The Developing Regularities And The Developing Zones Forcasting Of Secondary Pore Of Fu-Yu Reservoir In Qijiabei Area, Songliao Basin

Qijiabei oil field located in the north of qijia-gulong depression in the center depression of Songliao basin. Fuyu formation is an important reservoir, buried deeply, and strong diagenesis. Primary pore has poor preservation condition, so the secondry pores become a key factor for improving reservoir quality. The research on genetic mechanisms,models,control factors and developing regularities are very weak. It is difficult to forecast secondary pores zone too.Applying comprehensively reservoir microcosmic analyzing technology and combining with reservoir macroscopic research and oil geologic feature, we conduct a systemic research on the features,identified mark,developing regularities, genetic mechanism and model secondary pore in Qijiabei area. We bring forward a method that combing overlapping ichnography with subjective evaluation to forecast favorable areas, and forecast secondary pore zones for every sublayer in gu708 block which is main,then propose exploration advices for secondary pore zones of Fuyu reservoir in Qijiabei area.The types of secondary pore in researching area are mainly necked intergranular pore,enlarged dissolution intergranular pore,feldspar moldic pore,feldspar intragranular emposieu,volcanic detritus intragranular emposieu,carbonate cement emposieu.It can be summarized into four pore groups,which respectivelyenlarged dissolution intergranular pore and intragranular emposieu and moldic pore ; enlarged dissolution intergranular pore and intragranular emposieu and moldic pore and tectoclase;necked intergranular pore and enlarged dissolution intergranular pore and intragranular emposieu ; dissolution intergranular pore and intragranular emposieu and carbonate cemented emposieu.The porosity of these four pore groups is decreased progressively. Among them, the first one and the second one are main ,and the forth pore group has poor reservoir quality which respond to carbonate cemented lithogenous phase . The proportion of secondary pore among enlarged dissolution intergranular pore is about twenty percent. The average proportion of secondary-pore porosity of the whole porosity is about 39.21 percent. The average porosity of secondary pore is 3.54 percent and which has great contribution to the reservoir quality. The developing of secondary pore would be affected by Lithology,mineral composition and grain size. Lithic arkose and feldspathic litharenite containing aluminosilicate minerals would be favorable to the developing of secondary pore. Coarser medium-grained sand would also be favorable to the developing of secondary pore while too much argillaceous matrix content is unfavorable. The content of carbonate cement and effective porosity have negative correlation.Organic and inorganic diagenesis control the evolution of pores which is shown by compaction,cementation and metasomatism to the pore destruction. Denudation enlarge porosity. Fuyu reservoir is in the A to B stage of middle diagenetic stage on the whole ,and the A stage is main. The reservoir quality on the stage of AII is better than other diagenesis stage. It is divided into five diagenetic facies, which include siliceous cementation , authigenic clay mineral rimcementation,mixed cementation,argillaceous matrix cementation,early calcite cement,late calcite cementation. The effective porosity become worse in sequence.Delta plain deposition and delta front deposition are mainly developed in researching area. The microfacies include overwater distributary channel, natural barrier, alluvial flat,bay et al.. Sedimentary facies belts with stronger hydrodynamic force, good sorting of rocks, minor matrix ,coarser grain, approaching generating rock or underlied source bed are favorable for developing secondary pore. According to the statistical result of effective porosity , and the analyzing to the favorable conditions for developing secondary pores, we conclude that the sedimentary facies including overwater distributary channel,mouth bar and distributary channel are favorable for developing secondary pore.The effective porosity of oil-bearing sandstone is better than oil- free sandstone that proving the long-term inrush of oil is favorable to improve reservoir property of rock. Carbonate cementation is developed well in oil-free sandstone than in oil-bearing sandstone. Illite rim cementation is developed well in oil-free sandstone which show that saturated hydrocarbon constrict the growth of Illite. While the overgrowth of Quartz is developed well showing the inrush of oil does little influence on the overgrowth of Quartz. The correlation of depth and porosity or intragranular emposieu shown, during the range of depth in researching area, the depth has indistinct influence for developing secondary pore. The effective porosity of sandstone in lower layer is better than that in upper layer which maybe influenced by acidulous water in Yangdachengzi formation in lower part. Oiliness in lower layer is not good generally which is presumed that it is the result of secondary migration of hydrocarbon,orconcerned with the depth of hydrocarbon expulsion during the later hydrocarbon accumulation stage.Qijia depression located at the west of Aogula-xiaokelin faulted zone. The hydrocarbon generated from Qijia-gulong depression was blocked off by the faulted zone, which is a favorable background for hydrocarbon accumulation. Approaching to oil-generating center and being situated in La-xi nosing structure are favorable structure condition. By researching on overlaying plan of structure and pore isoline, we found T2 fault and micro-scales higher structure have obvious control to develop secondary pore zones. High porosity is mainly distributed in these two type areas. The faults in active state is favorable for fluid longitudinal movement, while the movement was blocked in closed stage. Dense fracture is favorable for secondary pore zones developing, forming the good channel for hydrocarbon migrating. Fracture belt paralleling with sand body trend are favorable for hydrocarbon and fluid migrating , while perpendicular relationship has adverse contribution.The fault has intently relationship with hyperpressure rupture in Qing-1 member , which may caused by active fault movements. Fracture matching sand body channel can form hydrocarbon traps relevant to fracturing. Upthrow especially nosing-upthrow which pointing to the center of depression is the directional migrating zone. It is favorable for forming secondary pore zones and accumulating hydrocarbon reservoir. Combining favorable structure with porosity isopleths, we confirm uplifted structure in the west and middle areas are the most favorable areas for secondary pore developing.Organic acid generated from Qing-1 member during its flushing period is the main reason for forming secondary pore in researching area. Acid expulsion of mudstone before the forming of hyperpressureof Qing-1 member can form small scale secondary pore zones. Organic acid and hydrocarbon , expulsed by hyperpressure ,along T2 faults, in the manner of multiple phases and episodic process,flush into reservoir sandstones, and then form secondary pore zones . For high geotemperature, silico aluminate minerals is rich in sandstones,organic acid generated from thermolysis of petroleum have certain contribution to secondary pore forming. The first fluid flushing phase during the fastigium of acid expulsion is the main phase for forming secondary pores. During the last two phases, fluid can improve quality of secondary pore. Evolution pattern in this area can be summarized as follows: alkaline fluid of early stage -mudstone acid expulsion of early stage-hydrocarbon and organic acid flushing phases-diagenetic evolution of later phase.We adopt to the method of combing overlapping plan map with subjective estimate to forecast favorable areas. The overlap plan map including favorable structure area, carbonate content, diagenetic stage, sedimentary microfacies. When overlapping ,we separate sublayer into several blocks, and then score every block according to score system,then, amalgamate the blocks during the same score phase into one block as the same grade. According to this method ,we forecast secondary pore zones for every sublayer in gu708 block.By analyzing the developing and affected factors of secondary pores in Qijiabei oil field, we propose the favorable exploratory direction of secondary pore zones in Fyyu reservoir of Qijiabei area. The favorable structure position is the nosing uplift on the boundary of the depression approaching to the hydrocarbon generating center. The depth ranges from 1900 to 2300 meters underground is the main secondary pore developing zone. Fractures of T2 with small slip of fault are developed and densely set. Fuyu reservoir Overlying Qing-1mudstone formation with greater thickness that generate oil, which is good ductile cap rock. The flexibility contribute to the sealing of reservoir. Underwater distributary channel, mouth bar, distal bar ,overwater distributary channel are favorable sedimentary facies belts. For grain supported effect, sandstone with coarser grain is favorable for the conservation of primary pore and provide room for acid fluid migrating, and develop secondary pore zones. If fracture densely set overlapping higher structure,it is more easier to develop secondary pore zones.