoir, and complicated factors controlling reservoir, etc. This paper presented a general idea of rapid proven reserves and building capacity rapidly and eff iciently. By means of scientifi c demonstration, optimized deployment, and comprehensive geological research, this paper used such techniques as seismic feature identif ication and seismic attribute analysis to predict sandbody boundary, built and updated structural-lithologic reservoir-forming models. Through rolling block-expanding assessment, assessment of sub-trough exploration, assessment of rolling boundary-extending step by step and other rapid assessment means, monoblock proved oil reserves reached 34.3627 million tons and annual production capacity closed to 400 000 tons in less than three years.

Maxi subsag is one of the hydrocarbon-richest oil-generating subsags in Raoyang sag, which has abundant remaining resources. With increasing exploration, the third member of Shahejie Formation of low exploration degree, huge potential and lithologic reservoir- forming conditions becomes the important series of strata for further exploration. However, the third member of Shahejie Formation is diff icult to be explored, because of its complicated sedimentary features during sedimentary stage. This paper suggested analyzing reservoir-forming conditions again and looking for favorable lithologic exploration zones based on tectonic setting study, carrying out sequence stratigraphic research and confirming favorable lithologic exploration series of strata, comprehensively analyzing sedimentary facies and establishing multiple lithologic reservoir-forming mode, using full 3D interpretation techniques for meticulous interpretation and identifying lithologic traps, evaluating and optimizing exploration targets to implement drilling and exploration. Well Xi61x, Well Xi64x and Well Ma98 were drilled successfully in the lithologic traps of the western slope and the eastern fracture zone. In 2012, probable petroleum reserves submitted by Maxi area were 26.96 million tons. Exploration practice shows that the deep layers of oil-rich subsags are favorable targets for lithologic reservoir exploration.

Central Lixian slope of Raoyang sag is a favorable area for carbonate development, which is dominated by biolithite limestone, oolitic limestone and dolomitic limestone. Now industrial oil run has been got or good hydrocarbon indication has been seen in many wells of the series of strata, which presents the exploration potential of carbonate in lower submember of the fi rst member of Shahejie Formation. In the past two years, such techniques as the integration of well logging and seismic, core slice observation, log interpretation, and core facies analysis have been used for in-depth research on carbonate sedimentary reservoir features in lower submember of the f irst member of Shahejie Formation, clarifying the planar distribution and favorable oil-bearing facies belt of the carbonate here. Carbonate reservoir here features in middle porosity and middle permeability, structural-lithologic and lithologic strata are dominant reservoir types, and reservoir-forming conditions are complicated and controlled by sedimentary microfacies and reservoir physical property. Gaoyang area is located in shallow lake, carbonate in lower submember of the f irst member of Shahejie Formation is the thickest, and biolithite limestone and oolitic limestone mainly developed. Xiliu area is located in fairly deep lake, where dolomitic limestone mainly developed and reservoir physical property is the best. The two areas are focal zones for carbonate exploration in central section of Lixian slope

As having a relatively lower exploration degree inside buried hill in the Wen’an slope of Baxian sag, based on jointing prestack 3D seismic data of high precision in the sag, the research about structure characteristics and reservoir conditions has been carried out systemically inside buried hill in the Wen’an slope. It is thought that the western layer inside buried hill in slope connects hydrocarbon source rocks of the fourth member of Shahejie Formation and Kongdian Formation in subsags, with wide oil supply window that oil and gas perfuse inside buried hill along unconformities and faults, which can accumulate in multiple buried hill traps of the slope, such as anticline, fault nose, and fault block. Therefore, a reservoir mode has been built for layered inside buried hill and layered anticline of “ young source in old reservoir ” in Wen’an slope. It is studied comprehensively that the next favorable exploration direction is anticline, fault nose and fault block in the southern slope with good trap type and shallow depth, closing to hydrocarbon subsags of Baxian and Maozhou, both of which supply oil.

Shennan anticline is a main oil-bearing composition of Shenxian sag with “small, fractured, lean and disseminated” reservoirs. Based on analyzing the factors restricting exploration and development, this paper proposed “re-recognition, meticulous evaluation and overall deployment” to re-evaluate hydrocarbon reservoir. Favorable prospecting targets are discovered through carrying out high-resolution seismic data merging processing, oil group division and correlation based on well-log and seismic data, multi-means meticulous structure interpretation, meticulous sandbody distribution analysis, and meticulous old well reexamination. The research indicates that the reservoir sandbody of Shennan anticline develops moderately and bears oil throughout all its structure, especially, toothbrush-shape reservoir model could be generated in anticlinal wing. This model features in multiple oil bearing series, big total thickness, and high production. The fault cross-range is the main factor controlling reservoirs, which is mainly determined by lithological array and evolving process. The evolving process of inherited faults is favorable for creating shale smear, which endows the faults with better cross-range. Considering the characteristics of the reservoir, multi-target deviated well drilling is the most effective way to enhance exploration. The good effect has been proved by practice

According to the seismic, drilling, well logging, analysis and test data, the detailed sequence stratigraphic characteristics are researched about the fourth member of Shahejie Formation—Kongdian Formation of paleogene in the south of Jinxian sag by using sequence stratigraphic principle. The sedimentary models of different positions in the sag are established. At the same time, the sedimentary facies distribution and evolution characteristics are analyzed. The favorable direction of oil-gas exploration is determined. Research shows that the fourth member of Shahejie Formation—the third member of Kongdian Formation is a second-grade sequence, which can be divided into three third-grade sequences or eight fourth-grade sequences. Five kinds of sedimentary systems are identifi ed in this area, which are alluvial fan, delta, fan delta, nearshore subaqueous fan and alluvial plain. Two lithologic and structural-lithologic oil-gas accumulation areas come into being, which are the key zone for oil-gas exploration.

Jiergalangtu sag is oil riched in Erlian Basin, where heavy oil reservoir, conventional oil reservoir and structural-lithologic reservoir were discovered one after another after three rounds of exploration. It features in coexistence of structural and lithologic reservoirs, and group distribution of heavy oil reservoirs and conventional thin oil reservoirs. There are various oil reservoirs in Jiergalangtu sag where hydrocarbon accumulation is complex. Continuous exploration is realized in oil enriched depression through changing thoughts in many aspects, such as structural to lithologic reservoir, slope to trough, shallow layer to deep exploration, etc. It is pointed out that new and big discoveries should only be realized by changing the way of thinking and deepening understanding continuously. There are still 50 million tons of remaining resources to be explored in the sag. Through illustrating known reservoirs and analyzing hydrocarbon occurrence rules, it is thought that the important direction of expanded structural reservoir is the two fl anks in slope belt of Baorao structure. There is greater potential in exploration of lithologic deposit in trough area. Tight reservoirs are important succeeding f ield for discovering large-scale reserves

Anan subsag has been explored for more than 30 years. Structural reservoir here has high exploration degree, but lithologic reservoir has low exploration degree. Comprehensive geologic study is made on the structural feature, oil source conditions, sequence stratigraphy, reservoir attributes, source-reservoir-caprock conf iguration, and reservoir-forming mode, etc., with an aim to make breakthrough in exploration of lithologic reservoirs in the subsag. Research results show that structure evolution in the subsag generates different types of geologic structure, high-quality source rocks developed in the lower submember of the fi rst member of Tenggeer Formation and the fourth member of Aershan Formation, sequence stratigraphy distribution rules are different in the third and fourth members of Aershan Formation, the middle and lower submember of the f irst member of Tenggeer Formation, conventional strata developed in the third and fourth members of Aershan Formation and unconventional strata developed in the lower submember of the fi rst member of Tenggeer Formation, different types of lithologic-stratigraphic reservoir-forming modes are formed in different structural units. Analysis shows that the fourth member of Aershan Formation and the lower submember of the f irst member of Tenggeer Formation are lithologic reservoir and tight oil potential exploration strata in Anan subsag; limbs in large-scale structures such as Anan anticline, Jihe nosal structure, Hanan substrata elevating anticline are favorable for lithologic reservoir exploration, and the lower submember of the fi rst member of Tenggeer Formation is favorable for tight oil reservoir exploration.

Intuitive understanding of basin characteristics such as early paleostructure, paleoenvironment and paleocurrent could be got based on paleogeomorphy restoring prototype basins, laying solid basis for further oil and gas exploration. Taking Wulanhua sag as an example, this paper analyzed the structural characteristics of Mesozoic residual sags in Erlian Basin, combined multiple paleogeomorphic restoring methods including the geophysical method, the residual thickness method, and sequence stratigraphic method, used 3D visualization technique as a medium, and truly refl ected the structural development history characteristics of the sag. Paleogeomorphic restoring shows that Wulanhua sag took shape during the sedimentary stage of Early Cretaceous Aershan Formation; the sedimentary stage of Tenggeer Formation is the expansion stage of fault depression; lacustrine basin shrank and structure reversed during the sedimentary stage of Saihantala Formation, which as a whole exhibited the characteristics that source rocks were thick at early stage and eroded at late stage.

As a main method for reservoir forecast, seismic attributes play an important role in oil-gas exploration and evaluation. However, the limitations and ambiguity of seismic attributes make attribute optimization and multi-attribute combination more diffi cult, reducing the accuracy of forecast. To the above-mentioned problems, this paper mainly studied and analyzed the application of four methods such as the optimization of basic seismic attributes, attribute selection under the restraint of old structure, based on the geophysical and geological meaning of seismic attributes. The application of these methods signif icantly increases the pertinence of the seismic attributes in reservoir forecast and the forecast ability and accuracy, thus getting preferable application effect.

Xing9 Conglomerate is located in north-central downthrown side of Daxing fault west of Langgu sag, which is characterized by near supply sources, narrow facies zone and rapid facies variation. Oil and gas entry is the clumpy conglomerate in the lower submember of the third member of Shahejie Formation. But the boundary of clumpy conglomerate is diffi cult to be identifi ed and the favorable reservoir is diffi cult to be predicted, seriously affecting precise reserves calculation. For the above problems, based on in-depth analysis of seismic data, geologic data and well log, this paper predicted the spatial distribution characteristics of Xing9 Conglomerate reservoir and the oil-gas bearing distribution inside the reservoir, and described the distribution of effective reservoir meticulously, using such techniques as the acoustic impedance inversion technique, the reservoir parameter inversion technique and the pre-stack seismic attenuation attribute technique. The predicting results meet the accuracy requirement, providing important parameters and basis for reserves recalculation.

The surface elevation is changed drastically in river erosion feature area. Due to cost and acquisition device constraints, conventional seismic acquisition data is relatively sparse in vertical and horizontal physical points, and surface measurement data density is not enough to investigate the surface structure in detail. With the development of technology and application of satellite technology, the use of geographic information system can obtain more accurate DEM elevation data. Based on geographic information of river erosion feature area, and combined with the results of surface survey control points, a surface modeling is established, achieving good results.