Oil And Gas Reservoir Prediction In The High-resolution Sequence Stratigraphic Framework Of Tertiary In Qikou Sag

On the basis of thorough geological data, cores, log data and high-resolution 3D seismic data, the theories of sequence stratigraphy, sedimentology, oil and gas geology are used synthetically in this paper. Proceeding from known hydrocarbon reservoir, statistical analysis and summarization on the enrichment regularity are conducted in the sequence stratigraphic framework of Paleogene and Neogene. Combination of structure, sedimentation, oil and gas geological analysis to explore the causes of accumulation of the oil and gas reservoirs under the sequence stratigraphic framework and point out that horizon and direction of the favorable exploration. Characterize specific geologic bodies such as basin floor fan, slope fan, and turbidity body and wedge body in highstand system tract under the guidance of high-resolution sequence stratigraphy. The identification and contradistinction of subtle lithologic trap are simultaneously carried out in high-resolution sequence stratigraphic framework (fourth level sequence). Comprehensively utilize geology and geophysical technology to characterize geology bodies in application of multi-approaches and multi-angle analysis methods, on the basic of which forecast favorable trap range, and finally provide a scientific basis for the the deployment of further exploration of Qikou Sag. Summarize the enrichment regularity of Qikou Sag in sequence stratigraphic framework and propose the thinkings and methods of meticulous depiction, epurate the enrichment regularity with different approaches from another angle of view.This paper is comprised of six chapters:The first chapter mainly discusses the purpose and significance of the thesis, summarized the recent and front international research about the sequence stratigraphy, continental sequence stratigraphy, tectonic stratigraphy, as well as subtle reservoirs. According to the current exploration of Qikou sag and all sorts of available datas, such as seismic and geology, combined with the hot topics of sequence stratigraphy and subtle reservoirs, the study includes the following aspects: First analyzing distribution law of oil and gas reservoirs in the high-resolution sequence stratigraphic framework, moreover, depicting precisely geological bodies by combination of geological methods and geophysical methods, finally to predict the favorable areas. In addition, the feasibility and significance of study in this area is also demonstrated. Under the proposed research ideas, research content, research methods and technical line can be established. In general, this study takes Paleogene and Neogene strata of Qikou Sag as its research object, using the idea of combining "point-line-surface-body-time". Moreover, to get the study advanced, the most essensial work is to establish the region's Tertiary sequence stratigraphic framework, then analyze enrichment disciplines of the known hydrocarbon reservoirs under this framework, and investigate the spatial distribution rules and controlling factors of the favorable reservoirs, and, meanwhile, probe the methods and ideas of fine characterization of objective geobodies. After all of the above studies, it is ultimately to direct the exploration of subtle reservoirs for its final goalsThe second chapter describes the basic geological Qikou sag profile. Qikou Sag, located in Huanghua Depression central, Bohai Bay Basin, Eastern China, is a long-term development rift basin since Eocene. The sag is bounded by the Shaleitian uplift to the east, the Cangxian uplift to the west, the Chennin uplift to the south and Yanshan fold belt front to the north. The sag is adjacent to Nanpu sag. Its exploration area is approximately 5,280km2.Qikou sag is major region for exploration breakthrough in the future in Dagang Oilfield. For the whole basin structure, the structural framework is composed vertically by four different structures layer, which are:(1) pre-Tertiary basin basement structural layer, (2) the basin bottom structural layer from Eocene Kongdian Formation (Ek) to the third member of Shahejie Formation (Es3); (3) the central basin structural layer from Oligocene the first member of Shahejie Formation (Esl) to Dongying Formation(Ed); (4)the basin upper structural layer of Neogene. Five positive tectonic units(Chenbei step-fault zone, Nandagang buried hill, Beidagang buried hill, Binhai fault tectonic belt, Tanggu-Xingang buried hill) and five negative tectonic units(Qikou main sag, Beitang sub-sag, Banqiao sub-sag, Qibei sub-sag, Qinan sub-sag) developed in the margin and interior of sag.The Qikou sag is a successive developing sag, with deeper sedimentation, including Kongdian, Shahejie, Dongying, Guantao and Minhuazheng Formation. There developed fan delta, braided river delta, littoral sediments and density current, controlled by Yanshan provenance in Northern part, Changxian provenance in North-West, Cengning uplift provenance in Southern part and low uplift provenance inner depression. There are many hydrocarbon systems, such as, third, second and first member of Shahejie Formation and Dongying Formation, and there also developed various types of reservoir.The third chapter mainly builds the sequence stratigraphic framework of Tertiary in Qikou sag. Guiding by Exxon model of sequence stratigraphy, and according to the drilling, lithology, well-logs, the way of stratal terminations in seismic profiles, and seismogram synthesis, the paper identifies sequence boundaries.100 wells have synthetic seismogram in area about 3150 km2, and based on the synthetic seismogram, seismic profiles, sequence stratigraphy have been rebuilt and explained preciously. For NE02 as example, recognizing the sequence boundary, building division scheme, tracing and closing to 800 m* 800 m. Sequence framework character and inner texture have been explained precisely, for Trace 2564 and Line 1968 as examples.In the Tertiary strata of Qikou sag, the paper has identified one interface of first-order sequence, four interfaces of second-order sequence,17 interfaces of third-order sequence, and 11 interfaces of the largest lake flooding surface (the paper hasn't identified the largest lake flooding surface in the Neogene stratra), and established the sequence stratigraphic framework of Paleogene and Neogene in Qikou Sag. The study found that a significant phase of basin evolution, and multi-screen sex, and the process can be divided into fault-depression period and the depression period, while the faulted phase can be further divided into three fault-screen, each screen was a the second-order sequence.The forth chapter put forward the research thinking, that is, based on sequence stratigraphy framework, project the reservoir to the framework and make data statistic to analyze the distribution, illuminate the enrichment mechanism.1340 drill holes in Qikou Sag have been used in the research. We select oil layers data of 3m thick or thicker to study the distribution rules of hydrocarbon reservoirs, and select oil layers and oil-water layers data of 3m thick or thicker to analyze favorable reservoirs.304 layers in 155 drill holes, totally 1836.2m oil layers have been selected, and 384 layers of oil and oil-water favorable reservoirs in 207 drill holes, totally 2593.9m have been selected, to analyze distribution rules of favorable reservoirs. It is found that these layers are almost all around the secondary sequence boundary (Eslx:30.59%), Es2:14.47%, Ng: 6.91%), account almost 52%, and the nearer to sequence boundary, the reservoir became richer, that is:reservoirs always developed in EST and LST upper the sequence boundary, while developed in HST lower the sequence boundary. In summary, the reservoirs almost developed in EST and LST.According to the border fault's contributing factor, pattern in profile and association on the surface, the boundary of Qikou depression are divided into fault steep slope zone, fault multi-level zone, fault-terrace steep slope zone, flexure slope break zone and so on. Basin margin slope-break type impacts pattern of sequence, sedimentary systems, and sand distributed system spatial distribution. According to the slope break division,188 wells have been classified and statistics. The result showed, fault-controlled steep slope belt enriched 40 percent reservoir, fault step steep slope belt enriched 28 percent, multi-fault step enriched 25 percent, and twist slope break just only 7 percent. Based on structure, sedimentary, sequence stratigraphy and reservoir study, illustrate distribution reason and put forward the research thinking, that is, second-order sequence boundary+relevant third-order system tract+slope break type=favorable proposed triple-coupled control zone.The main contents of Chapter five is that the author depicted the special geological bodies in the high-resolution sequence stratigraphic framework preciously and pointed out that favorable zone. The general idea is that:under the guidance of the high-resolution sequence stratigraphy theory and the macroscopic ideas of a favorable proposed triple-coupled control zone concluded in front, in the high-frequency sequence stratigraphic framework (fourth-order sequences), we could look for the special geological bodies, carry out the analytical work of the geological bodies'formation cause and the study on the law of spatial distribution, compare to the known oil and gas reservoirs, predicted favorable zone and subtle oil and gas reservoirs, using single-well's identification and calibration, seismic identification and tracking (fourth-order sequences), seismic attribute analysis (third-order+fourth-order sequences), even the crosswell analysis (parasequence), drilling constrained inversion, multi-level and multi-angle fine portray geological body, combined with structure-the ancient landforms, depositional system analysis. There has been conducive to a proper understanding of lateral changes in reservoir characteristics, and further improve the reservoir predicted reliability, through the carrying out geologic body identification and contrast to improve the accuracy of sand body horizontal comparison, avoiding sand body when wearing horizontal contrast in the high-resolution sequence stratigraphic framework,.The author used the basin-floor fan, slope fan, and the highstand systems tract of high turbidite body and wedge as the research object, such geologic bodies mainly developed in the lake center, the slope edge,the root of the boundary fault basin margin, sand bodies developed in the geological bodies share quite a few characteristics including that the onlap, toplap (updippinchout) (the downlap, truncation), or two-way onlap, or sand bodies' oneside controlled by faults which was blochaded, the other side of the onlap and toplap. Special geological bodies could be easy to form lithologic reservoirs because they in generally and directly developed in the deep lake-semi-deep lake mudstone, with very good conditions for the upper and lower closure and directly contacted with the high-quality hydrocarbon source rocks, with its proximity advantages. Based on the research findings, and compared the known oil and gas reservoir, we could predicted a favorable geological target zone.In chapter six, based on the previous works, comparing with former hydrocarbon accumulation theory, there put forward the thought of analyzing reservoir-forming rules under sequence stratigraphic framework. The study steps are listed as follows:build high-resolution sequence stratigraphic framework; project known reservoirs into framework and summarize the distribution characteristics; analyze the reason of hydrocarbon accumulation combined with structure, sedimentation, diagenesis, and so on; refine reservoir-forming rules for predicting favorable exploration area; based on all the previous works, meticulously depict the high-resolution sequence stratigraphic framework of geological target; predict favorable reservoir area and prove the correctness with examples to proof and revise summarized reservoir-forming rules, and put forward better ones from another angle of view.The innovations are as follows:1. Based on sequence stratigraphy, the author analyzes and summarizes the reservoir distribution characteristics of Tertiary in Qikou sag. According to data statistics and examples proof, second-order sequence boundary or structure transfer surface is one important reservoir accumulation belt:upper the surface, reservoir always accumulated in EST and LST, while lower the surface, reservoir accumulated in HST. In summary, the EST and LST are favorable for reservoir accumulation. In the plane, reservoir accumulation are controlled by structural geology, such as, fault-controlled steep slope belt is abundant in reservoir, while twist break slope is poor in reservoir. The favorable triple-coupled control zone is proposed, that is:second-order sequence boundary+relevant third-order system tract+slope break type=favorable proposed triple-coupled control zone.2. According to this paper, the author put forward analyze reservoir accumulation regularity under sequence stratigraphy framework, whose steps can be listed as follows:build high-resolution sequence stratigraphic framework; project known reservoirs into framework and summarize the distribution characteristics; analyze the reason of hydrocarbon accumulation combined with structure, sedimentation, diagenesis, and so on; refine reservoir-forming rules for predicting favorable exploration area; based on all the previous works, meticulously depict the high-resolution sequence stratigraphic framework of geological target; predict favorable reservoir area and prove the correctness with examples to proof and revise summarized reservoir-forming rules, and put forward better ones from another angle of view.