Hydrocarbon Enrichment Patterns And Exploration Direction In Lixian Slope, Raoyang Sag

This thesis focuses on Lixian Slope, Raoyang Sag, Jizhong Depression. Starting with the reservoir conditions, this study tries to deepen the understanding of the control factors of the reservoir formation and oil and gas enrichment patterns to invent a method of exploring weak tectonic zone of slope and ascertain the hydrocarbon accumulation rules through changing the thinking, constructing reservoir forming mode and innovating geologic knowledge. The abstract includes the major contents and innovations as follows:Background and significance of the projectThe slope region is a very important structure type and exploration target. In recent years, companies both at home and abroad have already paid great attention to and placed new research on it and discovered a large number of favorable structures, stratigraphic-lithologic reservoirs, which marks the noticeable efficient exploration. Deepening the exploration of slope region has become an assured direction in highly mature oilfields. The worldwide preexisting explorations show that new oil and gas discoveries in the highly explored areas especially in the slope regions are made by either new technologies and methods or innovative thinking which helps discover fairly subtle stratigraphic-lithologic reservoir whose control factors and accumulation rules are studied so as to improve the exploration efficiency.Lixian Slope exploration area, about2,000km2, is the largest in Raoyang Sag, even in Huabei Oilfield. Important discoveries have been achieved in the past years’exploration. Since almost all the easily explored and identified structural reservoirs have been found with the constantly increased exploration, it is increasingly difficult to make new discoveries. The challenge faced by the researchers is how to find new types of reservoirs in the weak tectonic areas of Lixian Slope by deepening the knowledge of the reservoir conditions and hydrocarbon enrichment patterns. This study is practically significant because it finds the consequent oil reserves in Lixian Slope that can ensure the stable oil production.Research objectives and technical problemsThis thesis aims to make clear the main reservoir types, oil and gas accumulation rules and the control factors to ascertain the exploration direction through further study on the control factors of Lixian Slope reservoirs and hydrocarbon enrichment patterns. The major technical problems are (1) incapability of knowing well the stratigraphic-lithologic reservoir formation mode, i. e. the researcher has difficulty constructing new reservoir formation modes to direct the exploration and (2) the subtle stratigraphic-lithologic traps that are hard to identify, i. e. the researcher has difficulty finding stratigraphic-lithologic reservoirs and new oil areas in Lixian Slope that has been explored a lot by using effective technical means.Research clues and contentsGuided by the geologic theories of the hydrocarbon reservoir and trying to change the existing thinking, this thesis focuses on the forming conditions and dominant factors of the stratigraphic-lithologic reservoir so as to deepen the understanding of the hydrocarbon enrichment patterns while studying the structural reservoir. The following four aspects of research are mainly done:1. Further understanding of the reservoir conditions based on the new and high-quality3D seismic dataThe hydrocarbon source rocks analyzed and evaluated, Sha1Sub-member is the major hydrocarbon source rock that is potentially rich. The study on the sedimentary microfacies and reservoir identifies the types of sand bodies, reservoir characteristics and reservoir performance and thus shows that Lixian Slope develops delta sand body, beach-bar sand body and river-facies sand body, among which the delta front sand body and beach-bar facies sand body have good petrophysical property and are favorable for forming lithological trap.The analysis of the causes of the slope formation and the structural settings indicates that Lixian Slope developed two fault systems of mainly north-east trend and accessorily north-west, four large broad and gentle north-west nose-like structures and three local structure patterns, all of which are favorable for the formation of large nosing structural trap and local structural trap.2. Fine identification and evaluation of the traps, especially of the stratigraphic-litholoigic traps, to discover the favorable exploration targets3. Analysis of the predominant forming factors of the typical reservoir forming so as to recognize its basic characteristics4. Analysis of the control factors to find out the new formation model of different types of reservoirs, sum up the oil and gas accumulation rules and ascertain the prospecting targetsMajor achievements and new recognitions:This study has achieved the following results and new geological recognitions:First, three new recognitions of the factors controlling the reservoir formation and the hydrocarbon accumulation rules.1. The hydrocarbon generating region of the high quality hydrocarbon source rock in Lower Sha1Sub-member dominates the distribution of oil and gas in the slope zone. The hydrocarbon source rocks are developed in middle and lower of the slope where oil source is abundant and the widely covered reservoir is likely to form.2. Lixian Slope consists of two major structures:the north-west trend nose-like structure and the north-east trend main fault, which dominates the most part of the oil and gas accumulation zone. Further study shows that the nose uplift background is the most favorable zone to which oil and gas migrate and controls the degree of the oil and gas enrichment, that the development scale of the controlling fault controls the oil and gas migration and accumulation, that the location relationship of the controlling fault trend and the sand body distribution direction controls the enrichment degree of the nosing structure, that the continuity of the controlling fault influences the oil and gas accumulation, and that the intersection relationship between the controlling fault and the nose structure axis dominates the oil and gas migration mode and reservoir type.3. The stratigraphic-lithologic trap development is dominated by three kinds of microfacies sand bodies of which the development regions are controlled by the lithologic reservoir distribution. The delta front sand body dominates the lithologic trap of the Upper Sha1Member and Lower Sha1Sub-member slope; the beach-bar facies sand body of the platform region controls the lithologic trap of the middle and northern part of the Lower Sha1Sub-member slope; the braided river sand body controls the stratigraphic-lithologic trap of Sha2Member.Second, finding out four new types of reservoir formation in the weak tectonic area of Lixian SlopeThe four types of reservoir formation are:"stratigraphic-lithologic reservoir in the slope-break zone of the buried hill rim slope","upper-source-lower-accumulation structure-lithologic reservoir in the downdip terrace of the slope area","structure-lithologic reservoir in the widely covered low-uplift insolated sand body combined zone of the slope region with high quality hydrocarbon" and "lower-source-upper-accumulation structure-lithologic reservoir in the contra-dip terrace of the slope area".Third, innovating the efficient technical method of recognizing the detailed structure-lithologic trap in the slope areaThis method mainly includes techniques such as "delicate depiction and interpretation of minor-fault micro-range structure to macro-forecast the development region of stratigraphic-lithologic trap" and "precise sequence classification and comparison to build up the sand body seismic prediction isochronal framework model".Fourth, implementing the meticulous trap identification and evaluation to optimize the favorable oil zones and point out the main exploration direction.Based on the study of hydrocarbon accumulation control factors and the new knowledge of hydrocarbon enrichment rules, we carry out structure-lithologic trap identification, characterization and evaluation. Recently we have found a number of favorable traps of clear identification with better accumulation condition in favorable areas like Gaoyang-Tongkou structural zone, Xiliu-Zhaohuangzhuang area so that we focus on the Gaoyang-Tongkou fault zone and Xiliu-Zhaohuangzhuang as the main exploration direction, which plays a certain guiding role in further exploration of Lixian Slope.