The Analysis Of Main Controlling Factors Of Reservoir Formation Of Delta Front Sand Body And Its Distribution Rule

With the continuous development of petroleum geology theory of China’s continentalfacies basin, the formation of the "Continental Source Theory",“Oil and Gas Source ControlTheory of Depression Basin "," Theory of Multiple Oil and gas Accumulation Belt", providean effective guidance for oil and gas exploration of continental basin. The theory and methodof lithologic reservoir in the slope area adjacent to main source sag are in the process ofresearch.According to the current research of exploration method and theory of reservoir in slopearea, based on core data, logging data and seismic data, this paper first analyzed tectonicfeature, depositional system of Western Slope in Northern Songliao Basin, then madethoroughly study on main controlling factors and oil&gas distribution law of sand bodyreservoir of delta front facies in larger slope area, integrating petroleum geology, sequencestratigraphy and seismic sedimentology. The innovative results and understandings have beenobtained as followings:(1) With the guidance of high resolution sequence stratigraphy, combining theclassification scheme of Saertu formation (S) in Western Slope, based on logging, core andgeophysical data,5mid-term cyclic sequences of Saertu oil layer are classified into MSC1toMSC5from bottom to top, respectively corresponding to S23, S1,and S0; also, high-precisionisochronous stratigraphic framework,taking mid-term cycle as comparison unit, isestablished, which lays the foundation for further analysis of reservoirs.(2) According to comprehensive analysis of drilling cores, well logging and distributionof heavy minerals, it is cleared that study area is mainly controlled by provenance ofnorthwest Qiqihar City, northern Lindian and short source of southwestern Tailai, forming thedeltaic depositional system of northwest, northern and southwestern area, in which a largearea of delta front and shore-shallow lake sediments are the most important.(3) Based on the study of mid-term cyclic sequence and sedimentary system, theascending half cycle sequence as drawing unit is firstly adopted to compile petrography palegeography map of each sequence of Saertu reservoir in western slope, which provides applicability in exploration process, revealing the sand body distribution characteristics andsedimentary facies evolution in different period of Saertu reservoir.(4) In accordance with the "flow chart" of the core facies-logging facies-seismic faciesand sedimentary facies, the sedimentology research in3D seismic work area of river75iscarried out; the interpretation formwork of seismic deposition with the geological meaning isestablished firstly, the sedimentary microfacies map is compiled for predicting the lateraldistribution with higher accuracy, which greatly enhanced the success rate of exploration forlithologic reservoir of delta front facies in slope area.(5)Through the study of tectonic characteristics and distribution relations of oil&gas, itis recognized that hydrocarbon accumulation in the slope is mainly controlled by thenortheast structure zones, which is determined to be the favorable area for oil&gasaccumulation, the previous exploration method for oil and gas along the northwest migrationchannel is changed therefore. According to fine interpretation of integrated structures,4reliefnose structure zones distributed in NE trending have been implemented on the slope.Combined with fine dissection of reservoirs, low amplitude structural reservoir,structural-lithologic composite reservoir, fault-lithologic reservoir, lithology updip pinch-outreservoir, sand lens reservoirs and other complex lithologic reservoirs are mainly developedin the studied area.(6) Based on the research of structure, sequence stratigraphy, sedimentary characteristics,hydrocarbon migration and accumulation, oil and gas accumulation pattern in large slope areais established in this paper, which points out main controlling factors of hydrocarbonaccumulation in the slope: firstly, sufficient oil supply in oil-rich depression is the materialbasis for the formation of reservoir in slope area; secondly, stratigraphic pinch-out belt,tectonic and fracture control hydrocarbon accumulation of delta front sand body in S23Formation, but under the background of nose structure, fracture control the hydrocarbonaccumulation of delta front and shallow sand dam in S1Formation; thirdly, a single andeffective trap is key factor for oil and gas accumulation. In combination of the explorationstatus of Western Slope, a favorable target for the next exploration has been determined.